Liquid crystal optical element and display device

Abstract

To provide a liquid crystal optical element which can limit a reflection band width.SOLUTION: According to an embodiment, the liquid crystal optical element includes: a transparent substrate; and a liquid crystal layer facing the transparent substrate, the liquid crystal layer having a cholesteric liquid crystal and a liquid crystal layer with an additive showing the liquid crystal property. The anisotropy of the index of refraction of the additive is smaller than that of the liquid crystal layer.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a liquid crystal optical element and a display device. [Background technology]

[0002] For example, a liquid crystal polarization grating using a liquid crystal material has been proposed. In order to achieve the desired optical performance, it is necessary to adjust various parameters such as the grating period, the refractive index anisotropy Δn of the liquid crystal layer (the difference between the refractive index ne of the liquid crystal layer for extraordinary light and the refractive index no of the liquid crystal layer for ordinary light), and the thickness d of the liquid crystal layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2017-522601 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the embodiments is to provide a liquid crystal optical element and a display device capable of limiting the reflection band. [Means for solving the problem]

[0005] According to one embodiment, the liquid crystal optical element comprises: The liquid crystal display device comprises a transparent substrate and a liquid crystal layer facing the transparent substrate and containing cholesteric liquid crystals and an additive exhibiting liquid crystallinity, the refractive index anisotropy of the additive being smaller than the refractive index anisotropy of the liquid crystal layer.

[0006] According to one embodiment, the liquid crystal optical element comprises: The liquid crystal layer is provided with a transparent substrate and a liquid crystal layer facing the transparent substrate and containing cholesteric liquid crystals and an additive exhibiting liquid crystallinity, the refractive index anisotropy of the additive being smaller than the refractive index anisotropy of the cholesteric liquid crystals.

[0007] According to one embodiment, the display device comprises: a display module configured to face the first main surface in a first region of the transparent substrate and emit display light; a first liquid crystal layer facing the second main surface in the first region and having a first cholesteric liquid crystal; a second liquid crystal layer overlapping the first liquid crystal layer and having a second cholesteric liquid crystal; and a third liquid crystal layer overlapping the second liquid crystal layer and having a third cholesteric liquid crystal, wherein each of the first liquid crystal layer, the second liquid crystal layer, and the third liquid crystal layer has an additive exhibiting liquid crystallinity, the first cholesteric liquid crystal, the second cholesteric liquid crystal, and the third cholesteric liquid crystal have mutually different helical pitches, and a refractive index anisotropy of the additive is smaller than a refractive index anisotropy of each of the first liquid crystal layer, the second liquid crystal layer, and the third liquid crystal layer.

[0008] According to one embodiment, the display device comprises: a first liquid crystal layer facing the second main surface in the first region of the transparent substrate and having a first cholesteric liquid crystal; a second liquid crystal layer overlapping the first liquid crystal layer and having a second cholesteric liquid crystal; and a third liquid crystal layer overlapping the second liquid crystal layer and having a third cholesteric liquid crystal, wherein each of the first liquid crystal layer, the second liquid crystal layer, and the third liquid crystal layer has an additive exhibiting liquid crystallinity, the first cholesteric liquid crystal, the second cholesteric liquid crystal, and the third cholesteric liquid crystal have mutually different helical pitches, and a refractive index anisotropy of the additive is smaller than a refractive index anisotropy of each of the first cholesteric liquid crystal, the second cholesteric liquid crystal, and the third cholesteric liquid crystal. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view that illustrates a liquid crystal optical element 100 according to this embodiment. [Diagram 2]FIG. 2 is a diagram illustrating an example of the cholesteric liquid crystal CL contained in the liquid crystal layer 3. As shown in FIG. [Diagram 3] FIG. 3 is a diagram for explaining another example of the cholesteric liquid crystal CL contained in the liquid crystal layer 3. As shown in FIG. [Figure 4] FIG. 4 is a plan view that diagrammatically illustrates the liquid crystal optical element 100. As shown in FIG. [Diagram 5] FIG. 5 is a diagram showing examples of materials that can be used as the additive 4 in this embodiment. [Figure 6] FIG. 6 is a diagram showing examples of materials that can be used as the additive 4 in this embodiment. [Figure 7] FIG. 7 is a diagram showing examples of materials that can be used as the additive 4 in this embodiment. [Figure 8] FIG. 8 is a diagram showing examples of materials that can be used as the additive 4 in this embodiment. [Figure 9] FIG. 9 is a diagram for explaining a method for manufacturing the liquid crystal optical element 100 according to this embodiment. [Figure 10] FIG. 10 is a diagram for explaining a method for manufacturing the liquid crystal optical element 100 according to this embodiment. [Figure 11] FIG. 11 is a diagram for explaining a method for manufacturing the liquid crystal optical element 100 according to this embodiment. [Figure 12] FIG. 12 is a diagram for explaining how additive 4 permeates liquid crystal layer 3. As shown in FIG. [Figure 13] FIG. 13 is a diagram showing an example of a configuration of the display device 200. As shown in FIG. [Figure 14] FIG. 14 is a diagram for explaining how the display light DL is reflected. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the present embodiment 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, the drawings may be schematic in terms of width, thickness, shape, etc. of each part compared to the actual embodiment in order to make the explanation clearer, but they are merely examples and do not limit the interpretation of the present invention. In addition, in this specification and each figure, components that perform the same or similar functions as those described above with respect to the previous figures are given the same reference numerals, and duplicate detailed explanations may be omitted as appropriate.

