Optical element, image display unit and head-mounted display

Abstract

To provide an optical element that can improve light utilization efficiency while increasing an optical path length, an image display unit, and a head-mounted display.SOLUTION: An optical element has, in this order, a first absorptive linear polarizer, a first reflective linear polarizer, a first retardation plate, a partial reflective mirror that transmits a portion of incident light and reflects a portion, a second retardation plate, and a second reflective linear polarizer. The swirling direction of circularly polarized light reflected by the first reflective linear polarizer when light passes through the first retardation plate and enters the first reflective linear polarizer, and the swirling direction of circularly polarized light reflected by the second reflective linear polarizer when light passes through the second retardation plate and enters the second reflective linear polarizer are opposite.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical element, an image display unit, and a head mounted display used in a head mounted display for VR (virtual reality). [Background technology]

[0002] There is an optical device that is worn by a user to experience so-called immersive virtual reality (VR) that does not transmit external light from the real world and directs an image to the user's eyes. This optical device employs a structure in which light emitted from an image display device is reflected once by a reflective polarizer or the like, and then reflected again by a mirror or the like to direct the light to the user's eyes. This makes it possible to increase the optical path length from the image display device to the user's eyes, and to make the entire optical device thinner.

[0003] For example, Patent Document 1 describes a head mounted display that has, from the image display device side, a linear polarizer, a quarter wave plate, a half mirror, a quarter wave plate, and a reflective polarizer in this order and can be used as an optical device for VR. In this optical element, the optical path length is increased by making light go back and forth between the half mirror and the reflective polarizer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2019-526075 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, in an optical device that makes the light go back and forth between a half mirror and a reflective polarizer to lengthen the optical path length, the half mirror transmits about 50% of the light incident thereon, and the half mirror also reflects about 50% of the light reflected by the reflective grating. This causes a problem that the light utilization efficiency of the image display device with respect to the amount of light emitted therefrom is low at about 25%.

[0006] An object of the present invention is to provide an optical element, an image display unit, and a head mounted display that can improve the efficiency of light utilization while increasing the optical path length. [Means for solving the problem]

[0007] In order to solve this problem, the present invention has the following configuration. [1] A first absorptive linear polarizer; A first reflective linear polarizer; A first retardation plate; a partial reflection mirror that transmits a portion of incident light and reflects a portion of it; A second retardation plate; and a second reflective linear polarizer, An optical element in which the rotation direction of the circularly polarized light reflected when light passes through a first retardation plate and enters a first reflective linear polarizing plate is opposite to the rotation direction of the circularly polarized light reflected when light passes through a second retardation plate and enters a second reflective linear polarizing plate. [2] The optical element according to [1], further comprising a second absorptive linear polarizing plate disposed on the opposite side of the second reflective linear polarizing plate to the second retardation plate. [3] a first absorptive linear polarizer; and A first retardation plate; A first reflective circular polarizer; a partial reflection mirror that transmits a portion of incident light and reflects a portion of it; A second reflective circular polarizer; and A second retardation plate; and a second absorptive linear polarizer, An optical element in which the rotation direction of the circularly polarized light reflected by the first reflective circular polarizer is opposite to the rotation direction of the circularly polarized light reflected by the second reflective circular polarizer. [4] The optical element according to [3], further comprising a second absorptive linear polarizer disposed on the opposite side of the second retardation plate to the second reflective circular polarizer. [5] The optical element according to [3] or [4], wherein at least one of the first reflective circular polarizer and the second reflective circular polarizer has a cholesteric liquid crystal layer having a fixed cholesteric liquid crystal phase. [6] The optical element according to [5], wherein at least one of the first reflective circular polarizer and the second reflective circular polarizer has a plurality of cholesteric liquid crystal layers having mutually different selective reflection center wavelengths. [7] The optical element according to [5] or [6], wherein the cholesteric liquid crystal layer has a pitch gradient structure. [8] The optical element according to any one of [3] to [7], further comprising a positive lens between the second reflective circular polarizing plate and the second retardation plate. [9] The optical element according to [1] or [2], further comprising a positive lens between the second reflective linear polarizer and the second absorptive linear polarizer.

[10] The optical element according to [8] or [9], wherein the positive lens is a diffractive lens using a diffractive element.

[11] The diffractive lens is a liquid crystal diffractive element having a liquid crystal layer containing a liquid crystal compound, the liquid crystal layer has a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane; An optical element according to

[10] , having an area in which the period of the diffraction structure varies within the plane, when the length over which the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern in the liquid crystal layer rotates 180° in the in-plane direction is defined as one period of the diffraction structure.

[12] An optical element according to

[11] , wherein in a cross section of the liquid crystal layer observed with a scanning electron microscope, the liquid crystal layer has regions in which the bright and dark areas derived from the liquid crystal phase are inclined with respect to the main surface of the liquid crystal layer.

[13] The optical element according to any one of [1] to

[12] , wherein the cross section of the partially reflecting mirror has a curved shape.

[14] The optical element according to any one of [1] to

[13] , wherein the first retardation plate and the second retardation plate are λ / 4 plates.

[15] An optical element according to any one of [1] to

[14] , and an image display device disposed on the first absorptive linear polarizer side of the optical element.

[16] A head-mounted display having an image display unit according to

[15] . Effect of the Invention

[0008] According to the present invention, it is possible to provide an optical element, an image display unit, and a head mounted display that can improve the efficiency of light utilization while increasing the optical path length. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram conceptually illustrating an example of an image display unit having the optical element according to a first embodiment of the present invention. [Diagram 2] 2 is a partial enlarged view for explaining the function of the image display unit of FIG. 1. FIG. [Diagram 3] 1 is a conceptual diagram for explaining the operation of a conventional image display unit. [Figure 4] FIG. 4 is a diagram conceptually illustrating another example of an image display unit having the optical element according to the first embodiment of the present invention. [Diagram 5] FIG. 4 is a diagram conceptually illustrating another example of an image display unit having the optical element according to the first embodiment of the present invention. [Figure 6] FIG. 11 is a diagram conceptually illustrating an example of an image display unit having an optical element according to a second embodiment of the present invention. [Figure 7] FIG. 11 is a diagram conceptually illustrating another example of an image display unit having the optical element according to the second embodiment of the present invention. [Figure 8] FIG. 1 is a conceptual diagram illustrating a cholesteric liquid crystal layer having a pitch gradient structure. [Figure 9] FIG. 1 is a diagram conceptually illustrating an example of a liquid crystal diffraction element. [Figure 10]10 is a diagram conceptually showing a liquid crystal layer of the liquid crystal diffraction element shown in FIG. [Figure 11] 10 is a plan view of a liquid crystal layer of the liquid crystal diffraction element shown in FIG. [Figure 12] 10 is a conceptual diagram showing the function of a liquid crystal layer of the liquid crystal diffraction element shown in FIG. [Figure 13] 10 is a conceptual diagram showing the function of a liquid crystal layer of the liquid crystal diffraction element shown in FIG. [Figure 14] 10 is a conceptual diagram showing the function of the liquid crystal diffraction element shown in FIG. [Figure 15] 10 is a diagram conceptually showing an example of an exposure apparatus for exposing an alignment film of the liquid crystal diffraction element shown in FIG. [Figure 16] 11 is a plan view of another example of a liquid crystal layer of the liquid crystal diffraction element. FIG. [Figure 17] 17 is a diagram conceptually illustrating an example of an exposure apparatus that exposes an alignment film that forms the liquid crystal layer shown in FIG. 16. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be described in detail below. The following description of the constituent elements may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment. In this specification, a numerical range expressed using "~" means a range including the numerical values ​​before and after "~" as the lower and upper limits. In addition, "perpendicular" and "parallel" in terms of angles mean a range of ±10° of the strict angle, and "same" and "different" in terms of angles can be determined based on whether the difference is less than 5°.

[0011] In this specification, the term "slow axis" refers to the in-plane direction in which the refractive index is maximum.

[0012] In this specification, reverse wavelength dispersion means the property that the absolute value of in-plane retardation increases as the wavelength becomes longer, and specifically means that the in-plane retardation value Re(450) measured at a wavelength of 450 nm, the in-plane retardation value Re(550) measured at a wavelength of 550 nm, and the in-plane retardation value Re(650) measured at a wavelength of 650 nm satisfy the relationship Re(450)≦Re(550)≦Re(650).

[0013] <Optical element of the first embodiment> The optical element according to the first embodiment of the present invention is A first absorptive linear polarizer; A first reflective linear polarizer; A first retardation plate; a partial reflection mirror that transmits a portion of incident light and reflects a portion of it; A second retardation plate; and a second reflective linear polarizer, This optical element has a rotation direction of the circularly polarized light reflected when light passes through a first retardation plate and enters a first reflective linear polarizing plate, which is opposite to the rotation direction of the circularly polarized light reflected when light passes through a second retardation plate and enters a second reflective linear polarizing plate.

[0014] Fig. 1 is a conceptual diagram of an image display unit having an optical element according to a first embodiment of the present invention. Fig. 2 is an enlarged diagram of a part (a portion surrounded by a dashed line) of the image display unit shown in Fig. 1, and is a diagram for explaining the operation of the image display unit.

[0015] The image display unit 50 shown in Figures 1 and 2 includes an optical element 10a having a first absorptive linear polarizer 12, a first reflective linear polarizer 14, a first retardation plate 16, a partial reflection mirror 18, a second retardation plate 20, a second reflective linear polarizer 22, and a second absorptive linear polarizer 24, in this order, and an image display device 52 arranged on the first absorptive linear polarizer 12 side of the optical element 10a.

[0016] In the image display unit 50, when the image display device 52 emits light (image), the light passes through the first absorptive linear polarizer 12, the first reflective linear polarizer 14, the first retardation plate 16, the partial reflection mirror 18, and the second retardation plate 20, is reflected by the second reflective linear polarizer 22, passes through the second retardation plate 20, is reflected by the partial reflection mirror 18, passes through the second retardation plate 20, the second reflective linear polarizer 22, and the second absorptive linear polarizer 24, and is emitted toward the user U. At this time, the light goes back and forth between the second reflective linear polarizer 22 and the partial reflection mirror 18, so that an optical path length can be gained in a limited space, which contributes to the miniaturization of the optical element and the image display unit.

[0017] Here, the operation of a conventional image display unit will be described with reference to Fig. 3. In Fig. 3, the polarization state and light amount of light after passing through each component are shown near each component. When the polarization state of light is linearly polarized, it is indicated by an up-down arrow or a left-right arrow, and when it is circularly polarized, it is indicated by a circular arrow. Furthermore, the linearly polarized light represented by the up-down arrow and the linearly polarized light represented by the left-right arrow are linearly polarized light that are perpendicular to each other. Furthermore, right-handed circularly polarized light is indicated by a clockwise arrow, and left-handed circularly polarized light is indicated by a counterclockwise arrow.

[0018] In the conventional image display unit shown in Fig. 3, when the image display device 52 emits light (image), the light passes through the first absorptive linear polarizer 12 and is converted into linearly polarized light. In the following description, the amount of light after passing through the first absorptive linear polarizer 12 is set to 100%. In addition, in the following description, the first absorptive linear polarizer 12 is assumed to transmit linearly polarized light as indicated by the left-right arrow in the figure.

[0019] The polarization state of the linearly polarized light transmitted through the first absorptive linear polarizer 12 is changed to circularly polarized light or elliptically polarized light by the first retardation plate 16. In the example of Fig. 3, the first retardation plate 16 is a λ / 4 plate, and the explanation will be given assuming that linearly polarized light is converted to circularly polarized light. In the example of Fig. 3, the explanation will be given assuming that the first retardation plate 16 converts linearly polarized light indicated by the left-right arrow into right-handed circularly polarized light, and right-handed circularly polarized light into linearly polarized light indicated by the left-right arrow. The amount of light after passing through the first retardation plate 16 is 100%.

[0020] The light that passes through the first retardation plate 16 is partially reflected by the partial reflection mirror 18 and partially transmitted. In the example of Fig. 3, it is assumed that 50% of the incident light is reflected and 50% is transmitted. The light reflected by the partial reflection mirror 18 is changed to left-handed circularly polarized light when reflected, and therefore becomes linearly polarized light indicated by the up-down arrow when passing through the first retardation plate 16, and enters the first absorptive linear polarizer 12. The first absorptive linear polarizer 12 transmits linearly polarized light indicated by the left-right arrow, and therefore absorbs the linearly polarized light indicated by the up-down arrow.

[0021] On the other hand, the right-handed circularly polarized light that has passed through the partial reflection mirror 18 has an amount of 50% and enters the second retardation plate 20. The second retardation plate 20 converts the circularly polarized light into linearly polarized light. In the example of FIG. 3, the second retardation plate 20 is a λ / 4 plate, and the explanation will be given assuming that circularly polarized light is converted into linearly polarized light and linearly polarized light is converted into circularly polarized light. In the example of FIG. 3, the explanation will be given assuming that the second retardation plate 20 converts right-handed circularly polarized light into linearly polarized light indicated by the left-right arrow.

[0022] The linearly polarized light that has passed through the second retardation plate 20 is reflected by the second reflective linear polarizer 22. That is, the second reflective linear polarizer 22 reflects linearly polarized light indicated by left-right arrows and transmits linearly polarized light indicated by up-down arrows. The linearly polarized light reflected by the second reflective linear polarizer 22 enters the second retardation plate 20 and is converted into right-handed circularly polarized light.

