Liquid crystal optical element

Abstract

To provide a liquid crystal optical element that can be mass-produced.SOLUTION: A liquid crystal optical element 1 includes a substrate 10, a plurality of structures 20, a first liquid crystal layer LC1 including a plurality of liquid crystal molecules whose alignment direction is fixed, and a second liquid crystal layer LC2 including a plurality of liquid crystal molecules whose alignment direction is fixed. In an area that overlapping with a groove g, a first director of the first liquid crystal layer LC1 is along the groove g, and a second director of the second liquid crystal layer LC2 is aligned with the first director on a second surface S2 side on a third surface S3 side and turns in a plan view.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] An embodiment of the present invention relates to a liquid crystal optical element. [Background technology]

[0002] For example, a liquid crystal polarization grating using a liquid crystal material has been proposed. When light with a wavelength λ is incident on such a liquid crystal polarization grating, the incident light is divided into zero-order diffracted light and first-order diffracted light. When realizing such a liquid crystal polarization grating, there is a demand for increasing productivity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-84679 A [Patent Document 2] Special Publication No. 2017-522601 [Patent Document 3] Japanese Patent Application Publication No. 8-262445 Summary of the Invention [Problem to be solved by the invention]

[0004] The present embodiment provides a liquid crystal optical element that can be mass-produced. [Means for solving the problem]

[0005] The liquid crystal optical element according to one embodiment comprises: a substrate having a main surface, a plurality of structures each having a bottom surface facing the main surface and a top surface opposite the bottom surface, the plurality of structures being arranged at intervals, a first surface facing the main surface, a second surface opposite the first surface, and a plurality of liquid crystal molecules having a fixed alignment direction, the plurality of structures being provided between the plurality of structures and being hardened, a third surface facing the top surface and in contact with the second surface, a fourth surface opposite the third surface, and a plurality of liquid crystal molecules having a fixed alignment direction, a second liquid crystal layer being hardened, The structure and a second structure disposed between the first structures, wherein the plurality of first structures are arranged at a first pitch in a first direction and at a second pitch different from the first pitch in a second direction intersecting the first direction, the pair of structures being a pair of first structures adjacent to each other in the first direction among the plurality of first structures, and the second structure has a different shape from the first structures and is curved. Moreover, the liquid crystal optical element according to one embodiment has a substrate having a main surface, a plurality of structures each having a bottom surface facing the main surface and a top surface opposite the bottom surface, the plurality of structures being arranged at intervals, a first surface facing the main surface, a second surface opposite the first surface, and a plurality of liquid crystal molecules having a fixed alignment direction, the first liquid crystal layer being provided between the plurality of structures and being hardened, a third surface facing the top surface and in contact with the second surface, a fourth surface opposite the third surface, and a plurality of liquid crystal molecules having a fixed alignment direction, and a second liquid crystal layer being hardened, the first director on the second surface side is aligned with the first director and rotates in a planar view, the plurality of structures has a plurality of curved first structures, the plurality of first structures are arranged at a first pitch in a first direction and at a second pitch different from the first pitch in a second direction intersecting the first direction, the pair of structures is a pair of first structures adjacent to each other in the first direction among the plurality of first structures, the plurality of first structures include a plurality of first structures belonging to a first group and arranged in the first direction, and a plurality of first structures belonging to a second group adjacent to the first group in the second direction and arranged in the first direction, the plurality of structures further has a third structure located between the first group and the second group and extending linearly in the first direction. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a plan view illustrating the alignment direction of a plurality of liquid crystal molecules in a first liquid crystal layer of a liquid crystal optical element according to one embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing the liquid crystal optical element along line II-II in FIG. [Diagram 3] FIG. 3 is a cross-sectional view for explaining the method for producing the liquid crystal optical element, showing a state in which the structural material is applied onto the substrate. [Figure 4]FIG. 4 is a cross-sectional view for explaining the method for producing the liquid crystal optical element, following FIG. 3, showing a state in which the mold is pressed against the substrate from above the structural material. [Diagram 5] FIG. 5 is a cross-sectional view for explaining the method for producing the liquid crystal optical element, following FIG. 4, showing a state in which a first liquid crystal layer is formed on a substrate and a plurality of structures. [Figure 6] FIG. 6 is a cross-sectional view for explaining the method for producing the liquid crystal optical element, following FIG. 5, showing a state in which a second liquid crystal layer is formed on a first liquid crystal layer. [Figure 7] FIG. 7 is a cross-sectional view showing the liquid crystal optical element along the line VII-VII in FIG. [Figure 8] FIG. 8 is a plan view showing an alignment pattern in the first liquid crystal layer. [Figure 9] FIG. 9 is a plan view showing a first layout of the plurality of structures. [Figure 10] FIG. 10 is a plan view showing a second layout of the plurality of structures. [Figure 11] FIG. 11 is a plan view showing a third layout of the plurality of structures. [Figure 12] FIG. 12 is a cross-sectional view showing a liquid crystal optical element according to a modified example of the above embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the disclosure is merely an example, and those who are skilled in the art can easily conceive of appropriate modifications while maintaining the gist of the invention are naturally included in the scope of the present invention. In addition, in order to make the explanation clearer, the drawings may show the width, thickness, shape, etc. of each part in a schematic manner compared to the actual embodiment, but these are merely examples and do not limit the interpretation of the present invention. In addition, in this specification and each figure, elements similar to those described above with respect to the previous figures may be given the same reference numerals, and detailed explanations may be omitted as appropriate.

