Optical element, image display device, head-mounted display, sensor device, and eye tracking device

Abstract

Provided is an optical element, an image display device, a head-mounted display, a sensor device, and an eye tracking device that suppresses the generation of side lobes and has high emissivity. The optical element of the present invention includes at least one set of: a pair of reflection layers that are a combination of two reflection layers whose rotation directions of reflected circularly polarized light are opposite and whose reflection wavelength bands at least partially overlap, wherein the reflection layers include a cholesteric liquid crystal layer in which a cholesteric liquid crystal phase is fixed, the cholesteric liquid crystal layer has a liquid crystal alignment pattern in which the orientation of an optical axis derived from a liquid crystal compound continuously rotates while changing in at least one direction in the plane, when a depth position corresponding to 10% of the total number of spiral pitches of the reflection layers is set as a depth position X and a depth position corresponding to 90% of the total number of spiral pitches of the reflection layers is set as a depth position Y from one surface toward the other surface side, a region from the one surface to the depth position X is set as a first region, a region from the depth position X to the depth position Y is set as a second region, and a region from the depth position Y to the other surface is set as a third region, at least one of the birefringence in the first region and the third region is less than the birefringence in the second region.

Description

Technical Field

[0001] This invention relates to an optical element, an image display device, a head-mounted display, a sensing device, and an eye-tracking device. Background Technology

[0002] A layer formed by fixing a cholesterol-type liquid crystal phase (hereinafter referred to as a "cholesterol-type liquid crystal layer") is widely known as a layer that selectively reflects either right-handed or left-handed circularly polarized light in a specific wavelength region. Optical elements are known that, by precisely controlling the orientation state of the cholesterol-type liquid crystal layer, the reflection direction of the reflected light is not specular reflection but oblique reflection (for example, Patent Document 1).

[0003] Previous technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2016 / 194961 Summary of the Invention

[0006] The technical problem to be solved by the invention

[0007] Such optical elements require more selective reflection characteristics, especially suppression of sidelobes. Additionally, such as Figure 1 As shown, a side lobe refers to a portion S of wavelength with relatively high reflectivity near the outer edge of the reflection wavelength band B. When such a side lobe is generated, it reflects light of wavelengths that should not be reflected, and therefore is not preferred.

[0008] In view of the above-mentioned actual situation, the present invention aims to provide an optical element with high reflectivity.

[0009] Furthermore, the present invention aims to provide an image display device, a head-mounted display, a sensing device, and an eye-tracking device.

[0010] means for solving technical problems

[0011] The inventors have discovered that the above-mentioned problems can be solved by the following structure.

[0012] (1) An optical element comprising at least one set of:

[0013] A reflective layer pair is a combination of two reflective layers that reflect circularly polarized light in opposite directions of rotation and whose reflected wavelength bands at least partially overlap.

[0014] The reflective layer comprises a cholesterol-type liquid crystal layer formed by fixing a cholesterol-type liquid crystal phase.

[0015] Cholesterol-type liquid crystal layers have liquid crystal alignment patterns that change as the optical axis of the liquid crystal compound rotates continuously along at least one in-plane direction.

[0016] When the depth position is defined as 10% of the total helical pitch of the reflective layer from one surface toward the other, and the depth position is defined as 90% of the total helical pitch of the reflective layer, and the region from one surface to depth position X is defined as region 1, the region from depth position X to depth position Y is defined as region 2, and the region from depth position Y to the other surface is defined as region 3, at least one of the birefringences in region 1 and region 3 is less than the birefringence in region 2.

[0017] (2) The optical element according to (1), wherein,

[0018] The reflective layer comprises multiple cholesterol-type liquid crystal layers.

[0019] In one of the two reflective layers, the optical axes derived from the liquid crystal compound in the liquid crystal alignment pattern of the multiple cholesterol-type liquid crystal layers all rotate in the same direction.

[0020] The optical axes of the liquid crystal compounds in the liquid crystal alignment patterns of the multiple cholesterol-type liquid crystal layers included in the other of the two reflective layers all rotate in the same direction.

[0021] (3) The optical element according to (1) or (2), wherein,

[0022] The rotation direction of the optical axis derived from the liquid crystal compound in the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer included in one of the two reflective layers is opposite to the rotation direction of the optical axis derived from the liquid crystal compound in the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer included in the other of the two reflective layers.

[0023] (4) The optical element according to any one of (1) to (3), wherein,

[0024] In the liquid crystal alignment pattern of a cholesterol-type liquid crystal layer, when the length of a 180° rotation of the orientation of the optical axis originating from the liquid crystal compound in one direction, which changes while the orientation of the optical axis originating from the liquid crystal compound rotates continuously, is defined as 1 period,

[0025] The length of one period in the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer included in one of the two reflective layers is the same as the length of one period in the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer included in the other of the two reflective layers.

[0026] (5) The optical element according to any one of (1) to (4), wherein,

[0027] At least one layer of the cholesterol-type liquid crystal layer has regions of different lengths in one period of a liquid crystal alignment pattern in the plane.

[0028] (6) The optical element according to any one of (1) to (5), wherein,

[0029] At least one layer of the cholesterol-type liquid crystal layer has a region in which the length of one period of the liquid crystal alignment pattern gradually changes in one direction.

[0030] (7) The optical element according to any one of (1) to (6), wherein,

[0031] The reflective layer comprises multiple cholesteric liquid crystal layers formed from compositions containing different liquid crystal compounds.

[0032] From the center of the film thickness of the cholesteric liquid crystal layer towards at least one surface side of the reflective layer, the birefringence of the cholesteric liquid crystal layer gradually decreases.

[0033] (8) The optical element according to (7), wherein,

[0034] In the reflective layer, the helical pitch number of the cholesteric liquid crystal layer with the lowest birefringence is less than half that of the cholesteric liquid crystal layer with the highest birefringence.

[0035] (9) The optical element according to any one of (1) to (8), wherein,

[0036] In the cross-section of the cholesterol-type liquid crystal layer observed by scanning electron microscopy

[0037] It has at least one cholesterol-type liquid crystal layer, in which the bright and dark portions originating from the cholesterol-type liquid crystal phase are tilted relative to the main surface of the cholesterol-type liquid crystal layer. Therefore, when the in-plane retardation is measured from the normal direction of the main surface of the cholesterol-type liquid crystal layer and the direction tilted relative to the normal, the direction in which the in-plane retardation is minimized is tilted from the normal direction in either the slow-axis plane or the fast-axis plane.

[0038] (10) The optical element according to (9) has a region in which the average tilt angle of the dark area gradually changes in one direction as the length of one period in the liquid crystal alignment pattern becomes shorter.

[0039] (11) The optical element according to (9) has a region in which the average tilt angle of the dark area increases as the length of one period in the liquid crystal alignment pattern becomes shorter.

[0040] (12) The optical element according to any one of (1) to (11) further comprises a phase difference layer.

[0041] (13) The optical element according to (12), wherein,

[0042] A phase difference layer is included between the first and second reflective layers.

[0043] (14) The optical element according to any one of (1) to (13), comprising a plurality of pairs of reflective layers,

[0044] Between different pairs of reflective layers, the selected reflection center wavelengths of the reflective layers that make up the reflective layer pair are different from each other.

[0045] (15) The optical element according to any one of (1) to (14), comprising a plurality of pairs of reflective layers,

[0046] Between different pairs of reflective layers, the arrangement of the lengths of the selective reflection center wavelengths in the cholesterol-type liquid crystal layers comprising the reflective layers of the reflective layer pair is consistent with the arrangement of the lengths of one period.

[0047] (16) An image display unit comprising:

[0048] The optical element as described in any one of (1) to (15); and

[0049] Image display panel.

[0050] (17) A head-mounted display comprising the image display device described in (16).

[0051] (18) A sensing device comprising the optical element described in any one of (1) to (15).

[0052] (19) An eye-tracking device comprising any one of (1) to (15) an optical element.

[0053] Invention Effects

[0054] According to the present invention, an optical element that can suppress the generation of side lobes and has high reflectivity is provided.

[0055] Furthermore, according to the present invention, an image display device, a head-mounted display, a sensing device, and an eye-tracking device can also be provided. Attached Figure Description

[0056] Figure 1 This is a graph representing the general reflectivity characteristics of cholesterol-type liquid crystal layers.

[0057] Figure 2 This is a side view of an example of an optical element.

[0058] Figure 3 This is a cross-sectional view of the first cholesterol-type liquid crystal layer.

[0059] Figure 4 yes Figure 3 The diagram shows a plan view of the first cholesterol-type liquid crystal layer.

[0060] Figure 5 This is a plan view of the fourth cholesterol-type liquid crystal layer.

[0061] Figure 6 This is a cross-sectional view of the first reflective layer used to illustrate the necessary condition X.

[0062] Figure 7 This is a plan view of another example of a cholesterol-type liquid crystal layer.

[0063] Figure 8 This is a cross-sectional view of another embodiment of a cholesterol-type liquid crystal layer.

[0064] Figure 9 This is a cross-sectional view of another embodiment of a cholesterol-type liquid crystal layer.

[0065] Figure 10 This is a conceptual diagram of an example of an exposure apparatus for exposing an orientation film.

[0066] Figure 11 This is a conceptual diagram of an example of an image display device. Detailed Implementation

[0067] The present invention will now be described in detail.

[0068] Sometimes, the necessary conditions for the following construction are described according to representative embodiments of the present invention, but the present invention is not limited to such embodiments.

[0069] In this specification, the numerical range indicated by “~” refers to the range including the values ​​recorded before and after “~” as the lower and upper limits.

[0070] Furthermore, in this specification, each component may use a single substance corresponding to that component, or two or more substances may be used together. Where two or more substances are used simultaneously for each component, the content of that component, unless otherwise specified, represents the total content of the substances used simultaneously.

[0071] In this specification, "(meth)acrylate" is used to mean "one or both of acrylate and methacrylate".

[0072] In this specification, visible light refers to light of the electromagnetic spectrum with wavelengths observable to the naked eye, specifically light in the wavelength range of 380–780 nm. Non-visible light refers to light in the wavelength range below 380 nm and above 780 nm.

[0073] Furthermore, it is not limited to this. In visible light, light in the wavelength region of 420–490 nm is blue light, light in the wavelength region of 495–570 nm is green light, and light in the wavelength region of 620–750 nm is red light.

[0074] In this specification, the birefringence of the cholesterol-type liquid crystal layer and various regions refers to the birefringence at a wavelength of 550 nm.

[0075] In this specification, the reflected wavelength band refers to the range of wavelengths of circularly polarized light selectively reflected from the cholesterol-type liquid crystal layer.

[0076] A key feature of the optical element of this invention is that the reflective layer has regions with different birefringence in the film thickness direction, and two reflective layers are used to reflect right-handed and left-handed circularly polarized light, respectively. Because the reflective layer has regions with different birefringence in the film thickness direction, the reflected light interferes with each other, and the two polarizations weaken each other, resulting in fewer sidelobes. Furthermore, the reflectivity is improved by using two reflective layers to reflect right-handed and left-handed circularly polarized light.

[0077] Figure 2 The image shows a side view that conceptually illustrates an example of the optical element of the present invention.

[0078] The optical element 10 includes a first reflective layer 12 and a second reflective layer 14. The first reflective layer 12 includes three cholesterol-type liquid crystal layers: a first cholesterol-type liquid crystal layer 20, a second cholesterol-type liquid crystal layer 22, and a third cholesterol-type liquid crystal layer 24. The second reflective layer 14 includes three cholesterol-type liquid crystal layers: a fourth cholesterol-type liquid crystal layer 30, a fifth cholesterol-type liquid crystal layer 32, and a sixth cholesterol-type liquid crystal layer 34.

[0079] As will be described in detail later, the rotation direction of the circularly polarized light reflected by the first reflective layer 12 is opposite to the rotation direction of the circularly polarized light reflected by the second reflective layer 14. Furthermore, the reflection wavelength band of the first reflective layer 12 overlaps with the reflection wavelength band of the second reflective layer 14. That is, the first reflective layer 12 and the second reflective layer constitute a reflective layer pair, which is a combination of two reflective layers whose reflected circularly polarized light rotate in opposite directions and whose reflection wavelength bands overlap by at least a portion.

[0080] The cholesterol-type liquid crystal layers (first cholesterol-type liquid crystal layer 20 to sixth cholesterol-type liquid crystal layer 34) contained in the first reflective layer 12 and the second reflective layer 14 are equivalent to layers formed by fixing a cholesterol-type liquid crystal phase.

[0081] in addition, Figure 2 The invention describes a method in which the first reflective layer 12 and the second reflective layer 14 each include three cholesteric liquid crystal layers. However, the invention is not limited to this method. As long as the birefringence in the predetermined depth region of the reflective layer is satisfied, the cholesteric liquid crystal layer included in each reflective layer can be one layer or multiple layers.

