Optical element

Abstract

To provide an optical element that makes it possible to display a blur-free sharp image with respect to AR glasses, etc.SOLUTION: An optical element has a substrate and a laminate formed by laminating a plurality of liquid crystal layers provided on the substrate, wherein the liquid crystal layers which constitute the laminate have a liquid crystal alignment pattern changing in direction of an optical axis derived from a liquid crystal compound while continuously rotating along at least one direction in a plane, and at least one layer among the liquid crystal layers constituting the laminate is characterized in that the value obtained by mathematically averaging differences between maximum film thicknesses and minimum film thickness obtained by observing 10 cross sections through a scanning type electron microscope is 0.1 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an optical element used in AR glasses and the like. [Background technology]

[0002] In recent years, Augmented Reality (AR) glasses, such as those described in Non-Patent Document 1, which overlay virtual images and various types of information onto the actual view, have been put into practical use. AR glasses are also known as smart glasses, head-mounted displays (HMDs), and AR glasses.

[0003] As shown in Non-Patent Document 1, AR glasses, for example, display a virtual image overlaid on the scene the user is actually seeing by having the image displayed by a display (optical engine) enter and propagate through one end of a light guide plate and exit from the other end. In AR glasses, a diffracting element is used to diffract (refract) light from the display (projected light) and direct it into one end of a light guide plate. This introduces the light into the light guide plate at an angle, causing it to propagate within the plate. The light that has propagated through the light guide plate is then diffracted again by the diffracting element at the other end of the light guide plate, exits the plate, and is projected onto the user's observation position.

[0004] As an example of a diffraction element that can be used in AR glasses, which causes light to be incident on a light guide plate and causes light to be emitted from the light guide plate, a reflective structure using a cholesteric liquid crystal layer with a fixed cholesteric liquid crystal phase is described in Patent Document 1. This reflective structure comprises a plurality of helical structures, each extending along a predetermined direction. Furthermore, this reflective structure has a first incident surface intersecting the predetermined direction and onto which light is incident, and a reflective surface intersecting the predetermined direction and reflecting the light incident from the first incident surface. The first incident surface includes one of the ends of each of the plurality of helical structures. Each of the plurality of helical structures includes a plurality of structural units connected along the predetermined direction, and these structural units include a plurality of elements spirally stacked. Each of the plurality of structural units has a first end and a second end. Among adjacent structural units along the predetermined direction, the second end of one structural unit constitutes the first end of the other structural unit, and the orientation directions of the elements located at the multiple first ends included in the plurality of helical structures are aligned. Furthermore, the reflective surface includes at least one first end included in each of the plurality of helical structures and is non-parallel to the first incident surface.

[0005] The cholesteric liquid crystal layer (reflective structure) described in Patent Document 1 essentially has a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. The cholesteric liquid crystal layer described in Patent Document 1 has a reflective surface that is non-parallel to the first incident surface due to having such a liquid crystal orientation pattern. A typical cholesteric liquid crystal layer specularly reflects incident light. In contrast, the cholesteric liquid crystal layer described in Patent Document 1 does not use specular reflection, but diffracts the incident light and reflects it at a predetermined angle relative to specular reflection. For example, according to the cholesteric liquid crystal layer described in Patent Document 1, instead of reflecting light incident from the normal direction in the normal direction, the light is diffracted and reflected at an angle relative to the normal direction.

[0006] Therefore, by using this cholesteric liquid crystal layer as a diffraction element for insertion into the light guide plate, the image from the display can be diffracted, and the light can be introduced into the light guide plate at an angle, allowing it to propagate through total internal reflection within the light guide plate. Furthermore, by using the cholesteric liquid crystal layer as a diffraction element for emission from the light guide plate, the light propagated by the light guide plate can be diffracted and emitted from the light guide plate. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2016 / 194961 [Non-patent literature]

[0008] [Non-Patent Document 1] Bernard C. Kress et al., Towards the Ultimate Mixed Reality Experience: HoloLens Display Architecture Choices, SID 2017 DIGEST, pp.127-131 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] As described above, according to the reflective structure using a cholesteric liquid crystal layer described in Patent Document 1, the cholesteric liquid crystal layer diffracts the incident circularly polarized light, and the circularly polarized light is reflected at an angle with respect to the direction of incidence. As is well known, cholesteric liquid crystal layers selectively reflect light in a predetermined wavelength range depending on the helical pitch of the helical structure of the liquid crystal compound. Therefore, for example, by stacking cholesteric liquid crystal layers that selectively reflect light of each color, corresponding to red, green, and blue light, it is possible to support AR glasses that display full-color images.

[0010] In our investigation, we have found that when multiple liquid crystal layers are stacked, the diffraction angle of a diffraction element using a liquid crystal layer may vary in the in-plane direction of the liquid crystal layer. When a diffraction element having a variation in diffraction angle in the in-plane direction is used for an AR glass, blurring occurs in the displayed image.

[0011] An object of the present invention is to solve such problems of the prior art, and an optical element in which a plurality of liquid crystal layers are laminated on a substrate, suppressing variations in the diffraction angle of the liquid crystal layer in the in-plane direction, for example, when used for an AR glass or the like, to provide an optical element that enables clear image display without causing image blurring.

Means for Solving the Problem

[0012] To solve this problem, the manufacturing method of the optical element of the present invention has the following configuration. [1] It has a substrate and a laminate provided on the substrate with a plurality of liquid crystal layers laminated thereon. The liquid crystal layers constituting the laminate have a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. Among the liquid crystal layers constituting the laminate, at least one layer satisfies the following film thickness distribution requirement, which is an optical element. Film thickness distribution requirement The cross-section in the thickness direction of the liquid crystal layer is observed at 10,000 times magnification with a scanning electron microscope, and this is done at 20 locations by continuously moving the observation position in the in-plane direction of the liquid crystal layer to obtain an image of a 200 μm range in the in-plane direction of the liquid crystal layer, and obtaining the difference between the maximum film thickness and the minimum film thickness within the 200 μm range in the in-plane direction of the obtained liquid crystal layer. This operation is performed on any 10 cross-sections of the liquid crystal layer, and the arithmetic mean value of the differences between the maximum film thickness and the minimum film thickness in the obtained 10 cross-sections is 0.1 μm or less. [2] Among the liquid crystal layers constituting the laminate, the liquid crystal layer located at the end in the lamination direction satisfies the film thickness distribution requirement, which is the optical element according to [1]. [3] Among the liquid crystal layers constituting the laminate, the liquid crystal layer closest to the substrate side satisfies the film thickness distribution requirement, which is the optical element according to [2]. [4] Among the liquid crystal layers constituting the laminate, the liquid crystal layer other than the liquid crystal layer farthest from the substrate satisfies the film thickness distribution requirement, and the optical element according to any one of [1] to [3]. [5] All the liquid crystal layers constituting the laminate satisfy the film thickness distribution requirement, and the optical element according to any one of [1] to [4]. [6] The liquid crystal layer constituting the laminate is a cholesteric liquid crystal layer formed by fixing a cholesteric liquid crystal phase, and the optical element according to any one of [1] to [5]. [7] The substrate is a light guide plate, and has an incident portion for incident light on the light guide plate and an exit portion for emitting light from the light guide plate. The optical element according to any one of [1] to [6], wherein at least one of the incident portion and the exit portion is configured using the laminate. [8] The incident portion is configured using the laminate, and the optical element according to [7]. [9] The exit portion is configured using the laminate, and the optical element according to [8].

Advantages of the Invention

[0013] According to the present invention, for example, in AR glasses or the like, an optical element capable of displaying a clear image without blurring of the image can be provided.

Brief Description of the Drawings

[0014] [Figure 1] It is a diagram conceptually showing an example of the optical element of the present invention. [Figure 2] It is a conceptual diagram for explaining a cholesteric liquid crystal layer. [Figure 3] [[ID=3,3]]It is a plan view conceptually showing the cholesteric liquid crystal layer shown in FIG. 2. [Figure 4] It is a diagram conceptually showing a cross-sectional SEM image of the cholesteric liquid crystal layer shown in FIG. 3. [Figure 5] It is a conceptual diagram for explaining the operation of the cholesteric liquid crystal layer shown in FIG. 3. [Figure 6] It is a diagram conceptually showing another example of the cholesteric liquid crystal layer. [Figure 7]This is a conceptual diagram illustrating another example of a cholesteric liquid crystal layer. [Figure 8] This is a conceptual diagram of an example of an exposure apparatus for exposing a photo-alignment film. [Figure 9] This is a conceptual diagram to explain the function of laminates. [Figure 10] This is a conceptual diagram to explain the film thickness distribution requirements. [Modes for carrying out the invention]

[0015] The optical element of the present invention will be described in detail below based on preferred embodiments shown in the attached drawings.

[0016] In this specification, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively. In this specification, "(meth)acrylate" means "either acrylate or methacrylate, or both." In this specification, “identical” includes the margin of error generally accepted in the art. Furthermore, in this specification, “all,” “none,” and “entire” include not only 100% but also the margin of error generally accepted in the art, such as 99% or more, 95% or more, or 90% or more.

[0017] In this specification, visible light refers to electromagnetic waves with wavelengths visible to the human eye, specifically light in the wavelength range of 380 to 780 nm. Invisible light refers to light with wavelengths less than 380 nm and greater than 780 nm. Furthermore, although not limited to this, infrared light is defined as light with a wavelength range exceeding 780 nm and less than 1 mm, and among these, the near-infrared region is defined as light with a wavelength range exceeding 780 nm and less than or equal to 2000 nm. Furthermore, although not limited to this, within the visible light spectrum, light in the 420-490 nm wavelength range is blue light, light in the 495-570 nm wavelength range is green light, and light in the 620-750 nm wavelength range is red light.

[0018] Figure 1 conceptually shows an example of the optical element of the present invention. As shown in Figure 1, the optical element 10 has a light guide plate 12, an incident portion 14, and an outgoing portion 16. The incident portion 14 is provided near one end of one main surface of the light guide plate 12, and the outgoing portion 16 is provided near the other end of the same main surface of the light guide plate 12. The main surface is the largest surface of a sheet-like (plate-like) object, film, or layer.

[0019] The optical element 10 shown in the illustration is, for example, used in the AR glasses mentioned above, and is compatible with displaying a full-color image consisting of a red image R, a green image G, and a blue image B. In the AR glasses using the optical element 10, as an example, an image (video) consisting of a red image R, a green image G, and a blue image B displayed by a display (optical engine) (not shown) is transmitted through the light guide plate 12 and incident on the incident section 14. The incident section 14 diffracts and reflects the incident light (image), so that it is incident on the light guide plate 12 at an angle at which total internal reflection is possible. Light propagated through repeated total internal reflection (light guided) within the light guide plate 12 enters the emission unit 16. The emission unit 16 diffracts and reflects the incident light, causing a red image R, a green image G, and a blue image B to be emitted from the light guide plate 12, thereby superimposing virtual images onto the scene actually seen by the user U.

[0020] The incident section 14 includes an R incident liquid crystal layer 14R, a G incident liquid crystal layer 14G, and a B incident liquid crystal layer 14B. In a preferred embodiment, the R-incident liquid crystal layer 14R, the G-incident liquid crystal layer 14G, and the B-incident liquid crystal layer 14B are all reflective liquid crystal diffraction elements, each consisting of a cholesteric liquid crystal layer having a predetermined liquid crystal alignment pattern. The R-incident liquid crystal layer 14R selectively diffracts and reflects red (R) light, the G-incident liquid crystal layer 14G selectively diffracts and reflects green (G) light, and the B-incident liquid crystal layer 14B selectively diffracts and reflects blue (B) light.

[0021] On the other hand, the ejection unit 16 has an R ejection liquid crystal layer 16R, a G ejection liquid crystal layer 16G, and a B ejection liquid crystal layer 16B. In a preferred embodiment, the R-emitting liquid crystal layer 16R, the G-emitting liquid crystal layer 16G, and the B-emitting liquid crystal layer 16B are all reflective liquid crystal diffraction elements consisting of cholesteric liquid crystal layers having a predetermined liquid crystal orientation pattern. The R-emitting liquid crystal layer 16R selectively diffracts and reflects red light, the G-emitting liquid crystal layer 16G selectively diffracts and reflects green light, and the B-emitting liquid crystal layer 16B selectively diffracts and reflects blue light.

[0022] As is well known, the cholesteric liquid crystal layer selectively reflects right- or left-circularly polarized light within a predetermined wavelength range, while transmitting other light. Therefore, the user U can observe the background on the other side of the light emitter 16 through the light guide plate 12 and the light emitter 16.

