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

[0002] In recent years, AR (Augmented Reality) glasses that display virtual images and various information superimposed on an actually viewed scene, as described in Non-Patent Document 1, have been put to practical use. AR glasses are also called smart glasses, head mounted displays (HMDs), AR glasses, and the like.

[0003] As shown in non-patent document 1, as an example, AR glasses display an image displayed by a display (optical engine) by having the image enter one end of a light guide plate, propagate therethrough, and exit from the other end, thereby superimposing a virtual image on the scene that the user actually sees. In AR glasses, a diffraction element is used to diffract (refract) the light from the display (projection light) and make it enter one end of the light guide plate. This allows the light to be introduced into the light guide plate at an angle and propagates within the light guide plate. The light that propagates through the light guide plate is also diffracted by the diffraction element at the other end of the light guide plate, emitted from the light guide plate, and irradiated (projected) onto the user's viewing position.

[0004] An example of a diffraction element that can be used in AR glasses and that causes light to enter a light guide plate and emit light from the light guide plate is a reflective structure that uses a cholesteric liquid crystal layer formed by fixing a cholesteric liquid crystal phase, as described in Patent Document 1. The reflection structure includes a plurality of spiral structures each extending along a predetermined direction. The reflection structure includes a first incident surface that intersects with the predetermined direction and on which light is incident, and a reflection surface that intersects with the predetermined direction and reflects the light incident from the first incident surface, and the first incident surface includes one end of each of the plurality of spiral structures. Each of the plurality of spiral structures includes a plurality of structural units aligned along a predetermined direction, and the plurality of structural units includes a plurality of elements spirally wound and stacked. Each of the plurality of structural units has a first end and a second end, and among the structural units adjacent to each other 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 plurality of first ends included in the plurality of spiral structures are aligned. Furthermore, the reflection surface includes at least one first end included in each of the plurality of spiral structures, and is non-parallel to the first incident surface.

[0005] The cholesteric liquid crystal layer (reflective structure) described in Patent Document 1 has a liquid crystal orientation 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. The cholesteric liquid crystal layer described in Patent Document 1 has such a liquid crystal orientation pattern, and thus has a reflective surface that is non-parallel to the first incident surface. A typical cholesteric liquid crystal layer specularly reflects incident light. In contrast, the cholesteric liquid crystal layer described in Patent Document 1 does not reflect light in a specular manner, but diffracts the incident light and reflects it at a predetermined angle relative to the specular reflection. For example, the cholesteric liquid crystal layer described in Patent Document 1 diffracts light incident from the normal direction and reflects it at an angle relative to the normal direction, rather than reflecting the light in the normal direction.

[0006] Therefore, by using this cholesteric liquid crystal layer as a diffraction element for incidence on 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 the light to be totally reflected and propagated 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 Summary of the Invention [Problem to be solved by the invention]

[0009] As described above, the reflection structure using the cholesteric liquid crystal layer described in Patent Document 1 can diffract incident circularly polarized light by the cholesteric liquid crystal layer and reflect the circularly polarized light at an angle with respect to the incident direction. As is well known, a cholesteric liquid crystal layer selectively reflects light in a predetermined wavelength range according to 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 light, green light, and blue light, it is possible to use them for AR glasses that display full-color images.

[0010] According to the inventors' investigations, a diffraction element using a liquid crystal layer may have variations in the diffraction angle in the in-plane direction of the liquid crystal layer when a plurality of liquid crystal layers are laminated. When a diffraction element having a variation in the diffraction angle in the in-plane direction is used in AR glasses, the displayed image becomes blurred.

[0011] The object of the present invention is to solve such problems of the conventional technology, and to provide an optical element in which multiple liquid crystal layers are laminated on a substrate, which suppresses the variation in the diffraction angle of the liquid crystal layer in the in-plane direction, and enables the display of clear images without blurring when used, for example, in AR glasses. [Means for solving the problem]

[0012] In order to solve this problem, the method for producing an optical element of the present invention has the following configuration. [1] A liquid crystal display device comprising: a substrate; and a laminate including a plurality of liquid crystal layers laminated on the substrate; The liquid crystal layer constituting the laminate has a liquid crystal orientation 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, An optical element, in which at least one of the liquid crystal layers constituting the laminate satisfies the following film thickness distribution requirements. Film thickness distribution requirements A cross-section of the thickness direction of the liquid crystal layer is observed at 10,000 times magnification using a scanning electron microscope, and the observation position is moved continuously in the in-plane direction of the liquid crystal layer at 20 locations to obtain images of a range of 200 μm in the in-plane direction of the liquid crystal layer. This operation is then performed on any 10 cross-sections of the liquid crystal layer to obtain the difference between the maximum film thickness and the minimum film thickness within the obtained range of 200 μm in the in-plane direction of the liquid crystal layer. The arithmetic average 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] The optical element according to [1], wherein the liquid crystal layer located at the end in the stacking direction among the liquid crystal layers constituting the stack satisfies a film thickness distribution requirement. [3] The optical element according to [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 [1] to [3], wherein among the liquid crystal layers constituting the laminate, a liquid crystal layer other than the liquid crystal layer farthest from the substrate satisfies a thickness distribution requirement. [5] The optical element according to any one of [1] to [4], wherein all the liquid crystal layers constituting the laminate satisfy a thickness distribution requirement. [6] The optical element according to any one of [1] to [5], wherein the liquid crystal layer constituting the laminate is a cholesteric liquid crystal layer having a fixed cholesteric liquid crystal phase. [7] The substrate is a light guide plate having an incident portion for introducing light into the light guide plate and an exit portion for causing the light to exit from the light guide plate; The optical element according to any one of [1] to [6], wherein at least one of the entrance portion and the exit portion is configured using a laminate. [8] The optical element according to [7], wherein the incident portion is formed using a laminate. [9] The optical element according to [8], wherein the exit portion is formed using a laminate. Effect of the Invention

[0013] According to the present invention, it is possible to provide an optical element that enables the display of clear images without blurring, for example in AR glasses or the like. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram conceptually illustrating an example of an optical element of the present invention. [Diagram 2] FIG. 2 is a conceptual diagram for explaining a cholesteric liquid crystal layer. [Diagram 3] FIG. 3 is a plan view conceptually showing the cholesteric liquid crystal layer shown in FIG. 2. [Figure 4] FIG. 4 is a conceptual diagram showing a cross-sectional SEM image of the cholesteric liquid crystal layer shown in FIG. [Diagram 5] FIG. 4 is a conceptual diagram for explaining the function of the cholesteric liquid crystal layer shown in FIG. [Figure 6] FIG. 13 is a diagram conceptually illustrating another example of a cholesteric liquid crystal layer. [Figure 7]FIG. 13 is a diagram conceptually illustrating another example of a cholesteric liquid crystal layer. [Figure 8] FIG. 2 is a conceptual diagram of an example of an exposure apparatus for exposing a photo-alignment film. [Figure 9] FIG. 2 is a conceptual diagram for explaining the function of a laminate. [Figure 10] FIG. 1 is a conceptual diagram for explaining film thickness distribution requirements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the optical element of the present invention will be described in detail based on the preferred embodiments shown in the accompanying drawings.

[0016] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In this specification, "(meth)acrylate" is used to mean "either one or both of acrylate and methacrylate." In this specification, "same" includes a generally acceptable margin of error in the technical field. In addition, in this specification, when "all", "any", "all over", etc. are used, it includes not only 100% but also a generally acceptable margin of error in the technical field, for example, 99% or more, 95% or more, or 90% or more.

[0017] In this specification, visible light is electromagnetic light with wavelengths visible to the human eye, in the wavelength range of 380 to 780 nm, while non-visible light is light with wavelengths below 380 nm and above 780 nm. In addition, although not limited thereto, infrared rays (infrared light) are light in a wavelength range exceeding 780 nm and not exceeding 1 mm, and in particular, the near-infrared region is light in a wavelength range exceeding 780 nm and not exceeding 2000 nm. Furthermore, although not limited thereto, among visible light, light in the wavelength region of 420 to 490 nm is blue light, light in the wavelength region of 495 to 570 nm is green light, and light in the wavelength region of 620 to 750 nm is red light.

[0018] FIG. 1 conceptually illustrates an example of the optical element of the present invention. 1, the optical element 10 has a light guide plate 12, an incident portion 14, and an exit portion 16. The incident portion 14 is provided near one end of one main surface of the light guide plate 12, and the exit portion 16 is provided near the other end of the same main surface of the light guide plate 12. The main surface is the maximum surface of a sheet-like (plate-like) material, film, layer, etc.