[0023] The right-handed circularly polarized light that has passed through the second retardation plate 20 is partially reflected and partially transmitted by the partial reflection mirror 18. After passing through the first retardation plate 16, 25% of the light that has passed through the partial reflection mirror 18 becomes linearly polarized light as indicated by the left-right arrow and enters the first absorptive linear polarizer 12. Since the first absorptive linear polarizer 12 transmits linearly polarized light as indicated by the left-right arrow, this linearly polarized light passes through the first absorptive linear polarizer 12 and returns to the image display device 52.

[0024] On the other hand, the right-handed circularly polarized light reflected by the partial reflection mirror 18 has an amount of light of 25%, and is converted to left-handed circularly polarized light during reflection, and enters the second retardation plate 20. The second retardation plate 20 converts the left-handed circularly polarized light into linearly polarized light indicated by the up-down arrow. The second reflective linear polarizer 22 transmits linearly polarized light indicated by the up-down arrow, so the linearly polarized light that passes through the second retardation plate 20 is transmitted as is. The linearly polarized light that has passed through the second reflective linear polarizer 22 is incident on the second absorbing linear polarizer 24. The second absorbing linear polarizer 24 absorbs linearly polarized light indicated by the left-right arrow and transmits linearly polarized light indicated by the up-down arrow, so the incident linearly polarized light is transmitted as is. Therefore, linearly polarized light with an amount of light of 25% is output from the image display unit.

[0025] In this way, in conventional image display units, the partial reflection mirror transmits about 50% of the incident light, and the partial reflection mirror also reflects about 50% of the light reflected by the reflective linear polarizer. As a result, the light utilization efficiency of the image emitted by the image display device is low at about 25%.

[0026] In contrast to this, the operation of an image display unit having the optical element of the present invention will be described with reference to FIG. 2, when the image display device 52 emits light (image), the light passes through the first absorptive linear polarizer 12 and is converted into linearly polarized light indicated by the left-right arrow. In the following description, the amount of light after passing through the first absorptive linear polarizer 12 is set to 100%.

[0027] The linearly polarized light transmitted through the first absorptive linear polarizer 12 is incident on the first reflective linear polarizer 14. The first reflective linear polarizer 14 transmits linearly polarized light in the same direction as the first absorptive linear polarizer, that is, linearly polarized light indicated by the left-right arrow. The polarization state of the linearly polarized light transmitted through the first reflective linear polarizer 14 is changed to circularly polarized light or elliptically polarized light by the first retardation plate 16. In the example of Fig. 2, the first retardation plate 16 is a λ / 4 plate, and the explanation will be given assuming that linearly polarized light is converted into circularly polarized light. In the example of Fig. 2, the explanation will be given assuming that the first retardation plate 16 converts linearly polarized light indicated by the left-right arrow into right-handed circularly polarized light. The amount of light after passing through the first retardation plate 16 is 100%.

[0028] The light that passes through the first retardation plate 16 is partially reflected by the partial reflection mirror 18 and partially transmitted. In the example of FIG. 2, it is assumed that half of the incident light is reflected and the other half is transmitted. 50% of the right-handed circularly polarized light that has transmitted through the partial reflection mirror 18 is incident on the second retardation plate 20. The second retardation plate 20 converts the circularly polarized light into linearly polarized light. In the example of FIG. 2, it is assumed that the second retardation plate 20 is a λ / 4 plate, and that circularly polarized light is converted into linearly polarized light and linearly polarized light is converted into circularly polarized light. In the example of FIG. 2, it is assumed that the second retardation plate 20 converts right-handed circularly polarized light into linearly polarized light indicated by the left-right arrow.

[0029] The linearly polarized light that has passed through the second retardation plate 20 is reflected by the second reflective linear polarizer 22. That is, the second reflective linear polarizer 22 reflects linearly polarized light indicated by left-right arrows and transmits linearly polarized light indicated by up-down arrows. The linearly polarized light reflected by the second reflective linear polarizer 22 enters the second retardation plate 20 and is converted into right-handed circularly polarized light.

[0030] The right-handed circularly polarized light that has passed through the second retardation plate 20 is partially reflected by the partial reflection mirror 18 and partially transmitted. After passing through the first retardation plate 16, 25% of the right-handed circularly polarized light becomes linearly polarized light indicated by the left-right arrow and enters the first reflective linear polarizer 14. Since the first reflective linear polarizer 14 transmits linearly polarized light indicated by the left-right arrow, this linearly polarized light passes through the first reflective linear polarizer 14 and enters the first absorbing linear polarizer 12. Since the first absorbing linear polarizer 12 transmits linearly polarized light indicated by the left-right arrow, this linearly polarized light passes through the first absorbing linear polarizer 12 and returns to the image display device 52.

[0031] On the other hand, the right circularly polarized light reflected by the partial reflection mirror 18 has an amount of 25% and is converted to left circularly polarized light during reflection, and enters the second retardation plate 20. The second retardation plate 20 converts the left circularly polarized light into linearly polarized light indicated by the up and down arrows. Since the second reflective linear polarizer 22 transmits linearly polarized light indicated by the up and down arrows, the linearly polarized light that passes through the second retardation plate 20 is transmitted as it is. The linearly polarized light that has passed through the second reflective linear polarizer 22 is incident on the second absorbing linear polarizer 24. Since the second absorbing linear polarizer 24 absorbs linearly polarized light indicated by the left and right arrows and transmits linearly polarized light indicated by the up and down arrows, the incident linearly polarized light is transmitted as it is. As a result, 25% of the light is emitted.

[0032] Here, 50% of the light that has passed through first retardation plate 16 and is reflected by partial reflection mirror 18 is converted to left-handed circularly polarized light when reflected, and therefore becomes linearly polarized light indicated by the up-down arrow after passing through first retardation plate 16, and enters first reflective linear polarizer 14. First reflective linear polarizer 14 transmits linearly polarized light indicated by the left-right arrow and reflects linearly polarized light indicated by the up-down arrow, so the linearly polarized light indicated by the up-down arrow is reflected.

[0033] The 50% of the linearly polarized light reflected by the first reflective linear polarizer 14 enters the first retardation plate 16 and is converted into left-handed circularly polarized light.

[0034] Of the left-handed circularly polarized light that passes through the first retardation plate 16, 25% is reflected and 25% is transmitted by the partial reflection mirror 18. The 25% of the left-handed circularly polarized light that transmits through the partial reflection mirror 18 enters the second retardation layer 20 and is converted into linearly polarized light as indicated by the up-down arrow.

[0035] The linearly polarized light that has passed through the second retardation layer 20 is incident on the second reflective linear polarizer 22. Since the second reflective linear polarizer 22 transmits linearly polarized light indicated by the up-down arrow, the linearly polarized light that has passed through the second retardation layer 20 is transmitted as is. The linearly polarized light that has passed through the second reflective linear polarizer 22 is incident on the second absorbing linear polarizer 24. Since the second absorbing linear polarizer 24 absorbs linearly polarized light indicated by the left-right arrow and transmits linearly polarized light indicated by the up-down arrow, the incident linearly polarized light is transmitted as is. As a result, an additional 25% of the light is emitted.

[0036] In this way, in the image display unit 50 having the optical element of the present invention, the total of 25% of the component reflected and emitted by the second reflective linear polarizer 22 and the partial reflecting mirror 18 and 25% of the component reflected and emitted by the partial reflecting mirror 18 and the first reflective linear polarizer 14 makes it possible to emit approximately 50% of the amount of light of the image emitted by the image display device 52. This makes it possible to improve the light utilization efficiency.

[0037] In the example shown in FIG. 1 and FIG. 2, as a preferred embodiment, the second absorbing linear polarizer 24 is disposed on the opposite side of the second reflective linear polarizer 22 from the second retardation plate 20. In reality, the phase difference given to light by the second retardation plate 20 deviates from the ideal phase difference depending on the wavelength and the angle of incidence. Therefore, the linearly polarized light converted by the second retardation plate 20 is not converted into a completely linearly polarized light, so that a part of the light that should be reflected by the second reflective linear polarizer 22 may be transmitted, resulting in a ghost image. In contrast, by having the second absorbing linear polarizer 24, the light that is not reflected by the second reflective linear polarizer 22 and transmitted can be absorbed, and the occurrence of a ghost image can be suppressed.

[0038] Here, as described above, the circularly polarized light reflected when the light passes through the first retardation plate 16 and enters the first reflective linear polarizer 14 is left-handed circularly polarized light. On the other hand, the circularly polarized light reflected when the light passes through the second retardation plate 20 and enters the second reflective linear polarizer 22 is right-handed circularly polarized light. In other words, the rotation direction of the circularly polarized light reflected when the light passes through the first retardation plate 16 and enters the first reflective linear polarizer 14 is opposite to the rotation direction of the circularly polarized light reflected when the light passes through the second retardation plate 20 and enters the second reflective linear polarizer 22. By configuring the combination of the first retardation plate 16 and the first reflective linear polarizer 14 so that the rotation direction of the circularly polarized light reflected by the combination of the second retardation plate 20 and the second reflective linear polarizer 22 is opposite to that of the circularly polarized light reflected by the combination of the second retardation plate 20 and the second reflective linear polarizer 22, it is possible to emit approximately 50% of the amount of light of the image emitted by the image display device 52 as described above.

[0039] Here, in the example shown in FIG. 1, as a preferred embodiment, the cross section of the partial reflection mirror 18 has a curved shape. That is, the partial reflection mirror 18 is curved. By making the partial reflection mirror 18 curved, the traveling direction of the light emitted from the image display device 52 can be adjusted. Specifically, in the example shown in FIG. 1, the partial reflection mirror 18 is curved convexly toward the image display device 52 with a predetermined curvature. This makes it possible to change the reflection direction when the light is reflected by the partial reflection mirror 18 depending on the position in the surface direction. Therefore, in the example shown in FIG. 1, the light emitted in various directions from approximately the center of the image display device 52 can be made to travel in a direction approximately perpendicular to the display surface of the image display device 52. In the illustrated example, the partial reflection mirror 18 is curved, so that the diffused light emitted from the image display device 52 is made to be approximately parallel light. The parallelism of the light emitted from the image display device 52 is adjusted depending on the distance at which the image is displayed as a virtual image. For example, when the light emitted from the image display device 52 is parallel light, the image appears to be located at infinity to the user.

[0040] 1, the first reflective linear polarizer 14 and the first retardation plate 16 are curved into substantially the same shape as the curved shape of the partial reflection mirror 18. This makes it possible to adjust the traveling direction of the light reflected by the first reflective linear polarizer 14.

[0041] In the example shown in Fig. 1, the first reflective linear polarizer 14, the first retardation plate 16, and the partial reflection mirror 18 are curved, and the other members are flat, but this is not limiting, and in addition to the first reflective linear polarizer 14, the first retardation plate 16, and the partial reflection mirror 18, the second retardation plate 20b, the second reflective linear polarizer 22b, and the second absorbing linear polarizer 24b may also be curved, as in the optical element 10b of the image display system 50b shown in Fig. 4. This makes it possible to adjust the traveling direction of the light reflected by the second reflective linear polarizer 22b.

[0042] The curved shape of the partial reflection mirror 18 may be appropriately set according to the traveling direction of the light emitted from the image display device 52, the desired emission direction of the light emitted from the image display system, and the like.

[0043] 1, the partial reflection mirror 18 has a curved shape, but is not limited to this. As shown in the example of FIG 5, the partial reflection mirror 18 may have a flat plate shape, and a positive lens 29 may be provided between the second reflective linear polarizer 22 and the second absorptive linear polarizer 24.

[0044] 5, when the partial reflection mirror 18 or the like has a flat plate shape, the light emitted in an oblique direction from the image display device 52 travels in an oblique direction even when reflected by the partial reflection mirror 18 or the like, but by providing the positive lens 29, the light can be condensed and the traveling direction of the light emitted from the image display device 52 can be adjusted. In the illustrated example, the light emitted in an oblique direction from the image display device 52 is made to travel in a direction approximately perpendicular to the display surface of the image display device 52. In other words, in the illustrated example, the positive lens 29 converts the diffuse light emitted from the image display device 52 into parallel light.

[0045] 5, the image display system has a configuration in which the partial reflection mirrors 18, etc. are flat and have a positive lens 29, but this is not limited to the configuration. The image display system may have a configuration in which the partial reflection mirrors 18, etc. are curved and have a positive lens 29. In this case, the traveling direction of the light emitted from the image display device 52 can be adjusted by combining the effects of the curved shape of the partial reflection mirrors 18, etc. and the positive lens 29.

[0046] Although there is no particular restriction on the distance between each member, the optical path length can be increased as the distance between the partial reflecting mirror 18 and the first reflective linear polarizer 14 and the distance between the partial reflecting mirror 18 and the second reflective linear polarizer 22 are increased. From this viewpoint, the distance between the partial reflecting mirror 18 and the first reflective linear polarizer 14 and the distance between the partial reflecting mirror 18 and the second reflective linear polarizer 22 are each preferably 0.1 mm to 100 mm, and more preferably 1 mm to 50 mm.

[0047] Furthermore, from the viewpoint of making the optical path length of the light reflected by the partial reflection mirror 18 and the first reflective linear polarizer 14 the same as the optical path length of the light reflected by the second reflective linear polarizer 22 and the partial reflection mirror 18, it is preferable that the distance between the partial reflection mirror 18 and the first reflective linear polarizer 14 is the same as the distance between the second reflective linear polarizer 22 and the partial reflection mirror 18.

