Optical elements, variable focus elements, and head-mounted displays

Abstract

The present invention provides an optical element, a variable focus element and a head-mounted display. The optical element includes: a liquid crystal unit, which includes a first substrate, a liquid crystal layer and a second substrate; and a 1 / 4 wavelength film, the liquid crystal layer contains liquid crystal molecules with a twisted orientation, the liquid crystal unit has electrodes, and the electrodes are configured to be able to switch between a first state and a second state by applying a voltage to the liquid crystal layer. The switching between the first state and the second state controls the polarization state of light incident on the liquid crystal unit. When circularly polarized light is incident on the liquid crystal unit, in the first state, the circularly polarized light is converted into a first linearly polarized light, and in the second state, the circularly polarized light is converted into a second linearly polarized light. When linearly polarized light is incident on the liquid crystal unit, in the first state, the linearly polarized light is converted into a first circularly polarized light, and in the second state, the linearly polarized light is converted into a second circularly polarized light.

Description

Technical Field

[0001] The following disclosure relates to an optical element, a variable focus element including the optical element, and a head-mounted display including the variable focus element. Background Art

[0002] In recent years, variable focus optical systems combining Pancharatnam Berry (PB) lenses and switchable half-wave plates (sHWP) have been proposed for applications such as head-mounted displays. The sHWP is a device that switches the polarization state of left and right circularly polarized light, using liquid crystals.

[0003] As a technology related to a variable-focus optical system, for example, patent document 1 discloses a display device comprising a waveguide tube and a broadband adaptive lens assembly, wherein the waveguide tube is configured to guide light in a lateral direction parallel to an output surface of the waveguide tube, and further configured to externally combine the guided light through the output surface, and the broadband adaptive lens assembly is configured to internally combine and diffract the externally combined light from the waveguide tube through the broadband adaptive lens assembly.

[0004] Patent Document 2 discloses a variable focus block including an sHWP and a plurality of liquid crystal lenses.

[0005] Patent document 3 discloses an achromatic polarization switch that converts linearly polarized light with an initial polarization orientation, and comprises: a first liquid crystal (LC) unit having a first alignment axis with respect to the initial polarization orientation; and a second LC unit having a second alignment axis with respect to the first alignment axis.

[0006] Patent Document 4 discloses an optical element comprising a first stacked birefringent layer and a second stacked birefringent layer, wherein the local optical axes of the first and second stacked birefringent layers are rotated at respective twist angles within the thickness of the first and second layers and are arranged along the interface between the first and second layers.

[0007] Prior art literature

[0008] Patent Literature

[0009] [Patent Document 1]: Japanese Patent Publication No. 2021-501361 [Patent Document 2]: U.S. Patent No. 10379419 [Patent Document 3]: Japanese Patent Publication No. 2009-524106 [Patent Document 4]: Japanese Patent Publication No. 2014-528597 Summary of the Invention

[0010] Technical problems to be solved by the present invention

[0011] In the above-mentioned patent documents 1 to 4, there are the following problems: it is difficult to switch between polarization light modulation and polarization light non-modulation in a wide band, wherein polarization light modulation is to convert the polarization state of the left and right circularly polarized light, and polarization light non-modulation is to not convert the polarization state of the left and right circularly polarized light, and it is difficult to achieve a thin device structure.

[0012] The present invention has been made in view of the above-mentioned situation, and its object is to provide an optical element that can switch between polarization modulation and polarization non-modulation in a wide band and can be thinned, a variable focus element having the above-mentioned optical element, and a head-mounted display having the above-mentioned variable focus element.

[0013] Technical solutions to technical problems

[0014] (1) An optical element according to one embodiment of the present invention includes: a liquid crystal unit having a first substrate, a liquid crystal layer and a second substrate; and a quarter wavelength film, wherein the liquid crystal layer contains liquid crystal molecules in a twisted orientation between the first substrate and the second substrate, the liquid crystal unit having an electrode for applying a voltage to the liquid crystal layer on at least one of the first substrate and the second substrate, the electrode being configured to switch between a first state and a second state by applying a voltage to the liquid crystal layer, the first state being a state in which the liquid crystal molecules on the first substrate side are arranged in a first orientation direction, and the second state being a state in which the liquid crystal molecules on the first substrate side are arranged in a second orientation direction orthogonal to the first orientation direction when viewed from above, The switching between the first state and the second state is used to control the polarization state of light incident on the liquid crystal unit. When circularly polarized light is incident on the liquid crystal unit, in the first state, the circularly polarized light is converted into first linearly polarized light, and in the second state, the circularly polarized light is converted into second linearly polarized light. The second linearly polarized light has a polarization direction orthogonal to the polarization direction of the first linearly polarized light when viewed from above. When linearly polarized light is incident on the liquid crystal unit, in the first state, the linearly polarized light is converted into first circularly polarized light, and in the second state, the linearly polarized light is converted into second circularly polarized light. The second circularly polarized light rotates in a direction opposite to the rotation direction of the first circularly polarized light.

[0015] (2) In addition, in an optical element of a certain embodiment of the present invention, based on the structure of (1) above, the liquid crystal unit further has: a horizontal orientation film with a first weak anchoring force, which is arranged between the first substrate and the liquid crystal layer; and a horizontal orientation film with a second weak anchoring force, which is arranged between the liquid crystal layer and the second substrate. The electrode has a first comb-tooth electrode on the first substrate, and the first comb-tooth electrode is arranged in a manner that the comb teeth of the comb-shaped pixel electrode and the common electrode are interlocked with each other. The electrode has a second comb-tooth electrode on the second substrate, and the second comb-tooth electrode is arranged in a manner that the comb teeth of the comb-toothed pixel electrode and the common electrode are interlocked with each other. When viewed from above, the extension direction of the first comb-tooth electrode is inclined relative to the extension direction of the second comb-tooth electrode.

[0016] (3) In addition, in an optical element of a certain embodiment of the present invention, based on the structure of (1) above, the liquid crystal unit further has: a horizontal orientation film with a weak anchoring force, which is arranged between the first substrate and the liquid crystal layer; and a vertical orientation film, which is arranged between the liquid crystal layer and the second substrate, and the electrode has: a first comb-tooth electrode, which is arranged on the first substrate in a manner that the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other; and a second comb-tooth electrode, which overlaps with the first comb-tooth electrode via an insulating layer and is arranged in a manner that the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other, and when viewed from above, the extension direction of the first comb-tooth electrode is orthogonal to the extension direction of the second comb-tooth electrode.

[0017] (4) In addition, in an optical element of a certain embodiment of the present invention, based on the structure of (1) above, the above-mentioned electrode has: a first comb-tooth electrode, which is arranged on the above-mentioned first substrate in a manner that the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other; a second comb-tooth electrode, which overlaps with the above-mentioned first comb-tooth electrode via a first insulating layer and is arranged in a manner that the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other; a third comb-tooth electrode, which is arranged on the above-mentioned second substrate in a manner that the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other; and a fourth comb-tooth electrode, which overlaps with the above-mentioned third comb-tooth electrode via a second insulating layer and is arranged in a manner that the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other, when viewed from above, the extension direction of the above-mentioned first comb-tooth electrode is orthogonal to the extension direction of the above-mentioned second comb-tooth electrode, the extension direction of the above-mentioned third comb-tooth electrode is orthogonal to the extension direction of the above-mentioned fourth comb-tooth electrode, and the extension direction of the above-mentioned first comb-tooth electrode is arranged obliquely relative to the extension direction of the above-mentioned third comb-tooth electrode.

[0018] (5) In addition, in an optical element according to a certain embodiment of the present invention, based on the structure of (1) above, the liquid crystal unit further has a bistable orientation film arranged between the first substrate and the liquid crystal layer, having orientation stability directions in two directions, the electrode has a first comb-tooth electrode on the first substrate, the first comb-tooth electrode is arranged in a manner that the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other, and the second comb-tooth electrode is arranged on the second substrate, the second comb-tooth electrode is arranged in a manner that the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other, and when viewed from above, the extension direction of the first comb-tooth electrode is inclined relative to the extension direction of the second comb-tooth electrode.

[0019] (6) In addition, in an optical element according to a certain embodiment of the present invention, based on the structure of (1), the liquid crystal unit further comprises: a first vertical orientation film arranged between the first substrate and the liquid crystal layer; and a second vertical orientation film arranged between the liquid crystal layer and the second substrate, the electrode comprises a planar first electrode and a second electrode on the first substrate, the second electrode overlaps with the first electrode via a first insulating layer and is provided with a slit portion, and the electrode comprises a planar third electrode and a fourth electrode on the second substrate, the fourth electrode overlaps with the third electrode via a second insulating layer and is provided with a slit portion, and when viewed from above, the extension direction of the slit portion provided on the second electrode is arranged to be inclined relative to the extension direction of the slit portion provided on the fourth electrode.

[0020] (7) In addition, in an optical element according to a certain embodiment of the present invention, based on the configurations of (1), (2), (3), (4), (5) and (6), the refractive index anisotropy Δn of the liquid crystal layer is less than 0.12.

[0021] (8) In addition, in an optical element of a certain embodiment of the present invention, based on the structures of (1), (2), (3), (4), (5), (6) and (7), the 1 / 4 wavelength film is a first 1 / 4 wavelength film, and a second 1 / 4 wavelength film is further provided on the side of the first 1 / 4 wavelength film opposite to the liquid crystal unit.

[0022] (9) In addition, in an optical element according to a certain embodiment of the present invention, in addition to the configuration of (8) above, the first quarter-wavelength film has an inverse wavelength dispersion characteristic.

[0023] (10) In addition, in an optical element of a certain embodiment of the present invention, based on the structure of the above-mentioned (8) or (9), the in-plane phase difference of the above-mentioned first 1 / 4 wavelength film at a wavelength of 450nm is greater than 0.7 times and less than 1 times the in-plane phase difference of the above-mentioned wavelength of 550nm.

[0024] (11) In addition, in an optical element of a certain embodiment of the present invention, based on the structure of the above-mentioned (8), (9) or (10), the in-plane phase difference of the above-mentioned first 1 / 4 wavelength film at a wavelength of 650nm is greater than 1 times and less than 1.3 times the in-plane phase difference of the above-mentioned wavelength of 550nm.

[0025] (12) In addition, in an optical element of a certain embodiment of the present invention, based on the structure of the above-mentioned (8), (9), (10) or (11), the in-plane phase difference of the above-mentioned first 1 / 4 wavelength film at a wavelength of 550nm is greater than 30nm and less than 230nm.

[0026] (13) In addition, in an optical element of a certain embodiment of the present invention, based on the structure of the above-mentioned (8), (9), (10), (11) or (12), the above-mentioned second 1 / 4 wavelength film has a flat wavelength dispersion characteristic.

[0027] (14) In addition, in an optical element of a certain embodiment of the present invention, based on the structure of the above-mentioned (8), (9), (10), (11), (12) or (13), the in-plane phase difference of the above-mentioned second 1 / 4 wavelength film at a wavelength of 550nm is greater than 110nm and less than 175nm.

[0028] (15) In addition, the variable focus element of other embodiments of the present invention comprises: the optical element described in (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13) or (14); and a Pancharatnam-Berry lens.

[0029] (16) In addition, in a variable focus element according to a certain embodiment of the present invention, based on the configuration of (15), the Pancharatnam-Berry lens is arranged in the optical element.

[0030] (17) In addition, a head-mounted display according to another embodiment of the present invention includes the variable focus element of (15) or (16).

[0031] (18) In addition, in the optical element of other embodiments of the present invention, based on the structure of (1) above, the liquid crystal unit further has: a first vertical orientation film, which is arranged between the first substrate and the liquid crystal layer; and a second vertical orientation film, which is arranged between the liquid crystal layer and the second substrate, the liquid crystal layer contains liquid crystal molecules with negative dielectric constant anisotropy, and at least one of the first vertical orientation film and the second vertical orientation film controls the tilt direction of the liquid crystal molecules in a state where no voltage is applied.

[0032] (19) In addition, in an optical element of a certain embodiment of the present invention, based on the structure of the above-mentioned (18), the above-mentioned electrode has, on at least one of the above-mentioned first substrate and the above-mentioned second substrate: a planar electrode; and an electrode which overlaps with the above-mentioned planar electrode via an insulating layer and is provided with a slit portion.

[0033] (20) In addition, in an optical element according to a certain embodiment of the present invention, based on the structure of (18) or (19), the pitch of the electrodes provided with the slit portion is greater than or equal to 1 μm and less than or equal to 5 μm.

[0034] (21) In addition, in an optical element of a certain embodiment of the present invention, based on the structure of the above-mentioned (18), the above-mentioned (19) or the above-mentioned (20), at least one of the above-mentioned first vertical orientation film and the above-mentioned second vertical orientation film is a vertical orientation film with a weak anchoring force.

[0035] (22) In addition, in an optical element of a certain embodiment of the present invention, based on the structure of the above-mentioned (18), the above-mentioned (19), the above-mentioned (20) or the above-mentioned (21), the delay Δnd of the above-mentioned liquid crystal layer under the applied voltage state at a wavelength of 550nm is greater than 180nm and less than 280nm.

[0036] (23) In addition, in an optical element according to a certain embodiment of the present invention, based on the structure of (18), (19), (20), (21) or (22), the refractive index anisotropy Δn of the liquid crystal layer is less than 0.12.

[0037] (24) In addition, in an optical element according to a certain embodiment of the present invention, based on the structure of (18), (19), (20), (21), (22) or (23), the light incident on the optical element is circularly polarized light.

[0038] (25) In addition, a variable focus element according to a certain embodiment of the present invention comprises an optical element described in (18), (19), (20), (21), (22), (23) or (24) and a Pancharatnam-Berry lens.

[0039] (26) In addition, in a variable focus element according to a certain embodiment of the present invention, based on the configuration of (25), the Pancharatnam-Berry lens is arranged in the optical element.

[0040] (27) In addition, a head-mounted display according to a certain embodiment of the present invention includes a variable focus element as described in (25) or (26).

[0041] Beneficial effects

[0042] According to the present invention, it is possible to provide an optical element capable of switching between polarization modulation and polarization non-modulation in a wide band and capable of being reduced in thickness, a variable focus element including the optical element, and a head-mounted display including the variable focus element. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic cross-sectional view of the optical element according to the first embodiment.

[0044] Figure 2 It is a schematic perspective view of a liquid crystal cell included in the optical element according to the first embodiment.

[0045] Figure 3 These are schematic diagrams for explaining the alignment of liquid crystal molecules in the first state and the second state of the optical element according to the first embodiment.

[0046] Figure 4 These are schematic diagrams for explaining the polarization states in the first state and the second state of the optical element according to the first embodiment.

[0047] Figure 5 This is a diagram showing an example of the axial orientation of the optical element according to the first embodiment.

[0048] Figure 6 This is a diagram showing the Stokes curves of each layer in the first state of the optical element according to the first embodiment.

[0049] Figure 7 This is a schematic cross-sectional view of the optical element of Comparative Example 1.

[0050] Figure 8 This is a schematic cross-sectional view of the optical element of Comparative Example 2.

[0051] Figure 9 This is a graph showing an example of the wavelength dispersion of the Stokes parameter S3 during modulation of the optical elements of the first embodiment, comparative example 1, and comparative example 2.

[0052] Figure 10It is a schematic cross-sectional view of a liquid crystal cell included in the optical element of the second embodiment.

[0053] Figure 11 It is a schematic perspective view of a liquid crystal cell included in the optical element according to the second embodiment.

[0054] Figure 12 It is a schematic plan view showing the direction of the electric field applied to the optical element of the second embodiment.

[0055] Figure 13 This is a diagram showing an example of the axial orientation of the optical element according to the second embodiment.

[0056] Figure 14 It is a schematic perspective view of a liquid crystal cell included in the optical element according to the third embodiment.

[0057] Figure 15 These are schematic diagrams for explaining the alignment of liquid crystal molecules in the first state and the second state of the optical element according to the third embodiment.

[0058] Figure 16 It is a schematic perspective view of a liquid crystal cell included in the optical element according to the fourth embodiment.

[0059] Figure 17 It is a schematic cross-sectional view of a liquid crystal cell included in the optical element of the fifth embodiment.

[0060] Figure 18 It is a schematic perspective view of a liquid crystal cell included in the optical element according to the fifth embodiment.

[0061] Figure 19 This is a diagram showing an example of the axial orientation of the optical element according to the fifth embodiment.

[0062] Figure 20 These are schematic diagrams for explaining the alignment of liquid crystal molecules in the first state and the second state of the optical element according to the fifth embodiment.

[0063] Figure 21 It is a schematic cross-sectional view of an optical element according to a sixth embodiment.

[0064] Figure 22 It is a schematic perspective view of a liquid crystal cell included in the optical element according to the sixth embodiment.

[0065] Figure 23 This is a diagram showing an example of the axial orientation of the optical element according to the sixth embodiment.

[0066] Figure 24 It is a schematic cross-sectional view of a variable focus element according to the seventh embodiment.

[0067] Figure 25This is an example of a schematic cross-sectional view of a PB lens included in the variable focus element according to the seventh embodiment.

[0068] Figure 26 It is a schematic cross-sectional view of a variable focus element according to Modification 1 of the seventh embodiment.

[0069] Figure 27 It is an enlarged cross-sectional schematic diagram of a variable focus element according to Modification 1 of the seventh embodiment.

[0070] Figure 28 It is a schematic plan view showing an orientation pattern of a PB lens included in a variable focus element according to Modification 1 of the seventh embodiment.

[0071] Figure 29 It is a schematic cross-sectional view illustrating the detailed structure of a variable focus element according to Modification 1 of the seventh embodiment.

[0072] Figure 30 These are diagrams for explaining the polarization state of the variable focus element in the F-2.5 mode according to Modification 1 of the seventh embodiment.

[0073] Figure 31 It is a schematic cross-sectional view of a head-mounted display according to an eighth embodiment.

[0074] Figure 32 It is a perspective schematic diagram showing an example of the appearance of a head mounted display according to the eighth embodiment.

[0075] Figure 33 This is a graph explaining the voltage applied to the optical element of Example 1.

[0076] Figure 34 This is a graph showing the Stokes parameter S3 in the non-modulation state relative to the retardation of the liquid crystal layer included in the optical element of Example 1.

[0077] Figure 35 This is a graph showing the Stokes parameter S3 during modulation with respect to the retardation of the liquid crystal layer included in the optical element of Example 1.

[0078] Figure 36 This is a graph showing the Stokes parameter S3 in the non-modulation state relative to the twist angle of the liquid crystal layer included in the optical element of Example 1.

[0079] Figure 37 This is a graph showing the Stokes parameter S3 during modulation with respect to the twist angle of the liquid crystal layer included in the optical element of Example 1.

[0080] Figure 38This is a graph showing the Stokes parameter S3 in the non-modulation state relative to the azimuth angle of the slow axis of the quarter-wavelength film with reverse wavelength dispersion included in the optical element of Example 1.

[0081] Figure 39 This is a graph showing the Stokes parameter S3 during modulation with respect to the azimuth angle of the slow axis of the quarter-wavelength film with reverse wavelength dispersion included in the optical element of Example 1.

[0082] Figure 40 This is a graph showing the Stokes parameter S3 in the non-modulation state relative to the phase difference of the quarter-wavelength film with reverse wavelength dispersion included in the optical element of Example 1.

[0083] Figure 41 This is a graph showing the Stokes parameter S3 during modulation relative to the phase difference of the quarter-wavelength film with reverse wavelength dispersion included in the optical element of Example 1.

[0084] Figure 42 This is a graph showing the Stokes parameter S3 in the non-modulation state relative to the azimuth angle of the slow axis of the quarter-wavelength film with flat wavelength dispersion included in the optical element of Example 1.

[0085] Figure 43 This is a graph showing the Stokes parameter S3 during modulation relative to the azimuth angle of the slow axis of the quarter-wavelength film with flat wavelength dispersion included in the optical element of Example 1.

[0086] Figure 44 This is a graph showing the Stokes parameter S3 in the non-modulation state relative to the phase difference of the quarter-wavelength film with flat wavelength dispersion included in the optical element of Example 1.

[0087] Figure 45 This is a graph showing the Stokes parameter S3 during modulation relative to the phase difference of the quarter-wavelength film with flat wavelength dispersion included in the optical element of Example 1.

[0088] Figure 46 This is a schematic cross-sectional view of the optical element of Comparative Example 1.

[0089] Figure 47 This is a schematic cross-sectional view of the optical element of Comparative Example 2.

[0090] Figure 48 This is a graph showing the wavelength dispersion of the Stokes parameter S3 of the optical elements of Example 1, Comparative Example 1, and Comparative Example 2 during modulation.

[0091] Figure 49This is a graph showing the wavelength dispersion of the Stokes parameter S3 of the optical elements of Example 1, Comparative Example 1, and Comparative Example 2 in the non-modulated state.

[0092] Figure 50 This is a graph showing the wavelength dispersion of the Stokes parameter S3 of the optical elements of Example 1, Example 2, and Comparative Example 1 during modulation.

[0093] Figure 51 This is a graph showing the wavelength dispersion of the Stokes parameter S3 of the optical elements of Example 1, Example 2, and Comparative Example 1 in the non-modulated state.

[0094] Figure 52 This is a diagram illustrating the alignment direction of the bistable alignment film included in the optical element of Example 4-1.

[0095] Figure 53 This is a diagram illustrating the alignment direction of the bistable alignment film included in the optical element of Example 4-2.

[0096] Figure 54 This is a graph illustrating the applied voltage in the first state of the optical element of Example 5.

[0097] Figure 55 This is a graph showing the wavelength dispersion of the Stokes parameter S3 during modulation of the optical elements of Example 1, Example 2, Example 5, Comparative Example 1, and Comparative Example 2.

[0098] Figure 56 This is a graph showing the wavelength dispersion of the Stokes parameter S3 in the non-modulation state for the optical elements of Example 1, Example 2, Example 5, Comparative Example 1, and Comparative Example 2.

[0099] Figure 57 This is a graph showing the wavelength dispersion of the Stokes parameter S3 during modulation of the optical elements of Example 1, Example 2, Example 5, Example 6, Comparative Example 1, and Comparative Example 2.

[0100] Figure 58 This is a graph showing the wavelength dispersion of the Stokes parameter S3 in the non-modulation state for the optical elements of Example 1, Example 2, Example 5, Example 6, Comparative Example 1, and Comparative Example 2.

[0101] Figure 59 It is a diagram showing the axial orientation of the optical element included in the zoom element of Example 7.

[0102] Figure 60 This is a schematic diagram illustrating the first alignment treatment in the manufacturing process of the variable focus element of Example 7.

[0103] Figure 61This is a schematic diagram illustrating the second alignment treatment in the manufacturing process of the variable focus element of Example 7.

[0104] Figure 62 This is a schematic diagram illustrating the third orientation treatment in the manufacturing process of the variable focus element of Example 7.

[0105] Figure 63 This is a schematic diagram illustrating the fourth orientation treatment in the manufacturing process of the variable focus element of Example 7.

[0106] Figure 64 It is a schematic cross-sectional view of an optical element according to a ninth embodiment.

[0107] Figure 65 It is a schematic cross-sectional view of a liquid crystal cell included in the optical element of the ninth embodiment.

[0108] Figure 66 These are schematic diagrams for explaining the alignment of liquid crystal molecules in the first state and the second state of the optical element according to the ninth embodiment.

[0109] Figure 67 It is a diagram showing the Stokes curve of each layer in the first state of the optical element according to the ninth embodiment.

[0110] Figure 68 This is a schematic diagram illustrating the polarization state of the optical element according to the ninth embodiment in the first state.

[0111] Figure 69 It is a schematic cross-sectional view of an optical element according to a tenth embodiment.

[0112] Figure 70 It is a schematic cross-sectional view of a liquid crystal cell included in the optical element according to the tenth embodiment.

[0113] Figure 71 These are schematic diagrams for explaining the alignment of liquid crystal molecules in the first state and the second state of the optical element according to the tenth embodiment.

[0114] Figure 72 It is a schematic cross-sectional view of an optical element according to the eleventh embodiment.

[0115] Figure 73 It is a schematic cross-sectional view of a liquid crystal cell included in the optical element according to the eleventh embodiment.

[0116] Figure 74 These are schematic diagrams for explaining the alignment of liquid crystal molecules in the first state and the second state of the optical element according to the eleventh embodiment.

[0117] Figure 75 It is a schematic cross-sectional view of an optical element according to a twelfth embodiment.

[0118] Figure 76 It is a schematic cross-sectional view of a liquid crystal cell included in the optical element according to the twelfth embodiment.

[0119] Figure 77 These are schematic diagrams for explaining the alignment of liquid crystal molecules in the first state and the second state of the optical element according to the twelfth embodiment.

[0120] Figure 78 It is a schematic cross-sectional view of a variable focus element according to a modified example of the thirteenth embodiment.

[0121] Figure 79 It is an enlarged cross-sectional schematic diagram of a variable focus element according to a modified example of the thirteenth embodiment.

[0122] Figure 80 These are schematic diagrams for explaining the alignment of liquid crystal molecules in the first state and the second state of an optical element according to a modification of the thirteenth embodiment.

[0123] Figure 81 It is a schematic cross-sectional view illustrating the detailed structure of a variable focus element according to a modification of the thirteenth embodiment.

[0124] Figure 82 These are diagrams explaining the polarization state of a zoom element in an F-2.5 mode according to a modification of the thirteenth embodiment.

[0125] Figure 83 This is a graph illustrating the applied voltage in the first state of the optical element of Example 8.

[0126] Figure 84 This is a graph illustrating the applied voltage in the second state of the optical element of Example 8.

[0127] Figure 85 This is a schematic cross-sectional view of the optical element of Comparative Example 3.

[0128] Figure 86 This is a schematic cross-sectional view of the optical element of Comparative Example 4.

[0129] Figure 87 This is a graph showing the wavelength dispersion of the Stokes parameter S3 during modulation of the optical elements of Example 8, Comparative Examples 3, and 4.

[0130] Figure 88 This is a graph showing the wavelength dispersion of the Stokes parameter S3 of the optical elements of Example 8, Comparative Examples 3, and 4 in the non-modulated state.

[0131] Figure 89 This is a graph illustrating the applied voltage in the first state of the optical element of Example 9.

[0132] Figure 90 This is a graph illustrating the applied voltage in the second state of the optical element of Example 9.

[0133] Figure 91 This is a graph showing the wavelength dispersion of the Stokes parameter S3 of the optical elements of Example 8, Example 9, and Comparative Example 3 during modulation.

[0134] Figure 92 This is a graph showing the wavelength dispersion of the Stokes parameter S3 of the optical elements of Example 8, Example 9, and Comparative Example 3 in the non-modulated state.

[0135] Figure 93 This is a graph illustrating the applied voltage in the first state of the optical element of Example 10.

[0136] Figure 94 This is a graph illustrating the applied voltage in the second state of the optical element of Example 10.

[0137] Figure 95 This is a graph showing the wavelength dispersion of the Stokes parameter S3 of the optical elements of Examples 8 to 10 and Comparative Example 3 during modulation.

[0138] Figure 96 This is a graph showing the wavelength dispersion of the Stokes parameter S3 of the optical elements of Examples 8 to 10 and Comparative Example 3 in the non-modulated state.

[0139] Figure 97 This is a graph illustrating the applied voltage in the first state of the optical element of Example 11.

[0140] Figure 98 This is a graph illustrating the applied voltage in the second state of the optical element of Example 11.

[0141] Figure 99 This is a graph illustrating the applied voltage in the first state of the optical element of Example 12.

[0142] Figure 100 This is a graph illustrating the applied voltage in the second state of the optical element of Example 12.

[0143] Figure 101 Graphs showing simulation results of viewing angle characteristics of the optical element of Comparative Example 3 in the non-modulation state.

[0144] Figure 102 Graphs showing simulation results of viewing angle characteristics of the optical element of Comparative Example 3 during modulation.

[0145] Figure 1031 and 2 are diagrams showing simulation results of the viewing angle characteristics of the optical element of Example 9 in the non-modulation state.

[0146] Figure 104 It is a diagram showing the simulation results of the viewing angle characteristics of the optical element of Example 9 during modulation.

[0147] Figure 105 This is a diagram showing simulation results of the viewing angle characteristics of the optical element of Example 12 in the non-modulation state.

[0148] Figure 106 This is a diagram showing simulation results of the viewing angle characteristics of the optical element of Example 12 during modulation.

[0149] Figure 107 This is a diagram showing the simulation results of the viewing angle characteristics of the optical element of Example 13 when it is not modulated.

[0150] Figure 108 This is a diagram showing simulation results of the viewing angle characteristics of the optical element of Example 13 during modulation. DETAILED DESCRIPTION

[0151] Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the contents described in the following embodiments, and design changes can be appropriately made within the scope of the present invention. In addition, in the following description, for the same parts or parts with the same functions, the same reference numerals are appropriately used between different drawings, and repeated descriptions are appropriately omitted. The various embodiments of the present invention can also be appropriately combined within the scope of the present invention.

[0152] (Definition of terms)

[0153] In this specification, the azimuth refers to the direction when the direction of the object is projected onto the substrate surface on the exit side of the optical element, and is expressed by the angle (azimuth) formed with the azimuth serving as a reference. Here, the azimuth (0°) serving as a reference is set to the direction when the orientation direction of the liquid crystal molecules on the first substrate side in the first state is projected onto the substrate surface on the exit side of the optical element. That is, the azimuth of the orientation direction of the liquid crystal molecules on the first substrate side in the first state is set to 0°. The azimuth is a positive angle in the counterclockwise direction from the azimuth serving as a reference, and a negative angle in the clockwise direction from the azimuth serving as a reference. Both the counterclockwise direction and the clockwise direction indicate the rotation direction when observing the optical element from the exit side. In addition, the azimuth represents a value measured in a state of looking down at the optical element from the exit side.