[0019] The optical element 10 in the illustrated example is, for example, used in the above-mentioned AR glasses and the like, and is capable of displaying a full-color image consisting of a red image R, a green image G, and a blue image B. As an example, the AR glasses using the optical element 10 transmit an image (video) consisting of a red image R, a green image G, and a blue image B displayed on a display (optical engine) (not shown) through the light guide plate 12 and enter the incident section 14. The incident section 14 diffracts and reflects the incident light (image) so that the light enters the light guide plate 12 at an angle that allows total reflection. The light that is propagated (guided) by repeated total reflection within the light guide plate 12 enters the exit unit 16. The exit unit 16 diffracts and reflects the incident light, causing a red image R, a green image G, and a blue image B to exit from the light guide plate 12, and displays a virtual image superimposed on the scene that the user U is actually viewing.

[0020] 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. 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 made of cholesteric liquid crystal layers having a predetermined liquid crystal orientation 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 emission section 16 has an R-emission liquid crystal layer 16R, a G-emission liquid crystal layer 16G, and a B-emission 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 made 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-handed circularly polarized light in a specific wavelength range and transmits other light. Therefore, the user U can observe the background behind the exit portion 16 through the light guide plate 12 and the exit portion 16.

[0023] The light guide plate 12 is a substrate in the present invention. Moreover, the entrance section 14 and the exit section 16 are both laminates in which a plurality of liquid crystal layers are laminated in the optical element of the present invention, which are provided on a substrate. Therefore, at least one of the R-emitting liquid crystal layer 16R, the G-emitting liquid crystal layer 16G, and the B-emitting liquid crystal layer 16B satisfies a predetermined film thickness distribution requirement in the incident section 14. Also, at least one of the R-emitting liquid crystal layer 16R, the G-emitting liquid crystal layer 16G, and the B-emitting liquid crystal layer 16B in the exit section 16 satisfies a predetermined film thickness distribution requirement, which will be described later.

[0024] In the optical element of the present invention, the entrance section 14 and the exit section 16 are not limited to this configuration. That is, the entrance section 14 and the exit section 16 may have two cholesteric liquid crystal layers or four or more cholesteric liquid crystal layers as long as they have a plurality of 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 in the illustrated example, but may also correspond to, for example, a two-color image such as red and blue or red and green, a color image having four or more colors, or one that corresponds to non-visible light such as infrared light.

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

[0026] In other words, in the optical element of the present invention, the input section 14 and the output section 16, i.e., the laminate in which multiple liquid crystal layers are stacked, have two or more liquid crystal layers, and various layer configurations can be used as long as at least one layer satisfies the film thickness distribution requirements described above. However, regardless of the layer structure, the entrance section 14 and the exit section 16 basically have liquid crystal layers that selectively reflect light of the same color (wavelength range).

[0027] Each of the components constituting the optical element 10 of the present invention will now be described. [Light guide plate] The light guide plate 12 is a known light guide plate that reflects and propagates (guides) light that has entered the inside. There are no limitations on the light guide plate 12, and various known light guide plates used in AR glasses, backlight units of liquid crystal displays, and the like can be used.

[0028] [Inlet and outlet parts] 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, in a preferred embodiment, each incident liquid crystal layer is a cholesteric liquid crystal layer having a predetermined liquid crystal orientation pattern formed by fixing a cholesteric liquid crystal phase, and is a reflective liquid crystal diffraction element that selectively reflects right-handed or left-handed circularly polarized light. The rotation directions of the circularly polarized light selectively reflected by R-incident liquid crystal layer 14R, G-incident liquid crystal layer 14G, and B-incident liquid crystal layer 14B, that is, the helical twist directions of the liquid crystal compounds in the cholesteric liquid crystal phase, may be the same or different.

[0029] On the other hand, the emission section 16 has an R-emission liquid crystal layer 16R, a G-emission liquid crystal layer 16G, and a B-emission liquid crystal layer 16B. As described above, in a preferred embodiment, each exit liquid crystal layer is a cholesteric liquid crystal layer having a predetermined liquid crystal orientation pattern formed by fixing a cholesteric liquid crystal phase, and is a reflective liquid crystal diffraction element that selectively reflects right-handed or left-handed circularly polarized light. The rotation 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, that is, the helical twist directions of the liquid crystal compounds 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-exiting liquid crystal layer 16R, the G-exiting liquid crystal layer 16G, and the B-incident liquid crystal layer 14B, basically have the same configuration except that the wavelength ranges of light that are selectively reflected and / or the rotation directions of the circularly polarized light that are selectively reflected are different. Therefore, in the following description, when there is no need to distinguish between the liquid crystal layers, these liquid crystal layers will be collectively referred to as "liquid crystal layer".

[0031] (Liquid crystal layer) The liquid crystal layer will be described with reference to FIGS. 2, a photo-alignment film 32 is formed on a support 30, and the cholesteric liquid crystal layer 34 having a predetermined liquid crystal alignment pattern is formed on the photo-alignment film 32. The cholesteric liquid crystal layer 34 becomes the incident liquid crystal layer and the exit liquid crystal layer that constitute the incident section 14 and the exit section 16 and act as reflective liquid crystal diffraction elements. 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 photo-alignment film 32 and transferred and laminated as a liquid crystal layer (incident liquid crystal layer or exiting liquid crystal layer) onto the substrate, that is, the light guide plate 12, or onto the underlying liquid crystal layer.

[0032] FIG. 3 is a schematic diagram showing the alignment state of liquid crystal compounds in the plane of the main surface of the cholesteric liquid crystal layer 34. As shown in FIG. In the following description, the principal surface of the cholesteric liquid crystal layer 34 is defined as the XY plane, and the cross section perpendicular to the XY plane is defined as the XZ plane. That is, Fig. 2 corresponds to a schematic diagram of the XZ plane of the cholesteric liquid crystal layer 34, and Fig. 3 corresponds to a schematic diagram of the XY plane of the cholesteric liquid crystal layer 34. 2 to 4, the cholesteric liquid crystal layer 34 is a layer in which a liquid crystal compound is cholesterically oriented. In addition, Figs. 2 to 4 show an example in which the liquid crystal compound constituting the cholesteric liquid crystal layer 34 is a rod-shaped liquid crystal compound.

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

[0034] There is no limitation on the thickness of the support 30, and the thickness capable of supporting the photo-alignment film 32 and the cholesteric liquid crystal layer 34 may be appropriately set depending on the application of the liquid crystal diffraction element and the material from which the support 30 is formed. The thickness of the support 30 is preferably from 1 to 2000 μm, more preferably from 3 to 500 μm, and further preferably from 5 to 250 μm.

[0035] The support 30 may be a single layer or multiple layers. Examples of the support 30 in the case of a single layer include support 30 made of glass, triacetyl cellulose (TAC), polyethylene terephthalate (PET), polycarbonate, polyvinyl chloride, acrylic, polyolefin, etc. Examples of the support 30 in the case of a multilayer include a support that includes any of the above-mentioned single-layer supports as a substrate, and another layer is provided on the surface of this substrate. Among these, glass is preferably used as the support 30 because it allows the formation of a photo-alignment film 32 with a high surface smoothness.

[0036] <Photo-alignment film> In the liquid crystal diffraction element, a photo-alignment film 32 is formed on the surface of a support 30 . The photo-alignment film 32 is a photo-alignment film for aligning the liquid crystal compound 40 in a predetermined liquid crystal alignment pattern when the cholesteric liquid crystal layer 34 is formed. As will be described later, in the present invention, the cholesteric liquid crystal layer 34 has a liquid crystal alignment pattern in which the direction of the optical axis 40A (see FIG. 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 description, "the orientation of the optical axis 40A rotates" will also be simply referred to as "the optical axis 40A rotates."