[0082] The first reflective layer 12 and the second reflective layer 14, through their respective cholesterol-type liquid crystal layers, are capable of reflecting light of a specified wavelength (e.g., visible light; more specifically, blue light, green light, i.e., red light, etc.).

[0083] <Explanation of the reflective layer and cholesterol-type liquid crystal layer>

[0084] To illustrate the cholesterol-type liquid crystal layer, Figure 3 A cross-sectional view of the first cholesterol-type liquid crystal layer 20 is shown in the figure. Figure 4 It shows Figure 3 The plan view shown is of the first cholesterol-type liquid crystal layer 20. Furthermore, the plan view is a top view of the first cholesterol-type liquid crystal layer 20. Figure 3 yes Figure 4 A sectional view of line A-A in the diagram.

[0085] exist Figure 3 In the diagram, the X and Z directions represent the orientations of two mutually orthogonal coordinate axes on the observation plane. The Z direction is parallel to the thickness direction of the first cholesterol-type liquid crystal layer 20.

[0086] exist Figure 4 In the diagram, the X and Y directions represent the orientations of two mutually orthogonal coordinate axes on the observation plane.

[0087] like Figure 3 As shown conceptually, similar to a cholesterol-type liquid crystal layer formed by fixing a conventional cholesterol-type liquid crystal phase, the first cholesterol-type liquid crystal 20 has a helical structure in which liquid crystal compounds LC are stacked by rotating along a helical axis in the thickness direction. Figure 3 The diagram briefly illustrates a structure formed by stacking liquid crystal compounds (LCs) that are rotated in a spiral (360° rotation) once, designated as a helical pitch 1. A structure consisting of multiple pitch layers of liquid crystal compounds (LCs) rotating in a spiral is also described. The same applies to the second cholesterol-type liquid crystal layer 22 through the sixth cholesterol-type liquid crystal layer 34.

[0088] However, as will be described later, in the first cholesterol liquid crystal layer 20 to the third cholesterol liquid crystal layer 24 and the fourth cholesterol liquid crystal layer 30 to the sixth cholesterol liquid crystal layer 34, the rotation directions of the optical axes derived from the liquid crystal compounds in the liquid crystal alignment pattern are opposite.

[0089] The first cholesterol-type liquid crystal layer 20 to the sixth cholesterol-type liquid crystal layer 34 have wavelength-selective reflectivity.

[0090] Cholesterol-type liquid crystal phases are known to exhibit selective reflectivity at specific wavelengths. The center wavelength λ of selective reflection depends on the pitch P (helical pitch) of the helical structure in the cholesterol-type liquid crystal phase and follows the relationship between the average refractive index n of the sterol-type liquid crystal phase and λ = n × P. Therefore, the center wavelength of selective reflection can be adjusted by regulating the pitch of this helical structure. The helical pitch of the cholesterol-type liquid crystal phase depends on the type or concentration of the chiral reagent used simultaneously with the liquid crystal compound during the formation of the cholesterol-type liquid crystal phase; therefore, the desired pitch can be obtained by adjusting these factors. Furthermore, the pitch P (helical pitch) of the helical structure in the cholesterol-type liquid crystal phase is the helical period of the helical structure of the cholesterol-type liquid crystal phase.

[0091] Furthermore, the adjustment of the pitch is described in detail in FUJIFILM Research Report No. 50 (2005), pp. 60-63. The methods for determining the direction of the helix and the pitch can be found in "Introduction to Liquid Crystal Chemistry Experiments," edited by the Japan Liquid Crystal Society, published by Sigma Publishing in 2007, page 46, and "Liquid Crystal Handbook," edited by Maruzen of the Liquid Crystal Handbook Editorial Committee, page 196.

[0092] In addition, in this specification, the selection of the reflection center wavelength (for example, the selection of the reflection center wavelength of the reflective layer, the selection of the reflection center wavelength of the cholesterol-type liquid crystal layer) means that, when the minimum value of the transmittance in the material (component) to be targeted is set as Tmin (%), it represents the average of the two wavelengths of the half-value transmittance T1 / 2 (%) expressed by the following formula.

[0093] The formula for calculating half-value transmittance is: T1 / 2 = 100 - (100 - Tmin) ÷ 2

[0094] Cholesterol-type liquid crystal phases exhibit selective reflectivity for either right- or left-hand circularly polarized light at specific wavelengths. Whether the reflected light is right-handed or left-handed circularly polarized depends on the direction of twist (helix) of the cholesterol-type liquid crystal phase's spiral. In the selective reflection of circularly polarized light by cholesterol-type liquid crystal phases, right-handed circularly polarized light is reflected when the spiral twists to the right, and left-handed circularly polarized light is reflected when the spiral twists to the left.

[0095] therefore, Figure 3 In the first cholesterol-type liquid crystal layer 20 shown, the cholesterol-type liquid crystal layer is a layer formed by right-hand twisting of a fixed cholesterol-type liquid crystal phase.

[0096] Furthermore, the rotation direction of the cholesterol-type liquid crystal phase can be adjusted by the type of liquid crystal compound forming the cholesterol-type liquid crystal layer and / or the type of chiral reagent added.

[0097] Furthermore, the full width at half maximum (FWHM) Δλ (nm) of the selectively reflected wavelength band (circularly polarized reflection band) depends on the birefringence Δn of the cholesterol-type liquid crystal layer and the pitch P of the helix, following the relationship Δλ = Δn × P. Therefore, the width of the reflection wavelength band can be controlled by adjusting Δn. Δn can be adjusted according to the type and mixing ratio of the liquid crystal compound forming the cholesterol-type liquid crystal layer, as well as the temperature at which the orientation is fixed.

[0098] The half-peak width of the reflection wavelength band is adjusted according to the application of the optical element 10, preferably 10-500 nm, more preferably 20-300 nm, and even more preferably 30-150 nm.

[0099] When the reflective layer included in the optical element comprises multiple cholesterol-type liquid crystal layers, the absolute value of the difference between the selective reflection center wavelength of the cholesterol-type liquid crystal layer representing the maximum reflection center wavelength and the cholesterol-type liquid crystal layer representing the minimum selective reflection center wavelength is preferably 50 nm or less, more preferably 25 nm or less, from the viewpoint of further suppressing the generation of side lobes. There is no particular limitation on the lower limit, but 0.

[0100] like Figure 3 and Figure 4 As shown, the first cholesterol-type liquid crystal layer 20 has a liquid crystal alignment pattern in which the orientation of the optical axis 20A of the liquid crystal compound LC, which forms the cholesterol-type liquid crystal phase, changes as it rotates continuously in one direction within the plane of the cholesterol-type liquid crystal layer. The same applies to the second cholesterol-type liquid crystal layers 22 through the sixth cholesterol-type liquid crystal layers 34.

[0101] Furthermore, the optical axis 20A derived from the liquid crystal compound LC is the axis with the highest refractive index in the liquid crystal compound LC. For example, in the case where the liquid crystal compound LC is a rod-shaped liquid crystal compound, the optical axis 20A is along the long axis direction of the rod shape. In the following description, the optical axis 20A derived from the liquid crystal compound LC will also be referred to as "optical axis 20A of the liquid crystal compound LC" or "optical axis 20A".

[0102] like Figure 4 As shown, the liquid crystal compound LC constituting the first cholesterol-type liquid crystal layer 20 is arranged in a two-dimensional configuration in the X direction and in a direction orthogonal to the X direction (Y direction).

[0103] The liquid crystal compound LC forming the first cholesterol-type liquid crystal layer 20 has a liquid crystal alignment pattern in which the orientation of the optical axis 20A in the in-plane direction changes as it rotates continuously along the X direction. In the example shown, the liquid crystal alignment pattern of the liquid crystal compound LC has an optical axis 20A that changes as it rotates continuously in a clockwise direction along the hollow arrow.

[0104] The orientation of the optical axis 20A of the liquid crystal compound LC changes as it rotates continuously in the direction of the hollow arrow (a specified direction). Specifically, the angle between the optical axis 20A of the liquid crystal compound LC arranged along the direction of the hollow arrow and the direction of the hollow arrow varies depending on the position of the direction of the hollow arrow. Along the direction of the hollow arrow, the angle between the optical axis 20A and the direction of the hollow arrow changes sequentially from θ to θ+180° or θ-180°.

[0105] Furthermore, the angle difference between the optical axes 20A of the liquid crystal compound LCs that are adjacent to each other in the direction of the hollow arrow is preferably 45° or less, more preferably 15° or less, and even more preferably a smaller angle.

[0106] On the other hand, in the liquid crystal compound LC that forms the first cholesterol-type liquid crystal layer 20, the orientation of the optical axis 20A is equal to that of the Y direction orthogonal to the direction of the arrow X, that is, the Y direction orthogonal to a direction in which the optical axis 20A rotates continuously.

[0107] In other words, in the liquid crystal compound LC that forms the first cholesterol-type liquid crystal layer 20, the angle between the optical axis 20A of the liquid crystal compound LC and the X direction is equal in the Y direction.

[0108] In the optical element 10 of the present invention, in the liquid crystal alignment pattern of the liquid crystal compound LC, the length (distance) by which the optical axis 20A of the liquid crystal compound LC is rotated 180° in the X direction, which changes due to continuous rotation of the in-plane optical axis 20A, is set as the length Λ of one cycle in the liquid crystal alignment pattern.

[0109] That is, the distance between the centers of two liquid crystal compounds (LCs) with equal angles relative to the X-direction in the X-direction is defined as the length Λ of one period. Specifically, as... Figure 4 As shown, the distance between the centers of two liquid crystal compound LCs whose X-direction is aligned with the optical axis 20A is set as the length Λ of one period.

[0110] In the following explanation, the length Λ of this 1-cycle will also be referred to as "1-cycle Λ".

[0111] The liquid crystal alignment pattern of the cholesterol-type liquid crystal layer repeats one cycle Λ in a direction that changes as it rotates continuously in the X direction, i.e., the direction of the optical axis 20A.

[0112] The first cholesterol-type liquid crystal layer 20 has a liquid crystal alignment pattern that changes as it rotates continuously along the optical axis 20A in the X direction (a defined direction) within the plane.

[0113] Cholesterol-type liquid crystal layers formed by fixing a cholesterol-type liquid crystal phase typically exhibit specular reflection of incident light (circularly polarized light).

[0114] In contrast, the first cholesterol-type liquid crystal layer 20 having the aforementioned liquid crystal alignment pattern causes incident light to be reflected relative to the specular surface in a direction having an angle in the X direction. Specifically, as Figure 3 As shown, the first cholesterol-type liquid crystal layer 20 does not reflect light incident from the normal direction in the direction of normal, but rather reflects it at an angle relative to the normal direction. Light incident from the normal direction refers to light incident from the front, which is light incident perpendicularly to the main surface. The main surface refers to the largest surface of the sheet-like object.

[0115] Furthermore, in a cholesteric liquid crystal layer whose optical axis 20A rotates continuously in one direction (X direction) based on a liquid crystal compound LC, the angle of light reflection varies depending on the wavelength of the reflected light. Specifically, the longer the wavelength of the light, the larger the angle of the reflected light relative to the incident light becomes.

[0116] Furthermore, the reflection angle of light from a cholesterol-type liquid crystal layer whose optical axis 20A rotates continuously in one direction (X direction) based on the liquid crystal compound LC varies in the X direction according to the length Λ of one period of the liquid crystal alignment pattern with the optical axis 20A rotated by 180°, i.e., one period Λ. Specifically, the shorter the one period Λ, the larger the angle of reflected light relative to the incident light becomes.

[0117] Furthermore, the aforementioned period Λ is not particularly limited and can be appropriately set according to the application of the optical element 10, etc. For example, it is preferably 50 μm or less, more preferably 10 μm or less. Considering the accuracy of the liquid crystal alignment pattern, it is preferably 0.1 μm or more.

[0118] As described above, the cholesterol-type liquid crystal layer (first cholesterol-type liquid crystal layer 20 to sixth cholesterol-type liquid crystal layer 34) included in the optical element 10 has the liquid crystal alignment pattern described above.

[0119] In the first reflective layer 12, the optical axes of the liquid crystal compounds in the liquid crystal alignment patterns of the first cholesterol liquid crystal layer 20 to the third cholesterol liquid crystal layer 24 are rotated in the same direction.

[0120] Among them, the optical axes derived from the liquid crystal compound in the liquid crystal alignment patterns of the fourth cholesterol-type liquid crystal layer 30 to the sixth cholesterol-type liquid crystal layer 34 included in the second reflective layer 14 have the same rotation direction.