[0011] In addition, 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 Z-axis is referred to as the Z direction or the first direction A1, the direction along the Y-axis is referred to as the Y direction or the second direction A2, and the direction along the X-axis is referred to as the X direction or the third direction A3. The plane defined by the X-axis and the Y-axis is referred to as the XY plane, the plane defined by the X-axis and the Z-axis is referred to as the XZ plane, and the plane defined by the Y-axis and the Z-axis is referred to as the YZ plane.

[0012] FIG. 1 is a cross-sectional view that illustrates a liquid crystal optical element 100 according to this embodiment. The liquid crystal optical element 100 includes a transparent substrate 1 , an alignment film 2 , and a liquid crystal layer 3 .

[0013] The transparent substrate 1 is, for example, made of a transparent glass plate or a transparent synthetic resin plate. The transparent substrate 1 may be, for example, made of a flexible transparent synthetic resin plate. The transparent substrate 1 may have any shape. For example, the transparent substrate 1 may be curved.

[0014] In this specification, "light" includes visible light and invisible light. For example, the lower limit of the visible light range is 350 nm to 400 nm, and the upper limit of the visible light range is 700 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.

[0015] The transparent substrate 1 is formed in a flat plate shape along the XY plane, and has a first main surface (outer surface) F1, a second main surface (inner surface) F2, and a side surface S1. The first main surface F1 and the second main surface F2 are surfaces that are substantially parallel to the XY plane, and face each other in the first direction A1. The side surface S1 is a surface that extends along the first direction A1. In the example shown in FIG. 1, the side surface S1 is a surface that is substantially parallel to the XZ plane, but the side surface S1 includes a surface that is substantially parallel to the YZ plane.

[0016] The alignment film 2 is disposed on the second main surface F2. The alignment film 2 is a horizontal alignment film having an alignment regulating force along the XY plane. The alignment film 2 is, for example, a photo-alignment film that can be aligned by light irradiation, but may also be an alignment film that is aligned by rubbing, or may be an alignment film having minute irregularities. Instead of the alignment film 2, an adhesive layer that bonds the liquid crystal layer 3 to the transparent substrate 1 may be provided.

[0017] The liquid crystal layer 3 overlaps the alignment film 2 in the first direction A1. That is, the alignment film 2 is located between the transparent substrate 1 and the liquid crystal layer 3, and is in contact with the transparent substrate 1 and the liquid crystal layer 3. The liquid crystal layer 3 has a third main surface (inner surface) F3 and a fourth main surface (outer surface) F4. The third main surface F3 and the fourth main surface F4 are surfaces substantially parallel to the XY plane and face each other in the first direction A1. The third main surface F3 is in contact with the alignment film 2. The fourth main surface F4 is in contact with, for example, an air layer, but may be covered with a transparent protective layer.

[0018] As shown enlarged and schematic, the liquid crystal layer 3 contains cholesteric liquid crystal CL rotated in a first rotation direction. The cholesteric liquid crystal CL has a helical axis AX substantially parallel to the first direction A1, and has a helical pitch P along the first direction A1. The helical pitch P indicates one period of the helix (the layer thickness along the helical axis AX required for the liquid crystal molecules to rotate 360 ​​degrees).

[0019] The liquid crystal layer 3 has a reflecting surface 3R. The reflecting surface 3R reflects circularly polarized light in a selective reflection band determined according to the helical pitch P of the cholesteric liquid crystal CL and the refractive index anisotropy Δn of the liquid crystal layer 3, among the light incident on the liquid crystal layer 3. For example, when the first rotation direction is clockwise, clockwise circularly polarized light is reflected by the reflecting surface 3R, and when the first rotation direction is counterclockwise, counterclockwise circularly polarized light is reflected by the reflecting surface 3R. In this specification, the "reflection" in the liquid crystal layer 3 involves diffraction inside the liquid crystal layer 3. In this specification, the circularly polarized light may be strictly circularly polarized light or may be circularly polarized light that is close to elliptically polarized light.

[0020] In the example shown in Fig. 1, the liquid crystal layer 3 is configured to reflect a part of the light LTi incident from the first main surface F1 side toward the transparent substrate 1. The liquid crystal layer 3 can also be configured to reflect a part of the light incident from the fourth main surface F4 side. In the liquid crystal optical element 100, a liquid crystal layer having another cholesteric liquid crystal may be laminated on the liquid crystal layer 3 shown in Fig. 1. The other cholesteric liquid crystal may be, for example, a cholesteric liquid crystal having a helical pitch different from the helical pitch P, or a cholesteric liquid crystal rotated in a second rotation direction opposite to the first rotation direction.

[0021] Next, the optical action of the liquid crystal optical element 100 shown in FIG. 1 will be described.

[0022] The light LTi incident on the liquid crystal optical element 100 includes, for example, visible light, ultraviolet light, and infrared light. 1, for ease of understanding, the light LTi is assumed to be incident on the transparent substrate 1 substantially perpendicularly. The incident angle of the light LTi on the transparent substrate 1 is not particularly limited. For example, the light LTi may be incident on the transparent substrate 1 at a plurality of mutually different incident angles.

[0023] The light LTi enters the transparent substrate 1 from the first main surface F1, exits from the second main surface F2, passes through the alignment film 2, and enters the liquid crystal layer 3. The liquid crystal layer 3 reflects a portion of the light LTi at the reflecting surface 3R, and transmits the remaining light LTt. The reflected light LTr is circularly polarized light with a wavelength λ. In one example, the light LTr is a first circularly polarized light in the wavelength band of visible light. The light LTt also contains a second circularly polarized light in the wavelength band of visible light, in addition to infrared and ultraviolet light. The second circularly polarized light is circularly polarized in the opposite direction to the first circularly polarized light.