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

[0038] Examples of photo-alignment materials used in the photo-alignment film that can be used in the present invention include those described in JP-A-2006-285197, JP-A-2007-076839, JP-A-2007-138138, JP-A-2007-094071, JP-A-2007-121721, JP-A-2007-140465, JP-A-2007-156439, and JP-A-2007-160144. azo compounds described in JP-A-7-133184, JP-A-2009-109831, JP-B-3883848 and JP-B-4151746, aromatic ester compounds described in JP-A-2002-229039, maleimides and / or amides having photo-orientable units described in JP-A-2002-265541 and JP-A-2002-317013 or alkenyl-substituted nadimide compounds, photocrosslinkable silane derivatives described in Japanese Patent No. 4205195 and Japanese Patent No. 4205198, photocrosslinkable polyimides, photocrosslinkable polyamides and photocrosslinkable polyesters described in JP-T-2003-520878, JP-T-2004-529220 and Japanese Patent No. 4162850, and photodimerizable compounds described in JP-A-9-118717, JP-T-10-506420, JP-T-2003-505561, WO 2010 / 150748, JP-A-2013-177561 and JP-A-2014-012823, in particular 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 preferably used.

[0039] There is no limitation on the thickness of the photo-alignment film 32, and the thickness may be appropriately set so as to obtain the necessary alignment function depending on the material from which the photo-alignment film 32 is formed. 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 is no limitation on the method for forming the photo-alignment film 32, and various known methods according to the material for forming the photo-alignment film 32 can be used. As an example, a method is exemplified in which a composition containing a photo-alignment material for forming a photo-alignment film 32 is prepared, the composition is applied to the surface of the support 30, and dried, and then the photo-alignment film 32 is subjected to interference exposure with laser light to form an alignment pattern.

[0041] FIG. 8 conceptually shows an example of an exposure apparatus for forming an alignment pattern by exposing the photo-alignment film 32 to interference light. The exposure device 60 shown in Figure 8 includes a light source 64 equipped with a laser 62, a λ / 2 plate 65 that changes the polarization direction of laser light M emitted by the laser 62, a polarizing beam splitter 68 that splits the laser light M emitted by the laser 62 into two light beams MA and MB, mirrors 70A and 70B that are respectively arranged on the optical paths of the two split light beams MA and MB, and λ / 4 plates 72A and 72B. The light source 64 is a linearly polarized light P 0 The λ / 4 plate 72A emits linearly polarized light P 0 (Light ray MA) is right-handed circularly polarized P R The λ / 4 plate 72B is linearly polarized P 0 (Light ray MB) is circularly polarized to the left P L , respectively.

[0042] A support 30 having a photo-alignment film 32 before an alignment pattern is formed is placed in an exposure section, and two light beams MA and MB are caused to intersect and interfere on the photo-alignment film 32, and the photo-alignment film 32 is exposed to the interference light. Due to the interference at this time, the polarization state of the light irradiated to the photo-alignment film 32 changes periodically in the form of interference fringes. This results in a photo-alignment film having an alignment pattern in which the alignment state changes periodically. In the following description, the photo-alignment film having this alignment pattern is also referred to as a "patterned photo-alignment film." In the exposure device 60, the period of the alignment pattern can be adjusted by changing the crossing angle α of the two light beams MA and MB. That is, in the exposure device 60, in an alignment pattern in which the optical axis 40A derived from the liquid crystal compound 40 continuously rotates along one direction, the length of one period in which the optical axis 40A rotates by 180° in one direction in which the optical axis 40A rotates can be adjusted by adjusting the crossing angle α. By forming a cholesteric liquid crystal layer on a photo-alignment film 32 having an alignment pattern in which the alignment state changes periodically, a cholesteric liquid crystal layer 34 can be formed having a liquid crystal alignment pattern in which the optical axis 40A derived from the liquid crystal compound 40 rotates continuously along one direction, as described below. Moreover, by rotating the optical axes of the λ / 4 plates 72A and 72B by 90°, respectively, the rotation direction of the optical axis 40A can be reversed.

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

[0044] <Cholesteric liquid crystal layer (entrance liquid crystal layer / exit liquid crystal layer)> A cholesteric liquid crystal layer 34 is formed on the surface of the photo-alignment film 32 . The cholesteric liquid crystal layer 34 is a cholesteric liquid crystal layer having a fixed cholesteric liquid crystal phase, and has a liquid crystal orientation 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.

[0045] As conceptually shown in FIG. 2, the cholesteric liquid crystal layer 34 has a helical structure in which liquid crystal compounds 40 are spirally wound and stacked, similar to a cholesteric liquid crystal layer formed by fixing a normal cholesteric liquid crystal phase, and has a structure in which liquid crystal compounds 40 spirally wound are stacked at multiple pitches, with one helical pitch (helical pitch P) being one helical rotation (360° rotation) of the liquid crystal compounds 40.

[0046] It is known that a cholesteric liquid crystal phase exhibits selective reflectivity, that is, selectively reflecting light in a specific wavelength range. In a cholesteric liquid crystal phase, the central wavelength of selective reflection (selective reflection central wavelength λ) depends on the length of one helical pitch (helical pitch P) in the cholesteric liquid crystal phase, and follows the relationship λ = n × P with the average refractive index n of the cholesteric liquid crystal phase. Therefore, by adjusting the helical pitch, it is possible to adjust the selective reflection central wavelength, i.e., the selective reflection wavelength range. The longer the helical pitch P, the longer the selective reflection central wavelength of the cholesteric liquid crystal phase becomes.

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

[0048] Furthermore, the half-width Δλ (nm) of the wavelength range showing selective reflection (circularly polarized light reflection wavelength range) depends on the Δn and helical pitch P of the cholesteric liquid crystal phase, and follows 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 and mixing ratio of the liquid crystal compounds forming the cholesteric liquid crystal layer, as well as the temperature at which the orientation is fixed. The half width of the reflection wavelength range is adjusted depending on the application of the optical element (liquid crystal diffraction element) and may be, 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 reflection for either left-handed or right-handed circularly polarized light in a specific wavelength range. Whether the reflected light is right-handed or left-handed circularly polarized light depends on the twist direction (sense) of the helix of the cholesteric liquid crystal phase. When the helix of the cholesteric liquid crystal phase is twisted to the right, right-handed circularly polarized light is reflected, and when the helix is ​​twisted to the left, left-handed circularly polarized light is reflected. 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-handed circularly polarized light, the cholesteric liquid crystal layer 34 which constitutes these liquid crystal layers has a right-handed helical twist direction of the cholesteric liquid crystal phase. 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] 3, in the XY plane of the cholesteric liquid crystal layer 34, the liquid crystal compounds 40 are aligned along a plurality of alignment axes D parallel to each other in the XY plane. On each alignment axis D, the direction of the optical axis 40A of the liquid crystal compounds 40 changes while continuously rotating in one direction in the plane along the alignment axis D. Here, as an example, it is assumed that the alignment axis D is oriented in the X direction. In addition, in the Y direction, the liquid crystal compounds 40 having the same direction of the optical axis 40A are aligned at equal intervals. Here, "the orientation of the optical axis 40A of the liquid crystal compound 40 changes while continuously rotating in one direction in the plane along the arrangement axis D" means that the angle between the optical axis 40A of the liquid crystal compound 40 and the arrangement axis D varies depending on the position along the arrangement axis D, and the angle between the optical axis 40A and the arrangement axis D gradually changes from θ to θ+180° or θ-180° along the arrangement axis D. In other words, the optical axes 40A of the multiple liquid crystal compounds 40 aligned along the arrangement axis D change while rotating at a constant angle at a time along the arrangement axis D, as shown in FIG. The difference in angle between the optical axes 40A of the liquid crystal compounds 40 adjacent to each other in the direction of the alignment axis D is preferably 45° or less, more preferably 15° or less, and even more preferably a smaller angle. In addition, 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 refers to the molecular long axis of the rod-shaped liquid crystal compound. On the other hand, when the liquid crystal compound 40 is a discotic liquid crystal compound, the optical axis 40A of the liquid crystal compound 40 refers to the axis parallel to the normal direction to the disc surface of the discotic 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 alignment axis D along which the optical axis 40A continuously rotates and changes within the plane of the liquid crystal orientation pattern of the liquid crystal compound 40 is defined as the length Λ of one period of the liquid crystal orientation pattern. That is, the length Λ of one period is defined as the distance between the centers in the direction of the arrangement axis D of two liquid crystal compounds 40 that are at the same angle with respect to the direction of the arrangement axis D. Specifically, as shown in Fig. 3, the length Λ of one period is defined as the distance between the centers in the direction of the arrangement axis D of two liquid crystal compounds 40 whose directions of the arrangement axis D and the optical axis 40A coincide with each other. In the following description, this length Λ of one period is also referred to as "one period Λ". The liquid crystal orientation pattern of the cholesteric liquid crystal layer 34 repeats this one period Λ in one direction along the direction of the arrangement axis D, i.e., the direction of the optical axis 40A, which continuously rotates and changes. In the liquid crystal diffraction element, this one period Λ becomes the period of the diffraction structure.