[0121] That is, when each reflective layer constituting the reflective layer pair includes multiple cholesteric liquid crystal layers, it is preferable that the rotation direction of the optical axis derived from the liquid crystal compound in the liquid crystal alignment pattern of the multiple cholesteric liquid crystal layers included in each reflective layer is the same.

[0122] Furthermore, as described above, the rotation direction of the circularly polarized light reflected by the first reflective layer 12 and the rotation direction of the circularly polarized light reflected by the second reflective layer 14 are opposite.

[0123] That is, in the optical element 10, the rotation direction of the optical axis originating from the liquid crystal compound in the liquid crystal alignment pattern of the cholesterol-type liquid crystal layers (first cholesterol-type liquid crystal layer 20 to third cholesterol-type liquid crystal layer 24) included in the first reflective layer 12 is opposite to the rotation direction of the optical axis originating from the liquid crystal compound in the liquid crystal alignment pattern of the cholesterol-type liquid crystal layers (fourth cholesterol-type liquid crystal layer 30 to sixth cholesterol-type liquid crystal layer 34) included in the second reflective layer 14. More specifically, Figure 5 The diagram shows a plan view of the fourth cholesterol-type liquid crystal layer 30 as a representative example, as shown below. Figure 5 As shown, the rotation direction of the optical axis originating from the liquid crystal compound in the liquid crystal alignment pattern of the fourth cholesterol-type liquid crystal layer 30 is... Figure 4 The rotation directions of the optical axes derived from the liquid crystal compound in the liquid crystal alignment pattern of the first cholesterol-type liquid crystal layer 20 shown are opposite.

[0124] In optical element 10, the reflection wavelength band of the first reflective layer 12 overlaps with that of the second reflective layer 14. As described above, the rotation direction of the circularly polarized light reflected by the first reflective layer 12 is opposite to that of the circularly polarized light reflected by the second reflective layer 14. Therefore, as described above, when the reflection wavelength bands of the first reflective layer 12 and the second reflective layer 14 overlap, both right-handed and left-handed circularly polarized light of a specified wavelength can be reflected simultaneously, resulting in superior reflection characteristics.

[0125] Whether at least a portion of the reflected wavelength bands of each reflective layer are repeated can be confirmed by measuring the wavelength distribution of the reflected light.

[0126] The width and position of the reflection wavelength band of the reflective layers (first and second reflective layers) can be controlled by adjusting the reflection characteristics of the cholesterol-type liquid crystal layers included in the reflective layers (first and second reflective layers).

[0127] In addition, the reflection wavelength bands of the first reflective layer and the second reflective layer are not limited to being completely repeated, as long as the reflection wavelength bands of the two reflective layers (the first reflective layer and the second reflective layer) that constitute the reflective layer pair are at least partially repeated.

[0128] From the viewpoint of the amount of reflected light from an optical element, it is preferable that the overlapping region of the reflection wavelength bands of the two reflective layers (the first reflective layer and the second reflective layer) constituting the reflective layer pair is relatively wide. Specifically, the difference between the selective reflection center wavelengths of the two reflective layers (the first reflective layer and the second reflective layer) constituting the reflective layer pair is preferably less than 50 nm, more preferably less than 25 nm. Further preferably, the selective reflection center wavelengths of the two reflective layers (the first reflective layer and the second reflective layer) constituting the reflective layer pair are identical.

[0129] Furthermore, the length of the period Λ of the liquid crystal alignment pattern of the first cholesterol liquid crystal layer 20 to the third cholesterol liquid crystal layer 24 included in the first reflective layer 12 is the same.

[0130] Furthermore, the fourth to sixth cholesterol-type liquid crystal layers 30 and 34 included in the second reflective layer 14 each have the same length of one period Λ of the liquid crystal alignment pattern.

[0131] When each reflective layer constituting the reflective layer pair includes multiple cholesteric liquid crystal layers, it is preferable that the length of the period Λ of the liquid crystal alignment pattern of the multiple cholesteric liquid crystal layers included in each reflective layer is the same.

[0132] Furthermore, the length of one period Λ of the liquid crystal alignment pattern in the cholesterol-type liquid crystal layer (first cholesterol-type liquid crystal layer 20 to third cholesterol-type liquid crystal layer 24) included in the first reflective layer 12 is the same as the length of one period Λ of the liquid crystal alignment pattern in the cholesterol-type liquid crystal layer (fourth cholesterol-type liquid crystal layer 30 to sixth cholesterol-type liquid crystal layer 34) included in the second reflective layer 14.

[0133] Preferably, the length of one period Λ in the liquid crystal alignment pattern of the cholesteric liquid crystal layer included in one of the reflective layers is the same as the length of one period Λ in the liquid crystal alignment pattern of the cholesteric liquid crystal layer included in the other of the two reflective layers.

[0134] Furthermore, in this invention, the same length of one period Λ in the liquid crystal alignment pattern means that the difference in the length of one period Λ is 30% or less. As a method for calculating the above difference, when the two compared periods Λ are set as one period Λx and one period Λy respectively, if one period Λx is larger, it is calculated using the formula: {(one period Λx - one period Λy) / (one period Λx)} × 100. And, if one period Λx and one period Λy are the same value, the difference is 0%.

[0135] As described above, it is preferable that the difference in the length of the period Λ of the liquid crystal alignment pattern in each cholesteric liquid crystal layer is small. As mentioned above, the shorter the period Λ, the larger the reflection angle relative to the incident light becomes. Therefore, the smaller the difference in the length of the period Λ, the closer the reflection directions of the light from the cholesteric liquid crystal layers that reflect light in the same direction of reflection can be.

[0136] In the first reflective layer 12, the optical axes of the liquid crystal compounds in the liquid crystal alignment patterns of the cholesterol-type liquid crystal layers (first cholesterol-type liquid crystal layer 20 to third cholesterol-type liquid crystal layer 24) all change in the same direction. In this way, the reflection direction of light based on the cholesterol-type liquid crystal layers included in the first reflective layer 12 can be made consistent.

[0137] Furthermore, the optical axis of the liquid crystal compound in the liquid crystal alignment pattern of the second reflective layer 14 (the fourth to sixth cholesteric liquid crystal layers 30 to 34) all changes in the same direction. In this manner, the reflection direction of light based on the cholesteric liquid crystal layer included in the second reflective layer 14 can be made consistent.

[0138] That is, when each reflective layer constituting the reflective layer pair includes multiple cholesterol-type liquid crystal layers, it is preferable that the optical axis of the liquid crystal compound in the liquid crystal alignment pattern of the multiple cholesterol-type liquid crystal layers included in each reflective layer changes in the same direction.

[0139] Furthermore, in this invention, the direction of continuous change of the optical axis of the liquid crystal compound in the liquid crystal alignment pattern of the two cholesterol-type liquid crystal layers is the same, meaning that the angle between the directions of continuous change of the optical axis of the liquid crystal compound in the liquid crystal alignment pattern of the two cholesterol-type liquid crystal layers is preferably within 10°, more preferably within 1°, and even more preferably within 0.5°.

[0140] The present invention is not limited to the above-described manner; the directions in which the optical axes of the liquid crystal compounds in the cholesteric liquid crystal layer included in the first reflective layer continuously change can be different. For example, the angle between the directions of continuous change of the optical axes of the liquid crystal compounds in the cholesteric liquid crystal layer included in the first reflective layer and each other can be 20°.

[0141] Furthermore, the optical axis of the liquid crystal compound in the cholesteric liquid crystal layer included in the second reflective layer can change in different directions.

[0142] The birefringence of the second cholesterol-type liquid crystal layer 22 in the first reflective layer 12 can be greater than that of the first cholesterol-type liquid crystal layer 20 and the third cholesterol-type liquid crystal layer 24. Furthermore, the first cholesterol-type liquid crystal layer 20 and the third cholesterol-type liquid crystal layer 24 exhibit the same birefringence.

[0143] Furthermore, the birefringence of the fifth cholesterol-type liquid crystal layer 32 in the second reflective layer 14 can be greater than that of the fourth cholesterol-type liquid crystal layer 30 and the sixth cholesterol-type liquid crystal layer 34. Additionally, the fourth cholesterol-type liquid crystal layer 30 and the sixth cholesterol-type liquid crystal layer 34 exhibit the same birefringence.

[0144] Furthermore, the optical element of the present invention is not limited to the above-described manner, and its configuration is not particularly limited as long as the condition X described later is met.

[0145] As a method for adjusting the birefringence of each cholesterol-type liquid crystal layer, one example is adjusting the birefringence of the liquid crystal compound used to form the cholesterol-type liquid crystal layer. For example, as a liquid crystal compound used to form the second cholesterol-type liquid crystal layer 22, one example is selecting a liquid crystal compound with a larger birefringence than the liquid crystal compounds used to form the first cholesterol-type liquid crystal layer 20 and the third cholesterol-type liquid crystal layer 24.

[0146] That is, the reflective layer preferably comprises a plurality of cholesterol-type liquid crystal layers formed using a composition containing different types of liquid crystal compounds.

[0147] In the optical element of the present invention, preferably as in the first reflective layer 12 and the second reflective layer 14 of optical element 10, the birefringence of the cholesteric liquid crystal layer gradually decreases from the center of the film thickness of the reflective layer (corresponding to the second cholesteric liquid crystal layer 22 and the fifth cholesteric liquid crystal layer 32) toward at least one surface side of the reflective layer. By employing the above method, the generation of side lobes is further suppressed.

[0148] The thickness of the cholesterol-type liquid crystal layer in each reflective layer of the optical element is not particularly limited, and its structure is not particularly limited as long as condition X described later is met. Figure 2 As shown, preferably, among the cholesterol-type liquid crystal layers in the reflective layer, the cholesterol-type liquid crystal layer located at the center of the film thickness of the reflective layer (the second cholesterol-type liquid crystal layer 22 and the fifth cholesterol-type liquid crystal layer 32) has the thickest film thickness.

[0149] Furthermore, in the optical element of the present invention, it is preferable that the helical pitch number of the cholesteric liquid crystal layer with the lowest birefringence is less than half of the helical pitch number of the cholesteric liquid crystal layer with the highest birefringence in the reflective layer. By adopting the above method, the generation of side lobes is further suppressed. Preferably, the helical pitch number of the cholesteric liquid crystal layer with the lowest birefringence is less than 1 / 2.5 of the helical pitch number of the cholesteric liquid crystal layer with the highest birefringence, and more preferably more than 1 / 10.

[0150] From the perspective of improving reflectivity, the number of helical pitches of the cholesteric liquid crystal layer with the highest birefringence is preferably 6 or more, more preferably 8 or more, and even more preferably 10 or more.

[0151] Furthermore, from the viewpoint of further suppressing the generation of side lobes, the helical pitch number of the cholesterol-type liquid crystal layer with the minimum birefringence is preferably 5.0 or less, more preferably 3.0 or less. There is no particular limitation on the lower limit, but it can be 1.0 or more.

[0152] (Explanation of necessary condition X)

[0153] The first reflective layer 12 and the second reflective layer 14 included in the optical element 10 both satisfy the following necessary condition X.

[0154] Necessary condition X: When a depth position equivalent to 10% of the total helical pitch of the reflective layer is defined as depth position X from one surface of the reflective layer towards the other surface, and a depth position equivalent to 90% of the total helical pitch of the reflective layer is defined as depth position Y from one surface of the reflective layer towards the other surface, when the region from one surface to depth position X is defined as region 1, the region from depth position X to depth position Y is defined as region 2, and the region from depth position Y to the other surface is defined as region 3, at least one of the birefringences in region 1 and region 3 is less than the birefringence in region 2.

[0155] Hereinafter, regarding the aforementioned necessary condition X, the first reflective layer 12 will be used as a representative example. Figure 6 Please provide an explanation.

[0156] Figure 6 This is a cross-sectional view showing only the first reflective layer 12 in the optical element 10.

[0157] First, such as Figure 6 As shown by the hollow arrow, a depth position X is defined as the depth position corresponding to 10% of the total helical pitch of the first reflective layer 12 from one surface 120 towards the other surface 122. That is, with one surface 120 of the first reflective layer 12 as a reference, a depth position X is defined as the depth position corresponding to 10% of the total helical pitch of the first reflective layer 12. The region from one surface 120 of the first reflective layer 12 to depth position X is defined as the first region R1. Furthermore, the total helical pitch of the first reflective layer 12 refers to the total number of helical pitches of the cholesterol-type liquid crystal layers included in the first reflective layer 12. For example, in... Figure 2 In the optical element 10 shown, the number of helical pitches represents the sum of the number of helical pitches of the first cholesterol-type liquid crystal layer 20, the second cholesterol-type liquid crystal layer 22, and the third cholesterol-type liquid crystal layer included in the first reflective layer 12. Furthermore, as an example, when the total number of helical pitches of the first reflective layer 12 is 19, the aforementioned depth position X represents a depth position from one surface side of the first reflective layer towards the other surface side, corresponding to a position where the number of helical pitches is 1.9.