[0008] In the drawings, an X-axis, a Y-axis, and a Z-axis that are orthogonal to each other are shown as necessary for ease of understanding. The direction along the X-axis is called the X-direction or the first direction, the direction along the Y-axis is called the Y-direction, the second direction, or the direction intersecting with the X-direction, and the direction along the Z-axis is called the Z-direction or the third direction. The plane defined by the X-axis and the Y-axis is called the XY plane, and the plane defined by the X-axis and the Z-axis is called the XZ plane. Viewing the XY plane is called planar view.

[0009] Fig. 1 is a plan view illustrating the alignment direction of a plurality of liquid crystal molecules LM in a first liquid crystal layer LC1 of a liquid crystal optical element 1 according to an embodiment of the present invention. Fig. 2 is a cross-sectional view showing the liquid crystal optical element 1 along line II-II in Fig. 1. 2, the liquid crystal optical element 1 includes a substrate 10, a plurality of structures 20, a first liquid crystal layer LC1, and a second liquid crystal layer LC2. Note that Fig. 2 is a cross-sectional view passing through an intersection between the structures 20 and a tangent line (a virtual straight line in the Y direction) of the structures 20.

[0010] The substrate 10 is a transparent substrate that transmits light, and is made of, for example, a transparent glass plate or a transparent synthetic resin plate. The substrate 10 may be made of, for example, a flexible transparent synthetic resin plate. The substrate 10 may have any shape. For example, the substrate 10 may be curved. The refractive index of the substrate 10 is, for example, greater than the refractive index of air.

[0011] In this specification, "light" includes visible light and invisible light. For example, the lower limit of the visible light range is 360 nm to 400 nm, and the upper limit of the visible light range is 760 nm to 830 nm. Visible light includes a first component (blue component) in a first wavelength band (e.g., 400 nm to 500 nm), a second component (green component) in a second wavelength band (e.g., 500 nm to 600 nm), and a third component (red component) in a third wavelength band (e.g., 600 nm to 700 nm). Invisible light includes ultraviolet light in a wavelength band shorter than the first wavelength band, and infrared light in a wavelength band longer than the third wavelength band. In this specification, "transparent" preferably means colorless transparency, however, "transparent" may also mean translucent or colored transparency.

[0012] The substrate 10 is formed in a flat plate shape along the XY plane, and has a main surface F1 and a main surface F2 opposite to the main surface F1. The main surfaces F1 and F2 are surfaces approximately parallel to the XY plane and face each other in the Z direction. The main surface F2 is in contact with air, for example, but may be covered with another thin film.

[0013] The plurality of structures 20 are disposed above the main surface F1. In this embodiment, the plurality of structures 20 are disposed on the main surface F1. Each of the structures 20 is in contact with the main surface F1, but a thin film such as an insulating film may be interposed between the structures 20 and the main surface F1. The structures 20 are formed of, for example, an organic material, but may also be formed of an inorganic material.

[0014] The multiple structures 20 are arranged at intervals in the X direction at a predetermined first pitch p1. Here, the structures 20 are convex bodies extending in the Z direction from the main surface F1. As will be described in detail later, the multiple structures 20 have a function of determining the alignment direction of the liquid crystal molecules LM contained in the first liquid crystal layer LC1.

[0015] The structure 20 has a cross-sectional shape that tapers along the Z direction in the XZ plane. That is, the structure 20 has a bottom surface 20B facing the main surface F1 and a top surface 20T opposite the bottom surface 20B. In this embodiment, the bottom surface 20B is in contact with the main surface F1. In the direction in which the pair of structures 20 are adjacent to each other (X direction), the width WB of the bottom surface 20B is greater than the width WT of the top surface 20T.

[0016] 1, the main surface F1 is exposed between the adjacent bottom surfaces 20B. However, the main surface F1 between the adjacent bottom surfaces 20B may be covered with a thin film. Furthermore, the structure 20 has a side surface 20S between the bottom surface 20B and the top surface 20T. The side surface 20S of one structure 20 and the side surface 20S of an adjacent structure 20 face each other in the X direction. Each of the side surfaces 20S is an inclined surface inclined with respect to the Z direction.

[0017] In a configuration example in which the structure 20 is in contact with the substrate 10, the refractive index of the structure 20 is substantially the same as the refractive index of the substrate 10. Therefore, light that reaches the interface between the substrate 10 and the structure 20 is hardly refracted.

[0018] Each of the structures 20 has a substantially constant height T20. The height T20 corresponds to the distance from the bottom surface 20B to the top surface 20T in the Z direction. The height T20 of the structures 20 exceeds the width WB of the bottom surface 20B. In one example, the height T20 is 100 to 2000 nm, and preferably 300 to 1000 nm. As described above, it is preferable that the height T20 be 1 μm or less, and the retardation of the first liquid crystal layer LC1 be small.

[0019] The width WB is, for example, 50 to 1500 nm, and preferably 100 to 1000 nm. The ratio (WB / T20) of the width WB to the height T20 is smaller than 1 and larger than 0.1.

[0020] The angle θ between the side surface 20S and the bottom surface 20B of the structure 20 is preferably smaller than 90°. In one example, the angle θ is 65° to 88°, and preferably 75° to 85°. A pair of adjacent structures 20 among the multiple structures 20 forms a groove g between them.