[0024] The approach angle θ of the light LTr reflected by the liquid crystal layer 3 is set so as to satisfy the optical waveguide condition. The approach angle θ here corresponds to an angle equal to or greater than the critical angle at which total reflection occurs at the interface between the liquid crystal layer 3 and air. The approach angle θ indicates the angle with respect to the normal N of the transparent substrate 1.

[0025] When the transparent substrate 1, the alignment film 2, and the liquid crystal layer 3 have the same refractive index, these laminates can serve as a single optical waveguide. In this case, the light LTr is guided toward the side surface S1 while repeatedly being reflected at the interface between the transparent substrate 1 and the air and at the interface between the liquid crystal layer 3 and the air.

[0026] FIG. 2 is a diagram illustrating an example of the cholesteric liquid crystal CL contained in the liquid crystal layer 3. As shown in FIG. 2, the liquid crystal layer 3 is illustrated enlarged in the first direction A1. For simplification, the liquid crystal molecule LM1 constituting the cholesteric liquid crystal CL is illustrated as one of a plurality of liquid crystal molecules located on the same plane parallel to the XY plane. The orientation direction of the illustrated liquid crystal molecule LM1 corresponds to the average orientation direction of the plurality of liquid crystal molecules located on the same plane.

[0027] The liquid crystal layer 3 contains a cholesteric liquid crystal CL and an additive (guest liquid crystal) 4 exhibiting liquid crystallinity.

[0028] Focusing on one cholesteric liquid crystal CL surrounded by a dotted line, the cholesteric liquid crystal CL is composed of a plurality of liquid crystal molecules LM1 stacked in a spiral shape along the first direction A1 while rotating. The plurality of liquid crystal molecules LM1 include a liquid crystal molecule LM11 at one end side of the cholesteric liquid crystal CL and a liquid crystal molecule LM12 at the other end side of the cholesteric liquid crystal CL. The liquid crystal molecule LM11 is adjacent to the third main surface F3 or the alignment film 2. The liquid crystal molecule LM12 is adjacent to the fourth main surface F4.

[0029] In the liquid crystal layer 3 of the example shown in Fig. 2, the alignment directions of the multiple cholesteric liquid crystals CL adjacent to each other along the second direction A2 are aligned. That is, the alignment directions of the multiple liquid crystal molecules LM11 adjacent to each other along the second direction A2 are substantially aligned. Also, the alignment directions of the multiple liquid crystal molecules LM12 adjacent to each other along the second direction A2 are substantially aligned.

[0030] The reflecting surface 3R of the liquid crystal layer 3 is formed in a planar shape extending along the XY plane, as indicated by the dashed line in the figure. The reflecting surface 3R here corresponds to a surface on which the alignment direction of the liquid crystal molecules LM1 is uniform, or a surface on which the spatial phase is uniform (an equiphase surface).

[0031] Such a liquid crystal layer 3 is hardened with the alignment direction of the liquid crystal molecules LM1 fixed. In other words, the alignment direction of the liquid crystal molecules LM1 is not controlled according to an electric field. For this reason, the liquid crystal optical element 100 does not include electrodes for forming an electric field in the liquid crystal layer 3.

[0032] The additive 4 permeates the liquid crystal layer 3 almost uniformly. The additive 4 is aligned in the same manner as the cholesteric liquid crystal CL. Such an additive 4 has a refractive index anisotropy Δn4. The refractive index anisotropy Δn4 is smaller than the refractive index anisotropy Δn3 of the cholesteric liquid crystal CL (Δn4<Δn3). Therefore, the refractive index anisotropy Δn of the liquid crystal layer 3 decreases according to the amount of the additive 4 added to the liquid crystal layer 3. The refractive index anisotropy Δn does not exceed the refractive index anisotropy Δn4. In other words, the refractive index anisotropy Δn4 is smaller than the refractive index anisotropy Δn (Δn4<Δn). The refractive index anisotropy Δn4 of the additive 4 may be zero. That is, the additive 4 may be an isotropic material.

[0033] Generally, in a liquid crystal layer 3 containing cholesteric liquid crystal CL, the selective reflection band Δλ for perpendicularly incident light is expressed by the following formula (1) based on the helical pitch P of the cholesteric liquid crystal CL and the refractive index anisotropy Δn (the difference between the refractive index ne for extraordinary light and the refractive index no for ordinary light) of the liquid crystal layer 3. Δλ=Δn*P …(1) A specific wavelength range of the selective reflection band Δλ is a range not less than (no*P) and not more than (ne*P).

[0034] The central wavelength λm of the selective reflection band Δλ is expressed by the following formula (2) based on the helical pitch P of the cholesteric liquid crystal CL and the average refractive index nav (=(ne+no) / 2) of the liquid crystal layer 3. λm=nav*P …(2) In one example, the central wavelength λm is a wavelength in the visible light range of 350 nm to 700 nm.

[0035] Based on the above formula (1), in order to limit the selective reflection band Δλ to a small value, it is necessary to reduce the refractive index anisotropy Δn or to reduce the helical pitch P. However, as shown in the above formula (2), the helical pitch P also affects the central wavelength λm. Therefore, in order to narrow the selective reflection band Δλ while suppressing the shift of the central wavelength λm to the short wavelength side, it is effective to reduce the refractive index anisotropy Δn.

[0036] According to this embodiment, the liquid crystal layer 3 contains the additive 4 in addition to the cholesteric liquid crystal CL. The refractive index anisotropy Δn4 of the additive 4 is smaller than the refractive index anisotropy Δn3 of the cholesteric liquid crystal CL. Therefore, the refractive index anisotropy Δn of the liquid crystal layer 3 can be reduced compared to a case where the liquid crystal layer 3 does not contain the additive 4. This allows the selective reflection band Δλ in the liquid crystal layer 3 to be limited to a small value.