[0158] Next, from one surface 120 of the first reflective layer 12 towards the other surface 122, a depth position corresponding to 90% of the total helical pitch of the first reflective layer 12 is defined as depth position Y. That is, with one surface 120 of the first reflective layer 12 as a reference, a depth position corresponding to 90% of the total helical pitch of the first reflective layer 12 is defined as depth position Y. The region from depth position X to depth position X is defined as the second region R2. Furthermore, as an example, when the total helical pitch of the first reflective layer 12 is 19, the aforementioned depth position Y represents a depth position from one surface side of the first reflective layer towards the other surface side, corresponding to a position where the helical pitch is 17.1.

[0159] In addition, the region from depth position Y to another surface 122 is designated as region 3, R3.

[0160] In the first reflective layer 12, the birefringence in both the first region R1 and the third region R3 is less than that in the second region R2. Therefore, the first reflective layer 12 satisfies the necessary condition X.

[0161] The above description only covers the first reflective layer 12, but the second reflective layer 14 also satisfies the above-mentioned necessary condition X.

[0162] By satisfying the necessary condition X through the reflective layer included in the optical element, the generation of side lobes is suppressed.

[0163] There are no particular restrictions on the birefringence of the first and third regions. From the viewpoint of further suppressing the generation of side lobes, when the birefringence of the second region is taken as the reference (1), the birefringence is preferably 0.01 to 0.80, more preferably 0.01 to 0.70, and even more preferably 0.05 to 0.50.

[0164] One method for measuring the birefringence (Δn) in the aforementioned regions is to determine it by cutting a cross-section of the reflective layer and analyzing polarized light. Using microscopy measurements employing the rotating photon detection method and the rotating phase-son method—common polarized light analysis methods—Δn×d and the optical axis can be determined by analyzing the measured values ​​in regions where periodically occurring liquid crystal compounds caused by cholesterol-type liquid crystals are parallel to the cross-section of the slice. Alternatively, birefringence (Δn) can be calculated by separately measuring the slice thickness d.

[0165] This measurement is performed at the center thickness position of each of the 10 equal parts when the total thickness of each region is divided into 10 equal parts. The arithmetic mean of the birefringence of each of the 10 equal parts is then calculated as the birefringence (Δn) of each region.

[0166] As a method for forming a reflective layer that satisfies the aforementioned necessary condition X, examples such as those described above can be given. Figure 2 As shown in the optical element 10, the birefringence of the cholesterol-type liquid crystal layer is gradually reduced from the center of the film thickness of the reflective layer toward at least one surface side of the reflective layer. For example, the method described above... Figure 2 As shown, by adjusting the thicknesses of the first cholesterol-type liquid crystal layer 20, the second cholesterol-type liquid crystal layer 22, and the third cholesterol-type liquid crystal layer 24, which have the same helical pitch length, to 10%, 80%, and 10% of the total thickness of the reflective layer, respectively, a reflective layer that satisfies the above-mentioned necessary condition X can be formed.

[0167] (Examples of other liquid crystal alignment patterns)

[0168] Figure 2 In the optical element 10 shown, the optical axis of the liquid crystal compound in the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer rotates continuously only along the X direction.

[0169] However, the present invention is not limited thereto. In the cholesterol-type liquid crystal layer, various structures can be used as long as the optical axis of the liquid crystal compound rotates continuously in one direction.

[0170] As an example, such as Figure 7 As conceptually shown in the plan view, an example is a cholesterol-type liquid crystal layer 40, in which the liquid crystal alignment pattern is a radial pattern that radiates from the inside to the outside, changing the orientation of the optical axis of the liquid crystal compound LC while rotating continuously.

[0171] Figure 7 In the cholesterol-type liquid crystal layer 40 shown, the optical axis of the liquid crystal compound LC (not shown) is the length direction of the liquid crystal compound LC.

[0172] In the cholesterol-type liquid crystal layer 40, the orientation of the optical axis of the liquid crystal compound LC changes along multiple directions from the center of the cholesterol-type liquid crystal layer 40 outward, such as the direction indicated by arrow A1, the direction indicated by arrow A2, the direction indicated by arrow A3, etc., as it rotates continuously.

[0173] Furthermore, as a preferred approach, examples include... Figure 7 As shown, the changes occur while the center of the cholesterol-type liquid crystal layer 40 rotates radially in the same direction. Figure 7 The orientation shown is counterclockwise. Figure 7 In the arrows A1, A2, and A3, the direction of rotation of the optical axis becomes counterclockwise as it moves from the center outwards.

[0174] In this cholesterol-type liquid crystal layer 40, which has a liquid crystal alignment pattern that changes as the optical axis rotates radially, incident light can be reflected as diverging or focused light depending on the rotation direction of the optical axis of the liquid crystal compound LC and the direction of circular polarization of the reflected light.

[0175] That is, by setting the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer to a radial shape, the optical element of the present invention functions as, for example, a concave mirror or a convex mirror.

[0176] In the above description, a method in which the period Λ remains constant in one direction of continuous rotation toward the optical axis has been described. However, the present invention is not limited to this method. Depending on the application of the optical element, the cholesterol-type liquid crystal layer may also have a portion of regions with different periods Λ in one direction of continuous rotation toward the optical axis. That is, at least one layer of the cholesterol-type liquid crystal layer may have regions with different lengths of one period in the liquid crystal alignment pattern within the plane.

[0177] Furthermore, in the optical element of the present invention, depending on the application of the optical element, the length of one period Λ can be gradually varied in one direction, which rotates continuously toward the optical axis. That is, the cholesterol-type liquid crystal layer can have a region in which the length of one period in the liquid crystal alignment pattern gradually varies along one direction.

[0178] (Orientation example of liquid crystal compound LC-)

[0179] exist Figure 3 In the example shown, in the XZ plane of the cholesterol-type liquid crystal layer, the liquid crystal compound LC is configured to be aligned parallel to its optical axis relative to the main surface (XY plane), but the present invention is not limited to this configuration. For example, as Figure 8 As shown, it can also be a structure in which the optical axis of the liquid crystal compound LC is tilted relative to the main surface (XY plane) on the XZ plane of the cholesterol-type liquid crystal layer 42.

[0180] Furthermore, in Figure 8 In the example shown, the tilt angle (tilt angle) relative to the main surface (XY plane) of the liquid crystal compound LC on the XZ plane of the cholesterol-type liquid crystal layer 42 is the same in the thickness direction (Z direction), but the present invention is not limited thereto. In a cholesterol-type liquid crystal layer, there may be regions where the tilt angle of the liquid crystal compound LC differs in the thickness direction.

[0181] For example, Figure 9 In the example shown, the configuration is such that the optical axis of the liquid crystal compound LC on one surface of the cholesterol-type liquid crystal layer 44 is parallel to the main surface (pretilt angle is 0°). As it separates from one surface in the thickness direction, the tilt angle of the liquid crystal compound LC increases, and then the liquid crystal compound is oriented at a predetermined tilt angle until it reaches the other surface side.

[0182] Thus, in a cholesterol-type liquid crystal layer, there can be a structure where the optical axis of the liquid crystal compound (LC) has a pretilt angle at one of the upper and lower interfaces, or a structure where there are pretilt angles at both interfaces. Furthermore, the pretilt angles at the two interfaces can also be different.

[0183] like Figure 3 As shown, when the XZ plane of a cholesterol-type liquid crystal layer having a liquid crystal alignment pattern whose orientation changes continuously with rotation due to the optical axis originating from the liquid crystal compound is observed using a SEM (Scanning Electron Microscope), a stripe pattern is observed where the arrangement direction of the alternating bright and dark portions is tilted at a predetermined angle relative to the main surface (XY plane). That is, in a cross-section of the cholesterol-type liquid crystal layer included in the optical element of the present invention observed by SEM, the bright and dark portions originating from the cholesterol-type liquid crystal phase are tilted relative to the main surface.

[0184] In the cholesterol-type liquid crystal layer, when measuring the in-plane retardation Re from the normal direction and in a direction inclined relative to the normal, it is preferable that, in either the slow-axis plane or the fast-axis plane, the direction in which the in-plane retardation Re is minimized is inclined from the normal direction. Specifically, it is preferable that the absolute value of the measurement angle between the direction in which the in-plane retardation Re is minimized and the normal is 5° or more. In other words, it is preferable that the liquid crystal compound of the cholesterol-type liquid crystal layer is inclined relative to the main surface, and the inclination direction is approximately consistent with the bright and dark parts of the cholesterol-type liquid crystal layer. Furthermore, the normal direction is orthogonal to the main surface.

[0185] By giving the cholesterol-type liquid crystal layer this structure, it is possible to diffract circularly polarized light with high diffraction efficiency compared to liquid crystal compounds (LC) and liquid crystal layers with parallel main surfaces.

[0186] In a structure where the liquid crystal compound in a cholesterol-type liquid crystal layer is tilted relative to the main surface, and the tilt direction is approximately aligned with the bright and dark regions, the bright and dark regions corresponding to the reflecting surface are aligned with the optical axis of the liquid crystal compound. Therefore, the effect of the liquid crystal compound on light reflection (diffraction) is increased, thereby improving diffraction efficiency. Consequently, the amount of reflected light relative to the incident light can be further increased.

[0187] Furthermore, the cholesterol-type liquid crystal layer included in the optical element of the present invention can have a region in which the average tilt angle of the dark area gradually varies along one direction. A cholesterol-type liquid crystal layer having such a region is obtained by gradually varying the length of one period in a liquid crystal alignment pattern along one direction.

[0188] In the aforementioned region, the average tilt angle of the dark areas can gradually increase or gradually decrease.

[0189] In addition, the gradual change in the average tilt angle of the dark area refers to both the continuous change in the average tilt angle and the staged change in the average tilt angle.

[0190] Furthermore, depending on the application of the optical element, the optical element may have a region in which the average tilt angle of the dark area increases as the length of one period in the liquid crystal alignment pattern decreases.

[0191] (Structure with multiple pairs of reflective layers)

[0192] The above Figure 2 The optical element 10 shown includes a pair of reflective layers, which is a combination of two reflective layers (a first reflective layer and a second reflective layer) that reflect circularly polarized light in opposite directions and repeat at least a portion of the reflected wavelength band.

[0193] The present invention is not limited to the above-described manner, and may include multiple pairs of the above-described reflective layers. When multiple pairs of reflective layers are included, it is preferable that the selected reflection center wavelengths of the reflective layers constituting the different pairs of reflective layers are different from each other.

[0194] Furthermore, it is preferable that, between different pairs of reflective layers, the arrangement of the lengths of the selective reflection center wavelengths in the cholesterol-type liquid crystal layers comprising the reflective layers constituting the reflective layer pair is consistent with the arrangement of the lengths of one period.

[0195] exist Figure 2 In the optical element 10 shown, each reflective layer is described as including three cholesteric liquid crystal layers. However, the present invention is not limited to the above-described manner. As long as the reflective layer satisfies the above-described necessary condition X, one to two or more cholesteric liquid crystal layers may be included in each reflective layer.

[0196] <Methods for forming cholesterol-type liquid crystal layers and reflective layers>

[0197] The reflective layer is a layer that includes a cholesterol-type liquid crystal layer.

[0198] Cholesterol-type liquid crystal layers can be formed by fixing cholesterol-type liquid crystal phases into layers.

[0199] The structure formed by fixing the cholesterol-type liquid crystal phase can be any structure that maintains the orientation of the liquid crystal compound that is a cholesterol-type liquid crystal phase. A typical preferred structure for fixing the cholesterol-type liquid crystal phase is as follows: Based on the orientation state of the polymerizable liquid crystal compound as a cholesterol-type liquid crystal phase, polymerization and curing are carried out by ultraviolet irradiation or heating to form a non-flowing layer, while simultaneously changing the orientation morphology to a state that will not change due to external fields or forces.

[0200] Furthermore, in structures formed by fixing a cholesterol-type liquid crystal phase, it is sufficient to retain the optical properties of the cholesterol-type liquid crystal phase; in a cholesterol-type liquid crystal layer, the liquid crystal compound may not exhibit liquid crystal properties. For example, polymerizable liquid crystal compounds can lose their liquid crystal properties by undergoing a curing reaction to increase their molecular weight.

[0201] As an example of materials used in the formation of a cholesterol-type liquid crystal layer formed by fixing a cholesterol-type liquid crystal phase, a liquid crystal composition comprising a liquid crystal compound can be cited. The liquid crystal compound is preferably a polymerizable liquid crystal compound.