[0021] The first liquid crystal layer LC1 is provided between the multiple structures 20 and surrounds each of the structures 20. The first liquid crystal layer LC1 has a first surface S1 facing the main surface F1 and a second surface S2 opposite to the first surface S1. In this embodiment, the top surface 20T is covered with the first liquid crystal layer LC1 and is located between the main surface F1 and the second surface S2.

[0022] The first surface S1 is an uneven surface, and is in contact with the top surface 20T and the side surface 20S. Moreover, in the example shown in Fig. 1, the first surface S1 is in contact with the main surface F1 between adjacent structures 20. Note that a horizontal alignment film may be interposed between the first liquid crystal layer LC1 and the base including the substrate 10 and the plurality of structures 20. When the horizontal alignment film is used, it is not necessary to perform an alignment treatment on the horizontal alignment film.

[0023] The first liquid crystal layer LC1 has a thickness DLC1. The thickness DLC1 corresponds to the distance in the Z direction from the first surface S1 to the second surface S2 in a region outside the structures 20. In this embodiment, the thickness DLC1 exceeds the height T20.

[0024] Furthermore, the distance L between the bottom surfaces 20B of a pair of structures 20 adjacent in the X direction is substantially the same as or less than the height T20. In one example, the ratio (L / T20) of the distance L to the height T20 is 1 or less and exceeds 0.3. The distance L is 50 to 1500 nm, and preferably 100 to 1000 nm.

[0025] In this embodiment, the width WB is less than the distance L and is less than the height T20. Also, in this embodiment, WB=130 nm, L=280 nm, and T20=450 nm.

[0026] From the viewpoint of defining the alignment direction of the liquid crystal molecules LM, it is desirable that the distance L is short and that the height T20 is large. However, in consideration of the productivity in forming the structure 20 by a manufacturing method using a mold described later, it is desirable that the distance L is large and that the height T20 is small.

[0027] The liquid crystal molecules LM of the first liquid crystal layer LC1 are located between adjacent structures 20 and also above the structures 20. The alignment direction of the liquid crystal molecules LM of the first liquid crystal layer LC1 is determined by the adjacent structures 20. The relationship between the alignment direction and the structures 20 will be described later with reference to FIG.

[0028] In the first liquid crystal layer LC1, the alignment direction of the multiple liquid crystal molecules LM that are continuous in the Z direction is uniform. In other words, the director of the first liquid crystal layer LC1 is uniform over the entire area that is continuous in the Z direction. The multiple liquid crystal molecules LM of the first liquid crystal layer LC1 are aligned due to the excluded volume effect. In the groove g, the director of the first liquid crystal layer LC1 extends along the groove g. As a result, the multiple liquid crystal molecules LM are each aligned in a predetermined direction in the XY plane.

[0029] The first liquid crystal layer LC1 has nematic liquid crystal. The first liquid crystal layer LC1 is made of ultraviolet-curable nematic liquid crystal. Therefore, the liquid crystal molecules LM that are continuous in the Z direction are not twisted.

[0030] Here, let us assume that the first liquid crystal layer LC1 is made of ultraviolet-curable cholesteric liquid crystal. In the case of cholesteric liquid crystal, multiple liquid crystal molecules LM that are continuous in the Z direction are twisted. This is because the size of the liquid crystal molecules LM of cholesteric liquid crystal is several nm, and from a geometrical point of view, the liquid crystal molecules LM are not aligned along the grooves g.

[0031] The first liquid crystal layer LC1 using nematic liquid crystal is hardened with the alignment direction of the liquid crystal molecules LM fixed. In other words, the alignment direction of the liquid crystal molecules LM is not controlled according to an electric field. Such a first liquid crystal layer LC1 is formed, for example, by applying energy such as light to a monomer to polymerize it. The first liquid crystal layer LC1 functions as an alignment film.

[0032] The second liquid crystal layer LC2 has a third surface S3 that faces the top surface 20T and is in contact with the second surface S2, and a fourth surface S4 on the opposite side to the third surface S3. In this embodiment, the third surface S3 is not in contact with the top surface 20T. The second liquid crystal layer LC2 has a thickness DLC2. The thickness DLC2 corresponds to the distance from the third surface S3 to the fourth surface S4 in the Z direction. In one example, the thickness DLC2 is 1000 to 14000 nm, and preferably 5000 to 12000 nm.

[0033] 2, no other thin films or substrates are overlapped on the second liquid crystal layer LC2 in the Z direction. That is, in the second liquid crystal layer LC2, the fourth surface S4 is the surface in contact with the air. Note that the fourth surface S4 may be covered with other thin films such as a horizontal alignment film or a protective film.

[0034] The second liquid crystal layer LC2 has a plurality of liquid crystal structures LMS. The liquid crystal structure LMS has first liquid crystal molecules LM1 located at one end of the second liquid crystal layer LC2 and second liquid crystal molecules LM2 located at the other end of the second liquid crystal layer LC2. The first liquid crystal molecules LM1 are adjacent to the third surface S3, and the second liquid crystal molecules LM2 are adjacent to the fourth surface S4.