[0037] Furthermore, by limiting the selective reflection band Δλ in the liquid crystal layer 3, the transmittance of the liquid crystal optical element 100 is improved.

[0038] Furthermore, even if it is difficult to select a material for forming the cholesteric liquid crystal CL that provides the desired refractive index anisotropy Δn, the desired refractive index anisotropy Δn can be easily achieved by adjusting the amount of additive 4 added.

[0039] FIG. 3 is a diagram for explaining another example of the cholesteric liquid crystal CL contained in the liquid crystal layer 3. As shown in FIG. The example shown in Fig. 3 differs from the example shown in Fig. 2 in that the alignment directions of the plurality of cholesteric liquid crystals CL adjacent to each other along the second direction A2 are different from each other. In addition, the spatial phases of the cholesteric liquid crystals CL adjacent to each other along the second direction A2 are different from each other. The alignment direction of the plurality of liquid crystal molecules LM11 changes continuously along the second direction A2. The alignment direction of the plurality of liquid crystal molecules LM12 also changes continuously along the second direction A2. These alignment directions will be described later.

[0040] The reflecting surface 3R of the liquid crystal layer 3 is inclined with respect to the XY plane as indicated by the dashed line in the figure. The angle φ between the reflecting surface 3R and the XY plane is an acute angle. The shape of the reflecting surface 3R is not limited to the flat shape shown in Figures 2 and 3, and may be a concave or convex curved shape, and is not particularly limited. Also, the reflecting surface 3R may have a part with unevenness, the inclination angle φ of the reflecting surface 3R may not be uniform, and the multiple reflecting surfaces 3R may not be regularly aligned. The reflecting surface 3R can be configured in any shape according to the spatial phase distribution of the multiple cholesteric liquid crystals CL.

[0041] FIG. 4 is a plan view that diagrammatically illustrates the liquid crystal optical element 100. As shown in FIG. An example of the spatial phase of the cholesteric liquid crystal CL is shown in Figure 4. The spatial phase shown here is shown as the alignment direction of the liquid crystal molecule LM11 located in the vicinity of the third main surface F3, among the liquid crystal molecules LM1 contained in the cholesteric liquid crystal CL.

[0042] The alignment directions of the liquid crystal molecules LM11 of the cholesteric liquid crystals CL aligned along the second direction A2 are different from each other, that is, the spatial phases of the cholesteric liquid crystals CL are different along the second direction A2. On the other hand, the alignment directions of the liquid crystal molecules LM11 of the cholesteric liquid crystals CL aligned along the third direction A3 are substantially the same, that is, the spatial phases of the cholesteric liquid crystals CL are substantially the same in the third direction A3.

[0043] In particular, when focusing on the cholesteric liquid crystal CL aligned in the second direction A2, the alignment direction of each liquid crystal molecule LM11 differs by a certain angle. That is, the alignment direction of the liquid crystal molecules LM11 aligned along the second direction A2 changes linearly. Therefore, the spatial phase of the cholesteric liquid crystals CL aligned along the second direction A2 changes linearly along the second direction A2. As a result, a reflection surface 3R inclined with respect to the XY plane is formed, as in the liquid crystal layer 3 shown in FIG. 3. Here, "linearly changes" indicates that, for example, the amount of change in the alignment direction of the liquid crystal molecule LM11 is expressed by a linear function. The alignment direction of the liquid crystal molecule LM11 here corresponds to the long axis direction of the liquid crystal molecule LM11 in the XY plane. Such an alignment direction of the liquid crystal molecule LM11 can be controlled by an alignment treatment performed on the alignment film 2.

[0044] Here, as shown in Fig. 4, the interval between two liquid crystal molecules LM11 when the alignment direction of the liquid crystal molecules LM11 changes by 180 degrees along the second direction A2 in one plane is defined as a period T. In Fig. 4, DP indicates the twist direction of the liquid crystal molecules LM11. The inclination angle φ of the reflecting surface 3R shown in Fig. 3 is appropriately set by the period T and the helical pitch P. The period T is, for example, 350 nm to 700 nm.

[0045] Here, examples of materials that can be used as the additive 4 will be described with reference to FIGS.

[0046] The material examples (1) and (2) shown in Fig. 5 are examples of nematic liquid crystal materials, and are alkoxycyclohexylcyclohexane-based materials. When the major axis of such a nematic liquid crystal material is parallel to the Y axis in the liquid crystal layer 3, the refractive index ny along the Y axis is greater than the refractive index nx along the X axis (ny>nx). In other words, the nematic liquid crystal material has a refractive index anisotropy Δn in the XY plane. Material examples (3) to (6) shown in FIG. 5 are examples of nematic liquid crystal materials, and are cyclohexylcyclohexanevinyl-based materials.

[0047] The material example (7) shown in FIG. 6 is an example of a nematic liquid crystal material, and is an alkylphenylcyclohexane-based material. Material examples (8) to (10) shown in FIG. 6 are examples of nematic liquid crystal materials, and are alkoxyphenylcyclohexane-based materials. Material examples (11) and (12) shown in FIG. 6 are examples of nematic liquid crystal materials, and are fluorophenylcyclohexane-based materials.

[0048] Material examples (13) to (15) shown in FIG. 7 are examples of nematic liquid crystal materials, and are cyanophenylcyclohexane-based materials.