[0202] Furthermore, the liquid crystal composition used in the formation of the cholesterol-type liquid crystal layer may also include surfactants and chiral reagents.

[0203] --Polymerizable liquid crystal compounds--

[0204] Polymerizable liquid crystal compounds can be rod-shaped or disc-shaped.

[0205] Rod-shaped nematic liquid crystal compounds are examples of rod-shaped polymerizable liquid crystal compounds that form cholesterol-type liquid crystal phases. Preferably, rod-shaped nematic liquid crystal compounds are methylimine derivatives, azo derivatives, cyanobiphenyl derivatives, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexane derivatives, cyano-substituted phenylpyrimidine derivatives, alkoxy-substituted phenylpyrimidine derivatives, phenyl dioxane derivatives, diphenylacetylene derivatives, and alkenylcyclohexylbenzonitrile derivatives.

[0206] Polymerizable liquid crystal compounds are obtained by introducing polymerizable groups into liquid crystal compounds. Examples of polymerizable groups include unsaturated polymerizable groups, epoxy groups, and aziridinyl groups; unsaturated polymerizable groups are preferred, and olefinically unsaturated polymerizable groups are more preferred. Polymerizable groups can be introduced into the molecules of liquid crystal compounds using various methods. The number of polymerizable groups in the polymerizable liquid crystal compound is preferably 1 to 6, more preferably 1 to 3.

[0207] Examples of polymerizable liquid crystal compounds include Makromol. Chem., Vol. 190, p. 2255 (1989), Advanced Materials. Compounds described in Volume 5, 107 pages (1993), US Patent No. 4,683,327, US Patent No. 5,622,648, US Patent No. 5,770,107, International Publications Nos. 95 / 022586, 95 / 024455, 97 / 000600, 98 / 023580, and 98 / 052905, Japanese Patent Application Publications Nos. 1-272551, 6-016616, 7-110469, 11-080081, and 2001-328973, etc. Two or more polymerizable liquid crystal compounds can be used simultaneously. Using two or more polymerizable liquid crystal compounds simultaneously can lower the orientation temperature.

[0208] Furthermore, as polymerizable liquid crystal compounds other than those mentioned above, cyclic organopolysiloxane compounds having a cholesterol phase, such as those disclosed in Japanese Patent Application Publication No. 57-165480, can be used. Additionally, as the aforementioned polymeric liquid crystal compounds, polymers with mesocrystalline groups for displaying liquid crystals incorporated into the main chain, side chain, or both the main chain and side chain, cholesteric liquid crystals with cholesterol groups incorporated into the side chains, liquid crystal polymers such as those disclosed in Japanese Patent Application Publication No. 9-133810, and liquid crystal polymers such as those disclosed in Japanese Patent Application Publication No. 11-293252 can be used.

[0209] --Disc-shaped liquid crystal compound--

[0210] As a disc-shaped liquid crystal compound, the disc-shaped liquid crystal compound described in Japanese Patent Application Publication No. 2007-108732 and Japanese Patent Application Publication No. 2010-244038 are preferred, for example.

[0211] Furthermore, the content of the polymerizable liquid crystal compound in the liquid crystal composition is preferably 75 to 99.9% by mass relative to the mass of the solid components of the liquid crystal composition (mass after removing the solvent), more preferably 80 to 99% by mass, and even more preferably 85 to 90% by mass.

[0212] --surfactants--

[0213] The liquid crystal composition used to form a cholesterol-type liquid crystal layer may include a surfactant.

[0214] The surfactant is preferably a compound that functions as an orientation control agent, which helps to stabilize or rapidly form a planar-oriented cholesterol-type liquid crystal phase. Examples of surfactants include silicone-based surfactants and fluorinated surfactants, with fluorinated surfactants being preferred.

[0215] Specific examples of surfactants include the compounds described in paragraphs

[0082] to

[0090] of Japanese Patent Application Publication No. 2014-119605, the compounds described in paragraphs

[0031] to

[0034] of Japanese Patent Application Publication No. 2012-203237, the compounds illustrated in paragraphs

[0092] and

[0093] of Japanese Patent Application Publication No. 2005-099248, the compounds illustrated in paragraphs

[0076] to

[0078] and

[0082] to

[0085] of Japanese Patent Application Publication No. 2002-129162, and Japanese Patent Application Publication No. 2007-272185.

[0018] Fluoro(meth)acrylate polymers, etc., as described in paragraph

[0043] . In addition, one surfactant can be used alone, or two or more surfactants can be used at the same time. As a fluorinated surfactant, the compounds described in paragraphs