[0035] The director of the second liquid crystal layer LC2 is aligned with the director of the first liquid crystal layer LC1 on the second surface S2 side at the third surface S3 side. For example, in the region overlapping with the groove g, the director of the second liquid crystal layer LC2 is aligned with the director of the first liquid crystal layer LC1 on the second surface S2 side at the third surface S3 side. In the cross section of FIG. 2, the director of the second liquid crystal layer LC2 on the third surface S3 side and the director of the first liquid crystal layer LC1 on the second surface S2 side are parallel to the Y direction. In a plan view, the director of the second liquid crystal layer LC2 is rotated.

[0036] The alignment direction of the first liquid crystal molecules LM1 is determined by the alignment restraining force of the first liquid crystal layer LC1 functioning as an alignment film. Each liquid crystal structure LMS can be regarded as a continuum in which a plurality of liquid crystal molecules, including the first liquid crystal molecules LM1 and the second liquid crystal molecules LM2, are aligned in the Z direction. Therefore, by determining the alignment direction of the first liquid crystal molecules LM1, the alignment direction of the plurality of liquid crystal molecules aligned in the Z direction, including the second liquid crystal molecules LM2, is determined according to the alignment direction of the first liquid crystal molecules LM1. As a result, the plurality of liquid crystal molecules, including the first liquid crystal molecules LM1 and the second liquid crystal molecules LM2 in each liquid crystal structure LMS, are each aligned in a predetermined direction in the XY plane.

[0037] The second liquid crystal layer LC2 has cholesteric liquid crystal. The second liquid crystal layer LC2 is formed of ultraviolet-curable cholesteric liquid crystal. The second liquid crystal layer LC2 is cured in a state in which the alignment direction of the liquid crystal molecules LM including the first liquid crystal molecules LM1 and the second liquid crystal molecules LM2 is fixed. In other words, the alignment direction of the liquid crystal molecules LM is not controlled according to an electric field. Such a second liquid crystal layer LC2 is formed, for example, by applying energy such as light to a monomer to polymerize it. The second liquid crystal layer LC2 functions as an optical layer.

[0038] In the first liquid crystal layer LC1 and the second liquid crystal layer LC2, the alignment direction of the liquid crystal molecules LM is not controlled in response to an electric field, and therefore the liquid crystal optical element 1 does not include electrodes for alignment control.

[0039] 1, the multiple structures 20 are formed to have substantially the same shape in a plan view, and are each curved. In a plan view, each groove g is also curved. The multiple structures 20 are arranged at intervals in the X direction.

[0040] The liquid crystal molecules LM of the first liquid crystal layer LC1 between a pair of structures 20 adjacent in the X direction are hardened with their long axes LX aligned along a tangent line TL of the structures 20. The tangent line TL here is, for example, a tangent line that contacts the outer edge of the bottom surface 20B of the structures 20. In other words, in the region overlapping with the groove g, the director of the first liquid crystal layer LC1 is aligned with the groove g.

[0041] 3, 4, 5, and 6 are diagrams for explaining an example of a method for manufacturing the liquid crystal optical element 1. FIG. 3, when the manufacturing of the liquid crystal optical element 1 is started, first, in step ST1, the substrate 10 is prepared, a transparent structural material 20M is applied to the main surface F1 of the substrate 10, and the solvent is removed to form a provisionally cured state of the structural material 20M. Here, an ultraviolet curable resin can be used as the structural material 20M.

[0042] 4, when the process proceeds to step ST2, a mold MD in which recesses corresponding to the shape of the structure 20 are prepared in advance is placed on the structure material 20M, and ultraviolet light is applied while applying pressure to the mold MD. This causes the structure material 20M to harden into a shape corresponding to the recesses of the mold MD, forming the structure 20. Thereafter, the mold MD is removed.

[0043] 4, ultraviolet light is applied in a state in which the convex portion CV of the mold MD is in contact with the main surface F1. As a result, the formed structures 20 are separated from each other, and the main surface F1 between the structures 20 is exposed. When the mold MD is pressed, ultraviolet rays may be irradiated in a state in which the structural material 20M is interposed between the protrusions CV and the main surface F1. In this case, the main surface F1 between the structural bodies 20 is covered with a thin film of the same material as the structural bodies 20.

[0044] 5, proceeding to step ST3, a first liquid crystal layer LC1 is formed on the substrate 10 and the structure 20. The first liquid crystal layer LC1 is formed, for example, as follows. First, ultraviolet-curable nematic liquid crystal is applied so as to contact the main surface F1 and the structure 20. Then, light such as ultraviolet light is irradiated to cure the ultraviolet-curable nematic liquid crystal, thereby forming the first liquid crystal layer LC1.

[0045] However, before the nematic liquid crystal is cured, the alignment direction of the liquid crystal molecules LM contained in the nematic liquid crystal is fixed as follows. That is, in the region overlapping with the groove g, the liquid crystal molecules LM of the first liquid crystal layer LC1 are aligned along the groove g, are horizontally aligned along the XY plane, and the long axes of the liquid crystal molecules LM are aligned along the tangent line of the structure 20. The alignment directions of the liquid crystal molecules LM aligned in the Z direction are substantially the same. The liquid crystal molecules LM located above the structure 20 are aligned following the liquid crystal molecules LM around them. In this manner, after the alignment direction of the plurality of liquid crystal molecules LM is fixed, a hardening process of the nematic liquid crystal is carried out.