[0023] The light guide plate 12 is the substrate in the present invention. The incident portion 14 and the output portion 16 are both laminates of multiple liquid crystal layers, which are provided on the substrate and are part of the optical element of the present invention. Therefore, in the inlet section 14, at least one of the R output liquid crystal layer 16R, the G output liquid crystal layer 16G, and the B output liquid crystal layer 16B satisfies the predetermined film thickness distribution requirements. Also, in the outlet section 16, at least one of the R output liquid crystal layer 16R, the G output liquid crystal layer 16G, and the B output liquid crystal layer 16B satisfies the predetermined film thickness distribution requirements described later.

[0024] Furthermore, the optical element of the present invention is not limited to this configuration for the incident portion 14 and the outgoing portion 16. That is, the incident portion 14 and the outgoing portion 16 may have multiple cholesteric liquid crystal layers, or they may have two cholesteric liquid crystal layers, or four or more cholesteric liquid crystal layers. Therefore, the optical element of the present invention is not limited to one that corresponds to a three-color full-color image as shown in the illustrated example, but may also correspond to a two-color image such as red and blue, or red and green, or to a color image having four or more colors, or to an invisible light such as infrared light.

[0025] Furthermore, the cholesteric liquid crystal layers in the input section 14 and the output section 16 are not limited to cholesteric liquid crystal layers that selectively reflect red light, liquid crystal layers that selectively reflect green light, and liquid crystal layers that selectively emit blue light. The cholesteric liquid crystal layers in the incident section 14 and the outgoing section 16 may be, for example, a cholesteric liquid crystal layer that selectively reflects red and green light, a cholesteric liquid crystal layer that selectively reflects green and blue light, a cholesteric liquid crystal layer that selectively reflects infrared light, and a layer that selectively reflects ultraviolet light.

[0026] In other words, in the optical element of the present invention, the incident portion 14 and the output portion 16, that is, the laminate in which a plurality of liquid crystal layers are stacked, have two or more liquid crystal layers, and at least one layer satisfies the above-mentioned film thickness distribution requirement, so various layer configurations can be used. However, regardless of the layer configuration, the incident section 14 and the outgoing section 16 basically have liquid crystal layers that selectively reflect light of the same color (wavelength range).

[0027] The following describes each component that makes up the optical element 10 of the present invention. [Light guide plate] The light guide plate 12 is a known light guide plate that reflects and propagates (guides light) light that enters its interior. There are no restrictions on the light guide plate 12; various known light guide plates used in AR glasses and backlight units of liquid crystal displays can be used.

[0028] [Injection section and output section] The incident section 14 has an R incident liquid crystal layer 14R, a G incident liquid crystal layer 14G, and a B incident liquid crystal layer 14B. As described above, each incident liquid crystal layer is, in a preferred embodiment, a cholesteric liquid crystal layer having a predetermined liquid crystal alignment pattern, with a fixed cholesteric liquid crystal phase, and is a reflective liquid crystal diffraction element that selectively reflects right-circularly polarized or left-circularly polarized light. Furthermore, the rotational directions of the circularly polarized light selectively reflected by the R-incident liquid crystal layer 14R, the G-incident liquid crystal layer 14G, and the B-incident liquid crystal layer 14B, i.e., the twisting direction of the helix of the liquid crystal compound in the cholesteric liquid crystal phase, may be the same or different.

[0029] On the other hand, the ejection unit 16 has an R ejection liquid crystal layer 16R, a G ejection liquid crystal layer 16G, and a B ejection liquid crystal layer 16B. As described above, each output liquid crystal layer is, in a preferred embodiment, a cholesteric liquid crystal layer having a predetermined liquid crystal alignment pattern, with a fixed cholesteric liquid crystal phase, and is a reflective liquid crystal diffraction element that selectively reflects right-circularly polarized or left-circularly polarized light. The rotational directions of the circularly polarized light selectively reflected by the R-emitting liquid crystal layer 16R, the G-emitting liquid crystal layer 16G, and the B-emitting liquid crystal layer 16B, i.e., the twisting direction of the helix of the liquid crystal compound in the cholesteric liquid crystal phase, may be the same or different.

[0030] The R-incident liquid crystal layer 14R, the G-incident liquid crystal layer 14G, and the B-incident liquid crystal layer 14B, as well as the R-exit liquid crystal layer 16R, the G-exit liquid crystal layer 16G, and the B-incident liquid crystal layer 14B, have essentially the same configuration except that they differ in the wavelength range of light they selectively reflect and / or the direction of rotation of the circularly polarized light they selectively reflect. Therefore, in the following explanation, when it is not necessary to distinguish between each liquid crystal layer, these liquid crystal layers will be collectively referred to as the "liquid crystal layer."

[0031] (Liquid crystal layer) The liquid crystal layer will be explained using Figures 2 to 4. A cholesteric liquid crystal layer 34 having a predetermined liquid crystal alignment pattern is formed, for example, conceptually as shown in Figure 2, on a photo-alignment film 32 formed on a support 30. This cholesteric liquid crystal layer 34 becomes the incident liquid crystal layer and the exit liquid crystal layer that act as reflective liquid crystal diffraction elements constituting the incident portion 14 and the exit portion 16. As will be described later, in the optical element of the present invention, the cholesteric liquid crystal layer 34 is basically peeled off from the photoalignment film 32 and transferred as a liquid crystal layer (incident liquid crystal layer or output liquid crystal layer) to the substrate, which is the light guide plate 12 or the lower liquid crystal layer, and then laminated.

[0032] Figure 3 is a schematic diagram showing the orientation state of the liquid crystal compound in the plane of the main surface of the cholesteric liquid crystal layer 34. In the following explanation, the main surface of the cholesteric liquid crystal layer 34 will be described as the XY plane, and the cross section perpendicular to this XY plane will be described as the XZ plane. In other words, Figure 2 corresponds to a schematic diagram of the XZ plane of the cholesteric liquid crystal layer 34, and Figure 3 corresponds to a schematic diagram of the XY plane of the cholesteric liquid crystal layer 34. As shown in Figures 2 to 4, the cholesteric liquid crystal layer 34 is a layer in which liquid crystal compounds are cholesterically oriented. Figures 2 to 4 also show examples where the liquid crystal compounds constituting the cholesteric liquid crystal layer 34 are rod-shaped liquid crystal compounds.

[0033] <Support> The support 30 supports the photo-alignment film 32 and the cholesteric liquid crystal layer 34. The support 30 can be any type of sheet material (film, plate) as long as it can support the photo-alignment film 32 and the cholesteric liquid crystal layer 34. Furthermore, the support 30 preferably has a transmittance of 50% or more for the corresponding light, more preferably 70% or more, and even more preferably 85% or more.

[0034] There are no restrictions on the thickness of the support 30; the thickness should be set appropriately to be able to hold the photo-alignment film 32 and the cholesteric liquid crystal layer 34, depending on the application of the liquid crystal diffraction element and the material used to form the support 30. The thickness of the support 30 is preferably 1 to 2000 μm, more preferably 3 to 500 μm, and even more preferably 5 to 250 μm.

[0035] The support 30 may be single-layered or multi-layered. Examples of a single-layer support 30 include glass, triacetylcellulose (TAC), polyethylene terephthalate (PET), polycarbonate, polyvinyl chloride, acrylic, and polyolefin. Examples of a multilayer support 30 include one of the aforementioned single-layer supports as a substrate, with other layers provided on the surface of this substrate. In particular, crow is suitably used as the support 30 because it can form a photo-aligned film 32 with high surface smoothness.

[0036] <Photoalignment film> In a liquid crystal diffraction element, a photo-alignment film 32 is formed on the surface of the support 30. The photo-alignment film 32 is a photo-alignment film used to orient the liquid crystal compound 40 into a predetermined liquid crystal alignment pattern when forming the cholesteric liquid crystal layer 34. As will be described later, in the present invention, the cholesteric liquid crystal layer 34 has a liquid crystal alignment pattern in which the orientation of the optical axis 40A (see Figure 3) derived from the liquid crystal compound 40 changes while continuously rotating along one direction in the plane. Therefore, the photo-alignment film 32 is formed with an alignment pattern so that the cholesteric liquid crystal layer 34 can form this liquid crystal alignment pattern. In the following explanation, "the orientation of optical axis 40A rotates" will also be simply referred to as "optical axis 40A rotates."

[0037] In the present invention, the photo-alignment film 32 includes a photo-alignment material. That is, the photo-alignment film 32 is a so-called photo-alignment film obtained by irradiating a photo-alignable material with polarized or unpolarized light to form a photo-alignment film. The photo-alignment film 32 is formed by coating a support 30 with a composition containing a photo-alignment material, and then, by interference exposure, an alignment pattern is formed in which the orientation of the optical axis 40A (see Figure 3) originating from the liquid crystal compound 40 of the cholesteric liquid crystal layer 34 is changed by continuously rotating along one direction in the plane.

[0038] Examples of photo-alignment materials that can be used in the photo-alignment film applicable to the present invention include those described in Japanese Patent Publication No. 2006-285197, Japanese Patent Publication No. 2007-076839, Japanese Patent Publication No. 2007-138138, Japanese Patent Publication No. 2007-094071, Japanese Patent Publication No. 2007-121721, Japanese Patent Publication No. 2007-140465, Japanese Patent Publication No. 2007-156439, and Japanese Patent Publication No. 200 Azo compounds described in Japanese Patent Publication No. 7-133184, Japanese Patent Publication No. 2009-109831, Japanese Patent Publication No. 3883848 and Japanese Patent Publication No. 4151746, aromatic ester compounds described in Japanese Patent Publication No. 2002-229039, maleimides having photo-orienting units described in Japanese Patent Publication No. 2002-265541 and Japanese Patent Publication No. 2002-317013 and / Alternatively, alkenyl-substituted nadiimide compounds, photocrosslinkable silane derivatives described in Japanese Patent No. 4205195 and Japanese Patent No. 4205198, photocrosslinkable polyimides, photocrosslinkable polyamides and photocrosslinkable polyesters described in Japanese Patent Publication No. 2003-520878, Japanese Patent Publication No. 2004-529220 and Japanese Patent No. 4162850, and photodimerizable compounds described in Japanese Patent Publication No. 9-118717, Japanese Patent Publication No. 10-506420, Japanese Patent Publication No. 2003-505561, International Publication No. 2010 / 150748, Japanese Patent Publication No. 2013-177561 and Japanese Patent Publication No. 2014-012823, particularly cinnamate compounds, chalcone compounds and coumarin compounds, are exemplified as preferred examples. Among these, azo compounds, photocrosslinkable polyimides, photocrosslinkable polyamides, photocrosslinkable polyesters, cinnamate compounds, and chalcone compounds are particularly suitable for use.

[0039] There are no restrictions on the thickness of the photo-alignment film 32; the thickness should be set appropriately to obtain the necessary alignment function depending on the material used to form the photo-alignment film 32. The thickness of the photo-alignment film 32 is preferably 0.01 to 5 μm, and more preferably 0.05 to 2 μm.

[0040] There are no restrictions on the method for forming the photo-alignment film 32, and various known methods depending on the material used to form the photo-alignment film 32 can be used. As an example, a method is described in which a composition containing a photo-alignment material for forming a photo-alignment film 32 is prepared, this composition is applied to the surface of a support 30 and dried, and then the photo-alignment film 32 is interference-exposed with laser light to form an alignment pattern.

[0041] Figure 8 conceptually shows an example of an exposure apparatus that forms an alignment pattern by interference exposure of the photo-alignment film 32. The exposure apparatus 60 shown in Figure 8 comprises a light source 64 equipped with a laser 62, a λ / 2 plate 65 that changes the polarization direction of the laser light M emitted by the laser 62, a polarizing beam splitter 68 that separates the laser light M emitted by the laser 62 into two beams MA and MB, mirrors 70A and 70B positioned on the optical paths of the two separated beams MA and MB, respectively, and λ / 4 plates 72A and 72B. The light source 64 emits linearly polarized light P0. The λ / 4 plate 72A converts the linearly polarized light P0 (ray MA) into right-circularly polarized light P R λ / 4 plate 72B converts linearly polarized light P0 (ray MB) to left-circularly polarized light P L Convert them to the following:

[0042] A support 30 having a photo-alignment film 32 before the orientation pattern is formed is placed in the exposure section, and two light rays MA and MB are intersected and interfered with on the photo-alignment film 32, and the photo-alignment film 32 is exposed by irradiating it with the resulting interference light. Due to the interference in this process, the polarization state of the light irradiated onto the photo-alignment film 32 changes periodically in an interference fringe pattern. As a result, a photo-alignment film having an orientation pattern in which the orientation state changes periodically is obtained. In the following explanation, this photo-alignment film having an orientation pattern will also be called a "pattern photo-alignment film". In the exposure apparatus 60, the period of the orientation pattern can be adjusted by changing the intersection angle α of the two light rays MA and MB. That is, in the exposure apparatus 60, by adjusting the intersection angle α, the length of one period in which the optical axis 40A rotates 180° in one direction can be adjusted in an orientation pattern in which the optical axis 40A originating from the liquid crystal compound 40 rotates continuously along one direction. By forming a cholesteric liquid crystal layer on a photo-alignment film 32 having an orientation pattern in which such an orientation state changes periodically, a cholesteric liquid crystal layer 34 can be formed having a liquid crystal orientation pattern in which the optical axis 40A originating from the liquid crystal compound 40 rotates continuously along one direction, as will be described later. Furthermore, by rotating the optical axes of the λ / 4 plates 72A and 72B by 90°, the rotation direction of the optical axis 40A can be reversed.