[0052] On the other hand, the liquid crystal compound 40 forming the cholesteric liquid crystal layer 34 has the same orientation of the optical axis 40A in a direction perpendicular to the direction of the alignment axis D (Y direction in Figure 3), i.e., in the Y direction perpendicular to the direction in which the optical axis 40A continuously rotates. In other words, the liquid crystal compound 40 forming the cholesteric liquid crystal layer 34 has an angle between the optical axis 40A of the liquid crystal compound 40 and the direction of the arrow X in the Y direction equal to one another.

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

[0054] The diffraction effect caused by the cholesteric liquid crystal layer 34 having such a liquid crystal orientation pattern will now be described.

[0055] In a normal cholesteric liquid crystal layer that does not have a liquid crystal alignment pattern, the helical axis derived from the cholesteric liquid crystal phase is perpendicular to the main surface (XY plane), and the reflection surface is a plane parallel to the main surface (XY plane). In addition, the optical axis of the liquid crystal compound is not inclined with respect to the main surface (XY plane). In other words, the optical axis is parallel to the main surface (XY plane). Therefore, when a cross section (XZ plane) of a typical cholesteric liquid crystal layer in the thickness direction is observed with an SEM, as described above, the alternating arrangement of light and dark areas is parallel to the main surface (XY plane), i.e., the alternating arrangement direction of the light and dark areas is perpendicular to the main surface. Since the cholesteric liquid crystal phase has specular reflectivity, for example, when light is incident on a 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 in the direction of the alignment axis D (one predetermined direction) within the plane. The cholesteric liquid crystal layer 34 having such a liquid crystal orientation pattern reflects incident light with a tilt in the direction of the alignment axis D relative to specular reflection. Hereinafter, a description will be given with reference to FIG.

[0057] As an example, the cholesteric liquid crystal layer 34 is configured to polarize right-handed circularly polarized red light R R Therefore, when light is incident on the cholesteric liquid crystal layer 34, the cholesteric liquid crystal layer 34 selectively reflects right-handed circularly polarized light R R It reflects only light and transmits 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 alignment axis D (one direction). The liquid crystal orientation pattern formed in the cholesteric liquid crystal layer 34 is a periodic pattern in the direction of the alignment axis D. Therefore, the right-handed circularly polarized light R of red light incident on the cholesteric liquid crystal layer 34 RAs conceptually shown in Figure 5, is not specularly reflected, but is diffracted in a direction according to the period of the liquid crystal orientation pattern, and is reflected by being diffracted in a direction tilted toward the alignment axis D with respect to the XY plane (the main surface of the cholesteric liquid crystal layer).

[0059] Therefore, by using the 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 reflection within the light guide plate, and can then be incident on the light guide plate 12. Furthermore, by using the cholesteric liquid crystal layer 34 as the exit liquid crystal layer of the exit section 16, the light that is totally reflected and propagated 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 can be emitted from the light guide plate 12.

[0060] In the cholesteric liquid crystal layer 34, the direction of the alignment axis D, which is one direction in which the optical axis 40A rotates, can be appropriately set to adjust the diffraction direction of light, that is, the reflection direction.

[0061] When circularly polarized light of the same wavelength and rotation direction is reflected, the reflection direction 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 alignment axis D. For example, in Figures 2 and 3, the rotation direction of optical axis 40A toward the direction of array axis D is clockwise, and some circularly polarized light is reflected with an inclination toward the direction of array axis D, but by changing this to counterclockwise, some circularly polarized light is reflected with an inclination in the opposite direction to the direction of array axis D.

[0062] Furthermore, in liquid crystal layers having the same liquid crystal orientation pattern, the reflection direction is reversed depending on the helical rotation direction of the liquid crystal compound 40, that is, the rotation direction of the reflected circularly polarized light. For example, when the direction of rotation of the helix is ​​right-twisted, right-handed circularly polarized light is selectively reflected, and by having a liquid crystal orientation pattern in which the optical axis 40A rotates clockwise along the direction of the array axis D, right-handed circularly polarized light is reflected at an inclination toward the direction of the array axis D. Furthermore, for example, when the direction of rotation of the helix is ​​left twisted, left-handed circularly polarized light is selectively reflected, and a liquid crystal layer having a liquid crystal orientation pattern in which the optical axis 40A rotates clockwise along the direction of the arrangement axis D reflects left-handed circularly polarized light tilted in the direction opposite to the direction of the arrangement axis D.

[0063] Therefore, the R-incident liquid crystal layer 14R, the G-incident liquid crystal layer 14G, and the B-incident liquid crystal layer 14B that constitute 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 orientation pattern according to the rotation direction of the selectively reflected circularly polarized light, i.e., the spiral rotation direction, so that the incident light is directed appropriately toward the exit section 16. On the other hand, the R-emitting liquid crystal layer 16R, the G-emitting liquid crystal layer 16G, and the 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 orientation pattern so that the incident light is appropriately emitted to the observation position by the user U, depending on the rotation direction of the selectively reflected circularly polarized light, i.e., the spiral rotation direction.

[0064] In this liquid crystal diffraction element, one period Λ, which is the length for the optical axis of the liquid crystal compound to rotate 180° in the liquid crystal orientation pattern of the liquid crystal compound in the liquid crystal layer, is the period (one period) of the diffraction structure. Also, in the liquid crystal layer, one direction (direction of the array axis D) in which the optical axis of the liquid crystal compound changes while rotating is the periodic direction of the diffraction structure. In the optical element 10 of the present invention, there is no limitation on the length of one period Λ of the diffraction element, and it may be set appropriately depending on the angle of incidence on the light guide plate 12, the degree of diffraction of the light to be emitted from the light guide plate 12, etc. The length of one period Λ is preferably from 0.1 to 10 μm, more preferably from 0.15 to 2 μm, and even more preferably from 0.2 to 1 μm.

[0065] In a liquid crystal layer having a liquid crystal alignment pattern, the shorter the period Λ, the larger the angle of the reflected light with respect to the incident light. In other words, the shorter the period Λ, the greater the inclination at which the reflected light is reflected with respect to the specular reflection of the incident light. In addition, in a liquid crystal layer having this liquid crystal orientation pattern, the angle of reflection (diffraction angle) of light varies depending on the wavelength of the reflected light. Specifically, the longer the wavelength of light, the more the reflected light is tilted 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 multiple liquid crystal layers (cholesteric liquid crystal layers) are stacked has a sequence in which the wavelength of light selectively reflected by each liquid crystal layer matches the sequence of one period Λ. Specifically, in the optical element 10, the wavelengths of 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 constituting the incident section 14 become shorter in this order: R-incident liquid crystal layer 14R, G-incident liquid crystal layer 14G, and B-incident liquid crystal layer 14B. Therefore, it is preferable that one period Λ also becomes shorter in the order of the R-incident liquid crystal layer 14R, the G-incident liquid crystal layer 14G, and the B-incident liquid crystal layer 14B. On the other hand, the wavelengths of 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 constituting the emission section 16 become shorter in the order of the R-emitting liquid crystal layer 16R, the G-emitting liquid crystal layer 16G, and the B-emitting liquid crystal layer 16B. Therefore, it is preferable that one period Λ is also shortened in the order of the R-emitting liquid crystal layer 16R, the G-emitting liquid crystal layer 16G, and the B-emitting liquid crystal layer 16B. This point is the same whether the liquid crystal layer in the entrance section 14 and the exit section 16 is two layers or four or more layers.

[0067] With this configuration, it is possible to match the incidence directions of the red image R, the green image G, and the blue image B on the light guide plate 12 through the entrance portion 14. Furthermore, with this configuration, it is possible to match the emission directions of the red image R, the green image G, and the blue image B emitted from the exit portion 16. As a result, a color image without color shift can be emitted from the light guide plate 12 to the viewing position of the user U of the AR glasses.

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

[0069] 6, the inclination angle (tilt angle) of the liquid crystal compound 40 with respect to the principal surface (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 to this. The cholesteric liquid crystal layer 34 may have a region in which the tilt angle of the liquid crystal compound 40 varies in the thickness direction. For example, in the example shown in FIG. 7, the optical axis 40A of the liquid crystal compound 40 at the interface on the photo-alignment film 32 side of the liquid crystal layer is parallel to the main surface (pretilt angle is 0°), and the tilt angle of the liquid crystal compound 40 increases with increasing distance in the thickness direction from the interface on the photo-alignment film 32 side, and thereafter, the liquid crystal compound is oriented at a constant tilt angle up to the other interface (air interface).