[0046] As shown in Fig. 5, thereafter, the process proceeds to step ST4, where a second liquid crystal layer LC2 is formed on the first liquid crystal layer LC1. The second liquid crystal layer LC2 is formed, for example, as follows. First, ultraviolet-curable cholesteric liquid crystal is applied so as to contact the second surface S2. Then, the ultraviolet-curable cholesteric liquid crystal is cured by irradiating it with light such as ultraviolet light, thereby forming the second liquid crystal layer LC2.

[0047] However, before the cholesteric liquid crystal is cured, the alignment direction of the liquid crystal molecules contained in the cholesteric liquid crystal is fixed as follows. That is, the first liquid crystal molecules LM1 adjacent to the first liquid crystal layer LC1 are aligned along the liquid crystal molecules LM of the first liquid crystal layer LC1. The alignment direction of the liquid crystal molecules (including the second liquid crystal molecules LM2) LM overlapping the first liquid crystal molecules LM1 in the Z direction is determined according to the alignment direction of the first liquid crystal molecules LM1. The cholesteric liquid crystal is a chiral nematic liquid crystal in which a chiral agent is added to a nematic liquid crystal. The liquid crystal molecules LM of the second liquid crystal layer LC2 overlap in the Z direction while rotating with the first liquid crystal molecule LM1 as the starting point.

[0048] In this way, after the alignment direction of each liquid crystal molecule LM is fixed in accordance with the alignment direction of the first liquid crystal molecule LM1, a hardening process of the cholesteric liquid crystal is carried out. Through the above-mentioned steps, the production of the liquid crystal optical element 1 is completed.

[0049] According to the liquid crystal optical element 1 configured as described above, the structure 20 is formed by utilizing nanoimprint technology. The minute structure 20 can be easily formed by using a mold MD having minute irregularities on the order of the wavelength of light. Such a structure 20 has a function of determining the alignment direction of liquid crystal molecules LM contained in nematic liquid crystal when the nematic liquid crystal is applied. The nematic liquid crystal itself has the property of aligning the alignment direction of a plurality of liquid crystal molecules LM along the Z direction.

[0050] The pattern of the structure 20 is formed so that the liquid crystal molecules LM form a desired alignment pattern. Therefore, the nematic liquid crystal is cured with the alignment direction of each liquid crystal molecule fixed in a predetermined direction, and a first liquid crystal layer LC1 is formed. The cholesteric liquid crystal is also cured with the alignment direction of each liquid crystal molecule fixed in a predetermined direction, and a second liquid crystal layer LC2 is formed. The second liquid crystal layer LC2 having a predetermined retardation is formed. Therefore, it is possible to obtain a liquid crystal optical element 1 having desired optical characteristics. Also, it is possible to obtain a liquid crystal optical element 1 that can be mass-produced.

[0051] It is also possible to perform an orientation process by patterning the orientation instead of forming the structure 20. It is assumed that the orientation patterning can be realized by mask exposure, interference, or direct drawing, but the problem is that it is not suitable for mass production. In addition, by adopting nanoimprint technology, it is possible to handle large sizes, which are difficult to achieve by interference or linear drawing.

[0052] Next, a specific configuration example of the liquid crystal optical element 1 according to this embodiment will be described. Fig. 7 is a cross-sectional view showing the liquid crystal optical element 1 taken along line VII-VII in Fig. 1. The liquid crystal optical element 1 functions as a reflective diffraction grating.

[0053] As shown in Fig. 7, the second liquid crystal layer LC2 has cholesteric liquid crystal. In Fig. 7, for the sake of simplicity, one liquid crystal molecule LM is shown as a representative of the liquid crystal molecules positioned in the XY plane that are aligned in the average alignment direction. In other words, the direction of each liquid crystal molecule LM is the same as the director. The alignment direction of the first liquid crystal molecules LM1 aligned along the second surface S2 of the first liquid crystal layer LC1 changes continuously in the Y direction.

[0054] Focusing on one liquid crystal structure LMS, a plurality of liquid crystal molecules LM are stacked in a spiral shape in the Z direction while rotating. The alignment direction of the first liquid crystal molecule LM1 and the alignment direction of the second liquid crystal molecule LM2 are substantially the same. The liquid crystal structure LMS has a helical pitch pLC2. The helical pitch pLC2 represents one period of the helix (360°).

[0055] The second liquid crystal layer LC2 has a plurality of reflecting surfaces 13 as indicated by dashed lines. In one example, the plurality of reflecting surfaces 13 are substantially parallel to one another. The reflecting surfaces 13 are inclined with respect to the second surface S2 and have a substantially planar shape extending in a fixed direction. The reflecting surfaces 13 selectively reflect a portion of the light LTr of the incident light LTi according to Bragg's law, and transmit the remaining light LTt. The reflecting surfaces 13 reflect the light LTr according to the inclination angle φ of the reflecting surfaces 13 with respect to the second surface S2.

[0056] In the example shown in Figure 7, the helical pitch pLC2 is shown as the distance in the Z direction between the first liquid crystal molecule LM1 and the second liquid crystal molecule LM2, but from the standpoint of improving the reflectance at the reflective surface 13, it is desirable for the thickness DLC2 of the second liquid crystal layer LC2 to be five times or more the helical pitch pLC2.

[0057] The second liquid crystal layer LC2 made of cholesteric liquid crystal selectively reflects light. The reflection efficiency of the second liquid crystal layer LC2 varies depending on the relationship between the thickness DLC2 and the helical pitch pLC2. The thickness DLC2 depends on the parameters of the second liquid crystal layer LC2, such as the helical pitch pLC2.

