Liquid crystal optical element

Abstract

To provide a liquid crystal optical element with which light-guide losses can be suppressed.SOLUTION: According to the present embodiment, a liquid crystal optical element comprises a transparent substrate having a first principal surface, an orientation control layer having a plurality of protrusions and located on the first principal surface, and a liquid crystal layer having a cholesteric liquid crystal and located on the orientation control layer. The orientation control layer includes a first alignment region in which the plurality of protrusions are aligned at a first period and a second alignment region in which the plurality of protrusions are aligned at a second period, the second period being smaller than the first period. The liquid crystal layer includes a first liquid crystal region having a first reflection face overlapping the first alignment region and inclined at a first angle with respect to the first principal surface, and a second liquid crystal region having a second reflection face overlapping the second alignment region and inclined at a second angle with respect to the first principal surface, the second angle being larger than the first angle.SELECTED DRAWING: Figure 1

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. In order to realize the desired optical performance, various parameters such as the grating period, the refractive index anisotropy 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 of the liquid crystal layer are adjusted. In a liquid crystal optical element that guides light by repeating total reflection inside a transparent substrate, it is desired to suppress light guide loss caused by leakage of light to the outside. [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 embodiment is to provide a liquid crystal optical element capable of suppressing light guide loss. [Means for solving the problem]

[0005] According to one embodiment, the liquid crystal optical element comprises: a transparent substrate having a first main surface; an alignment control layer disposed on the first main surface and having a plurality of convex bodies; and a liquid crystal layer disposed on the alignment control layer and having a cholesteric liquid crystal, wherein the alignment control layer has a first alignment region in which the plurality of convex bodies are arranged in a first period and a second alignment region in which the plurality of convex bodies are arranged in a second period, the second period being smaller than the first period; the liquid crystal layer has a first liquid crystal region overlapping the first alignment region and having a first reflective surface inclined at a first angle with respect to the first main surface, and a second liquid crystal region overlapping the second alignment region and having a second reflective surface inclined at a second angle with respect to the first main surface, the second angle being larger than the first angle.

[0006] According to one embodiment, the liquid crystal optical element comprises: A liquid crystal layer having a cholesteric liquid crystal and disposed on the alignment control layer, the liquid crystal layer having a first liquid crystal region having a first reflecting surface inclined at a first angle with respect to the first principal surface, and a second liquid crystal region having a second reflecting surface inclined at a second angle with respect to the first principal surface, wherein a helical pitch of the cholesteric liquid crystal contained in the first liquid crystal region is equal to a helical pitch of the cholesteric liquid crystal contained in the second liquid crystal region, and the second angle is different from the first angle. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view that illustrates a schematic configuration example of a liquid crystal optical element 100. As shown in FIG. [Diagram 2] FIG. 2 is a plan view showing an example of the orientation control layer 2 shown in FIG. [Diagram 3] FIG. 3 is a diagram showing an example of the shape of the convex body 20. As shown in FIG. [Figure 4] FIG. 4 is a diagram illustrating an example of the cholesteric liquid crystal CL contained in the liquid crystal layer 3. As shown in FIG. [Diagram 5] FIG. 5 is a plan view diagrammatically illustrating the orientation pattern of liquid crystal molecules in the liquid crystal layer 3. As shown in FIG. [Figure 6]FIG. 6 is a diagram for explaining the optimum ranges of the width L21 and the width L22. [Figure 7] FIG. 7 is a diagram showing a comparative example. [Figure 8] FIG. 8 is a plan view showing a first modified example of the convex body. [Figure 9] FIG. 9 is a plan view showing a second modified example of the convex body. [Figure 10] FIG. 10 is a plan view showing a third modified example of the convex body. [Figure 11] FIG. 11 is a plan view showing a fourth modified example of the convex body. [Figure 12] FIG. 12 is a plan view showing a fifth modified example of the convex body. [Figure 13] FIG. 13 is a plan view showing a sixth modified example of the convex body. [Figure 14] FIG. 14 is a cross-sectional view that illustrates a schematic configuration example of the liquid crystal optical element 100. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] 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.

[0009] 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 X-axis is referred to as the first direction X, the direction along the Y-axis is referred to as the second direction Y, and the direction along the Z-axis is referred to as the third direction Z. 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.

[0010] FIG. 1 is a cross-sectional view that illustrates a schematic configuration example of a liquid crystal optical element 100. As shown in FIG.