[0154] In this specification, "two straight lines (including axes, directions, and orientations) are orthogonal to each other" means that they are orthogonal when viewing the optical element from the emission side. Furthermore, "one of the two straight lines is inclined relative to the other" means that the one straight line is inclined relative to the other straight line when viewing the optical element from the emission side. Furthermore, "the angle formed by the two straight lines" refers to the angle formed between the one straight line and the other straight line when viewing the optical element from the emission side.

[0155] In this specification, two straight lines (including axes, directions, and orientations) are orthogonal, which means that the angle between them is 90°±3°, preferably 90°±1°, more preferably 90°±0.5°, and particularly preferably 90° (completely orthogonal). Two straight lines are parallel, which means that the angle between them is 0°±3°, preferably 0°±1°, more preferably 0°±0.5°, and particularly preferably 0° (completely parallel).

[0156] In this specification, in-plane retardation (in-plane phase difference) Rp is defined by Rp = (ns - nf)d. Furthermore, thickness-direction retardation Rth is defined by Rth = (nz - (nx + ny) / 2)d. ns represents the larger of nx and ny, and nf represents the smaller. Furthermore, nx and ny represent the principal refractive index in the in-plane direction of the birefringent layer (including the retardation film and liquid crystal layer), nz represents the principal refractive index in the out-of-plane direction, i.e., the direction perpendicular to the plane of the birefringent layer, and d represents the thickness of the birefringent layer.

[0157] In this specification, unless otherwise specified, the measurement wavelength for optical parameters such as the principal refractive index and phase difference is 550 nm.

[0158] The present invention is not limited to the following embodiments, and appropriate design changes can be made within the scope of the present invention.

[0159] (First embodiment)

[0160] Figure 1 It is a schematic cross-sectional view of the optical element according to the first embodiment. Figure 2 It is a schematic perspective view of a liquid crystal cell included in the optical element according to the first embodiment. Figure 3 These are schematic diagrams for explaining the alignment of liquid crystal molecules in the first state and the second state of the optical element according to the first embodiment. Figure 4 These are schematic diagrams for explaining the polarization states in the first state and the second state of the optical element according to the first embodiment. Figure 5 This is a diagram showing an example of the axial orientation of the optical element according to the first embodiment.

[0161] Figures 1 to 5As shown, the optical element 10 of this embodiment includes a liquid crystal cell 11 and a first quarter-wavelength film 12 serving as the quarter-wavelength film. The liquid crystal cell 11 includes a first substrate 100, a liquid crystal layer 300, and a second substrate 200. The liquid crystal layer 300 contains liquid crystal molecules 310 in a twisted alignment between the first substrate 100 and the second substrate 200. The liquid crystal cell 11 includes an electrode 11E on at least one of the first substrate 100 and the second substrate 200 for applying a voltage to the liquid crystal layer 300. The electrode 11E is configured to switch between a first state and a second state by applying a voltage to the liquid crystal layer 300. The first state is when the liquid crystal molecules 311 on the first substrate 100 side are aligned in a first alignment direction 311A, and the second state is when the liquid crystal molecules 311 on the first substrate 100 side are aligned in a second alignment direction 311B that is orthogonal to the first alignment direction 311A ​​when viewed from above. Switching between the first and second states controls the polarization state of light incident on the liquid crystal cell 11. When circularly polarized light enters the liquid crystal cell 11, in the first state, the circularly polarized light is converted to first linearly polarized light. In the second state, the circularly polarized light is converted to second linearly polarized light, which has a polarization direction orthogonal to that of the first linearly polarized light when viewed from above. When linearly polarized light enters the liquid crystal cell 11, in the first state, the linearly polarized light is converted to first circularly polarized light. In the second state, the linearly polarized light is converted to second circularly polarized light, which rotates in a direction opposite to that of the first circularly polarized light. This configuration allows switching between a state in which circularly polarized light incident on the optical element 10 is emitted without modulation and a state in which circularly polarized light is emitted with modulation over a wide bandwidth, while reducing the thickness of the optical element 10. This allows for a thinner optical element 10 that can switch between polarization modulation and non-modulation over a wide bandwidth.

[0162] In the first state, the liquid crystal molecules 311 on the first substrate 100 side are aligned in a first alignment direction 311A. In the second state, the liquid crystal molecules 311 on the first substrate 100 side are aligned in a second alignment direction 311B, which is orthogonal to the first alignment direction 311A, when viewed from above. Here, the alignment direction of the liquid crystal molecules on the first substrate side refers to the alignment direction of the liquid crystal molecules horizontally aligned near the first substrate. More specifically, when the alignment film provided on the liquid crystal layer side of the first substrate is a horizontal alignment film, the alignment direction of the liquid crystal molecules on the first substrate side refers to the alignment direction of the liquid crystal molecules located at the interface of the liquid crystal layer on the first substrate side. When the alignment film provided on the liquid crystal layer side of the first substrate is a vertical alignment film, since the liquid crystal molecules at the interface of the liquid crystal layer on the first substrate side are vertically aligned, the alignment direction of the liquid crystal molecules on the first substrate side refers to the alignment direction of the liquid crystal molecules located inward of the interface on the first substrate side of the liquid crystal layer and in a horizontal alignment state.

[0163] Similarly, the alignment direction of the liquid crystal molecules on the second substrate side refers to the alignment direction of the liquid crystal molecules horizontally aligned near the second substrate. More specifically, when the alignment film provided on the liquid crystal layer side of the second substrate is a horizontal alignment film, the alignment direction of the liquid crystal molecules on the second substrate side refers to the alignment direction of the liquid crystal molecules located at the interface of the liquid crystal layer on the second substrate side. When the alignment film provided on the liquid crystal layer side of the second substrate is a vertical alignment film, since the liquid crystal molecules located at the interface of the liquid crystal layer on the second substrate side are vertically aligned, the alignment direction of the liquid crystal molecules on the second substrate side refers to the alignment direction of the liquid crystal molecules located inward of the liquid crystal layer relative to the interface on the second substrate side and in a horizontal alignment state.

[0164] Here, the alignment direction of the liquid crystal molecules on the first substrate side and the alignment direction of the liquid crystal molecules on the second substrate side can be measured by measuring the liquid crystal cell using Axostan (manufactured by Opto Science). The measurement is performed from the output Mueller matrix. Specifically, when the liquid crystal cell is filled with positive liquid crystal molecules, the measurement is performed when no voltage is applied, and when the liquid crystal cell is filled with negative liquid crystal molecules, the measurement is performed when a voltage (e.g., 5V) is applied. Furthermore, the alignment direction of the liquid crystal molecules on the first substrate side and the alignment direction of the liquid crystal molecules on the second substrate side can be determined by software that fits the cell thickness and twist angle of the liquid crystal within Axostan.

[0165] The switching between the first and second states controls the polarization state of light incident on the liquid crystal cell 11. When circularly polarized light enters the liquid crystal cell 11, in the first state, the circularly polarized light is converted to first linearly polarized light. In the second state, the circularly polarized light is converted to second linearly polarized light, which has a polarization direction orthogonal to that of the first linearly polarized light when viewed from above. When linearly polarized light enters the liquid crystal cell 11, in the first state, the linearly polarized light is converted to first circularly polarized light. In the second state, the linearly polarized light is converted to second circularly polarized light, which rotates in a direction opposite to that of the first circularly polarized light.

[0166] Here, when circularly polarized light enters the liquid crystal cell 11, in the first state, the circularly polarized light can be substantially converted to first linearly polarized light. For example, in the first state, the light can be first linearly polarized light at wavelengths around 550 nm (specifically, between 530 nm and 570 nm), and elliptically polarized light at other wavelengths. Furthermore, in the second state, the circularly polarized light can be substantially converted to second linearly polarized light. For example, in the second state, the light can be second linearly polarized light at wavelengths around 550 nm (specifically, between 530 nm and 570 nm), and elliptically polarized light at other wavelengths.

[0167] Furthermore, when linearly polarized light is incident on the liquid crystal cell 11, in the first state, the linearly polarized light can be substantially converted to first circularly polarized light. For example, in the first state, the linearly polarized light can be first circularly polarized light at wavelengths around 550 nm (specifically, wavelengths between 530 nm and 570 nm), and elliptically polarized light at other wavelengths. Furthermore, in the second state, the linearly polarized light can be substantially converted to second circularly polarized light. For example, in the second state, the linearly polarized light can be second circularly polarized light at wavelengths around 550 nm (specifically, wavelengths between 530 nm and 570 nm), and elliptically polarized light at other wavelengths.

[0168] In this embodiment, the case where circularly polarized light is incident on the liquid crystal cell 11 is described, but the same effect can be obtained also when linearly polarized light is incident on the liquid crystal cell 11 .

[0169] The liquid crystal cell 11 sequentially includes a first substrate 100, a liquid crystal layer 300, and a second substrate 200. In the optical element 10, a bidirectional electric field is generated in the in-plane direction on at least one of the first substrate 100 and the second substrate 200, thereby switching between a first state and a second state.

[0170] For example, by disposing an alignment film with a weak anchoring force, whose alignment-regulating force is as close to zero as possible, between at least one of the first substrate 100 and the liquid crystal layer 300 and between the second substrate 200 and the liquid crystal layer 300, it is possible to switch between the first and second states. Specifically, examples include using an alignment film, known as a slide film, that maintains the alignment of liquid crystal molecules, and using an alignment film that has alignment-regulating force in both azimuth angles of 0° and 90°. Details are described below.

[0171] like Figure 1 As shown, the optical element 10 of this embodiment preferably includes a second quarter-wavelength film 13 on the side opposite the liquid crystal cell 11 of the first quarter-wavelength film 12. This configuration enables switching between polarization modulation and polarization non-modulation over a wider frequency band. The following describes an embodiment in which the optical element 10 includes the liquid crystal cell 11, the first quarter-wavelength film 12, and the second quarter-wavelength film 13, in this order, from the incident side to the exit side.

[0172] like Figure 2 As shown, the liquid crystal cell 11 further includes: a first weak anchoring force horizontal alignment film 411 disposed between the first substrate 100 and the liquid crystal layer 300; and a second weak anchoring force horizontal alignment film 421 disposed between the liquid crystal layer 300 and the second substrate 200. The electrode 11E includes a first comb-tooth electrode 120 on the first substrate 100, arranged so that the comb teeth of the pixel electrode and the common electrode interlock with each other; and a second comb-tooth electrode 220 on the second substrate 200, arranged so that the comb teeth of the pixel electrode and the common electrode interlock with each other. In a plan view, the extension direction 120A of the first comb-tooth electrode 120 is inclined relative to the extension direction 220A of the second comb-tooth electrode 220.

[0173] By adopting this approach, when the first comb-tooth electrode 120 is set to a no-voltage state and the second comb-tooth electrode 220 is set to a voltage-applied state, circularly polarized light (e.g., right-handed circularly polarized light) incident on the liquid crystal cell 11 becomes first linearly polarized light after passing through the liquid crystal cell 11. In other words, the first state is achieved. Furthermore, the first linearly polarized light passes through the first quarter-wavelength film 12 and the second quarter-wavelength film 13, thereby being converted over a wide bandwidth into circularly polarized light (e.g., left-handed circularly polarized light) having a polarization state different from that of the circularly polarized light incident on the liquid crystal cell 11. Thus, in the first state, circularly polarized light incident on the optical element 10 is converted into circularly polarized light having a different polarization state (e.g., right-handed circularly polarized light is converted into left-handed circularly polarized light), and polarization modulation of the emitted light is achieved over a wide bandwidth.

[0174] Furthermore, when the first comb-tooth electrode 120 is in a voltage-applied state and the second comb-tooth electrode 220 is in a voltage-free state, circularly polarized light (e.g., right-handed circularly polarized light) incident on the liquid crystal cell 11, after passing through the liquid crystal cell 11, becomes second linearly polarized light having a polarization direction orthogonal to that of the first linearly polarized light in a plan view. In other words, the second state is achieved. Furthermore, the second linearly polarized light passes through the first quarter-wave film 12 and the second quarter-wave film 13, thereby maintaining the same polarization state as the circularly polarized light incident on the liquid crystal cell 11 (e.g., right-handed circularly polarized light) and emitting it over a wide bandwidth. Thus, in the second state, the circularly polarized light incident on the optical element 10 maintains the same polarization state (e.g., right-handed circularly polarized light), and the polarized light emitted is non-modulated over a wide bandwidth.

[0175] In this embodiment, the liquid crystal cell 11, the first quarter-wavelength film 12, and the second quarter-wavelength film 13 are described in this order from the incident side to the exit side. However, the stacking order may be reversed. Specifically, the second quarter-wavelength film 13, the first quarter-wavelength film 12, and the liquid crystal cell 11 may be provided in this order from the incident side to the exit side. In this case, in the first state, circularly polarized light incident on the optical element 10 is converted to circularly polarized light with a different polarization state (for example, right-handed circularly polarized light is converted to left-handed circularly polarized light) and then exits, achieving broadband polarization modulation. In the second state, circularly polarized light incident on the optical element 10 maintains the same polarization state (for example, remains right-handed circularly polarized light) and then exits, achieving broadband polarization non-modulation. Furthermore, when the stacking order is reversed, the slow axes 12A of the first quarter-wavelength film 12 and the slow axes 13A of the second quarter-wavelength film 13 are appropriately adjusted.

[0176] The liquid crystal layer 300 includes liquid crystal molecules 310 twisted and aligned between the first substrate 100 and the second substrate 200. In each of the first state and the second state, the liquid crystal molecules 310 are twisted and aligned from the first substrate 100 side to the second substrate 200 side.

[0177] The twisted orientation of the liquid crystal molecules 310 can be achieved, for example, by adding a chiral agent to the liquid crystal material. The chiral agent is not particularly limited, and conventionally known chiral agents can be used. For example, S-811 (manufactured by Melku Corporation) can be used.

[0178] In a plan view, the angle formed by the alignment direction (first alignment direction) 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side and the alignment direction 312A of the liquid crystal molecules 312 on the second substrate 200 side in the first state is preferably 57° to 82°, more preferably 63° to 75°, and even more preferably 66° to 72°. By adopting this approach, it is possible to switch between polarization modulation and polarization non-modulation over a wider bandwidth. Hereinafter, the angle formed by the alignment direction of the liquid crystal molecules on the first substrate side and the alignment direction of the liquid crystal molecules on the second substrate side in a plan view is also referred to as the twist angle.

[0179] In a top view, the angle formed by the alignment direction (second alignment direction) 311B of the liquid crystal molecules 311 on the first substrate 100 side and the alignment direction 312B of the liquid crystal molecules 312 on the second substrate 200 side in the second state is preferably 57° to 82°, more preferably 63° to 75°, and even more preferably 66° to 72°. This approach allows for efficient switching between polarization modulation and polarization non-modulation over a wide bandwidth. The twist angle in the first state and the twist angle in the second state may be the same or different, but are preferably the same.

[0180] In a plan view, the angle α (where α is a real number greater than 0° and less than 90°) formed between the extension direction 120A and the extension direction 220A, and the twist angle A of the liquid crystal molecules 310 included in the liquid crystal layer 300, preferably satisfy the following (Formula AX1) in the first state and the second state, more preferably satisfy the following (Formula AX2), and even more preferably satisfy the following (Formula AX3). By adopting this approach, it is possible to effectively switch between polarization modulation and polarization non-modulation over a wide bandwidth.

[0181] 85°-A≤α≤95°-A……(Formula AX1)

[0182] 88°-A≤α≤92°-A……(Formula AX2)

[0183] α=90°-A……(Formula AX3)

[0184] The twist angle A is preferably 60° to 80°, more preferably 64° to 76°, and even more preferably 68° to 72°. This allows for more efficient switching between polarization modulation and polarization non-modulation over a wide bandwidth.

[0185] When the azimuth angle of the extension direction 120A is 0°, the azimuth angle of the extension direction 220A is 160° (i.e., the angle α formed by the extension direction 120A and the extension direction 220A is 20° when viewed from above), the twist angle A of the liquid crystal molecules 310 is 70°, and the liquid crystal layer 300 contains positive liquid crystal molecules 310, as shown in FIG. Figures 3 to 5 As shown, when the first comb-tooth electrodes 120 are in a no-voltage-applied state and the second comb-tooth electrodes 220 are in a voltage-applied state, the first state is achieved when the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side is 0°, and the azimuth angle of the alignment direction 312A of the liquid crystal molecules 312 on the second substrate 200 side is 70°. Furthermore, when the first comb-tooth electrodes 120 are in a voltage-applied state and the second comb-tooth electrodes 220 are in a no-voltage-applied state, the second state is achieved when the azimuth angle of the alignment direction 311B of the liquid crystal molecules 311 on the first substrate 100 side is 90°, and the azimuth angle of the alignment direction 312B of the liquid crystal molecules 312 on the second substrate 200 side is 160°.

[0186] Furthermore, when the liquid crystal layer 300 contains negative-type liquid crystal molecules 310, when a voltage is applied to the first comb-teeth electrodes 120 and no voltage is applied to the second comb-teeth electrodes 220, a first state can be achieved in which the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side is 0°, and the azimuth angle of the alignment direction 312A of the liquid crystal molecules 312 on the second substrate 200 side is 70°. Furthermore, when no voltage is applied to the first comb-teeth electrodes 120 and a voltage is applied to the second comb-teeth electrodes 220, a second state can be achieved in which the azimuth angle of the alignment direction 311B of the liquid crystal molecules 311 on the first substrate 100 side is 90°, and the azimuth angle of the alignment direction 312B of the liquid crystal molecules 312 on the second substrate 200 side is 160°.

[0187] Figure 6 This is a diagram showing the Stokes curves of the respective layers in the first state of the optical element according to the first embodiment. Figure 6 Indicates the polarization state when passing through each layer in the first state (the role of each layer). Figure 6 The principle of polarization modulation of the optical element 10 according to the first embodiment will be described in detail using the Poincare sphere.

[0188] like Figure 6 As shown in (1), right circularly polarized light (S3=+1) is incident on the liquid crystal cell 11.

[0189] After passing through the 70° twisted liquid crystal unit 11, it is converted into Figure 6The polarization state of the plot (2) is shown. Each plot point represents a different plot for wavelengths between 380 nm and 780 nm. Wavelengths around 550 nm are linearly polarized light (on the equator on the Poincare sphere), while wavelengths other than this are plotted in the northern hemisphere of the Poincare sphere and become elliptically polarized light.

[0190] Then, it passes through the first quarter-wavelength film 12 (specifically, the quarter-wavelength film with reverse wavelength dispersion) and becomes Figure 6 Drawing of (3).

[0191] Furthermore, if the light passes through the second quarter wavelength film 13 (specifically, a quarter wavelength film with flat wavelength dispersion), as shown in FIG. Figure 6 As shown in the plot of (4), almost all wavelengths are emitted as left circularly polarized light (at the South Pole position on the Poincare sphere). In other words, it can be seen that modulation is performed from right circularly polarized light to left circularly polarized light.

[0192] In the second state (non-modulation), light similarly passes through the 70° twisted liquid crystal cell 11 and becomes linearly polarized light. However, since the overall orientation of the liquid crystal cell 11 is rotated 90°, the light becomes linearly polarized light at an angle of approximately 90°, different from that in the first state (modulation). Subsequently, after passing through the first quarter-wavelength film 12 and the second quarter-wavelength film 13, all wavelengths become right-handed circularly polarized light. In other words, right-handed circularly polarized light can be emitted as right-handed circularly polarized light, achieving non-modulation.

[0193] Thus, the first and second states are defined as the same orientation of the liquid crystal molecules 310 (i.e., a 70° twist), but the orientation of the system as a whole differs by 90°. The optical element 10 of this embodiment can reversibly switch between the first and second states, achieving a thin, switchable half-wave plate (sHWP) with a wide bandwidth, both when polarization is non-modulated and when polarization is modulated.

[0194] Here, if you want to achieve sHWP in the liquid crystal layer 1, consider Figure 7 The structure of the optical element 10R1 of Comparative Example 1 using a liquid crystal cell 11R1 having a 90° twisted TN liquid crystal layer 300R1 is shown. More specifically, the optical element 10R1 of Comparative Example 1 includes, in this order: a quarter-wavelength film 14R having a slow axis azimuth angle of 75°, a half-wavelength film 15R having a slow axis azimuth angle of 15°, the liquid crystal cell 11R1, a half-wavelength film 16R having a slow axis azimuth angle of -75°, and a quarter-wavelength film 17R having a slow axis azimuth angle of -15°. Figure 7 This is a schematic cross-sectional view of the optical element of Comparative Example 1.

[0195] In addition, if you want to realize sHWP with 2 liquid crystal layers, you can consider Figure 8 As shown, the optical element 10R2 of Comparative Example 2 has a structure in which a TN liquid crystal layer 300R2 with a 70° twist and a TN liquid crystal layer 300R3 with a −70° twist are stacked. Figure 8 This is a schematic cross-sectional view of the optical element of Comparative Example 2.

[0196] Figure 9 This is a graph showing an example of the wavelength dispersion of the Stokes parameter S3 during modulation of the optical elements of the first embodiment, comparative example 1, and comparative example 2. Figure 9 This shows the wavelength dependence of the polarization state of the outgoing light when right-handed circularly polarized light (Stokes parameter S3 = +1) is incident. The closer S3 = -1, the more the light is converted to left-handed circularly polarized light. The modulation over a wide wavelength range, closer to -1, can be considered broadband.

[0197] Although the optical element 10R1 of Comparative Example 1 is easy to design, it is affected by the wavelength dispersion of the TN liquid crystal layer 300R1 with a 90° twist, as shown in FIG. Figure 9 As shown, it is difficult to achieve broadband. In addition, in the optical element 10R2 of comparative mode 2, although broadband can be achieved, it is difficult to achieve thinning. In addition, when polarized light is modulated (when right circularly polarized light is converted into left circularly polarized light), it is broadband, but owing to being driven by a longitudinal electric field, therefore when polarized light is non-modulated (when right circularly polarized light is directly emitted as right circularly polarized light), when voltage is applied, all liquid crystal molecules will not be vertical orientation, will be affected by residual delay and will not become broadband. On the other hand, in the optical element 10 of the present embodiment, it is possible to switch the circularly polarized light to the left and right in a broadband.

[0198] Patent Document 1 above does not disclose polarization modulation properties at all. Patent Document 1 discloses a single-layer TN liquid crystal layer configuration, but this configuration only appropriately converts polarization at specific wavelengths during polarization modulation (inactive or voltage-off as in Patent Document 1), failing to achieve broadband polarization conversion. Furthermore, Patent Document 1 discloses a configuration with multiple stacked liquid crystal layers, but this presents challenges in complicating the manufacture of the optical element and increasing its thickness.

[0199] More specifically, in the single-layer structure disclosed in Patent Document 1, the liquid crystal molecules adopt a 90° twisted orientation during polarization modulation, while the liquid crystal molecules are vertically aligned due to the application of a longitudinal electric field during polarization non-modulation. The 90° twisted orientation of the liquid crystal molecules during polarization modulation is wavelength-dependent, making it impossible to achieve polarization modulation over a wide bandwidth. Even if polarization modulation can be achieved over a wide bandwidth by adjusting the twist angle of the liquid crystal molecules and the cell thickness of the liquid crystal layer, the residual retardation caused by the liquid crystal molecules near the substrate during polarization non-modulation will prevent the wide-band polarization non-modulation. In other words, it is impossible to achieve both polarization modulation and polarization non-modulation over a wide bandwidth.

[0200] Meanwhile, in the optical element 10 of this embodiment, the liquid crystal molecules 310 maintain a 70° twist state both during polarization modulation and non-polarization modulation. These two states are driven identically, except that the entire system is rotated 90°. As a result, polarization modulation and non-polarization modulation can be achieved over a wide bandwidth.

[0201] The above-mentioned patent document 2 discloses a variable focus element that combines multiple groups of sHWP and Pancharatnam Berry (PB: Pancharatnam Berry) lens groups (for example, 6 groups) to give tunability to the depth of focus. Therefore, if the sHWP becomes thicker, there is a problem that the entire variable focus element becomes thicker. In the structure of realizing sHWP with two liquid crystal layers (70° twisted TN liquid crystal layer 300R2 and -70° twisted TN liquid crystal layer 300R3) such as the above-mentioned comparison method 2, 12 layers of liquid crystal layers in 6 groups are required, and there is a problem that it is difficult to make the variable focus element thinner. Therefore, the sHWP, that is, the optical element, is required to be thin and capable of realizing polarization modulation and polarization non-modulation in a wide band.

[0202] The first substrate 100 includes a first support substrate 110 and a first comb-shaped electrode 120 . The second substrate 200 includes a second support substrate 210 and a second comb-shaped electrode 220 .

[0203] Examples of the first support substrate 110 and the second support substrate 210 include insulating substrates such as glass substrates and plastic substrates. Examples of materials for the glass substrates include float glass, soda-lime glass, and the like. Examples of materials for the plastic substrates include plastics such as polyethylene terephthalate, polybutylene terephthalate, polyethersulfone, polycarbonate, and alicyclic polyolefins.

[0204] The first comb-tooth electrode 120 includes a first pixel electrode as a comb-tooth electrode and a first common electrode as a comb-tooth electrode. The second comb-tooth electrode 220 includes a second pixel electrode as a comb-tooth electrode and a second common electrode as a comb-tooth electrode. Hereinafter, the first pixel electrode and the second pixel electrode are referred to as pixel electrodes, and the first common electrode and the second common electrode are referred to as common electrodes. The pixel electrode and the common electrode can be formed, for example, by forming a transparent conductive material such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), tin oxide (SnO), or an alloy thereof in a single layer or multiple layers by sputtering, and then patterning them using photolithography.

[0205] The pitch of the first comb-tooth electrode 120 is preferably greater than 1 μm and less than 5 μm. By adopting this method, the liquid crystal molecules 311 on the first substrate 100 side can be efficiently rotated, and a uniform twist orientation can be easily obtained. Similarly, the pitch of the second comb-tooth electrode 220 is preferably greater than 1 μm and less than 5 μm. By adopting this method, the liquid crystal molecules 312 on the second substrate 200 side can be effectively rotated, and a uniform twist orientation can be easily obtained. Here, the comb-tooth electrode has a structure in which linear electrode portions and slit portions are alternately and repeatedly arranged, and the pitch of the comb-tooth electrode refers to the sum of the widths of a group of linear electrode portions and slit portions.

[0206] In this specification, the applied voltage state in which a voltage above the threshold is applied between a pair of common electrodes and the pixel electrode is also referred to as the "applied voltage state" or "when voltage is applied", and the no-voltage-applied state in which no voltage is applied between a pair of common electrodes and the pixel electrode (including the case where a voltage less than the threshold is applied) is also referred to as the "no-voltage-applied state" or "when no voltage is applied".

[0207] The liquid crystal layer 300 includes a liquid crystal material. When a voltage is applied to the liquid crystal layer 300 , the alignment state of liquid crystal molecules 310 in the liquid crystal material changes according to the applied voltage, thereby changing the polarization state of light passing through the liquid crystal layer 300 .

[0208] The liquid crystal molecules 310 can be either positive liquid crystal molecules having a positive dielectric anisotropy (Δε) as defined by the following formula (L), or negative liquid crystal molecules having a negative dielectric anisotropy (Δε). However, in this embodiment, positive liquid crystal molecules are used as an example for description. In addition, the long axis direction of the liquid crystal molecules is the direction of the lag axis. In addition, the liquid crystal molecules are homogeneously oriented in a state where no voltage is applied (no voltage applied state), and the direction of the long axis of the liquid crystal molecules in the no voltage applied state is also referred to as the direction of the initial orientation of the liquid crystal molecules.

[0209] Δε=(dielectric constant of the liquid crystal molecule in the long axis direction)-(dielectric constant of the liquid crystal molecule in the short axis direction)……(L)

[0210] The retardation Δnd of the liquid crystal layer 300 at a wavelength of 550 nm in the no-voltage state is preferably 180 nm to 280 nm, more preferably 200 nm to 260 nm, and even more preferably 220 nm to 240 nm. This approach enables switching between polarization modulation and non-polarization modulation over a wider bandwidth.

[0211] The refractive index anisotropy Δn of the liquid crystal layer 300 is preferably 0.12 or less, more preferably 0.1 or less. This reduces the wavelength dispersion of the liquid crystal layer 300 itself, and enables switching between polarization modulation and polarization non-modulation over a wider bandwidth.

[0212] The thickness d of the liquid crystal layer 300 is preferably not less than 2 μm and not more than 4.2 μm.

[0213] The horizontal orientation film 411 with a first weak anchoring force and the horizontal orientation film 421 with a second weak anchoring force are described. A weak anchoring force orientation film refers to an orientation film having a weak orientation limiting force relative to the liquid crystal molecules. In the weak anchoring force orientation film of this embodiment, viscoelasticity becomes an important factor compared to simple anchoring energy (elasticity). The weak anchoring force orientation film can be, for example, a lubricated interface. In this specification, a lubricated interface refers to an interface induced by a lubricated interface sensing region. A lubricated interface sensing region refers to a region of low order compared to the liquid crystal phase.

[0214] The lubricity interface sensing region may also be a lubricity interface inducing liquid region. The lubricity interface inducing liquid region refers to a region within the lubricity interface sensing region that is a liquid phase. The lubricity interface sensing region is not limited to the lubricity interface inducing liquid region (liquid phase) but may also include a region forming a gel layer, a region with a low order parameter (degree of orientation order), a region with a low clearing point, an ordered region containing a partially disordered region, or a region containing a region with high mobility.