[0049] Material examples (16) to (17) shown in Figure 8 are examples of discotic liquid crystal materials. When the minor axis of such a discotic liquid crystal material is parallel to the Z axis in the liquid crystal layer 3, the refractive index nx along the X axis is equal to the refractive index ny along the Y axis (nx ≒ ny). In other words, the discotic liquid crystal material exhibits isotropy in the XY plane, and the refractive index anisotropy Δn is almost zero.

[0050] Next, a method for manufacturing the liquid crystal optical element 100 will be described.

[0051] First, as shown in FIG. 9, the transparent substrate 1 is cleaned (step ST1). Then, the alignment film 2 is formed on the second main surface F2 of the transparent substrate 1 (step ST2). The alignment film 2 is subjected to a predetermined alignment treatment.

[0052] Then, a liquid crystal material (a solution containing a monomer material for forming cholesteric liquid crystal) is applied onto the alignment film 2 (step ST3). After that, the pressure inside the chamber is reduced to remove the solvent, and the applied liquid crystal material is dried (step ST4), and further, the liquid crystal material is baked (step ST5). By baking, the liquid crystal molecules contained in the liquid crystal material are aligned in a predetermined direction according to the alignment treatment direction of the alignment film 2. Then, the liquid crystal material is cooled to about room temperature (step ST6), and then the liquid crystal material is irradiated with ultraviolet light to harden the liquid crystal material (step ST7). As a result, a liquid crystal layer 3 having cholesteric liquid crystal CL is formed.

[0053] Next, as shown in FIG. 10, a liquid crystal solution is prepared by dissolving the additive 4 in a solvent. The solvent may be an organic solvent such as hexane, cyclohexane, cyclohexanone, heptane, toluene, anisole, or propylene glycol monomethyl ether acetate (PGMEA). Then, the liquid crystal solution is applied to the liquid crystal layer 3 (step ST8). The application here includes immersing the liquid crystal layer 3 in the liquid crystal solution or dropping the liquid crystal solution onto the liquid crystal layer 3. This allows the additive 4 contained in the liquid crystal solution to uniformly permeate the liquid crystal layer 3 together with the solvent. Of the applied liquid crystal solution, excess liquid crystal solution is removed using a spinner or the like. If necessary, an organic solvent may be used to remove the liquid crystal solution. Thereafter, the transparent substrate 1 is heated to remove the solvent that has permeated into the liquid crystal layer 3, and the liquid crystal layer 3 is dried (step ST9). Then, the transparent substrate 1 is cooled to about room temperature (step ST10). The amount of additive 4 added to the liquid crystal layer 3 can be adjusted by the number of times steps ST8 to ST10 are performed. In other words, if it is desired to increase the amount added, steps ST8 to ST10 can be repeated multiple times. In this way, a liquid crystal optical element 100 having the desired reflectivity is manufactured.

[0054] Instead of the process shown in Fig. 10, the process shown in Fig. 11 may be applied. The process shown in Fig. 11 will be described below. First, a liquid additive 4 is prepared. The additive 4 has a relatively low melting point and is liquefied by heating without using a solvent. Then, the additive 4 is applied to the liquid crystal layer 3 (step ST11). The application here includes immersing the liquid crystal layer 3 in the additive 4 and dropping the additive 4 onto the liquid crystal layer 3. This allows the additive 4 to uniformly permeate the liquid crystal layer 3.

[0055] Thereafter, the excess additive 4 is removed using a spinner or the like (step ST12). Note that an organic solvent may be used to remove the excess additive 4, if necessary. Then, the transparent substrate 1 is heated to dry the liquid crystal layer 3 (step ST13). Then, the transparent substrate 1 is cooled to about room temperature (step ST14). The amount of additive 4 added to the liquid crystal layer 3 can be adjusted by the number of times steps ST11 to ST14 are performed. In other words, if it is desired to increase the amount added, steps ST11 to ST14 can be repeated multiple times. In this way, a liquid crystal optical element 100 having the desired reflectivity is manufactured.

[0056] FIG. 12 is a diagram for explaining how additive 4 permeates liquid crystal layer 3. As shown in FIG.

[0057] The left side of Fig. 12 shows the liquid crystal optical element 100 before the liquid crystal solution is applied, and the right side of Fig. 12 shows the liquid crystal optical element 100 after the liquid crystal solution is applied. Note that Fig. 12 is a schematic diagram showing the state in which the additive 4 is added.

[0058] In the liquid crystal layer 3 before the liquid crystal solution is applied, the cholesteric liquid crystal CL has a helical pitch P0. After the liquid crystal solution is applied, the liquid crystal layer 3 swells due to the penetration of the liquid crystal solution containing the additive 4. As a result, the helical pitch P of the cholesteric liquid crystal CL becomes larger than the helical pitch P0.

[0059] The helical pitch P obtained by swelling the liquid crystal layer 3 is set according to the central wavelength λm of the selective reflection band Δλ to be reflected. For example, when the central wavelength λm is 450 nm and the average refractive index nav of the liquid crystal layer 3 is 1.6, the helical pitch P is set to about 280 nm. Furthermore, when the central wavelength λm is 500 nm and the average refractive index nav of the liquid crystal layer 3 is 1.6, the helical pitch P is set to approximately 310 nm. Furthermore, when the central wavelength λm is 600 nm and the average refractive index nav of the liquid crystal layer 3 is 1.6, the helical pitch P is set to approximately 380 nm.