[0058] As described above, from the viewpoint of reflection efficiency, it is desirable that the thickness DLC2 is 5 times or more the helical pitch pLC2. However, even if the thickness DLC2 is 4 times or more the helical pitch pLC2, the desired reflection efficiency may be obtained. When the thickness DLC2 is about 4.5 times the helical pitch pLC2, the reflection efficiency tends to saturate.

[0059] If the thickness DLC2 is about three times the helical pitch pLC2, it is difficult to obtain a desired reflection efficiency, because if the thickness DLC2 is too small, the reflection efficiency decreases. On the other hand, if the thickness DLC2 becomes too large, it will not affect the reflection efficiency, but it will be difficult to apply liquid crystal. Also, it will be difficult to align the liquid crystal molecules LM on the fourth surface S4 side of the second liquid crystal layer LC2, because an alignment regulating force cannot be applied to the liquid crystal molecules LM on the fourth surface S4 side of the second liquid crystal layer LC2 from the side facing the fourth surface S4.

[0060] The reflecting surface 13 here corresponds to a surface on which the liquid crystal molecules LM are aligned in the same direction, or a surface on which the spatial phase is aligned (equiphase surface). The shape of the reflecting surface 13 is not limited to a flat shape, and may be a concave or convex curved shape, and is not particularly limited. Also, the reflecting surface 13 may have a part with unevenness, the inclination angle φ of the reflecting surface 13 may not be uniform, or the multiple reflecting surfaces 13 may not be regularly aligned. The reflecting surface 13 of any shape can be configured according to the spatial phase distribution of the liquid crystal structure LMS.

[0061] The cholesteric liquid crystal, which is the liquid crystal structure LMS, reflects circularly polarized light having the same rotation direction as the cholesteric liquid crystal, among the light of a specific wavelength λ included in the selective reflection band Δλ. For example, when the rotation direction of the cholesteric liquid crystal is clockwise, it reflects right-handed circularly polarized light and transmits left-handed circularly polarized light among the light of the specific wavelength λ. Similarly, when the rotation direction of the cholesteric liquid crystal is counterclockwise, it reflects left-handed circularly polarized light and transmits right-handed circularly polarized light among the light of the specific wavelength λ.

[0062] If the helical pitch of the cholesteric liquid crystal is expressed as pLC2, the refractive index of the liquid crystal molecule for extraordinary light as ne, and the refractive index of the liquid crystal molecule for ordinary light as no, then the selective reflection band Δλ of the cholesteric liquid crystal for perpendicularly incident light is generally expressed as "no*pLC2 to ne*pLC2." In more detail, the selective reflection band Δλ of the cholesteric liquid crystal changes within the range of "no*pLC2 to ne*pLC2" depending on the inclination angle φ of the reflecting surface 13, the incident angle θi, and the like.

[0063] In the liquid crystal optical element 1 that functions as a reflective diffraction grating, the cholesteric liquid crystal of the second liquid crystal layer LC2 has periodicity, for example, by having a reflective surface 13. The second liquid crystal layer LC2 is capable of reflecting and diffracting only light of a specific wavelength.

[0064] (Example of orientation pattern) Next, an example of the alignment pattern in the first liquid crystal layer LC1 will be described. Fig. 8 is a plan view showing the alignment pattern in the first liquid crystal layer LC1. In Fig. 8, the structures 20 are omitted.

[0065] As shown in Fig. 8, the alignment directions of the liquid crystal molecules LM aligned in the Y direction are different from each other. In other words, the spatial phase in the XY plane is different along the Y direction. For example, the alignment direction of each of the liquid crystal molecules LM changes by a certain angle along the Y direction (from left to right in the figure). Here, the amount of change in the alignment direction of the liquid crystal molecules LM is constant along the Y direction, but it may gradually increase or decrease.

[0066] Here, as shown in FIG. 8, the interval between two liquid crystal molecules LM when the alignment direction of the first liquid crystal molecule LM1 changes by 180° along the Y direction is defined as an alignment pitch α. On the other hand, the alignment directions of the liquid crystal molecules LM aligned in the X direction are substantially the same, that is, the spatial phases in the XY plane are substantially the same in the X direction.

[0067] Next, some layout examples of the structure 20 for realizing the orientation pattern shown in FIG. 8 will be described.

[0068] (First layout) Fig. 9 is a plan view showing a first layout of a plurality of structures 20. As shown in Fig. 9, the first layout corresponds to an example in which the plurality of structures 20 have one type of structure (first structure) 21. Each of the structures 21 is similarly curved in plan view.

[0069] The multiple structures 21 are arranged in the X direction and the Y direction. The multiple structures 21 are lined up in the X direction at a first pitch p1. The multiple structures 21 are lined up in the Y direction at a second pitch p2 different from the first pitch p1. In one example, the second pitch p2 is larger than the first pitch p1. The second pitch p2 is equivalent to the orientation pitch α shown in FIG. 8. The pair of structures 20 that form the groove g is a pair of structures 21 that are adjacent to each other in the X direction among the multiple structures 21.

[0070] According to such a first layout, the liquid crystal molecules in the grooves g are aligned so as to be aligned along the tangents of the structures 21. The liquid crystal molecules in the grooves g are aligned along the grooves g. The alignment direction of the liquid crystal molecules aligned in the Y direction changes continuously. The liquid crystal molecules between the structures 21 adjacent in the Y direction are aligned in the X direction.