[0070] In this way, in the cholesteric liquid crystal layer 34, the optical axis of the liquid crystal compound may have a pretilt angle at one of the upper and lower interfaces, or may have pretilt angles at both interfaces. Also, the pretilt angles may be different at both interfaces. When the liquid crystal compound has a tilt angle (is inclined) in this way, the effective birefringence of the liquid crystal compound increases when light is diffracted, and the diffraction efficiency can be improved.

[0071] The average angle (average tilt angle) between the optical axis 40A of the liquid crystal compound 40 and the principal surface (XY plane) is preferably 5 to 45°, 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, the optical axis 40A of the liquid crystal compound 40 is preferably tilted in the same direction with respect to the principal surface (XY plane). The tilt angle is an arithmetic average of angles between the optical axis 40A of the liquid crystal compound 40 and the principal surface measured at any five or more points in a cross section of the cholesteric liquid crystal layer observed under a polarizing microscope.

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

[0073] Also, the tilt angle is preferably controlled by treatment of 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 performing a pretilt treatment on the photo-alignment film. For example, when forming the photo-alignment film, the photo-alignment film is exposed to ultraviolet light from the front and then obliquely exposed, so that a pretilt 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 pretilted in the direction in which the single axis side is visible with respect to the second irradiation direction. However, since the liquid crystal compound in the direction perpendicular to the second irradiation direction does not pretilt, there are regions in the plane that are pretilted and regions that are not pretilted. This contributes to increasing the birefringence in the desired direction when diffracting light in that direction, and is therefore suitable for increasing diffraction efficiency. Furthermore, an additive that promotes the pretilt angle can be added to the liquid crystal layer or the photo-alignment film, in which case the additive can be used as a factor for further increasing the diffraction efficiency. This additive can also be used to control the pretilt angle of the air-side interface.

[0074] Here, in the cross section of the cholesteric liquid crystal layer 34 observed by SEM, the bright and dark areas derived from the cholesteric liquid crystal phase are inclined with respect to the main surface. When the in-plane retardation Re of the liquid crystal layer is measured from the normal direction and the direction inclined with respect to the normal, it is preferable that the direction in which the in-plane retardation Re is minimum is inclined with respect to the normal direction in either the slow axis plane or the fast axis plane. Specifically, it is preferable that the absolute value of the measurement angle between the normal line and the direction in which the in-plane retardation Re is minimum 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 surface, and the inclination direction approximately coincides with the bright and dark areas of the liquid crystal layer. The normal direction is a direction perpendicular to the main surface. The liquid crystal layer having such a configuration can diffract circularly polarized light with higher diffraction efficiency than a liquid crystal layer in which the liquid crystal compound is parallel to the main surface.

[0075] In a configuration in which the liquid crystal compound of the liquid crystal layer is tilted with respect to the main surface and the tilt direction is approximately the same as the light and dark areas, the light and dark areas corresponding to the reflecting surface are aligned with the optical axis of the liquid crystal compound. Therefore, the effect of the liquid crystal compound on the reflection (diffraction) of light 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 fast axis plane or slow axis plane of the liquid crystal layer, the absolute value of the optical axis tilt 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 possible to more suitably match the directions of the liquid crystal compounds with the light and dark areas, which is preferable in terms of improving the diffraction efficiency.

[0077] <Thickness distribution requirements for the incident and outgoing liquid crystal layers> The R incident liquid crystal layer 14R, the G incident liquid crystal layer 14G and the B incident liquid crystal layer 14B constituting the incident section 14 are formed by the cholesteric liquid crystal layer 34 which is the above-mentioned reflective liquid crystal diffraction element. Similarly, the R-emitting liquid crystal layer 16R, the G-emitting liquid crystal layer 16G, and the B-emitting liquid crystal layer 16B constituting the emission section 16 are also formed of the cholesteric liquid crystal layer 34 which is the above-mentioned reflective liquid crystal diffraction element. Here, in the optical element 10 of the present invention, at least one liquid crystal layer has high film thickness uniformity in the incident section 14 and the exit section 16. Specifically, at least one liquid crystal layer in the incident section 14 and the exit section 16 satisfies the film thickness distribution requirements shown below.

[0078] In the present invention, the film thickness distribution requirements are as follows. The film thickness distribution requirement is determined by observing a cross section of the liquid crystal layer (cholesteric liquid crystal layer) in the thickness direction at 10,000 times magnification using a SEM (Scanning Electron Microscope). Here, when determining the in-plane direction of the liquid crystal layer, when laser light is incident on the liquid crystal layer at various angles of incidence and azimuth directions, the incident light is diffracted and the light guide direction of the outgoing light is determined. This makes it possible to determine the in-plane direction of the liquid crystal orientation pattern in the liquid crystal layer, in which the direction of the optical axis derived from the liquid crystal compound changes while rotating continuously. In the present invention, the film thickness distribution requirement is determined by observing a cross section parallel to the in-plane direction of this liquid crystal orientation pattern. The cross section of the liquid crystal layer was observed 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, thereby obtaining images of a range of 200 μm in the in-plane direction of the liquid crystal layer (see Figure 10). The difference between the maximum thickness and the minimum thickness of the liquid crystal layer within a range of 200 μm in the in-plane direction of the liquid crystal layer thus obtained is obtained. This operation is carried out on 10 random cross sections. The differences between the maximum and minimum film thicknesses in the 10 cross sections thus obtained are then arithmetically averaged. When the value obtained by this arithmetic mean is 0.1 μm or less, the liquid crystal layer satisfies the film thickness distribution requirement of the present invention. The value obtained by this arithmetic mean is preferably 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 for the entrance portion 14 and the exit portion 16. With this, as described above, an image displayed by the display is incident on the light guide plate 12 by the entrance portion 14, propagates through total reflection, and is output from the light guide plate 12 by the exit portion 16, so that it can be output to a position observed by the user U. In addition, the cholesteric liquid crystal layer 34 selectively reflects circularly polarized light in a specific rotation direction in a specific wavelength range, and transmits other light. Therefore, by stacking liquid crystal layers with different selectively reflected wavelength ranges (selective reflection center wavelengths), it is possible to handle a full-color image with a red image R, a green image G, and a blue image B as in the illustrated example, or to handle a two-color image, etc.

[0080] Here, according to the inventors' investigations, when an optical element formed by stacking liquid crystal layers that act as a liquid crystal diffraction element, such as the cholesteric liquid crystal layer 34 having the above-mentioned liquid crystal orientation pattern, is used as a diffraction element for making light enter / exit a light guide plate in AR glasses or the like, the image displayed may become blurred. The present inventors have conducted extensive research into the cause of this image blurring, and have found that in an optical element in which a liquid crystal layer acting as a liquid crystal diffraction element, such as the cholesteric liquid crystal layer 34 having the above-mentioned liquid crystal orientation pattern, is laminated, the diffraction angle may be distributed within the plane of the liquid crystal layer. If a distribution of diffraction angles occurs within the plane of the liquid crystal layer, for example in AR glasses, the image will not be projected to the correct position at the observation position of the user U, resulting in a blurred image. In particular, if such a distribution of diffraction angles occurs at the entrance portion, the image will become significantly blurred.

[0081] The inventors have conducted extensive research into the cause of this phenomenon. As a result, they have found that the image blur, i.e., the distribution of diffraction angles, is caused by unevenness in the film thickness (variation in film thickness) of the lower liquid crystal layer, i.e., the liquid crystal layer that is closer to the substrate among the stacked liquid crystal layers. Furthermore, the inventors have found that the distribution of diffraction angles is caused not by minute irregularities in the lower liquid crystal layer, but by gentle unevenness in the film thickness, such as undulations, of the lower liquid crystal layer.

[0082] As conceptually shown in FIG. 9, it is assumed that a reflective layer B, a reflective layer G and a reflective layer R each made of a cholesteric liquid crystal layer 34 having the above-mentioned liquid crystal orientation pattern are laminated on a substrate S in this order. In this case, as shown on the left side of FIG. 9, if there is no unevenness in the thickness of any of the reflective layers, the reflective layers B, G and R can all reflect light at the same diffraction angle over the entire surface.