[0060] Thus, in order to set the central wavelength λm to a visible light wavelength of 350 nm to 700 nm in the liquid crystal layer 3 having an average refractive index nav of 1.6, the helical pitch P is set to 200 nm or more and 450 nm or less. In this case, for example, the refractive index anisotropy Δn of the liquid crystal layer 3 is larger than 0.1, and the additive 4 can be a material having a refractive index anisotropy Δn4 smaller than 0.1. From another point of view, for example, the refractive index anisotropy Δn3 of the cholesteric liquid crystal CL is larger than 0.1, and the additive 4 can be a material having a refractive index anisotropy Δn4 smaller than 0.1.

[0061] Application Examples Next, a display device 200 capable of providing augmented reality will be described as an application example of the liquid crystal optical element 100 according to this embodiment.

[0062] FIG. 13 is a diagram showing an example of a configuration of the display device 200. As shown in FIG.

[0063] The display device 200 includes a transparent substrate 1, a display module DM, a first liquid crystal layer 31, a second liquid crystal layer 32, a third liquid crystal layer 33, a fourth liquid crystal layer 34, a fifth liquid crystal layer 35, and a sixth liquid crystal layer 36.

[0064] The transparent substrate 1 is made of a transparent glass plate or a transparent synthetic resin plate, and has a first main surface F1 and a second main surface F2. The transparent substrate 1 also has a first region 1A on one end side thereof and a second region 1B on the other end side thereof. In the illustrated example, the first region 1A and the second region 1B are aligned in the second direction A2 and spaced apart from each other.

[0065] The display module DM faces the first main surface F1 in the first region 1A. The display module DM is configured to emit display light DL. The display module DM may be a combination of a liquid crystal panel and an illumination device including light-emitting elements, or may be a display panel equipped with light-emitting elements such as organic electroluminescence (EL) elements, micro LEDs, and mini LEDs. The display module DM has red light-emitting elements, green light-emitting elements, and blue light-emitting elements as light-emitting elements.

[0066] The red light emitting element is configured to emit red light with a central wavelength λr. The green light emitting element is configured to emit green light with a central wavelength λg. The blue light emitting element is configured to emit blue light with a central wavelength λb. In other words, the display light DL emitted from the display module DM has red light with a central wavelength λr, green light with a central wavelength λg, and blue light with a central wavelength λb.

[0067] The first liquid crystal layer 31 faces the second main surface F2 in the first region 1A and has a first cholesteric liquid crystal CL1. The first liquid crystal layer 31 may be adhered to the second main surface F2 or may be formed on an alignment film (not shown). The first cholesteric liquid crystal CL1 has a helical pitch P1. The first liquid crystal layer 31 has a reflective surface 31R inclined with respect to the second main surface F2.

[0068] The second liquid crystal layer 32 overlaps the first liquid crystal layer 31 and includes a second cholesteric liquid crystal CL2. The second liquid crystal layer 32 is bonded to the first liquid crystal layer 31. The second cholesteric liquid crystal CL2 has a helical pitch P2. The helical pitch P2 is larger than the helical pitch P1 (P2>P1). The second liquid crystal layer 32 also includes a reflective surface 32R inclined with respect to the second main surface F2.

[0069] The third liquid crystal layer 33 overlaps the second liquid crystal layer 32 and has a third cholesteric liquid crystal CL3. The third liquid crystal layer 33 is bonded to the second liquid crystal layer 32. The third cholesteric liquid crystal CL3 has a helical pitch P3. The helical pitch P3 is larger than the helical pitch P2 (P3>P2). The third liquid crystal layer 33 also has a reflective surface 33R inclined with respect to the second main surface F2.

[0070] The reflecting surfaces 31R, 32R, and 33R are all inclined in the same manner. In the illustrated example, the distances between the second main surface F2 and each of the reflecting surfaces 31R, 32R, and 33R in the first direction A1 gradually increase in the direction from the first region 1A to the second region 1B.

[0071] In the illustrated example, the first cholesteric liquid crystal CL1, the second cholesteric liquid crystal CL2, and the third cholesteric liquid crystal CL3 are all rotated in the same direction, but any one of them may be rotated in the opposite direction. Furthermore, the stacking order of the first liquid crystal layer 31, the second liquid crystal layer 32, and the third liquid crystal layer 33 is not limited to the example shown in the figure.

[0072] The fourth liquid crystal layer 34 faces the second main surface F2 in the second region 1B and has a fourth cholesteric liquid crystal CL4. The fourth liquid crystal layer 34 may be adhered to the second main surface F2 or may be formed on an alignment film (not shown). The fourth liquid crystal layer 34 has a reflection surface 34R inclined with respect to the second main surface F2. The fourth cholesteric liquid crystal CL4 has a helical pitch P4. The helical pitch P4 is equal to the helical pitch P1 (P4=P1). The helical pitch P1 and the helical pitch P4 are set according to the central wavelength λb. The first cholesteric liquid crystal CL1 and the fourth cholesteric liquid crystal CL4 are twisted in the same direction.

[0073] The fifth liquid crystal layer 35 overlaps the fourth liquid crystal layer 34, and includes a fifth cholesteric liquid crystal CL5. The fifth liquid crystal layer 35 is adhered to the fourth liquid crystal layer 34. The fifth liquid crystal layer 35 also includes a reflective surface 35R that is inclined with respect to the second main surface F2. The fifth cholesteric liquid crystal CL5 has a helical pitch P5. The helical pitch P5 is larger than the helical pitch P4 (P5>P4) and is equal to the helical pitch P2 (P5=P2). The helical pitch P2 and the helical pitch P5 are set according to the central wavelength λg. The second cholesteric liquid crystal CL2 and the fifth cholesteric liquid crystal CL5 are twisted in the same direction.