[0043] As described above, the patterned photo-alignment film has an orientation pattern that aligns the liquid crystal compounds such that the orientation of the optical axis of the liquid crystal compounds in the liquid crystal layer formed on the patterned photo-alignment film changes while continuously rotating along at least one direction in the plane, resulting in a liquid crystal alignment pattern. If the orientation axis of a patterned photo-alignment film is the axis along the direction in which it orients the liquid crystal compound, then the patterned photo-alignment film can be said to have an orientation pattern in which the orientation axis changes while continuously rotating along at least one direction in the plane. The orientation axis of a patterned photo-alignment film can be detected by measuring its absorption anisotropy. For example, when a patterned photo-alignment film is irradiated with linearly polarized light while rotating, and the amount of light transmitted through the patterned photo-alignment film is measured, the direction in which the light amount is maximum or minimum is observed to gradually change along one direction in the plane.

[0044] <Cholesteric liquid crystal layer (incident liquid crystal layer / exit liquid crystal layer)> The cholesteric liquid crystal layer 34 is formed on the surface of the photoalignment film 32. The cholesteric liquid crystal layer 34 is a cholesteric liquid crystal layer having a fixed cholesteric liquid crystal phase, and is a cholesteric liquid crystal layer having a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane.

[0045] As conceptually shown in Figure 2, the cholesteric liquid crystal layer 34 has a helical structure in which the liquid crystal compound 40 is spirally stacked, similar to a cholesteric liquid crystal layer in which a normal cholesteric liquid crystal phase is fixed. The structure is such that multiple spirally spiraling liquid crystal compounds 40 are stacked, with one spiral rotation (360° rotation) of the liquid crystal compound 40 being defined as one spiral pitch (spiral pitch P).

[0046] Cholesteric liquid crystal phases are known to exhibit selective reflectivity, selectively reflecting light in specific wavelength ranges. In the cholesteric liquid crystal phase, the center wavelength of selective reflection (selective reflection center wavelength λ) depends on the length of one helical pitch (helical pitch P) in the cholesteric liquid crystal phase, and follows the relationship between the average refractive index n of the cholesteric liquid crystal phase and λ = n × P. Therefore, by adjusting this helical pitch, the selective reflection center wavelength, or the selective reflection wavelength range, can be adjusted. The selective reflection center wavelength of the cholesteric liquid crystal phase becomes longer as the helical pitch P increases.

[0047] The helical pitch of the cholesteric liquid crystal phase depends on the type of chiral agent used with the liquid crystal compound 40 when forming the cholesteric liquid crystal layer, and the concentration of the chiral agent added. Therefore, by adjusting these factors, a desired helical pitch can be obtained. For details on adjusting the pitch, see Fujifilm Research Report No. 50 (2005), pp. 60-63. For measuring the helical sense and pitch, the methods described in "Introduction to Liquid Crystal Chemistry Experiments," edited by the Japanese Liquid Crystal Society, Sigma Publishing, 2007, p. 46, and "Liquid Crystal Handbook," edited by the Liquid Crystal Handbook Editorial Committee, Maruzen, p. 196, can be used.

[0048] Furthermore, the full width at half maximum (FWHM) Δλ (nm) of the wavelength range exhibiting selective reflection (circularly polarized reflection wavelength range) depends on the Δn of the cholesteric liquid crystal phase and the helical pitch P, following the relationship Δλ = Δn × P. Therefore, the width of the selective reflection wavelength range can be controlled by adjusting Δn. Δn can be adjusted by the type of liquid crystal compound forming the cholesteric liquid crystal layer, its mixing ratio, and the temperature during orientation fixing. The full width at half maximum in the reflection wavelength range is adjusted according to the application of the optical element (liquid crystal diffraction element), and is, for example, 10 to 500 nm, preferably 20 to 300 nm, and more preferably 30 to 100 nm.

[0049] As is well known, cholesteric liquid crystal phases exhibit selective reflectivity for either right-handed or left-handed circularly polarized light in a specific wavelength range. Whether the reflected light is right-handed or left-handed depends on the twist direction (sense) of the helix of the cholesteric liquid crystal phase. Selective reflection of circularly polarized light by the cholesteric liquid crystal phase occurs when the twist direction of the helix of the cholesteric liquid crystal phase is to the right, and when the twist direction of the helix is ​​to the left, it reflects left-handed circularly polarized light. Therefore, for example, in the incident section 14, if the R incident liquid crystal layer 14R, the G incident liquid crystal layer 14G, and the B incident liquid crystal layer 14B selectively reflect right-circular polarization, then the cholesteric liquid crystal layers 34 that make up these liquid crystal layers have a rightward twist direction of the helix of the cholesteric liquid crystal phase. Furthermore, the direction of rotation of the cholesteric liquid crystal phase can be adjusted by the type of liquid crystal compound forming the cholesteric liquid crystal layer and / or the type of chiral agent added.

[0050] As shown in Figure 3, in the XY plane of the cholesteric liquid crystal layer 34, the liquid crystal compounds 40 are arranged along multiple parallel array axes D within the XY plane. On each array axis D, the orientation of the optical axis 40A of the liquid crystal compounds 40 changes while continuously rotating in one direction within the plane along the array axis D. Here, as an example, let's assume that the array axis D is oriented in the X direction. In the Y direction, liquid crystal compounds 40 with the same optical axis 40A orientation are oriented at equal intervals. Furthermore, the statement that "the orientation of the optical axis 40A of the liquid crystal compound 40 changes while continuously rotating in one direction within the plane along the array axis D" means that the angle between the optical axis 40A of the liquid crystal compound 40 and the array axis D differs depending on the position along the array axis D, and that the angle between the optical axis 40A and the array axis D gradually changes from θ to θ+180° or θ-180° along the array axis D. In other words, as shown in Figure 3, the optical axis 40A of multiple liquid crystal compounds 40 arranged along the array axis D changes while rotating at a constant angle along the array axis D. Furthermore, the difference in angle between the optical axes 40A of liquid crystal compounds 40 adjacent to each other in the direction of the array axis D is preferably 45° or less, more preferably 15° or less, and even more preferably a smaller angle. Furthermore, in this specification, when the liquid crystal compound 40 is a rod-shaped liquid crystal compound, the optical axis 40A of the liquid crystal compound 40 is intended to be the molecular long axis of the rod-shaped liquid crystal compound. On the other hand, when the liquid crystal compound 40 is a disc-shaped liquid crystal compound, the optical axis 40A of the liquid crystal compound 40 is intended to be an axis parallel to the direction normal to the disc surface of the disc-shaped liquid crystal compound.

[0051] In the cholesteric liquid crystal layer 34, the length (distance) over which the optical axis 40A of the liquid crystal compound 40 rotates 180° in the direction of the array axis D, which changes as the optical axis 40A continuously rotates within the plane of the liquid crystal alignment pattern of the liquid crystal compound 40, is defined as the length of one period Λ in the liquid crystal alignment pattern. In other words, the distance between the centers of two liquid crystal compounds 40 whose angles with respect to the array axis D are equal in the direction of the array axis D is defined as the length of one period Λ. Specifically, as shown in Figure 3, the distance between the centers of two liquid crystal compounds 40 whose array axis D coincides with the direction of the optical axis 40A is defined as the length of one period Λ. In the following explanation, this length of one period Λ will also be referred to as "period Λ". The liquid crystal alignment pattern of the cholesteric liquid crystal layer 34 repeats this one period Λ in one direction, where the orientation of the array axis D, i.e., the optical axis 40A, continuously rotates and changes. In a liquid crystal diffraction element, this one period Λ becomes the period of the diffraction structure.

[0052] On the other hand, in the liquid crystal compound 40 that forms the cholesteric liquid crystal layer 34, the orientation of the optical axis 40A is the same in the direction perpendicular to the arrangement axis D direction (Y direction in Figure 3), that is, in the Y direction perpendicular to the direction in which the optical axis 40A rotates continuously. In other words, in the liquid crystal compound 40 that forms the cholesteric liquid crystal layer 34, the angle between the optical axis 40A of the liquid crystal compound 40 and the direction of arrow X is equal in the Y direction.

[0053] When a cross-section of a cholesteric liquid crystal layer in the thickness direction is observed using a Scanning Electron Microscope (SEM), a striped pattern of alternating light and dark areas is observed, due to the cholesteric liquid crystal phase. The cross-section of a cholesteric liquid crystal layer in the thickness direction is the cross-section perpendicular to the main plane, and is the cross-section in the stacking direction of each layer (film). In a typical cholesteric liquid crystal layer that does not have a liquid crystal alignment pattern, these striped patterns of light and dark areas are parallel to the main plane. In contrast, when the cross-section in the thickness direction, i.e., the XZ plane, of the cholesteric liquid crystal layer 34 having a liquid crystal alignment pattern as shown in Figure 2 is observed with a SEM, a striped pattern is observed in which alternately arranged light areas 42 and dark areas 44 are inclined at a predetermined angle with respect to the main plane (XY plane), as conceptually shown in Figure 4. In such an SEM cross-section, the spacing between adjacent bright areas 42 and bright areas 42, or between dark areas 44 and dark areas 44, in the direction normal to the line formed by the bright areas 42 or dark areas 44, corresponds to a 1 / 2 pitch. That is, as shown by P in Figure 4, two bright areas 42 and two dark areas 44 correspond to one helical pitch (one turn of the helix), i.e., the helical pitch P.

[0054] The diffraction effect of the cholesteric liquid crystal layer 34 having such a liquid crystal alignment pattern will be explained below.

[0055] In a typical cholesteric liquid crystal layer without a liquid crystal alignment pattern, the helical axis originating from the cholesteric liquid crystal phase is perpendicular to the principal plane (XY plane), and its reflective surface is parallel to the principal plane (XY plane). Furthermore, the optical axis of the liquid crystal compound is not inclined with respect to the principal plane (XY plane). In other words, the optical axis is parallel to the principal plane (XY plane). Therefore, when observing a cross-section (XZ plane) in the thickness direction of a typical cholesteric liquid crystal layer with a scanning electron microscope (SEM), the alternatingly arranged light and dark areas are parallel to the main plane (XY plane), as described above. In other words, the alternating direction of the light and dark areas is perpendicular to the main plane. Because the cholesteric liquid crystal phase is specularly reflective, for example, when light is incident on the cholesteric liquid crystal layer from the normal direction, the light is reflected in the normal direction.

[0056] On the other hand, as described above, the cholesteric liquid crystal layer 34 has a liquid crystal alignment pattern in which the optical axis 40A changes while continuously rotating along the alignment axis D direction (a predetermined one direction) within the plane. A cholesteric liquid crystal layer 34 having such a liquid crystal alignment pattern reflects incident light at an angle in the direction of the alignment axis D relative to specular reflection. This will be explained below with reference to Figure 5.

[0057] As an example, the cholesteric liquid crystal layer 34 is a right-circular polarized red light R R Assume that this is a cholesteric liquid crystal layer that selectively reflects R. Therefore, when light is incident on the cholesteric liquid crystal layer 34, the cholesteric liquid crystal layer 34 reflects the right-circular polarization of red light. R It reflects only certain types of light, while transmitting all other light.

[0058] In the cholesteric liquid crystal layer 34, the optical axis 40A of the liquid crystal compound 40 changes while rotating along the direction of the array axis D (one direction). The liquid crystal alignment pattern formed in the cholesteric liquid crystal layer 34 is a periodic pattern in the direction of the alignment axis D. Therefore, when red light incident on the cholesteric liquid crystal layer 34 is right-circularly polarized R RAs conceptually shown in Figure 5, the light is not specularly reflected, but is diffracted in a direction corresponding to the period of the liquid crystal alignment pattern, and is diffracted and reflected in a direction tilted in the direction of the alignment axis D with respect to the XY plane (the main plane of the cholesteric liquid crystal layer).