[0011] The liquid crystal optical element 100 includes a transparent substrate 1 , an alignment control layer 2 , and a liquid crystal layer 3 .

[0012] 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.

[0013] 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.

[0014] The transparent substrate 1 is formed in a flat plate shape along the XY plane, and has a first main surface (inner surface) F1 and a second main surface (outer surface) F2. The first main surface F1 and the second main surface F2 are surfaces approximately parallel to the XY plane and face each other in the third direction Z.

[0015] The alignment control layer 2 is disposed on the first principal surface F1. The alignment control layer 2 has a plurality of minute protrusions 20. Each of the protrusions 20 extends from the first principal surface F1 along the third direction Z. The plurality of protrusions 20 have the function of determining the alignment direction of liquid crystal molecules contained in the liquid crystal layer 3, as will be described in detail later.

[0016] The orientation control layer 2 has a first orientation region 21 in which a plurality of convex bodies 20 are arranged in a first direction X with a first period Λ1, and a second orientation region 22 in which a plurality of convex bodies 20 are arranged in the first direction X with a second period Λ2. The first orientation region 21 and the second orientation region 22 are arranged alternately along the first direction X. The first period Λ1 and the second period Λ2 are different from each other, and in the illustrated example, the second period Λ2 is smaller than the first period Λ1.

[0017] The liquid crystal layer 3 is disposed on the alignment control layer 2 in the third direction Z, covering each of the convex bodies 20. 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 third direction Z, and also has a helical pitch P along the third direction Z. 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).

[0018] The liquid crystal layer 3 has a first liquid crystal region 31 overlapping the first alignment region 21 and a second liquid crystal region 32 overlapping the second alignment region 22. The first liquid crystal region 31 and the second liquid crystal region 32 are alternately arranged along the first direction X. The first liquid crystal region 31 has a first reflecting surface 31R inclined at a first angle α1 with respect to the first main surface F1. The second liquid crystal region 32 has a second reflecting surface 32R inclined at a second angle α2 with respect to the first main surface F1. The first angle α1 and the second angle α2 are different from each other, and in the illustrated example, the second angle α2 is larger than the first angle α1.

[0019] The first reflecting surface 31R and the second reflecting surface 32R reflect 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, out of the light incident on the liquid crystal layer 3. The selective reflection band may be a specific wavelength of visible light, or invisible light such as ultraviolet light or infrared light.

[0020] For example, when the first rotation direction is clockwise, clockwise circularly polarized light is reflected by the first reflecting surface 31R and the second reflecting surface 32R, and when the first rotation direction is counterclockwise, counterclockwise circularly polarized light is reflected by the first reflecting surface 31R and the second reflecting surface 32R. In this specification, "reflection" in the liquid crystal layer 3 involves diffraction within 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.

[0021] Such a liquid crystal optical element 100 is configured to reflect a portion of light incident from, for example, the transparent substrate 1 side toward the transparent substrate 1 by the first reflecting surface 31R and the second reflecting surface 32R of the liquid crystal layer 3. The light reflected by the first reflecting surface 31R and the second reflecting surface 32R is propagated along the second direction Y while being repeatedly reflected at the interface between the transparent substrate 1 and the air layer and at the interface between the liquid crystal layer 3 and the air layer. Such a liquid crystal optical element 100 functions as a light guide element for light in a selective reflection band.

[0022] 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 is, for example, a cholesteric liquid crystal having a helical pitch different from the helical pitch P shown in the figure, or a cholesteric liquid crystal twisted in a second twist direction opposite to the first twist direction.

[0023] FIG. 2 is a plan view showing an example of the orientation control layer 2 shown in FIG.

[0024] In the first alignment region 21, each of the convex bodies 20 is formed in a similarly curved arch shape in a plan view. The multiple convex bodies 20 are arranged in the first direction X and the second direction Y, respectively. A first period Λ1 of the convex bodies 20 adjacent to each other in the first direction X is different from a pitch P20 of the convex bodies 20 adjacent to each other in the second direction Y. In one example, the first period Λ1 is larger than the pitch P20. A width L21 of the first alignment region 21 along the first direction X is an integer multiple of the first period Λ1.