[0083] In contrast, as shown on the right side of Fig. 9, for example, if there is unevenness in the thickness of the reflective layer B closest to the substrate S, the reflective layer G laminated on top of it (on the opposite side to the substrate S) will have an inclined interface with the reflective layer B. As a result, the angle of orientation (cholesteric orientation) of the cholesteric liquid crystal phase of the liquid crystal compound will change in the plane of the reflective layer G. Furthermore, the reflective layer R laminated on top of the reflective layer G also has a region where the interface with the reflective layer G is inclined, so similarly, the angle of orientation of the cholesteric liquid crystal phase of the liquid crystal compound will change in the plane. As a result, as shown on the right side of FIG. 9, in the reflective layer G (reflective layer R), a distribution of diffraction angles occurs within the plane, resulting in blurring of the image.

[0084] In contrast, in the optical element 10 of the present invention, at least one of the input liquid crystal layers constituting the input section 14 and at least one of the output liquid crystal layers constituting the output section 16 satisfy a thickness distribution requirement that the arithmetic mean of the difference between the maximum thickness and the minimum thickness within a 200 μm range in ten cross sections obtained as described above is 0.1 μm or less. A liquid crystal layer that satisfies this thickness distribution requirement has extremely small gradual thickness unevenness such as undulations. As a result, as shown on the left side of FIG. 9, the distribution of diffraction angles within the plane in each liquid crystal layer is extremely small, and when used as AR glasses, blurring of images of each color can be prevented.

[0085] In the optical element of the present invention, in incident section 14, at least one of R-incident liquid crystal layer 14R, G-incident liquid crystal layer 14G, and B-incident liquid crystal layer 14B needs to satisfy the film thickness distribution requirement. In the emission section 16, at least one of the R-emission liquid crystal layer 16R, the G-emission liquid crystal layer 16G, and the B-emission liquid crystal layer 16B needs to satisfy the film thickness distribution requirement.

[0086] Here, the distribution of diffraction angles due to the unevenness in thickness does not occur in the liquid crystal layer itself having the unevenness in thickness, but occurs in the liquid crystal layer laminated on the liquid crystal layer having the unevenness in thickness. Note that "below" refers to the substrate side, and "above" refers to the opposite side. That is, the distribution of the diffraction angle due to the unevenness in the thickness occurs in the liquid crystal layer located on the side farther away from the substrate with respect to the liquid crystal layer having the unevenness in the thickness. Taking this into consideration, it is preferable that, among the stacked liquid crystal layers, at least the liquid crystal layer located at the end in the stacking direction satisfies 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. That is, in the illustrated example, it is preferable that at least the B-entrance liquid crystal layer 14B of the entrance section 14 satisfies the film thickness distribution requirement. Also, 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 farthest from the substrate, that is, at least the liquid crystal layers other than the uppermost liquid crystal layer, satisfy the film thickness distribution requirement. That is, in the illustrated optical element 10, it is more preferable that at least the B-incident liquid crystal layer 14B and the G-incident liquid crystal layer 14G in the incident section 14 satisfy the film thickness distribution requirement. Also, it is more preferable that at least the B-exiting liquid crystal layer 16B and the G-exiting liquid crystal layer 16G in 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 the liquid crystal layers constituting the laminate satisfy the film thickness distribution requirement. That is, in the illustrated optical element 10, it is most preferable that the R-incident liquid crystal layer 14R, the G-incident liquid crystal layer 14G, and the B-incident liquid crystal layer 14B satisfy the film thickness distribution requirement in the incident section 14. Also, it is most preferable that the R-exiting liquid crystal layer 16R, the G-exiting liquid crystal layer 16G, and the B-exiting liquid crystal layer 16B satisfy the film thickness distribution requirement in the exit section 16.

[0089] In addition, the optical element 10 shown in the figure is a laminate in the optical element of the present invention, in which the liquid crystal layers laminated in both the incident portion 14 and the exit portion 16 have a predetermined liquid crystal orientation pattern and at least one layer satisfies the film thickness distribution requirement, as a preferred embodiment. 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 exit portion 16 to a light guide plate 12 as a substrate, only the incident portion 14 may be the laminate in the optical element of the present invention, or only the exit portion 16 may be the laminate in the present invention. In the illustrated optical element 10 having the incident portion 14 and the exit portion 16 to a light guide plate 12, it is preferable that at least the incident portion 14 is the laminate in the present invention. Furthermore, in the optical element 10 of the present invention having the incident portion 14 and the exit portion 16 to a light guide plate 12, it is more preferable that the incident portion 14 and the exit portion 16 are the laminate in the present invention, as in the illustrated example.

[0090] <<Method of forming a cholesteric liquid crystal layer>> The cholesteric liquid crystal layer 34, which constitutes the incident liquid crystal layer 14R, the G incident liquid crystal layer 14G, and the B incident liquid crystal layer 14B constituting the incident section 14, and the R output liquid crystal layer 16R, the G output liquid crystal layer 16G, and the B output liquid crystal layer 16B constituting the output section 16, can be formed by fixing a liquid crystal phase in a layer shape, in which a liquid crystal compound is oriented in a predetermined orientation state. For example, in the case of a cholesteric liquid crystal layer, the cholesteric liquid crystal layer can be formed by fixing a cholesteric liquid crystal phase in a layer shape. The structure in which the cholesteric liquid crystal phase is fixed may be any structure in which the orientation of the liquid crystal compound in the liquid crystal phase is maintained. Typically, the polymerizable liquid crystal compound is brought into a predetermined liquid crystal phase orientation state, and then polymerized and hardened by ultraviolet irradiation, heating, etc. to form a layer with no fluidity, and at the same time, the structure is changed to a state in which the orientation form is not changed by an external field or external force. In the structure in which the liquid crystal phase is fixed, 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 crystallinity in the liquid crystal layer. For example, the polymerizable liquid crystal compound may be polymerized by a curing reaction and lose its liquid crystallinity.

[0091] An example of a material used to form the liquid crystal layer is a liquid crystal composition containing a liquid crystal compound, which is preferably a polymerizable liquid crystal compound. The liquid crystal composition used to form the liquid crystal layer may further 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 discotic liquid crystal compound. Examples of rod-shaped polymerizable liquid crystal compounds include rod-shaped nematic liquid crystal compounds.As rod-shaped nematic liquid crystal compounds, azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoates, cyclohexane carboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes, and alkenylcyclohexylbenzonitriles are preferably used.Not only low molecular weight liquid crystal compounds but also high molecular weight liquid crystal compounds can be used.

[0093] The polymerizable liquid crystal compound is obtained by introducing a polymerizable group into a liquid crystal compound. Examples of the polymerizable group include an unsaturated polymerizable group, an epoxy group, and an aziridinyl group, and an unsaturated polymerizable group is preferable, and an ethylenically unsaturated polymerizable group is more preferable. The polymerizable group can be introduced into the molecule of the liquid crystal compound by various methods. The number of polymerizable groups that the polymerizable liquid crystal compound has is preferably 1 to 6, more preferably 1 to 3. Examples of the polymerizable liquid crystal compound include compounds described in Makromol.Chem., Vol. 190, p. 2255 (1989), Advanced Materials, Vol. 5, p. 107 (1993), U.S. Pat. No. 4,683,327, U.S. Pat. No. 5,622,648, U.S. Pat. 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, JP-A-1-272551, JP-A-6-16616, JP-A-7-110469, JP-A-11-80081, and JP-A-2001-328973. Two or more polymerizable liquid crystal compounds may be used in combination. The alignment temperature can be lowered by using two or more kinds of polymerizable liquid crystal compounds in combination.

[0094] As other polymerizable liquid crystal compounds, a cyclic organopolysiloxane compound having a cholesteric phase as disclosed in JP-A-57-165480 can be used. As the above-mentioned polymer liquid crystal compounds, a polymer having a mesogen group exhibiting liquid crystal property introduced into the main chain, the side chain, or both the main chain and the side chain, a polymer cholesteric liquid crystal having a cholesteryl group introduced into the side chain, a liquid crystal polymer as disclosed in JP-A-9-133810, and a liquid crystal polymer as disclosed in JP-A-11-293252 can be used.

[0095] --Discoid Liquid Crystal Compounds-- As the discotic liquid crystal compound, for example, those described in JP-A-2007-108732 and JP-A-2010-244038 can be preferably used.