[0059] Therefore, by using a cholesteric liquid crystal layer 34, which is a reflective liquid crystal diffraction element, as the incident liquid crystal layer of the incident section 14, light incident from a direction perpendicular to the main surface of the light guide plate 12 can be diffracted and reflected at an angle that causes total internal reflection within the light guide plate, and then incident onto the light guide plate 12. Furthermore, by using the cholesteric liquid crystal layer 34 as the output liquid crystal layer of the output section 16, the light propagated through total internal reflection within the light guide plate 12 can be diffracted and reflected in a direction perpendicular to the main surface of the light guide plate 12 and emitted from the light guide plate 12.

[0060] In the cholesteric liquid crystal layer 34, the diffraction direction of light, i.e., the reflection direction, can be adjusted by appropriately setting the direction of the array axis D, which is the one direction in which the optical axis 40A rotates.

[0061] Furthermore, when reflecting circularly polarized light of the same wavelength and direction of rotation, the direction of reflection of the circularly polarized light can be reversed by reversing the rotation direction of the optical axis 40A of the liquid crystal compound 40 facing the array axis D. For example, in Figures 2 and 3, the rotation direction of the optical axis 40A toward the array axis D is clockwise, and a certain circularly polarized light is reflected tilted toward the array axis D. However, by changing this to counterclockwise rotation, a certain circularly polarized light is reflected tilted in the opposite direction to the array axis D.

[0062] Furthermore, in liquid crystal layers having the same liquid crystal alignment pattern, the reflection direction is reversed depending on the spiral direction of the liquid crystal compound 40, i.e., the spiral direction of the reflected circularly polarized light. For example, if the spiral rotation direction is a right-handed twist, it selectively reflects right-handed circularly polarized light. By having a liquid crystal alignment pattern in which the optical axis 40A rotates clockwise along the direction of the array axis D, it reflects right-handed circularly polarized light at an angle in the direction of the array axis D. Furthermore, for example, if the spiral rotation direction is left-handed, it selectively reflects left-handed circularly polarized light. A liquid crystal layer having a liquid crystal alignment pattern in which the optical axis 40A rotates clockwise along the alignment axis D reflects left-handed circularly polarized light tilted in the opposite direction to the alignment axis D.

[0063] Therefore, the R incident liquid crystal layer 14R, G incident liquid crystal layer 14G, and B incident liquid crystal layer 14B constituting the incident section 14 set the direction of the array axis D and the rotation direction of the optical axis 40A in the liquid crystal alignment pattern so that the incident light is properly directed towards the exit section 16, according to the rotation direction of the circularly polarized light that is selectively reflected, i.e., the rotation direction of the helix. On the other hand, the R-emitting liquid crystal layer 16R, G-emitting liquid crystal layer 16G, and B-emitting liquid crystal layer 16B that constitute the emission section 16 set the direction of the array axis D and the rotation direction of the optical axis 40A in the liquid crystal alignment pattern so that the incident light is emitted to the observation position by the user U in accordance with the rotation direction of the selectively reflected circularly polarized light, i.e., the rotation direction of the helix.

[0064] In this liquid crystal diffraction element, the period Λ of the diffraction structure is the length of a 180° rotation of the optical axis of the liquid crystal compound in the liquid crystal alignment pattern of the liquid crystal compound in the liquid crystal layer. Furthermore, in the liquid crystal layer, the direction in which the optical axis of the liquid crystal compound changes while rotating (the direction of the alignment axis D) is the periodic direction of the diffraction structure. In the optical element 10 of the present invention, there is no limit to the length of one period Λ of the diffraction element, and it can be set appropriately according to the incident angle on the light guide plate 12, the magnitude of diffraction of the light to be emitted from the light guide plate 12, etc. The length of one period Λ is preferably 0.1 to 10 μm, more preferably 0.15 to 2 μm, and even more preferably 0.2 to 1 μm.

[0065] In a liquid crystal layer with a liquid crystal alignment pattern, the shorter the period Λ, the larger the angle of reflected light relative to the incident light. In other words, the shorter the period Λ, the greater the angle at which the reflected light can be reflected relative to the specular reflection of the incident light. Furthermore, in a liquid crystal layer having this liquid crystal alignment pattern, the angle of reflection (diffraction angle) of light differs depending on the wavelength of the reflected light. Specifically, the longer the wavelength of light, the greater the tilt of the reflected light relative to the specular reflection of the incident light.

[0066] Therefore, in the optical element of the present invention, it is preferable that the laminate, in which a plurality of liquid crystal layers (cholesteric liquid crystal layers) are stacked, has a permutation of the wavelength of light selectively reflected by each liquid crystal layer and one period Λ. Specifically, in the optical element 10, the wavelength of light selectively reflected by the R-incident liquid crystal layer 14R, G-incident liquid crystal layer 14G, and B-incident liquid crystal layer 14B constituting the incident portion 14 decreases in the order of R-incident liquid crystal layer 14R, G-incident liquid crystal layer 14G, and B-incident liquid crystal layer 14B. Therefore, it is preferable that the period Λ also decreases in the order of R-incident liquid crystal layer 14R, G-incident liquid crystal layer 14G, and B-incident liquid crystal layer 14B. On the other hand, the wavelength of light selectively reflected by the R-emitting liquid crystal layer 16R, G-emitting liquid crystal layer 16G, and B-emitting liquid crystal layer 16B constituting the emission section 16 decreases in the order of R-emitting liquid crystal layer 16R, G-emitting liquid crystal layer 16G, and B-emitting liquid crystal layer 16B. Therefore, it is preferable that the period Λ also decreases in the order of R-emitting liquid crystal layer 16R, G-emitting liquid crystal layer 16G, and B-emitting liquid crystal layer 16B. In this regard, the same applies when the liquid crystal layers of the input section 14 and the output section 16 are two layers, and when they are four or more layers.

[0067] This configuration allows the incident directions of the red image R, green image G, and blue image B onto the light guide plate 12 by the incident section 14 to be aligned. Furthermore, this configuration allows the emission directions of the red image R, green image G, and blue image B emitted from the emission section 16 to be the same. As a result, a color image without color shift can be emitted from the light guide plate 12 to the observation position of the AR glasses user U.

[0068] The example shown in Figure 2 is a configuration in which, in the XZ plane of the cholesteric liquid crystal layer 34, the liquid crystal compound 40 is oriented with its optical axis 40A parallel to the main plane (XY plane). However, the present invention is not limited thereto. For example, as conceptually shown in Figure 6, the liquid crystal compound 40 may be oriented in a configuration in which its optical axis 40A is inclined with respect to the main plane (XY plane) in the XZ plane of the cholesteric liquid crystal layer 34.

[0069] Furthermore, in the example shown in Figure 6, the tilt angle of the liquid crystal compound 40 with respect to the main plane (XY plane) in the XZ plane of the cholesteric liquid crystal layer 34 is uniform in the thickness direction (Z direction), but the present invention is not limited thereto. The cholesteric liquid crystal layer 34 may have regions in which the tilt angle of the liquid crystal compound 40 differs in the thickness direction. For example, in the example shown in Figure 7, the optical axis 40A of the liquid crystal compound 40 is parallel to the main plane (pre-tilt angle is 0°) at the interface on the photo-alignment film 32 side of the liquid crystal layer, and as the distance from the interface on the photo-alignment film 32 side in the thickness direction increases, the tilt angle of the liquid crystal compound 40 increases, and thereafter the liquid crystal compound is oriented at a constant tilt angle all the way to the other interface (air interface).

[0070] Thus, in the cholesteric liquid crystal layer 34, the optical axis of the liquid crystal compound may have a pre-tilt angle at one of the upper and lower interfaces, or it may have a pre-tilt angle at both interfaces. Furthermore, the pre-tilt angles at the two interfaces may be different. Because the liquid crystal compound has a tilt angle (is inclined), the effective birefringence of the liquid crystal compound increases when light diffracts, thereby improving the diffraction efficiency.

[0071] The average angle (average tilt angle) between the optical axis 40A of the liquid crystal compound 40 and the main plane (XY plane) is preferably 5 to 45°, and more preferably 12 to 22°. The average tilt angle can be measured by observing the XZ plane of the cholesteric liquid crystal layer 34 with a polarizing microscope. In particular, in the XZ plane of the cholesteric liquid crystal layer 34, it is preferable that the optical axis 40A of the liquid crystal compound 40 is tilted in the same direction as the main plane (XY plane). The tilt angle mentioned above is the value obtained by measuring the angle between the optical axis 40A of the liquid crystal compound 40 and the main surface at five or more arbitrary locations during polarized light microscopy observation of the cross-section of the cholesteric liquid crystal layer, and arithmetically averaging these values.

[0072] Light incident perpendicularly on the cholesteric liquid crystal layer 34 (diffractive element) travels diagonally within the liquid crystal layer due to a bending force. As light travels within the liquid crystal layer, a deviation occurs from the conditions such as the diffraction period, which are originally set to obtain the desired diffraction angle for perpendicular incidence, resulting in diffraction loss. When a liquid crystal compound is tilted, there is a direction in which a higher birefringence occurs relative to the direction in which light diffracts, compared to when the compound is not tilted. In this direction, the effective anomalous refractive index becomes larger, and therefore the birefringence, which is the difference between the anomalous refractive index and the ordinary refractive index, becomes higher. By setting the tilt angle to match the desired diffraction direction, it is possible to suppress the deviation from the original diffraction conditions in that direction. As a result, it is thought that higher diffraction efficiency can be obtained when using a liquid crystal compound with a tilt angle.

[0073] Furthermore, it is preferable that the tilt angle is controlled by processing the interface of the cholesteric liquid crystal layer 34. At the interface on the support side, the tilt angle of the liquid crystal compound can be controlled by pre-tilting the photo-alignment film. For example, by exposing the photo-alignment film to ultraviolet light from the front and then from an oblique angle during its formation, a pre-tilt angle can be generated in the liquid crystal compound in the liquid crystal layer formed on the photo-alignment film. In this case, the liquid crystal compound is pre-tilted in a direction where the uniaxial side is visible with respect to the second irradiation direction. However, since the liquid crystal compound perpendicular to the second irradiation direction does not pre-tilt, there are regions in the plane that are pre-tilted and regions that are not. This is suitable for increasing diffraction efficiency because it contributes to maximizing birefringence in the direction in which light is diffracted. Furthermore, additives that enhance the pre-tilt angle can be added to the liquid crystal layer or the photo-alignment film. In this case, the additives can be used as a factor to further increase diffraction efficiency. This additive can also be used to control the pre-tilt angle of the air-side interface.

[0074] Here, in the cross-section observed by SEM, the cholesteric liquid crystal layer 34 has light and dark areas originating from the cholesteric liquid crystal phase that are inclined with respect to the main plane. When the in-plane retardation Re of the liquid crystal layer is measured from the normal direction and a direction inclined with respect to the normal, it is preferable that the direction in which the in-plane retardation Re is minimized in either the slow-phase axis plane or the fast-phase axis plane is inclined with respect to the normal direction. Specifically, it is preferable that the absolute value of the measurement angle that the direction in which the in-plane retardation Re is minimized makes with respect to the normal is 5° or more. In other words, it is preferable that the liquid crystal compound of the liquid crystal layer is inclined with respect to the main plane, and that the direction of inclination substantially coincides with the light and dark areas of the liquid crystal layer. The normal direction is the direction perpendicular to the main plane. Because the liquid crystal layer has this configuration, it can diffract circularly polarized light with higher diffraction efficiency compared to a liquid crystal layer in which the liquid crystal compound is parallel to the main plane.

[0075] In a configuration where the liquid crystal compound in the liquid crystal layer is tilted with respect to the main surface, and the direction of the tilt substantially coincides with the bright and dark areas, the optical axis of the liquid crystal compound coincides with the bright and dark areas corresponding to the reflective surfaces. Therefore, the effect of the liquid crystal compound on light reflection (diffraction) is increased, and the diffraction efficiency can be improved. As a result, the amount of reflected light relative to the incident light can be further improved.

[0076] In the phase-advancing or phase-lagging axis plane of the liquid crystal layer, the absolute value of the optical axis inclination angle of the liquid crystal layer is preferably 5° or more, more preferably 15° or more, and even more preferably 20° or more. By setting the absolute value of the optical axis tilt angle to 15° or more, it is preferable to more preferably align the direction of the liquid crystal compound with the light and dark areas, thereby improving diffraction efficiency.