[0025] In the second alignment region 22, each of the convex bodies 20 is formed in a similarly curved arch shape in a plan view. However, the shape of the convex body 20 in the second alignment region 22 is different from the shape of the convex body 20 in the first alignment region 21. The multiple convex bodies 20 are arranged in the first direction X and the second direction Y, respectively. The second period Λ2 of the convex bodies 20 adjacent to the first direction X is different from the pitch P20 of the convex bodies 20 adjacent to the second direction Y. In one example, the second period Λ2 is larger than the pitch P20. In the illustrated example, the pitch P20 of the first alignment region 21 and the pitch P20 of the second alignment region 22 are equal to each other, but may be different from each other. The width L22 of the second alignment region 22 along the first direction X is an integer multiple of the second period Λ2. The width L22 is equal to or larger than the width L21.

[0026] FIG. 3 is a diagram showing an example of the shape of the convex body 20. As shown in FIG.

[0027] The convex body 20 is formed of, for example, an organic material, but may be formed of an inorganic material. The refractive index of the convex body 20 is equal to the refractive index of the transparent substrate 1. Therefore, the light that reaches the interface between the transparent substrate 1 and the convex body 20 is hardly refracted.

[0028] Each of the convex bodies 20 has a substantially constant height H20 along the third direction Z. The height H20 is greater than the width W20 of the convex body 20. From the viewpoint of defining the alignment direction of the liquid crystal molecules, it is desirable that the height H20 be large. The height H20 is, for example, four times or more the width W20. In one example, the width W20 is 100 nm, and the height H20 is 400 nm.

[0029] FIG. 4 is a diagram illustrating an example of the cholesteric liquid crystal CL contained in the liquid crystal layer 3. As shown in FIG.

[0030] 4, the liquid crystal layer 3 is illustrated enlarged in the third direction Z. For simplification, the liquid crystal molecule LM1 constituting the cholesteric liquid crystal CL is illustrated as one liquid crystal molecule LM1 among a plurality of liquid crystal molecules positioned 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 positioned on the same plane.

[0031] The width L31 of the first liquid crystal region 31 in the first direction X is equivalent to the width L21 of the first alignment region 21 shown in Fig. 2. The width L32 of the second liquid crystal region 32 in the first direction X is equivalent to the width L22 of the second alignment region 22 shown in Fig. 2.

[0032] The cholesteric liquid crystal CL contained in the first liquid crystal region 31 and the cholesteric liquid crystal CL contained in the second liquid crystal region 32 both twist in the same direction and have the same helical pitch P.

[0033] 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 that are stacked in a spiral shape along the third direction Z while rotating. The plurality of liquid crystal molecules LM1 include a liquid crystal molecule LM11 on one end side of the cholesteric liquid crystal CL.

[0034] In the liquid crystal layer 3, the alignment directions of the plurality of cholesteric liquid crystals CL adjacent to each other along the first direction X are different from each other. In addition, the spatial phases of the cholesteric liquid crystals CL adjacent to each other along the first direction X are different from each other.

[0035] The alignment directions of the liquid crystal molecules LM11 adjacent to each other along the first direction X are different from each other. In addition, the alignment directions of the liquid crystal molecules LM11 change continuously along the first direction X. The alignment directions of the liquid crystal molecules LM11 will be described later.

[0036] The first reflecting surface 31R and the second reflecting surface 32R are inclined with respect to the XY plane. Here, the first reflecting surface 31R and the second reflecting surface 32R correspond to a surface on which the alignment direction of the liquid crystal molecules LM1 is aligned or a surface on which the spatial phase is aligned (an equiphase surface).

[0037] 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.

[0038] 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).

[0039] 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)

[0040] FIG. 5 is a plan view diagrammatically illustrating the orientation pattern of liquid crystal molecules in the liquid crystal layer 3. As shown in FIG.

[0041] Here, the orientation pattern of liquid crystal molecule LM11 at one end side of liquid crystal molecule LM1 contained in cholesteric liquid crystal CL is shown.

[0042] The alignment directions of the liquid crystal molecules LM11 aligned along the first direction X are different from each other, whereas the alignment directions of the liquid crystal molecules LM11 aligned along the second direction Y are substantially the same.

[0043] Here, when focusing on the liquid crystal molecules LM11 aligned in the first direction X, the alignment directions of the liquid crystal molecules LM11 differ by a certain angle. That is, the alignment directions of the liquid crystal molecules LM11 aligned along the first direction X change linearly. Therefore, the spatial phase of the cholesteric liquid crystals CL aligned along the first direction X changes linearly along the first direction X. As a result, as in the liquid crystal layer 3 shown in FIG. 4, the first reflecting surface 31R and the second reflecting surface 32R inclined with respect to the XY plane are formed. Here, "linearly changing" indicates, for example, that 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 the convex body 20 of the alignment control layer 2.