[0074] The sixth liquid crystal layer 36 overlaps the fifth liquid crystal layer 35, and includes a sixth cholesteric liquid crystal CL6. The sixth liquid crystal layer 36 is bonded to the fifth liquid crystal layer 35. The sixth liquid crystal layer 36 also includes a reflective surface 36R that is inclined with respect to the second principal surface F2. The sixth cholesteric liquid crystal CL6 has a helical pitch P6. The helical pitch P6 is larger than the helical pitch P5 (P6>P5) and is equal to the helical pitch P3 (P6=P3). The helical pitch P3 and the helical pitch P6 are set according to the central wavelength λr. The third cholesteric liquid crystal CL3 and the sixth cholesteric liquid crystal CL6 are twisted in the same direction.

[0075] The reflecting surfaces 34R, 35R, and 36R are all inclined in the same manner. In the illustrated example, the distances between the reflecting surfaces 34R, 35R, and 36R and the second main surface F2 along the first direction A1 gradually decrease along the direction from the first region 1A to the second region 1B.

[0076] In the illustrated example, the fourth cholesteric liquid crystal CL4, the fifth cholesteric liquid crystal CL5, and the sixth cholesteric liquid crystal CL6 are all rotated in the same direction, but any one of them may be rotated in the opposite direction. Furthermore, the stacking order of the fourth liquid crystal layer 34, the fifth liquid crystal layer 35, and the sixth liquid crystal layer 36 is not limited to the example shown in the figure.

[0077] The second principal surface F2 is in contact with an air layer between the first region 1A and the second region 1B, or between the first liquid crystal layer 31 and the fourth liquid crystal layer 34. The first principal surface F1 is in contact with an air layer over the entire area including the first region 1A and the second region 1B.

[0078] Here, the first liquid crystal layer 31, the second liquid crystal layer 32, the third liquid crystal layer 33, the fourth liquid crystal layer 34, the fifth liquid crystal layer 35, and the sixth liquid crystal layer 36 contain the additive 4 as described with reference to Fig. 3. The refractive index anisotropy of the additive 4 is smaller than the refractive index anisotropy of each of the liquid crystal layers. The refractive index anisotropy of the additive 4 is also smaller than the refractive index anisotropy of each of the cholesteric liquid crystals.

[0079] Next, the optical action of the display device 200 shown in FIG. 13 will be described.

[0080] The display module DM emits display light DL including red light with a central wavelength λr, green light with a central wavelength λg, and blue light with a central wavelength λbr toward the transparent substrate 1. The display light DL enters the transparent substrate 1 from the first main surface F1, exits from the second main surface F2, and enters the first liquid crystal layer 31, the second liquid crystal layer 32, and the third liquid crystal layer 33. Then, a part of the display light DL is reflected by the reflecting surface 31R of the first liquid crystal layer 31, the reflecting surface 32R of the second liquid crystal layer 32, and the reflecting surface 33R of the third liquid crystal layer 33. The reflected light LTr enters the transparent substrate 1 again, and is guided toward the second region 1B while being repeatedly reflected at the interface between the transparent substrate 1 and the air layer between the first region 1A and the second region 1B.

[0081] In the second region 1B, the light LTr exits from the second principal surface F2 and enters the fourth liquid crystal layer 34, the fifth liquid crystal layer 35, and the sixth liquid crystal layer 36. Then, a portion of the light LTr is reflected by the reflective surface 34R of the fourth liquid crystal layer 34, the reflective surface 35R of the fifth liquid crystal layer 35, and the reflective surface 36R of the sixth liquid crystal layer 36. The reflected light LTr passes through the transparent substrate 1. The light LTt that has passed through the transparent substrate 1 is guided to the pupil E of the user.

[0082] On the other hand, each of the first liquid crystal layer 31, the second liquid crystal layer 32, the third liquid crystal layer 33, the fourth liquid crystal layer 34, the fifth liquid crystal layer 35, and the sixth liquid crystal layer 36 reflects only light in a specific selective reflection band included in the external light LTE, and transmits light in other bands. Also, the transparent substrate 1 transmits most of the components of the external light LTE. Therefore, the user can view the image displayed on the display module DM while viewing the surrounding environment of the display device 200.

[0083] FIG. 14 is a diagram for explaining how the display light DL is reflected.

[0084] In the first liquid crystal layer 31, the alignment direction of adjacent first cholesteric liquid crystals CL1 changes linearly to form a reflective surface 31R. The reflective surface 31R reflects circularly polarized blue light having a central wavelength λb out of the display light DL.

[0085] In the second liquid crystal layer 32, the alignment direction of adjacent second cholesteric liquid crystals CL2 changes linearly to form a reflective surface 32R. The reflective surface 32R reflects circularly polarized green light having a central wavelength λg out of the display light DL.

[0086] In the third liquid crystal layer 33, the alignment direction of adjacent third cholesteric liquid crystals CL3 changes linearly to form a reflective surface 33R. The reflective surface 33R reflects circularly polarized red light with a central wavelength λr out of the display light DL.

[0087] In the fourth liquid crystal layer 34, the alignment direction of adjacent fourth cholesteric liquid crystals CL4 changes linearly to form a reflective surface 34R. The reflective surface 34R reflects the blue light LTr with the central wavelength λb reflected by the reflective surface 31R.

[0088] In the fifth liquid crystal layer 35, the alignment direction of the adjacent fifth cholesteric liquid crystal CL5 changes linearly to form a reflective surface 35R. The reflective surface 35R reflects the green light LTr with the central wavelength λg reflected by the reflective surface 32R.