[0077] <Requirements for film thickness distribution of the incident and output liquid crystal layers> The R incident liquid crystal layer 14R, G incident liquid crystal layer 14G, and B incident liquid crystal layer 14B that constitute the incident section 14 are formed by the cholesteric liquid crystal layer 34, which is a reflective liquid crystal diffraction element as described above. Similarly, the R-emitting liquid crystal layer 16R, G-emitting liquid crystal layer 16G, and B-emitting liquid crystal layer 16B that constitute the emission section 16 are also formed by the cholesteric liquid crystal layer 34, which is a reflective liquid crystal diffraction element as described above. Here, in the optical element 10 of the present invention, the incident portion 14 and the output portion 16 each have at least one liquid crystal layer with high uniformity of film thickness. Specifically, the incident portion 14 and the output portion 16 each have at least one liquid crystal layer that satisfies the film thickness distribution requirements shown below.

[0078] In this invention, the film thickness distribution requirements are as follows: The thickness distribution requirement is determined by observing a cross-section of the liquid crystal layer (cholesteric liquid crystal layer) in the thickness direction using a Scanning Electron Microscope (SEM) at 10,000x magnification. In determining the in-plane orientation of the liquid crystal layer, by irradiating the liquid crystal layer with laser light at various incidence angles and orientations, the incident light is diffracted, and the direction of the emitted light's guidance can be determined. This allows us to determine the in-plane orientation of the liquid crystal alignment pattern, where the orientation of the optical axis originating from the liquid crystal compound in the liquid crystal layer changes while continuously rotating. In this invention, the film thickness distribution requirement is determined by observing a cross-section parallel to the in-plane direction of this liquid crystal alignment pattern. By observing the cross-section of the liquid crystal layer at 10,000x magnification using this SEM at 20 locations by continuously moving the observation position in the in-plane direction of the liquid crystal layer, an image of the 200 μm range in the in-plane direction of the liquid crystal layer is obtained (see Figure 10). The difference between the maximum and minimum film thickness of the liquid crystal layer is obtained within a 200 μm range in the in-plane direction of the liquid crystal layer. Perform this operation on any 10 cross-sections. The differences between the maximum and minimum film thicknesses obtained in this way are then arithmetically averaged across the 10 cross-sections. If the value obtained by this arithmetic mean is 0.1 μm or less, then this liquid crystal layer satisfies the film thickness distribution requirements of the present invention. Preferably, the value obtained by this arithmetic mean is 0.07 μm or less, and more preferably 0.03 μm or less.

[0079] The optical element 10 in the illustrated example is used as AR glasses, and as a preferred example, a cholesteric liquid crystal layer 34, which is a reflective liquid crystal diffraction element, is used in the incident section 14 and the output section 16. As described above, the image displayed by the display is incident on the light guide plate 12 by the incident section 14, propagates through total internal reflection, and is emitted from the light guide plate 12 by the output section 16, so that it can be emitted to the observation position of the user U. Furthermore, the cholesteric liquid crystal layer 34 selectively reflects circularly polarized light of a specific wavelength range and direction, while transmitting other light. Therefore, by stacking liquid crystal layers with different wavelength ranges that are selectively reflected (selective reflection center wavelengths), it is possible to support full-color images with red image R, green image G, and blue image B as shown in the illustrated example, or to support two-color images, etc.

[0080] Herein, according to the inventors' studies, when an optical element comprising a stacked liquid crystal layer that acts as a liquid crystal diffraction element, such as the cholesteric liquid crystal layer 34 having the above-described liquid crystal alignment pattern, is used as a diffraction element for injecting / emitting light into a light guide plate in AR glasses or the like, the displayed image may become blurred. The inventors diligently investigated the cause of the blurring in this image. As a result, they found that in optical elements in which liquid crystal layers acting as liquid crystal diffraction elements, such as the cholesteric liquid crystal layer 34 having the liquid crystal alignment pattern described above, a distribution in the diffraction angle may occur within the plane of the liquid crystal layer. If a distribution of diffraction angles occurs within the surface of the liquid crystal layer, for example in AR glasses, the image may not be projected to the correct position at the user's (U) observation position, resulting in a blurred image. In particular, if such a distribution of diffraction angles occurs at the incident point, the blurring of the image will be greater.

[0081] The inventors diligently investigated the cause of this phenomenon. As a result, they discovered that the blurring of the image, or the distribution of diffraction angles, was caused by uneven film thickness (variation in film thickness) in the lower liquid crystal layer, that is, in the liquid crystal layer closer to the substrate among the stacked liquid crystal layers. Furthermore, the inventors discovered that this distribution of diffraction angles was not caused by fine irregularities in the lower liquid crystal layer, but rather by gentle, wave-like variations in film thickness in the lower liquid crystal layer.

[0082] As conceptually shown in Figure 9, assume that reflective layers B, G, and R, each consisting of a cholesteric liquid crystal layer 34 having the liquid crystal alignment pattern described above, are stacked on a substrate S in this order. In this case, as shown on the left side of Figure 9, if there is no thickness unevenness in all reflective layers, reflective layer B, reflective layer G, and reflective layer R can all reflect light at the same diffraction angle across their entire surface.

[0083] In contrast, as shown on the right side of Figure 9, for example, if there is unevenness in the film thickness of the reflective layer B closest to the substrate S, the reflective layer G laminated on top of it (on the opposite side from the substrate S) will have an oblique interface with reflective layer B. As a result, the orientation angle of the cholesteric liquid crystal phase of the liquid crystal compound (cholesteric orientation) changes within the plane of the reflective layer G. Furthermore, since the reflective layer R laminated on top of reflective layer G also has regions where the interface with reflective layer G is oblique, the orientation angle of the cholesteric liquid crystal phase of the liquid crystal compound also changes within the plane. As a result, as shown on the right side of Figure 9, a distribution of diffraction angles occurs within the plane of the reflective layer G (reflective layer R), which causes blurring in the image.

[0084] In contrast, the optical element 10 of the present invention satisfies the film thickness distribution requirement that at least one incident liquid crystal layer constituting the incident section 14 and at least one exit liquid crystal layer constituting the exit section 16 have an arithmetic mean of the difference between the maximum and minimum film thickness in the 200 μm range in the cross-section 10 obtained as described above, which is 0.1 μm or less. Liquid crystal layers that satisfy this film thickness distribution requirement have extremely small gradual film thickness variations such as undulations. As a result, as shown on the left side of Figure 9, the distribution of diffraction angles within the plane is extremely small in each liquid crystal layer, which prevents blurring in images of each color when used as AR glasses.

[0085] In the optical element of the present invention, the incident portion 14 only needs to satisfy the film thickness distribution requirement if at least one of the R incident liquid crystal layer 14R, G incident liquid crystal layer 14G, and B incident liquid crystal layer 14B. Furthermore, the injection unit 16 only needs to satisfy the film thickness distribution requirement if at least one of the R injection liquid crystal layer 16R, G injection liquid crystal layer 16G, and B injection liquid crystal layer 16B is present.

[0086] Here, the diffraction angle distribution due to film thickness variations does not occur in the liquid crystal layer with film thickness variations itself, but rather in the liquid crystal layer laminated on top of the liquid crystal layer with film thickness variations. Note that "down" refers to the substrate side, and "up" refers to the opposite side. In other words, the diffraction angle distribution due to film thickness variations occurs in the liquid crystal layer located away from the substrate relative to the liquid crystal layer with film thickness variations. Considering this point, it is preferable that at least the liquid crystal layers located at the edges in the stacking direction satisfy the film thickness distribution requirement, and it is even more preferable that at least the liquid crystal layer closest to the substrate satisfies the film thickness distribution requirement. In other words, in the illustrated example, it is preferable that at least the B incident liquid crystal layer 14B of the incident section 14 satisfies the film thickness distribution requirement. Similarly, it is preferable that at least the B exit liquid crystal layer 16B of the exit section 16 satisfies the film thickness distribution requirement.

[0087] For the same reason, it is more preferable that at least the liquid crystal layers other than the liquid crystal layer furthest from the substrate, i.e., at least the liquid crystal layers other than the topmost liquid crystal layer, satisfy the film thickness distribution requirement. In other words, for the optical element 10 shown in the illustration, it is more preferable that at least the incident liquid crystal layer 14B and the incident liquid crystal layer 14G of the incident section 14 satisfy the film thickness distribution requirement. Similarly, it is more preferable that at least the exit liquid crystal layer 16B and the exit liquid crystal layer 16G of the exit section 16 satisfy the film thickness distribution requirement.

[0088] Furthermore, in the optical element of the present invention, it is most preferable that all liquid crystal layers constituting the laminate satisfy the film thickness distribution requirement. In other words, for the optical element 10 shown in the illustration, it is most preferable that the incident section 14 satisfies the film thickness distribution requirements for the R incident liquid crystal layer 14R, the G incident liquid crystal layer 14G, and the B incident liquid crystal layer 14B. Similarly, it is most preferable that the exit section 16 satisfies the film thickness distribution requirements for the R exit liquid crystal layer 16R, the G exit liquid crystal layer 16G, and the B exit liquid crystal layer 16B.

[0089] In the illustrated example, the optical element 10 is, in a preferred embodiment, a laminate in the optical element of the present invention in which both the incident portion 14 and the exit portion 16 have a predetermined liquid crystal alignment pattern in the laminated liquid crystal layers, and at least one layer satisfies the film thickness distribution requirement. However, the present invention is not limited thereto. For example, in the optical element of the present invention having an incident portion 14 and an outgoing portion 16 to a light guide plate 12 which is a substrate, only the incident portion 14 may be a laminate in the optical element of the present invention, or only the outgoing portion 16 may be a laminate in the optical element of the present invention. In the illustrated example of the optical element 10 having an incident portion 14 and an outgoing portion 16 to a light guide plate 12, it is preferable that at least the incident portion 14 is a laminate in the present invention. Furthermore, in the optical element 10 of the present invention having an incident portion 14 and an outgoing portion 16 to a light guide plate 12, it is more preferable that the incident portion 14 and the outgoing portion 16 are laminates in the present invention, as shown in the illustrated example.

[0090] <<Method for forming a cholesteric liquid crystal layer>> The cholesteric liquid crystal layers 34, which constitute the incident liquid crystal layer 14R, G incident liquid crystal layer 14G, and B incident liquid crystal layer 14B of the incident section 14, and the R exit liquid crystal layer 16R, G exit liquid crystal layer 16G, and B exit liquid crystal layer 16B of the exit section 16, can be formed, for example, by fixing liquid crystal phases in layers in which liquid crystal compounds are oriented in a predetermined orientation state. For example, in the case of a cholesteric liquid crystal layer, it can be formed by fixing cholesteric liquid crystal phases in layers. The structure in which the cholesteric liquid crystal phase is fixed can be any structure in which the orientation of the liquid crystal compound that constitutes the liquid crystal phase is maintained. Typically, a polymerizable liquid crystal compound is brought into a predetermined liquid crystal phase orientation state, and then polymerized and cured by ultraviolet irradiation, heating, etc., to form a non-fluid layer, and at the same time, a structure is preferred in which the orientation form does not change due to an external field or external force. In a structure with a fixed liquid crystal phase, it is sufficient that the optical properties of the liquid crystal phase are maintained, and the liquid crystal compound 40 does not need to exhibit liquid crystalline properties in the liquid crystal layer. For example, a polymerizable liquid crystal compound may lose its liquid crystalline properties due to its high molecular weight resulting from a curing reaction.

[0091] As an example of a material used to form a liquid crystal layer, a liquid crystal composition containing a liquid crystal compound is used. Preferably, the liquid crystal compound is a polymerizable liquid crystal compound. Furthermore, the liquid crystal composition used to form the liquid crystal layer may also contain a surfactant and a chiral agent.

[0092] --Polymerizable liquid crystal compound-- The polymerizable liquid crystal compound may be a rod-shaped liquid crystal compound or a disc-shaped liquid crystal compound. Examples of rod-shaped polymerizable liquid crystal compounds include rod-shaped nematic liquid crystal compounds. Preferred rod-shaped nematic liquid crystal compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyanosubstituted phenylpyrimidines, alkoxysubstituted phenylpyrimidines, phenyldioxanes, trans, and alkenylcyclohexylbenzonitriles. Not only low molecular weight liquid crystal compounds but also high molecular weight liquid crystal compounds can be used.