[0048] <Optical element according to the second embodiment> The optical element according to the second embodiment of the present invention is A first absorptive linear polarizer; A first retardation plate; A first reflective circular polarizer; a partial reflection mirror that transmits a portion of incident light and reflects a portion of it; A second reflective circular polarizer; and a second retardation plate, This optical element has a rotation direction of the circularly polarized light reflected by the first reflective circular polarizer and a rotation direction of the circularly polarized light reflected by the second reflective circular polarizer that are opposite to each other.

[0049] FIG. 6 is a diagram illustrating an enlarged view of a part of an image display unit having an optical element according to a second embodiment of the present invention, and is a diagram for explaining the function of the image display unit.

[0050] The image display unit 51 shown in Figure 6 has an optical element 11 having a first absorptive linear polarizer 12, a first retardation plate 16, a first reflective circular polarizer 26, a partial reflection mirror 18, a second reflective circular polarizer 28, a second retardation plate 20, and a second absorptive linear polarizer 24, in this order, and an image display device 52 arranged on the first absorptive linear polarizer 12 side of the optical element 11.

[0051] In the image display unit 51, when the image display device 52 emits light (image), the light passes through the first absorptive linear polarizer 12, the first retardation plate 16, the first reflective circular polarizer 26, and the partial reflection mirror 18, is reflected by the second reflective circular polarizer 28, is reflected by the partial reflection mirror 18, passes through the second reflective circular polarizer 28, the second retardation plate 20, and the second absorptive linear polarizer 24, and is emitted toward the user U. At this time, the light goes back and forth between the second reflective circular polarizer 28 and the partial reflection mirror 18, so that the optical path length can be increased in a limited space, which contributes to the miniaturization of the optical element and the image display unit.

[0052] The reflective circular polarizer reflects circularly polarized light in one rotation direction and transmits circularly polarized light in the other rotation direction. In the present invention, the rotation direction of the circularly polarized light reflected by the first reflective circular polarizer 26 is opposite to the rotation direction of the circularly polarized light reflected by the second reflective circular polarizer 28. In the following description, the first reflective circular polarizer 26 is assumed to reflect left-handed circularly polarized light and transmit right-handed circularly polarized light, and the second reflective circular polarizer 28 is assumed to reflect right-handed circularly polarized light and transmit left-handed circularly polarized light.

[0053] 6, when an image display device 52 emits light (image), the light passes through the first absorptive linear polarizer 12 and is converted into linearly polarized light indicated by the left-right arrow. In the following description, the amount of light after passing through the first absorptive linear polarizer 12 is set to 100%.

[0054] The linearly polarized light transmitted through the first absorptive linear polarizer 12 enters the first retarder 16. The polarization state of the linearly polarized light entering the first retarder 16 is changed to circularly polarized light or elliptically polarized light by the first retarder 16. In the example of FIG. 6, the first retarder 16 is a λ / 4 plate, and the explanation will be given assuming that linearly polarized light is converted into circularly polarized light. In the example of FIG. 6, the explanation will be given assuming that the first retarder 16 converts linearly polarized light indicated by the left-right arrow into right-handed circularly polarized light. The amount of light after passing through the first retarder 16 is 100%.

[0055] The right-handed circularly polarized light that has passed through the first retardation plate 16 is incident on the first reflective circular polarizer 26. As described above, the first reflective circular polarizer 26 transmits right-handed circularly polarized light, and therefore, the right-handed circularly polarized light with a light amount of 100% is transmitted through the first reflective circular polarizer 26 and incident on the partial reflection mirror 18.

[0056] The light incident on the partial reflection mirror 18 is partially reflected and partially transmitted by the partial reflection mirror 18. In the example of FIG. 6, it is assumed that half of the incident light is reflected and the other half is transmitted. The 50% of the right-handed circularly polarized light that has transmitted through the partial reflection mirror 18 is incident on the second reflective circular polarizer 28. As described above, the second reflective circular polarizer 28 reflects right-handed circularly polarized light, and so the right-handed circularly polarized light that has entered the second reflective circular polarizer 28 is reflected and enters the partial reflection mirror 18.

[0057] The 50% right-handed circularly polarized light incident on the partial reflection mirror is partially reflected and partially transmitted. The 25% right-handed circularly polarized light transmitted through the partial reflection mirror 18 is incident on the first reflective circular polarizer 26, which transmits right-handed circularly polarized light and passes through as is and then enters the first retardation plate 16. The light incident on the first retardation plate 16 becomes linearly polarized light as indicated by the left-right arrow and enters the first absorbing linear polarizer 12. The first absorbing linear polarizer 12 transmits linearly polarized light as indicated by the left-right arrow, and this linearly polarized light passes through the first absorbing linear polarizer 12 and returns to the image display device 52.

[0058] On the other hand, the right-handed circularly polarized light reflected by the partial reflection mirror 18 has an amount of 25% and is converted to left-handed circularly polarized light upon reflection, and enters the second reflective circular polarizer 28. The second reflective circular polarizer 28 transmits left-handed circularly polarized light, so the light passes through as is and enters the second retardation plate 20. The second retardation plate 20 converts the left-handed circularly polarized light into linearly polarized light indicated by the up-down arrow. The second absorbing linear polarizer 24 transmits linearly polarized light indicated by the up-down arrow, so the linearly polarized light that passed through the second retardation plate 20 is transmitted as is. As a result, 25% of the light is emitted.

[0059] Here, 50% of the light reflected by the partial reflection mirror 18 after passing through the first reflective circular polarizer 26 is converted to left-handed circularly polarized light when reflected, and is then incident on the first reflective circular polarizer 26 and reflected there. Of the 50% of the left-handed circularly polarized light reflected by the first reflective circular polarizer 26, 25% is reflected by the partial reflection mirror 18, and 25% is transmitted. The 25% of the left-handed circularly polarized light transmitted through the partial reflection mirror 18 is incident on the second reflective circular polarizer 28, which transmits left-handed circularly polarized light, and passes through as is and enters the second retardation plate 20. The left-handed circularly polarized light incident on the second retardation layer 20 is converted to linearly polarized light as indicated by the up-down arrow.

[0060] The linearly polarized light that has passed through the second retardation layer 20 is incident on the second absorptive linear polarizer 24. The second absorptive linear polarizer 24 absorbs linearly polarized light indicated by the left-right arrow and transmits linearly polarized light indicated by the up-down arrow, so the incident linearly polarized light is transmitted as is. As a result, an additional 25% of the light is emitted.

[0061] In this way, in the image display unit 51 having the optical element of the present invention, the sum of 25% of the component reflected and emitted by the second reflective circular polarizer 28 and the partial reflecting mirror 18 and 25% of the component reflected and emitted by the partial reflecting mirror 18 and the first reflective circular polarizer 26 makes it possible to emit approximately 50% of the light amount of the image emitted by the image display device 52. This makes it possible to improve the light utilization efficiency.

[0062] In the example shown in FIG. 6, as a preferred embodiment, the second retardation plate 20 has a second absorbing linear polarizer 24 disposed on the opposite side of the second retardation plate 20 from the second reflective circular polarizer 28. In reality, the phase difference given to the light by the second retardation plate 20 deviates from the ideal phase difference depending on the wavelength and the angle of incidence. Therefore, the linearly polarized light converted by the second retardation plate 20 is not converted into a completely linearly polarized light, and there is a risk of a ghost image being generated. In contrast, by having the second absorbing linear polarizer 24, it is possible to convert the light into a more completely linearly polarized light, and the generation of a ghost image can be suppressed.

[0063] Here, in the example shown in FIG. 6, as in the example shown in FIG. 1, as a preferred embodiment, the cross section of the partial reflection mirror 18 has a curved shape. That is, the partial reflection mirror 18 is curved. By making the partial reflection mirror 18 curved, the traveling direction of the light emitted from the image display device 52 can be adjusted. Specifically, in the example shown in FIG. 6, the partial reflection mirror 18 is curved convexly toward the image display device 52 with a predetermined curvature. This makes it possible to change the reflection direction when the light is reflected by the partial reflection mirror 18 depending on the position in the surface direction. Therefore, in the example shown in FIG. 6, the light emitted in various directions from approximately the center of the image display device 52 can be made to travel in a direction approximately perpendicular to the display surface of the image display device 52. In the illustrated example, the partial reflection mirror 18 has a curved shape, so that the diffused light emitted from the image display device 52 is made into parallel light.

[0064] 6, the first reflective circular polarizer 26, the second reflective circular polarizer 28, the second retardation plate 20, and the second absorptive linear polarizer 24 are curved into substantially the same shape as the curved shape of the partial reflection mirror 18. This makes it possible to adjust the traveling direction of the light reflected by the first reflective circular polarizer 26 and the second reflective circular polarizer 28.

[0065] 6, the partial reflection mirror 18 and the like are curved, but the present invention is not limited to this. As shown in the example of FIG 7, each member such as the partial reflection mirror 18 may be flat, and a positive lens 29 may be provided between the second reflective circular polarizer 28 and the second retardation plate 20.

[0066] 7, when the partial reflection mirror 18 and the like are flat, the light emitted in an oblique direction from the image display device 52 also travels in an oblique direction when reflected by the partial reflection mirror 18 and the reflective circular polarizer, but by providing the positive lens 29, the light can be condensed and the traveling direction of the light emitted from the image display device 52 can be adjusted. In the illustrated example, the light emitted in an oblique direction from the image display device 52 is made to travel in a direction approximately perpendicular to the display surface of the image display device 52. In the illustrated example, the positive lens 29 converts the diffused light emitted from the image display device 52 into parallel light.

[0067] 7, the image display system has the partial reflection mirror 18 etc. in a flat shape and the positive lens 29, but is not limited to this. The image display system may have the partial reflection mirror 18 etc. in a curved shape and the positive lens 29. In this case, the traveling direction of the light emitted from the image display device 52 can be adjusted by combining the effects of the curved shape of the partial reflection mirror 18 etc. and the positive lens 29.

[0068] Furthermore, although there are no particular limitations on the distance between each member, the optical path length can be increased as the distance between the partial reflecting mirror 18 and the first reflective circular polarizer 26 and the distance between the partial reflecting mirror 18 and the second reflective circular polarizer 28 are increased. From this viewpoint, the distance between the partial reflecting mirror 18 and the first reflective circular polarizer 26 and the distance between the partial reflecting mirror 18 and the second reflective circular polarizer 28 are each preferably 0.1 mm to 100 mm, and more preferably 1 mm to 50 mm.

[0069] Furthermore, from the viewpoint of making the optical path length of the light reflected by the partial reflection mirror 18 and the first reflective circular polarizer 26 the same as the optical path length of the light reflected by the second reflective circular polarizer 28 and the partial reflection mirror 18, it is preferable that the distance between the partial reflection mirror 18 and the first reflective circular polarizer 26 is the same as the distance between the second reflective circular polarizer 28 and the partial reflection mirror 18.

[0070] <Components that make up optical elements> The optical elements of the first and second embodiments and members of the image display system will be described below.

[0071] (Absorptive linear polarizer) The first and second absorptive linear polarizers are not particularly limited as long as they are absorptive linear polarizers that have the function of transmitting linearly polarized light in one polarization direction and absorbing linearly polarized light in the other polarization direction, and any conventionally known absorptive linear polarizers can be used. As the absorption type linear polarizing plate, an absorption type polarizer such as an iodine type polarizer, a dye type polarizer using a dichroic dye, and a polyene type polarizer is used. The iodine type polarizer and the dye type polarizer include a coating type polarizer and a stretch type polarizer, and either one can be applied. Among them, a polarizer produced by adsorbing iodine or a dichroic dye to polyvinyl alcohol and stretching it is preferable. In addition, methods of obtaining a polarizer by stretching and dyeing a laminated film in which a polyvinyl alcohol layer is formed on a substrate can be exemplified by Japanese Patent No. 5048120, Japanese Patent No. 5143918, Japanese Patent No. 4691205, Japanese Patent No. 4751481, and Japanese Patent No. 4751486. ​​These known techniques related to polarizers can also be preferably used. As the absorption type polarizer, a polarizer in which a dichroic dye is aligned using the alignment property of liquid crystal without stretching is particularly preferred. The polarizer has many advantages, such as being able to be made very thin with a thickness of about 0.1 μm to 5 μm, being less likely to crack when folded as described in JP-A-2019-194685, being less susceptible to thermal deformation, being excellent in durability even in a polarizing plate with a high transmittance of more than 50% as described in JP-A-6483486, and being excellent in heat moldability. It is also possible to peel off the support and transfer the polarizer for use.

[0072] (Reflective linear polarizer) The first and second reflective linear polarizers are not particularly limited as long as they are reflective linear polarizers that have the function of transmitting linearly polarized light in one polarization direction and reflecting linearly polarized light in the other polarization direction, and any conventionally known reflective linear polarizers can be used. As the reflective linear polarizing plate, a film in which a layer containing two kinds of polymers is stretched, a wire grid polarizer, etc., as described in JP-A-2011-053705, can be used. From the viewpoint of brightness, a film in which a layer containing a polymer is stretched is preferable. As a commercially available product, a reflective polarizer (product name: APF) manufactured by 3M Corporation, a wire grid polarizer (product name: WGF) manufactured by Asahi Kasei Corporation, etc. can be suitably used. Alternatively, a reflective linear polarizing plate in which a cholesteric liquid crystal film and a λ / 4 plate are combined may be used.