[0215] The lubricating interface sensing region preferably contains a lubricating interface inducer. The lubricating interface sensing region may contain only the lubricating interface inducer or a lubricating interface inducer and a liquid crystal component. Furthermore, the lubricating interface inducer may be contained within the liquid crystal layer 300 or introduced independently of the liquid crystal layer 300. The lubricating interface inducer may be pre-incorporated into the supporting substrate or chemically modified in advance and bonded to the supporting substrate.

[0216] The lubricating interface inducer is preferably a compound having a polar group, a polymerizable compound, a high molecular compound or an ionic liquid. The high molecular compound preferably has at least one of two or more alkyl groups of different chain lengths, a mesogenic group, and a group capable of photoisomerization.

[0217] The liquid crystal layer 300 and the lubricating interface inducer preferably exhibit a phase separation structure, wherein the liquid crystal layer 300 forms a liquid crystal phase and the lubricating interface inducer forms a liquid phase in the lubricating interface induction region. The lubricating interface inducer may also form a gel layer in the lubricating interface induction region that is lower in order than the liquid crystal phase.

[0218] The alignment film with a weak anchoring force is preferably provided at a slipper interface between the liquid crystal layer 300 and the lubricated interface sensing region, for example.

[0219] The first weak anchoring force horizontal alignment film 411 and the second weak anchoring force horizontal alignment film 421 are preferably a sliding interface (lubricating film). For example, a material containing lauryl acrylate is mixed into the liquid crystal layer 300. The liquid phase (isotropic phase) of the lauryl acrylate forms a lubricating interface sensing region between the liquid crystal layer 300 and the first substrate 100 and between the liquid crystal layer 300 and the second substrate 200, and a lubricating film is formed at the interface between the liquid crystal layer 300 and the lubricating interface sensing region.

[0220] By having such an interface, the liquid crystal molecules can be oriented in any direction using an electric field and maintained in that state. The film that stores this orientation on the lubricating film is sometimes called a sliding film. If an electric field is applied in another direction after alignment in a certain direction, the liquid crystal molecules can be oriented in another direction. In other words, multiple stable states can be created using an electric field. In this embodiment, both a first state and a second state can be created. In addition to the materials exemplified above, materials described in Japanese Patent Application Publication No. 2006-084536, International Publication No. 2017 / 034023, and the like can also be used.

[0221] For example, the oriented film with weak anchoring force can have an azimuthal anchoring energy less than 1×10 -4 J / m 2 The azimuthal anchoring energy can be calculated by various well-known methods such as the torque balance method, the Nevault method, the calculation based on the electric field response threshold, and the calculation based on the rotating magnetic field. In addition, the azimuthal anchoring energy described in this specification is calculated using the calculation method based on the electric field response threshold. The lower limit of the azimuthal anchoring energy of the weak anchoring force alignment film is not particularly limited. For example, the azimuthal anchoring energy of the weak anchoring force alignment film is 1×10 -10 J / m 2 above.

[0222] The azimuthal anchoring energy of the horizontal alignment film 411 with the first weak anchoring force is preferably 1×10 -10 J / m 2 More than and less than 1×10 -4 J / m 2 , more preferably 1×10-10 J / m 2 Above and 1×10 -5 J / m 2 Below, more preferably 1×10 -10 J / m 2 Above and 1×10 -6 J / m 2 By adopting such a method, it is possible to efficiently switch between polarization modulation and polarization non-modulation in a wide band.

[0223] The azimuthal anchoring energy of the horizontal alignment film 421 with the second weak anchoring force is preferably 1×10 -10 J / m 2 More than and less than 1×10 -4 J / m 2 , more preferably 1×10 -10 J / m 2 Above and 1×10 -5 J / m 2 Below, more preferably 1×10 -10 J / m 2 Above and 1×10 -6 J / m 2 By adopting such a method, it is possible to efficiently switch between polarization modulation and polarization non-modulation in a wide band.

[0224] The weak anchoring alignment film can be formed by an alignment treatment or without an alignment treatment. Specifically, the weak anchoring alignment film can be a rubbed alignment film, a photo-aligned film, or an untreated alignment film.

[0225] A rubbed alignment film can be obtained, for example, by forming an alignment film material containing a rubbed alignment film polymer onto a substrate, rotating a roller wrapped with a cloth made of rayon, cotton, or the like at a constant rotational speed and with a constant distance between the roller and the substrate, and rubbing the surface of the film containing the rubbed alignment film polymer in a predetermined direction (rubbing method). By varying the rubbing treatment conditions, the azimuthal anchoring energy of the alignment film can be adjusted, resulting in an alignment film with a weak anchoring force.

[0226] Examples of the polymer for the rubbed alignment film include polyimide, etc. The polymer for the rubbed alignment film contained in the rubbed alignment film may be one type or two or more types.

[0227] A photo-alignment film can be obtained, for example, by forming a film of an alignment film material containing a photo-alignment polymer having photofunctional groups on a substrate and then irradiating the film with polarized ultraviolet light to generate anisotropy on the surface of the film containing the photo-alignment polymer (photo-alignment method). By varying the photo-alignment treatment conditions and material structure, the azimuthal anchoring energy of the alignment film can be adjusted, resulting in an alignment film with a weak anchoring force.

[0228] Examples of the photo-aligning polymer include photo-aligning polymers having at least one photofunctional group selected from the group consisting of a cyclobutane group, an azophenyl group, a chalcone group, a cinnamate group, a coumarin group, a stilbene group, a phenolic ester group, and a phenyl benzoate group. The photo-aligning polymers included in the photo-aligning film may be one or more. The photofunctional groups of the photo-aligning polymer may be present in the main chain of the polymer, in the side chains of the polymer, or in both the main chain and the side chains of the polymer.

[0229] The photoreaction type of the above-mentioned photo-orientation polymer is not particularly limited, and examples of preferred photodegradable polymers, photorearrangement polymers (preferably photoFries rearrangement polymers), photoisomerization polymers, photodimerization polymers, and photocrosslinking polymers can be cited. Any one of these can be used alone, or two or more can be used simultaneously. Among them, from the viewpoint of orientation stability, photodegradable polymers with a reaction wavelength (main sensitivity wavelength) near 254 nm and photorearrangement polymers with a reaction wavelength (main sensitivity wavelength) near 254 nm are particularly preferred. Also preferred are photoisomerization polymers and photodimerization polymers with photofunctional groups in the side chains.

[0230] The main chain structure of the photo-alignment polymer is not particularly limited, and preferred examples include a polyamic acid structure, a polyimide structure, a poly(meth)acrylic acid structure, a polysiloxane structure, a polyethylene structure, a polystyrene structure, and a polyethylene structure.

[0231] The untreated alignment film is obtained, for example, by forming an alignment film material containing an alignment film polymer on a substrate. Examples of the alignment film polymer include polyimide and polyhexyl methacrylate. The untreated alignment film may contain one or more alignment film polymers.

[0232] Examples of the alignment film polymer contained in the untreated alignment film include, in addition to polyimide and polyhexyl methacrylate, polymers described in International Publication No. 2017 / 034023. Among them, polyalkylene oxides such as polyethylene glycol and polypropylene glycol are preferred.

[0233] The horizontal alignment film has the function of aligning the liquid crystal molecules in the liquid crystal layer horizontally relative to the surface of the horizontal alignment film when no voltage is applied. Here, "horizontally aligning the liquid crystal molecules relative to the surface of the horizontal alignment film" means that the pretilt angle of the liquid crystal molecules relative to the surface of the horizontal alignment film is 0° or greater and 5° or less, preferably 0° or greater and 2° or less, and more preferably 0° or greater and 1° or less. The pretilt angle of the liquid crystal molecules refers to the angle at which the long axis of the liquid crystal molecules is tilted relative to the main surface of the alignment film when no voltage is applied to the liquid crystal layer.

[0234] In this specification, the alignment film disposed between the first substrate 100 and the liquid crystal layer 300 is referred to as a first alignment film 410 , and the alignment film disposed between the second substrate 200 and the liquid crystal layer 300 is referred to as a second alignment film 420 .

[0235] The quarter-wave films (specifically, the first quarter-wave film 12 and the second quarter-wave film 13 ) only need to provide an in-plane phase difference of 20 nm to 240 nm inclusive to light having a wavelength of at least 550 nm.

[0236] Examples of materials for the quarter-wavelength film include photopolymerizable liquid crystal materials, etc. Examples of photopolymerizable liquid crystal materials include structures having photopolymerizable groups such as acrylate groups and methacrylate groups at the ends of the liquid crystal molecule skeleton.

[0237] The quarter-wavelength film can be formed, for example, by the following method. First, a photopolymerizable liquid crystal material is dissolved in an organic solvent such as propylene glycol monomethyl ether acetate (PGMEA). Next, the resulting solution is applied to the surface of a substrate (e.g., a polyethylene terephthalate (PET) film) to form a coating of the solution. The coating of the solution is then subjected to pre-firing, light irradiation (e.g., ultraviolet irradiation), and final firing in sequence to form a quarter-wavelength film.

[0238] Alternatively, a liquid crystal polymer obtained by adding a chiral agent to the above-mentioned photopolymerizable liquid crystal material and polymerizing the material in a 70° twisted state may be used as a quarter-wavelength film.

[0239] As the quarter-wavelength film, for example, a stretched polymer film may be used. Examples of the material of the polymer film include cycloolefin polymer, polycarbonate, polysulfone, polyethersulfone, polyethylene terephthalate, polyethylene, polyvinyl alcohol, norbornene, triacetyl cellulose, and diacetyl cellulose.

[0240] The first 1 / 4 wavelength film 12 preferably has a reverse wavelength dispersion characteristic. By adopting this method, it is possible to switch between polarization modulation and polarization non-modulation in a wider band. Here, in this specification, the "wavelength dispersion of the phase difference film" refers to the correlation between the absolute value of the phase difference imparted by the phase difference film and the wavelength of the incident light. The property that the absolute value of the phase difference imparted by the phase difference film does not change even if the wavelength of the incident light changes in the visible light region is called "flat wavelength dispersion characteristic". In addition, the property that the absolute value of the phase difference imparted by the phase difference film in the visible light region becomes smaller as the wavelength of the incident light becomes larger is called "positive wavelength dispersion characteristic", and the property that the absolute value of the phase difference imparted by the phase difference film in the visible light region becomes larger as the wavelength of the incident light becomes larger is called "reverse wavelength dispersion characteristic".

[0241] The in-plane retardation of the first quarter-wavelength film 12 at a wavelength of 450 nm is preferably 0.7 to 1 times the in-plane retardation at a wavelength of 550 nm. This configuration enables switching between polarization modulation and polarization non-modulation over a wider bandwidth.

[0242] The in-plane retardation of the first quarter-wavelength film 12 at a wavelength of 650 nm is preferably 1 to 1.3 times that of the in-plane retardation at a wavelength of 550 nm.

[0243] The in-plane phase difference of the first quarter-wavelength film 12 at a wavelength of 550 nm is preferably 30 nm or more and 230 nm or less. By adopting such a configuration, it is possible to switch between polarization modulation and polarization non-modulation in a wider bandwidth.

[0244] When the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is set to 0°, the azimuth angle of the slow axis of the quarter-wavelength film on the side away from the light emission side of the first quarter-wavelength film 12 and the second quarter-wavelength film 13 (in this embodiment, the slow axis 12A of the first quarter-wavelength film 12) is preferably 48° to 66°. This approach enables switching between polarization modulation and polarization non-modulation over a wider bandwidth.

[0245] The second quarter-wavelength film 13 preferably has a flat wavelength dispersion characteristic. By adopting this method, it is possible to switch between polarization modulation and polarization non-modulation in a wider frequency band.

[0246] The in-plane phase difference of the second quarter-wavelength film 13 at a wavelength of 550 nm is preferably 110 nm to 175 nm. By adopting this configuration, it is possible to switch between polarization modulation and polarization non-modulation in a wider bandwidth.

[0247] When the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is 0°, the azimuth angle of the lag axis of the lag axis on the side of the first quarter-wavelength film 12 and the second quarter-wavelength film 13 closer to the light emitting side (in this embodiment, the lag axis 13A of the second quarter-wavelength film 13) is preferably 3° or more and 22° or less. This approach enables switching between polarization modulation and polarization non-modulation over a wider bandwidth.

[0248] The angle between the slow axis 12A of the first quarter-wavelength film 12 and the slow axis 13A of the second quarter-wavelength film 13 is preferably 40° to 50°, more preferably 42° to 48°, further preferably 44° to 46°, and particularly preferably 45°.

[0249] In this embodiment, in which the liquid crystal layer 300 includes positive liquid crystal molecules 310, in a plan view, the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state coincides with the extension direction 120A of the first comb-tooth electrode 120. Therefore, when the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is set to 0°, for example, Figure 5 As shown, the azimuth angle of the extension direction 120A can be set to 0°, the azimuth angle of the extension direction 220A can be set to 160°, the azimuth angle of the lag axis 12A of the first 1 / 4 wavelength film 12 can be set to 57.2°, and the azimuth angle of the lag axis 13A of the second 1 / 4 wavelength film 13 can be set to 12.2°.

[0250] It is preferable that the light incident on the optical element 10 is circularly polarized light. By adopting such a configuration, it is possible to realize the optical element 10 capable of switching the polarization state of circularly polarized light.

[0251] (Second embodiment)

[0252] In this embodiment, the features unique to this embodiment will be mainly described, and the description of the contents overlapping with the first embodiment will be omitted. This embodiment is substantially the same as the first embodiment except that the configuration of the liquid crystal cell 11 is different.

[0253] Figure 10 It is a schematic cross-sectional view of a liquid crystal cell included in the optical element of the second embodiment. Figure 11 It is a schematic perspective view of a liquid crystal cell included in the optical element according to the second embodiment. Figure 12 It is a schematic plan view showing the direction of the electric field applied to the optical element of the second embodiment. Figure 13 This is a diagram showing an example of the axial orientation of the optical element according to the second embodiment.

[0254] like Figure 10 as well as Figure 11 As shown, the liquid crystal cell 11 included in the optical element 10 of this embodiment further includes: a horizontal alignment film 412 with a weak anchoring force, disposed between the first substrate 100 and the liquid crystal layer 300; and a vertical alignment film 422, disposed between the liquid crystal layer 300 and the second substrate 200. The electrode 11E includes: a first comb-tooth electrode 121, disposed on the first substrate 100, with the comb-teeth of the comb-shaped pixel electrode and the common electrode interlocking; and a second comb-tooth electrode 122, overlapping the first comb-tooth electrode 121 with the insulating layer 140 interposed therebetween, with the comb-teeth of the comb-shaped pixel electrode and the common electrode interlocking. In a plan view, the extension direction 121A of the first comb-tooth electrode 121 is orthogonal to the extension direction 122A of the second comb-tooth electrode 122.

[0255] By adopting this approach, Figure 12 and Figure 13 As shown, when the first comb-tooth electrode 121 is in a no-voltage state and the second comb-tooth electrode 122 is in a voltage-applied state, circularly polarized light (e.g., right-handed circularly polarized light) incident on the liquid crystal cell 11 becomes first linearly polarized light after passing through the liquid crystal cell 11. In other words, the first state is achieved. Furthermore, the first linearly polarized light passes through the first quarter-wavelength film 12 and the second quarter-wavelength film 13, thereby being converted over a wide bandwidth into circularly polarized light (e.g., left-handed circularly polarized light) having a polarization state different from that of the circularly polarized light incident on the liquid crystal cell 11. Thus, in the first state, circularly polarized light incident on the optical element 10 is converted into circularly polarized light of a different polarization state (e.g., right-handed circularly polarized light is converted into left-handed circularly polarized light), and polarization modulation of the emitted light is achieved over a wide bandwidth.

[0256] Furthermore, when the first comb-tooth electrode 121 is in a voltage-applied state and the second comb-tooth electrode 122 is in a voltage-free state, circularly polarized light (e.g., right-handed circularly polarized light) incident on the liquid crystal cell 11, after passing through the liquid crystal cell 11, becomes second linearly polarized light having a polarization direction orthogonal to that of the first linearly polarized light in a plan view. In other words, the second state is achieved. Furthermore, the second linearly polarized light passes through the first quarter-wavelength film 12 and the second quarter-wavelength film 13, maintaining the same polarization state as the circularly polarized light incident on the liquid crystal cell 11 (e.g., right-handed circularly polarized light) while being emitted over a wide bandwidth. Thus, in the second state, the circularly polarized light incident on the optical element 10 maintains the same polarization state (e.g., right-handed circularly polarized light) while being emitted without modulation over a wide bandwidth.

[0257] like Figure 10As shown, the liquid crystal cell 11 of this embodiment is a twisted HAN (Hybrid Aligned Nematic) cell, which comprises, from the incident side to the outgoing side, a first substrate 100, a horizontal alignment film 412 with a weak anchoring force acting as a lubricating film, a liquid crystal layer 300 to which a chiral agent is added, a vertical alignment film 422, and a second substrate 200. The liquid crystal molecules 310 contained in the liquid crystal layer 300 can be either negative-type or positive-type. In this embodiment, the case where the liquid crystal layer 300 contains positive-type liquid crystal molecules 310 is used as an example for description.

[0258] like Figure 11 As shown, the first substrate 100 includes a first support substrate 110 , a second comb-tooth electrode 122 , an insulating layer 140 , and a first comb-tooth electrode 121 in this order. The second substrate 200 includes a second support substrate 210 .

[0259] The insulating layer 140 has the function of insulating the first comb-tooth electrode 121 from the second comb-tooth electrode 122. As the insulating layer 140, an inorganic insulating film, an organic insulating film, or a laminate of the organic insulating film and the inorganic insulating film can be used. As the inorganic insulating film, for example, silicon nitride (SiN x ), inorganic films such as silicon oxide (SiO2) (relative dielectric constant ε = 5 to 7), and laminated films thereof. As the organic insulating film, for example, an organic film with a low relative dielectric constant (relative dielectric constant ε = 2 to 5) such as a photosensitive acrylic resin or laminated films thereof can be used. More specifically, as the organic insulating film, an organic film such as an acrylic resin, a polyimide resin, or a novolac resin or laminated bodies thereof can be used.

[0260] The first comb-tooth electrode 121 includes a first pixel electrode as a comb-tooth electrode and a first common electrode as a comb-tooth electrode. The second comb-tooth electrode 122 includes a second pixel electrode as a comb-tooth electrode and a second common electrode as a comb-tooth electrode.

[0261] The pitch of the first comb-tooth electrodes 121 is preferably between 1 μm and 5 μm. This allows the liquid crystal molecules 311 on the first substrate 100 side to rotate efficiently, facilitating uniform twist alignment. Similarly, the pitch of the second comb-tooth electrodes 122 is preferably between 1 μm and 5 μm. This allows the liquid crystal molecules 311 on the first substrate 100 side to rotate efficiently, facilitating uniform twist alignment.

[0262] like Figure 12As shown, when a voltage is applied to the second comb-tooth electrode 122 and no voltage is applied to the first comb-tooth electrode 121, an electric field is generated in the first electric field direction 120E1 (first state). When no voltage is applied to the second comb-tooth electrode 122 and a voltage is applied to the first comb-tooth electrode 121, an electric field is generated in the second electric field direction 120E2 (second state). In this way, the optical element 10 of the second embodiment can rotate the azimuth angle of the alignment direction of the liquid crystal molecules 311 on the first substrate 100 side by 90 degrees using the electric field.

[0263] The vertical alignment film 422 has the function of aligning the liquid crystal molecules in the liquid crystal layer perpendicularly to the surface of the vertical alignment film when no voltage is applied. Here, the liquid crystal molecules being aligned perpendicularly to the surface of the vertical alignment film means that the pretilt angle of the liquid crystal molecules relative to the surface of the vertical alignment film is 86° to 90°, preferably 87° to 89°, and more preferably 87.5° to 89°.

[0264] The vertical alignment film 422 is preferably a strongly anchored vertical alignment film. A strongly anchored alignment film refers to an alignment film with a strong orientation restriction force on liquid crystal molecules, for example, an azimuthal anchoring energy of 1×10 -4 J / m 2 The upper limit of the azimuthal anchoring energy of the strongly anchored alignment film is not particularly limited, but the azimuthal anchoring energy of the strongly anchored alignment film is, for example, 1×10 -1 J / m 2 the following.

[0265] The azimuthal anchoring energy of the vertical alignment film 422 is preferably 1×10 -4 J / m 2 Above and 1×10 -1 J / m 2 By adopting such a method, it is possible to switch between polarization modulation and polarization non-modulation in a wider frequency band.

[0266] The horizontal alignment film 412 with a weak anchoring force is preferably a lubricating film. By adopting this method, it is possible to switch between polarization modulation and polarization non-modulation in a wider frequency band.

[0267] In the first embodiment described above, since the alignment films on both sides have weak anchoring forces, there is room for improvement in the alignment twist and response speed. In this embodiment in which one side is vertically aligned (HAN structure), since one side is strongly anchored by the vertical alignment film 422, the alignment is easily stabilized, and an optical element 10 with excellent reliability can be formed. In the case of the HAN structure, not only the azimuthal anchoring energy of the weakly anchored horizontal alignment film 412 is important, but also the polar anchoring energy. Due to the HAN orientation, if the polar anchoring energy of the weakly anchored horizontal alignment film 412 is small, it will be affected by the strongly anchored alignment film (vertical alignment film 422) on the second substrate 200 side, and it will be easy to collapse from the ideal HAN orientation.

[0268] Therefore, the polar angle anchoring energy of the horizontal alignment film 412 with weak anchoring force is preferably 1×10 -5 J / m 2 More than 1×10 -4 J / m 2 More than 1×10 -3 J / m 2 The upper limit of the polar angle anchoring energy of the horizontal alignment film 412 with a weak anchoring force is not particularly limited. For example, the polar angle anchoring energy of the horizontal alignment film 412 with a weak anchoring force is 1×10 -1 J / m 2 Polar angle anchoring energy can be measured by the same method as azimuthal angle anchoring energy. In addition, polar angle anchoring energy of an alignment film can be adjusted by the same method as azimuthal angle anchoring energy.

[0269] The polar angle anchoring energy of the horizontal alignment film 412 with weak anchoring force is preferably 1×10 -5 J / m 2 Above and 1×10- 1 J / m 2 Below, more preferably 1×10 -4 J / m 2 Above and 1×10 -1 J / m 2 Below, more preferably 1×10 -3 J / m 2 Above and 1×10 - 1 J / m 2 By adopting such a method, it is easy to obtain an ideal HAN orientation.

[0270] In this embodiment, in which the liquid crystal layer 300 includes positive liquid crystal molecules 310, in a plan view, the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state coincides with the extension direction 121A of the first comb-tooth electrodes 121. Therefore, when the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is set to 0°, for example, Figure 13 As shown, the azimuth angle of the extension direction 121A can be set to 0°, the azimuth angle of the extension direction 122A can be set to 90°, the azimuth angle of the lag axis 13A of the second 1 / 4 wavelength film 13 can be set to 4°, and the azimuth angle of the lag axis 12A of the first 1 / 4 wavelength film 12 can be set to 49°.

[0271] (Third embodiment)

[0272] In this embodiment, the features unique to this embodiment will be mainly described, and the description of the contents overlapping with those in the first and second embodiments will be omitted. This embodiment is substantially the same as the first embodiment except that the configuration of the liquid crystal cell 11 is different.

[0273] Figure 14 It is a schematic perspective view of a liquid crystal cell included in the optical element according to the third embodiment. Figure 15 These are schematic diagrams for explaining the alignment of liquid crystal molecules in the first state and the second state of the optical element according to the third embodiment.

[0274] like Figure 14 and Figure 15 As shown, the electrode 11E possessed by the optical element 10 of this embodiment has on the first substrate 100: a first comb-tooth electrode 121, which is arranged in a manner that the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other; and a second comb-tooth electrode 122, which overlaps with the first comb-tooth electrode 121 via the first insulating layer 141 and is arranged in a manner that the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other, and has on the second substrate 200: a third comb-tooth electrode 221, which is arranged in a manner that the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other; and a fourth comb-tooth electrode 222, which overlaps with the third comb-tooth electrode 221 via the second insulating layer 241 and is arranged in a manner that the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other. When viewed from above, the extension direction 121A of the first comb-tooth electrode 121 is orthogonal to the extension direction 122A of the second comb-tooth electrode 122, the extension direction 221A of the third comb-tooth electrode 221 is orthogonal to the extension direction 222A of the fourth comb-tooth electrode 222, and the extension direction 121A of the first comb-tooth electrode 121 is inclined relative to the extension direction 221A of the third comb-tooth electrode 221.

[0275] By adopting this approach, Figure 15As shown, when the first comb-tooth electrode 121 is in a no-voltage state, the second comb-tooth electrode 122 is in a voltage-applied state, the third comb-tooth electrode 221 is in a voltage-applied state, and the fourth comb-tooth electrode 222 is in a no-voltage state, circularly polarized light (e.g., right-handed circularly polarized light) incident on the liquid crystal cell 11 becomes first linearly polarized light after passing through the liquid crystal cell 11. In other words, the first state is achieved. Furthermore, the first linearly polarized light passes through the first quarter-wavelength film 12 and the second quarter-wavelength film 13, thereby being converted over a wide bandwidth into circularly polarized light (e.g., left-handed circularly polarized light) having a polarization state different from that of the circularly polarized light incident on the liquid crystal cell 11. Thus, in the first state, circularly polarized light incident on the optical element 10 is converted into circularly polarized light of a different polarization state (e.g., right-handed circularly polarized light is converted into left-handed circularly polarized light), and polarization modulation of the emitted light is achieved over a wide bandwidth.

[0276] Furthermore, when the first comb-tooth electrode 121 is in a voltage-applied state, the second comb-tooth electrode 122 is in a voltage-free state, the third comb-tooth electrode 221 is in a voltage-free state, and the fourth comb-tooth electrode 222 is in a voltage-applied state, circularly polarized light (e.g., right-handed circularly polarized light) incident on the liquid crystal cell 11 becomes second linearly polarized light after passing through the liquid crystal cell 11. This second linearly polarized light has a polarization direction orthogonal to that of the first linearly polarized light when viewed from above. In other words, the second state is achieved. Furthermore, the second linearly polarized light passes through the first quarter-wavelength film 12 and the second quarter-wavelength film 13, maintaining the same polarization state as the circularly polarized light incident on the liquid crystal cell 11 (e.g., right-handed circularly polarized light) and exiting the optical element 10 over a wide bandwidth. Thus, in the second state, the circularly polarized light incident on the optical element 10 maintains the same polarization state (e.g., right-handed circularly polarized light) and exits the optical element 10 unmodulated over a wide bandwidth.

[0277] Thus, in the optical element 10 of this embodiment, a first state and a second state can be achieved by applying a voltage to both the first substrate 100 and the second substrate 200 and then reducing the voltage. In the first and second states, the direction of the electric field on each substrate differs by 90°. In this embodiment, the orientation of both the first substrate 100 and the second substrate 200 can be controlled by voltage, thereby improving the response speed.

[0278] like Figure 14 As shown, the first substrate 100 includes a first support substrate 110, a second comb-tooth electrode 122, a first insulating layer 141, and the first comb-tooth electrode 121 in this order. The second substrate 200 includes a second support substrate 210, a third comb-tooth electrode 221, a second insulating layer 241, and a fourth comb-tooth electrode 222 in this order.

[0279] First insulating layer 141 insulates first comb-tooth electrode 121 from second comb-tooth electrode 122. Second insulating layer 241 insulates third comb-tooth electrode 221 from fourth comb-tooth electrode 222. The same insulating layers as insulating layer 140 can be used as first insulating layer 141 and second insulating layer 241.

[0280] The first comb-tooth electrode 121 includes a first pixel electrode serving as a comb-tooth electrode and a first common electrode serving as a comb-tooth electrode. The second comb-tooth electrode 122 includes a second pixel electrode serving as a comb-tooth electrode and a second common electrode serving as a comb-tooth electrode. The third comb-tooth electrode 221 includes a third pixel electrode serving as a comb-tooth electrode and a third common electrode serving as a comb-tooth electrode. The fourth comb-tooth electrode 222 includes a fourth pixel electrode serving as a comb-tooth electrode and a fourth common electrode serving as a comb-tooth electrode.

[0281] The pitch of the first comb-tooth electrodes 121 is preferably between 1 μm and 5 μm. This allows the liquid crystal molecules 311 on the first substrate 100 side to rotate efficiently, facilitating uniform twist alignment. Similarly, the pitch of the second comb-tooth electrodes 122 is preferably between 1 μm and 5 μm. This allows the liquid crystal molecules 311 on the first substrate 100 side to rotate efficiently, facilitating uniform twist alignment.

[0282] The pitch of the third comb-tooth electrodes 221 is preferably between 1 μm and 5 μm. This arrangement effectively rotates the liquid crystal molecules 312 on the second substrate 200 side, facilitating uniform twist alignment. Similarly, the pitch of the fourth comb-tooth electrodes 222 is preferably between 1 μm and 5 μm. This arrangement effectively rotates the liquid crystal molecules 312 on the second substrate 200 side, facilitating uniform twist alignment.

[0283] In a plan view, the angle β (where β is a real number greater than 0° and less than 90°) formed between the extension direction 121A and the extension direction 221A, and the twist angle B of the liquid crystal molecules 310 contained in the liquid crystal layer 300, preferably satisfy the following (Equation BX1) in the first state and the second state, more preferably satisfy the following (Equation BX2), and even more preferably satisfy the following (Equation BX3). By adopting this approach, it is possible to effectively switch between polarization modulation and polarization non-modulation over a wide bandwidth.