[0044] In one plane, the interval between two liquid crystal molecules LM11 in the first direction X when the alignment direction of the liquid crystal molecules LM11 changes by 180 degrees along the first direction X is defined as the period Λ. For example, in the first liquid crystal region 31, the alignment direction of the liquid crystal molecules LM11 changes counterclockwise by a constant angle from the left to the right in the figure. The period Λ1 of the first liquid crystal region 31 coincides with the first period Λ1 of the first alignment region 21 shown in FIG. 2. The period Λ2 of the second liquid crystal region 32 coincides with the second period Λ2 of the second alignment region 22 shown in FIG. 2.

[0045] 1 is set according to the first period Λ1 and the helical pitch P. Similarly, the second angle α2 of the second reflecting surface 32R of the second liquid crystal region 32 shown in FIG. 1 is set according to the second period Λ2 and the helical pitch P.

[0046] The liquid crystal optical element 100 is formed, for example, by the following method.

[0047] First, an ultraviolet-curing resin material is applied onto the transparent substrate 1. Then, a mold with a recess formed in advance according to the shape of the convex body 20 is prepared, the mold is placed over the resin material, and ultraviolet light is applied while applying pressure. This causes the resin material to cure into a shape according to the recess of the mold, forming the convex body 20.

[0048] Next, a liquid crystal material (a solution containing a monomer material for forming a cholesteric liquid crystal CL) is applied onto the alignment control layer 2. After that, the pressure inside the chamber is reduced to remove the solvent, the applied liquid crystal material is dried, and the liquid crystal material is baked. As a result, the liquid crystal molecules contained in the liquid crystal material are aligned in a predetermined direction according to the shape of the convex body 20. For example, among the liquid crystal molecules LM1, the liquid crystal molecule LM11 in the vicinity of the first main surface F1 is aligned horizontally along the XY plane between the adjacent convex bodies 20, and is aligned so that its long axis is aligned along the tangent line of the convex body 20. The other liquid crystal molecule LM1 located directly above the liquid crystal molecule LM11 overlaps in a spiral shape along the third direction Z while rotating with the liquid crystal molecule LM11 as the starting point. In this way, the alignment direction of the liquid crystal molecule LM1 is fixed according to the alignment direction of the liquid crystal molecule LM11.

[0049] Thereafter, the liquid crystal material is cooled to about room temperature and irradiated with ultraviolet light to harden the liquid crystal material, thereby forming a liquid crystal layer 3 having cholesteric liquid crystal CL.

[0050] Next, the optimum ranges of the width L21 of the first alignment region 21 and the width L22 of the second alignment region 22 will be considered.

[0051] FIG. 6 is a diagram for explaining the optimum ranges of the width L21 and the width L22.

[0052] The transparent substrate 1 has a thickness d along the third direction Z and a refractive index nw. In the alignment control layer 2, convex bodies are arranged with a period Λ, though this will not be described in detail. The liquid crystal layer 3 has a refractive index nCLC, the cholesteric liquid crystal CL has a helical pitch P, and the reflecting surface 3R is inclined at an angle α.

[0053] Here, we consider the case where light LTi, which is circularly polarized light, is incident along the normal to the transparent substrate 1. After transmitting through the transparent substrate 1 and the alignment control layer 2, the light LTi enters the liquid crystal layer 3 and is reflected and diffracted by the reflective surface 3R. The light LTr reflected by the reflective surface 3R enters the transparent substrate 1 again and reaches the interface between the transparent substrate 1 and the air layer. The angle of incidence of the light LTr reaching the interface is greater than the critical angle β. For this reason, the light LTr is totally reflected at the interface.

[0054] At this time, the angle between the light LTi and the light LTr is defined as the diffraction angle θCLC of the light. The diffraction angle θCLC is equivalent to twice the angle α.

[0055] The angle α is set in a range larger than 1 / 2 of the critical angle β and smaller than the limit tilt angle α', as shown by the relational expression (11) in the figure.