[0073] (phase plate) The first and second retardation plates are retardation plates that convert the phase of the incident polarized light. The retardation plates are arranged with the direction of the slow axis adjusted depending on whether the incident polarized light is to be converted to be close to linearly polarized light or close to circularly polarized light. Specifically, the retardation plates may be arranged so that the slow axis is at +45° or -45° with respect to the transmission axis of the linear polarizer (absorptive linear polarizer or reflective linear polarizer) arranged adjacent to them.

[0074] The retardation plate used in the present invention may be a single-layer type composed of one optically anisotropic layer, or may be a multi-layer type composed of two or more optically anisotropic layers each having a plurality of different slow axes. Examples of multi-layer retardation plates include, but are not limited to, WO13 / 137464, WO2016 / 158300, JP2014-209219, JP2014-209220, WO14 / 157079, JP2019-215416, and WO2019 / 160044.

[0075] From the viewpoint of converting linearly polarized light into circularly polarized light or converting circularly polarized light into linearly polarized light, the retardation plate is preferably a λ / 4 plate.

[0076] There is no limitation on the λ / 4 plate, and various plates having known λ / 4 functions can be used. Specific examples of λ / 4 plates include those described in U.S. Patent Application Publication No. 2015 / 0277006.

[0077] For example, specific examples of the λ / 4 plate 26 having a single layer structure include a stretched polymer film, and a retardation film having an optically anisotropic layer having a λ / 4 function provided on a support, etc. Also, specific examples of the λ / 4 plate having a multi-layer structure include a broadband λ / 4 plate formed by laminating a λ / 4 plate and a λ / 2 wave plate.

[0078] The thickness of the λ / 4 plate is not particularly limited, but is preferably 1 to 500 μm, more preferably 1 to 50 μm, and even more preferably 1 to 5 μm.

[0079] The retardation plate used in the present invention preferably has reverse wavelength dispersion. By having reverse wavelength dispersion, the phase change in the retardation plate becomes ideal, and the conversion between linearly polarized light and circularly polarized light becomes ideal. Therefore, when reflected by the reflective linear polarizer and / or the reflective circular polarizer, the light can be efficiently reflected, and the light utilization efficiency is improved.

[0080] (Partially reflecting mirror) A partially reflecting mirror is a semi-transparent optical element that specularly reflects a portion of incident light and transmits the remaining light. The partially reflecting mirror may be a semi-transparent reflector with no polarization selectivity, or a reflector with polarization selectivity. In the case of a reflector with polarization selectivity, the polarized light reflected and transmitted may be linearly polarized light or circularly polarized light.

[0081] As the partial reflection mirror, various known partial reflection mirrors (half mirrors) can be used.

[0082] (Reflective circular polarizer) A reflective circular polarizer is a circular polarizer that reflects circularly polarized light having one rotation direction and transmits circularly polarized light having the other rotation direction.

[0083] As a reflective circular polarizer having selective reflectivity for circularly polarized light, a reflective circular polarizer having a cholesteric liquid crystal layer in which a cholesteric liquid crystal phase is fixed can be used. The cholesteric liquid crystal layer may be a single layer or may be a multi-layer structure of two or more layers. When it has two or more layers, it may be formed by lamination coating, lamination lamination, lamination transfer, or a combination of these.

[0084] Here, as is well known, the cholesteric liquid crystal layer has wavelength selective reflectivity. The selective reflection central wavelength of the cholesteric liquid crystal layer may be set according to the wavelength of the light emitted by the image display device 52. In addition, when the image display device 52 displays a color image using, for example, RGB light, the reflective circular polarizer may have a configuration having three cholesteric liquid crystal layers, that is, a cholesteric liquid crystal layer that selectively reflects R light (red light), a cholesteric liquid crystal layer that selectively reflects G light (green light), and a cholesteric liquid crystal layer that selectively reflects B light (blue light). In other words, it is preferable that the reflective circular polarizer has a configuration having a plurality of cholesteric liquid crystal layers having mutually different selective reflection central wavelengths according to the wavelength of the light emitted by the image display device 52.

[0085] The cholesteric liquid crystal layer may have a pitch gradient structure. As is well known, the selective reflection central wavelength of the cholesteric liquid crystal layer is determined according to the pitch of the helical structure in the cholesteric liquid crystal phase. The pitch gradient structure is a structure in which the helical pitch changes in the film thickness direction, as shown in FIG. 8. FIG. 8 is a schematic diagram showing a striped pattern in which light portions 42 and dark portions 44 are alternately arranged, as seen when a cross section of the cholesteric liquid crystal layer is observed with a SEM (scanning electron microscope). The interval between the light portions 42 and the interval P between the dark portions 44 correspond to the helical pitch.

[0086] 8, the helical pitch of the cholesteric liquid crystal layer 34 gradually increases (or decreases) from one main surface side to the other main surface side of the cholesteric liquid crystal layer 34. The helical pitch P of the cholesteric liquid crystal layer 34 changes in the film thickness direction, thereby enabling the selective reflection wavelength to be broadened. Therefore, when the image display device 52 emits light of two or more different wavelengths, light of a plurality of wavelengths can be reflected.

[0087] (positive lens) The positive lens is a lens that collects incident light. As the positive lens, a conventionally known convex lens can be used. Also, a diffraction element having a diffraction structure configured to focus light may be used as the positive lens. In this case, it is preferable to use any one of the above-mentioned surface relief type diffraction element, volume hologram type diffraction element, and polarized diffraction element as the diffraction element. As the polarized diffraction element, a liquid crystal diffraction element can be used.

[0088] As an example, FIG. 9 shows a conceptual diagram of a positive lens using a liquid crystal diffraction element. The liquid crystal diffraction element in the illustrated example has a support 30, an alignment film 32, and a liquid crystal layer (hereinafter also referred to as an optically anisotropic layer) . The liquid crystal diffraction element has a liquid crystal layer formed using a composition containing a liquid crystal compound and having a predetermined liquid crystal orientation pattern in which the optical axis derived from the liquid crystal compound rotates. In the example shown in Fig. 9, one period Λ of the liquid crystal orientation pattern described later has different regions in the plane.

[0089] As will be described later, the liquid crystal layer 36 has the effect of diffracting circularly polarized light. Here, as shown in FIG. 2, the polarization state of the light that has passed through the second reflective linear polarizer 22 is linearly polarized light. Therefore, when a liquid crystal diffraction element having the liquid crystal layer 36 is disposed downstream of the second reflective linear polarizer 22 as the positive lens 29, it is necessary to dispose a λ / 4 plate between the second reflective linear polarizer 22 and the positive lens 29 to convert the light that is incident on the positive lens 29 (liquid crystal layer 36) into circularly polarized light. In addition, when the image display unit emits linearly polarized light, a λ / 4 plate may be disposed between the positive lens 29 and the second absorbing linear polarizer 24 to convert the circularly polarized light that has passed through the positive lens 29 into linearly polarized light.

[0090] Furthermore, although the liquid crystal diffraction element in the illustrated example has the support 30, the support 30 may not be provided. For example, the optical element of the present invention may be configured by peeling off the support 30 from the above configuration and leaving only the alignment film and liquid crystal layer, or by peeling off the alignment film as well and leaving only the liquid crystal layer.

[0091] That is, the liquid crystal diffraction element can have various layer configurations as long as the liquid crystal layer has a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound rotates in one direction.

[0092] <<Support>> In the liquid crystal diffraction element, a support 30 supports an alignment film 32 and a liquid crystal layer 36 .

[0093] The support 30 may be any type of sheet-like material (film, plate-like material) that can support the alignment film and the liquid crystal layer. The support 30 is preferably a transparent support, and examples of such support include polyacrylic resin films such as polymethyl methacrylate, cellulose resin films such as cellulose triacetate, cycloolefin polymer films (for example, trade name "Arton" manufactured by JSR Corporation, trade name "ZEONOR" manufactured by Zeon Corporation), polyethylene terephthalate (PET), polycarbonate, and polyvinyl chloride. The support is not limited to a flexible film, and may be a non-flexible substrate such as a glass substrate. In addition, the support 30 may be multi-layered, and examples of multi-layered support include those that include any of the supports described above as a substrate, with other layers provided on the surface of this substrate.

[0094] There is no limitation on the thickness of the support 30, and the thickness capable of supporting the alignment film and the liquid crystal layer may be appropriately set depending on the application of the liquid crystal diffraction element and the material from which the support 30 is formed. The thickness of the support 30 is preferably from 1 to 1000 μm, more preferably from 3 to 250 μm, and further preferably from 5 to 150 μm.

[0095] <<Alignment film>> In the liquid crystal diffraction element, an alignment film 32 is formed on the surface of a support 30 . The alignment film 32 is an alignment film for aligning the liquid crystal compound 30 in a predetermined liquid crystal alignment pattern when forming the liquid crystal layer 36 of the liquid crystal diffraction element.

[0096] As will be described later, in the liquid crystal diffraction element, the liquid crystal layer has a liquid crystal orientation pattern in which the direction of the optical axis 40A (see FIG. 11) derived from the liquid crystal compound 30 changes while continuously rotating along one in-plane direction (the direction of the array axis D described later). Therefore, the alignment film of the liquid crystal diffraction element is formed so that the liquid crystal layer can form this liquid crystal orientation pattern. In addition, in one direction in which the orientation of the optical axis 40A in the liquid crystal alignment pattern changes while rotating continuously, the length over which the orientation of the optical axis 40A rotates 180° is defined as one period Λ (rotation period of the optical axis).

[0097] In the following description, "the orientation of the optical axis 40A rotates" will also be simply referred to as "the optical axis 40A rotates."

[0098] As the alignment film, various known films can be used. Examples include rubbed films made of organic compounds such as polymers, obliquely evaporated films of inorganic compounds, films with microgrooves, and films formed by stacking LB (Langmuir-Blodgett) films made of organic compounds such as ω-tricosanoic acid, dioctadecylmethylammonium chloride, and methyl stearate using the Langmuir-Blodgett method.

[0099] The alignment film by rubbing treatment can be formed by rubbing the surface of the polymer layer several times in a certain direction with paper or cloth. Preferred examples of materials used for the alignment film include polyimide, polyvinyl alcohol, polymers having polymerizable groups described in JP-A-9-152509, and materials used for forming alignment films described in JP-A-2005-97377, JP-A-2005-99228, and JP-A-2005-128503.

[0100] In the liquid crystal diffraction element, the alignment film is preferably a so-called photo-alignment film, which is formed by irradiating a photo-alignment material with polarized or non-polarized light. That is, in the liquid crystal diffraction element, the alignment film is preferably a photo-alignment film formed by applying a photo-alignment material onto the support 30. The photo-alignment film can be irradiated with polarized light from a vertical direction or an oblique direction, while the photo-alignment film can be irradiated with unpolarized light from an oblique direction.

[0101] Examples of photo-alignment materials used in the photo-alignment film that can be used in the present invention include those described in JP-A-2006-285197, JP-A-2007-76839, JP-A-2007-138138, JP-A-2007-94071, JP-A-2007-121721, JP-A-2007-140465, JP-A-2007-156439, and JP-A-2007-160144. azo compounds described in JP-A-07-133184, JP-A-2009-109831, JP-B-3883848 and JP-B-4151746; aromatic ester compounds described in JP-A-2002-229039; maleimides having photo-orientable units described in JP-A-2002-265541 and JP-A-2002-317013; and / or alkenyl-substituted nadimide compounds, photocrosslinkable silane derivatives described in Japanese Patent Nos. 4205195 and 4205198, photocrosslinkable polyimides, photocrosslinkable polyamides and photocrosslinkable esters described in JP-T-2003-520878, JP-T-2004-529220 and JP-T-4162850, and photodimerizable compounds described in JP-A-9-118717, JP-T-10-506420, JP-T-2003-505561, WO 2010 / 150748, JP-A-2013-177561 and JP-A-2014-12823, in particular cinnamate compounds, chalcone compounds and coumarin compounds, are exemplified as preferred examples. Among these, azo compounds, photocrosslinkable polyimides, photocrosslinkable polyamides, photocrosslinkable esters, cinnamate compounds, and chalcone compounds are preferably used.

[0102] There is no limitation on the thickness of the alignment film, and the thickness may be appropriately set so as to obtain the necessary alignment function depending on the material from which the alignment film is formed. The thickness of the alignment film is preferably from 0.01 to 5 μm, and more preferably from 0.05 to 2 μm.

[0103] There is no limitation on the method for forming the alignment film, and various known methods can be used according to the material for forming the alignment film. One example is a method in which an alignment film is applied to the surface of the support 30 and dried, and then the alignment film is exposed to laser light to form an alignment pattern.

[0104] FIG. 15 conceptually shows an example of an exposure apparatus for forming an alignment pattern by exposing an alignment film.

[0105] The exposure device 60 shown in Figure 15 includes a light source 64 equipped with a laser 62, a λ / 2 plate 65 that changes the polarization direction of laser light M emitted by the laser 62, a polarizing beam splitter 68 that splits the laser light M emitted by the laser 62 into two light beams MA and MB, mirrors 70A and 70B arranged on the optical paths of the two split light beams MA and MB, respectively, and λ / 4 plates 72A and 72B. The light source 64 emits linearly polarized light P0. The λ / 4 plate 72A converts the linearly polarized light P0 (light beam MA) into right-handed circularly polarized light P R The λ / 4 plate 72B converts the linearly polarized light P0 (light beam MB) into left-handed circularly polarized light P L , respectively.