[0082] to

[0090] of Japanese Patent Application Publication No. 2014-119605 are preferred. The content of surfactant in the liquid crystal composition relative to the total mass of the liquid crystal compound is preferably 0.01 to 10% by mass, more preferably 0.01 to 5% by mass, and even more preferably 0.02 to 1% by mass. --Chiral reagents (optically active compounds)-- Chiral reagents have the function of inducing helical structures in cholesterol-type liquid crystal phases. Since the direction of helical twist or the helical pitch induced by the compound varies, the chiral reagent can be selected according to the purpose. There are no particular restrictions on the use of chiral reagents, and well-known compounds can be used (e.g., as described in the Liquid Crystal Devices Handbook, Chapter 3, Item 4-3, TN (twisted nematic), STN (Super Twisted Nematic) chiral reagents, page 199, edited by the 142nd Committee of the Japan Society for the Promotion of Science, 1989), isosorbide and isomannitol derivatives, etc. Chiral reagents typically include asymmetric carbon atoms, but axially asymmetric or surface-asymmetric compounds that do not include asymmetric carbon atoms can also be used as chiral reagents. Examples of axially asymmetric or surface-asymmetric compounds include binatene, helicene, p-xylene dimers, and their derivatives. Chiral reagents may also have polymerizable groups. When both the chiral reagent and the liquid crystal compound have polymerizable groups, a polymer having repeating units derived from the polymerizable liquid crystal compound and repeating units derived from the chiral reagent can be formed through a polymerization reaction between the polymerizable chiral reagent and the polymerizable liquid crystal compound. In this manner, the polymerizable groups possessed by the polymerizable chiral reagent are preferably the same as those possessed by the polymerizable liquid crystal compound. Therefore, the polymerizable groups of the chiral reagent are preferably unsaturated polymerizable groups, epoxy groups, or acridine groups, more preferably unsaturated polymerizable groups, and even more preferably olefinic unsaturated polymerizable groups. Furthermore, the chiral reagent can also be a liquid crystal compound. When the chiral reagent has a photoisomerizing group, it is preferable that a pattern corresponding to the desired reflection wavelength is formed by irradiation with a photomask such as activated light after coating and orientation. As the photoisomerizing group, isomerization sites of compounds exhibiting photochromic properties, azo groups, oxyazo groups, or cinnamyl groups are preferred. As specific compounds, the compounds described in Japanese Patent Application Publication Nos. 2002-080478, 2002-080851, 2002-179668, 2002-179669, 2002-179670, 2002-179681, 2002-179682, 2002-338575, 2002-338668, 2003-313189, and 2003-313292 may be used. The content of the chiral reagent in the liquid crystal composition relative to the molar content of the liquid crystal compound is preferably 0.01 to 200 mol%, more preferably 1 to 30 mol%. --Polymerization Initiator-- When the liquid crystal composition includes a polymerizable compound, the liquid crystal composition preferably includes a polymerization initiator. In the case of polymerization reaction carried out by ultraviolet irradiation, a photopolymerization initiator capable of initiating polymerization reaction by ultraviolet irradiation is preferred as the polymerization initiator used. Examples of photopolymerization initiators include α-carbonyl compounds (described in U.S. Patent Nos. 2,367,661 and 2,367,670), azobin ethers (described in U.S. Patent No. 2,448,828), α-hydrocarbon-substituted aromatic azobin compounds (described in U.S. Patent No. 2,722,512), polynucleoquinone compounds (described in U.S. Patent Nos. 3,046,127 and 2,951,758), combinations of triarylimidazolium dimers and p-aminophenyl ketones (described in U.S. Patent No. 3,549,367), acridine and phenazine compounds (described in Japanese Patent Application Publication No. 60-105,667 and U.S. Patent No. 4,239,850), and oxadiazole compounds (described in U.S. Patent No. 4,212,970). The content of photopolymerization initiator in the liquid crystal composition is preferably 0.1 to 20% by mass relative to the content of liquid crystal compound, more preferably 0.5 to 12% by mass. --Cross-linking agent-- To improve the strength and durability of the cured film, the liquid crystal composition may contain a crosslinking agent. Preferably, a crosslinking agent that is cured by ultraviolet light, heat, or moisture is used. There are no particular limitations on the crosslinking agent; it can be appropriately selected according to the purpose. Examples include polyfunctional acrylate compounds such as trimethylolpropane tri(meth)acrylate and pentaerythritol tri(meth)acrylate; epoxy compounds such as glycidyl methacrylate and ethylene glycol diglycidyl ether; acridine compounds such as 2,2-dihydroxymethylbutanol-tris[3-(1-acrylidinyl)propionate] and 4,4-bis(ethyleneiminocarbonylamino)diphenylmethane; isocyanate compounds such as hexamethylene diisocyanate and biuret-type isocyanate; polyoxazoline compounds with oxazoline groups on the side chains; and alkoxysilane compounds such as vinyltrimethoxysilane and N-(2-aminoethyl)3-aminopropyltrimethoxysilane. Furthermore, known catalysts can be used depending on the reactivity of the crosslinking agent, which can improve not only film strength and durability but also productivity. One of these can be used alone, or two or more can be used simultaneously. The content of the crosslinking agent relative to the mass of the solid components of the liquid crystal composition is preferably 3 to 20% by mass, more preferably 5 to 15% by mass. --Other Additives-- Polymerization inhibitors, antioxidants, ultraviolet absorbers, light stabilizers, colorants, and metal oxide particles can be added to the liquid crystal composition as needed, without reducing optical performance, etc. When forming a cholesterol-type liquid crystal layer, the liquid crystal composition is preferably used as a liquid. The liquid crystal composition may include a solvent. There are no particular limitations on the solvent; it can be appropriately selected depending on the purpose, but organic solvents are preferred. Examples of organic solvents include ketones, haloalkanes, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. One of these can be used alone, or two or more can be used simultaneously. When forming a cholesterol-type liquid crystal layer, it is preferable to coat the liquid crystal composition onto the forming surface of the cholesterol-type liquid crystal layer, orient the liquid crystal compound to a state of cholesterol-type liquid crystal phase, and then cure the liquid crystal compound to form the cholesterol-type liquid crystal layer. That is, when a cholesterol-type liquid crystal layer is formed on an alignment film, it is preferable to coat the liquid crystal composition onto the alignment film, align the liquid crystal compound to a cholesterol-type liquid crystal phase, and then cure the liquid crystal compound to form a cholesterol-type liquid crystal layer with a fixed cholesterol-type liquid crystal phase. The coating of liquid crystal compositions can be achieved using all printing methods such as inkjet and roll printing, as well as known methods such as spin coating, bar coating, and spray coating, which can similarly coat liquids onto sheets. The coated liquid crystal composition is dried and / or heated as needed, and then cured to form a cholesterol-type liquid crystal layer. In this drying and / or heating process, it is sufficient that the liquid crystal compounds in the liquid crystal composition are oriented as a cholesterol-type liquid crystal phase. When heating is performed, the heating temperature is preferably below 200°C, more preferably below 130°C. The oriented liquid crystal compound is then polymerized as needed. Polymerization can be either thermal polymerization or photopolymerization based on light irradiation, but photopolymerization is preferred. Ultraviolet light is preferably used for light irradiation. The irradiation energy is preferably 20 mJ / cm². 2 ~50J / cm 2 More preferably, it is 50–1500 mJ / cm². 2 To promote the photopolymerization reaction, light irradiation can also be carried out under heating conditions or in a nitrogen atmosphere. The wavelength of the irradiated ultraviolet light is preferably 250–430 nm. There is no limit to the thickness of the cholesterol liquid crystal layer. The thickness can be appropriately set to obtain the necessary light reflectivity, depending on the application of the optical element, the required light reflectivity of the cholesterol liquid crystal layer, and the forming material of the cholesterol liquid crystal layer. There are no particular limitations on the method for forming the reflective layer included in the optical element. For example, a method can be used to form a cholesterol-type liquid crystal layer by the above method, and then to form a cholesterol-type liquid crystal layer on the formed cholesterol-type liquid crystal layer by the above method, and so on. <Other Components> The optical element of the present invention may include other components besides the reflective layer. (Support structure) Optical components may include a support. As long as the support can support the reflective layer and the orientation film described later, various sheet-like materials (films, plates) can be used. Furthermore, the transmittance of the support relative to the corresponding light (e.g., light with a wavelength of 550 nm) is preferably 50% or more, more preferably 70% or more, and even more preferably 85% or more. There are no particular limitations on the thickness of the support. The thickness can be appropriately set according to the application of the optical element and the forming material of the support to maintain the thickness of the alignment film and the cholesterol liquid crystal layer. The thickness of the support is preferably 1 to 1000 μm, more preferably 3 to 250 μm, and even more preferably 5 to 150 μm. The support structure can be a single layer or multiple layers. Examples of single-layer supports include supports made of glass, triacetyl cellulose (TAC), polyethylene terephthalate (PET), polycarbonate, polyvinyl chloride, acrylic acid, and polyolefins. Examples of multi-layer supports include supports comprising any of the aforementioned single-layer supports as a substrate, with other layers of supports disposed on the surface of the substrate. (Orientation film) Optical components may include alignment films. The cholesterol-type liquid crystal layer is preferably formed on the alignment film. Furthermore, this alignment film is used to form the aforementioned liquid crystal alignment pattern. Orientation films can utilize a variety of known orientation films. Examples include triboelectric films composed of organic compounds such as polymers, tilted vapor-deposited films of inorganic compounds, films with microgrooves, and films that accumulate organic compounds such as ω-trisanoic acid, dioctadecylmethylammonium chloride, and methyl stearate using the Langmuir-Blodgett (LB) process. Orientation films based on triboelectric processing can be formed by rubbing the surface of a polymer layer several times in a specified direction with paper or cloth. As materials used in the alignment film, polyimide, polyvinyl alcohol, polymers with polymerizable groups as described in Japanese Patent Application Publication No. 9-152509, and materials used in the formation of alignment films as described in Japanese Patent Application Publication Nos. 2005-097377, 2005-099228, and 2005-128503 are preferred. In the optical element of the present invention, the alignment film is preferably a so-called photoalignment film, which is formed by irradiating a light-oriented raw material with polarization or non-polarization. That is, in the optical element of the present invention, as the alignment film, a photoalignment film formed by coating a light-oriented material on a support is preferably used. It can irradiate the optical alignment film with polarized light from a vertical or inclined direction, and can also irradiate the optical alignment film with unpolarized light from an inclined direction. As preferred examples of photoalignment materials that can be used in the photoalignment film of the present invention, examples include Japanese Patent Application Publication Nos. 2006-285197, 2007-076839, 2007-138138, 2007-094071, 2007-121721, 2007-140465, and 20... Japanese Patent Application Publication No. 07-156439, Japanese Patent Application Publication No. 2007-133184, Japanese Patent Application Publication No. 2009-109831, Japanese Patent No. 3883848 and Japanese Patent No. 4151746, aromatic ester compounds described in Japanese Patent Application Publication No. 2002-229039, Japanese Patent Application Publication No. 2002-265541 and Japanese Patent Application Publication No. 2002-31701 The maleimide and / or alkenyl-substituted nadicimide compounds having photooriented units described in No. 3 Publication, the photocrosslinkable silane derivatives described in Japanese Patent Nos. 4205195 and 4205198, the photocrosslinkable polyimide, photocrosslinkable polyamide and [other compounds described in Japanese Patent Nos. 2003-520878, 2004-529220 and 4162850] Photocrosslinkable polyesters and photodimerizable compounds, particularly cinnamic acid ester compounds, chalcone compounds and coumarin compounds, as described in Japanese Patent Application Publication Nos. 9-118717, 10-506420, 2003-505561, International Publication No. 2010 / 150748, 2013-177561 and 2014-12823. Among them, azo compounds, photocrosslinked polyimides, photocrosslinked polyamides, photocrosslinked polyesters, cinnamic acid ester compounds and chalcone compounds can be preferentially utilized. There is no limit to the thickness of the alignment film; the required thickness for the alignment function can be obtained by appropriately setting the thickness according to the forming material of the alignment film. The thickness of the alignment film is preferably 0.01 to 5 μm, more preferably 0.05 to 2 μm. There are no limitations on the method for forming the alignment film, and various known methods corresponding to the materials used to form the alignment film can be employed. As an example, a method can be illustrated by coating the alignment film onto the surface of a support and allowing it to dry, then exposing the alignment film with a laser beam to form an alignment pattern. Figure 10 The image shows a conceptual example of an exposure apparatus that exposes an orientation film to form an orientation pattern. Figure 10 The exposure apparatus 60 shown includes: a light source 64 with a laser 62; a λ / 2 plate 65 that changes the polarization direction of the laser beam M emitted from the laser 62; a polarization beam splitter 68 that separates the laser beam M emitted from the laser 62 into two rays, MA and MB; mirrors 70A and 70B respectively disposed on the optical paths of the two separated rays MA and MB; and λ / 4 plates 72A and 72B. Additionally, although not shown in the figure, the light source 64 emits linearly polarized light P0. The λ / 4 plate 72A converts the linearly polarized light P0 (ray MA) into right-hand circularly polarized light P... R The λ / 4 plate 72B converts linearly polarized light P0 (ray MB) into left-handed circularly polarized light P L . The λ / 4 plates 72A and 72B used here can be λ / 4 plates corresponding to the wavelength of the irradiated light. The exposure apparatus 60 irradiates the laser beam M, so for example, if the center wavelength of the laser beam M is 325 nm, then a λ / 4 plate that works with light of a wavelength of 325 nm can be used. A support 82 for an alignment film 80 before the alignment pattern is formed is disposed in an exposure unit, so that two rays MA and MB intersect on the alignment film 80 and interfere with each other, and the interference light is irradiated onto the alignment film 80 to expose it. Through this interference, the polarization state of the light illuminating the alignment film 80 becomes a state that changes periodically in the form of interference fringes. Thus, an alignment pattern in the alignment film 80 in which the alignment state changes periodically can be obtained. In the exposure apparatus 60, the period of the alignment pattern can be adjusted by changing the cross angle α of the two light rays MA and MB. That is, in the exposure apparatus 60, by adjusting the cross angle α, the length of one period in which the optical axis originating from the liquid crystal compound LC rotates continuously in one direction can be adjusted in the alignment pattern. By forming a cholesteric liquid crystal layer on an alignment film having an alignment pattern that periodically changes in this alignment state, it is possible to form the aforementioned cholesteric liquid crystal layer having a liquid crystal alignment pattern originating from the liquid crystal compound LC with the optical axis continuously rotating in one direction. Furthermore, the rotation direction of the optical axis can be reversed by rotating the optical axes of λ / 4 plates 72A and 72B by 90° respectively. (Phase difference plate) The optical element of the present invention may include a retardation plate. In particular, a retardation plate may be included between two reflective layers constituting a reflective layer pair. There are no particular restrictions on the type of phase retarder. The best phase retarder is selected based on the application of the optical element, such as the C-plate. (Adhesive layer) The optical element of the present invention may have an adhesive layer. The bonding layer, as long as it is a layer used to bond objects together, can be made of various known materials. As a bonding layer, it can be a layer made of an adhesive that is fluid during bonding and then becomes solid; it can be a layer made of a gel-like (rubber-like) soft solid that remains in a gel-like state after bonding; or it can be a layer made of a material that has the characteristics of both an adhesive and a gel. Therefore, the bonding layer can be any known layer used for bonding sheet-like objects with optical devices and optical elements, such as optically clear adhesives (OCA), optically clear double-sided tapes, and UV-curable resins. Furthermore, in the optical element of the present invention, the optical element of the present invention can be formed by holding each layer with a frame or clamp, etc., without using an adhesive layer. <Uses> The optical element of this invention can be used for a variety of purposes. The optical element of the present invention can be applied to an image display device. More specifically, an image display device including the optical element of the present invention and an image display panel can be described. There are no particular restrictions on the structure of image display devices, but examples include those that also include light guide plates. More specifically, Figure 11 The image display device 90 shown includes an optical element 10, a light guide plate 92, and an image display panel 94. The optical element 10 is attached to one end of the main surface of the light guide plate 92, and to the other end. In this configuration, light emitted from the image display panel 94 is reflected by one optical element 10, and the reflected light undergoes total internal reflection and is guided within the light guide plate 92. The light guided within the light guide plate 92 is reflected by another optical element 10 at an angle deviating from the total internal reflection condition and emitted to the user U side. That is, the optical element 10 serves as both an incident diffraction element and an exit diffraction element. The image display panel 94 is not particularly limited, but can utilize known display elements (display devices, projectors) used in various AR glasses, etc. Examples of display elements include liquid crystal displays (including LCOS: Liquid Crystal On Silicon), organic electroluminescent displays, and scanning displays using DLP (Digital Light Processing) and MEMS (Micro Electro Mechanical Systems) mirrors. In addition, the display element can be a monitor that displays a monochrome image, a monitor that displays a dichromatic image, or a monitor that displays a color image. Projection lenses can also be the well-known projection lenses (focusing lenses) used in AR (Augmented Reality) glasses, etc. The aforementioned image display device is preferably used as a head-mounted display. Furthermore, in addition to the above-mentioned uses, the optical elements of the present invention can also be applied to, for example, sensors and eye-tracking devices. Example The following examples and comparative examples illustrate the features of the present invention in more detail. The materials, amounts, proportions, processing contents, and processing steps shown in the following examples can be appropriately modified without departing from the spirit of the present invention. However, the scope of the present invention should not be interpreted as limited by the specific examples shown below. <Raw Materials> The following raw materials are used to prepare a liquid crystal composition for forming a cholesterol-type liquid crystal layer. Raw material A for photoorientation [Chemical Formula 1] Liquid crystal compound L-1 [Chemical Formula 2] Liquid crystal compound L-2 [Chemical Formula 3] Liquid crystal compound L-3 [Chemical Formula 4] Liquid crystal compound L-4 [Chemical Formula 5] Chiral reagent C-1 [Chemical Formula 6] Chiral reagent C-2 [Chemical Formula 7] Leveling agent T-1 [Chemical Formula 8] <Comparative Example 1> A glass substrate was prepared as a support. The following alignment film forming coating solution is applied to a support by spin coating. The support with the coating solution is then dried on a hot plate at 60°C for 60 seconds to form an alignment film. Coating solution for oriented film formation (Exposure of the alignment film) use Figure 9 The exposure apparatus shown exposes the alignment film, thereby forming an alignment film P-1 with an alignment pattern. The exposure apparatus uses a laser beam with an emitted wavelength of 325 nm as the laser source. The exposure dose based on the interference light is set to 1000 mJ / cm². 2 Furthermore, the period of the orientation pattern formed by the two laser beams and their interference (the length of 180° rotation of the optical axis) is controlled by changing the cross angle (cross angle α) of the two beams. As a liquid crystal composition for forming a cholesterol-type liquid crystal layer, the following composition A-1 was prepared. Composition A-1 First, the above composition A-1 is coated onto the alignment film P-1. The coating is heated to 80°C on a hot plate, and then subjected to a high-pressure mercury lamp at 300 mJ / cm² under nitrogen atmosphere at 80°C. 2 The coating is irradiated with ultraviolet light of wavelength 365nm to fix the orientation of the liquid crystal compound, thereby forming a cholesterol-type liquid crystal layer. Next, composition A-1 is overlaid onto the cholesterol-type liquid crystal layer, and then heated and cooled under the same conditions as described above, followed by ultraviolet curing. This process is repeated until the total thickness of the formed cholesterol-type liquid crystal layer reaches the desired film thickness, thereby