[0284] 85°-B≤β≤95°-B……(Formula BX1)

[0285] 88°-B≤β≤92°-B……(Formula BX2)

[0286] β=90°-B……(Formula BX3)

[0287] The twist angle B is preferably 60° to 80°, more preferably 64° to 76°, and even more preferably 68° to 72°. This allows for more efficient switching between polarization modulation and polarization non-modulation over a wide bandwidth.

[0288] When the azimuth angle of the extension direction 121A is 0°, the azimuth angle of the extension direction 221A is 160° (i.e., the angle β formed by the extension direction 121A and the extension direction 221A is 20° when viewed from above), the twist angle B of the liquid crystal molecules 310 is 70°, and the liquid crystal layer 300 contains positive liquid crystal molecules 310, as shown in FIG. Figure 15 As shown, when the first comb-teeth electrode 121 is in a no-voltage-applied state, the second comb-teeth electrode 220 is in a voltage-applied state, the third comb-teeth electrode 221 is in a voltage-applied state, and the fourth comb-teeth electrode 222 is in a no-voltage-applied state, a first state can be achieved in which the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side is 0°, and the azimuth angle of the alignment direction 312A of the liquid crystal molecules 312 on the second substrate 200 side is 70°. Furthermore, when the first comb-teeth electrode 120 is in a voltage-applied state, the second comb-teeth electrode 220 is in a no-voltage-applied state, the third comb-teeth electrode 221 is in a voltage-applied state, and the fourth comb-teeth electrode 222 is in a voltage-applied state, a second state can be achieved in which the azimuth angle of the alignment direction 311B of the liquid crystal molecules 311 on the first substrate 100 side is 90°, and the azimuth angle of the alignment direction 312B of the liquid crystal molecules 312 on the second substrate 200 side is 160°.

[0289] Furthermore, when the liquid crystal layer 300 contains negative-type liquid crystal molecules 310, when a voltage is applied to the first comb-teeth electrodes 121, no voltage is applied to the second comb-teeth electrodes 122, no voltage is applied to the third comb-teeth electrodes 221, and a voltage is applied to the fourth comb-teeth electrodes 222, a first state can be achieved in which the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side is 0°, and the azimuth angle of the alignment direction 312A of the liquid crystal molecules 312 on the second substrate 200 side is 70°. Furthermore, when no voltage is applied to the first comb-teeth electrodes 121, no voltage is applied to the second comb-teeth electrodes 122, a voltage is applied to the third comb-teeth electrodes 221, and no voltage is applied to the fourth comb-teeth electrodes 222, a second state can be achieved in which the azimuth angle of the alignment direction 311B of the liquid crystal molecules 311 on the first substrate 100 side is 90°, and the azimuth angle of the alignment direction 312B of the liquid crystal molecules 312 on the second substrate 200 side is 160°.

[0290] In this embodiment, in which the liquid crystal layer 300 includes positive liquid crystal molecules 310, in a plan view, the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state coincides with the extension direction 121A of the comb-tooth electrodes provided on the first comb-tooth electrodes 121. Therefore, assuming the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is 0°, for example, the azimuth angle of the extension direction 121A can be set to 0°, the azimuth angles of the extension direction 121A can be set to 90°, the azimuth angle of the extension direction 122A and the extension direction 222A can be set to 160°, the azimuth angle of the slow axis 12A of the first quarter-wavelength film 12 can be set to 57.2°, and the azimuth angle of the slow axis 13A of the second quarter-wavelength film 13 can be set to 12.2°.

[0291] Similar to the first and second embodiments, the optical element 10 of this embodiment preferably includes: a horizontal alignment film with a first weak anchoring force disposed between the first substrate 100 and the liquid crystal layer 300; and a horizontal alignment film with a second weak anchoring force disposed between the liquid crystal layer 300 and the second substrate 200. This arrangement allows the liquid crystal molecules near the interface to be uniformly aligned while maintaining their horizontal alignment.

[0292] (Fourth embodiment)

[0293] This embodiment mainly describes its unique features, and omit descriptions of the contents repeated in the first to third embodiments. This embodiment is substantially the same as the first embodiment except that a bistable alignment film is used instead of the first weak anchor horizontal alignment film 411.

[0294] Figure 16 : is a perspective view of a liquid crystal unit included in the optical element of the fourth embodiment. Figure 16 As shown, the liquid crystal cell 11 included in the optical element 10 of this embodiment further includes a bistable alignment film 413 disposed between the first substrate 100 and the liquid crystal layer 300, having stable alignment in two directions. The electrode 11E includes a first comb-tooth electrode 120 on the first substrate 100, arranged so that the comb-teeth of the pixel electrode and the common electrode interlock with each other. It also includes a second comb-tooth electrode 220 on the second substrate 200, arranged so that the comb-teeth of the pixel electrode and the common electrode interlock with each other. In a plan view, the extension direction 120A of the first comb-tooth electrode 120 is inclined relative to the extension direction 220A of the second comb-tooth electrode 220.

[0295] By adopting this approach, when the first comb-tooth electrode 120 is set to a no-voltage state and the second comb-tooth electrode 220 is set to a voltage-applied state, circularly polarized light (e.g., right-handed circularly polarized light) incident on the liquid crystal cell 11 becomes first linearly polarized light after passing through the liquid crystal cell 11. In other words, the first state is achieved. Furthermore, the first linearly polarized light passes through the first quarter-wavelength film 12 and the second quarter-wavelength film 13, thereby being converted over a wide bandwidth into circularly polarized light (e.g., left-handed circularly polarized light) having a polarization state different from that of the circularly polarized light incident on the liquid crystal cell 11. Thus, in the first state, circularly polarized light incident on the optical element 10 is converted into circularly polarized light having a different polarization state (e.g., right-handed circularly polarized light is converted into left-handed circularly polarized light), and polarization modulation of the emitted light is achieved over a wide bandwidth.

[0296] Furthermore, when the first comb-tooth electrode 121 is in a voltage-applied state and the second comb-tooth electrode 122 is in a voltage-free state, circularly polarized light (e.g., right-handed circularly polarized light) incident on the liquid crystal cell 11, after passing through the liquid crystal cell 11, becomes second linearly polarized light having a polarization direction orthogonal to that of the first linearly polarized light in a plan view. In other words, the second state is achieved. Furthermore, the second linearly polarized light passes through the first quarter-wave film 12 and the second quarter-wave film 13, thereby maintaining the same polarization state as the circularly polarized light incident on the liquid crystal cell 11 (e.g., right-handed circularly polarized light) and being emitted over a wide bandwidth. Thus, in the second state, the circularly polarized light incident on the optical element 10 maintains the same polarization state (e.g., right-handed circularly polarized light) and is emitted without modulation over a wide bandwidth.

[0297] The bistable alignment film 413 has two directions (a first direction 413A and a second direction 413B) that are stable in orientation. Preferably, when viewed from above, the first direction 413A and the second direction 413B are orthogonal to each other, and the first direction 413A is parallel to the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state. The azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side is 0° in the first state and 90° in the second state. Therefore, when viewed from above, the first direction 413A and the second direction 413B are orthogonal to each other, and the first direction 413A is parallel to the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state. Consequently, the bistable alignment film 413 can energetically stabilize the alignment direction of the liquid crystal molecules 311 on the first substrate 100 side in both the first and second states. As a result, compared with the first embodiment in which the alignment direction of the liquid crystal molecules 310 is regulated only by voltage, the optical element 10 having excellent alignment stability can be realized.

[0298] The bistable alignment film 413 can be formed by light irradiation or by rubbing with a concavo-convex substrate.

[0299] When light irradiation is used, for example, a material formed by mixing two polymers having mutually different photofunctional wavelengths can be used to form the bi-stable alignment film 413. After applying a solution containing the two polymers having mutually different photofunctional wavelengths to a substrate, the substrate is irradiated with, for example, polarized ultraviolet light of a certain wavelength and then irradiated with polarized ultraviolet light of a different wavelength and direction, thereby forming a bi-stable alignment film 413 having stable alignment directions in both a first direction and a second direction.

[0300] When using a concave-convex substrate and rubbing, for example, a structure with grooves in a specific direction is formed on the substrate using a polymer, and rubbing is performed in a direction different from the grooves. Liquid crystal molecules experience two forces: forces that align along the grooves and forces that align along the rubbing direction, resulting in a bi-stable alignment film 413 with stable alignment in both directions.

[0301] The optical element 10 of this embodiment may also include a second alignment film 420 between the second substrate 200 and the liquid crystal layer 300. The second alignment film 420 is, for example, a horizontal alignment film 423 with a weak anchoring force. The horizontal alignment film 423 with a weak anchoring force is preferably a lubricating film. This approach enables switching between polarization modulation and polarization non-modulation over a wider frequency band.

[0302] The second alignment film 420 may be, for example, a vertical alignment film. As the vertical alignment film, the same alignment film as the vertical alignment film 422 can be used.

[0303] (Fifth embodiment)

[0304] In this embodiment, the features unique to this embodiment will be mainly described, and descriptions of the contents overlapping with those of the first to fourth embodiments will be omitted. This embodiment is substantially the same as the first embodiment except that the configuration of the liquid crystal cell 11 is different.

[0305] Figure 17 It is a schematic cross-sectional view of a liquid crystal cell included in the optical element of the fifth embodiment. Figure 18 It is a schematic perspective view of a liquid crystal cell included in the optical element according to the fifth embodiment. Figure 19 The figure shows an example of the axis orientation of the optical element of the fifth embodiment. The liquid crystal molecules near the interface of the substrate are aligned vertically and the orientation cannot be determined. Figure 19 In the process, the orientation of the liquid crystal molecules is determined by the direction of the electrodes.

[0306] like Figures 17 to 19As shown, the liquid crystal cell 11 included in the optical element 10 of this embodiment further includes a first vertical alignment film 414 disposed between the first substrate 100 and the liquid crystal layer 300, and a second vertical alignment film 424 disposed between the liquid crystal layer 300 and the second substrate 200. The electrode 11E includes a planar first electrode 131 on the first substrate 100, and a second electrode 132 overlapping the first electrode 131 via a first insulating layer 141 and having a slit 132S. On the second substrate 200, the electrode 11E includes a planar third electrode 231 and a fourth electrode 232 overlapping the third electrode 231 via a second insulating layer 241 and having a slit 232S.

[0307] In a plan view, the extending direction 132A of the slit portion 132S provided in the second electrode 132 is arranged to be inclined with respect to the extending direction 232A of the slit portion 232S provided in the fourth electrode 232 .

[0308] By adopting this method, when a voltage is applied between the first electrode 131 and the second electrode 132, and no voltage is applied between the third electrode 231 and the fourth electrode 232, circularly polarized light (e.g., right-handed circularly polarized light) incident on the liquid crystal cell 11 becomes first linearly polarized light after passing through the liquid crystal cell 11. In other words, the first state is achieved. Furthermore, the first linearly polarized light passes through the first quarter-wavelength film 12 and the second quarter-wavelength film 13, thereby being converted over a wide bandwidth into circularly polarized light (e.g., left-handed circularly polarized light) with a polarization state different from that of the circularly polarized light incident on the liquid crystal cell 11. Thus, in the first state, circularly polarized light incident on the optical element 10 is converted into circularly polarized light with a different polarization state (e.g., right-handed circularly polarized light is converted into left-handed circularly polarized light), and polarization modulation of the emitted light is achieved over a wide bandwidth.

[0309] Furthermore, when no voltage is applied between the first electrode 131 and the second electrode 132, and a voltage is applied between the third electrode 231 and the fourth electrode 232, circularly polarized light (e.g., right-handed circularly polarized light) incident on the liquid crystal cell 11 passes through the liquid crystal cell 11 and becomes second linearly polarized light having a polarization direction orthogonal to that of the first linearly polarized light when viewed from above. This achieves the second state. Furthermore, the second linearly polarized light passes through the first quarter-wavelength film 12 and the second quarter-wavelength film 13, maintaining the same polarization state as the circularly polarized light incident on the liquid crystal cell 11 (e.g., right-handed circularly polarized light) and exiting the optical element 10 over a wide bandwidth. Thus, in the second state, the circularly polarized light incident on the optical element 10 maintains the same polarization state (e.g., right-handed circularly polarized light) and exits the optical element 10 unmodulated over a wide bandwidth.

[0310] In addition, one of the first electrode 131 and the second electrode 132 is a pixel electrode, and the other is a common electrode. One of the third electrode 231 and the fourth electrode 232 is a pixel electrode, and the other is a common electrode. Figure 18 In the figure, both the first substrate 100 and the second substrate 200 have planar electrodes and electrodes with slit portions in sequence facing the liquid crystal layer 300 side, but the configuration of the planar electrodes and electrodes with slit portions is not limited to this. They may also have electrodes with slit portions and planar electrodes in sequence facing the liquid crystal layer 300 side.

[0311] In a plan view, the angle γ (where γ is a real number greater than 0° and less than 90°) formed between the extension direction 132A and the extension direction 232A, and the twist angle C of the liquid crystal molecules 310 included in the liquid crystal layer 300, preferably satisfy the following (Formula CX1) in the first state and the second state, more preferably satisfy the following (Formula CX2), and even more preferably satisfy the following (Formula CX3). By adopting this approach, it is possible to effectively switch between polarization modulation and polarization non-modulation over a wide bandwidth.

[0312] 85°-C≤γ≤95°-C……(Formula CX1)

[0313] 88°-C≤γ≤92°-C……(Formula CX2)

[0314] γ=90°-C……(Formula CX3)

[0315] The twist angle C is preferably 60° to 80°, more preferably 64° to 76°, and even more preferably 68° to 72°. This allows for more efficient switching between polarization modulation and non-polarization modulation over a wide bandwidth.

[0316] When the azimuth angle of the extension direction 132A is 0°, the azimuth angle of the extension direction 232A is 160° (that is, the angle γ formed by the extension direction 132A and the extension direction 232A when viewed from above is 20°), the twist angle C of the liquid crystal molecule 310 is 70°, and the liquid crystal layer 300 contains negative liquid crystal molecules 310, when the voltage is applied between the first electrode 131 and the second electrode 132 and the voltage is not applied between the third electrode 231 and the fourth electrode 232, the first state can be achieved in which the azimuth angle of the orientation direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side is 0° and the azimuth angle of the orientation direction 312A of the liquid crystal molecules 312 on the second substrate 200 side is 70°. In addition, when the state between the first electrode 131 and the second electrode 132 is set to no voltage application and the state between the third electrode 231 and the fourth electrode 232 is set to voltage application, a second state can be achieved in which the azimuth angle of the orientation direction 311B of the liquid crystal molecules 311 on the first substrate 100 side is 90° and the azimuth angle of the orientation direction 312B of the liquid crystal molecules 312 on the second substrate 200 side is 160°.

[0317] Furthermore, when the liquid crystal layer 300 contains positive liquid crystal molecules 310, when no voltage is applied between the first electrode 131 and the second electrode 132 and a voltage is applied between the third electrode 231 and the fourth electrode 232, a first state can be achieved in which the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side is 0° and the azimuth angle of the alignment direction 312A of the liquid crystal molecules 312 on the second substrate 200 side is 70°. Furthermore, when a voltage is applied between the first electrode 131 and the second electrode 132 and no voltage is applied between the third electrode 231 and the fourth electrode 232, a second state can be achieved in which the azimuth angle of the alignment direction 311B of the liquid crystal molecules 311 on the first substrate 100 side is 90° and the azimuth angle of the alignment direction 312B of the liquid crystal molecules 312 on the second substrate 200 side is 160°.

[0318] The first substrate 100 includes, in order, a first supporting substrate 110, a planar first electrode 131, a first insulating layer 141, and a second electrode 132 having a slit portion 232S. The second substrate 200 includes, in order, a second supporting substrate 210, a planar third electrode 231, a second insulating layer 241, and a fourth electrode 232 having a slit portion 232S.

[0319] The spacing of the second electrode 132 provided with the slit portion 132S is preferably greater than 1 μm and less than 5 μm. By adopting this method, the liquid crystal molecules 311 on the first substrate 100 side can be efficiently rotated, and a uniform twist orientation can be easily obtained. In addition, the spacing of the fourth electrode 232 provided with the slit portion 232S is preferably greater than 1 μm and less than 5 μm. By adopting this method, the liquid crystal molecules 312 on the second substrate 200 side can be effectively rotated, and a uniform twist orientation can be easily obtained. Here, the electrode provided with the slit portion has a structure in which linear electrode portions and slit portions are alternately and repeatedly arranged, and the spacing of the electrode provided with the slit portion refers to the sum of the widths of a group of linear electrode portions and slit portions.

[0320] The liquid crystal molecules 310 are preferably negative liquid crystal molecules. By adopting this method, a large longitudinal voltage is applied between the first substrate 100 and the second substrate 200, so that the negative liquid crystal molecules 310 can be pushed down and horizontally oriented. In the first state and the second state, the voltage difference between the first electrode 131 and the third electrode 231 is preferably 1V or more, more preferably 3V or more, and further preferably 5V or more. By adopting this method, the liquid crystal molecules 310 can be more effectively horizontally oriented. There is no particular limit to the upper limit of the voltage difference between the first electrode 131 and the third electrode 231, but the voltage difference between the first electrode 131 and the third electrode 231 is, for example, 20V or less. The voltage difference between the first electrode 131 and the third electrode 231 is preferably 1V or more and 20V or less, more preferably 3V or more and 20V or less, and further preferably 5V or more and 20V or less.

[0321] Furthermore, a weak voltage can be applied between the pixel electrode and the common electrode, between the first electrode 131 and the second electrode 132, and between the third electrode 231 and the fourth electrode 232, to control the in-plane orientation of the liquid crystal molecules 310. If the liquid crystal molecules 310 are negative-type liquid crystal molecules, they align in-plane in the direction extending from the slits 132S and 232S (a direction perpendicular to the electric field). At this time, a strong transverse electric field prevents the orientational twist of the liquid crystal caused by chiral forces, so a weak transverse electric field is preferred.

[0322] For example, the voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 3 V or less, more preferably 1 V or less, and even more preferably 0.5 V or less. Furthermore, the voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is preferably 3 V or less, more preferably 1 V or less, and even more preferably 0.5 V or less. The lower limit of the voltage difference between the first electrode 131 and the second electrode 132 in the first state is not particularly limited, but the voltage difference between the first electrode 131 and the second electrode 132 in the first state is, for example, 0.01 V or more. Furthermore, the lower limit of the voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is not particularly limited, but the voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is, for example, 0.01 V or more.

[0323] The voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 0.01 V to 3 V, more preferably 0.05 V to 1 V. Furthermore, the voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is preferably 0.01 V to 3 V, more preferably 0.05 V to 1 V.

[0324] The first and second vertical alignment films 414 and 424 may be the same vertical alignment films as the vertical alignment film 422. In the optical element 10 of this embodiment, since the vertical alignment films are disposed on both substrates, the optical element 10 can be more productive than when horizontal alignment films are disposed.

[0325] The first and second vertical alignment films 414 and 424 may also provide a slight tilt angle to the liquid crystal molecules. Specifically, the first and second vertical alignment films 414 and 424 may also provide a pretilt angle of 85° to 90° to the liquid crystal molecules 310.

[0326] Figure 20 Schematic diagram for explaining the alignment of liquid crystal molecules in the first state and the second state of the optical element of the fifth embodiment. Figure 20 As shown, the liquid crystal molecules 310 are vertically aligned in the immediate vicinity of the first substrate 100 and the second substrate 200 , but are horizontally aligned within the liquid crystal layer 300 with a twisted alignment of approximately 70°.

[0327] In this embodiment, in which the liquid crystal layer 300 includes negative-type liquid crystal molecules 310, in a plan view, the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state coincides with the extension direction 132A of the slit portion 132S provided in the second electrode 132. Therefore, assuming that the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is 0°, for example, the azimuth angle of the extension direction 132A can be set to 0°, the azimuth angle of the extension direction 232A can be set to 160°, the azimuth angle of the slow axis 12A of the first quarter-wavelength film 12 can be set to 57.2°, and the azimuth angle of the slow axis 13A of the second quarter-wavelength film 13 can be set to 12.2°.

[0328] Regarding the optical element 10 of this embodiment, similarly to the other embodiments, the modulation characteristics and the non-modulation characteristics can be appropriately adjusted by designing the retardation Δnd and the twist angle of the liquid crystal layer 300 .

[0329] (Sixth embodiment)

[0330] In this embodiment, the features unique to this embodiment will be mainly described, and the description of the contents overlapping with the first to fifth embodiments will be omitted. This embodiment is substantially the same as the first embodiment except that the second quarter-wavelength film 13 is not included.

[0331] Figure 21 It is a schematic cross-sectional view of an optical element according to a sixth embodiment. Figure 22 It is a schematic perspective view of a liquid crystal cell included in the optical element according to the sixth embodiment. Figure 23 This is a diagram showing an example of the axial orientation of the optical element according to the sixth embodiment.

[0332] like Figures 21 to 23 As shown, the optical element 10 of this embodiment includes the liquid crystal cell 11 similar to the first embodiment, and a quarter-wavelength film with reverse wavelength dispersion as the first quarter-wavelength film 12. This configuration allows the thickness of the optical element 10 to be reduced while enabling wide-band switching between a state in which circularly polarized light incident on the optical element 10 is emitted without modulation and a state in which circularly polarized light is emitted with modulation. In other words, an optical element 10 capable of switching between polarization modulation and non-polarization modulation over a wide band and capable of being reduced in thickness can be realized.

[0333] As described in this embodiment, when the first quarter-wavelength film 12 is disposed on the emission side of the liquid crystal cell 11, the azimuth angle of the slow axis 12A of the first quarter-wavelength film 12 is preferably greater than or equal to 3° and less than or equal to 22°. Furthermore, when the first quarter-wavelength film 12 is disposed on the incident side of the liquid crystal cell 11, the azimuth angle of the slow axis 12A of the first quarter-wavelength film 12 is preferably greater than or equal to 48° and less than or equal to 67°. This approach enables switching between polarization modulation and polarization non-modulation over a wider bandwidth.

[0334] So far, the description has focused on the case where the liquid crystal molecules are either positive or negative. However, dual-frequency driven liquid crystals can also be used as liquid crystal molecules. Dual-frequency driven liquid crystals are liquid crystal molecules that behave as positive liquid crystal molecules (where Δε is positive) at low frequencies and as negative liquid crystal molecules (where Δε is negative) at high frequencies. Using dual-frequency liquid crystals allows for simpler electrode configurations, even without providing comb-tooth electrodes with different angles on the upper and lower substrates (the first substrate 100 and the second substrate 200). By driving a single comb-tooth electrode at a low frequency, the liquid crystal molecules align perpendicular to the electrode's extension direction. By driving at a high frequency, the liquid crystal molecules align in the electrode's extension direction, thereby simplifying the electrode configuration.

[0335] (Seventh embodiment)

[0336] In this embodiment, the features unique to this embodiment are mainly described, and the description of the contents overlapping with the first to sixth embodiments is omitted. In this embodiment, a variable focus element including the optical element (sHWP) of the first to sixth embodiments is described. Figure 24 It is a schematic cross-sectional view of a variable focus element according to the seventh embodiment. Figure 24 The variable focus element 30 of the illustrated embodiment includes an optical element 10 and a Pancharatnam Berry (PB) lens 20 .

[0337] As described above, the optical element 10 of the first to sixth embodiments can modulate circularly polarized light. Furthermore, the PB lens 20 has different focal lengths for right circularly polarized light and left circularly polarized light, so a variable focus element 30 can be realized by combining the optical element 10 and the PB lens 20 .

[0338] The PB lens 20 has the function of focusing and diverging circularly polarized light. The PB lens 20 can be manufactured by the method described in International Publication No. 2019 / 189818, for example.

[0339] Figure 25 FIG. 1 is an example of a cross-sectional schematic diagram of a PB lens included in the variable focus element of the seventh embodiment. Figure 25As shown in FIG. 3 , the PB lens 20 includes an optical anisotropic layer 320A. As an example, the PB lens 20 targets circularly polarized light and refracts the incident light in a predetermined direction and transmits the light. Figure 25 In the example, the incident light is set to be left circularly polarized light.

[0340] exist Figure 25 In the portion shown, the optically anisotropic layer 320A has Figure 25 There are three regions R0, R1, and R2 from the left side, and the length Λ of one period in each region is different. Specifically, the length Λ of one period becomes shorter in the order of regions R0, R1, and R2. In addition, regions R1 and R2 have a structure in which the optical axis is twisted and rotated in the thickness direction of the optical anisotropic layer (hereinafter also referred to as a twisted structure). The twist angle of region R1 in the thickness direction is smaller than the twist angle of region R2 in the thickness direction. In addition, region R0 is a region without a twisted structure (i.e., the twist angle is 0°). In addition, the twist angle is set to the twist angle of the entire thickness direction.

[0341] In the optical element 10, when left-circularly polarized light LC1 is incident on region R1 within the plane of the optically anisotropic layer 320, it is refracted and transmitted at a predetermined angle relative to the incident direction in the direction of arrow X, i.e., the direction of the optical axis of the liquid crystal molecules 320, which continuously rotates and changes. Similarly, when left-circularly polarized light LC2 is incident on region R2 within the plane of the optically anisotropic layer 320A, it is refracted and transmitted at a predetermined angle relative to the incident direction in the direction of arrow X. Similarly, when left-circularly polarized light LC0 is incident on region R0 within the plane of the optically anisotropic layer 320A, it is refracted and transmitted at a predetermined angle relative to the incident direction in the direction of arrow X.

[0342] Here, regarding the refraction angle of the optically anisotropic layer 320A, the period Λ of the liquid crystal alignment pattern in the region R2 is R2 One period of the liquid crystal alignment pattern in region R1 is Λ R1 Short, therefore, Figure 25 As shown, the angle θ of the transmitted light in region R2 is the angle of refraction relative to the incident light. R2 Greater than the angle θ of the transmitted light in region R1 R1 In addition, the period of the liquid crystal orientation pattern in region R0 is R0 One period of the liquid crystal alignment pattern in region R1 is Λ R1 Longer, so Figure 25 As shown, the angle θ of the transmitted light in region R0 is the angle of refraction relative to the incident light. R0 smaller than the angle θ of the transmitted light in region R1 R1 .

[0343] In the diffraction of light by an optically anisotropic layer having a liquid crystal orientation pattern, the direction of the optical axis of the liquid crystal molecules changes while continuously rotating within the plane. This leads to a problem in which the diffraction efficiency decreases as the diffraction angle increases, that is, the intensity of the diffracted light weakens. Therefore, when the optically anisotropic layer is configured with regions having different lengths of one period where the direction of the optical axis of the liquid crystal molecules rotates 180° within the plane, the diffraction angle varies depending on the incident position of the light, and thus the amount of diffracted light varies depending on the incident position within the plane. In other words, regions where the transmitted or diffracted light becomes darker occur depending on the incident position within the plane.

[0344] In contrast, the PB lens 20 of the present embodiment has a region where the optically anisotropic layer is twisted and rotated in the thickness direction, and has regions where the twist angles in the thickness direction are different in size. Figure 25 In the example shown, the twist angle of the region R2 in the thickness direction of the optically anisotropic layer 320 is Greater than the twist angle in the thickness direction of region R1 Furthermore, the region R0 does not have a twisted structure in the thickness direction, thereby suppressing a decrease in the diffraction efficiency of the refracted light.

[0345] exist Figure 25 In the example shown, by providing a twisted structure in regions R1 and R2, where the diffraction angle is greater than that of region R0, it is possible to suppress a decrease in the amount of light refracted in regions R1 and R2. Furthermore, by making the twist angle of the twisted structure in region R2, where the diffraction angle is greater than that of region R1, larger than that of region R1, it is possible to suppress a decrease in the amount of light refracted in region R2. This makes it possible to make the amount of transmitted light uniform depending on the incident position within the plane.

[0346] Thus, in the PB lens 20 of this embodiment, in the in-plane regions where the refraction due to the optically anisotropic layer is large, incident light is refracted through the layer having a large twist angle in the thickness direction. Conversely, in the in-plane regions where the refraction due to the optically anisotropic layer is small, incident light is refracted through the layer having a small twist angle in the thickness direction. In other words, by setting the in-plane twist angle in the thickness direction according to the refraction of the optically anisotropic layer, the PB lens 20 can brighten the amount of light transmitted by the incident light. Therefore, the PB lens 20 can reduce the refraction angle dependence of the in-plane transmitted light.

[0347] The angle of refracted light in the plane of the optical anisotropic layer 320 increases as the period Λ of the liquid crystal alignment pattern decreases. Furthermore, the twist angle in the thickness direction of the optical anisotropic layer 320 in the plane has a larger area where the period Λ is shorter, which rotates the direction of the optical axis by 180° in the direction of arrow X in the liquid crystal alignment pattern, than where the period Λ is larger. In the PB lens 20, as an example, Figure 25As shown, one period Λ of the liquid crystal alignment pattern in the region R2 of the optically anisotropic layer 320A is R2 One period of the liquid crystal alignment pattern in region R1 is Λ R1 Short, twist angle in thickness direction That is, the region R2 of the optically anisotropic layer 320A on the light incident side refracts light to a greater extent.

[0348] Therefore, the twist angle in the thickness direction of the surface is set by setting the period Λ of the liquid crystal alignment pattern as the target. Transmitted light refracted at different angles in different regions within the plane can be preferably brightened.

[0349] As described above, in the PB lens 20, the shorter the period Λ of the liquid crystal alignment pattern, the larger the angle of refraction. Therefore, regions with shorter periods Λ in the liquid crystal alignment pattern increase the twist angle in the thickness direction, thereby brightening the transmitted light. Therefore, in the PB lens 20, it is preferable that regions with different lengths of one period of the liquid crystal alignment pattern have regions with different arrangements of the length of the one period and the magnitude of the twist angle in the thickness direction.