[0106] A support 30 having an alignment film 32 before an alignment pattern is formed is placed in an exposure section, and two light beams MA and MB are caused to intersect and interfere on the alignment film 32, and the alignment film 32 is exposed by being irradiated with the interference light. Due to the interference at this time, the polarization state of the light irradiated to the alignment film 32 changes periodically in the form of interference fringes, thereby obtaining an alignment film having an alignment pattern in which the alignment state changes periodically (hereinafter also referred to as a pattern alignment film).

[0107] In the exposure device 60, the period of the alignment pattern can be adjusted by changing the crossing angle α of the two light beams MA and MB. That is, in the exposure device 60, in an alignment pattern in which the optical axis 40A derived from the liquid crystal compound 40 continuously rotates along one direction, the length of one period in which the optical axis 40A rotates by 180° in one direction in which the optical axis 40A rotates can be adjusted by adjusting the crossing angle α.

[0108] By forming a cholesteric liquid crystal layer on the alignment film 32 having an alignment pattern in which the alignment state changes periodically, a liquid crystal layer 36 can be formed having a liquid crystal alignment pattern in which the optical axis 40A derived from the liquid crystal compound 40 rotates continuously along one direction, as described below. Moreover, by rotating the optical axes of the λ / 4 plates 72A and 72B by 90°, respectively, the rotation direction of the optical axis 40A can be reversed.

[0109] As described above, the patterned alignment film has an alignment pattern that aligns the liquid crystal compound so that the direction of the optical axis of the liquid crystal compound in the liquid crystal layer formed on the patterned alignment film changes while continuously rotating along at least one direction in the plane. If the axis along which the patterned alignment film aligns the liquid crystal compound is defined as the alignment axis, the patterned alignment film can be said to have an alignment pattern in which the direction of the alignment axis changes while continuously rotating along at least one direction in the plane. The alignment axis of the patterned alignment film can be detected by measuring the absorption anisotropy. For example, when the patterned alignment film is irradiated with linearly polarized light while rotating and the amount of light transmitted through the patterned alignment film is measured, the direction in which the amount of light is maximum or minimum is observed to change gradually along one direction in the plane.

[0110] In the liquid crystal diffraction element, the alignment film is provided as a preferred embodiment, but is not an essential component. For example, by forming an orientation pattern on the support 30 by a method such as rubbing the support 30 or processing the support 30 with laser light, it is possible to configure the liquid crystal layer 36, etc. to have a liquid crystal orientation pattern in which the orientation of the optical axis 40A derived from the liquid crystal compound 40 changes while continuously rotating along at least one direction in the plane.

[0111] <<Liquid crystal layer>> In the liquid crystal diffraction element, a liquid crystal layer 36 is formed on the surface of an alignment film 32 . 12 and 13 described later, in order to simplify the drawings and clearly show the configuration of the liquid crystal diffraction element, only the liquid crystal compound 30 (liquid crystal compound molecules) on the surface of the alignment film is shown in the liquid crystal layer 36. However, as conceptually shown by way of example in FIG. 10, the liquid crystal layer 36 has a structure in which aligned liquid crystal compounds 30 are stacked, similar to a liquid crystal layer formed using a composition containing a normal liquid crystal compound.

[0112] As described above, in the liquid crystal diffraction element, the liquid crystal layer 36 is formed using a composition containing a liquid crystal compound. When the in-plane retardation value of the liquid crystal layer is set to λ / 2, the liquid crystal layer functions as a general λ / 2 plate, that is, it imparts a phase difference of half the wavelength, or 180°, to the two orthogonal linearly polarized components contained in the light incident on the liquid crystal layer. In this case, the liquid crystal layer is oriented with the liquid crystal compound rotated in the plane direction, so that the incident circularly polarized light is refracted (diffracted) in a direction in which the optical axis direction is continuously rotating, and then transmitted. At that time, the direction of diffraction differs depending on the rotation direction of the incident circularly polarized light. That is, the liquid crystal layer transmits circularly polarized light and diffracts the transmitted light. Furthermore, the liquid crystal layer changes the rotation direction of the transmitted circularly polarized light to the opposite direction.

[0113] The liquid crystal layer has a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating in one direction indicated by the alignment axis D within the plane of the liquid crystal layer. The optical axis 40A derived from the liquid crystal compound 40 is the axis along which the refractive index is highest in the liquid crystal compound 40, that is, the slow axis. For example, when the liquid crystal compound 40 is a rod-like liquid crystal compound, the optical axis 40A is aligned along the long axis direction of the rod shape. In the following description, "one direction indicated by the array axis D" will also be simply referred to as "the direction of the array axis D." In addition, in the following description, the optical axis 40A originating from the liquid crystal compound 40 will also be referred to as "the optical axis 40A of the liquid crystal compound 40" or "the optical axis 40A." In the liquid crystal layer, the liquid crystal compounds 40 are two-dimensionally aligned in a plane parallel to the alignment axis D and the Y direction perpendicular to the alignment axis D. In Fig. 9, Fig. 10, and Figs. 12 to 14 described later, the Y direction is perpendicular to the paper.

[0114] FIG. 11 conceptually shows a plan view of the liquid crystal layer . 9, that is, a view of the liquid crystal diffraction element from the thickness direction (= the lamination direction of each layer (film)). In other words, a view of the liquid crystal layer 36 from a direction perpendicular to the main surface. 11, in order to clearly show the configuration of the liquid crystal diffraction element, only the liquid crystal compound 40 on the surface of the alignment film 32 is shown. However, as described above, the liquid crystal layer 36 has a structure in which the liquid crystal compound 40 is stacked in the thickness direction, starting from the liquid crystal compound 40 on the surface of the alignment film 32, as shown in FIG.

[0115] In Figure 11, a portion of the plane of the liquid crystal layer 36 is described as a representative example, but the liquid crystal layers described later basically have the same configuration and effects, except for the length of one period of the liquid crystal orientation pattern (one period Λ).

[0116] The liquid crystal layer 36 has a liquid crystal alignment pattern in which the direction of the optical axis 40A derived from the liquid crystal compound 40 changes while continuously rotating along the alignment axis D within the plane of the liquid crystal layer 36. The orientation of the optical axis 40A of the liquid crystal compound 40 changes while continuously rotating in the direction of the arrangement axis D (a predetermined direction), specifically means that the angle between the optical axis 40A of the liquid crystal compound 40 arranged along the arrangement axis D direction and the arrangement axis D direction differs depending on the position in the arrangement axis D direction, and the angle between the optical axis 40A and the arrangement axis D direction changes sequentially from θ to θ+180° or θ-180° along the arrangement axis D direction. The difference in angle between the optical axes 40A of the liquid crystal compounds 40 adjacent to each other in the direction of the alignment axis D is preferably 45° or less, more preferably 15° or less, and even more preferably a smaller angle.

[0117] On the other hand, the liquid crystal compounds 40 forming the liquid crystal layer 36 are arranged at equal intervals in the Y direction perpendicular to the direction of the arrangement axis D, i.e., in the Y direction perpendicular to the one direction in which the optical axis 40A continuously rotates, with the liquid crystal compounds 40 having the same orientation of the optical axis 40A being aligned. In other words, in the liquid crystal compounds 40 forming the liquid crystal layer 36, the angles between the optical axes 40A and the alignment axis D direction are equal to each other among the liquid crystal compounds 40 aligned in the Y direction.

[0118] In the liquid crystal diffraction element, the length (distance) over which the optical axis 40A of the liquid crystal compound 40 rotates 180° in the direction of the arrangement axis D along which the orientation of the optical axis 40A continuously rotates and changes in the plane in the liquid crystal orientation pattern of the liquid crystal compound 40 is defined as the length Λ of one period of the liquid crystal orientation pattern. In other words, the length of one period of the liquid crystal orientation pattern is defined as the distance from when the angle between the optical axis 40A of the liquid crystal compound 40 and the direction of the arrangement axis D changes from θ to θ+180°. That is, the length Λ of one period is defined as the distance between the centers in the direction of the arrangement axis D of two liquid crystal compounds 40 that are at the same angle with respect to the direction of the arrangement axis D. Specifically, as shown in Fig. 11, the length Λ of one period is defined as the distance between the centers in the direction of the arrangement axis D of two liquid crystal compounds 40 whose directions of the arrangement axis D and the optical axis 40A coincide with each other. In the following description, this length Λ of one period is also referred to as "one period Λ". In the liquid crystal diffraction element, the liquid crystal orientation pattern of the liquid crystal layer repeats this one period Λ in the direction of the arrangement axis D, that is, in one direction in which the direction of the optical axis 40A changes by continuously rotating.

[0119] As described above, in the liquid crystal layer, the liquid crystal compounds aligned in the Y direction have the same angle between the optical axis 40A and the alignment axis D (one direction in which the optical axis of the liquid crystal compound 40 rotates). A region where the liquid crystal compounds 40, whose optical axes 40A and the alignment axis D form the same angle, are arranged in the Y direction is referred to as Region R. In this case, the value of the in-plane retardation (Re) in each region R is preferably half the wavelength, i.e., λ / 2. These in-plane retardations are calculated by the product of the refractive index difference Δn associated with the refractive index anisotropy of the region R and the thickness of the liquid crystal layer. Here, the refractive index difference associated with the refractive index anisotropy of the region R in the liquid crystal layer is a refractive index difference defined by the difference between the refractive index in the direction of the slow axis in the plane of the region R and the refractive index in the direction perpendicular to the direction of the slow axis. In other words, the refractive index difference Δn associated with the refractive index anisotropy of the region R is equal to the difference between the refractive index of the liquid crystal compound 40 in the direction of the optical axis 40A and the refractive index of the liquid crystal compound 40 in the direction perpendicular to the optical axis 40A in the plane of the region R. In other words, the refractive index difference Δn is equal to the refractive index difference of the liquid crystal compound.

[0120] When circularly polarized light enters such a liquid crystal layer 36, the light is refracted and the direction of the circular polarization is changed. This action is conceptually shown in Figures 12 and 13. It is assumed that the product of the refractive index difference of the liquid crystal compound and the thickness of the liquid crystal layer 36 is λ / 2. As shown in Figure 12, when the product of the refractive index difference of the liquid crystal compound in the liquid crystal layer 36 and the thickness of the liquid crystal layer 36 is λ / 2, when incident light L1 that is left-handed circularly polarized light is incident on the liquid crystal layer 36, the incident light L1 is given a phase difference of 180° as it passes through the liquid crystal layer 36, and the transmitted light L2 is converted into right-handed circularly polarized light. In addition, since the liquid crystal orientation pattern formed in the liquid crystal layer 36 is a periodic pattern in the direction of the array axis D, the transmitted light L2 travels in a direction different from that of the incident light L1. In this way, the left-handed circularly polarized incident light L1 is converted into right-handed circularly polarized transmitted light L2 that is tilted at a certain angle in the direction of the array axis D with respect to the incident direction.

[0121] On the other hand, as shown in Figure 13, when the product of the refractive index difference of the liquid crystal compound in the liquid crystal layer 36 and the thickness of the liquid crystal layer 36 is λ / 2, when right-handed circularly polarized incident light L4 is incident on the liquid crystal layer 36, the incident light L4 is given a phase difference of 180° as it passes through the liquid crystal layer 36, and is converted into left-handed circularly polarized transmitted light L5. Furthermore, since the liquid crystal orientation pattern formed in the liquid crystal layer 36 is a periodic pattern in the direction of the array axis D, the transmitted light L5 travels in a direction different from that of the incident light L4. At this time, the transmitted light L5 travels in a different direction from that of the transmitted light L2, that is, in the opposite direction to the array axis D with respect to the incident direction. In this way, the incident light L4 is converted into left-handed circularly polarized transmitted light L5 tilted at a certain angle in the opposite direction to the array axis D with respect to the incident direction.

[0122] The liquid crystal layer 36 can adjust the angle of refraction of the transmitted light L2 and L5 by changing one period Λ of the formed liquid crystal orientation pattern. Specifically, the shorter the period Λ of the liquid crystal orientation pattern, the stronger the interference between the lights that have passed through adjacent liquid crystal compounds 40, so that the liquid crystal layer 36 can refract the transmitted light L2 and L5 to a greater extent. Furthermore, the direction of refraction of transmitted light can be reversed by reversing the direction of rotation of the optical axis 40A of the liquid crystal compound 40, which rotates along the direction of the arrangement axis D. That is, in the example shown in Figures 12 and 13, the direction of rotation of the optical axis 40A facing the direction of the arrangement axis D is clockwise, but by changing this rotation direction to counterclockwise, the direction of refraction of transmitted light can be reversed.