[0071] (2nd layout) Fig. 10 is a plan view showing a second layout of a plurality of structures 20. As shown in Fig. 10, the second layout corresponds to an example in which the plurality of structures 20 have a plurality of types of structures (first structures) 21 and structures (second structures) 22. That is, the second layout differs from the first layout in that structures 22 are added. Each of the structures 22 has a different shape from the structures 21 in a plan view and is curved.

[0072] The different shapes here include cases where the overall length of the structure 22 is different from the overall length of the structure 21, and cases where the curvature of the structure 22 is different from the curvature of the structure 21. In the example shown in FIG. 10, the overall length of the structure 22 is shorter than the overall length of the structure 21, but the curvature of the structure 22 is substantially the same as the curvature of the structure 21.

[0073] The multiple structures 22 are arranged in the X direction and the Y direction. In the X direction, the structures 21 and the structures 22 are arranged alternately. Focusing on one structure 22, the structure 22 is disposed between a pair of structures 21 adjacent to each other in the X direction. Moreover, one structure 22 is disposed at approximately the midpoint between the pair of structures 21. Note that multiple structures 22 may be disposed between the pair of structures 21.

[0074] The multiple structures 22 are arranged in the X direction at a pitch p11. The multiple structures 22 are also arranged in the Y direction at a pitch p12 different from the pitch p11. In one example, the pitch p11 is equal to the first pitch p1, the pitch p12 is equal to the second pitch p2, and the pitch p12 is equal to the orientation pitch α.

[0075] According to such a second layout, the liquid crystal molecules between the structures 21 and 22 adjacent to each other in the X direction are aligned along the tangents of the structures 21 and 22. The structures 21 and 22 form a groove ga therebetween, and the liquid crystal molecules are aligned in the groove ga along the groove ga. The alignment direction of the liquid crystal molecules aligned in the Y direction changes continuously. The liquid crystal molecules between the structures 21 adjacent to each other in the Y direction are aligned in the X direction.

[0076] (3rd layout) Fig. 11 is a plan view showing a third layout of a plurality of structures 20. As shown in Fig. 11, the third layout corresponds to an example in which the plurality of structures 20 have a plurality of types of structures (first structures) 21 and structures (third structures) 23. That is, the third layout differs from the first layout in that structures 23 are added. Note that in the third layout, structures 22 may be further added as in the second layout shown in Fig. 10.

[0077] The plurality of structures 21 include a plurality of first structures 21 that belong to each group Gr and are arranged in the X direction. For example, the plurality of first structures 21 that belong to the first group Gr1 and the plurality of first structures 21 that belong to the second group Gr2 are adjacent to each other in the Y direction.

[0078] Each of the structures 23 has a different shape from the structures 21 in a plan view, and extends linearly in the X direction. The structures 23 are disposed between the structures 21 adjacent to each other in the Y direction. For example, the structures 23 are positioned between the first group Gr1 and the second group Gr2. The structures 23 are arranged at a pitch p22 in the Y direction. In one example, the pitch p22 is equal to the second pitch p2, and the pitch p22 is equal to the orientation pitch α.

[0079] According to such a third layout, the liquid crystal molecules between the structures 21 adjacent to each other in the X direction are oriented along the tangents of the structures 21, and the orientation direction of the liquid crystal molecules aligned in the Y direction changes continuously. The liquid crystal molecules between the structures 21 adjacent to each other in the Y direction are oriented along the structures 23.

[0080] As described above, according to this embodiment, it is possible to obtain the liquid crystal optical element 1 that can be mass-produced.

[0081] Although the embodiment of the present invention has been described, the above embodiment is presented as an example and is not intended to limit the scope of the invention. The above novel embodiment can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. The above embodiment and its modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

[0082] 12, the second surface S2 of the first liquid crystal layer LC1 may be located on the same plane as the top surface 20T of the structure 20. The third surface S3 of the second liquid crystal layer LC2 is in contact with the second surface S2 and the multiple top surfaces 20T. In the second liquid crystal layer LC2, the alignment direction of the first liquid crystal molecules LM1 directly above the structure 20 is also restricted. This is because the first liquid crystal molecules LM1 directly above the structure 20 do not receive an alignment restricting force from the first liquid crystal layer LC1, but an alignment restricting force acts between the first liquid crystal layers LC1 adjacent in the X direction or Y direction.