[0350] In summary, the PB lens 20 preferably includes an optically anisotropic layer 320A formed using a liquid crystal composition containing liquid crystal molecules 320, the optically anisotropic layer 320A having a liquid crystal orientation pattern in which the direction of the optical axis originating from the liquid crystal molecules continuously rotates and changes along at least one direction within the plane, and has regions where the optical axis is twisted and rotated in the thickness direction of the optically anisotropic layer 320A, and has regions with different twist angles in the thickness direction.

[0351] The PB lens 20 preferably has regions in the liquid crystal alignment pattern where the length of one period is different when the direction of the optical axis of the liquid crystal molecules 320 is rotated 180° in the plane as one period.

[0352] The optically anisotropic layer 320A preferably has a plurality of regions with different lengths of the above-mentioned one period in the above-mentioned liquid crystal orientation pattern arranged in the order of the lengths of the above-mentioned one period, and a plurality of regions with different sizes of the twist angles in the above-mentioned thickness direction arranged in the order of the sizes of the twist angles in the above-mentioned thickness direction, with the region having a direction of arrangement of the length of the above-mentioned one period and a direction of arrangement of the sizes of the twist angles in the above-mentioned thickness direction being different.

[0353] The optically anisotropic layer 320A preferably has a region where the twist angle in the thickness direction is 10° to 360°.

[0354] Preferably, the optically anisotropic layer 320A continuously rotates and changes in the one direction in the liquid crystal alignment pattern in which the direction of the optical axis of the liquid crystal molecules 320 is changed, and the one period of the liquid crystal alignment pattern gradually shortens.

[0355] Preferably, the liquid crystal alignment pattern of the optically anisotropic layer 320A is a concentric circular pattern in which the one direction changes from the inside to the outside while the direction from the optical axis of the liquid crystal molecules 320 continuously rotates.

[0356] Figure 25 The PB lens 20 shown has a twist angle that varies within the plane, and thus exhibits high diffraction efficiency even at large diffraction angles. However, the PB lens 20 may also have a twist angle that remains constant within the plane. Specifically, the PB lens 20 may have no twist in the thickness direction or a twist angle that remains constant within the plane. For example, a polarization diffraction grating as described in Japanese Unexamined Patent Application Publication No. 2008-532085 may be used.

[0357] Preferably, the PB lens 20 is a PB lens including a plurality of optically anisotropic layers 320A, and includes the optically anisotropic layers 320A having twist angles in different directions in the thickness direction of the optically anisotropic layers 320A.

[0358] Preferably, the PB lens 20 is a PB lens including a plurality of optically anisotropic layers 320A, and includes the optically anisotropic layers 320A having twist angles different from each other in the thickness direction of the optically anisotropic layers 320A.

[0359] Preferably, the PB lens 20 is a PB lens having a multilayer optical anisotropic layer 320A having a liquid crystal orientation pattern in which directions of the optical axes of the liquid crystal molecules 320 continuously rotated along at least one direction in a plane are identical.

[0360] It is preferable that the length of the said 1 period in the said liquid crystal orientation pattern is 50 micrometers or less.

[0361] The variable focus element 30 may be a binary variable focus element 30A comprising a single stack of optical elements 10 and PB lenses 20, or a multi-stage variable focus element 30B comprising two or more stacks of optical elements 10 and PB lenses 20. By combining multiple sets of optical elements 10 and PB lenses 20, a variable focus element 30B having multi-stage tunability can be realized.

[0362] The variable focus element 30 can be manufactured by attaching the PB lens 20 manufactured by the method described in International Publication No. 2019 / 189818 to the optical element 10, for example.

[0363] (Variation 1 of the Seventh Embodiment)

[0364] In this modification, a description will be given of a variable focus element 30 in which the PB lens 20 in the seventh embodiment is arranged in the optical element 10 and formed into an in-cell. Figure 26 It is a schematic cross-sectional view of a variable focus element according to Modification 1 of the seventh embodiment. Figure 27 It is an enlarged cross-sectional schematic diagram of a variable focus element according to Modification 1 of the seventh embodiment.

[0365] like Figure 26 As shown, the variable focus element 30 of this modification is a multi-stage variable focus element 30B including two or more stacked bodies composed of the optical element 10 and the PB lens 20 .

[0366] like Figure 27 As shown in FIG. 1 , the PB lens 20 of the variable focus element 30 of this modification is configured inside the optical element 10. In this way, by embedding the PB lens 20, there is no need to install the PB lens 20 externally, thereby significantly reducing the manufacturing cost. In addition, the thickness of the variable focus element 30 can be suppressed. Figure 26 , for convenience, the optical element 10 and the PB lens 20 are shown separately.

[0367] More specifically, the variable focus element 30 of this variation includes, in order from the incident side to the exit side, a second quarter-wavelength film 13, a first quarter-wavelength film 12, a first substrate 100, a liquid crystal layer 300, a PB lens 20, and a second substrate 200. The variable focus element 30 may also include a first alignment film 410 between the first substrate 100 and the liquid crystal layer 300. Furthermore, the variable focus element 30 may also include a second alignment film 420 between the second substrate 200 and the liquid crystal layer 300.

[0368] Here, when the first quarter-wavelength film 12 and the second quarter-wavelength film 13 are arranged on the emission side of the liquid crystal cell 11 as in the first to seventh embodiments, in the first state, circularly polarized light (e.g., right circularly polarized light) incident on the optical element 10 first enters the liquid crystal cell 11 and is converted into first linearly polarized light. This first linearly polarized light enters the first quarter-wavelength film 12 and the second quarter-wavelength film 13 and is converted into circularly polarized light (e.g., left circularly polarized light). Furthermore, in the second state, circularly polarized light (e.g., right circularly polarized light) incident on the optical element 10 first enters the liquid crystal cell 11 and is converted into second linearly polarized light. This second linearly polarized light enters the first quarter-wavelength film 12 and the second quarter-wavelength film 13 and is converted into circularly polarized light (e.g., right circularly polarized light).

[0369] On the other hand, as in this modified example, when the first quarter-wavelength film 12 and the second quarter-wavelength film 13 are arranged on the incident side of the liquid crystal cell 11, in the first state, circularly polarized light (e.g., right circularly polarized light) incident on the optical element 10 first enters the first quarter-wavelength film 12 and the second quarter-wavelength film 13 and is converted into linearly polarized light. This linearly polarized light then enters the liquid crystal cell 11 and is converted into first circularly polarized light (e.g., left circularly polarized light). Furthermore, in the second state, circularly polarized light (e.g., right circularly polarized light) incident on the optical element 10 first enters the first quarter-wavelength film 12 and the second quarter-wavelength film 13 and is converted into linearly polarized light. This linearly polarized light then enters the liquid crystal cell 11 and is converted into second circularly polarized light (e.g., right circularly polarized light).

[0370] When the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is set to 0°, the azimuth angle of the slow axis of the quarter-wavelength film on the light-emitting side of the first quarter-wavelength film 12 and the second quarter-wavelength film 13 (the slow axis 12A of the first quarter-wavelength film 12 in this modified example) is preferably 3° or more and 22° or less. This approach enables switching between polarization modulation and polarization non-modulation over a wider bandwidth.

[0371] When the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is set to 0°, the azimuth angle of the slow axis of the quarter-wavelength film on the side farther from the light emission side of the first quarter-wavelength film 12 and the second quarter-wavelength film 13 (the slow axis 13A of the second quarter-wavelength film 13 in this modified example) is preferably 48° to 66°. This approach enables switching between polarization modulation and polarization non-modulation over a wider bandwidth.

[0372] In other words, the embedded PB lens 20 (PB lens layer) is a built-in phase difference layer patterned so that the slow axis direction is rotated within the plane.

[0373] The PB lens can be embedded, for example, as follows: A photosensitive material for forming an embedded PB lens, comprising a polymer represented by the following general formula (PB-1), is applied to the second substrate 200 to form a PB lens-forming film. This film is then subjected to an orientation treatment to embed the PB lens 20.

[0374] [Chemical Formula 1]

[0375]

[0376] (In the above formula, V represents a spacer, W represents a divalent organic group having a photofunctional group, R 5 represents a monovalent group, and p represents an integer greater than 1.)

[0377] In the general formula (PB-1), V represents a spacer. V preferably comprises an alkylene group having 2 or more carbon atoms and represented by -(CH2)n- (wherein n is an integer of 2 or more). By adopting this approach, a good phase difference can be exhibited. The alkylene group is preferably linear.

[0378] W in the above-mentioned general formula (PB-1) represents a divalent organic group having a photofunctional group. As the divalent organic group having a photofunctional group, there can be mentioned a divalent organic group containing a photofunctional group (photoreactive site) that undergoes reactions such as photodimerization, photoisomerization, photoFries rearrangement, and photodecomposition. As the photofunctional group capable of photodimerization and photoisomerization, for example, a cinnamate group, a chalcone group, a coumarin group, a stilbene group, etc. can be listed. As the photofunctional group capable of photoisomerization, for example, an azophenyl group, etc. can be listed. As the photofunctional group capable of photoFries rearrangement, for example, a phenolic ester group, etc. can be listed. As the photofunctional group capable of photodecomposition, for example, a cyclobutane ring, etc. can be listed.

[0379] R in the above general formula (PB-1) 5 Represents a monovalent group. 5 It is preferably a hydrogen atom or a monovalent hydrocarbon group, more preferably a hydrogen atom, a methyl group or an ethyl group.

[0380] The PB lens-forming film is oriented using multiple alignment treatments, each of which uses polarized light with different directions. For example, the alignment treatments include: a first alignment treatment using polarized light at an azimuth angle of 0°; a second alignment treatment using polarized light at an azimuth angle of 45°; a third alignment treatment using polarized light at an azimuth angle of 90°; and a fourth alignment treatment using polarized light at an azimuth angle of 135°.

[0381] Figure 28 : is a schematic plan view showing the orientation pattern of the PB lens included in the variable focus element of the modification 1 of the seventh embodiment. Figure 28 As shown, the orientation pattern of the PB lens 20 rotates continuously from the center toward the periphery, for example. In addition, when viewed from above, the orientation directions of the liquid crystal molecules 310 at the radius R are all the same. In other words, there is a prescribed angular distribution corresponding to the distance from the center. The period P1 of the orientation pattern and the diffraction angle θ are represented by P1 = 2×λ / sinθ. The shorter the period of the orientation pattern, the greater the diffraction of light. Therefore, when it is desired to obtain a lens effect with a connected focus, this is achieved by making the spacing wider (the smaller the diffraction angle) closer to the center of the optical element and making the spacing shorter (the larger the diffraction angle) closer to the periphery.

[0382] The PB lens 20 described later can be manufactured by changing the design of the alignment pattern period. In addition, the alignment pattern can also be set based on International Publication No. 2020 / 186123, Japanese Patent Application Laid-Open No. 2008-532085, etc.

[0383] This embodiment describes an alignment process using four exposures. However, increasing the number of exposure splits yields a variable focus element 30 with improved diffraction efficiency. Multi-photon alignment using a photo-alignment device provides excellent compatibility with existing liquid crystal factories and enables high-productivity production. This embodiment describes the production of a PB lens 20 using a multi-photon alignment process. However, alignment patterns can also be produced using existing methods such as optical interferometry and laser direct writing.

[0384] The phase difference of the embedded PB lens 20 (PB lens layer) is preferably 100 nm to 500 nm, more preferably 200 nm to 350 nm, and particularly preferably λ / 2 (i.e., 275 nm). The diffraction efficiency is expressed by the following (Equation 1), and therefore reaches its maximum value when Δnd = λ / 2.

[0385] [Mathematical formula 1]

[0386]

[0387] The variable focus element 30 of this modification, that is, the multi-stage variable focus element 30 formed by combining a plurality of stacked bodies of the optical element 10 and the PB lenses 20 embedded in the optical element 10 , has the following characteristics, for example.

[0388] Figure 29 1 is a cross-sectional schematic diagram illustrating the detailed structure of the variable focus element of the modification example 1 of the seventh embodiment. Figure 29 As shown, the variable focus element 30 has, from the incident side to the exit side, an optical element 10, a first PB lens 20A1, an optical element 10, a first PB lens 20A1, an optical element 10, a second PB lens 20A2, an optical element 10, a second PB lens 20A2, an optical element 10, a second PB lens 20A2, an optical element 10, a third PB lens 20A3, an optical element 10 and a third PB lens 20A3.

[0389] The first PB lens 20A1 has a refractive power of ±0.25, the second PB lens 20A2 has a refractive power of ±0.5, and the third PB lens 20A3 has a refractive power of ±1. These lenses exhibit a positive (converging) characteristic when right-handed circularly polarized light is incident, and a negative (diverging) characteristic when left-handed circularly polarized light is incident.

[0390] Table 1 below is a table illustrating the states of the optical element 10 and the PB lenses 20A1 , 20A2 , and 20A3 in each mode of the variable focus element 30 according to Modification 1 of the seventh embodiment.

[0391] [Table 1]

[0392]

[0393] The F0 mode is explained using Table 1 above. In this mode, all optical elements 10 are in the second state (non-modulated). If right-handed circularly polarized light is incident, it is not modulated by the initial optical element 10 and directly enters the first PB lens 20A1. Here, it receives a focused beam of 0.25D. The outgoing light then becomes left-handed circularly polarized light. Even after passing through the PB lens 20, the direction of the circularly polarized light changes, a characteristic of the PB lens 20. Because the optical element 10 is non-modulated, it passes through the second optical element 10 as left-handed circularly polarized light. The second first PB lens 20A1 produces a divergence of -0.25D. As a result, the incident light passes directly through the first four frames from the incident side (optical element 10, first PB lens 20A1, optical element 10, and first PB lens 20A1). Similarly, the incident light passes through the second PB lens 20A2 and PB lens 20A3, and the outgoing light remains as incident light and is directly emitted at OD.

[0394] The F1 mode is explained using Table 1 above. In this mode, only the fourth optical element 10 from the incident side is in the first state. In this state, after passing through the first second PB lens 20A2, the light is left-circularly polarized, imparting 0.5D, similar to the F0 mode. Next, the light is converted to right-circularly polarized light by the optical elements in the first state. Next, the light passes through the second second PB lens 20A2, imparting +0.5D to a total of 1D, and is then emitted. Afterwards, the light is directly emitted as left-circularly polarized light of 1D. Since the light becomes left-circularly polarized light after passing through the second second PB lens 20A2, the sign of the light from the third PB lens 20A3 is opposite to that of the F0 mode.

[0395] Using Table 1 above and Figure 30 This section describes the F-2.5 mode. Figure 30 This is a diagram illustrating the polarization state of the variable focus element in the F-2.5 mode of the modification 1 of the seventh embodiment. Figure 30 As shown, in the F-2.5 mode, the first four frames from the incident side (optical element 10, first PB lens 20A1, optical element 10 and first PB lens 20A1) impart -0.5D of right circular polarized light, and the last four frames from the exit side (optical element 10, third PB lens 20A3, optical element 10 and third PB lens 20A3) impart -2D, and are emitted as right circular polarized light with a total of -2.5D.

[0396] Furthermore, based on the same principle, multiple focal lengths can be achieved depending on which optical element 10 is set to the first modulation state. In this modification, only three conditions are extracted and shown.

[0397] In the seventh embodiment and the first modification of the seventh embodiment, a film-shaped (embedded polymer-shaped) PB lens is described. However, the PB lens itself can also be formed using a liquid crystal layer. In this modification, a PB lens formed using a liquid crystal layer is described.

[0398] As in the seventh embodiment and its variation 1, a polymeric PB lens itself cannot change under voltage and is therefore called a passive PB lens. On the other hand, a PB lens formed of a liquid crystal layer having fluidity can be driven by voltage and is therefore called an active PB lens.

[0399] The active PB lens can be produced by the following steps. First, the orientation film of one side of a pair of substrates is oriented with a PB lens pattern. The orientation film of the other side of the substrate is a weak anchoring force orientation film (sliding interface). In addition, a transparent electrode is provided on either substrate. When the pair of substrates are bonded together by clamping the liquid crystal layer, the liquid crystal molecules are oriented along the pattern to which the orientation treatment has been applied, and the liquid crystal layer also adopts the orientation of the PB lens pattern. In this way, an active PB lens can be realized. More preferably, a PSA (Polymer sustained alignment) treatment is subsequently performed to stabilize the orientation of the interface of the liquid crystal molecules, thereby obtaining an active PB lens with higher orientation stability and reliability.

[0400] The active PB lens has a PB lens pattern in the OFF state, so it focuses or diverges light depending on the incident polarization state. In the ON state, the liquid crystal molecules are vertically aligned, so the light is neither focused nor diverged, but transmitted directly.

[0401] In contrast to the variable focus element combining an sHWP and a passive PB lens, as in the seventh embodiment, which switches between two levels (convergence / divergence), the variable focus element combining an sHWP and an active PB lens, as in this variation, can switch between three levels (convergence / divergence / transmission). This results in smoother focus control. Alternatively, the number of voltage-driven elements required to achieve the same focal length can be reduced.

[0402] (Eighth Embodiment)

[0403] In this embodiment, the features unique to this embodiment will be mainly described, and the description of the contents overlapping with the first to seventh embodiments and their modifications will be omitted. In this embodiment, a head-mounted display including a variable focus element 30 will be described. Figure 31 It is a schematic cross-sectional view of a head-mounted display according to an eighth embodiment. Figure 32 It is a perspective schematic diagram showing an example of the appearance of a head mounted display according to the eighth embodiment.

[0404] like Figure 31 as well as Figure 32 As shown, the head-mounted display 1 of this embodiment includes a display panel 1P for displaying images, a phase shift plate 40, and a variable focus element 30. When the head-mounted display 1 is used, light emitted from the display panel 1P, such as a liquid crystal display device or an organic electroluminescent display device, is converted into circularly polarized light by the phase shift plate 40, and then is viewed by the user U through the variable focus element 30.

[0405] (Ninth embodiment)

[0406] This embodiment mainly describes its unique features, and omit descriptions of the contents overlapping with the first to eighth embodiments and their modifications. This embodiment is substantially the same as the fifth embodiment except for the configuration of the liquid crystal cell 11 .

[0407] Figure 64 It is a schematic cross-sectional view of an optical element according to a ninth embodiment. Figure 65 It is a schematic cross-sectional view of a liquid crystal cell included in the optical element of the ninth embodiment. Figure 66 This is a schematic diagram illustrating the orientation of liquid crystal molecules in the first and second states of the optical element of the ninth embodiment. The orientation of liquid crystal molecules near the interface of the substrate is vertical and cannot be determined. Figure 66 In the process, the orientation of the liquid crystal molecules is determined by the direction of the electrodes.

[0408] In addition, in the above-mentioned first to seventh embodiments, variant example 1 of the seventh embodiment, the eighth embodiment and the present embodiment, the reference orientation (0°) is set to the direction when the orientation direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is projected onto the substrate surface on the exit side of the optical element 10, and the orientation direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is consistent with the horizontal right direction of the screen of the liquid crystal unit 11 when the optical element 10 is observed from the exit side.

[0409] Figures 64 to 66 The liquid crystal cell 11 included in the optical element 10 of this embodiment further includes a first vertical alignment film 414 disposed between the first substrate 100 and the liquid crystal layer 300, and a second vertical alignment film 424 disposed between the liquid crystal layer 300 and the second substrate 200. The liquid crystal layer 300 contains liquid crystal molecules 310 having negative dielectric anisotropy. At least one of the first vertical alignment film 414 and the second vertical alignment film 424 controls the tilt direction of the liquid crystal molecules 310 when no voltage is applied.

[0410] Preferably, the electrode 11E includes, on at least one of the first substrate 100 and the second substrate 200, a planar electrode and an electrode that overlaps the planar electrode with an insulating layer interposed therebetween and has a slit portion. A pair of electrodes consisting of the planar electrode and the electrode that overlaps the planar electrode with an insulating layer interposed therebetween and has a slit portion is also referred to as an FFS electrode.

[0411] More specifically, Figures 64 to 66 The liquid crystal cell 11 included in the optical element 10 of this embodiment further includes a first vertical alignment film 414 disposed between the first substrate 100 and the liquid crystal layer 300, and a second vertical alignment film 424 disposed between the liquid crystal layer 300 and the second substrate 200. The liquid crystal layer 300 contains liquid crystal molecules 310 having negative dielectric anisotropy. The electrode 11E includes a planar first electrode 131 on the first substrate 100, and a second electrode 132 overlapping the first electrode 131 with a first insulating layer 141 interposed therebetween and having a slit 132S. The electrode 11E includes a solid-surface electrode 240 on the second substrate 200. In a planar view, the extending direction 132A of the slit 132S provided in the second electrode 132 is orthogonal to the alignment direction 311X of the liquid crystal molecules 311 on the first substrate 100 side when no voltage is applied.

[0412] By adopting this approach, Figure 66 As shown, when a voltage less than a threshold value is applied between the first electrode 131 and the second electrode 132, and a voltage greater than a threshold value is applied between at least one of the first electrode 131 and the second electrode 132 and the solid-surface electrode 240, circularly polarized light (for example, right-handed circularly polarized light) incident on the liquid crystal cell 11 becomes first linearly polarized light after passing through the liquid crystal cell 11. In other words, the first state can be achieved.

[0413] In addition, if Figure 66 As shown, when a voltage greater than or equal to the threshold value is applied between the first electrode 131 and the second electrode 132, and a voltage greater than or equal to the threshold value is applied between at least one of the first electrode 131 and the second electrode 132 and the solid-surface electrode 240, circularly polarized light (e.g., right-handed circularly polarized light) incident on the liquid crystal cell 11 becomes second linearly polarized light having a polarization direction orthogonal to that of the first linearly polarized light in a plan view after passing through the liquid crystal cell 11. In other words, the second state can be achieved.

[0414] In addition, one of the first electrode 131 and the second electrode 132 is a pixel electrode, and the other is a common electrode. Figure 65 In the embodiment, the first substrate 100 has a planar electrode and an electrode with a slit portion in sequence facing the liquid crystal layer 300 side, but the configuration of the planar electrode and the electrode with a slit portion is not limited to this. The first substrate 100 may also have an electrode with a slit portion and a planar electrode in sequence facing the liquid crystal layer 300 side.

[0415] In this embodiment, the alignment films on the first substrate 100 side and the second substrate 200 side serve as vertical alignment films. Furthermore, an FFS electrode is provided on at least one substrate (the first substrate 100 in this embodiment), and the liquid crystal molecules 310 are driven by voltage applied to an opposing substrate (the second substrate 200 in this embodiment) and the FFS substrate opposite to the substrate on which the FFS electrode is provided. Negative-type liquid crystal molecules 310 are used for the liquid crystal molecules 310, and by adding a chiral agent, the liquid crystal molecules 310 are adjusted to be oriented while being twisted 70°. At this time, by adjusting the tilt direction applied to the alignment film, the pixel electrodes constituting the FFS electrode, and the voltage between the common electrodes, a first state in which the overall orientation of the system is rotated 90° and a second state in which the orientation is rotated 90° are achieved.

[0416] In this specification, the tilt direction refers to the orientation of the liquid crystal molecules in the absence of applied voltage, also referred to as the tilt direction. Furthermore, the tilt angle is the same as the pretilt angle described above. Furthermore, "having a tilt" means having a tilt angle of less than 89.9° (more specifically, 0° or more and less than 89.9°), and "not having a tilt" means having a tilt angle of 89.9° or more (more specifically, 89.9° or more and 90° or less).

[0417] At least one of the liquid crystal molecules 311 on the first substrate 100 side and the liquid crystal molecules 312 on the second substrate 200 side preferably has a tilt. For example, when the liquid crystal molecules 311 on the first substrate 100 side have a tilt, the tilt azimuth of the liquid crystal molecules 311 on the first substrate 100 side is preferably orthogonal to the extension direction of the FFS electrode. More specifically, when no voltage is applied, the orientation direction 311X of the liquid crystal molecules 311 on the first substrate 100 side is preferably orthogonal to the extension direction 132A of the slit portion 132S provided in the second electrode 132. In this case, the tilt azimuth of the liquid crystal molecules 311 on the first substrate 100 side is preferably approximately 0° (e.g., greater than -10° and less than +10°), and the liquid crystal molecules 312 on the second substrate 200 side preferably have no tilt.

[0418] In addition, when the liquid crystal molecules 312 on the second substrate 200 side have a tilt, the tilt orientation of the liquid crystal molecules 312 on the second substrate 200 side is preferably approximately 70° (for example, greater than 60° and less than 80°), and the liquid crystal molecules 311 on the first substrate 100 side preferably do not have a tilt.

[0419] In addition, both the liquid crystal molecules 311 on the first substrate 100 side and the liquid crystal molecules 312 on the second substrate 200 side may have a tilt.

[0420] When the azimuth angle of the extension direction 132A is 90°, the azimuth angle of the alignment direction 311X of the liquid crystal molecules 311 on the first substrate 100 side in the no-voltage state is 0°, the twist angle of the liquid crystal molecules 310 is 70°, and the liquid crystal layer 300 contains negative liquid crystal molecules 310, as shown in FIG. Figures 64 to 66 As shown, when a voltage less than a threshold value is applied between the first electrode 131 and the second electrode 132, and a voltage greater than a threshold value is applied between the first and second electrodes 131, 132, and the solid-surface electrode 240, a first state can be achieved in which the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side is 0°, and the azimuth angle of the alignment direction 312A of the liquid crystal molecules 312 on the second substrate 200 side is 70°. Furthermore, when a voltage greater than a threshold value is applied between the first and second electrodes 131, 132, and a voltage greater than a threshold value is applied between the first and second electrodes 131, 132, and the solid-surface electrode 240, a second state can be achieved in which the azimuth angle of the alignment direction 311B of the liquid crystal molecules 311 on the first substrate 100 side is 90°, and the azimuth angle of the alignment direction 312B of the liquid crystal molecules 312 on the second substrate 200 side is 160°.

[0421] The retardation Δnd of the liquid crystal layer 300 in the no-voltage-applied state at a wavelength of 550 nm is preferably 180 nm to 280 nm. The refractive index anisotropy Δn of the liquid crystal layer 300 is preferably 0.12 or less, more preferably 0.1 or less.

[0422] In this embodiment, when the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is set to 0°, the azimuth angle of the slow axis of the quarter-wavelength film on the side farther from the light emission side of the first quarter-wavelength film 12 and the second quarter-wavelength film 13 (in this embodiment, the slow axis 12A of the first quarter-wavelength film 12) is preferably 58° or more and 78° or less. This approach enables switching between polarization modulation and polarization non-modulation over a wider bandwidth.

[0423] In this embodiment, when the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is set to 0°, the azimuth angle of the slow axis of the quarter-wavelength film on the light-emitting side of the first quarter-wavelength film 12 and the second quarter-wavelength film 13 (in this embodiment, the slow axis 13A of the second quarter-wavelength film 13) is preferably 13° or more and 33° or less. This approach enables switching between polarization modulation and polarization non-modulation over a wider bandwidth.

[0424] The angle between the slow axis 12A of the first quarter-wavelength film 12 and the slow axis 13A of the second quarter-wavelength film 13 is preferably 40° to 50°, more preferably 42° to 48°, further preferably 44° to 46°, and particularly preferably 45°.

[0425] In this embodiment, by setting the azimuth angle of the slow axis 12A of the first quarter-wave film 12 to 58° or more and 78° or less, and by setting the azimuth angle of the slow axis 13A of the second quarter-wave film 13 to 13° or more and 33° or less, in the first state, the first linearly polarized light passes through the first quarter-wave film 12 and the second quarter-wave film 13, and is thereby converted over a wide band into circularly polarized light (e.g., left circularly polarized light) having a polarization state different from that of the circularly polarized light (e.g., right circularly polarized light) incident on the liquid crystal cell 11. Thus, in the first state, the circularly polarized light incident on the optical element 10 is converted into circularly polarized light having a different polarization state (e.g., right circularly polarized light is converted into left circularly polarized light), and the polarization modulation of the emitted light is achieved over a wide band. Furthermore, the second linearly polarized light passes through the first quarter-wavelength film 12 and the second quarter-wavelength film 13, thereby maintaining the same circularly polarized state as the circularly polarized light incident on the liquid crystal cell 11 (e.g., right-handed circularly polarized light) and being emitted over a wide bandwidth. Thus, in the second state, the circularly polarized light incident on the optical element 10 maintains the same polarization state (e.g., right-handed circularly polarized light) and the polarized light emitted is non-modulated over a wide bandwidth.

[0426] Figure 67 It is a diagram showing the Stokes curve of each layer in the first state of the optical element according to the ninth embodiment. Figure 68 This is a schematic diagram illustrating the polarization state of the optical element in the first state according to the ninth embodiment. Figure 67 The polarization state when passing through each layer in the first state (the role of each layer) is shown. Figure 67 The Poincare sphere and Figure 68 , the principle of polarization modulation of the optical element 10 of the ninth embodiment is described in detail.

[0427] like Figure 67 As shown in (1), right circularly polarized light (S3=+1) is incident on the liquid crystal cell 11.

[0428] After passing through the 70° twisted liquid crystal unit 11, it is converted into Figure 67 The polarization state of the plot (2) in the figure. Each plot point represents a different plot for wavelengths between 380nm and 780nm. Wavelengths around 550nm are linearly polarized light (on the equator on the Poincare sphere), while wavelengths other than this are plotted in the northern hemisphere of the Poincare sphere and become elliptically polarized light.

[0429] Then, it passes through the first quarter-wavelength film 12 (specifically, the quarter-wavelength film with reverse wavelength dispersion) and becomes Figure 67 (3) pattern.