[0123] In the liquid crystal layer 36, the in-plane retardation value of the multiple regions R is preferably a half wavelength. The in-plane retardation Re(550) of the multiple regions R of the liquid crystal layer 36 for incident light having a wavelength of 550 nm is Re(550)=Δn 550 ×d is preferably within the range defined by the following formula (1): where Δn 550 is the refractive index difference associated with the refractive index anisotropy of the region R when the wavelength of the incident light is 550 nm, and d is the thickness of the liquid crystal layer 36. 200nm≦Δn 550 ×d≦350 nm (1) That is, the in-plane retardation Re(550) of the regions R of the liquid crystal layer 36 is expressed as Δn 550 If ×d satisfies formula (1), a sufficient amount of the circularly polarized component of the light incident on the liquid crystal layer 36 can be converted into circularly polarized light traveling in a direction tilted in the forward or reverse direction with respect to the direction of the alignment axis D. In-plane retardation Re(550)=Δn 550 ×d is 225 nm ≤ Δn 550 ×d≦340 nm is more preferable, and 250 nm≦Δn 550 It is more preferable that ×d≦330 nm. The above formula (1) is the range for incident light having a wavelength of 550 nm, but the in-plane retardation Re(λ) of the multiple regions R of the liquid crystal layer for incident light having a wavelength of λ nm is expressed as follows: λ ×d is preferably within the range defined by the following formula (1-2), and can be set appropriately. 0.7×(λ / 2)nm≦Δn λ ×d≦1.3×(λ / 2)nm···(1-2)

[0124] In addition, the in-plane retardation values ​​of the regions R in the liquid crystal layer 36 may be outside the range of the above formula (1). 550 ×d<200nm or 350nm<Δn 550 ×d, it is possible to separate light traveling in the same direction as the incident light and light traveling in a direction different from the incident light. 550 When ×d approaches 0 nm or 550 nm, the component of light traveling in the same direction as the incident light increases, and the component of light traveling in a direction different from the incident light decreases.

[0125] Furthermore, the in-plane retardation Re(450) of each region R of the liquid crystal layer 36 for incident light having a wavelength of 450 nm is expressed as Re(450)=Δn 450 ×d and the in-plane retardation Re(550)=Δn of the region R of the liquid crystal layer 36 for incident light having a wavelength of 550 nm. 550 ×d preferably satisfies the following formula (2): where Δn 450is the refractive index difference associated with the refractive index anisotropy of region R when the wavelength of incident light is 450 nm. (Δn 450 ×d) / (Δn 550 ×d)<1.0 (2) Formula (2) indicates that the liquid crystal compound 40 contained in the liquid crystal layer 36 has reverse dispersion. That is, when formula (2) is satisfied, the liquid crystal layer 36 can accommodate incident light in a wide band of wavelengths.

[0126] The liquid crystal layer is made of a hardened layer of a liquid crystal composition containing a rod-shaped liquid crystal compound or a discotic liquid crystal compound, and has a liquid crystal alignment pattern in which the optical axis of the rod-shaped liquid crystal compound or the optical axis of the discotic liquid crystal compound is aligned as described above. A liquid crystal layer consisting of a cured layer of the liquid crystal composition can be obtained by forming an alignment film on the support 30, and applying and curing a liquid crystal composition on the alignment film. Although it is the liquid crystal layer that functions as a so-called λ / 2 plate, the present invention also includes an embodiment in which a laminate integrally comprising the support 30 and the alignment film functions as a λ / 2 plate. In addition, the liquid crystal composition for forming the liquid crystal layer contains a rod-shaped liquid crystal compound or a discotic liquid crystal compound, and may further contain other components such as a leveling agent, an alignment control agent, a polymerization initiator, and an alignment assistant.

[0127] In addition, the liquid crystal layer is preferably broadband with respect to the wavelength of the incident light, and is preferably composed of a liquid crystal material with a birefringence that exhibits reverse dispersion. In addition, it is also preferable to give a twist component to the liquid crystal composition, or to laminate different retardation layers, so that the liquid crystal layer is substantially broadband with respect to the wavelength of the incident light. For example, a method of realizing a patterned λ / 2 plate with a broadband by laminating two layers of liquid crystal with different twist directions in the liquid crystal layer is shown in JP2014-089476A and the like, and can be preferably used in the present invention.

[0128] -Rod-shaped liquid crystal compound- As the rod-shaped liquid crystal compound, azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoates, cyclohexane carboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes, and alkenylcyclohexylbenzonitriles are preferably used. Not only the above-mentioned low molecular weight liquid crystal molecules, but also polymeric liquid crystal molecules can be used.

[0129] It is more preferable to fix the orientation of the rod-shaped liquid crystal compound by polymerization. As the polymerizable rod-shaped liquid crystal compound, compounds described in Makromol. Chem., Vol. 190, p. 2255 (1989), Advanced Materials, Vol. 5, p. 107 (1993), U.S. Patent Nos. 4,683,327, 5,622,648, and 5,770,107, International Publication Nos. 95 / 22586, 95 / 24455, 97 / 00600, 98 / 23580, and 98 / 52905, JP-A-1-272551, 6-16616, 7-110469, and 11-80081, and Japanese Patent Application No. 2001-64627, etc., can be used. Furthermore, as the rod-shaped liquid crystal compound, for example, those described in JP-T-11-513019 and JP-A-2007-279688 can also be preferably used.

[0130] -Disc-shaped liquid crystal compounds- As the discotic liquid crystal compound, for example, those described in JP-A-2007-108732 and JP-A-2010-244038 can be preferably used. When a discotic liquid crystal compound is used in the liquid crystal layer, the liquid crystal compound 40 stands in the thickness direction in the liquid crystal layer, and the optical axis 40A originating from the liquid crystal compound is defined as an axis perpendicular to the disc surface, i.e., a so-called fast axis.

[0131] <Function of optical elements> As described above, a liquid crystal layer formed using a composition containing a liquid crystal compound and having a liquid crystal orientation pattern in which the direction of the optical axis 40A rotates along the direction of the alignment axis D refracts circularly polarized light, and the smaller the period Λ of the liquid crystal orientation pattern, the larger the angle of refraction. Therefore, as shown in FIG. 9, when a pattern is formed so that one period Λ of the liquid crystal alignment pattern is different in different regions in the plane, light incident on different regions in the plane is refracted at different angles.

[0132] The function of the liquid crystal diffraction element will be described in detail below with reference to the conceptual diagram of FIG. In the liquid crystal diffraction element, it is basically only the liquid crystal layer that exerts an optical effect. Therefore, in order to simplify the drawing and clearly show the configuration and the effects, in FIG. 14, only the liquid crystal layer 36 of the liquid crystal diffraction element is shown.

[0133] As described above, the liquid crystal diffraction element includes a liquid crystal layer 36 . The liquid crystal diffraction element, for example, refracts incident light in a predetermined direction and transmits the light, for example, circularly polarized light. Note that in FIG. 14, the incident light is left-handed circularly polarized light.

[0134] In the portion shown in FIG. 14, the liquid crystal layer 26A has three regions A0, A1, and A2 from the left side in FIG. 14, and the length Λ of one period is different in each region. Specifically, the length Λ of one period is shorter in the order of region A0, A1, and A2. Furthermore, regions A1 and A2 have a structure in which the optical axis is twisted and rotated in the thickness direction of the liquid crystal layer (hereinafter also referred to as a twisted structure). The twist angle in the thickness direction of region A1 is smaller than the twist angle in the thickness direction of region A2. Note that region A0 is a region that does not have a twisted structure (i.e., the twist angle is 0°). The twist angle is the twist angle in the entire thickness direction. When the liquid crystal layer has a twisted structure, in a cross section observed by SEM, the bright and dark areas are inclined with respect to the main surface of the liquid crystal layer.

[0135] In the liquid crystal diffraction element, when left-handed circularly polarized light LC1 enters region A1 in the plane of the liquid crystal layer 36, as described above, it is refracted at a predetermined angle in the direction of the array axis D with respect to the incident direction, i.e., in one direction in which the orientation of the optical axis of the liquid crystal compound changes while continuously rotating, and is then transmitted. Similarly, when left-handed circularly polarized light LC2 enters region A2 in the plane of the liquid crystal layer 36, it is refracted at a predetermined angle in the direction of the array axis D with respect to the incident direction and is then transmitted. Similarly, when left-handed circularly polarized light LC0 enters region A0 in the plane of the liquid crystal layer 36, it is refracted at a predetermined angle in the direction of the array axis D with respect to the incident direction and is then transmitted. Here, the angle of refraction by the liquid crystal layer 36 is one period Λ of the liquid crystal alignment pattern in the region A1. A1 The period Λ of the liquid crystal alignment pattern in the region A2 is A2 Since the distance between the incident light and the incident surface is short, the angle of refraction of the incident light is the angle θ A2 The angle θ of the transmitted light in the area A1 A1 In addition, one period Λ of the liquid crystal alignment pattern in the region A1 is larger than A1 The period Λ of the liquid crystal alignment pattern in the region A0 is A0 Since the angle of refraction of the incident light is long, as shown in FIG. 14, the angle of the transmitted light in the area A0 is θ A0 The angle θ of the transmitted light in the area A1 A1 will be smaller than

[0136] By shortening the liquid crystal orientation pattern Λ of the region from the center to the end of the liquid crystal diffraction element, light that is incident on the end side can be refracted more than light that is incident near the center of the liquid crystal diffraction element, allowing it to function as a positive lens that focuses light.

[0137] Here, in the diffraction of light by a liquid crystal layer having a liquid crystal orientation pattern in which the direction of the optical axis of the liquid crystal compound changes while continuously rotating within the plane, there is a risk that the diffraction efficiency will decrease as the diffraction angle increases. Therefore, if the liquid crystal layer is configured to have regions with different lengths of one period in which the direction of the optical axis of the liquid crystal compound rotates 180° in the plane, the diffraction angle will differ depending on the position of incidence of the light, and there is a risk that the amount of diffracted light will differ depending on the position of incidence in the plane. In other words, there is a risk that regions where the transmitted and diffracted light becomes dark will be created depending on the position of incidence in the plane.

[0138] In contrast, if the liquid crystal diffraction element has a region where the liquid crystal layer is twisted and rotated in the thickness direction, the decrease in the diffraction efficiency of the refracted light can be suppressed. Therefore, it is preferable that the liquid crystal diffraction element has a region where the liquid crystal layer is twisted and rotated in the thickness direction, and has a region with a different magnitude of the twist angle in the thickness direction. Specifically, by increasing the twist angle in the thickness direction in regions where one period Λ of the liquid crystal alignment pattern is shorter, the amount of transmitted light can be made uniform regardless of the incident position within the plane.

[0139] Moreover, the liquid crystal diffraction element preferably has a region where the twist angle in the thickness direction is 10° to 360°. In the liquid crystal diffraction element, the twist angle in the thickness direction may be appropriately set according to one period Λ of the in-plane liquid crystal orientation pattern.

[0140] Here, in the example shown in FIG. 9, the liquid crystal diffraction element has a configuration including one liquid crystal layer, but is not limited to this, and may have two or more liquid crystal layers. Furthermore, when the liquid crystal diffraction element has two or more liquid crystal layers, the liquid crystal layers may further have liquid crystal layers whose directions of twisting and rotating in the thickness direction (directions of twist angle) are different from each other. For example, a liquid crystal layer having a liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal compound rotates in one direction, and further having a region in which the optical axis twists and rotates in the thickness direction of the liquid crystal layer, and having regions in which the twist angle of rotation is different within the plane, and in which the directions of twisting and rotating in the thickness direction are different from each other, may be stacked and used. In this way, by further having a liquid crystal layer that is twisted and rotated in different directions in the thickness direction, transmitted light can be efficiently refracted for incident light of various polarization states in the region having a twist angle in the thickness direction.

[0141] Here, in the case of having liquid crystal layers having different directions of twist and rotation in the thickness direction, it is preferable that the twist angle in the thickness direction is the same for each region in the plane.

[0142] However, the present invention is not limited to this, and there is no restriction on the twist angle in the thickness direction of the liquid crystal diffraction element either, and it may be set appropriately depending on the application of the optical element, etc.

[0143] In addition, the liquid crystal layer having different twisted and rotated directions in the thickness direction has an in-plane retardation Re(λ)=Δn λ It is preferable that xd are the same.

[0144] However, the present invention is not limited to this. In the liquid crystal diffraction element, the in-plane retardation Re(λ) of the multiple regions R of the liquid crystal layer for incident light having a wavelength of λ nm is expressed as follows: λ There is no limitation on ×d either, and it may be set appropriately depending on the application of the optical element, etc.

[0145] In a liquid crystal diffraction element, there is no limitation on one period Λ in the alignment pattern of the liquid crystal layer, and it may be set appropriately depending on the application of the optical element, etc.

[0146] (Method of forming regions with different twist angles in a twisted structure) A configuration in which the twist structure in a liquid crystal layer has regions with different twist angles can be formed by using a chiral agent that undergoes back isomerization, dimerization, isomerization and dimerization, etc., upon irradiation with light, thereby changing the helical twisting power (HTP), and irradiating each region with light of a wavelength that changes the HTP of the chiral agent, with different amounts of irradiation, before or during the curing of the liquid crystal composition that forms the liquid crystal layer. For example, by using a chiral agent whose HTP decreases when irradiated with light, the HTP of the chiral agent decreases when irradiated with light. Here, by changing the amount of light irradiation for each region, for example, in regions with a high amount of irradiation, the HTP decreases significantly and the induction of the helix decreases, resulting in a smaller twist angle of the twisted structure. On the other hand, in regions with a low amount of irradiation, the decrease in HTP is small, resulting in a larger twist angle of the twisted structure.