forming a cholesterol-type liquid crystal layer and fabricating a reflective layer. The cross-section of the coating layer was confirmed using a scanning electron microscope (SEM), revealing a helical pitch of 9 pitches relative to the normal direction (thickness direction) of the host surface. Furthermore, the bright and dark areas were tilted relative to the host surface. The bright and dark areas described here refer to the bright and dark areas originating from the cholesterol-type liquid crystal phase visible when observing the cross-section of the cholesterol-type liquid crystal layer using SEM. Polarized light microscopy confirmed that the cholesterol-type liquid crystal layer was as follows. Figure 4 The periodic alignment surface is shown. Furthermore, the cross-section of the cholesterol-type liquid crystal layer was confirmed by SEM. In the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer, one period Λ of 180° rotation of the optical axis of the liquid crystal compound is 0.7 μm. The reflectance spectrum of the fabricated reflective layer was measured using a UV-Vis-NIR spectrophotometer (“UV-3100”, manufactured by SHIMADZU CORPORATION). Based on the obtained reflectance spectrum, a reflectance center wavelength of 530 nm was selected. Furthermore, the Δn(550) of the cholesterol-type liquid crystal layer was 0.15. <Example 1> An alignment film was formed on a glass substrate in the same manner as in Comparative Example 1, and the alignment film was exposed to form an alignment film P-1 with an alignment pattern. (Formation of the first cholesterol-type liquid crystal layer) As a liquid crystal composition for forming the first cholesterol-type liquid crystal layer, in composition A-1 of Comparative Example 1, liquid crystal compound L-1 was changed to liquid crystal compound L-2 and liquid crystal compound L-3, the mixing ratio was adjusted, and the amount of chiral agent C-1 added was adjusted to prepare composition B-1. Similar to Comparative Example 1, the above composition B-1 was coated on the alignment film P-1 in such a way that the desired film thickness was achieved, thus forming a first cholesterol-type liquid crystal layer. (Formation of the second cholesterol-type liquid crystal layer) As a liquid crystal composition for forming the second cholesterol-type liquid crystal layer, composition B-2 with the same composition as composition A-1 of Comparative Example 1 was prepared. Similar to Comparative Example 1, the above composition B-2 was coated on the first cholesterol-type liquid crystal layer in such a way that the desired film thickness was achieved, thus forming a second cholesterol-type liquid crystal layer. (Formation of the third cholesterol-type liquid crystal layer) Similar to Comparative Example 1, the above composition B-1 was coated on the second cholesterol-type liquid crystal layer in such a way that the desired film thickness was achieved, to form the third cholesterol-type liquid crystal layer. (Formation of the orientation film) An alignment film was formed on a glass substrate in the same manner as in Comparative Example 1, and the alignment film was exposed to form an alignment film P-2 with an alignment pattern. At this time, the alignment film was exposed to reverse the rotation direction of the optical axis of the liquid crystal alignment pattern originating from the liquid crystal compound. (Formation of the fourth cholesterol-type liquid crystal layer) In composition B-1, chiral reagent C-1 is replaced with chiral reagent C-2, and the amount added is adjusted to prepare composition B-3. Similar to Comparative Example 1, the above composition B-3 was coated on the alignment film P-2 in such a way that the desired film thickness was achieved, to form a fourth cholesterol-type liquid crystal layer. (Formation of the fifth cholesterol-type liquid crystal layer) In composition B-2, chiral reagent C-1 is replaced with chiral reagent C-2, and the amount added is adjusted to prepare composition B-4. Similar to Comparative Example 1, the above composition B-4 was coated on the fourth cholesterol-type liquid crystal layer in such a way that the desired film thickness was achieved, to form the fifth cholesterol-type liquid crystal layer. (Formation of the 6th cholesterol-type liquid crystal layer) Similar to Comparative Example 1, the above composition B-3 was coated on the fifth cholesterol-type liquid crystal layer in such a way that the desired film thickness was achieved, to form the sixth cholesterol-type liquid crystal layer. The laminate of the fourth to sixth cholesterol liquid crystal layers is temporarily transferred onto a dummy support, and the fourth cholesterol liquid crystal layer is bonded together with an adhesive in a manner that it is disposed on the third cholesterol liquid crystal layer, thereby forming an optical element including two reflective layers. The cross-sections of the first to sixth cholesterol-type liquid crystal layers were confirmed by SEM. The results showed that the number of pitches relative to the normal direction (thickness direction) of the main surface was 5 for the first cholesterol-type liquid crystal layer, 9 for the second, 5 for the third, 5 for the fourth, 9 for the fifth, and 5 for the sixth. Furthermore, each layer in the bright and dark areas is tilted relative to the main surface. In the liquid crystal alignment pattern of each cholesterol-type liquid crystal layer (the first to the sixth cholesterol-type liquid crystal layer), the period Λ of the optical axis of the liquid crystal compound rotating 180° is 0.7 μm. The optical element was designed with a reflection center wavelength of 530nm. Furthermore, the birefringence Δn(550) of the cholesterol-type liquid crystal layers are 0.08 for the first cholesterol-type liquid crystal layer, 0.15 for the second cholesterol-type liquid crystal layer, 0.08 for the third cholesterol-type liquid crystal layer, 0.08 for the fourth cholesterol-type liquid crystal layer, 0.15 for the fifth cholesterol-type liquid crystal layer, and 0.08 for the sixth cholesterol-type liquid crystal layer. <Examples 2-3> In Example 1, the amounts of chiral reagent C-1 and chiral reagent C-2 were appropriately adjusted to form each cholesterol-type liquid crystal layer of a specified film thickness in such a way as the number of helical pitches described in Table 1 below. Otherwise, optical elements were formed in the same manner. <Examples 4-5> In Example 1, the mixing ratio of liquid crystal compound L-2 and liquid crystal compound L-3, as well as the amount of chiral reagent C-1 and chiral reagent C-2, were appropriately adjusted to form each cholesterol-type liquid crystal layer of a specified film thickness in a manner that achieves the helical pitch number described in Table 1 below. Otherwise, optical elements were formed in the same manner. <Example 6> An alignment film was formed on a glass substrate in the same manner as in Comparative Example 1, and the alignment film was exposed to form an alignment film P-1 with an alignment pattern. (Formation of the first cholesterol-type liquid crystal layer) The liquid crystal compounds used in composition B-1 were changed to liquid crystal compounds L-1 to L-4, and the mixing ratio of these compounds was adjusted. The amount of chiral reagent C-1 added was further adjusted appropriately to obtain the desired composition. Next, in the same manner as Comparative Example 1, the obtained composition was coated on the alignment film P-1 to achieve the desired film thickness, and a first cholesteric liquid crystal layer of the desired film thickness was formed to achieve the number of helical pitches described in Table 3 below. (Formation of the second cholesterol-type liquid crystal layer) The liquid crystal compounds used in composition B-1 were changed to liquid crystal compounds L-1 to L-4, and their mixing ratios were adjusted. The amount of chiral reagent C-1 added was further adjusted appropriately to obtain the desired composition. Next, in the same manner as Comparative Example 1, the obtained composition was coated onto the first cholesterol-type liquid crystal layer to a desired film thickness, and a second cholesterol-type liquid crystal layer of the desired film thickness was formed to a number of helical pitches as described in Table 3 below. (Formation of the third cholesterol-type liquid crystal layer) A composition identical to composition A-1 of Comparative Example 1 was obtained. Next, in the same manner as Comparative Example 1, the obtained composition was coated onto the second cholesterol-type liquid crystal layer in such a way that the desired film thickness was achieved, and a third cholesterol-type liquid crystal layer of a predetermined film thickness was formed in such a way that the number of helical pitches was recorded in Table 3 described later. (Formation of the fourth cholesterol-type liquid crystal layer) The liquid crystal compounds used in composition B-1 were changed to liquid crystal compounds L-1 to L-4, and their mixing ratios were adjusted. The amount of chiral reagent C-1 added was further adjusted appropriately to obtain the desired composition. Next, in the same manner as Comparative Example 1, the obtained composition was coated onto the third cholesterol-type liquid crystal layer to achieve the desired film thickness, and a fourth cholesterol-type liquid crystal layer of the desired film thickness was formed to achieve the number of helical pitches described in Table 3 below. (Formation of the fifth cholesterol-type liquid crystal layer) The liquid crystal compounds used in composition B-1 were changed to liquid crystal compounds L-1 to L-4, and their mixing ratios were adjusted. The amount of chiral reagent C-1 added was further adjusted appropriately to obtain the desired composition. Next, in the same manner as Comparative Example 1, the obtained composition was coated onto the fourth cholesterol-type liquid crystal layer to achieve the desired film thickness, and a fifth cholesterol-type liquid crystal layer of the desired film thickness was formed to achieve the number of helical pitches described in Table 3 below. (Formation of the orientation film) An alignment film was formed on a glass substrate in the same manner as in Comparative Example 1, and the alignment film was exposed to form an alignment film P-2 with an alignment pattern. At this time, the alignment film was exposed to reverse the rotation direction of the optical axis of the liquid crystal alignment pattern originating from the liquid crystal compound. (Formation of the 6th cholesterol-type liquid crystal layer) The liquid crystal compounds used in composition B-3 were changed to liquid crystal compounds L-1 to L-4, their mixing ratio was adjusted, and the amount of chiral reagent C-2 was further adjusted appropriately to obtain the desired composition. Next, in the same manner as Comparative Example 1, the obtained composition was coated on the alignment film P-2 to achieve the desired film thickness, and a sixth cholesterol-type liquid crystal layer of the desired film thickness was formed to achieve the number of helical pitches described in Table 3 below. (Formation of the 7th cholesterol-type liquid crystal layer) The liquid crystal compounds used in composition B-3 were changed to liquid crystal compounds L-1 to L-4, their mixing ratio was adjusted, and the amount of chiral reagent C-2 was further adjusted appropriately to obtain the desired composition. Next, in the same manner as Comparative Example 1, the obtained composition was coated onto the sixth cholesterol-type liquid crystal layer to achieve the desired film thickness, and a seventh cholesterol-type liquid crystal layer of the desired film thickness was formed to achieve the number of helical pitches described in Table 3 below. (Formation of the 8th cholesterol-type liquid crystal layer) In Comparative Example 1, composition A-1 was modified by replacing chiral reagent C-1 with chiral reagent C-2 and adjusting the amount added to obtain a predetermined composition. Next, in the same manner as Comparative Example 1, the obtained composition was coated onto the 7th cholesterol-type liquid crystal layer to achieve the desired film thickness, and an 8th cholesterol-type liquid crystal layer of predetermined thickness was formed to achieve the number of helical pitches described in Table 3 below. (Formation of the 9th cholesterol-type liquid crystal layer) The liquid crystal compounds used in composition B-3 were changed to liquid crystal compounds L-1 to L-4, their mixing ratio was adjusted, and the amount of chiral reagent C-2 was further adjusted appropriately to obtain the desired composition. Next, in the same manner as Comparative Example 1, the obtained composition was coated onto the eighth cholesterol-type liquid crystal layer to achieve the desired film thickness, and a ninth cholesterol-type liquid crystal layer of the desired film thickness was formed to achieve the number of helical pitches described in Table 3 below. (Formation of the 10th cholesterol-type liquid crystal layer) The liquid crystal compounds used in composition B-3 were changed to liquid crystal compounds L-1 to L-4, their mixing ratio was adjusted, and the amount of chiral reagent C-2 was further adjusted appropriately to obtain the desired composition. Next, in the same manner as Comparative Example 1, the obtained composition was coated onto the 9th cholesterol-type liquid crystal layer to achieve the desired film thickness, thus forming a 10th cholesterol-type liquid crystal layer of the desired film thickness, with the helical pitch number described in Table 3 below. The laminate of the sixth to tenth cholesterol liquid crystal layers is temporarily transferred onto a dummy support, and the sixth cholesterol liquid crystal layer is bonded together with an adhesive in a manner that places it on the fifth cholesterol liquid crystal layer, thereby forming an optical element including two reflective layers. The selective reflection center wavelength of the laminate including the first to fifth cholesterol liquid crystal layers (hereinafter also referred to as the "first reflective layer") and the selective reflection center wavelength of the laminate including the sixth to tenth cholesterol liquid crystal layers (hereinafter also referred to as the "second reflective layer") are both 530 nm. Furthermore, the combination of the first and second reflective layers is equivalent to a pair of reflective layers consisting of two reflective layers whose rotation directions of the reflected circularly polarized light are opposite and whose reflected wavelength bands are repeated at least a portion thereof. <Comparative Example 2> In the exposure of the alignment film in Comparative Example 1, the cross angle of the two lights (cross angle α) was changed, and the alignment film P-3 was fabricated in the same manner. In Comparative Example 1, the amount of chiral reagent C-1 added was adjusted to change the film thickness of the cholesterol-type liquid crystal layer. Otherwise, the optical element was fabricated in the same manner. <Example 7> In the exposure of the alignment film in Example 1, the cross angle (cross angle α) of the two lights was changed. Otherwise, the alignment film P-1 was changed in the same way and alignment film P-3 was made, and alignment film P-2 was changed and alignment film P-4 was made. In Example 1, alignment film P-3 was used instead of alignment film P-1, and alignment film P-4 was used instead of alignment film P-2. The amounts of chiral reagent C-1 and chiral reagent C-2 were adjusted to form each cholesterol-type liquid crystal layer of a specified thickness in a manner that corresponds to the number of helical pitches described in Table 2 below. Otherwise, optical elements were fabricated in the same manner. <Examples 8-9> In Example 7, the amounts of chiral reagent C-1 and chiral reagent C-2 were appropriately adjusted to form each cholesterol-type liquid crystal layer of a specified film thickness in such a way as the number of helical pitches described in Table 2 below. Otherwise, optical elements were formed in the same manner. <Examples 10-11> In Example 7, the contents of liquid crystal compounds L-1 to L-3 and the amounts of chiral reagents C-1 and C-2 were appropriately adjusted to form each cholesterol-type liquid crystal layer with a specified film thickness in a manner that achieves the helical pitch number described in Table 2 below. Otherwise, an optical element was formed in the same manner. <Example 12> In the exposure of the alignment film in Example 1, the cross angle (cross angle α) of the two lights was changed. Otherwise, the alignment film P-1 was changed in the same way and alignment film P-3 was made, and alignment film P-2 was changed and alignment film P-4 was made. In Example 6, alignment film P-3 was used instead of alignment film P-1, and alignment film P-4 was used instead of alignment film P-2. The amounts of chiral reagent C-1 and chiral reagent C-2 were adjusted to form each cholesterol-type liquid crystal layer of a specified thickness in a manner that corresponds to the number of helical pitches described in Table 2 below. Otherwise, optical elements were fabricated in the same manner. <Side lobe generation and reflectivity evaluation> The reflectance of the fabricated optical element was measured using a UV-Vis-NIR spectrophotometer (“UV-3100”, manufactured by SHIMADZU CORPORATION). Based on the obtained reflectance spectral data, such as Figure 1As shown, the wavelengths of the short-wavelength end E1 and the long-wavelength end E2 of the selected reflection wavelength band are determined. The short-wavelength end E1 of the reflection wavelength band refers to the wavelength representing the lowest reflectivity at the concave portion where the initial reflectivity from the reflection wavelength band towards the short-wavelength side becomes less than 5%. The long-wavelength end E2 of the reflection wavelength band refers to the wavelength representing the lowest reflectivity at the concave portion where the initial reflectivity from the reflection wavelength band towards the long-wavelength side becomes less than 5%. Calculate the cumulative reflectance V1 between the wavelength of end E1 and the wavelength of position P1, which is 100 nm less than the wavelength of end E1. Also, calculate the cumulative reflectance V2 between the wavelength of end E2 and the wavelength of position P2, which is 100 nm more than the wavelength of end E2. The reflectivity of the sidelobe is calculated by adding the obtained cumulative values ​​V1 and V2. Furthermore, the reflectivity of the selected center reflection wavelength in the reflection wavelength band was evaluated. In addition, in Examples 1 to 5 and Examples 7 to 11, the selective reflection center wavelength of the laminate including the first cholesterol-type liquid crystal layer to the third cholesterol-type liquid crystal layer (hereinafter also referred to as the "first reflective layer") and the selective reflection center wavelength of the laminate including the fourth cholesterol-type liquid crystal layer to the sixth cholesterol-type liquid crystal layer (hereinafter also referred to as the "second reflective layer") are both 530 nm. Furthermore, the combination of the first and second reflective layers is equivalent to a pair of reflective layers consisting of two reflective layers whose rotation directions of the reflected circularly polarized light are opposite and whose reflected wavelength bands are repeated at least a portion thereof. Furthermore, the optical axis of the liquid crystal compound in the cholesteric liquid crystal layer included in the first and second reflective layers changes in the same direction. Furthermore, in Example 6, the selective reflection center wavelength of the laminate including the first to fifth cholesterol-type liquid crystal layers (hereinafter also referred to as the "third reflective layer") and the selective reflection center wavelength of the laminate including the sixth to tenth cholesterol-type liquid crystal layers (hereinafter also referred to as the "fourth reflective layer") are both 530 nm. Furthermore, the combination of the third and fourth reflective layers is equivalent to a pair of reflective layers consisting of two reflective layers whose rotation directions of the reflected circularly polarized light are opposite and whose reflected wavelength bands are repeated at least a portion thereof. Furthermore, the optical axis of the liquid crystal compound in the cholesteric liquid crystal layer included in the third and fourth reflective layers changes in the same direction. Furthermore, in Example 12, the selective reflection center wavelength of the laminate including the first to fifth cholesterol-type liquid crystal layers (hereinafter also referred to as the "fifth reflective layer") and the selective reflection center wavelength of the laminate including the sixth to tenth cholesterol-type liquid crystal layers (hereinafter also referred to as the "sixth reflective layer") are both 980 nm. Furthermore, the combination of the 5th and 6th reflective layers is equivalent to a pair of reflective layers consisting of two reflective layers whose rotation directions of the reflected circularly polarized light are opposite and whose reflected wavelength bands are repeated at least a portion thereof. Furthermore, the optical axis of the liquid crystal compound in the cholesteric liquid crystal layer included in the 5th and 6th reflective layers changes in the same direction. In Tables 1 to 3, the column “Selected center reflection wavelength (nm)” indicates the selected center reflection wavelength (nm) of the optical element. In Tables 1 to 3, the column “One period Λ (μm) of liquid crystal alignment pattern” represents the value of one period Λ of the liquid crystal alignment pattern of each cholesterol-type liquid crystal layer. In Tables 1 to 3, “1st layer” to “10th layer” respectively represent the 1st cholesterol-type liquid crystal layer to the 10th cholesterol-type liquid crystal layer. In Tables 1 to 3, “Birefringence Δn(550) in Region 1”, “Birefringence Δn(550) in Region 2” and “Birefringence Δn(550) in Region 3” represent the birefringence Δn(550) in Region 1 to Region 3 as defined by the necessary condition X of the first and second reflective layers (birefringence at wavelength 550 nm). [Table 1] [Table 2] [Table 3] Compared with Comparative Example 1, the reduction in sidelobe reflectance in Examples 1 to 6 was confirmed. Furthermore, compared with Examples 1 to 5, Example 6 showed a higher effect in reducing sidelobe reflectance. Compared with Comparative Example 2, the reduction in sidelobe reflectance in Examples 7 to 12 was confirmed. Furthermore, compared with Examples 7 to 11, Example 12 showed a higher effect in reducing sidelobe reflectance. The above results demonstrate that the present invention is highly effective. Symbol Explanation 10-Optical element, 12-First reflective layer, 14-Second reflective layer, 20-First cholesterol-type liquid crystal layer, 22-Second cholesterol-type liquid crystal layer, 24-Third cholesterol-type liquid crystal layer, 30-Fourth cholesterol-type liquid crystal layer, 32-Fifth cholesterol-type liquid crystal layer, 34-Sixth cholesterol-type liquid crystal layer, 40, 42, 44-Cholesterol-type liquid crystal layer, 60-Exposure device, 62-Laser, 64-Light source, 65-λ / 2 plate, 68-Polarization beam splitter, 70A, 70B-Reflectors, 72A, 72B-λ / 4 plate, 80-Orientation film, 82-Support, 90-Image display device, 92-Light guide plate, 94-Image display panel.