[0430] Furthermore, if the light passes through the second quarter wavelength film 13 (specifically, a quarter wavelength film with flat wavelength dispersion), as shown in FIG. Figure 67 As shown in the plot of (4), almost all wavelengths are transformed into left circularly polarized light (at the South Pole position on the Poincare sphere) and emitted. That is, as Figure 68 As shown, it can be seen that modulation is performed from right circularly polarized light to left circularly polarized light.

[0431] In the second state (non-modulation), the light passes through the 70° twisted liquid crystal cell 11 and is converted to linear polarization. However, since the orientation of the liquid crystal cell 11 is rotated 90° as a whole, the light becomes linearly polarized at an angle of approximately 90°, which is different from the first state (modulation). Subsequently, after passing through the first quarter-wave film 12 and the second quarter-wave film 13, all wavelengths become right-handed circularly polarized light. In other words, the right-handed circularly polarized light can be emitted as right-handed circularly polarized light, thus achieving non-modulation.

[0432] Thus, the first and second states are defined as the same orientation of the liquid crystal molecules 310 (i.e., a 70° twist), but the orientation of the system as a whole differs by 90°. The optical element 10 of this embodiment can reversibly switch between the first and second states, achieving a thin, switchable half-wave plate (sHWP) with a wide bandwidth, both when polarization is non-modulated and when polarization is modulated.

[0433] The second quarter-wavelength film 13 (specifically, a quarter-wavelength film with flat wavelength dispersion) is, for example, a positive A-plate or a negative A-plate. The second quarter-wavelength film 13 (specifically, a quarter-wavelength film with flat wavelength dispersion) is preferably a negative A-plate. This approach improves viewing angle characteristics during non-modulation.

[0434] The pitch of the second electrodes 132 provided with the slit portions 132S is preferably not less than 1 μm and not more than 5 μm. By reducing the pitch in this way, the alignment of the liquid crystal molecules 310 changes more uniformly, and the modulation characteristics can be improved.

[0435] The solid surface electrode 240 is an electrode that has no slits or openings in the area that overlaps the optical aperture of the pixel, at least when viewed from above. The solid surface electrode 240 can be formed, for example, by forming a transparent conductive material such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), or tin oxide (SnO), or an alloy thereof, in a single or multilayer film using a sputtering method, followed by patterning using photolithography.

[0436] The liquid crystal molecules 310 of this embodiment are negative liquid crystal molecules 310. By adopting this method, a large longitudinal voltage is applied between the first substrate 100 and the second substrate 200, so that the negative liquid crystal molecules 310 can be pushed down and horizontally oriented. In the first state and the second state, the voltage difference between the first electrode 131 and the second electrode 132 and the whole-surface electrode 240 is preferably 1V or more, more preferably 3V or more, and further preferably 4V or more. By adopting this method, the liquid crystal molecules 310 can be more effectively horizontally oriented. The upper limit of the voltage difference between the first electrode 131 and the second electrode 132 and the whole-surface electrode 240 is not particularly limited, but the voltage difference between the first electrode 131 and the second electrode 132 and the whole-surface electrode 240 is, for example, 7V or less. The voltage difference between the first electrode 131 and the second electrode 132 and the whole-surface electrode 240 is preferably 1V or more and 7V or less, more preferably 3V or more and 7V or less, and further preferably 4V or more and 7V or less.

[0437] Furthermore, a weak voltage can be applied between the first electrode 131 and the second electrode 132, or between the pixel electrode and the common electrode, to control the in-plane orientation of the liquid crystal molecules 310. If the liquid crystal molecules 310 are negative-type, they align in the direction of the slits 132S (a direction perpendicular to the electric field). At this time, a strong transverse electric field prevents the orientational twist of the liquid crystal caused by chiral forces, so a weak transverse electric field is preferred.

[0438] When the voltage difference between the first electrode 131 and the second electrode 132 and the full-surface electrode 240 is 7V or less, for example, the voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 0.6V or less. In addition, the voltage difference between the first electrode 131 and the second electrode 132 in the second state is preferably 2V or less. There is no particular limitation on the lower limit of the voltage difference between the first electrode 131 and the second electrode 132 in the first state, but the voltage difference between the first electrode 131 and the second electrode 132 in the first state is, for example, 0.01V or more. There is no particular limitation on the lower limit of the voltage difference between the first electrode 131 and the second electrode 132 in the second state, but the voltage difference between the first electrode 131 and the second electrode 132 in the second state is, for example, 0.6V or more.

[0439] The voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 0.01 V to 0.6 V. In addition, the voltage difference between the first electrode 131 and the second electrode 132 in the second state is preferably 0.6 V to 2 V.

[0440] The first and second vertical alignment films 414 and 424 can be the same vertical alignment films as those in the fifth embodiment. In this embodiment, since the vertical alignment films are disposed on both substrates, the optical element 10 can be realized with higher productivity than when horizontal alignment films are disposed.

[0441] At least one of the first vertical alignment film 414 and the second vertical alignment film 424 is preferably a vertical alignment film with a weak anchoring force. This allows switching between polarization modulation and polarization non-modulation over a wider bandwidth and at a lower voltage. The vertical alignment film with a weak anchoring force only needs to have a weak anchoring force at at least one of the polar angle and the azimuth angle.

[0442] It is preferable that the light incident on the optical element 10 is circularly polarized light. By adopting such a configuration, it is possible to realize the optical element 10 capable of switching the polarization state of circularly polarized light.

[0443] (Modification of the Ninth Embodiment)

[0444] In the ninth embodiment, in both the first and second states, the voltage difference between the first and second electrodes 131, 132 and the solid-surface electrode 240 is preferably 8V or greater. This arrangement allows the liquid crystal molecules 310 to be more effectively aligned horizontally. While the upper limit of the voltage difference between the first and second electrodes 131, 132 and the solid-surface electrode 240 is not particularly limited, the voltage difference between the first and second electrodes 131, 132 and the solid-surface electrode 240 is, for example, 20V or less. The voltage difference between the first and second electrodes 131, 132 and the solid-surface electrode 240 is preferably 8V or greater and 20V or less.

[0445] In the case where the voltage difference between the first electrode 131 and the second electrode 132 and the full-surface electrode 240 is 8V or more, for example, the voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 2V or less. In addition, the voltage difference between the first electrode 131 and the second electrode 132 in the second state is preferably 3V or less. There is no particular limitation on the lower limit of the voltage difference between the first electrode 131 and the second electrode 132 in the first state, but the voltage difference between the first electrode 131 and the second electrode 132 in the first state is, for example, 0.01V or more. There is no particular limitation on the lower limit of the voltage difference between the first electrode 131 and the second electrode 132 in the second state, but the voltage difference between the first electrode 131 and the second electrode 132 in the second state is, for example, 1.1V or more.

[0446] Preferably, the voltage difference between the first electrode 131 and the second electrode 132 in the first state is greater than or equal to 0.01 V and less than or equal to 2 V. Furthermore, preferably, the voltage difference between the first electrode 131 and the second electrode 132 in the second state is greater than or equal to 1.1 V and less than or equal to 3 V.

[0447] By applying a voltage as in this modification, the liquid crystal molecules 310 that fall down near the interface can be realized, thereby achieving a sHWP with a wide viewing angle. In this case, the cell thickness, twist pitch, and angle of the retardation film can be appropriately changed.

[0448] (Tenth embodiment)

[0449] This embodiment mainly describes the unique features of this embodiment, and omits the description of the contents overlapping with the first to ninth embodiments and their variations. This embodiment is substantially the same as the ninth embodiment, except for the configuration of the liquid crystal cell 11 and the preferred voltages applied to the electrodes.

[0450] Figure 69 It is a schematic cross-sectional view of an optical element according to a tenth embodiment. Figure 70 It is a schematic cross-sectional view of a liquid crystal cell included in the optical element according to the tenth embodiment. Figure 71 The diagram is a diagram illustrating the orientation of liquid crystal molecules in the first and second states of the optical element of the tenth embodiment. The orientation of liquid crystal molecules near the interface of the substrate is vertical and cannot be determined. Figure 71 In the process, the orientation of the liquid crystal molecules is determined by the direction of the electrodes.

[0451] In addition, in this embodiment, the orientation (0°) serving as a reference is set to the direction when the orientation direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is projected onto the substrate surface on the exit side of the optical element 10, and the orientation direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is consistent with the horizontal right direction of the screen of the liquid crystal unit 11 when the optical element 10 is observed from the exit side.

[0452] Figures 69 to 71The liquid crystal cell 11 included in the optical element 10 of this embodiment further includes a first vertical alignment film 414 disposed between the first substrate 100 and the liquid crystal layer 300, and a second vertical alignment film 424 disposed between the liquid crystal layer 300 and the second substrate 200. The liquid crystal layer 300 contains liquid crystal molecules 310 having negative dielectric anisotropy. The electrode 11E includes a planar first electrode 131 on the first substrate 100, and a second electrode 132 that overlaps with the first electrode 131 via a first insulating layer 141 and has a slit portion. On the second substrate 200, the electrode 11E includes a planar third electrode 231 and a fourth electrode 232 that overlaps with the third electrode 231 via a second insulating layer 241 and has a slit portion 232S. When viewed from above, the extension direction 132A of the slit portion 132S provided in the second electrode 132 is arranged at an angle relative to the extension direction 232A of the slit portion 232S provided in the fourth electrode 232, and is parallel to the orientation direction 311X of the liquid crystal molecules 311 on the side of the first substrate 100 in a state where no voltage is applied. The extension direction 232A of the slit portion 232S provided in the fourth electrode 232 is parallel to the orientation direction 312X of the liquid crystal molecules 312 on the side of the second substrate 200 in a state where no voltage is applied.

[0453] By adopting this approach, Figure 71 As shown, when a voltage is applied between the first electrode 131 and the second electrode 132 and no voltage is applied between the third electrode 231 and the fourth electrode 232, circularly polarized light (e.g., right-handed circularly polarized light) incident on the liquid crystal cell 11 becomes first linearly polarized light after passing through the liquid crystal cell 11. In other words, the first state is achieved.

[0454] In addition, if Figure 71 As shown, when no voltage is applied between the first electrode 131 and the second electrode 132, and a voltage is applied between the third electrode 231 and the fourth electrode 232, circularly polarized light (e.g., right-handed circularly polarized light) incident on the liquid crystal cell 11 passes through the liquid crystal cell 11 and becomes second linearly polarized light having a polarization direction orthogonal to that of the first linearly polarized light in a plan view. In other words, the second state is achieved.

[0455] In addition, one of the first electrode 131 and the second electrode 132 is a pixel electrode, and the other is a common electrode. One of the third electrode 231 and the fourth electrode 232 is a pixel electrode, and the other is a common electrode. Figure 70 In the figure, both the first substrate 100 and the second substrate 200 have planar electrodes and electrodes with slit portions in sequence facing the liquid crystal layer 300 side, but the configuration of the planar electrodes and electrodes with slit portions is not limited to this. They may also have electrodes with slit portions and planar electrodes in sequence facing the liquid crystal layer 300 side.

[0456] At least one of the liquid crystal molecules 311 on the first substrate 100 side and the liquid crystal molecules 312 on the second substrate 200 side preferably has a tilt. For example, when the liquid crystal molecules 311 on the first substrate 100 side have a tilt, the tilt azimuth of the liquid crystal molecules 311 on the first substrate 100 side is preferably parallel to the extension direction of the FFS electrode on the first substrate 100 side. More specifically, the orientation direction 311X of the liquid crystal molecules 311 on the first substrate 100 side in the no-voltage state is preferably parallel to the extension direction 132A of the slit 132S provided in the second electrode 132. In this case, the tilt azimuth of the liquid crystal molecules 311 on the first substrate 100 side is preferably approximately 0° (for example, greater than -10° and less than +10°), and the liquid crystal molecules 312 on the second substrate 200 side preferably have no tilt.

[0457] Furthermore, when the liquid crystal molecules 312 on the second substrate 200 side have a tilt, the tilt azimuth of the liquid crystal molecules 312 on the second substrate 200 side is preferably parallel to the extension direction of the FFS electrode on the second substrate 200 side. More specifically, in the no-voltage state, the orientation direction 312X of the liquid crystal molecules 312 on the second substrate 200 side is preferably parallel to the extension direction 232A of the slit portion 232S provided in the fourth electrode 232. In this case, the tilt azimuth of the liquid crystal molecules 312 on the second substrate 200 side is preferably approximately 160° (e.g., 150° or more and 170° or less), and the liquid crystal molecules 311 on the first substrate 100 side preferably have no tilt.

[0458] In addition, both the liquid crystal molecules 311 on the first substrate 100 side and the liquid crystal molecules 312 on the second substrate 200 side may have a tilt.

[0459] In a plan view, the angle γ (where γ is a real number greater than 0° and less than 90°) formed between the extension direction 132A and the extension direction 232A and the twist angle C of the liquid crystal molecules 310 included in the liquid crystal layer 300 preferably satisfy the above (Equation CX1) in the first state and the second state, more preferably satisfy the above (Equation CX2), and even more preferably satisfy the above (Equation CX3). By adopting this approach, it is possible to effectively switch between polarization modulation and polarization non-modulation over a wide bandwidth.

[0460] The twist angle C is preferably 60° to 80°, more preferably 64° to 76°, and even more preferably 68° to 72°. This allows for more efficient switching between polarization modulation and non-polarization modulation over a wide bandwidth.

[0461] When the azimuth angle of the extension direction 132A is 0°, the azimuth angle of the alignment direction 311X of the liquid crystal molecules 311 on the first substrate 100 side in the state where no voltage is applied is 0°, the azimuth angle of the extension direction 232A is 160°, the azimuth angle of the alignment direction 312X of the liquid crystal molecules 312 on the second substrate 200 side in the state where no voltage is applied is 160°, the twist angle of the liquid crystal molecules 310 is 70°, and the liquid crystal layer 300 contains negative-type liquid crystal molecules 310, as shown in FIG. Figures 69 to 71 As shown, when a voltage is applied between the first electrode 131 and the second electrode 132 and no voltage is applied between the third electrode 231 and the fourth electrode 232, a first state can be achieved in which the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side is 0° and the azimuth angle of the alignment direction 312A of the liquid crystal molecules 312 on the second substrate 200 side is 70°. Furthermore, when no voltage is applied between the first electrode 131 and the second electrode 132 and a voltage is applied between the third electrode 231 and the fourth electrode 232, a second state can be achieved in which the azimuth angle of the alignment direction 311B of the liquid crystal molecules 311 on the first substrate 100 side is 90° and the azimuth angle of the alignment direction 312B of the liquid crystal molecules 312 on the second substrate 200 side is 160°.

[0462] The pitch between the second electrodes 132 provided with slits 132S is preferably 1 μm or more and 5 μm or less. This reduced pitch allows the liquid crystal molecules 310 to have a more uniform orientation, resulting in improved modulation characteristics. Furthermore, the pitch between the fourth electrodes 232 provided with slits 232S is preferably 1 μm or more and 5 μm or less. This allows the liquid crystal molecules 310 to have a more uniform orientation, resulting in improved modulation characteristics.

[0463] The liquid crystal molecules 310 in this embodiment are negative-type liquid crystal molecules 310. By applying a large longitudinal voltage between the first substrate 100 and the second substrate 200 in this manner, the negative-type liquid crystal molecules 310 can be pushed down and aligned horizontally. In the first and second states, the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is preferably 1V or greater, more preferably 3V or greater, and even more preferably 4V or greater. By adopting this approach, the liquid crystal molecules 310 can be aligned horizontally more effectively. There is no particular upper limit to the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232; however, the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is, for example, 7V or less. The voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is preferably 1V or greater and 7V or less, more preferably 3V or greater and 7V or less, and even more preferably 4V or greater and 7V or less.

[0464] Furthermore, a weak voltage can be applied between the pixel electrode and the common electrode, between the first electrode 131 and the second electrode 132, and between the third electrode 231 and the fourth electrode 232, to control the in-plane orientation of the liquid crystal molecules 310. If the liquid crystal molecules 310 are negative-type liquid crystal molecules, they align in-plane in the direction extending from the slits 132S and 232S (a direction perpendicular to the electric field). At this time, a strong transverse electric field prevents the orientational twist of the liquid crystal caused by chiral forces, so a weak transverse electric field is preferred.

[0465] When the voltage difference between the first electrode 131 and the second electrode 132 and the third electrode 231 and the fourth electrode 232 is 7 V or less, for example, the voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 2 V or less. The voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is preferably 0.6 V or less. The lower limit of the voltage difference between the first electrode 131 and the second electrode 132 in the first state is not particularly limited, but the voltage difference between the first electrode 131 and the second electrode 132 in the first state is, for example, 0.7 V or more. In addition, the lower limit of the voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is not particularly limited, but the voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is, for example, 0.01 V or more.

[0466] The voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 0.7 V to 2 V. The voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is preferably 0.01 V to 0.6 V.

[0467] In addition, the voltage difference between the first electrode 131 and the second electrode 132 in the second state is preferably 0.6 V or less. The voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is preferably 2 V or less. The lower limit of the voltage difference between the first electrode 131 and the second electrode 132 in the second state is not particularly limited, but the voltage difference between the first electrode 131 and the second electrode 132 in the second state is, for example, 0.01 V or more. In addition, the lower limit of the voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is not particularly limited, but the voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is, for example, 0.7 V or more.

[0468] The voltage difference between the first electrode 131 and the second electrode 132 in the second state is preferably greater than or equal to 0.01 V and less than or equal to 0.6 V. The voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is preferably greater than or equal to 0.7 V and less than or equal to 2 V.

[0469] The first and second vertical alignment films 414 and 424 can be the same vertical alignment films as those in the fifth embodiment. In this embodiment, since the vertical alignment films are disposed on both substrates, the optical element 10 can be realized with higher productivity than when horizontal alignment films are disposed.

[0470] At least one of the first vertical alignment film 414 and the second vertical alignment film 424 is preferably a vertical alignment film with a weak anchoring force. This allows switching between polarization modulation and polarization non-modulation over a wider bandwidth and at a lower voltage. The vertical alignment film with a weak anchoring force only needs to have a weak anchoring force at at least one of the polar angle and the azimuth angle.

[0471] (Modification of the Tenth Embodiment)

[0472] In the tenth embodiment, in both the first and second states, the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is preferably 8V or greater. This arrangement allows the liquid crystal molecules 310 to be more effectively aligned horizontally. While the upper limit of the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is not particularly limited, the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is, for example, 20V or less. The voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is preferably 8V or greater and 20V or less.

[0473] When the voltage difference between the first electrode 131 and the second electrode 132 and the third electrode 231 and the fourth electrode 232 is 8V or more, for example, the voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 3V or less. The voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is preferably 2V or less. The lower limit of the voltage difference between the first electrode 131 and the second electrode 132 in the first state is not particularly limited, but the voltage difference between the first electrode 131 and the second electrode 132 in the first state is, for example, 1.1V or more. In addition, the lower limit of the voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is not particularly limited, but the voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is, for example, 0.01V or more.

[0474] The voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 1.1 V to 3 V. The voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is preferably 0.01 V to 2 V.

[0475] In addition, the voltage difference between the first electrode 131 and the second electrode 132 in the second state is preferably 2 V or less. The voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is preferably 3 V or less. The lower limit of the voltage difference between the first electrode 131 and the second electrode 132 in the second state is not particularly limited, but the voltage difference between the first electrode 131 and the second electrode 132 in the second state is, for example, 0.01 V or more. In addition, the lower limit of the voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is not particularly limited, but the voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is, for example, 1.1 V or more.

[0476] The voltage difference between the first electrode 131 and the second electrode 132 in the second state is preferably 0.01 V to 2 V. The voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is preferably 1.1 V to 3 V.

[0477] By applying a voltage as in this modification, the liquid crystal molecules 310 that fall down near the interface can be realized, thereby achieving a sHWP with a wide viewing angle. In this case, the cell thickness, twist pitch, and angle of the retardation film can be appropriately changed.

[0478] (Eleventh embodiment)

[0479] This embodiment primarily describes features unique to this embodiment, and any overlap with the first to tenth embodiments and their variations will be omitted. This embodiment is substantially the same as the ninth embodiment, except for the configuration of the liquid crystal cell 11, the preferred azimuth angles of the slow axis 12A of the first quarter-wavelength film 12 and the slow axis 13A of the second quarter-wavelength film 13, and the preferred voltages applied to the electrodes.

[0480] Figure 72 It is a schematic cross-sectional view of an optical element according to the eleventh embodiment. Figure 73 It is a schematic cross-sectional view of a liquid crystal cell included in the optical element according to the eleventh embodiment. Figure 74 This is a schematic diagram illustrating the orientation of liquid crystal molecules in the first and second states of the optical element of the eleventh embodiment. The orientation of liquid crystal molecules near the interface of the substrate is vertical and cannot be determined. Figure 74 In the process, the orientation of the liquid crystal molecules is determined by the direction of the electrodes.

[0481] In addition, in this embodiment, the orientation (0°) serving as a reference is set to the direction when the orientation direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is projected onto the substrate surface on the exit side of the optical element 10, and the orientation direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is consistent with the horizontal right direction of the screen of the liquid crystal unit 11 when the optical element 10 is observed from the exit side.

[0482] Figures 72 to 74 The liquid crystal cell 11 included in the optical element 10 of this embodiment further includes a first vertical alignment film 414 disposed between the first substrate 100 and the liquid crystal layer 300, and a second vertical alignment film 424 disposed between the liquid crystal layer 300 and the second substrate 200. The liquid crystal layer 300 contains liquid crystal molecules 310 having negative dielectric anisotropy. The electrode 11E includes a planar first electrode 131 on the first substrate 100, and a second electrode 132 overlapping the first electrode 131 with a first insulating layer 141 interposed therebetween and having a slit 132S. On the second substrate 200, the electrode 11E includes a planar third electrode 231 and a fourth electrode 232 overlapping the third electrode 231 with a second insulating layer 241 interposed therebetween and having a slit 232S interposed therebetween. When viewed from above, the orientation direction 311X of the liquid crystal molecules 311 on the side of the first substrate 100 in the no-voltage applied state is arranged between the extension direction 132A of the slit portion 132S provided on the second electrode 132 and the extension direction 232A of the slit portion 232S provided on the fourth electrode 232, and is arranged to be orthogonal to the extension direction 132A of the slit portion 132S provided on the second electrode 132, and is inclined relative to the extension direction 232A of the slit portion 232S provided on the fourth electrode 232.

[0483] By adopting this approach, Figure 74 As shown, when a voltage is applied between the first electrode 131 and the second electrode 132, and no voltage is applied between the third electrode 231 and the fourth electrode 232, circularly polarized light (for example, right-handed circularly polarized light) incident on the liquid crystal cell 11 becomes first linearly polarized light after passing through the liquid crystal cell 11. In other words, the first state is achieved.

[0484] In addition, if Figure 74 As shown, when no voltage is applied between the first electrode 131 and the second electrode 132, and a voltage is applied between the third electrode 231 and the fourth electrode 232, circularly polarized light (for example, right-handed circularly polarized light) incident on the liquid crystal cell 11 passes through the liquid crystal cell 11 and becomes second linearly polarized light having a polarization direction orthogonal to that of the first linearly polarized light in a plan view. In other words, the second state is achieved.

[0485] In addition, one of the first electrode 131 and the second electrode 132 is a pixel electrode, and the other is a common electrode. One of the third electrode 231 and the fourth electrode 232 is a pixel electrode, and the other is a common electrode. Figure 73 In the embodiment, both the first substrate 100 and the second substrate 200 have planar electrodes and electrodes with slit portions in sequence facing the liquid crystal layer 300 side, but the configuration of the planar electrodes and electrodes with slit portions is not limited to this, and the electrodes may also have electrodes with slit portions and planar electrodes in sequence facing the liquid crystal layer 300 side.

[0486] At least one of the liquid crystal molecules 311 on the first substrate 100 side and the liquid crystal molecules 312 on the second substrate 200 side preferably has a tilt. For example, when the liquid crystal molecules 311 on the first substrate 100 side have a tilt, the tilt azimuth of the liquid crystal molecules 311 on the first substrate 100 side is preferably orthogonal to the extension direction of the FFS electrode on the first substrate 100 side. More specifically, in the no-voltage state, the orientation direction 311X of the liquid crystal molecules 311 on the first substrate 100 side is preferably orthogonal to the extension direction 132A of the slit 132S provided in the second electrode 132. In this case, the tilt azimuth of the liquid crystal molecules 311 on the first substrate 100 side is preferably approximately -45° (for example, -55° or higher and -35° or lower), and the liquid crystal molecules 312 on the second substrate 200 side preferably have no tilt. Alternatively, the liquid crystal molecules 312 on the second substrate 200 side may have a tilt, while the liquid crystal molecules 311 on the first substrate 100 side may not have a tilt. Alternatively, both the liquid crystal molecules 311 on the first substrate 100 side and the liquid crystal molecules 312 on the second substrate 200 side may have a tilt.

[0487] Preferably, in a plan view, the angle δ (where δ is a real number greater than 0° and less than 90°) formed between the alignment direction 311X and the extension direction 232A, and the twist angle D1 of the liquid crystal molecules 310 included in the liquid crystal layer 300 satisfy the following (Equation DX1) in the first state and the second state. This approach allows for efficient switching between polarization modulation and polarization non-modulation over a wide bandwidth.

[0488] 80°-D1≤δ≤100°-D1……(Formula DX1)

[0489] The twist angle D1 is preferably 60° to 80°, more preferably 64° to 76°, and even more preferably 68° to 72°. This allows for more efficient switching between polarization modulation and polarization non-modulation over a wide bandwidth.

[0490] When the azimuth angle of the extension direction 132A is 90°, the azimuth angle of the alignment direction 311X of the liquid crystal molecules 311 on the first substrate 100 side in the no-voltage state is 0°, the azimuth angle of the extension direction 232A is 160°, the twist angle of the liquid crystal molecules 310 is 70°, and the liquid crystal layer 300 contains negative-type liquid crystal molecules 310, as shown in FIG. Figures 72 to 74 As shown, when a voltage is applied between the first electrode 131 and the second electrode 132 and no voltage is applied between the third electrode 231 and the fourth electrode 232, a first state can be achieved in which the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side is 0° and the azimuth angle of the alignment direction 312A of the liquid crystal molecules 312 on the second substrate 200 side is 70°. Furthermore, when no voltage is applied between the first electrode 131 and the second electrode 132 and a voltage is applied between the third electrode 231 and the fourth electrode 232, a second state can be achieved in which the azimuth angle of the alignment direction 311B of the liquid crystal molecules 311 on the first substrate 100 side is 90° and the azimuth angle of the alignment direction 312B of the liquid crystal molecules 312 on the second substrate 200 side is 160°.

[0491] When the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is 0°, the azimuth angle of the slow axis of the quarter-wavelength film on the side farther from the light emitting side of the first quarter-wavelength film 12 and the second quarter-wavelength film 13 (in this embodiment, the slow axis 12A of the first quarter-wavelength film 12) is preferably 58° to 78°. This approach enables switching between polarization modulation and polarization non-modulation over a wider bandwidth.

[0492] When the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is set to 0°, the azimuth angle of the lag axis of the lag axis on the light-emitting side of the first quarter-wavelength film 12 and the second quarter-wavelength film 13 (in this embodiment, the lag axis 13A of the second quarter-wavelength film 13) is preferably 13° or more and 33° or less. This approach enables switching between polarization modulation and polarization non-modulation over a wider bandwidth.

[0493] The angle between the slow axis 12A of the first quarter-wavelength film 12 and the slow axis 13A of the second quarter-wavelength film 13 is preferably 40° to 50°, more preferably 42° to 48°, further preferably 44° to 46°, and particularly preferably 45°.

[0494] In this embodiment, in the first state, the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side is set to 0°, the azimuth angle of the slow axis 12A of the first quarter-wavelength film 12 is set to 58° to 78°, and the azimuth angle of the slow axis 13A of the second quarter-wavelength film 13 is set to 13° to 33°. In this state, the first linearly polarized light passes through the first quarter-wavelength film 12 and the second quarter-wavelength film 13, and is converted over a wide bandwidth into circularly polarized light (e.g., left circularly polarized light) having a polarization state different from that of the circularly polarized light (e.g., right circularly polarized light) incident on the liquid crystal cell 11. Thus, in the first state, the circularly polarized light incident on the optical element 10 is converted into circularly polarized light with a different polarization state (e.g., right circularly polarized light is converted into left circularly polarized light), and the polarization modulation of the emitted light is achieved over a wide bandwidth. Furthermore, the second linearly polarized light passes through the first quarter-wavelength film 12 and the second quarter-wavelength film 13, thereby maintaining the same circularly polarized state as the circularly polarized light incident on the liquid crystal cell 11 (e.g., right-handed circularly polarized light) and being emitted over a wide bandwidth. Thus, in the second state, the circularly polarized light incident on the optical element 10 maintains the same polarization state (e.g., right-handed circularly polarized light) and the polarized light emitted is non-modulated over a wide bandwidth.

[0495] The pitch between the second electrodes 132 provided with slits 132S is preferably 1 μm or more and 5 μm or less. This reduced pitch allows the liquid crystal molecules 310 to have a more uniform orientation, resulting in improved modulation characteristics. Furthermore, the pitch between the fourth electrodes 232 provided with slits 232S is preferably 1 μm or more and 5 μm or less. This allows the liquid crystal molecules 310 to have a more uniform orientation, resulting in improved modulation characteristics.