[0147] There is no particular limitation on the method for changing the amount of light irradiated to each region, and methods that can be used include irradiating light through a gradation mask, changing the irradiation time for each region, or changing the irradiation intensity for each region. It should be noted that a gradation mask is a mask whose transmittance to the irradiated light varies within its surface.

[0148] In the optical element shown in FIGS. 9 to 14, the optical axis 40A of the liquid crystal compound 40 in the liquid crystal alignment pattern of the liquid crystal layer rotates continuously only along the direction of the alignment axis D. However, the present invention is not limited thereto, and various configurations can be used as long as the optical axis 40A of the liquid crystal compound 40 in the liquid crystal layer rotates continuously along one direction.

[0149] As an example, there is exemplified a liquid crystal layer 36 having a liquid crystal orientation pattern that has one direction in which the orientation of the optical axis of the liquid crystal compound 40 changes while rotating continuously, concentrically from the inside to the outside, as conceptually shown in the plan view of Fig. 16. In other words, the liquid crystal orientation pattern of the liquid crystal layer 36 shown in Fig. 16 is a liquid crystal orientation pattern in which one direction in which the orientation of the optical axis of the liquid crystal compound 40 changes while rotating continuously is provided radially from the center of the liquid crystal layer 34.

[0150] In addition, in FIG. 16 as in FIG. 12, only the liquid crystal compound 40 on the surface of the alignment film is shown, but as described above, in the liquid crystal layer 36, similar to the example shown in FIG. 10, the liquid crystal compound 40 has a structure in which the liquid crystal compound 40 is stacked starting from the liquid crystal compound 40 on the surface of the alignment film.

[0151] In the liquid crystal layer 36 shown in FIG. 16, the optical axis (not shown) of the liquid crystal compound 40 is the longitudinal direction of the liquid crystal compound 40. In the liquid crystal layer 36, the direction of the optical axis of the liquid crystal compound 40 changes while continuously rotating along a number of directions from the center of the liquid crystal layer 36 toward the outside, for example, the direction indicated by the arrow A1, the direction indicated by the arrow A2, the direction indicated by the arrow A3, etc. The circularly polarized light incident on the liquid crystal layer 36 having this liquid crystal orientation pattern changes in absolute phase in each local region having a different optical axis direction of the liquid crystal compound 40. At this time, the amount of change in each absolute phase differs depending on the optical axis direction of the liquid crystal compound 40 into which the circularly polarized light is incident.

[0152] Such a liquid crystal layer 34 having a concentric liquid crystal orientation pattern, i.e., a liquid crystal orientation pattern in which the optical axis changes by continuously rotating radially, can transmit incident light as divergent or converging light depending on the rotation direction of the optical axis of the liquid crystal compound 40 and the direction of the incident circularly polarized light. That is, by forming the liquid crystal orientation pattern of the liquid crystal layer in a concentric circular shape, the liquid crystal diffraction element exhibits a function as, for example, a convex lens or a concave lens.

[0153] Here, when the liquid crystal orientation pattern of the liquid crystal layer is concentric and the optical element acts as a convex lens, it is preferable to gradually shorten one period Λ in which the optical axis rotates by 180° in the liquid crystal orientation pattern from the center of the liquid crystal layer 34 toward the outside in one direction in which the optical axis continuously rotates. As described above, the angle of refraction of light with respect to the incident direction increases as the period Λ of the liquid crystal orientation pattern becomes shorter. Therefore, by gradually shortening the period Λ of the liquid crystal orientation pattern from the center of the liquid crystal layer 34 toward the outside in one direction in which the optical axis continuously rotates, the light focusing power of the liquid crystal layer 34 can be further improved, and the performance as a convex lens can be improved.

[0154] In the present invention, when the liquid crystal diffraction element is made to function as a convex lens, it is preferable that the following formula is satisfied. Φ(r)=(π / λ)[(r 2 +f 2 ) 1 / 2 -f] Here, r is the distance from the center of the concentric circle, and the formula is r=(x 2 +y 2 ) 1 / 2 where x and y represent the position in the plane, and (x, y) = (0, 0) represents the center of the concentric circles. Φ(r) represents the angle of the optical axis at distance r from the center, λ represents the wavelength, and f represents the desired focal length.

[0155] Conversely, in the present invention, one period Λ in the concentric liquid crystal alignment pattern may be gradually lengthened from the center of the liquid crystal layer 36 toward the outside in one direction in which the optical axis continuously rotates. Furthermore, depending on the application of the liquid crystal diffraction element, for example when it is desired to provide a light intensity distribution in transmitted light, it is also possible to use a configuration in which, rather than gradually changing the period Λ in one direction in which the optical axis rotates continuously, there are regions in which the period Λ differs partially in one direction in which the optical axis rotates continuously. In addition, the liquid crystal diffraction element may have a liquid crystal layer in which the period Λ is uniform all over and a liquid crystal layer having a region in which the period Λ is different. In this respect, the same applies to a configuration in which the optical axis rotates continuously in only one direction as shown in FIG.

[0156] FIG. 17 conceptually shows an example of an exposure apparatus for forming such a concentric circular alignment pattern on an alignment film. The exposure device 80 has a light source 84 equipped with a laser 82, a polarizing beam splitter 86 that splits laser light M from the laser 82 into S-polarized light MS and P-polarized light MP, a mirror 90A arranged in the optical path of the P-polarized light MP and a mirror 90B arranged in the optical path of the S-polarized light MS, a lens 92 arranged in the optical path of the S-polarized light MS, a polarizing beam splitter 94, and a λ / 4 plate 96.

[0157] The P-polarized light MP split by the polarizing beam splitter 86 is reflected by a mirror 90A and enters a polarizing beam splitter 94. On the other hand, the S-polarized light MS split by the polarizing beam splitter 86 is reflected by a mirror 90B, collected by a lens 92, and enters the polarizing beam splitter 94. The P polarized light MP and S polarized light MS are combined by the polarizing beam splitter 94 , and are converted by the λ / 4 plate 96 into right-handed circularly polarized light and left-handed circularly polarized light according to the polarization direction, and are incident on the alignment film 32 on the support 30 . Here, the interference between the right-handed and left-handed circularly polarized light causes the polarization state of the light irradiated onto the alignment film to periodically change in the form of interference fringes. As the crossing angle between the left-handed and right-handed circularly polarized light changes from the inside to the outside of the concentric circles, an exposure pattern is obtained in which the pitch changes from the inside to the outside. This results in a concentric alignment pattern in which the alignment state periodically changes on the alignment film.

[0158] In this exposure device 80, one period Λ of the liquid crystal orientation pattern in which the optical axis of the liquid crystal compound 40 continuously rotates 180° along one direction can be controlled by changing the refractive power of the lens 92 (F-number of the lens 92), the focal length of the lens 92, and the distance between the lens 92 and the orientation film 24, etc. In addition, by adjusting the refractive power of the lens 92 (the F-number of the lens 92), the length Λ of one period of the liquid crystal alignment pattern can be changed in one direction in which the optical axis rotates continuously. Specifically, the length Λ of one period of the liquid crystal orientation pattern can be changed in one direction in which the optical axis rotates continuously by changing the spread angle of the light spread by the lens 92 that interferes with the parallel light. More specifically, when the refractive power of the lens 92 is weakened, the light approaches parallel light, so that the length Λ of one period of the liquid crystal orientation pattern gradually shortens from the inside to the outside, and the F-number becomes larger. Conversely, when the refractive power of the lens 92 is strengthened, the length Λ of one period of the liquid crystal orientation pattern suddenly shortens from the inside to the outside, and the F-number becomes smaller.

[0159] In this way, the configuration in which the period Λ in which the optical axis rotates 180° is changed in one direction in which the optical axis rotates continuously can also be used in the configuration in which the optical axis 40A of the liquid crystal compound 40 rotates and changes continuously in only one direction, the direction of the alignment axis D, as shown in Figures 9 to 14. For example, by gradually shortening one period Λ of the liquid crystal alignment pattern in the direction of the alignment axis D, an optical element that transmits light in a condensing manner can be obtained. Furthermore, depending on the application of the liquid crystal diffraction element, for example when it is desired to provide a light amount distribution in transmitted light, it is also possible to use a configuration having a region in which one period Λ is partially different in the direction of the array axis D, rather than gradually changing one period Λ toward the direction of the array axis D. For example, as a method for partially changing one period Λ, a method of patterning a photo-alignment film by scanning exposure while arbitrarily changing the polarization direction of focused laser light, or the like, can be used.

[0160] (adhesive layer) The optical element of the present invention may include an adhesive layer between each layer in order to ensure adhesion between the layers. In this specification, the term "adhesion" is used as a concept that also includes "sticking". The adhesive layer may be formed from an adhesive or a pressure sensitive adhesive. From the viewpoint of curing method, adhesives include hot melt type, heat curing type, light curing type, reaction curing type, and pressure sensitive adhesive type that does not require curing, and as materials for each, compounds such as acrylate, urethane, urethane acrylate, epoxy, epoxy acrylate, polyolefin, modified olefin, polypropylene, ethylene vinyl alcohol, vinyl chloride, chloroprene rubber, cyanoacrylate, polyamide, polyimide, polystyrene, polyvinyl butyral, etc. From the viewpoint of workability and productivity, the light curing type is preferred as the curing method, and from the viewpoint of optical transparency and heat resistance, it is preferred to use acrylate, urethane acrylate, epoxy acrylate, etc. as materials.

[0161] Examples of the adhesive include an acrylic adhesive and a polyvinyl alcohol adhesive. Each layer may be bonded using a highly transparent adhesive transfer tape (OCA tape). As the highly transparent adhesive transfer tape, a commercially available product for image display devices, particularly a commercially available product for the surface of the image display part of an image display device, may be used. Examples of commercially available products include adhesive sheets (such as PD-S1) manufactured by Panac Corporation and MHM series adhesive sheets manufactured by Nichiei Kako Co., Ltd.

[0162] In addition, each member may be formed by directly laminating it on another member. For example, a cholesteric liquid crystal layer that becomes the first reflective circular polarizer may be formed on the first retardation plate using the first retardation plate as a support.

[0163] The image display unit having the optical element of the present invention described above can have a long optical path length while remaining compact, and therefore can be suitably used as an image display unit for a head mounted display. EXAMPLES

[0164] The features of the present invention will be described in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, processing contents, processing procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

[0165] <Preparation of second reflective circular polarizer>

[0166] (Formation of alignment film) A glass substrate was prepared as a support. The following coating solution for forming an alignment film was applied to the support by spin coating. The support on which the coating solution for forming an alignment film was formed was dried on a hot plate at 60° C. for 60 seconds to form an alignment film.

[0167] Coating solution for forming alignment film ------------------------------------------------------------------ 1.00 parts by weight of the following photoalignment material Water 16.00 parts by mass Butoxyethanol 42.00 parts by weight Propylene glycol monomethyl ether 42.00 parts by mass ------------------------------------------------------------------

[0168] -Material for photo alignment- [ka]

[0169] (Exposure of alignment film) The obtained alignment film P-1 was irradiated with polarized ultraviolet light (50 mJ / cm 2 The alignment film P-1 was exposed to light by a high-pressure mercury lamp.

[0170] (Formation of cholesteric liquid crystal layer) The following composition A-1 was prepared as a liquid crystal composition for forming a cholesteric liquid crystal layer. This composition A-1 is a liquid crystal composition that forms a cholesteric liquid crystal layer (cholesteric liquid crystal phase) that reflects right-handed circularly polarized light. Composition A-1 ------------------------------------------------------------------ Rod-shaped liquid crystal compound L-1 100.00 parts by mass Polymerization initiator (KAYACURE DETX-S, Nippon Kayaku Co., Ltd.) 1.00 parts by mass Chiral agent Ch-1 4.0 parts by mass Leveling agent T-1 0.08 parts by weight Methyl ethyl ketone 142.00 parts by mass ------------------------------------------------------------------

[0171] Rod-shaped liquid crystal compound L-1 [ka]

[0172] Chiral Agent Ch-1 [ka]

[0173] Leveling agent T-1 [ka]

[0174] The above composition A-1 was applied onto the alignment film P-1. The coating of composition A-1 was heated on a hot plate at 100°C for 3 minutes. Thereafter, a first exposure was performed to change the HTP of the chiral agent using a high-pressure mercury lamp at 100°C under a nitrogen atmosphere through a 300 nm long pass filter and a 350 nm short pass filter. The first exposure was performed with an irradiance of 9 mJ / cm2 measured at a wavelength of 315 nm. 2 It was carried out so that it became. Furthermore, at 100°C, a high-pressure mercury lamp was used to irradiate the specimen with ultraviolet light of 365 nm at 1000 mJ / cm under a nitrogen atmosphere. 2 The coating film was irradiated with light at an exposure dose of 1000 x 1000 for a second time to cure the liquid crystal composition, thereby curing the composition A-3 and fixing the alignment of the liquid crystal compound, thereby forming a cholesteric liquid crystal layer.

[0175] The cross section of the cholesteric liquid crystal layer was observed by SEM. As a result, it was observed that the bright and dark areas were parallel to the main surface of the cholesteric liquid crystal layer, and the distance between the bright and dark areas in the thickness direction, i.e., the surface pitch, increased continuously in the thickness direction from the alignment film side to the side away from the alignment film. That is, the cholesteric liquid crystal layer has a pitch gradient structure. The average surface pitch was 0.4 μm. It was confirmed that this cholesteric liquid crystal layer reflects right-handed circularly polarized light and transmits left-handed circularly polarized light over the visible range. The surface pitch was measured by setting the distance in the normal direction to the line from the bright area to the bright area or from the dark area to the dark area as 1 / 2 pitch. The bright and dark areas referred to here are the bright and dark areas derived from the cholesteric liquid crystal phase, as seen when the cross section of the cholesteric liquid crystal layer is observed by SEM, as described above. In this manner, a second reflective circular polarizing plate was prepared.