[0093] 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, with unsaturated polymerizable groups being preferred and ethylenically unsaturated polymerizable groups being more preferred. Polymerizable groups can be introduced into the molecule of the liquid crystal compound by various methods. The number of polymerizable groups in a polymerizable liquid crystal compound is preferably 1 to 6, more preferably 1 to 3. Examples of polymerizable liquid crystal compounds include those described in Makromol. Chem., Vol. 190, p. 2255 (1989), Advanced Materials, Vol. 5, p. 107 (1993), U.S. Patent No. 4,683,327, U.S. Patent No. 5,622,648, U.S. Patent No. 5,770,107, International Publication No. 95 / 22586, International Publication No. 95 / 24455, International Publication No. 97 / 00600, International Publication No. 98 / 23580, International Publication No. 98 / 52905, Japanese Patent Publication No. 1-272551, Japanese Patent Publication No. 6-16616, Japanese Patent Publication No. 7-110469, Japanese Patent Publication No. 11-80081, and Japanese Patent Publication No. 2001-328973, etc. Two or more polymerizable liquid crystal compounds may be used in combination. Using two or more polymerizable liquid crystal compounds in combination can lower the orientation temperature.

[0094] In addition, polymerizable liquid crystal compounds other than those mentioned above include cyclic organopolysiloxane compounds having a cholesteric phase, such as those disclosed in Japanese Patent Publication No. 57-165480. Furthermore, as the aforementioned polymeric liquid crystal compounds, polymers in which liquid crystal-resisting mesogenic groups are introduced in the main chain, side chains, or both the main chain and side chains, polymeric cholesteric liquid crystals in which cholesteryl groups are introduced in the side chains, liquid crystalline polymers such as those disclosed in Japanese Patent Publication No. 9-133810, and liquid crystalline polymers such as those disclosed in Japanese Patent Publication No. 11-293252 can be used.

[0095] --Disk-shaped liquid crystal compound-- As the disc-shaped liquid crystal compound, for example, those described in Japanese Patent Publication No. 2007-108732 and Japanese Patent Publication No. 2010-244038 can be preferably used.

[0096] Furthermore, the amount of polymerizable liquid crystal compound added to the liquid crystal composition is preferably 75 to 99.9% by mass, more preferably 80 to 99% by mass, and even more preferably 85 to 90% by mass, relative to the solid content mass (mass excluding solvent) of the liquid crystal composition.

[0097] --Surfactants-- The liquid crystal composition used to form the liquid crystal layer may contain a surfactant. The surfactant is preferably a compound that can function as an orientation control agent that contributes stably or rapidly to the orientation of the cholesteric liquid crystal phase. Examples of surfactants include silicate surfactants and fluorine-based surfactants, with fluorine-based surfactants being preferred.

[0098] Specific examples of surfactants include the compounds described in paragraphs

[0082] to

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

[0031] to

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

[0092] and

[0093] of Japanese Patent Publication No. 2005-99248, the compounds exemplified in paragraphs

[0076] to

[0078] and paragraphs

[0082] to

[0085] of Japanese Patent Publication No. 2002-129162, and fluorine (meth)acrylate polymers described in paragraphs

[0018] to

[0043] of Japanese Patent Publication No. 2007-272185, etc. Furthermore, a single surfactant may be used alone, or two or more surfactants may be used in combination. As a fluorine-based surfactant, the compounds described in paragraphs

[0082] to

[0090] of Japanese Patent Application Publication No. 2014-119605 are preferred.

[0099] The amount of surfactant added to the liquid crystal composition 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, relative to the total mass of the liquid crystal compound.

[0100] --Chiral agents (optically active compounds)-- Chiral agents have the function of inducing a helical structure in the cholesteric liquid crystal phase. Since different chiral agents induce different helical twist directions or helical pitches, they should be selected according to the purpose. There are no particular restrictions on the chiral agent, and known compounds (for example, described in the Liquid Crystal Device Handbook, Chapter 3, Section 4-3, Chiral Agents for TN (twisted nematic) and STN (Super Twisted Nematic), page 199, edited by the 142nd Committee of the Japan Society for the Promotion of Science, 1989), isosorbide, and isomannide derivatives can be used. Chiral agents generally contain an asymmetric carbon atom, but axially asymmetric compounds or planar asymmetric compounds that do not contain an asymmetric carbon atom can also be used as chiral agents. Examples of axially asymmetric compounds or planar asymmetric compounds include binaphthyl, helicene, paracyclophane, and their derivatives. Chiral agents may have polymerizable groups. If both the chiral agent and the liquid crystal compound have polymerizable groups, a polymerization reaction between the polymerizable chiral agent and the polymerizable liquid crystal compound can form a polymer having repeating units derived from the polymerizable liquid crystal compound and repeating units derived from the chiral agent. In this embodiment, it is preferable that the polymerizable group of the polymerizable chiral agent is of the same type as the polymerizable group of the polymerizable liquid crystal compound. Therefore, the polymerizable group of the chiral agent is preferably an unsaturated polymerizable group, an epoxy group, or an azilidinyl group, more preferably an unsaturated polymerizable group, and even more preferably an ethylenically unsaturated polymerizable group. Furthermore, the chiral agent may be a liquid crystal compound.

[0101] When the chiral agent has a photoisomerizing group, it is preferable because, after coating and orientation, a pattern of the desired reflected wavelength corresponding to the emission wavelength can be formed by photomask irradiation with active light or the like. Preferred photoisomerizing groups are the isomerization site of a photochromic compound, an azo group, an azoxy group, or a cinnamoyl group. Specific compounds that can be used include those described in Japanese Patent Publication No. 2002-80478, 2002-80851, 2002-179668, 2002-179669, 2002-179670, 2002-179681, 2002-179682, 2002-338575, 2002-338668, 2003-313189, and 2003-313292, etc.

[0102] In the liquid crystal composition, the content of the chiral agent is preferably 0.01 to 200 mol%, and more preferably 1 to 30 mol%, relative to the molar amount of the liquid crystal compound.

[0103] --Polymerization initiator-- If the liquid crystal composition contains a polymerizable compound, it is preferable that it contains a polymerization initiator. In the embodiment in which the polymerization reaction is carried out by ultraviolet irradiation, it is preferable that the polymerization initiator used is a photopolymerization initiator capable of initiating the polymerization reaction by ultraviolet irradiation. Examples of photopolymerization initiators include α-carbonyl compounds (described in U.S. Patent Nos. 2,367,661 and 2,367,670), acyloin ethers (described in U.S. Patent No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin compounds (described in U.S. Patent No. 2,722,512), polynuclear quinone compounds (described in U.S. Patent Nos. 3,046,127 and 2,951,758), combinations of triarylimidazole dimers and p-aminophenyl ketones (described in U.S. Patent No. 3,549,367), acridine and phenazine compounds (described in Japanese Patent 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 the photopolymerization initiator in the liquid crystal composition is preferably 0.1 to 20% by mass, and more preferably 0.5 to 12% by mass, relative to the content of the liquid crystal compound.

[0104] --Crosslinking agent-- The liquid crystal composition may optionally contain a crosslinking agent to improve the film strength and durability after curing. Suitable crosslinking agents include those that cure with ultraviolet light, heat, and moisture. There are no particular restrictions on the crosslinking agent, and it can be appropriately selected depending on the purpose. Examples include polyfunctional acrylate compounds such as trimethylolpropane tri(meth)acrylate and pentaerythritol tri(meth)acrylate; epoxy compounds such as glycidyl(meth)acrylate and ethylene glycol diglycidyl ether; aziridine compounds such as 2,2-bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate] and 4,4-bis(ethyleneiminocarbonylamino)diphenylmethane; isocyanate compounds such as hexamethylene diisocyanate and biuret-type isocyanate; polyoxazoline compounds having an oxazoline group in the side chain; and alkoxysilane compounds such as vinyltrimethoxysilane and N-(2-aminoethyl)3-aminopropyltrimethoxysilane. In addition, known catalysts can be used depending on the reactivity of the crosslinking agent, which can improve productivity in addition to improving film strength and durability. These may be used individually or in combination of two or more. The crosslinking agent content is preferably 3 to 20% by mass, and more preferably 5 to 15% by mass, relative to the solid content mass of the liquid crystal composition. When the crosslinking agent content is within the above range, the effect of improving crosslink density is easily obtained, and the stability of the liquid crystal phase is further improved.

[0105] --Other additives-- If necessary, polymerization inhibitors, antioxidants, ultraviolet absorbers, light stabilizers, colorants, and metal oxide fine particles may be added to the liquid crystal composition, to the extent that they do not degrade the optical performance.

[0106] --solvent-- The liquid crystal composition is preferably used as a liquid when forming the cholesteric liquid crystal layer 34. Therefore, it is preferable that the liquid crystal composition contains a solvent. There are no restrictions on the solvent, and it can be appropriately selected depending on the purpose, but an organic solvent is preferred. There are no restrictions on the organic solvents used; they can be appropriately selected depending on the purpose. Examples include ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. These may be used individually or in combination of two or more. Among these, ketones are preferred when considering the environmental impact.

[0107] In order to form a cholesteric liquid crystal layer 34 that satisfies the above-mentioned film thickness distribution requirements, it is preferable to increase the drying and / or heating (orientation) temperature of the coated liquid crystal composition and increase the drying time. Considering this point, it is preferable to use a solvent with a relatively high boiling point. Specifically, a solvent with a boiling point of 95°C or higher is preferred, and a solvent with a boiling point of 110°C or higher is more preferable. Alternatively, a mixed solvent may be used, obtained by mixing a solvent with a lower boiling point with a solvent with a higher boiling point to achieve the above boiling point. Examples of solvents that can be used include cyclopentanone, cyclohexanone, methyl isobutyl ketone, toluene, and mixed solvents of methyl ethyl ketone and cyclopentanone.

[0108] When forming the cholesteric liquid crystal layer 34, it is preferable to apply the above-mentioned liquid crystal composition to the formation surface of the cholesteric liquid crystal layer 34, orient the liquid crystal compound to a desired liquid crystal phase state, and then cure the liquid crystal compound to form a liquid crystal layer. In other words, when forming a cholesteric liquid crystal layer 34 on a photo-alignment film 32, it is preferable to apply a liquid crystal composition to the photo-alignment film 32 to orient the liquid crystal compound into a cholesteric liquid crystal phase, and then cure the liquid crystal compound to form a liquid crystal layer in which the cholesteric liquid crystal phase is fixed. For coating the liquid crystal composition, all known methods that can uniformly coat a sheet-like material with liquid, such as inkjet and scroll printing, as well as spin coating, bar coating, and spray coating, can be used.

[0109] The coated liquid crystal composition is dried and heated as needed, and then cured to form a liquid crystal layer. In this drying and heating process, the liquid crystal compounds in the liquid crystal composition should be oriented into the cholesteric liquid crystal phase. In order to form a cholesteric liquid crystal layer 34 that satisfies the above-mentioned film thickness distribution requirements, it is preferable to heat (orient) the coated liquid crystal composition at a relatively high temperature. That is, by increasing the heating temperature, the surface of the coating film of the liquid crystal composition can be made uniform (leveled), and as a result, a cholesteric liquid crystal layer 34 that satisfies the above-mentioned film thickness distribution requirements can be formed. However, if the heating temperature is too high, the liquid crystal layer will not be oriented into a cholesteric liquid crystal phase, but will instead become an isotropic layer. Considering this point, the heating temperature in this case is preferably 90 to 200°C, more preferably 90 to 130°C, and even more preferably 90 to 120°C.

[0110] The oriented liquid crystal compound is further polymerized as needed. Polymerization may be carried out by thermal polymerization or photopolymerization by light irradiation, but photopolymerization is preferred. Ultraviolet light irradiation is preferred. The irradiation energy is 20 mJ / cm². 2 ~50J / cm 2 Preferably, 50-1500 mJ / cm² 2 This is more preferable. To promote the photopolymerization reaction, light irradiation may be carried out under heating conditions or in a nitrogen atmosphere. The wavelength of the ultraviolet light used for irradiation is preferably 250 to 430 nm.

[0111] There are no restrictions on the thickness of the cholesteric liquid crystal layer 34. The thickness should be set appropriately to obtain the required light reflectivity, depending on the application of the diffraction element, the required light reflectivity of the liquid crystal layer, and the material used to form the cholesteric liquid crystal layer 34.

[0112] <Other liquid crystal layers (optical anisotropic layers)> The optical element in the illustrated example uses a reflective liquid crystal diffraction element with a cholesteric liquid crystal layer 34 in the incident liquid crystal layer of the incident section 14 and the output liquid crystal layer of the output section 16, but the present invention is not limited thereto. As an example, a liquid crystal layer that acts as a transmissive liquid crystal diffraction element is also available, having a liquid crystal orientation pattern that rotates continuously along at least one direction in the plane, and in which the liquid crystal compound does not form a cholesteric liquid crystal phase in the thickness direction. In addition, the liquid crystal diffraction element may have a configuration in which the liquid crystal compound is twisted and rotated in the thickness direction to such an extent that it does not form a cholesteric liquid crystal phase. Furthermore, in the present invention, different liquid crystal diffraction elements may be used in the incident section 14 and the output section 16. For example, a reflective liquid crystal diffraction element using a cholesteric liquid crystal layer 34 may be used in the incident section 14, and the above-described transmissive liquid crystal diffraction element may be used in the output section 16.