[0089] In the sixth liquid crystal layer 36, the alignment direction of the adjacent sixth cholesteric liquid crystals CL6 changes linearly to form a reflective surface 36R. The reflective surface 36R reflects the red light LTr with the central wavelength λr reflected by the reflective surface 33R.

[0090] The light LTt transmitted through the transparent substrate 1 includes blue light LTr with a central wavelength λb, green light LTr with a central wavelength λg, and red light LTr with a central wavelength λr.

[0091] Such a display device 200 can provide an augmented reality to a user.

[0092] As described above, according to the present embodiment, it is possible to provide a liquid crystal optical element and a display device capable of limiting the reflection band.

[0093] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0094] 100...Liquid crystal optical element 1...Transparent substrate F1...First main surface F2...Second main surface S1...Side surface 3...Liquid crystal layer CL...Cholesteric liquid crystal 3R...Reflective surface 4. Additives 200... Display device DM... Display module 31...First liquid crystal layer CL1...First cholesteric liquid crystal 31R...Reflective surface 32...Second liquid crystal layer CL2...Second cholesteric liquid crystal 32R...Reflective surface 33...Third liquid crystal layer CL3...Third cholesteric liquid crystal 33R...Reflective surface 34...fourth liquid crystal layer CL4...fourth cholesteric liquid crystal 34R...reflection surface 35...5th liquid crystal layer CL5...5th cholesteric liquid crystal 35R...Reflective surface 36...Sixth liquid crystal layer CL6...Sixth cholesteric liquid crystal 36R...Reflective surface

Claims

1. A transparent substrate; a liquid crystal layer facing the transparent substrate and containing a cholesteric liquid crystal and an additive exhibiting liquid crystallinity; The refractive index anisotropy of the additive is smaller than the refractive index anisotropy of the liquid crystal layer. Liquid crystal optical element.

2. A transparent substrate; a liquid crystal layer facing the transparent substrate and containing a cholesteric liquid crystal and an additive exhibiting liquid crystallinity; The refractive index anisotropy of the additive is smaller than the refractive index anisotropy of the cholesteric liquid crystal. Liquid crystal optical element.

3. The additive is formed of a nematic liquid crystal material or a discotic liquid crystal material. The liquid crystal optical element according to claim 1 or 2.

4. The additive is formed of an alkoxycyclohexylcyclohexane-based, cyclohexylcyclohexanevinyl-based, alkylphenylcyclohexane-based, alkoxyphenylcyclohexane-based, fluorophenylcyclohexane-based, or cyanophenylcyclohexane-based material. The liquid crystal optical element according to claim 3 .

5. The helical pitch of the cholesteric liquid crystal is 200 nm or more and 450 nm or less. The liquid crystal optical element according to claim 1 .

6. The refractive index anisotropy of the liquid crystal layer is greater than 0.1, The refractive index anisotropy of the additive is less than 0.

1. The liquid crystal optical element according to claim 1 .

7. The refractive index anisotropy of the cholesteric liquid crystal is greater than 0.1, The refractive index anisotropy of the additive is less than 0.

1. The liquid crystal optical element according to claim 2 .

8. A transparent substrate having a first main surface and a second main surface opposite to the first main surface; a display module configured to face the first main surface in a first region of the transparent substrate and to emit display light; a first liquid crystal layer facing the second major surface in the first region and having a first cholesteric liquid crystal; a second liquid crystal layer overlying the first liquid crystal layer and having a second cholesteric liquid crystal; a third liquid crystal layer overlying the second liquid crystal layer and having a third cholesteric liquid crystal; each of the first liquid crystal layer, the second liquid crystal layer, and the third liquid crystal layer contains an additive exhibiting liquid crystallinity; the first cholesteric liquid crystal, the second cholesteric liquid crystal, and the third cholesteric liquid crystal have different helical pitches; The refractive index anisotropy of the additive is smaller than the refractive index anisotropy of each of the first liquid crystal layer, the second liquid crystal layer, and the third liquid crystal layer. Display device.

9. A transparent substrate having a first main surface and a second main surface opposite to the first main surface; a display module configured to face the first main surface in a first region of the transparent substrate and to emit display light; a first liquid crystal layer facing the second major surface in the first region and having a first cholesteric liquid crystal; a second liquid crystal layer overlying the first liquid crystal layer and having a second cholesteric liquid crystal; a third liquid crystal layer overlying the second liquid crystal layer and having a third cholesteric liquid crystal; each of the first liquid crystal layer, the second liquid crystal layer, and the third liquid crystal layer contains an additive exhibiting liquid crystallinity; the first cholesteric liquid crystal, the second cholesteric liquid crystal, and the third cholesteric liquid crystal have different helical pitches; The refractive index anisotropy of the additive is smaller than the refractive index anisotropy of each of the first cholesteric liquid crystal, the second cholesteric liquid crystal, and the third cholesteric liquid crystal. Display device.

10. a fourth liquid crystal layer facing the second main surface in a second region of the transparent substrate separated from the first region, the fourth liquid crystal layer having a fourth cholesteric liquid crystal and the additive; a fifth liquid crystal layer overlying the fourth liquid crystal layer and having a fifth cholesteric liquid crystal and the additive; a sixth liquid crystal layer overlying the fifth liquid crystal layer, the sixth liquid crystal layer having a sixth cholesteric liquid crystal and the additive; The first cholesteric liquid crystal and the fourth cholesteric liquid crystal have the same helical pitch and rotate in the same direction, The second cholesteric liquid crystal and the fifth cholesteric liquid crystal have the same helical pitch and are twisted in the same direction; The third cholesteric liquid crystal and the sixth cholesteric liquid crystal have the same helical pitch and are twisted in the same direction. The display device according to claim 8 or 9.

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