[0176] <Preparation of the first reflective circular polarizer>

[0177] A cholesteric liquid crystal was formed in the same manner as in the method for producing the second reflective circular polarizer described above, except that 4.0 parts by mass of chiral material Ch-2 was used instead of chiral material Ch-1, to produce a first reflective circular polarizer.

[0178] Chiral Agent Ch-2 [ka]

[0179] When the cross section of the cholesteric liquid crystal layer was observed with an SEM, it was found that the light and dark areas were parallel to the main surface of the cholesteric liquid crystal layer, and the distance between the light and dark areas in the thickness direction, i.e., the surface pitch, increased continuously in the thickness direction from the alignment film side to the side away from the alignment film. In other words, the cholesteric liquid crystal layer has a pitch gradient structure. The average surface pitch was 0.4 μm. It was confirmed that this cholesteric liquid crystal layer reflected left-handed circularly polarized light and transmitted right-handed circularly polarized light across the visible range. In this manner, a first reflective circular polarizing plate was prepared.

[0180] [Comparative Example 1] <Creating a head-mounted display evaluation system> An optical element was fabricated using a first absorptive linear polarizer, a first retardation plate (λ / 4 plate), a partial reflection mirror, a second retardation plate (λ / 4 plate), a reflective linear polarizer, and a second absorptive linear polarizer, and an image display unit, which is a head-mounted display, was fabricated (see Fig. 3). A commercially available head-mounted display, Oculus Rift S, made by Oculus, was disassembled, and the display and the absorptive linear polarizer attached to its surface were used, and the absorption axis angle of the first absorptive linear polarizer was arranged to be 90°. As the partial reflection mirror A, an aluminum film was formed by sputtering on the convex surface of a lens with a diameter of 5 cm and a curvature radius of 10 cm so that the transmittance and reflectance were 50% and 50%, respectively. In other words, the partial reflection mirror A was curved. As the second reflective linear polarizer, DBEF made by 3M was used, and it was arranged so that the transmission axis angle was 90°. On the viewing side of the second reflective linear polarizer, a second absorbing linear polarizer was arranged so that the absorption axis angle was 0°. The first retardation plate and the second retardation plate were arranged so that the slow axes were 45° and -45°, respectively. Note that the axis angles described above were based on the horizontal direction of the head mounted display (0°), and the clockwise direction when the image display device was viewed from the viewing side was taken as positive.

[0181] [Example 1] In the configuration of Comparative Example 1, a first reflective linear polarizer was placed between the first absorptive linear polarizer and the first retardation plate (see FIG. 2). The transmission axis of the second reflective linear polarizer was parallel to the first reflective linear polarizer. DBEF by 3M was used as the first reflective linear polarizer.

[0182] [Example 2] With respect to the configuration of Example 1, the first reflective linear polarizer was removed, a first reflective circular polarizer was placed between the first retardation plate and the partial reflection mirror, and a second reflective circular polarizer was placed between the partial reflection mirror and the second retardation plate, and the second reflective linear polarizer was removed (see Figure 6).

[0183] [Example 3] In the configuration of Example 2, instead of the partial reflection mirror A (a laminate of a dielectric multilayer half mirror and a lens with a radius of curvature of 10 cm), a partial reflection mirror B was used. The partial reflection mirror B was formed by sputtering an aluminum film on a flat glass substrate so that the transmittance was 50% and the reflectance was 50%. Furthermore, the distance between the first reflective circular polarizer and the partial reflection mirror B and the distance between the partial reflection mirror B and the second reflective circular polarizer were both set to 5 mm. Furthermore, a liquid crystal diffraction element was inserted as a positive lens between the second reflective circular polarizer and the second retardation plate. The liquid crystal diffraction element was produced by adjusting the diffraction pitch so that the focal length was 5 cm as a lens characteristic as follows.

[0184] <Positive lens: Preparation of liquid crystal diffraction element> An alignment film was formed in the same manner as in the production of the second reflective circular polarizing plate of Example 2.

[0185] (Exposure of alignment film) The alignment film was exposed using the exposure apparatus shown in FIG. 17 to form an alignment film P-2 having an alignment pattern. The exposure device used was a laser that emitted a laser beam with a wavelength of 325 nm. The exposure dose by the interference light was 300 mJ / cm 2 By using the exposure apparatus shown in Fig. 17, one period of the alignment pattern was made gradually shorter toward the outside.

[0186] (Formation of the first liquid crystal layer) As a liquid crystal composition for forming a liquid crystal layer, the following composition B-1 was prepared.

[0187] Composition B-1 ---------------------------------------------------------------------------------- Liquid crystal compound L-1 100.00 parts by mass Chiral agent Ch-A 0.23 parts by mass Polymerization initiator (BASF, Irgacure (registered trademark) 907) 3.00 parts by mass Photosensitizer (KAYACURE DETX-S, Nippon Kayaku) 1.00 parts by mass Leveling agent T-1 0.08 parts by weight Methyl ethyl ketone 2000.00 parts by mass ----------------------------------------------------------------------------------

[0188] Chiral agent Ch-A [ka]

[0189] The first liquid crystal layer was formed by applying composition B-1 in multiple layers onto the alignment film P-2. First, composition B-1 was applied as a first layer onto the alignment film, heated, cooled, and then cured with UV light to produce a liquid crystal fixing layer. After that, the second and subsequent layers were repeatedly applied to the liquid crystal fixing layer, and similarly heated, cooled, and cured with UV light were repeatedly performed.

[0190] First, the first layer was formed by applying the following composition B-1 onto the alignment film P-2, heating the coating to 80°C on a hot plate, and then irradiating the coating with ultraviolet light having a wavelength of 365 nm at 300 mJ / cm2 using a high-pressure mercury lamp in a nitrogen atmosphere at 80°C. 2 The coating film was irradiated with an irradiation dose of 1000 nm to fix the alignment of the liquid crystal compound.

[0191] The second and subsequent layers were coated on top of the liquid crystal layer, heated and cooled under the same conditions as above, and then cured with UV light to form the liquid crystal fixation layer. In this way, coating was repeated until the desired total thickness was reached, forming the first liquid crystal layer.

[0192] The complex refractive index Δn of the cured layer of the liquid crystal composition B-1 was determined by measuring the retardation Re(λ) and film thickness of the liquid crystal fixed layer (cured layer) obtained by applying the liquid crystal composition B-1 onto a support with an alignment film for retardation measurement prepared separately, aligning the director of the liquid crystal compound so that it is horizontal to the substrate, and then irradiating it with ultraviolet light to fix it. The retardation Re(λ) was divided by the film thickness to obtain Δn λThe retardation Re(λ) was measured at the desired wavelength using an Axoscan from Axometrix, and the film thickness was measured using a SEM. In the notation of Re(λ), λ is the wavelength of the incident light. In the following, the wavelength λ of the incident light is set to 550 nm.

[0193] The first liquid crystal layer is finally 550 × thickness = Re(550) was 275 nm, and it was confirmed by a polarizing microscope that the alignment was periodic in a concentric pattern as shown in Figure 16. The period of the concentric pattern became shorter from the center toward the outside. The twist angle in the thickness direction of the first liquid crystal layer was 70° (right twist). In the following, unless otherwise specified, "Δn 550 Measurements such as "x thickness" were also performed in the same way. In addition, in the cross-sectional image taken by SEM, inclined light and dark lines were observed with respect to the lower interface of the liquid crystal layer (interface with the glass substrate). In the repeated pattern of light and dark lines, it was observed that the period became shorter from the center to the outside.

[0194] (Formation of the second liquid crystal layer) As a liquid crystal composition for forming a liquid crystal layer, the following composition B-2 was prepared.

[0195] Composition B-2 ---------------------------------------------------------------------------------- Liquid crystal compound L-1 100.00 parts by mass Chiral agent Ch-B 0.39 parts by mass Polymerization initiator (BASF, Irgacure (registered trademark) 907) 3.00 parts by mass Photosensitizer (KAYACURE DETX-S, Nippon Kayaku) 1.00 parts by mass Leveling agent T-1 0.08 parts by weight Methyl ethyl ketone 2000.00 parts by mass ----------------------------------------------------------------------------------

[0196] Chiral agent Ch-B [ka]

[0197] A second liquid crystal layer was formed on the first liquid crystal layer in the same manner as for the first liquid crystal layer, except that composition B-2 was used, to prepare a liquid crystal diffraction element.

[0198] The second liquid crystal layer is finally 550 It was confirmed by a polarizing microscope that × thickness = Re(550) was 275 nm, and that the liquid crystal had a periodic concentric alignment as shown in Figure 16. The period of the concentric pattern became shorter from the center toward the outside. The twist angle in the thickness direction of the first liquid crystal layer was 70° (left twist). In the cross-sectional image taken by SEM, bright and dark lines inclined to the lower interface of the liquid crystal layer (interface with the glass substrate) were observed. The inclination direction of the bright and dark lines of the first liquid crystal layer and the second liquid crystal layer from the normal line was opposite. It was observed that the period of the repeated pattern of bright and dark lines became shorter from the center toward the outside.

[0199] <Brightness evaluation of head mounted displays> The display was removed from the image display unit having the optical element of the present invention, and a light source for evaluation was placed therein. A laser pointer (wavelength 532 nm) was used as the light source for evaluation. Using the laser pointer, light was irradiated from the first absorptive linear polarizing plate side of the optical element, and the intensity of the emitted light was measured with a power meter. The intensity ratio with respect to the comparative example was calculated and evaluated according to the following criteria. A: Intensity ratio is 1.5 or more B: Intensity ratio is 1.2 or more and less than 1.5 C: Intensity ratio is 1.0 or more and less than 1.2

[0200] As a result of the evaluation, Examples 1 to 3 were all rated A. On the other hand, Comparative Example 1 was rated C. That is, it is understood that the examples of the present invention can improve the light utilization efficiency compared to the comparative examples. From the above, the effects of the present invention are clear. [Explanation of symbols]

[0201] 10a, 10b Optical element 12 First absorptive linear polarizer 14 First reflective linear polarizer 16 First retardation layer 18 Partially reflecting mirror 20 Second retardation plate 22, 22b Second reflective linear polarizer 24, 24b Second absorptive linear polarizer 26 First reflective circular polarizer 28 Second reflective circular polarizer 29 Positive Lens 30, 31 Support 32, 33 Alignment film 34 Cholesteric Liquid Crystal Layer 36 Optically anisotropic layer (liquid crystal layer) 40 Liquid crystal compounds 40A optical axis 42 Akabe 44 Dark part 50, 50b Image display unit 52 Image display device 60, 80 Exposure device 62, 82 Laser 64, 84 light source 65 λ / 2 plate 68, 86, 94 Polarizing Beam Splitter 70A, 70B, 90A, 90B Mirror 72A, 72B, 96 λ / 4 board 92 Lens D Array axis Λ 1 period Pitch U user M Laser light MA, MB rays MP P polarization MS S-polarized P0 Linearly polarized P R Right circular polarization P L Left circular polarization α intersection angle R area L1 light L2 light L4 light L5 light

Claims

1. A first absorptive linear polarizer; A first reflective linear polarizer; A first retardation plate; a partial reflection mirror that transmits a portion of incident light and reflects a portion of it; A second retardation plate; and a second reflective linear polarizer, a positive lens disposed on a side of the second reflective linear polarizer opposite to the second retardation plate, the positive lens is a diffractive lens using a diffractive element, a rotation direction of the circularly polarized light reflected when the light passes through the first retardation plate and is incident on the first reflective linear polarizer is opposite to a rotation direction of the circularly polarized light reflected when the light passes through the second retardation plate and is incident on the second reflective linear polarizer, the cross section of the partially reflecting mirror has a curved shape; Furthermore, the optical element includes the first reflective linear polarizing plate, the first retardation plate, the second retardation plate, and the second reflective linear polarizing plate, each of which has a curved cross section.

2. 2. The optical element according to claim 1, wherein the diffractive lens is a liquid crystal diffractive element having a liquid crystal layer containing a liquid crystal compound.

3. the diffractive lens is a liquid crystal diffractive element having a liquid crystal layer containing a liquid crystal compound, the liquid crystal layer has a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in a plane, The optical element described in claim 1 or 2, wherein, in the liquid crystal layer, when the length by which the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern rotates 180° in the in-plane direction is defined as one period of the diffraction structure, the period of the diffraction structure has regions that differ in the plane.

4. 4. The optical element according to claim 2, wherein the liquid crystal layer has regions in which bright and dark areas derived from the liquid crystal phase are inclined with respect to a main surface of the liquid crystal layer in a cross section of the liquid crystal layer observed with a scanning electron microscope.

5. 5. The optical element according to claim 1, wherein the first retardation plate and the second retardation plate are λ / 4 plates.

6. The optical element according to any one of claims 1 to 5, an image display device disposed on the first absorptive linear polarizer side of the optical element;

7. A head mounted display comprising the image display unit according to claim 6.

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