Claims

1. An optical element comprising at least one pair of reflective layers, which is a combination of two reflective layers whose reflected circularly polarized light rotates in opposite directions and whose reflected wavelength bands at least partially overlap, wherein, The reflective layer comprises a cholesterol-type liquid crystal layer formed by fixing a cholesterol-type liquid crystal phase. The cholesterol-type liquid crystal layer has a liquid crystal alignment pattern that changes as it rotates continuously along at least one in-plane direction, originating from the orientation of the optical axis of the liquid crystal compound. From one surface of the reflective layer towards the other surface, a depth position X is defined as 10% of the total helical pitch of the reflective layer, and a depth position Y is defined as 90% of the total helical pitch of the reflective layer. The region from one surface to depth position X is designated as region 1, the region from depth position X to depth position Y is designated as region 2, and the region from depth position Y to the other surface is designated as region 3. In this case, at least one of the birefringence values ​​in region 1 and region 3 is less than the birefringence value in region 2. In the cross-section of the cholesterol-type liquid crystal layer observed by scanning electron microscopy, The liquid crystal layer has at least one cholesteric liquid crystal layer, wherein the bright and dark portions of the cholesteric liquid crystal phase are inclined relative to the main surface of the cholesteric liquid crystal layer, and further, when the in-plane retardation is measured from the normal direction of the main surface of the cholesteric liquid crystal layer and the direction inclined relative to the normal, the direction in which the in-plane retardation is minimized in either the slow-axis plane or the fast-axis plane is inclined from the normal direction.

2. The optical element according to claim 1, wherein, The reflective layer includes a plurality of the cholesterol-type liquid crystal layers. In one of the two reflective layers, the optical axes originating from the liquid crystal compound in the liquid crystal alignment pattern of the plurality of cholesterol-type liquid crystal layers all rotate in the same direction. The rotation direction of the optical axis originating from the liquid crystal compound in the liquid crystal alignment pattern of the plurality of cholesterol-type liquid crystal layers included in the other of the two reflective layers is the same.

3. The optical element according to claim 1, wherein, The rotation direction of the optical axis originating from the liquid crystal compound in the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer included in one of the two reflective layers is opposite to the rotation direction of the optical axis originating from the liquid crystal compound in the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer included in the other of the two reflective layers.

4. The optical element according to claim 1, wherein, In the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer, when the length of a 180° rotation of the orientation of the optical axis originating from the liquid crystal compound in one direction, which changes simultaneously with the continuous rotation of the orientation of the optical axis originating from the liquid crystal compound, is defined as 1 period, The length of the period in the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer included in one of the two reflective layers is the same as the length of the period in the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer included in the other of the two reflective layers.

5. The optical element according to claim 1, wherein, In the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer, when the length of a 180° rotation of the orientation of the optical axis originating from the liquid crystal compound in one direction, which changes simultaneously with the continuous rotation of the orientation of the optical axis originating from the liquid crystal compound, is defined as 1 period, At least one layer of the cholesterol-type liquid crystal layer has regions in-plane with different lengths of the one period in the liquid crystal alignment pattern.

6. The optical element according to claim 1, wherein, In the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer, when the length of a 180° rotation of the orientation of the optical axis originating from the liquid crystal compound in one direction, which changes simultaneously with the continuous rotation of the orientation of the optical axis originating from the liquid crystal compound, is defined as 1 period, At least one layer of the cholesterol-type liquid crystal layer has a region in which the length of the one period in the liquid crystal alignment pattern gradually changes along the one direction.

7. The optical element according to claim 1, wherein, The reflective layer comprises a plurality of the cholesterol-type liquid crystal layers formed from compositions containing different liquid crystal compounds. Starting from the cholesteric liquid crystal layer located at the center of the film thickness of the reflective layer and moving towards at least one surface side of the reflective layer, the birefringence of the cholesteric liquid crystal layer gradually decreases.

8. The optical element according to claim 7, wherein, In the reflective layer, the number of helical pitches of the cholesterol-type liquid crystal layer with the lowest birefringence is less than half that of the number of helical pitches of the cholesterol-type liquid crystal layer with the highest birefringence.

9. The optical element according to claim 1, wherein, In the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer, when the length of a 180° rotation of the orientation of the optical axis originating from the liquid crystal compound in one direction, which changes simultaneously with the continuous rotation of the orientation of the optical axis originating from the liquid crystal compound, is defined as 1 period, The region having an average tilt angle of the dark area that gradually changes along one direction as the length of the 1st period in the liquid crystal alignment pattern decreases.

10. The optical element according to claim 1, wherein, In the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer, when the length of a 180° rotation of the orientation of the optical axis originating from the liquid crystal compound in one direction, which changes simultaneously with the continuous rotation of the orientation of the optical axis originating from the liquid crystal compound, is defined as 1 period, The region has a region in which the average tilt angle of the dark area increases as the length of the 1st period in the liquid crystal alignment pattern decreases.

11. The optical element according to claim 1, wherein, It also has a phase difference layer.

12. The optical element according to claim 11, wherein, The phase difference layer is included between the first reflective layer and the second reflective layer.

13. The optical element according to claim 1, wherein, Includes multiple pairs of the aforementioned reflective layers, Between different pairs of reflective layers, the selected reflection center wavelengths of the reflective layers constituting the pairs of reflective layers are different from each other.

14. The optical element according to claim 1, wherein, Includes multiple pairs of the aforementioned reflective layers, In the liquid crystal alignment pattern of the cholesterol-type liquid crystal layer, when the length of a 180° rotation of the orientation of the optical axis originating from the liquid crystal compound in one direction, which changes simultaneously with the continuous rotation of the orientation of the optical axis originating from the liquid crystal compound, is defined as 1 period, Between different pairs of reflective layers, the arrangement of the lengths of the selective reflection center wavelengths in the cholesterol-type liquid crystal layers comprising the reflective layers constituting the reflective layer pair is consistent with the arrangement of the lengths of the 1-period.

15. An image display device, comprising: The optical element according to any one of claims 1 to 14; and Image display panel.

16. A head-mounted display comprising the image display device of claim 15.

17. A sensing device comprising the optical element according to any one of claims 1 to 14.

18. An eye-tracking device comprising the optical element of any one of claims 1 to 14.

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