[0083] The application of the above-mentioned liquid crystal optical element 1 is not limited to a reflective diffraction grating. By patterning the liquid crystal orientation, the liquid crystal optical element 1 can also be applied to optical elements such as reflective lenses and holograms. 。 The invention as originally claimed in the present application is set forth below. [1] A substrate having a primary surface; a plurality of structures arranged at intervals, each having a bottom surface facing the main surface and a top surface opposite the bottom surface; a first liquid crystal layer having a first surface facing the main surface, a second surface opposite to the first surface, and a plurality of liquid crystal molecules having a fixed alignment direction, the first liquid crystal layer being provided between the plurality of structures and being hardened; a third surface facing the upper surface and in contact with the second surface, a fourth surface opposite the third surface, and a second liquid crystal layer having a plurality of liquid crystal molecules whose alignment direction is fixed, the second liquid crystal layer being hardened; A pair of adjacent structures among the plurality of structures forms a groove therebetween, In the region overlapping the groove, a first director of the first liquid crystal layer aligned along the groove; a second director of the second liquid crystal layer aligned with the first director on the second surface side on the third surface side and rotated in a plan view; Liquid crystal optical element. [2] the second surface is located on the same plane as the upper surface; or the upper surface is covered with the first liquid crystal layer and is located between the main surface and the second surface; The liquid crystal optical element according to [1]. [3] each of the structures is formed of a transparent organic material; In a direction in which the pair of structures are adjacent to each other, a width of the bottom surface is larger than a width of the top surface. The liquid crystal optical element according to [1]. [4] The refractive index of each of the structures is substantially the same as the refractive index of the substrate; The liquid crystal optical element according to [3]. [5] the height of each of the structures exceeds the width of the base; The liquid crystal optical element according to [3]. [6] A distance between the bottom surfaces of the pair of structures in a direction in which the pair of structures are adjacent to each other is substantially equal to or less than a height of each of the structures. The liquid crystal optical element according to [1]. [7] In a plan view, each of the pair of structures and the groove is curved. The liquid crystal optical element according to [1]. [8] The plurality of structures includes a plurality of curved first structures, the plurality of first structures are arranged at a first pitch in a first direction and at a second pitch different from the first pitch in a second direction intersecting the first direction; The pair of structures is a pair of first structures adjacent to each other in the first direction among the plurality of first structures. The liquid crystal optical element according to [1]. [9] The plurality of structures further includes a second structure disposed between the pair of first structures, The second structure has a different shape than the first structure and is curved. The liquid crystal optical element according to [8].

[10] The plurality of first structures are a plurality of first structures belonging to a first group and arranged in the first direction; a plurality of first structures that belong to a second group adjacent to the first group in the second direction and are arranged in the first direction, the plurality of structures further includes a third structure positioned between the first group and the second group and extending linearly in the first direction; The liquid crystal optical element according to [8].

[11] The first liquid crystal layer includes a nematic liquid crystal. The second liquid crystal layer has a cholesteric liquid crystal. The liquid crystal optical element according to [1]. [Explanation of symbols]

[0084] 1... liquid crystal optical element, 10... substrate, F1... main surface, 20, 21, 22, 23... structure, 20B...Bottom, 20S...Side, 20T...Top, Gr,Gr1,Gr2...Group, g, ga...groove, LC1...first liquid crystal layer, S1...first surface, S2...second surface, LC2...second liquid crystal layer, S3...third surface, S4...fourth surface, LM,LM1,LM2...liquid crystal molecules, LMS...liquid crystal structure, WB,WT...width, T20...height, L...distance, p1...first pitch, p2...second pitch, DLC1, DLC2...thickness. pLC2...helical pitch.

Claims

1. A substrate having a major surface; a plurality of structures arranged at intervals, each having a bottom surface facing the main surface and a top surface opposite the bottom surface; a first liquid crystal layer having a first surface facing the main surface, a second surface opposite to the first surface, and a plurality of liquid crystal molecules having a fixed alignment direction, the first liquid crystal layer being provided between the plurality of structures and being hardened; a second liquid crystal layer having a third surface facing the upper surface and in contact with the second surface, a fourth surface opposite to the third surface, and a plurality of liquid crystal molecules having a fixed alignment direction, the second liquid crystal layer being hardened; A pair of adjacent structures among the plurality of structures forms a groove therebetween, In the region overlapping the groove, a first director of the first liquid crystal layer aligned along the groove; a second director of the second liquid crystal layer is aligned with the first director of the second surface side on the third surface side and rotates in a plan view; The plurality of structures includes a plurality of curved first structures and a second structure disposed between the pair of structures, the plurality of first structures are arranged at a first pitch in a first direction and at a second pitch different from the first pitch in a second direction intersecting the first direction; the pair of structures is a pair of first structures adjacent to each other in the first direction among the plurality of first structures, The second structure has a different shape than the first structure and is curved. Liquid crystal optical element.

2. A substrate having a major surface; a plurality of structures arranged at intervals, each having a bottom surface facing the main surface and a top surface opposite the bottom surface; a first liquid crystal layer having a first surface facing the main surface, a second surface opposite to the first surface, and a plurality of liquid crystal molecules having a fixed alignment direction, the first liquid crystal layer being provided between the plurality of structures and being hardened; a second liquid crystal layer having a third surface facing the upper surface and in contact with the second surface, a fourth surface opposite to the third surface, and a plurality of liquid crystal molecules having a fixed alignment direction, the second liquid crystal layer being hardened; A pair of adjacent structures among the plurality of structures forms a groove therebetween, In the region overlapping the groove, a first director of the first liquid crystal layer aligned along the groove; a second director of the second liquid crystal layer is aligned with the first director of the second surface side on the third surface side and rotates in a plan view; The plurality of structures includes a plurality of curved first structures, the plurality of first structures are arranged at a first pitch in a first direction and at a second pitch different from the first pitch in a second direction intersecting the first direction; the pair of structures is a pair of first structures adjacent to each other in the first direction among the plurality of first structures, The plurality of first structures include A plurality of first structures belonging to a first group and arranged in the first direction; a plurality of first structures that belong to a second group adjacent to the first group in the second direction and are arranged in the first direction, the plurality of structures further includes a third structure positioned between the first group and the second group and extending linearly in the first direction; Liquid crystal optical element.

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