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

[0097] --Surfactant-- The liquid crystal composition used in forming the liquid crystal layer may contain a surfactant. The surfactant is preferably a compound that can function as an alignment control agent that contributes to the alignment of the cholesteric liquid crystal phase stably or quickly. Examples of the surfactant include silicone surfactants and fluorine surfactants, and fluorine surfactants are preferred.

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

[0082] to

[0090] of JP-A-2014-119605, the compounds described in paragraphs

[0031] to

[0034] of JP-A-2012-203237, the compounds exemplified in paragraphs

[0092] and

[0093] of JP-A-2005-99248, the compounds exemplified in paragraphs

[0076] to

[0078] and paragraphs

[0082] to

[0085] of JP-A-2002-129162, and the fluorine (meth)acrylate polymers described in paragraphs

[0018] to

[0043] of JP-A-2007-272185, etc. The surfactant may be used alone or in combination of two or more kinds. As the fluorine-based surfactant, the compounds described in paragraphs

[0082] to

[0090] of JP2014-119605A are preferred.

[0099] The amount of the surfactant added in the liquid crystal composition is preferably 0.01 to 10% by mass, more preferably 0.01 to 5% by mass, and further preferably 0.02 to 1% by mass, based on 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. Chiral agents can be selected according to the purpose, since the twist direction or helical pitch of the helix induced varies depending on the compound. The chiral agent is not particularly limited, and known compounds (for example, those described in Liquid Crystal Device Handbook, Chapter 3, Section 4-3, Chiral Agents for TN (twisted nematic) and STN (Super Twisted Nematic), p. 199, edited by the 142nd Committee of the Japan Society for the Promotion of Science, 1989), isosorbide, and isomannide derivatives can be used. Although the chiral agent generally contains an asymmetric carbon atom, an axially asymmetric compound or a planarly asymmetric compound that does not contain an asymmetric carbon atom can also be used as the chiral agent. Examples of the axially asymmetric compound or the planarly asymmetric compound include binaphthyl, helicene, paracyclophane, and derivatives thereof. The chiral agent may have a polymerizable group. When both the chiral agent and the liquid crystal compound have a polymerizable group, a polymer having a repeating unit derived from the polymerizable liquid crystal compound and a repeating unit derived from the chiral agent can be formed by a polymerization reaction between the polymerizable chiral agent and the polymerizable liquid crystal compound. In this embodiment, the polymerizable group of the polymerizable chiral agent is preferably the same type of group as the polymerizable group of the polymerizable liquid crystal compound. Therefore, the polymerizable group of the chiral agent is also preferably an unsaturated polymerizable group, an epoxy group, or an aziridinyl group, more preferably an unsaturated polymerizable group, and even more preferably an ethylenically unsaturated polymerizable group. The chiral agent may also be a liquid crystal compound.

[0101] When the chiral agent has a photoisomerizable group, it is preferable because a pattern of a desired reflection wavelength corresponding to the emission wavelength can be formed by irradiating a photomask with actinic rays or the like after coating and alignment. As the photoisomerizable group, an isomerization site of a compound exhibiting photochromic properties, an azo group, an azoxy group, or a cinnamoyl group is preferable. Specific compounds that can be used include those described in JP-A-2002-80478, JP-A-2002-80851, JP-A-2002-179668, JP-A-2002-179669, JP-A-2002-179670, JP-A-2002-179681, JP-A-2002-179682, JP-A-2002-338575, JP-A-2002-338668, JP-A-2003-313189, and JP-A-2003-313292.

[0102] The content of the chiral dopant in the liquid crystal composition is preferably 0.01 to 200 mol %, more preferably 1 to 30 mol %, based on the molar amount of the liquid crystal compound.

[0103] --Polymerization initiator-- When the liquid crystal composition contains a polymerizable compound, it preferably contains a polymerization initiator. In an embodiment in which the polymerization reaction is caused to proceed by ultraviolet irradiation, the polymerization initiator used is preferably a photopolymerization initiator capable of initiating the polymerization reaction by ultraviolet irradiation. Examples of the photopolymerization initiator include α-carbonyl compounds (described in U.S. Pat. Nos. 2,367,661 and 2,367,670), acyloin ethers (described in U.S. Pat. No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin compounds (described in U.S. Pat. No. 2,722,512), polynuclear quinone compounds (described in U.S. Pat. Nos. 3,046,127 and 2,951,758), combinations of triarylimidazole dimers and p-aminophenyl ketones (described in U.S. Pat. No. 3,549,367), acridine and phenazine compounds (described in JP-A-60-105,667 and U.S. Pat. No. 4,239,850), and oxadiazole compounds (described in U.S. Pat. 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, based on the content of the liquid crystal compound.

[0104] --Crosslinking agent-- The liquid crystal composition may contain a crosslinking agent in order to improve the film strength and durability after curing. As the crosslinking agent, those which are cured by ultraviolet light, heat, moisture, etc. can be suitably used. The crosslinking agent is not particularly limited and can be appropriately selected according to the purpose. For example, 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, a known catalyst can be used according to the reactivity of the crosslinking agent, which can improve productivity in addition to improving film strength and durability. These may be used alone or in combination of two or more. The content of the crosslinking agent is preferably 3 to 20% by mass, more preferably 5 to 15% by mass, based on the solid content by mass of the liquid crystal composition. When the content of the crosslinking agent is within the above range, the effect of improving the crosslinking density is easily obtained, and the stability of the liquid crystal phase is further improved.

[0105] --Other additives-- If necessary, a polymerization inhibitor, an antioxidant, an ultraviolet absorber, a light stabilizer, a colorant, metal oxide fine particles, etc. may be added to the liquid crystal composition within a range that does not deteriorate the optical performance, etc.

[0106] --solvent-- When forming the cholesteric liquid crystal layer 34, the liquid crystal composition is preferably used in the form of a liquid. Therefore, it is preferable that the liquid crystal composition contains a solvent. There is no limitation on the solvent and it can be appropriately selected depending on the purpose, but an organic solvent is preferable. The organic solvent is not limited and can be appropriately selected according to the purpose, and examples thereof include ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. These may be used alone or in combination of two or more. Among these, ketones are preferred when considering the burden on the environment.

[0107] Here, 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 temperature and time for drying and / or heating (orientation) of the applied liquid crystal composition. Considering this point, it is preferable to use a solvent having a relatively high boiling point. Specifically, a solvent having a boiling point of 95° C. or higher is preferable, and a solvent having a boiling point of 110° C. or higher is more preferable. The solvent may be a mixed solvent in which a solvent having a low boiling point is mixed with a solvent having a high boiling point to obtain the above boiling point. Specific examples of the solvent that can be used include cyclopentanone, cyclohexanone, methyl isobutyl ketone, toluene, and a mixed solvent 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 surface on which the cholesteric liquid crystal layer 34 is to be formed, align the liquid crystal compound in a desired liquid crystal phase state, and then harden the liquid crystal compound to form a liquid crystal layer. That is, when forming a cholesteric liquid crystal layer 34 on the photo-alignment film 32, it is preferable to apply a liquid crystal composition to the photo-alignment film 32, align the liquid crystal compound in a cholesteric liquid crystal phase state, and then harden the liquid crystal compound to form a liquid crystal layer in which the cholesteric liquid crystal phase is fixed. The liquid crystal composition can be applied by any known method capable of uniformly applying a liquid to a sheet-like material, such as printing methods including ink-jet printing and scroll printing, as well as spin coating, bar coating and spray coating.

[0109] The applied liquid crystal composition is dried and heated as necessary, and then cured to form a liquid crystal layer. During the drying and heating steps, the liquid crystal compounds in the liquid crystal composition may be aligned in a cholesteric liquid crystal phase. Here, in order to form a cholesteric liquid crystal layer 34 that satisfies the above-mentioned film thickness distribution requirement, it is preferable to heat (align) the applied liquid crystal composition at a relatively high temperature. That is, by increasing the heating temperature, the surface of the applied 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 requirement can be formed. However, if the heating temperature is too high, the liquid crystal layer will not be aligned in the cholesteric liquid crystal phase and will 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 further preferably 90 to 120°C.

[0110] The aligned liquid crystal compound is further polymerized as necessary. The polymerization may be either thermal polymerization or photopolymerization by light irradiation, but photopolymerization is preferred. The light irradiation is preferably performed using ultraviolet light. The irradiation energy is 20 mJ / cm. 2 ~50J / cm 2 is preferable, and 50 to 1500 mJ / cm 2 In order to promote the photopolymerization reaction, the light irradiation may be performed under heating conditions or in a nitrogen atmosphere. The wavelength of the ultraviolet light to be irradiated is preferably 250 to 430 nm.