[0496] The liquid crystal molecules 310 in this embodiment are negative-type liquid crystal molecules 310. By applying a large longitudinal voltage between the first substrate 100 and the second substrate 200 in this manner, the negative-type liquid crystal molecules 310 can be pushed down and aligned horizontally. In the first and second states, the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is preferably 1V or greater, more preferably 3V or greater, and even more preferably 4V or greater. By adopting this approach, the liquid crystal molecules 310 can be aligned horizontally more effectively. There is no particular upper limit to the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232; however, the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is, for example, 7V or less. The voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is preferably 1V or greater and 7V or less, more preferably 3V or greater and 7V or less, and even more preferably 4V or greater and 7V or less.

[0497] Furthermore, a weak voltage can be applied between the pixel electrode and the common electrode, between the first electrode 131 and the second electrode 132, and between the third electrode 231 and the fourth electrode 232, to control the in-plane orientation of the liquid crystal molecules 310. When the liquid crystal molecules 310 are negative-type liquid crystal molecules, they align in-plane in the direction extending from the slits 132S and 232S (a direction perpendicular to the electric field). At this time, a strong transverse electric field prevents the orientational twist of the liquid crystal caused by chiral forces, so a weak transverse electric field is preferred.

[0498] When the voltage difference between the first electrode 131 and the second electrode 132 and the third electrode 231 and the fourth electrode 232 is 7 V or less, for example, the voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 2 V or less. The voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is preferably 0.6 V or less. The lower limit of the voltage difference between the first electrode 131 and the second electrode 132 in the first state is not particularly limited, but the voltage difference between the first electrode 131 and the second electrode 132 in the first state is, for example, 0.7 V or more. In addition, the lower limit of the voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is not particularly limited, but the voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is, for example, 0.01 V or more.

[0499] The voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 0.7 V to 2 V. The voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is preferably 0.01 V to 0.6 V.

[0500] In addition, the voltage difference between the first electrode 131 and the second electrode 132 in the second state is preferably 0.6 V or less. The voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is preferably 2 V or less. The lower limit of the voltage difference between the first electrode 131 and the second electrode 132 in the second state is not particularly limited, but the voltage difference between the first electrode 131 and the second electrode 132 in the second state is, for example, 0.01 V or more. In addition, the lower limit of the voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is not particularly limited, but the voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is, for example, 0.7 V or more.

[0501] The voltage difference between the first electrode 131 and the second electrode 132 in the second state is preferably greater than or equal to 0.01 V and less than or equal to 0.6 V. The voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is preferably greater than or equal to 0.7 V and less than or equal to 2 V.

[0502] The first and second vertical alignment films 414 and 424 can be the same vertical alignment films as those in the fifth embodiment. In this embodiment, since the vertical alignment films are disposed on both substrates, the optical element 10 can be realized with higher productivity than when horizontal alignment films are disposed.

[0503] At least one of the first vertical alignment film 414 and the second vertical alignment film 424 is preferably a vertical alignment film with a weak anchoring force. This allows switching between polarization modulation and polarization non-modulation over a wider bandwidth and at a lower voltage. The vertical alignment film with a weak anchoring force only needs to have a weak anchoring force at at least one of the polar angle and the azimuth angle.

[0504] (Modification of the first embodiment)

[0505] In the eleventh embodiment described above, in the first and second states, the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is preferably 8V or greater. This arrangement allows the liquid crystal molecules 310 to be more effectively aligned horizontally. While the upper limit of the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is not particularly limited, the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is, for example, 20V or less. The voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is preferably 8V or greater and 20V or less.

[0506] When the voltage difference between the first electrode 131 and the second electrode 132 and the third electrode 231 and the fourth electrode 232 is 8V or more, for example, the voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 3V or less. The voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is preferably 2V or less. The lower limit of the voltage difference between the first electrode 131 and the second electrode 132 in the first state is not particularly limited, but the voltage difference between the first electrode 131 and the second electrode 132 in the first state is, for example, 1.1V or more. In addition, the lower limit of the voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is not particularly limited, but the voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is, for example, 0.01V or more.

[0507] The voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 1.1 V to 3 V. The voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is preferably 0.01 V to 2 V.

[0508] In addition, the voltage difference between the first electrode 131 and the second electrode 132 in the second state is preferably 2 V or less. The voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is preferably 3 V or less. The lower limit of the voltage difference between the first electrode 131 and the second electrode 132 in the second state is not particularly limited, but the voltage difference between the first electrode 131 and the second electrode 132 in the second state is, for example, 0.01 V or more. In addition, the lower limit of the voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is not particularly limited, but the voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is, for example, 1.1 V or more.

[0509] The voltage difference between the first electrode 131 and the second electrode 132 in the second state is preferably 0.01 V to 2 V. The voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is preferably 1.1 V to 3 V.

[0510] By applying a voltage as in this modification, the liquid crystal molecules 310 that fall down near the interface can be realized, thereby achieving a sHWP with a wide viewing angle. In this case, the cell thickness, twist pitch, and angle of the retardation film can be appropriately changed.

[0511] (Twelfth embodiment)

[0512] This embodiment primarily describes features unique to this embodiment, and any overlap with the first to eleventh embodiments and their variations will be omitted. This embodiment is substantially the same as the ninth embodiment, except for the configuration of the liquid crystal cell 11 and the preferred voltages applied to the electrodes.

[0513] Figure 75 It is a schematic cross-sectional view of an optical element according to a twelfth embodiment. Figure 76 It is a schematic cross-sectional view of a liquid crystal cell included in the optical element according to the twelfth embodiment. Figure 77 This is a schematic diagram illustrating the orientation of liquid crystal molecules in the first and second states of the optical element of the twelfth embodiment. The orientation of liquid crystal molecules near the interface of the substrate is vertical and the orientation cannot be specified. Figure 77 In the process, the orientation of the liquid crystal molecules is determined by the direction of the electrodes.

[0514] In addition, in this embodiment, the orientation (0°) serving as a reference is set to the direction when the orientation direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is projected onto the substrate surface on the exit side of the optical element 10, and the orientation direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is consistent with the horizontal right direction of the screen of the liquid crystal unit 11 when the optical element 10 is observed from the exit side.

[0515] Figures 75 to 77 The liquid crystal cell 11 included in the optical element 10 of this embodiment further includes a first vertical alignment film 414 disposed between the first substrate 100 and the liquid crystal layer 300, and a second vertical alignment film 424 disposed between the liquid crystal layer 300 and the second substrate 200. The liquid crystal layer 300 contains liquid crystal molecules 310 having negative dielectric anisotropy. The electrode 11E includes a planar first electrode 131 on the first substrate 100, and a second electrode 132 overlapping the first electrode 131 with a first insulating layer 141 interposed therebetween and having a slit 132S. On the second substrate 200, the electrode 11E includes a planar third electrode 231 and a fourth electrode 232 overlapping the third electrode 231 with a second insulating layer 241 interposed therebetween and having a slit 232S interposed therebetween. When viewed from above, the orientation direction 311X of the liquid crystal molecules 311 on the side of the first substrate 100 in the no-voltage-applied state is arranged between the extension direction 132A of the slit portion 132S provided on the second electrode 132 and the extension direction 232A of the slit portion 232S provided on the fourth electrode 232, and is arranged to be orthogonal to the extension direction 132A of the slit portion 132S provided on the second electrode 132 and inclined relative to the extension direction 232A of the slit portion 232S provided on the fourth electrode 232.

[0516] By adopting this approach, Figure 77As shown, when a voltage is applied between the first electrode 131 and the second electrode 132, and no voltage is applied between the third electrode 231 and the fourth electrode 232, circularly polarized light (for example, right-handed circularly polarized light) incident on the liquid crystal cell 11 becomes first linearly polarized light after passing through the liquid crystal cell 11. In other words, the first state is achieved.

[0517] In addition, if Figure 77 As shown, when no voltage is applied between the first electrode 131 and the second electrode 132, and a voltage is applied between the third electrode 231 and the fourth electrode 232, circularly polarized light (for example, right-handed circularly polarized light) incident on the liquid crystal cell 11 passes through the liquid crystal cell 11 and becomes second linearly polarized light having a polarization direction orthogonal to that of the first linearly polarized light in a plan view. In other words, the second state is achieved.

[0518] In addition, one of the first electrode 131 and the second electrode 132 is a pixel electrode, and the other is a common electrode. One of the third electrode 231 and the fourth electrode 232 is a pixel electrode, and the other is a common electrode. Figure 77 In the figure, both the first substrate 100 and the second substrate 200 have planar electrodes and electrodes with slit portions in sequence facing the liquid crystal layer 300 side, but the configuration of the planar electrodes and electrodes with slit portions is not limited to this. They may also have electrodes with slit portions and planar electrodes in sequence facing the liquid crystal layer 300 side.

[0519] At least one of the liquid crystal molecules 311 on the first substrate 100 side and the liquid crystal molecules 312 on the second substrate 200 side preferably has a tilt. For example, if the liquid crystal molecules 311 on the first substrate 100 side have a tilt, in this embodiment, the tilt of the liquid crystal molecules 311 on the first substrate 100 side is preferably orthogonal to the extension direction of the FFS electrode on the first substrate 100 side, and more preferably, the angle formed by the two is 90°. More specifically, in the no-voltage state, the orientation direction 311X of the liquid crystal molecules 311 on the first substrate 100 side is preferably orthogonal to the extension direction 132A of the slit 132S provided in the second electrode 132, and more preferably, the angle formed by the two is 90°. In this case, the tilt of the liquid crystal molecules 311 on the first substrate 100 side is preferably approximately 0° (for example, greater than -10° and less than +10°), and the liquid crystal molecules 312 on the second substrate 200 side preferably have no tilt. Alternatively, the liquid crystal molecules 312 on the second substrate 200 side may have a tilt, while the liquid crystal molecules 311 on the first substrate 100 side may not have a tilt. Alternatively, both the liquid crystal molecules 311 on the first substrate 100 side and the liquid crystal molecules 312 on the second substrate 200 side may have a tilt.

[0520] Preferably, in a plan view, the angle δ (where δ is a real number greater than 0° and less than 90°) formed between the alignment direction 311X and the extension direction 232A, and the twist angle D1 of the liquid crystal molecules 310 included in the liquid crystal layer 300 satisfy the above (Equation DX1) in the first state and the second state. This approach allows for efficient switching between polarization modulation and polarization non-modulation over a wide bandwidth.

[0521] The twist angle D1 is preferably 60° to 80°, more preferably 64° to 76°, and even more preferably 68° to 72°. This allows for more efficient switching between polarization modulation and polarization non-modulation over a wide bandwidth.

[0522] When the azimuth angle of the extension direction 132A is 90°, the azimuth angle of the alignment direction 311X of the liquid crystal molecules 311 on the first substrate 100 side in the no-voltage state is 0°, the azimuth angle of the extension direction 232A is 160°, the twist angle of the liquid crystal molecules 310 is 70°, and the liquid crystal layer 300 contains negative-type liquid crystal molecules 310, as shown in FIG. Figures 75 to 77 As shown, when no voltage is applied between the first electrode 131 and the second electrode 132 and when no voltage is applied between the third electrode 231 and the fourth electrode 232, a first state can be achieved in which the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side is 0° and the azimuth angle of the alignment direction 312A of the liquid crystal molecules 312 on the second substrate 200 side is 70°. Furthermore, when a voltage is applied between the first electrode 131 and the second electrode 132 and when a voltage is applied between the third electrode 231 and the fourth electrode 232, a second state can be achieved in which the azimuth angle of the alignment direction 311B of the liquid crystal molecules 311 on the first substrate 100 side is 90° and the azimuth angle of the alignment direction 312B of the liquid crystal molecules 312 on the second substrate 200 side is 160°.

[0523] The pitch between the second electrodes 132 provided with slits 132S is preferably 1 μm or more and 5 μm or less. This reduced pitch allows the liquid crystal molecules 310 to have a more uniform orientation, resulting in improved modulation characteristics. Furthermore, the pitch between the fourth electrodes 232 provided with slits 232S is preferably 1 μm or more and 5 μm or less. This allows the liquid crystal molecules 310 to have a more uniform orientation, resulting in improved modulation characteristics.

[0524] The liquid crystal molecules 310 in this embodiment are negative-type liquid crystal molecules 310. By applying a large longitudinal voltage between the first substrate 100 and the second substrate 200 in this manner, the negative-type liquid crystal molecules 310 can be pushed down and aligned horizontally. In the first and second states, the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is preferably 1V or greater, more preferably 3V or greater, and even more preferably 4V or greater. By adopting this approach, the liquid crystal molecules 310 can be aligned horizontally more effectively. There is no particular upper limit to the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232; however, the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is, for example, 7V or less. The voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is preferably 1V or greater and 7V or less, more preferably 3V or greater and 7V or less, and even more preferably 4V or greater and 7V or less.

[0525] Furthermore, a weak voltage can be applied between the pixel electrode and the common electrode, between the first electrode 131 and the second electrode 132, and between the third electrode 231 and the fourth electrode 232, to control the in-plane orientation of the liquid crystal molecules 310. If the liquid crystal molecules 310 are negative-type liquid crystal molecules, they align in-plane in the direction extending from the slits 132S and 232S (a direction perpendicular to the electric field). At this time, a strong transverse electric field prevents the orientational twist of the liquid crystal caused by chiral forces, so a weak transverse electric field is preferred.

[0526] When the voltage difference between the first electrode 131 and the second electrode 132 and the third electrode 231 and the fourth electrode 232 is 7 V or less, for example, the voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 0.6 V or less. The voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is preferably 0.6 V or less. The lower limit value of the voltage difference between the first electrode 131 and the second electrode 132 in the first state is not particularly limited, but the voltage difference between the first electrode 131 and the second electrode 132 in the first state is, for example, 0.01 V or more. In addition, the lower limit value of the voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is not particularly limited, but the voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is, for example, 0.01 V or more.

[0527] The voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 0.01 V to 0.6 V. The voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is preferably 0.01 V to 0.6 V.

[0528] In addition, the voltage difference between the first electrode 131 and the second electrode 132 in the second state is preferably 2 V or less. The voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is preferably 2 V or less. The lower limit of the voltage difference between the first electrode 131 and the second electrode 132 in the second state is not particularly limited, but the voltage difference between the first electrode 131 and the second electrode 132 in the second state is, for example, 0.7 V or more. In addition, the lower limit of the voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is not particularly limited, but the voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is, for example, 0.7 V or more.

[0529] The voltage difference between the first electrode 131 and the second electrode 132 in the second state is preferably 0.7 V to 2 V. The voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is preferably 0.7 V to 2 V.

[0530] The first and second vertical alignment films 414 and 424 can be the same vertical alignment films as those in the fifth embodiment. In this embodiment, since the vertical alignment films are disposed on both substrates, the optical element 10 can be realized with higher productivity than when horizontal alignment films are disposed.

[0531] (Variation of the twelfth embodiment)

[0532] In the twelfth embodiment, in the first and second states, the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is preferably 8V or greater. This arrangement allows the liquid crystal molecules 310 to be more effectively aligned horizontally. While the upper limit of the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is not particularly limited, the voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is, for example, 20V or less. The voltage difference between the first and second electrodes 131 and 132 and the third and fourth electrodes 231 and 232 is preferably 8V or greater and 20V or less.

[0533] When the voltage difference between the first electrode 131 and the second electrode 132 and the third electrode 231 and the fourth electrode 232 is 8V or more, for example, the voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 2V or less. The voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is preferably 2V or less. The lower limit of the voltage difference between the first electrode 131 and the second electrode 132 in the first state is not particularly limited, but the voltage difference between the first electrode 131 and the second electrode 132 in the first state is, for example, 0.01V or more. In addition, the lower limit of the voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is not particularly limited, but the voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is, for example, 0.01V or more.

[0534] The voltage difference between the first electrode 131 and the second electrode 132 in the first state is preferably 0.01 V to 2 V. The voltage difference between the third electrode 231 and the fourth electrode 232 in the first state is preferably 0.01 V to 2 V.

[0535] In addition, the voltage difference between the first electrode 131 and the second electrode 132 in the second state is preferably 3 V or less. The voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is preferably 3 V or less. The lower limit of the voltage difference between the first electrode 131 and the second electrode 132 in the second state is not particularly limited, but the voltage difference between the first electrode 131 and the second electrode 132 in the second state is, for example, 1.1 V or more. In addition, the lower limit of the voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is not particularly limited, but the voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is, for example, 1.1 V or more.

[0536] The voltage difference between the first electrode 131 and the second electrode 132 in the second state is greater than or equal to 1.1 V and less than or equal to 3 V. The voltage difference between the third electrode 231 and the fourth electrode 232 in the second state is preferably greater than or equal to 1.1 V and less than or equal to 3 V.

[0537] By applying a voltage as in this modification, the liquid crystal molecules 310 that fall down near the interface can be realized, thereby achieving a sHWP with a wide viewing angle. In this case, the cell thickness, twist pitch, and angle of the retardation film can be appropriately changed.

[0538] (Thirteenth embodiment)

[0539] In this embodiment, the features unique to this embodiment are mainly described, and the description of the contents repeated in the first to twelfth embodiments and their modifications is omitted. In this embodiment, a variable focus element having the optical element (sHWP) of the ninth to twelfth embodiments and their modifications is described.

[0540] Similar to the seventh embodiment, the optical elements (sHWP) according to the ninth to twelfth embodiments and their modified examples can also be combined with the PB lens 20 to constitute the variable focus element 30 .

[0541] (Variation of the Thirteenth Embodiment)

[0542] Similar to the first variation of the seventh embodiment, this variation describes a variable focus element 30 in which the PB lens 20 of the thirteenth embodiment is disposed within the optical element 10 and embedded therein. In this variation, the description of the details overlapping with the first variation of the seventh embodiment will be omitted.

[0543] Figure 78 It is a schematic cross-sectional view of a variable focus element according to a modified example of the thirteenth embodiment. Figure 79 It is an enlarged cross-sectional schematic diagram of a variable focus element according to a modified example of the thirteenth embodiment. Figure 80 This is a schematic diagram illustrating the orientation of liquid crystal molecules in the first and second states of an optical element according to a modification of the thirteenth embodiment. The orientation of liquid crystal molecules near the interface of the substrate is vertical and the orientation cannot be determined. Figure 80 In the process, the orientation of the liquid crystal molecules is determined by the direction of the electrodes.

[0544] In addition, in this embodiment, the orientation (0°) serving as a reference is set to the direction when the orientation direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is projected onto the substrate surface on the exit side of the optical element 10, and the orientation direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is consistent with the horizontal right direction of the screen of the liquid crystal unit 11 when the optical element 10 is observed from the exit side.

[0545] like Figure 78 As shown in FIG. 1 , the variable focus element 30 of this modification is a multi-stage variable focus element 30B including two or more stacked bodies composed of the optical element 10 and the PB lens 20 .

[0546] like Figure 79As shown in FIG. 1 , the PB lens 20 of the variable focus element 30 of this modification is configured inside the optical element 10. In this way, by embedding the PB lens 20, there is no need to install the PB lens 20 externally, thereby significantly reducing the manufacturing cost. In addition, the thickness of the variable focus element 30 can be suppressed. Figure 78 , for convenience, the optical element 10 and the PB lens 20 are shown separately.

[0547] More specifically, the variable focus element 30 of this variation includes, in order from the incident side to the exit side, a second quarter-wavelength film 13, a first quarter-wavelength film 12, a first substrate 100, a liquid crystal layer 300, a PB lens 20, and a second substrate 200. The variable focus element 30 may also include a first vertical alignment film 414 between the first substrate 100 and the liquid crystal layer 300. Furthermore, the variable focus element 30 may also include a second vertical alignment film 424 between the second substrate 200 and the liquid crystal layer 300.

[0548] Here, as in the ninth to twelfth embodiments and their variations, when the first quarter-wavelength film 12 and the second quarter-wavelength film 13 are disposed on the emission side of the liquid crystal cell 11, in the first state, circularly polarized light (e.g., right circularly polarized light) incident on the optical element 10 first enters the liquid crystal cell 11 and is converted into first linearly polarized light. This first linearly polarized light then enters the first quarter-wavelength film 12 and the second quarter-wavelength film 13 and is converted into circularly polarized light (e.g., left circularly polarized light). Furthermore, in the second state, circularly polarized light (e.g., right circularly polarized light) incident on the optical element 10 first enters the liquid crystal cell 11 and is converted into second linearly polarized light. This second linearly polarized light then enters the first quarter-wavelength film 12 and the second quarter-wavelength film 13 and is converted into circularly polarized light (e.g., right circularly polarized light).

[0549] On the other hand, as in this modified example, when the first quarter-wavelength film 12 and the second quarter-wavelength film 13 are arranged on the incident side of the liquid crystal cell 11, in the first state, circularly polarized light (e.g., right circularly polarized light) incident on the optical element 10 first enters the first quarter-wavelength film 12 and the second quarter-wavelength film 13 and is converted into linearly polarized light. This linearly polarized light then enters the liquid crystal cell 11 and is converted into first circularly polarized light (e.g., left circularly polarized light). Furthermore, in the second state, circularly polarized light (e.g., right circularly polarized light) incident on the optical element 10 first enters the first quarter-wavelength film 12 and the second quarter-wavelength film 13 and is converted into linearly polarized light. This linearly polarized light then enters the liquid crystal cell 11 and is converted into second circularly polarized light (e.g., right circularly polarized light).

[0550] In this modification, the case where the optical element of the ninth embodiment is used as the optical element 10 is described as an example. When the azimuth angle of the extension direction 132A is 90°, the azimuth angle of the alignment direction 311X of the liquid crystal molecules 311 on the first substrate 100 side in the no-voltage state is 0°, the twist angle of the liquid crystal molecules 310 is 70°, and the liquid crystal layer 300 contains negative-type liquid crystal molecules 310, as shown in FIG. Figures 78 to 80 As shown, when a voltage less than a threshold value is applied between the first electrode 131 and the second electrode 132, and a voltage greater than a threshold value is applied between the first and second electrodes 131, 132, and the solid-surface electrode 240, a first state can be achieved in which the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side is 0°, and the azimuth angle of the alignment direction 312A of the liquid crystal molecules 312 on the second substrate 200 side is 70°. Furthermore, when a voltage greater than a threshold value is applied between the first and second electrodes 131, 132, and a voltage greater than a threshold value is applied between the first and second electrodes 131, 132, and the solid-surface electrode 240, a second state can be achieved in which the azimuth angle of the alignment direction 311B of the liquid crystal molecules 311 on the first substrate 100 side is 90°, and the azimuth angle of the alignment direction 312B of the liquid crystal molecules 312 on the second substrate 200 side is 160°.

[0551] like Figure 80 As shown, when the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is set to 0°, the azimuth angle of the slow axis of the quarter-wavelength film on the side closer to the light emission side of the first quarter-wavelength film 12 and the second quarter-wavelength film 13 (the slow axis 12A of the first quarter-wavelength film 12 in this modified example) is preferably not less than -2° and not more than 18°. By adopting this method, it is possible to switch between polarization modulation and polarization non-modulation over a wider bandwidth.

[0552] like Figure 80 As shown, when the azimuth angle of the alignment direction 311A ​​of the liquid crystal molecules 311 on the first substrate 100 side in the first state is set to 0°, the azimuth angle of the slow axis of the quarter-wavelength film on the side farther from the light emission side of the first quarter-wavelength film 12 and the second quarter-wavelength film 13 (the slow axis 13A of the second quarter-wavelength film 13 in this modified example) is preferably 38° to 58°. By adopting this method, it is possible to switch between polarization modulation and polarization non-modulation over a wider bandwidth.

[0553] Figure 81 13 is a cross-sectional schematic diagram illustrating the detailed structure of a variable focus element according to a modified example of the thirteenth embodiment. Figure 81As shown, the variable focus element 30 has, from the incident side to the exit side, an optical element 10, a first PB lens 20A1, an optical element 10, a first PB lens 20A1, an optical element 10, a second PB lens 20A2, an optical element 10, a second PB lens 20A2, an optical element 10, a second PB lens 20A2, an optical element 10, a third PB lens 20A3, an optical element 10 and a third PB lens 20A3.

[0554] The first PB lens 20A1 has a refractive power of ±0.25, the second PB lens 20A2 has a refractive power of ±0.5, and the third PB lens 20A3 has a refractive power of ±1. These characteristics are positive (converging) when right-handed circularly polarized light is incident, and negative (diverging) when left-handed circularly polarized light is incident.

[0555] Table 2 below is a table illustrating the states of the optical element 10 and the PB lenses 20A1 , 20A2 , and 20A3 in each mode of the variable focus element 30 according to the modification of the thirteenth embodiment.

[0556] [Table 2]

[0557]

[0558] Table 2 above explains the F0 mode. In this mode, all optical elements 10 are in the second state (non-modulated). If right-handed circularly polarized light is incident, it is not modulated by the initial optical element 10 and directly enters the first PB lens 20A1. Here, it receives 0.25D of focused light. At this point, the outgoing light becomes left-handed circularly polarized light. Even after passing through the PB lens 20, the direction of the circularly polarized light changes, a characteristic of the PB lens 20. Because the optical element 10 is non-modulated, it passes through the second optical element 10 as left-handed circularly polarized light. The second first PB lens 20A1 produces a divergence of -0.25D. As a result, the incident light passes directly through the first four frames from the incident side (optical element 10, first PB lens 20A1, optical element 10, and first PB lens 20A1). Similarly, the incident light passes through the second PB lens 20A2 and PB lens 20A3, and as the outgoing light, it remains the incident light and is directly emitted at OD.

[0559] The F1 mode is explained using Table 2 above. In this mode, the fourth optical element 10 is in the first state, starting from the incident side. In this state, after passing through the first second PB lens 20A2, the light is left-circularly polarized, imparting 0.5D, similar to the F0 mode. Next, the light is converted to right-circularly polarized light by the optical elements in the first state. Next, the light passes through the second second PB lens 20A2, imparting +0.5D to a total of 1D, and is then emitted. Afterwards, the light is directly emitted as left-circularly polarized light of 1D. Since the light becomes left-circularly polarized light after passing through the second second PB lens 20A2, the sign of the light from the third PB lens 20A3 is opposite to that of the F0 mode.

[0560] Using Table 2 above and Figure 82 This section describes the F-2.5 mode. Figure 82 This is a diagram illustrating the polarization state of the variable focus element in the F-2.5 mode of the modified example of the thirteenth embodiment. Figure 82 As shown, in the F-2.5 mode, the first four frames from the incident side (optical element 10, first PB lens 20A1, optical element 10 and first PB lens 20A1) impart -0.5D right circularly polarized light, and the last four frames from the exit side (optical element 10, third PB lens 20A3, optical element 10 and third PB lens 20A3) impart -2D, and are emitted as right circularly polarized light with a total of -2.5D.

[0561] Furthermore, based on the same principle, multiple focal lengths can be realized depending on which optical element 10 is set to the first modulation state. In this modification, only three conditions are extracted and shown.

[0562] In the thirteenth embodiment and this modification, a mode of providing a film-shaped (embedded polymer-shaped) PB lens has been described. However, the PB lens itself may be formed of a liquid crystal layer as in the first modification of the seventh embodiment.

[0563] (Fourteenth embodiment)

[0564] In this embodiment, the features unique to this embodiment are mainly described, and the description of the contents overlapping with the first to thirteenth embodiments and their modifications is omitted. In this embodiment, a head-mounted display including the variable focus element 30 of the thirteenth embodiment and its modifications is described.

[0565] Similar to the eighth embodiment described above, the head-mounted display 1 of this embodiment includes a display panel 1P for displaying images, a phase shift plate 40, and a variable focus element 30. By using the head-mounted display 1, light emitted from the display panel 1P, such as a liquid crystal display device or an organic electroluminescent display device, is converted into circularly polarized light by the phase shift plate 40, and then viewed by the user U through the variable focus element 30.

[0566] Hereinafter, the effects of the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0567] (Example 1)

[0568] An optical element 10 of Example 1 having the same structure as the first embodiment described above was produced. The optical element 10 of Example 1 includes, in order from the incident side to the exit side, a liquid crystal cell 11, a quarter-wave film with reverse wavelength dispersion as a first quarter-wave film 12, and a quarter-wave film with flat wavelength dispersion as a second quarter-wave film 13. The azimuth angle of the lag axis of the quarter-wave film with reverse wavelength dispersion (lag axis 12A of the first quarter-wave film 12) is 57.2°, and the azimuth angle of the lag axis of the quarter-wave film with flat wavelength dispersion (lag axis 13A of the second quarter-wave film 13) is 12.2°. Specifically, the optical element 10 of Example 1 was produced as follows.

[0569] Prepare a first substrate 100 having a first comb-tooth electrode 120 and a second substrate 200 having a second comb-tooth electrode 220. The electrode direction of the first substrate 100 (the extension direction 120A of the first comb-tooth electrode 120) and the electrode direction of the second substrate 200 (the extension direction 220A of the second comb-tooth electrode 220) are formed so as to become Figure 5 Furthermore, photo spacers with a height of 3.6 μm are disposed on the second substrate 200 .

[0570] Next, PMMA (polymethyl methacrylate) films are formed on both the first substrate 100 having the first comb-tooth electrodes 120 and the second substrate 200 having the second comb-tooth electrodes 220. A sealing material is then drawn on the second substrate 200, and the first and second substrates 100 and 200 are bonded together with the liquid crystal material interposed therebetween, thereby fabricating the liquid crystal cell 11.

[0571] The liquid crystal material used here is a mixture of 5 wt% dodecyl acrylate (C12A) and the chiral agent S-811 mixed with positive-type liquid crystal molecules (Δn = 0.066) with positive dielectric anisotropy. The concentration of the chiral agent was set so that the twist angle between the upper and lower substrates of the liquid crystal cell was 70°.