[0113] [Method for manufacturing the injection and output sections] The injection section 14 and the discharge section 16 can be manufactured by various known methods. Preferably, they are formed by the transfer method described below. Since the inlet section 14 and the outlet section 16 can be formed in essentially the same way, the following explanation will use the inlet section 14 as a representative example.

[0114] First, as described above, a coating solution containing a photo-alignment material that will become the photo-alignment film 32 is applied to the support 30 and dried. Then, it is exposed using the exposure apparatus 60 shown in Figure 8 to form an alignment pattern and create the photo-alignment film 32. On the other hand, a liquid crystal composition for forming a cholesteric liquid crystal layer 34 is prepared by adding liquid crystal compound 40 and a chiral agent to the solvent. As mentioned above, it is preferable to use a solvent with a high boiling point in order to form a cholesteric liquid crystal layer 34 that satisfies the film thickness distribution requirements. Further, the above-described liquid crystal composition is applied onto the photo-alignment film 32, and the coating film is dried and heated. Further, by irradiating ultraviolet rays, an R-incident liquid crystal layer 14R, which is a cholesteric liquid crystal layer 34, is formed. At this time, as described above, by increasing the heating temperature, an R-incident liquid crystal layer 14R that satisfies the film thickness distribution requirement can be formed.

[0115] Similarly, a photo-alignment film 32 is formed on the support 30, and a G-incident liquid crystal layer 14G, which is a cholesteric liquid crystal layer 34, is formed on the photo-alignment film 32. Furthermore, similarly, a photo-alignment film 32 is formed on the support 30, and a B-incident liquid crystal layer 14B, which is a cholesteric liquid crystal layer 34, is formed on the photo-alignment film 32. At this time, it is preferable that the length of one period in the alignment pattern of the photo-alignment film 32, that is, the length of one period of the liquid crystal alignment pattern of the liquid crystal layer, is R-incident liquid crystal layer 14R > G-incident liquid crystal layer 14G > B-incident liquid crystal layer 14B, as described above.

[0116] First, the B-incident liquid crystal layer 14B is adhered to a temporary support with a weak adhesive layer. Then, peeling is performed at the interface between the B-incident liquid crystal layer 14B and the photo-alignment film 32. After adhering the B-incident liquid crystal layer 14B to the glass that will become the light guide plate 12 and then peeling off the temporary support, the B-incident liquid crystal layer 14B is formed on the surface of the light guide plate 12. At this time, prior to transfer, a SiO x layer or the like may be formed as an adhesive layer on the surface of the B-incident liquid crystal layer 14B on the photo-alignment film 32 side. The thickness of the adhesive layer is preferably 100 nm or less. The same applies to the other incident liquid crystal layers with respect to the adhesive layer.

[0117] Similarly, the G-incident liquid crystal layer 14G is adhered to a temporary support with a weak adhesive layer, and peeling is performed at the interface between the G-incident liquid crystal layer 14G and the photo-alignment film 32. Then, the G-incident liquid crystal layer 14G is laminated on the B-incident liquid crystal layer 14B previously transferred to the light guide plate 12, and by peeling off the temporary support, the G-incident liquid crystal layer 14G is formed on the surface of the B-incident liquid crystal layer 14B. Furthermore, similarly, the R-incident liquid crystal layer 14R is attached to a temporary support with a weak adhesive layer and peeled off at the interface between the R-incident liquid crystal layer 14R and the photo-alignment film 32. Next, the R-incident liquid crystal layer 14R is laminated onto the G-incident liquid crystal layer 14G that was previously transferred to the light guide plate 12, and the temporary support is peeled off to form the R-incident liquid crystal layer 14R on the surface of the G-incident liquid crystal layer 14G. This creates an incident section 14 on the surface of the light guide plate 12, which consists of three liquid crystal layers (cholesteric liquid crystal layers): B incident liquid crystal layer 14B, G incident liquid crystal layer 14G, and R incident liquid crystal layer 14R.

[0118] Although the optical elements of the present invention have been described in detail above, the present invention is not limited to the examples described above, and various improvements and modifications may be made without departing from the spirit of the present invention. [Examples]

[0119] The features of the present invention will be further described in detail below with reference to examples. The materials, reagents, amounts used, amounts of substance, ratios, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

[0120] [Examples] (Formation of photo-aligned film) A glass substrate was prepared as a support. The following photo-alignment film formation solution was applied to the support by spin coating. The support coated with this photo-alignment film formation solution was dried on a 60°C hot plate for 60 seconds to form a photo-alignment film.

[0121] Coating liquid for photo alignment film formation -------------------------------------------------- The following optical orientation material: 1.00 parts by mass Water 16.00 parts by mass Butoxyethanol 42.00 parts by mass Propylene glycol monomethyl ether 42.00 parts by mass --------------------------------------------------

[0122] -Material for photo alignment- [ka]

[0123] (Exposure of photoalignment film) A photo-alignment film having an alignment pattern was formed by exposing it using the exposure apparatus shown in Figure 8. In the exposure apparatus, a laser with a wavelength of 325 nm was used as the laser source. The exposure dose due to interference was 3000 mJ / cm². 2 The intersection angle (intersection angle α) of the two laser beams was set to 42.3°.

[0124] (Formation of R liquid crystal layer 1) Composition A-1 was prepared as a liquid crystal composition for forming the R liquid crystal layer 1 (R incident liquid crystal layer and R exit liquid crystal layer). Composition A-1 is a liquid crystal composition that forms a cholesteric liquid crystal layer in which the length of the helical pitch 1 (helical pitch P) in the cholesteric liquid crystal phase is 410 nm and selectively reflects right-circularly polarized red (R) light. The solid content concentration in composition A-1 is 35 wt%. Composition A-1 -------------------------------------------------- Rod-shaped liquid crystal compound L-1 100.00 parts by mass Polymerization initiator I-1: 3.00 parts by mass Chiral agent Ch-1: 4.6 parts by mass Methyl ethyl ketone 119.90 parts by mass Cyclopentanone 79.93 parts by mass --------------------------------------------------

[0125] Rod-shaped liquid crystal compound L-1 [ka]

[0126] Polymerization initiator I-1 [ka]

[0127] Chiral agent Ch-1 [ka]

[0128] The R liquid crystal layer 1 was formed by coating composition A-1 onto the photo-alignment film. Specifically, composition A-1 was applied to the photo-alignment film P-1 by spin coating, and the coating was heated on a hot plate to 120°C for 120 seconds. Subsequently, under a nitrogen atmosphere, ultraviolet light with a wavelength of 365 nm was applied at a rate of 500 mJ / cm² using a high-pressure mercury lamp. 2 By irradiating the coating film with the specified irradiation dose, the orientation of the liquid crystal compound was fixed, thereby forming the R liquid crystal layer 1. The thickness of the obtained R liquid crystal layer 1 was 5.2 μm.

[0129] Using a polarizing microscope, it was confirmed that the R liquid crystal layer 1 has a periodic orientation surface as shown in Figure 3. Furthermore, when the cross-section of the coated layer was examined using a scanning electron microscope, it was found that in the liquid crystal orientation pattern of the R liquid crystal layer 1, the period Λ, in which the optical axis of the liquid crystal compound rotates by 180°, was 0.45 μm.

[0130] Furthermore, the cross-section of the formed R liquid crystal layer 1 in the thickness direction was observed using a SEM at a magnification of 10,000 times, and this observation was performed at 20 locations by continuously moving the observation position in the in-plane direction, thereby obtaining images of a 200 μm range in the in-plane direction. In addition, the difference between the maximum and minimum film thickness within this 200 μm range in the in-plane direction was obtained. This operation was performed on any 10 cross-sections of the R liquid crystal layer 1. The arithmetic mean of the difference between the maximum and minimum film thicknesses at the 10 cross-sections of the R liquid crystal layer 1 obtained in this manner was calculated. As a result, the arithmetic mean of the difference between the maximum and minimum film thicknesses of the R liquid crystal layer 1 was 0.05 μm. Therefore, this R liquid crystal layer 1 satisfies the film thickness distribution requirements described above.

[0131] (Formation and exposure of the photo-alignment film for the G liquid crystal layer 1) Similar to the R liquid crystal layer 1, a photo-alignment film was formed on the surface of a glass support. Except for setting the intersection angle (intersection angle α) of the two laser beams to 49.2°, the photo-alignment film was exposed using the same exposure apparatus as shown in Figure 8 to form a photo-alignment film having an alignment pattern.

[0132] (Formation of G liquid crystal layer 1 (G incident liquid crystal layer and G exit liquid crystal layer)) Composition A-2 was prepared in the same manner as composition A-1, except that the amount of chiral agent added was changed to 5.3 parts by mass, the amount of methyl ethyl ketone was changed to 120.58 parts by mass, and the amount of cyclopentanone was changed to 80.38 parts by mass. Composition A-2 is a liquid crystal composition that forms a cholesteric liquid crystal layer in which the length of helical pitch 1 (helical pitch P) in the cholesteric liquid crystal phase is 360 nm and selectively reflects right-circularly polarized green (G) light. The G liquid crystal layer 1 was formed in the same manner as the R liquid crystal layer 1, except that composition A-2 was used. When measured in the same manner as the R liquid crystal layer 1, the film thickness of the G liquid crystal layer 1 was found to be 4.6 μm. In addition, in the liquid crystal alignment pattern of the G liquid crystal layer 1, the period Λ in which the optical axis of the liquid crystal compound rotates by 180° was 0.39 μm.

[0133] For the fabricated G liquid crystal layer 1, the arithmetic mean of the difference between the maximum and minimum film thicknesses in the 200 μm range across 10 cross-sections was calculated, similar to the R liquid crystal layer 1. As a result, the arithmetic mean of the difference between the maximum and minimum film thicknesses of G liquid crystal layer 1 was 0.04 μm. Therefore, this G liquid crystal layer 1 satisfies the film thickness distribution requirements described above.

[0134] (Formation and exposure of the photoalignment film for liquid crystal layer 1) Similar to the R liquid crystal layer 1, a photo-alignment film was formed on the surface of a glass support. Except for setting the intersection angle (intersection angle α) of the two laser beams to 61.0°, the photo-alignment film was exposed using the same exposure apparatus as shown in Figure 8 to form a photo-alignment film having an alignment pattern.

[0135] (Formation of B liquid crystal layer 1 (B incident liquid crystal layer and B exit liquid crystal layer)) Composition A-3 was prepared in the same manner as composition A-1, except that the amount of chiral agent added was changed to 6.3 parts by mass and the amount of methyl ethyl ketone was changed to 202.99 parts by mass. Composition A-3 is a liquid crystal composition that forms a cholesteric liquid crystal layer in which the length of helical pitch 1 (helical pitch P) in the cholesteric liquid crystal phase is 300 nm and selectively reflects right-circularly polarized blue (B) light. The B liquid crystal layer 1 was formed in the same manner as the R liquid crystal layer 1, except that composition A-3 was used. When measured in the same manner as the R liquid crystal layer, the film thickness of the B liquid crystal layer 1 was found to be 3.8 μm. In addition, in the liquid crystal alignment pattern of the B liquid crystal layer 1, the period Λ in which the optical axis of the liquid crystal compound rotates by 180° was 0.32 μm.

[0136] For the fabricated B liquid crystal layer 1, the arithmetic mean of the difference between the maximum and minimum film thicknesses in the 200 μm range across 10 cross-sections was calculated, similar to the R liquid crystal layer 1. As a result, the arithmetic mean of the difference between the maximum and minimum film thicknesses of B liquid crystal layer 1 was 0.04 μm. Therefore, this B liquid crystal layer 1 satisfies the film thickness distribution requirements described above.

[0137] [Fabrication of optical element 1] (Preparation of the light guide plate) I prepared a 1mm thick piece of glass for the light guide plate.

[0138] (Peeling off of liquid crystal layer B 1) Two B liquid crystal layers 1 were prepared, one for the incident liquid crystal layer and one for the output liquid crystal layer. A temporary support with a weak adhesive transfer layer (PanaProtect ST50, manufactured by Panac Co., Ltd.) was bonded to the B liquid crystal layer 1 and peeled off at the interface between the B liquid crystal layer 1 and the photoalignment film.