[0056] The critical tilt angle α' is defined by equation (12) in the figure. That is, when the light LTr is reflected by the reflecting surface 3R at a diffraction angle θCLC (=2*α') and travels from the liquid crystal layer 3 toward the transparent substrate 1, equation (12) is obtained by solving α' based on the condition that the light LTr is totally reflected at the interface between the liquid crystal layer 3 and the transparent substrate 1. Note that the existence of the alignment control layer 2 is ignored here. In short, in order for the light LTr reflected by the reflecting surface 3R to be incident on the transparent substrate 1 without being totally reflected at the interface between the liquid crystal layer 3 and the transparent substrate 1, the angle α should be set in a range smaller than the limit inclination angle α'.

[0057] The period Λ is shown by equation (13) in the figure.

[0058] The distance L along the first direction X from the incident position of the light LTi to the position where the light LTr is totally reflected at the interface between the transparent substrate 1 and the air layer is given by equation (14) in the drawing.

[0059] The angle α in the drawing can be replaced with the above-mentioned first angle α1 and second angle α2, and the period Λ can be replaced with the above-mentioned first period Λ1 and second period Λ2.

[0060] Now, the first alignment region 21 and the first liquid crystal region 31 will be considered. The first angle α1 of the first reflecting surface 31R is set in a range larger than ½ of the critical angle β and smaller than the limit tilt angle α' based on the relational expression (11). The first period Λ1 is expressed as P / (2*tanα1) based on equation (13). Based on the formula (14), the width L21 of the first alignment region 21 and the width L31 of the first liquid crystal region 31 are set to be equal to or smaller than twice the length L1 defined by the following formula: L1=2*d / tan(π / 2-2*α1)

[0061] Next, the second alignment region 22 and the second liquid crystal region 32 will be considered. The second angle α2 of the second reflecting surface 32R is set in a range larger than ½ of the critical angle β and smaller than the limit tilt angle α' based on the relational expression (11). The second period Λ2 is expressed as P / (2*tanα2) based on equation (13). Based on the formula (14), the width L22 of the second alignment region 22 and the width L32 of the second liquid crystal region 32 are set to be equal to or less than twice the length L2 defined by the following formula. L2=2*d / tan(π / 2-2*α2)

[0062] Here, the reason for setting the widths L21 and L31 to be equal to or less than twice the length L1 and the widths L22 and L32 to be equal to or less than twice the length L2 will be described with reference to a comparative example in FIG.

[0063] In the comparative example, the liquid crystal layer 3 has a uniformly inclined reflecting surface 3R. Note that the alignment control layer is not shown here.

[0064] The light LTi incident on the transparent substrate 1 is, for example, left-handed circularly polarized light. The light LTi is reflected by the reflecting surface 3R, maintains its polarization state, and is incident on the transparent substrate 1 as light LTr1. The light LTr1 is reflected at the interface between the transparent substrate 1 and the air layer, converted into right-handed circularly polarized light, and again incident on the liquid crystal layer 3 as light LTr2. Since the light LTr2 is circularly polarized in the opposite direction to the light LTi, it is not reflected by the liquid crystal layer 3, but is reflected at the interface between the liquid crystal layer 3 and the air layer. The light LTr3 reflected at the interface is left-handed circularly polarized light. Therefore, the light LTr3 is reflected by the reflecting surface 3R. At this time, when the light LTr4 reflected by the reflecting surface 3R reaches the interface between the liquid crystal layer 3 and the air layer at an incident angle smaller than the critical angle, the light LTr4 leaks out of the liquid crystal optical element 100. Such light leakage is one of the causes of light guide loss.

[0065] The distance along the first direction X from the position where the light LTi is incident on the transparent substrate 1 to the position where the light LTr2 reflected at the interface between the transparent substrate 1 and the air layer is again incident on the liquid crystal layer 3 is equivalent to 2*L.

[0066] According to the above embodiment, the width L31 of the first liquid crystal region 31 having the first reflecting surface 31R is less than twice the length L1, and the width L32 of the second liquid crystal region 32 having the second reflecting surface 32R is less than twice the length L2.

[0067] Therefore, when the light LTi is reflected by the first reflecting surface 31R of the first liquid crystal region 31, the light LTr2 reflected at the interface between the transparent substrate 1 and the air layer is incident on the second liquid crystal region 32. In the second liquid crystal region 32, the second reflecting surface 32R is inclined at an angle different from that of the first reflecting surface 31R. Therefore, when the light LTr3 is reflected by the second reflecting surface 32R, it is possible to reduce the probability that the angle of incidence of the light LTr4 deviates from the total reflection condition, and it is possible to suppress leakage of light.