[0572] After heating the liquid crystal cell 11 to an isotropic phase, the liquid crystal cell 11 was cooled to room temperature while applying a voltage to the first substrate 100. This resulted in a uniformly horizontally aligned liquid crystal cell 11 having a first weak anchoring force horizontal alignment film 411 and a second weak anchoring force horizontal alignment film 421. Furthermore, a quarter-wavelength film with reverse wavelength dispersion (first quarter-wavelength film 12) and a quarter-wavelength film with flat wavelength dispersion (second quarter-wavelength film 13) were attached to the liquid crystal cell 11 obtained above, yielding the optical element (sHWP element) 10 of Example 1.

[0573] Figure 33 This is a graph illustrating the voltage applied to the optical element of Example 1. Figure 33 As shown, for the optical element 10 of Example 1, when a voltage is applied to the second substrate 200, as shown in FIG. Figure 3 and Figure 4 As shown, the lateral electric field on the second substrate 200 side aligns the liquid crystal molecules 312 on the second substrate 200 side in the 70° direction. Subsequently, when the voltage on the second substrate 200 is reduced (not zero), the liquid crystal molecules 312 on the second substrate 200 side align in the 70° direction along the direction of the electric field, while the liquid crystal molecules 311 on the first substrate 100 side slide due to the chiral twisting force added to the liquid crystal material and align in the 0° direction. This is the first state. Furthermore, even after the voltage is turned off, this first state of alignment is maintained.

[0574] In the opposite manner to the above, a voltage is applied to the first substrate 100, and then reduced, as shown in FIG. Figure 3 and Figure 4 As shown, the liquid crystal molecules 311 on the first substrate 100 side are oriented at 90° (azimuth angle 90°), while the liquid crystal molecules 312 on the second substrate 200 side are oriented at 160° (azimuth angle 160°) due to chiral forces. This is the second state. Thus, the optical element 10 of Example 1 can switch between the second state and the first state by applying a voltage to the first substrate 100 or the second substrate 200.

[0575] like Figure 5 As shown, the 70° twist between the liquid crystal molecules 311 on the first substrate 100 side and the liquid crystal molecules 312 on the second substrate 200 side is the same in the first state and the second state, but the entire system is rotated 90°.

[0576] To investigate the optimal design of the liquid crystal cell, optical calculations were performed on the optical element 10 of Example 1 using the LCD-MASTER 1D manufactured by Shintech. Based on the simulation results, the range of 450nm to 630nm that achieves 90% or greater modulation (including non-modulation) is considered the optimal range. For simplicity, the following charts and graphs illustrate only the wavelengths of 450nm and 630nm.

[0577] First, in order to study the preferred range of the delay Δnd of the liquid crystal layer 300 in the no-voltage-applied state at a wavelength of 550nm, the Stokes parameter S3 of the liquid crystal layer 300 of the optical element 10 of Example 1 in non-modulated and modulated states relative to the wavelength dispersion of the delay in the no-voltage-applied state was obtained through simulation. Figure 34 This is a graph showing the Stokes parameter S3 in the non-modulation state relative to the retardation of the liquid crystal layer included in the optical element of Example 1. Figure 35 This is a graph showing the Stokes parameter S3 during modulation with respect to the retardation of the liquid crystal layer included in the optical element of Example 1.

[0578] like Figure 34 and Figure 35 As shown in FIG. 1 , it can be seen that the retardation Δnd of the liquid crystal layer 300 in the no-voltage-applied state at a wavelength of 550 nm is preferably 180 nm to 280 nm.

[0579] To investigate the preferred range of the twist angle of the liquid crystal layer 300 , the wavelength dispersion of the Stokes parameter S3 with respect to the twist angle of the liquid crystal layer 300 included in the optical element 10 of Example 1 in non-modulated and modulated conditions was determined by simulation. Figure 36 This is a graph showing the Stokes parameter S3 in the non-modulation state with respect to the twist angle of the liquid crystal layer included in the optical element of Example 1. Figure 37 Graph showing the Stokes parameter S3 during modulation relative to the twist angle of the liquid crystal layer of the optical element of Example 1. Figure 36 and Figure 37 As shown, it can be seen that in either the first state or the second state, the twist angle of the liquid crystal layer 300 is preferably not less than 57° and not more than 82°.

[0580] In order to study the preferred range of the azimuth angle of the lag axis of the 1 / 4 wavelength film with reverse wavelength dispersion, the wavelength dispersion of the Stokes parameter S3 in non-modulation and modulation relative to the azimuth angle of the lag axis of the 1 / 4 wavelength film with reverse wavelength dispersion possessed by the optical element 10 of Example 1 was obtained by simulation. Figure 38This is a graph showing the Stokes parameter S3 in the non-modulation state relative to the azimuth angle of the slow axis of the quarter-wavelength film with reverse wavelength dispersion included in the optical element of Example 1. Figure 39 Graph showing the Stokes parameter S3 during modulation relative to the azimuth angle of the slow axis of the quarter-wavelength film with reverse wavelength dispersion of the optical element of Example 1. Figure 38 and Figure 39 As shown in FIG. 1 , it is found that the azimuth angle of the slow axis of the quarter-wavelength film serving as the reverse wavelength dispersion of the first quarter-wavelength film 12 is preferably not less than 48° and not more than 66°.

[0581] In order to study the preferred range of the phase difference of the 1 / 4 wavelength film with reverse wavelength dispersion, the wavelength dispersion of the Stokes parameter S3 in non-modulation and modulation relative to the phase difference of the 1 / 4 wavelength film with reverse wavelength dispersion possessed by the optical element 10 of Example 1 was obtained by simulation. Figure 40 This is a graph showing the Stokes parameter S3 in the non-modulation state relative to the phase difference of the quarter-wavelength film with reverse wavelength dispersion included in the optical element of Example 1. Figure 41 Graph showing the phase difference of the 1 / 4 wavelength film with reverse wavelength dispersion and the Stokes parameter S3 during modulation of the optical element of Example 1. Figure 40 and Figure 41 As shown, it can be seen that the phase difference of the quarter-wave film as the reverse wavelength dispersion of the first quarter-wave film 12 is preferably 30 nm or more and 230 nm or less.

[0582] In order to study the preferred range of the azimuth angle of the lag axis of a 1 / 4 wavelength film with flat wavelength dispersion, the wavelength dispersion of the Stokes parameter S3 in non-modulated and modulated conditions relative to the azimuth angle of the lag axis of a 1 / 4 wavelength film with flat wavelength dispersion possessed by the optical element 10 of Example 1 was obtained by simulation. Figure 42 This is a graph showing the Stokes parameter S3 in the non-modulation state relative to the azimuth angle of the slow axis of the quarter-wavelength film with flat wavelength dispersion included in the optical element of Example 1. Figure 43 Graph showing the Stokes parameter S3 during modulation relative to the azimuth angle of the slow axis of the quarter-wavelength film with flat wavelength dispersion provided in the optical element of Example 1. Figure 42 and 43 As shown in FIG. 1 , it is found that the azimuth angle of the slow axis of the quarter-wavelength film having flat wavelength dispersion as the second quarter-wavelength film 13 is preferably 3° or more and 22° or less.

[0583] In order to study the preferred range of the phase difference of the 1 / 4 wavelength film with flat wavelength dispersion, the wavelength dispersion of the Stokes parameter S3 in non-modulation and modulation relative to the phase difference of the 1 / 4 wavelength film with flat wavelength dispersion possessed by the optical element 10 of Example 1 was obtained by simulation. Figure 44 This is a graph showing the Stokes parameter S3 in the non-modulation state relative to the phase difference of the quarter-wavelength film with flat wavelength dispersion included in the optical element of Example 1. Figure 45 This is a graph showing the phase difference of the 1 / 4 wavelength film with flat wavelength dispersion of the optical element of Example 1 and the Stokes parameter S3 during modulation. Figure 44 and Figure 45 As shown, it can be seen that the phase difference of the quarter-wavelength film as the flat wavelength dispersion of the second quarter-wavelength film 13 is preferably 110 nm or more and 175 nm or less.

[0584] (Comparative Example 1)

[0585] Figure 46 Schematic cross-sectional view of the optical element of Comparative Example 1. Figure 46 The optical element 10R1 of Comparative Example 1 is shown. The optical element 10R1 of Comparative Example 1 corresponds to the optical element of Comparative Example 1 described above. The optical element 10R1 of Comparative Example 1 includes, in order from the incident side to the exit side: a quarter-wavelength film 14R having a slow axis azimuth angle of 75°, a half-wavelength film 15R having a slow axis azimuth angle of 15°, a liquid crystal cell 11R1 including a 90° twisted TN liquid crystal layer 300R1, a half-wavelength film 16R having a slow axis azimuth angle of -75°, and a quarter-wavelength film 17R having a slow axis azimuth angle of -15°.

[0586] (Comparative Example 2)

[0587] Figure 47 Schematic cross-sectional view of the optical element of Comparative Example 2. Figure 47 The optical element 10R2 of Comparative Example 2 is shown. The optical element 10R2 of Comparative Example 2 corresponds to the optical element of Comparative Example 2 described above. The optical element 10R2 of Comparative Example 2 has a structure in which a 70° twist TN liquid crystal layer 300R2 and a -70° twist TN liquid crystal layer 300R3 are stacked in this order from the incident side to the exit side.

[0588] (Evaluation of Example 1, Comparative Example 1, and Comparative Example 2)

[0589] Regarding the optical elements (sHWP) of Example 1, Comparative Example 1 and Comparative Example 2, Figure 48 and Figure 49 Graph 2 shows the wavelength dispersion of the Stokes parameter S3 of the emitted light when right circularly polarized light (S3=+1) is incident. Figure 48 This is a graph showing the wavelength dispersion of the Stokes parameter S3 of the optical elements of Example 1, Comparative Example 1, and Comparative Example 2 during modulation. Figure 49 This is a graph showing the wavelength dispersion of the Stokes parameter S3 of the optical elements of Example 1, Comparative Example 1, and Comparative Example 2 in the non-modulated state.

[0590] like Figure 48 As shown, in the modulation of Example 1 (first state), the emitted light covers a wide wavelength band and is close to S3 = -1. In other words, it can be modulated from S3 = +1 to S3 = -1 (in other words, from right circularly polarized light to left circularly polarized light).

[0591] In addition, if Figure 49 As shown, in the non-modulated state (second state) of Example 1, the emitted light covers a wide wavelength band and approaches S3 = +1. In other words, it is possible to maintain S3 = +1 in the non-modulated state (in other words, right-handed circularly polarized light remains right-handed circularly polarized light).

[0592] On the other hand, in Comparative Example 1 (TN1 layer), while the non-modulated state exhibits extremely excellent characteristics, the modulation state exhibits significant wavelength dependence, indicating that proper modulation is possible only within a very narrow range. Furthermore, in Comparative Example 2 (TN2 layer), while broadband modulation improves compared to Comparative Example 1, the non-modulated state deteriorates.

[0593] (Example 2)

[0594] An optical element 10 of Example 2 having the same configuration as that of the second embodiment was produced. Specifically, the optical element 10 of Example 2 was produced in the same manner as Example 1, except that the configuration of the liquid crystal cell 11 was different. Specifically, the optical element 10 of Example 2 was produced as follows.

[0595] A substrate capable of applying a lateral electric field in two different directions was prepared as the first substrate 100. More specifically, the first substrate 100 was provided with first comb-shaped electrodes 121 and second comb-shaped electrodes 122. The first comb-shaped electrodes 121 were arranged such that their extension direction 121A was perpendicular to the extension direction 122A of the second comb-shaped electrodes 122. Photo spacers with a height of 7.6 μm were placed on the first substrate 100.

[0596] A film of PHMA (polyhexyl methacrylate) is deposited on the first substrate 100 to form a horizontal alignment film 412 with a weak anchoring force. A vertical alignment film 422 is formed on the second substrate 200. Next, a sealant is applied to the second substrate 200, and the first and second substrates 100 and 200 are bonded together with the liquid crystal material sandwiched therebetween, thereby fabricating the liquid crystal cell 11.

[0597] Here, the liquid crystal material used was a mixture of positive-type liquid crystal (Δn = 0.066) with a chiral agent S-811. The concentration of the chiral agent was set so that the twist angle between the upper and lower substrates in the liquid crystal cell was 106°.

[0598] After heating the liquid crystal cell 11 to an isotropic phase state, a voltage is applied to the first electric field direction of the first substrate 100 while cooling to room temperature to obtain a liquid crystal cell 11 with uniform horizontal alignment. Figure 13 A quarter-wave film with reverse wavelength dispersion as the first quarter-wave film 12 and a quarter-wave film with flat wavelength dispersion as the second quarter-wave film 13 were attached in the orientation shown, thereby obtaining an optical element (sHWP element) 10 of Example 2. When a voltage is applied in the direction of a first electric field, a first state (modulation state) is obtained, and when a voltage is applied in the direction of a second electric field, a second state (non-modulation state) is obtained.

[0599] (Evaluation of Example 1, Example 2 and Comparative Example 1)

[0600] The wavelength dispersion of the Stokes parameter S3 of the outgoing light when right circularly polarized light (S3 = +1) is incident on the optical elements (sHWP) of Example 1, Example 2, and Comparative Example 1 is shown in FIG. Figure 50 and Figure 51 . Figure 50 This is a graph showing the wavelength dispersion of the Stokes parameter S3 during modulation of the optical elements of Example 1, Example 2, and Comparative Example 1. Figure 51 This is a graph showing the wavelength dispersion of the Stokes parameter S3 in the non-modulation state of the optical elements of Example 1, Example 2, and Comparative Example 1.

[0601] like Figure 50 As shown, in Example 2, during modulation (the first state), the emitted light covers a wide wavelength band and approaches S3 = -1, similar to Example 1. That is, it is possible to modulate from S3 = +1 to S3 = -1 (in other words, from right circularly polarized light to left circularly polarized light).

[0602] In addition, if Figure 51 As shown, in the non-modulated state (second state) of Example 2, as in Example 1, the emitted light covers a wide wavelength band and approaches S3 = +1. In other words, the non-modulated state can be maintained with S3 = +1 (in other words, right-handed circularly polarized light remains right-handed circularly polarized light).

[0603] (Example 3)

[0604] An optical element 10 of Example 3, corresponding to the third embodiment described above, was produced. Specifically, the optical element 10 of Example 3 was produced in the same manner as in Example 1, except that a first substrate 100 having first and second comb-tooth electrodes 121 and 122 and a second substrate 200 having third and fourth comb-tooth electrodes 221 and 222 were used.

[0605] The optical element of Example 3, in the modulated state (first state), can be modulated from S3 = +1 to S3 = -1 (in other words, from right circularly polarized light to left circularly polarized light), similarly to Example 1. In the non-modulated state (second state), similarly to Example 1, the non-modulated state can be maintained with S3 = +1, and the light can be emitted with S3 = +1 (in other words, right circularly polarized light remains right circularly polarized light).

[0606] The optical element 10 of Example 3 can be configured in two states by applying a conduction voltage to both the first substrate 100 and the second substrate 200 and then reducing the voltage. In Example 3, the orientation of both the first substrate 100 and the second substrate 200 can be controlled by voltage, thereby improving the response speed.

[0607] (Example 4-1 and Example 4-2)

[0608] Optical elements 10 corresponding to Examples 4-1 and 4-2 of the fourth embodiment were fabricated. Specifically, the optical elements 10 of Examples 4-1 and 4-2 were fabricated in the same manner as in Example 1, except that the configurations of the first alignment film 410 disposed between the first substrate 100 and the liquid crystal layer 300 and the second alignment film 420 disposed between the second substrate 200 and the liquid crystal layer 300 were different. Figure 52 This is a diagram illustrating the alignment direction of the bistable alignment film included in the optical element of Example 4-1. Figure 53 This diagram illustrates the alignment direction of the bistable alignment film included in the optical element of Example 4-2. The optical element 10 of Examples 4-1 and 4-2 includes a horizontal alignment film (also called a lubricating film) 423 on the second substrate 200 side, which serves as a weak anchor for the second alignment film 420, and a bistable alignment film 413 on the first substrate 100 side, which serves as the first alignment film 410.

[0609] A PEG film was used as the horizontal alignment film (lubricating film) 423 with a weak anchoring force in the optical element 10 of Examples 4-1 and 4-2. The PEG film was formed according to the following steps: 5 wt% methoxypolyethylene glycol monoacrylate, 5 wt% polyethylene glycol diacrylate, Irgacure 2959 (0.1 wt%), and cyclopentanone (89.9 wt%) were prepared. The film was applied to the second substrate 200 and irradiated with 254 nm ultraviolet light at 2 J / cm 2Then, a sintering treatment is performed at 130° C. for 90 minutes. Thus, a horizontal alignment film 423 with a weak anchoring force is obtained.

[0610] The bistable alignment film 413 of the optical element 10 of Example 4-1 uses a film based on photo-alignment. Specifically, Figure 52 As shown, a bistable alignment film 413 is formed using a material comprising a mixture of two polymers (a first photo-alignment polymer and a second photo-alignment polymer) having mutually different photo-functional wavelengths. A solution comprising the two polymers having mutually different photo-functional wavelengths is applied to a substrate, and then irradiated with polarized ultraviolet light of a specific wavelength and then with polarized ultraviolet light of a different wavelength and direction. This forms a bistable alignment film 413 having stable alignment directions in both a first direction 413A regulated by the first photo-alignment polymer and a second direction 413B regulated by the second photo-alignment polymer.

[0611] In the bistable alignment film 413 of the optical element 10 of Example 4-2, a bistable alignment film based on a concave-convex substrate and a rubbing treatment is used. Specifically, Figure 53 As shown, a structure having grooves in a specific direction (first direction 413A) is formed on the first substrate 100 using a polymer, and a rubbing treatment is performed in a direction different from the groove direction (second direction 413B). Liquid crystal molecules 310 are subjected to two forces: a force that aligns them along the groove direction and a force that aligns them along the rubbing direction, forming a bistable alignment film 413 with stable alignment in two directions.

[0612] The optical elements of Examples 4-1 and 4-2, when modulated (in the first state), can be modulated from S3 = +1 to S3 = -1 (in other words, from right circularly polarized light to left circularly polarized light), similarly to Example 1. When non-modulated (in the second state), similarly to Example 1, the non-modulated state can be maintained with S3 = +1, and S3 = +1 can be emitted (in other words, right circularly polarized light remains right circularly polarized light).

[0613] (Example 5)

[0614] An optical element 10 of Example 5 corresponding to the fifth embodiment was produced. Specifically, the optical element 10 of Example 5 was produced in the same manner as in Example 1, except that the structure of the liquid crystal cell 11 was different. The liquid crystal cell 11 included in the optical element 10 of Example 5 includes, in order: a first substrate 100 having a first electrode 131 and a second electrode 132, a first vertical alignment film 414, a liquid crystal layer 300 containing liquid crystal molecules 310, a second vertical alignment film 424, and a second substrate 200 having a third electrode 231 and a fourth electrode 232. Figure 19As shown, the azimuth angle of the extension direction 132A of the slit portion 132S provided in the second electrode 132 is 0°, and the azimuth angle of the extension direction 232A of the slit portion 232S provided in the fourth electrode 232 is 160°.

[0615] Figure 54 : is a graph illustrating the applied voltage in the first state of the optical element of Example 5. Figure 54 As shown, in the optical element 10 of Example 5, the first state can be achieved by applying + / -1V to the common electrode of the first electrode 131 and the second electrode 132 on the first substrate 100 side, applying - / +1V to the pixel electrode, and applying + / -5V to both the third electrode 231 and the fourth electrode 232 on the second substrate 200 side. Furthermore, in the optical element 10 of Example 5, the second state can be achieved by applying + / -1V to the common electrode of the third electrode 231 and the fourth electrode 232 on the second substrate 200 side, applying - / +1V to the pixel electrode, and applying + / -5V to both the first electrode 131 and the second electrode 132 on the first substrate 100 side.

[0616] Figure 55 This is a graph showing the wavelength dispersion of the Stokes parameter S3 during modulation of the optical elements of Example 1, Example 2, Example 5, Comparative Example 1, and Comparative Example 2. Figure 56 Graphs showing the wavelength dispersion of the Stokes parameter S3 in the non-modulated state for the optical elements of Example 1, Example 2, Example 5, Comparative Example 1, and Comparative Example 2. The wavelength dispersion of the Stokes parameter S3 of the outgoing light when right circularly polarized light (S3 = +1) is incident on the optical element 10 of Example 5 is shown in FIG. Figure 55 and Figure 56 .

[0617] In Example 5, |S3|>0.9 was obtained over the wavelength range of 450nm to 650nm, and good characteristics were obtained. Figure 55 As shown in FIG. 1 , it can be seen that when modulating in Example 5 (in the first state), the emitted light covers a wide wavelength band and is close to S3 = -1. In other words, it is possible to modulate from S3 = +1 to S3 = -1 (in other words, from right circularly polarized light to left circularly polarized light). In addition, as Figure 56 As shown, in the non-modulated state (second state) of Example 5, the emitted light covers a wide wavelength band and approaches S3 = +1. In other words, the non-modulated state can be maintained with S3 = +1 (in other words, right-handed circularly polarized light remains right-handed circularly polarized light).

[0618] In this embodiment, as in other embodiments, the modulation characteristic and the non-modulation characteristic can be appropriately adjusted by designing the Δnd and the twist angle of the liquid crystal layer.

[0619] (Example 6)

[0620] An optical element 10 of Example 6 was fabricated, having the same configuration as that of the sixth embodiment. Specifically, the optical element 10 of Example ...

Claims

1. An optical element, characterized in that: A liquid crystal cell comprising a first substrate, a liquid crystal layer, and a second substrate; and 1 / 4 wavelength film, The liquid crystal layer contains liquid crystal molecules in a twisted orientation between the first substrate and the second substrate. The liquid crystal cell includes an electrode for applying a voltage to the liquid crystal layer on at least one of the first substrate and the second substrate. The electrodes are configured to switch between a first state and a second state by applying a voltage to the liquid crystal layer, the first state being a state in which the liquid crystal molecules on the first substrate side are aligned in a first alignment direction, and the second state being a state in which the liquid crystal molecules on the first substrate side are aligned in a second alignment direction orthogonal to the first alignment direction when viewed from above. The switching between the first state and the second state is used to control the polarization state of light incident on the liquid crystal cell. When circularly polarized light is incident on the liquid crystal cell, in the first state, the circularly polarized light is converted into first linearly polarized light. In the second state, the circularly polarized light is converted into second linearly polarized light. The second linearly polarized light has a polarization direction orthogonal to the polarization direction of the first linearly polarized light when viewed from above. When linearly polarized light is incident on the liquid crystal unit, in the first state, the linearly polarized light is converted into first circularly polarized light, and in the second state, the linearly polarized light is converted into second circularly polarized light, and the second circularly polarized light rotates in a direction opposite to the rotation direction of the first circularly polarized light.

2. The optical element according to claim 1, wherein The liquid crystal cell further comprises: a first horizontal alignment film with a weak anchoring force, disposed between the first substrate and the liquid crystal layer; as well as A second horizontal alignment film with a weak anchoring force is disposed between the liquid crystal layer and the second substrate. The electrode includes a first comb-tooth electrode on the first substrate, the first comb-tooth electrode being arranged so that the comb teeth of the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other, and a second comb-tooth electrode on the second substrate, the second comb-tooth electrode being arranged so that the comb teeth of the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other. In a plan view, an extending direction of the first comb-tooth electrode is inclined relative to an extending direction of the second comb-tooth electrode.

3. The optical element according to claim 1, wherein The liquid crystal cell further comprises: A horizontal alignment film with a weak anchoring force, disposed between the first substrate and the liquid crystal layer; and a vertical alignment film, which is arranged between the liquid crystal layer and the second substrate, The electrode has: a first comb-tooth electrode provided on the first substrate in such a manner that the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other; as well as The second comb-tooth electrode is overlapped with the first comb-tooth electrode via an insulating layer and is provided so that the comb teeth of the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other. In a plan view, an extending direction of the first comb-shaped electrode is orthogonal to an extending direction of the second comb-shaped electrode.

4. The optical element according to claim 1, wherein The electrode has: a first comb-tooth electrode provided on the first substrate in such a manner that the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other; a second comb-tooth electrode, which overlaps with the first comb-tooth electrode via a first insulating layer and is provided so that the comb teeth of the comb-tooth-shaped pixel electrode and the common electrode are interlocked; a third comb-tooth electrode provided on the second substrate in such a manner that the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other; as well as a fourth comb-tooth electrode, which overlaps with the third comb-tooth electrode via a second insulating layer and is provided so that the comb teeth of the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other; When viewed from above, the extension direction of the first comb-tooth electrode is orthogonal to the extension direction of the second comb-tooth electrode, the extension direction of the third comb-tooth electrode is orthogonal to the extension direction of the fourth comb-tooth electrode, and the extension direction of the first comb-tooth electrode is inclined relative to the extension direction of the third comb-tooth electrode.

5. The optical element according to claim 1, wherein The liquid crystal cell further includes a bistable alignment film disposed between the first substrate and the liquid crystal layer and having alignment-stable directions in two directions. The electrode includes a first comb-tooth electrode on the first substrate, the first comb-tooth electrode being arranged so that the comb teeth of the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other, and a second comb-tooth electrode on the second substrate, the second comb-tooth electrode being arranged so that the comb teeth of the comb-tooth-shaped pixel electrode and the common electrode are interlocked with each other. In a plan view, an extending direction of the first comb-tooth electrode is inclined relative to an extending direction of the second comb-tooth electrode.

6. The optical element according to claim 1, wherein The liquid crystal cell further comprises: a first vertical alignment film disposed between the first substrate and the liquid crystal layer; and a second vertical alignment film disposed between the liquid crystal layer and the second substrate; The electrode includes a planar first electrode and a second electrode on the first substrate, the second electrode overlapping the first electrode via a first insulating layer and having a slit portion, and a planar third electrode and a fourth electrode on the second substrate, the fourth electrode overlapping the third electrode via a second insulating layer and having a slit portion. In a plan view, the extending direction of the slit portion provided on the second electrode is arranged to be inclined with respect to the extending direction of the slit portion provided on the fourth electrode.

7. The optical element according to any one of claims 1 to 6, characterized in that The refractive index anisotropy Δn of the liquid crystal layer is 0.12 or less.

8. The optical element according to any one of claims 1 to 6, characterized in that The 1 / 4 wavelength film is a first 1 / 4 wavelength film, A second quarter-wavelength film is further provided on the side of the first quarter-wavelength film opposite to the liquid crystal cell.

9. The optical element according to claim 8, wherein The first quarter-wavelength film has an inverse wavelength dispersion characteristic.

10. The optical element according to claim 8, wherein The in-plane retardation of the first quarter-wavelength film at a wavelength of 450 nm is 0.7 times or more and 1 times or less relative to the in-plane retardation of the first quarter-wavelength film at a wavelength of 550 nm.

11. The optical element according to claim 8, wherein The in-plane retardation of the first quarter-wavelength film at a wavelength of 650 nm is 1 to 1.3 times the in-plane retardation of the first quarter-wavelength film at a wavelength of 550 nm.

12. The optical element according to claim 8, wherein The in-plane retardation of the first quarter-wavelength film at a wavelength of 550 nm is greater than or equal to 30 nm and less than or equal to 230 nm.

13. The optical element according to claim 8, wherein The second quarter-wavelength film has a flat wavelength dispersion characteristic.

14. The optical element according to claim 8, wherein The in-plane retardation of the second quarter-wavelength film at a wavelength of 550 nm is greater than or equal to 110 nm and less than or equal to 175 nm.

15. The optical element according to claim 1, wherein The liquid crystal cell further comprises: a first vertical alignment film disposed between the first substrate and the liquid crystal layer; and a second vertical alignment film disposed between the liquid crystal layer and the second substrate; The liquid crystal layer contains liquid crystal molecules having negative dielectric anisotropy. At least one of the first vertical alignment film and the second vertical alignment film controls the tilt direction of the liquid crystal molecules in a no-voltage-applied state.

16. The optical element according to claim 15, wherein The electrode has, on at least one of the first substrate and the second substrate: Surface electrodes; as well as The electrode overlaps with the planar electrode via an insulating layer and is provided with a slit portion.

17. The optical element according to claim 16, wherein The pitch between the electrodes provided with the slit portions is not less than 1 μm and not more than 5 μm.

18. The optical element according to claim 15 or 16, characterized in that At least one of the first vertical alignment film and the second vertical alignment film is a vertical alignment film having a weak anchoring force.

19. The optical element according to claim 15 or 16, characterized in that The liquid crystal layer has a retardation Δnd of 180 nm to 280 nm in a voltage-applied state at a wavelength of 550 nm.

20. The optical element according to claim 15 or 16, characterized in that The refractive index anisotropy Δn of the liquid crystal layer is 0.12 or less.

21. The optical element according to claim 15 or 16, characterized in that The light incident on the optical element is circularly polarized light.

22. A variable focus element, characterized in that: It has: The optical element according to any one of claims 1 to 6; and Pancharatnam-Berry Lens.

23. The variable focus element according to claim 22, characterized in that The Pancharatnam-Berry lens is disposed within the optical element.

24. A head-mounted display, characterized in that: It comprises the variable focus element according to claim 22.

25. A variable focus element, characterized in that: The optical element comprises the optical element according to claim 16 and a Pancharatnam-Berry lens.

26. The variable focus element according to claim 25, characterized in that The Pancharatnam-Berry lens is disposed within the optical element.

27. A head-mounted display, characterized in that: It comprises the variable focus element according to claim 25.

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