[0139] (Lamination of liquid crystal layer 1 to glass) On the alignment film side surface of the peeled B liquid crystal layer 1, SiO2 with a thickness of 50 nm or less is applied. x A layer was formed. SiO x The layers were formed using a vapor deposition apparatus manufactured by ULVAC (model number ULEYES). SiO2 powder was used as the vapor deposition source. After bonding the SiOx layer side of the B liquid crystal layer 1, which will be the incident liquid crystal layer and the exit liquid crystal layer, to the glass that will serve as the light guide plate, the temporary support was peeled off.

[0140] (Peeling off G liquid crystal layer 1) Two G liquid crystal layers 1 were prepared, one for the incident liquid crystal layer and one for the output liquid crystal layer. A temporary support with a weak adhesive layer for transfer (PanaProtect ST50, manufactured by Panac Co., Ltd.) was bonded to the G liquid crystal layer 1 and peeled off at the interface between the G liquid crystal layer and the photoalignment film.

[0141] (Bonding of G liquid crystal layer 1 onto B liquid crystal layer 1) On the alignment film side surface of the peeled G liquid crystal layer 1, SiO2 with a thickness of 50 nm or less is applied. x A layer was formed. SiO x The layer was formed using an ULVAC (model number ULEYES) deposition apparatus. SiO2 powder was used as the deposition source. Similarly, SiO2 was also deposited on the surface of the B liquid crystal layer 1 bonded to the light guide plate. x It formed a layer. On the B liquid crystal layer 1 bonded to the light guide plate, the SiO2 of the G liquid crystal layer 1, which will serve as the incident liquid crystal layer and the exit liquid crystal layer. x After bonding the layers together, the temporary support was removed.

[0142] (Peeling off R liquid crystal layer 1) Two R liquid crystal layers 1 were prepared, one for injection and one for output. A temporary support with a weak adhesive layer for transfer (PanaProtect ST50, manufactured by Panac Co., Ltd.) was bonded to the R liquid crystal layer 1 and peeled off at the interface between the R liquid crystal layer 1 and the photoalignment film.

[0143] (Lamination of R liquid crystal layer 1 onto G liquid crystal layer 1 (fabrication of optical element)) On the alignment film side surface of the peeled R liquid crystal layer 1, SiO2 with a thickness of 50 nm or less is applied. x A layer was formed. SiO x The layer was formed using an ULVAC (model number ULEYES) deposition apparatus. SiO2 powder was used as the deposition source. Similarly, SiO2 was also deposited on the surface of the G liquid crystal layer 1 bonded to the light guide plate. x It formed a layer. On the G liquid crystal layer 1 bonded to the light guide plate, an SiO2 liquid crystal layer 1 is formed, which serves as the incident liquid crystal layer and the exit liquid crystal layer. x After bonding the layers together, the temporary support was removed. As a result, an optical element 1 as shown in Figure 1 was fabricated, in which an incident section with a B incident liquid crystal layer, a G incident liquid crystal layer, and an R incident liquid crystal layer laminated on the main surface of the light guide plate, and an exit section with a B exit liquid crystal layer, a G exit liquid crystal layer, and an R exit liquid crystal layer laminated on the exit section. In this example, all liquid crystal layers satisfy the above-mentioned film thickness distribution requirements.

[0144] Furthermore, the periodic direction (direction of the arrangement axis) of the liquid crystal compound in each liquid crystal layer was determined by pre-marking the cholesteric liquid crystal layer to be laminated and the temporary support on the laminating side with a mark indicating the periodic direction, which was then used as a guide during bonding.

[0145] [Comparative Example]

[0146] (Formation of R liquid crystal layer 2) Composition A-4 was prepared in the same manner as composition A-1, except that the amount of methyl ethyl ketone was changed to 199.83 parts by mass and the amount of cyclopentanone was changed to 0 parts by mass. Composition A-4 is a liquid crystal composition that forms a cholesteric liquid crystal layer in which the length of helical pitch 1 (helical pitch P) in the cholesteric liquid crystal phase is 410 nm and selectively reflects right-circularly polarized red (R) light. Using composition A-4, R-liquid crystal layer 2 was formed in the same manner as R-liquid crystal layer 1, except that the heating temperature of the coating film was set to 70°C. When measured in the same manner as R-liquid crystal layer 1, the film thickness of R-liquid crystal layer 2 was found to be 5.2 μm. Furthermore, in the liquid crystal alignment pattern of R-liquid crystal layer 2, the period Λ in which the optical axis of the liquid crystal compound rotates by 180° was 0.45 μm.

[0147] For the fabricated R-liquid crystal layer 2, the arithmetic mean of the difference between the maximum and minimum film thicknesses in the 200 μm range across 10 cross-sections was calculated, similar to R-liquid crystal layer 1. As a result, the arithmetic mean of the difference between the maximum and minimum film thicknesses of R-liquid crystal layer 2 was 0.20 μm. Therefore, this R-liquid crystal layer 2 does not satisfy the film thickness distribution requirements described above.

[0148] (Formation of G liquid crystal layer 2) Composition A-5 was prepared in the same manner as composition A-2, except that the amount of methyl ethyl ketone was changed to 200.98 parts by mass and the amount of cyclopentanone was changed to 0 parts by mass. Composition A-5 is a liquid crystal composition that forms a cholesteric liquid crystal layer in which the length of helical pitch 1 (helical pitch P) in the cholesteric liquid crystal phase is 360 nm and selectively reflects right-circularly polarized green (G) light. Using composition A-5, a G liquid crystal layer 2 was formed in the same manner as for the R liquid crystal layer 1, except that the heating temperature of the coating film was set to 70°C. When measured in the same manner as for the R liquid crystal layer 1, the film thickness of the G liquid crystal layer 2 was found to be 4.6 μm. Furthermore, in the liquid crystal alignment pattern of the G liquid crystal layer 2, the period Λ in which the optical axis of the liquid crystal compound rotates by 180° was 0.39 μm.

[0149] For the fabricated G liquid crystal layer 2, the arithmetic mean of the difference between the maximum and minimum film thicknesses in the 200 μm range across 10 cross-sections was calculated, similar to the R liquid crystal layer 1. As a result, the arithmetic mean of the difference between the maximum and minimum film thicknesses of G liquid crystal layer 2 was 0.16 μm. Therefore, this G liquid crystal layer 2 does not satisfy the film thickness distribution requirements described above.

[0150] (Formation of liquid crystal layer 2) Composition A-6 was prepared in the same manner as composition A-3, except that the amount of methyl ethyl ketone was changed to 202.99 parts by mass and the amount of cyclopentanone was changed to 0 parts by mass. Composition A-6 is a liquid crystal composition that forms a cholesteric liquid crystal layer in which the length of helical pitch 1 (helical pitch P) in the cholesteric liquid crystal phase is 300 nm and selectively reflects right-circularly polarized blue (B) light. Using composition A-5, the B liquid crystal layer 2 was formed in the same manner as the R liquid crystal layer 1, except that the heating temperature of the coating film was set to 70°C. When measured in the same manner as the R liquid crystal layer 1, the film thickness of the B liquid crystal layer 2 was found to be 3.8 μm. Furthermore, in the liquid crystal alignment pattern of the B liquid crystal layer 2, the period Λ in which the optical axis of the liquid crystal compound rotates by 180° was 0.32 μm.

[0151] For the fabricated B liquid crystal layer 2, the arithmetic mean of the difference between the maximum and minimum film thicknesses in the 200 μm range across 10 cross-sections was calculated, similar to the R liquid crystal layer 1. As a result, the arithmetic mean of the difference between the maximum and minimum film thicknesses of B liquid crystal layer 2 was 0.14 μm. Therefore, this R liquid crystal layer 2 does not satisfy the film thickness distribution requirements described above. [Fabrication of optical element 2]

[0152] Optical element 2 was fabricated in the same manner as optical element 1, except that B liquid crystal layer 2 was used instead of B liquid crystal layer 1, G liquid crystal layer 2 was used instead of G liquid crystal layer 1, and R liquid crystal layer 2 was used instead of R liquid crystal layer 1, with an incident and an exit portion provided on the light guide plate. In this example, none of the liquid crystal layers satisfy the above-mentioned film thickness distribution requirements.

[0153] [evaluation] Using the fabricated optical element, as shown in Figure 1, an image consisting of a red image R, a green image G, and a blue image B was projected onto the incident surface using an LCOS-type projector, and visually evaluated by the user U at their observation position. As a result, when using the optical element 1 of the example, in which all liquid crystal layers satisfy the above-mentioned film thickness distribution requirements, the image was clearly visible and the characters were clearly readable. In contrast, when using the optical element of Comparative Example 1, in which all liquid crystal layers do not satisfy the above-mentioned film thickness distribution requirements, the image was blurry and it was somewhat difficult to read the characters. Based on the above results, the effects of the present invention are clear. [Industrial applicability]

[0154] It can be suitably used in various applications of refracting light in optical devices, such as diffracting elements that cause light to enter and exit the light guide plate of AR glasses. [Explanation of Symbols]

[0155] 10 Optical elements 12 Light guide plate 14 Input part 14R R incident liquid crystal layer 14G G incident liquid crystal layer 14B B incident liquid crystal layer 16. Ejection section 16R R output liquid crystal layer 16G G output liquid crystal layer 16B B output liquid crystal layer 30 Support 32 Photo-alignment film 34 Cholesteric liquid crystal layer 40 Liquid crystal compounds 40A optical axis 42 Akabe 44 Dark part 60 Exposure equipment 62 lasers 64 Light source 65 λ / 2 plate 68 Polarizing Beam Splitter 70A, 70B Mirror 72A,72B λ / 4 board R Red Image G Green image B Blue image R R Right-circular polarization of red light M laser light MA,MB rays P O Linear polarization P R Right-hand circular polarization P L Left-hand circular polarization U user D array axis Λ 1 period (period of diffraction structure) Pitch

Claims

1. The device comprises a substrate and a laminate comprising a plurality of liquid crystal layers, each of which is oriented a liquid crystal compound, provided on the substrate. The substrate and the laminate are laminated with an adhesive layer in between, and the adhesive layer and one of the liquid crystal layers of the laminate are directly laminated together. The adhesive layer is SiO X It is a layer, The liquid crystal layer constituting the laminate is a cholesteric liquid crystal layer having a fixed cholesteric liquid crystal phase that selectively reflects visible light and has a liquid crystal orientation pattern in which the orientation of the optical axis originating from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. In the plurality of liquid crystal layers, the cholesteric liquid crystal layers have the same twist direction of the helix of the liquid crystal compound in the cholesteric liquid crystal phase. At least one of the liquid crystal layers constituting the laminate is an optical element that satisfies the following film thickness distribution requirements. Film thickness distribution requirements The cross-section in the thickness direction of the liquid crystal layer is observed at 10,000x magnification using a scanning electron microscope at 20 locations by continuously moving the observation position in the in-plane direction of the liquid crystal layer. Images of a 200 μm range in the in-plane direction of the liquid crystal layer are obtained, and the difference between the maximum and minimum film thicknesses within that 200 μm range in the in-plane direction of the liquid crystal layer is obtained. This operation is performed on 10 arbitrary cross-sections of the liquid crystal layer, and the arithmetic mean of the difference between the maximum and minimum film thicknesses in the 10 obtained cross-sections is 0.1 μm or less.

2. The optical element according to claim 1, wherein the liquid crystal layer located at the end in the stacking direction of the laminate satisfies the film thickness distribution requirement.

3. The optical element according to claim 2, wherein the liquid crystal layer closest to the substrate among the liquid crystal layers constituting the laminate satisfies the film thickness distribution requirement.

4. The optical element according to any one of claims 1 to 3, wherein, among the liquid crystal layers constituting the laminate, the liquid crystal layers other than the liquid crystal layer furthest from the substrate satisfy the film thickness distribution requirement.

5. The optical element according to any one of claims 1 to 4, wherein all of the liquid crystal layers constituting the laminate satisfy the film thickness distribution requirement.

6. The substrate is a light guide plate, and has an incident portion for injecting light into the light guide plate, and an emission portion for emitting light from the light guide plate. The optical element according to any one of claims 1 to 5, wherein at least one of the incident portion and the exit portion is made using the laminate.

7. The optical element according to claim 6, wherein the incident portion is constructed using the laminate.

8. The optical element according to claim 7, wherein the emission portion is constructed using the laminate.

9. A method for manufacturing an optical element according to any one of claims 1 to 8, A method for manufacturing an optical element, wherein the liquid crystal layer is formed using a liquid crystal composition containing a liquid crystal compound and a solvent with a boiling point of 95°C or higher.

10. The method for producing an optical element according to claim 9, wherein the liquid crystal composition contains one or more of the following as a solvent having a boiling point of 95°C or higher: cyclopentanone, cyclohexanone, methyl isobutyl ketone, toluene, and a mixed solvent of methyl ethyl ketone and cyclopentanone.

Images