[0068] Similarly, when the light LTi is reflected by the second reflecting surface 32R of the second liquid crystal region 32, the light LTr2 reflected at the interface between the transparent substrate 1 and the air layer is incident on the first liquid crystal region 31. In the first liquid crystal region 31, when the light LTr3 is reflected by the first reflecting surface 31R, it is possible to reduce the probability that the angle of incidence of the light LTr4 deviates from the total reflection condition, and it is possible to suppress leakage of light.

[0069] Therefore, the light guide loss can be suppressed.

[0070] Example When the refractive index nw of the transparent substrate 1 is 1.5, the refractive index nCLC of the liquid crystal layer 3 is about 1.7, and the helical pitch P is about 570 nm, the critical tilt angle α' is about 29°. The critical angle β with respect to air is about 42°. Therefore, the first angle α1 and the second angle α2 are set in the range of more than 21° and less than 29° based on the relational expressions (11) and (12) shown in FIG. 6.

[0071] When the first angle α1 and the second angle α2 are in such a range, the first period Λ1 and the second period Λ2 are set in the range of about 510 nm or more and about 750 nm or less based on the formula (13) shown in Fig. 6. For example, in order to set the first angle α1 to 21°, the first period Λ1 is set to 750 nm. Also, in order to set the second angle α2 to 29°, the second period Λ2 is set to 510 nm.

[0072] When the thickness d of the transparent substrate 1 is 10 mm, the width L21 of the first alignment region 21 and the width L31 of the first liquid crystal region 31 are set to 36 mm or less, and the width L22 of the second alignment region 22 and the width L32 of the second liquid crystal region 32 are set to 64 mm or less. Note that the widths L21 and L31 need only be (2*L1) or less, and the widths L22 and L32 need only be (2*L2) or less. For this reason, the widths L21, L31, L22, and L32 may all be set equal to each other, for example, 35 mm.

[0073] Hereinafter, some modified examples of the layout of the convex bodies in the first alignment region 21 and the second alignment region 22 will be described.

[0074] FIG. 8 is a plan view showing a first modified example of the convex body. In the first modification, in addition to the arch-shaped convex body 20 shown in Fig. 2, a convex body 20L extending linearly along the second direction Y is added. The convex body 20L is located between the convex bodies 20 adjacent to each other in the first direction X.

[0075] FIG. 9 is a plan view showing a second modified example of the convex body. In the second modification, in addition to the arch-shaped convex body 20 shown in Fig. 2, a convex body 20A having a shorter overall length than the convex body 20 is added. The convex body 20A is formed in an arch shape. The convex bodies 20 and the convex bodies 20A are arranged alternately in the second direction Y.

[0076] FIG. 10 is a plan view showing a third modified example of the convex body. 9, a convex body 20L extending linearly along the second direction Y is added. The convex body 20L is located between the convex bodies 20 adjacent to each other in the first direction X.

[0077] FIG. 11 is a plan view showing a fourth modified example of the convex body. In the fourth modification, convex bodies 201 and 202 having different shapes are arranged alternately in the second direction Y. Each of the convex bodies 201 and 202 is formed in an arch shape, but has an asymmetric shape in the figure. However, the shape of the convex body 201 is line-symmetric with the shape of the convex body 202 with respect to an axis O parallel to the second direction Y. In the convex body 201, the length on the right side of the figure is shorter than the length on the left side of the figure, with the position of the peak 201P at which the convex body 201 intersects with the axis O as the center. In the convex body 202, the length on the right side of the figure is longer than the length on the left side of the figure, with the position of the peak 202P at which the convex body 202 intersects with the axis O as the center.

[0078] FIG. 12 is a plan view showing a fifth modified example of the convex body. 11, a convex body 20L extending linearly along the second direction Y is added. The convex body 20L is located between the convex body 201 and the convex body 202 adjacent to each other in the first direction X. However, the convex body 20L is spaced apart from the convex body 201 and the convex body 202.

[0079] FIG. 13 is a plan view showing a sixth modified example of the convex body. In the sixth modification, the convex body 201, the convex body 202, and the convex body 20L shown in FIG. 12 are integrated together.

[0080] Even when the modified examples shown in FIGS. 8 to 13 are applied, the same effects as those described above can be obtained.

[0081] FIG. 14 is a cross-sectional view that illustrates a schematic configuration example of the liquid crystal optical element 100. As shown in FIG. 14 differs from the configuration example shown in Fig. 1 in that the alignment control layer 2 is a photo-alignment film that is aligned by light irradiation. The liquid crystal optical element 100 does not include minute convex bodies between the transparent substrate 1 and the liquid crystal layer 3.

[0082] Such an orientation control layer 2 can be formed, for example, by the following method. First, a solution for an alignment film is applied onto a transparent substrate 1 to form a thin film. Then, an alignment process is performed to form an alignment axis pattern on the thin film. In the alignment process, interference fringes are formed with circularly polarized light having mutually opposite rotations, and a first region of the thin film is exposed to interference light having this interference fringe pattern. This forms a first alignment region 21. Then, a second region of the thin film is exposed to interference light having a different interference fringe pattern. This forms a second alignment region 22. Then, the thin film is baked to fix the alignment axis. By this method, an alignment control layer 2 having a predetermined alignment axis pattern is formed.

[0083] Even when a photo-alignment film is used as the alignment control layer 2, the same effects as those described above can be obtained.

[0084] As described above, according to this embodiment, it is possible to provide a liquid crystal optical element capable of suppressing light guide loss.

[0085] 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]

[0086] 100...Liquid crystal optical element 1...Transparent substrate F1...First main surface F2...Second main surface 2...Alignment control layer 20...Protrusion 21...First alignment region 22...Second alignment region 3...Liquid crystal layer 31...First liquid crystal area 32...Second liquid crystal area CL: Cholesteric liquid crystal

Claims

1. a transparent substrate having a first major surface; an orientation control layer disposed on the first main surface and having a plurality of convex bodies; a liquid crystal layer having a cholesteric liquid crystal and disposed on the alignment control layer; the alignment control layer has a first alignment region in which the plurality of convex bodies are arranged at a first period, and a second alignment region in which the plurality of convex bodies are arranged at a second period, the second period is smaller than the first period; the liquid crystal layer includes a first liquid crystal region overlapping the first alignment region and having a first reflective surface inclined at a first angle with respect to the first principal surface, and a second liquid crystal region overlapping the second alignment region and having a second reflective surface inclined at a second angle with respect to the first principal surface, The second angle is greater than the first angle. Liquid crystal optical element.

2. In a plan view, each of the plurality of convex bodies has a curved shape. The liquid crystal optical element according to claim 1 .

3. The height of the convex body is greater than the width of the convex body. The liquid crystal optical element according to claim 1 .

4. a helical pitch of the cholesteric liquid crystal contained in the first liquid crystal region is equal to a helical pitch of the cholesteric liquid crystal contained in the second liquid crystal region; The liquid crystal optical element according to claim 1 .

5. The width of the second alignment region is equal to or greater than the width of the first alignment region. The liquid crystal optical element according to claim 1 .

6. The width of the first alignment region is equal to or less than twice the length L1 defined by the following formula: L1=2*d / tan(π / 2-2*α1) (wherein the first angle is α1 and the thickness of the transparent substrate is d). The width of the second alignment region is equal to or less than twice the length L2 defined by the following formula: L2=2*d / tan(π / 2-2*α2) (wherein the second angle is α2) The liquid crystal optical element according to claim 1 .

7. a transparent substrate having a first major surface; An orientation control layer disposed on the first major surface; a liquid crystal layer having a cholesteric liquid crystal and disposed on the alignment control layer; the liquid crystal layer includes a first liquid crystal region having a first reflecting surface inclined at a first angle with respect to the first main surface, and a second liquid crystal region having a second reflecting surface inclined at a second angle with respect to the first main surface; a helical pitch of the cholesteric liquid crystal contained in the first liquid crystal region is equal to a helical pitch of the cholesteric liquid crystal contained in the second liquid crystal region; The second angle is different from the first angle. Liquid crystal optical element.

8. the orientation control layer has a plurality of convex bodies, Between the transparent substrate and the first liquid crystal region, the plurality of convex bodies are arranged at a first period, Between the transparent substrate and the second liquid crystal region, the plurality of convex bodies are arranged at a second period, The second period is different from the first period. The liquid crystal optical element according to claim 7.

9. the second period is smaller than the first period; The second angle is greater than the first angle. The liquid crystal optical element according to claim 8.

10. The alignment control layer is a photoalignment film. The liquid crystal optical element according to claim 7.

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