[0111] There is no limitation on the thickness of the cholesteric liquid crystal layer 34, and the thickness that provides the required light reflectance can be set appropriately depending on the application of the diffraction element, the light reflectance required for the liquid crystal layer, and the material from which the cholesteric liquid crystal layer 34 is formed, etc.

[0112] <Other liquid crystal layers (optically anisotropic layers)> The optical element in the illustrated example uses a reflective liquid crystal diffraction element using a cholesteric liquid crystal layer 34 for the entrance liquid crystal layer of the entrance section 14 and the exit liquid crystal layer of the exit section 16, but the present invention is not limited to this. As an example, a liquid crystal layer that has a liquid crystal orientation pattern that is continuously rotated 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, and acts as a transmission type liquid crystal diffraction element, can also be used. Note that 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. In the present invention, different liquid crystal diffraction elements may be used in the entrance section 14 and the exit section 16. For example, a reflective liquid crystal diffraction element using a cholesteric liquid crystal layer 34 may be used in the entrance section 14, and the above-mentioned transmissive liquid crystal diffraction element may be used in the exit section 16.

[0113] [How to make the entrance and exit parts] The input portion 14 and the output portion 16 can be produced by various known methods, but are preferably formed by the transfer method described below. Incidentally, since the incident portion 14 and the exit portion 16 can basically be formed in the same manner, the following description will be given using the incident portion 14 as a representative example.

[0114] First, as described above, a coating liquid containing a photo-alignment material that will become the photo-alignment film 32 is applied to the support 30 and dried. Thereafter, the coating liquid is exposed to light by an exposure device 60 shown in FIG. 8 to form an alignment pattern, thereby forming the photo-alignment film 32. Meanwhile, the liquid crystal compound 40 and the chiral agent are added to a solvent to prepare a liquid crystal composition for forming the cholesteric liquid crystal layer 34. In this case, as described above, it is preferable to use a solvent having a high boiling point in order to form the cholesteric liquid crystal layer 34 that satisfies the film thickness distribution requirement. Furthermore, the above-mentioned liquid crystal composition is applied onto the photo-alignment film 32, the coating is dried and heated, and then irradiated with ultraviolet light to form the R-incident liquid crystal layer 14R, which is the cholesteric liquid crystal layer 34. In this case, as described above, by increasing the heating temperature, the 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 a 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. 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. In this case, as described above, it is preferable that the length of one period in the orientation pattern of the photo-alignment film 32, i.e., one period in the liquid crystal orientation 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.

[0116] First, the B-incident liquid crystal layer 14B is attached to a temporary support with a weak adhesive layer. Then, the B-incident liquid crystal layer 14B and the photo-alignment film 32 are peeled off at their interface. After the B-incident liquid crystal layer 14B is attached to the glass that will become the light guide plate 12, the temporary support is peeled off, thereby forming the B-incident liquid crystal layer 14B on the surface of the light guide plate 12. Prior to the transfer, a layer of SiO 2 was applied as an adhesive layer to the surface of the B-entrance liquid crystal layer 14B on the side of the optical alignment film 32. x A layer or the like may be formed. The thickness of the adhesive layer is preferably 100 nm or less. The same applies to the adhesive layer for the other incident liquid crystal layers.

[0117] Similarly, the G-incident liquid crystal layer 14G is attached to a temporary support with a weak adhesive layer, and is peeled off at the interface between the G-incident liquid crystal layer 14G and the photoalignment film 32. Next, 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 the temporary support is peeled off, thereby forming the G-incident liquid crystal layer 14G on the surface of the B-incident liquid crystal layer 14B. Similarly, the R-incident liquid crystal layer 14R is attached to a temporary support with a weak adhesive layer, and is peeled off at the interface between the R-incident liquid crystal layer 14R and the photoalignment film 32. Next, the R-incident liquid crystal layer 14R is laminated on the G-incident liquid crystal layer 14G previously transferred to the light guide plate 12, and the temporary support is peeled off, thereby forming the R-incident liquid crystal layer 14R on the surface of the G-incident liquid crystal layer 14G. As a result, on the surface of light guide plate 12, incident section 14 is formed in which three liquid crystal layers (cholesteric liquid crystal layers), namely B incident liquid crystal layer 14B, G incident liquid crystal layer 14G, and R incident liquid crystal layer 14R, are laminated.

[0118] Although the optical element of the present invention has been described in detail above, the present invention is not limited to the above-mentioned examples, and various improvements and modifications may be made without departing from the gist of the present invention. EXAMPLES

[0119] The features of the present invention will be described in more detail below with reference to examples. The materials, reagents, amounts used, amounts of substances, ratios, processing contents, processing procedures, etc. shown in the following examples can be appropriately changed 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] [Example] (Formation of photo-alignment film) A glass substrate was prepared as a support. The following coating solution for forming a photo-alignment film was applied onto the support by spin coating. The support on which the coating film of the coating solution for forming a photo-alignment film was formed was dried on a hot plate at 60° C. for 60 seconds to form a photo-alignment film.

[0121] Coating liquid for photo alignment film formation ---------------------------------------------------------------------------------- 1.00 parts by weight of the following photoalignment material Water 16.00 parts by mass Butoxyethanol 42.00 parts by weight Propylene glycol monomethyl ether 42.00 parts by mass ----------------------------------------------------------------------------------

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

[0123] (Exposure of photo-alignment film) The photo-alignment film was exposed using the exposure device shown in FIG. 8 to form a photo-alignment film having an alignment pattern. The exposure device used was a laser that emitted a laser beam with a wavelength of 325 nm. The exposure dose by the interference light was 3000 mJ / cm 2 The crossing angle (crossing angle α) of the two laser beams was set to 42.3°.

[0124] (Formation of R liquid crystal layer 1) The following 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). This composition A-1 is a liquid crystal composition that forms a cholesteric liquid crystal layer in which the length of one helix pitch (helical pitch P) in the cholesteric liquid crystal phase is 410 nm and that selectively reflects right-handed circularly polarized red (R) light. The solid content 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 applying the composition A-1 onto the photo-alignment film. Specifically, the composition A-1 was applied onto the photo-alignment film P-1 by spin coating, and the coating film was heated on a hot plate at 120° C. for 120 seconds. Thereafter, ultraviolet rays having a wavelength of 365 nm were irradiated at 500 mJ / cm using a high-pressure mercury lamp under a nitrogen atmosphere. 2 The coating film was irradiated with light at an irradiation dose of 1000 nm to fix the alignment of the liquid crystal compound, thereby forming an R liquid crystal layer 1. The thickness of the obtained R liquid crystal layer 1 was 5.2 μm.

[0129] It was confirmed by a polarizing microscope that the R liquid crystal layer 1 had a periodic alignment surface as shown in Figure 3. When the cross section of the coating layer was observed by SEM, it was found that in the liquid crystal alignment pattern of the R liquid crystal layer 1, one period Λ, in which the optical axis of the liquid crystal compound rotates by 180°, was 0.45 μm.

[0130] In addition, the cross section of the R liquid crystal layer 1 in the thickness direction was observed by SEM at 10,000 times magnification, and the observation position was continuously moved in the in-plane direction to perform 20 observations, thereby obtaining images of a range of 200 μm in the in-plane direction. Furthermore, the difference between the maximum film thickness and the minimum film thickness within this range of 200 μm in the in-plane direction was obtained. This operation was carried out on 10 arbitrary cross sections of the R liquid crystal layer 1 . The arithmetic mean of the difference between the maximum and minimum thicknesses in the 10 cross sections of the R liquid crystal layer 1 thus obtained was calculated. As a result, the arithmetic mean of the difference between the maximum and minimum thicknesses of the R liquid crystal layer 1 was 0.05 μm. Therefore, this R liquid crystal layer 1 satisfies the above-mentioned thickness distribution requirement.

[0131] (Formation and exposure of photo-alignment film for G liquid crystal layer 1) As in the case of the R liquid crystal layer 1, a photo-alignment film was formed on the surface of a glass support. The photo-alignment film thus formed was exposed to light using the exposure apparatus shown in FIG. 8 in the same manner, except that the crossing angle (crossing angle α) of the two laser beams was set to 49.2°, thereby forming 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 one helical pitch (helical pitch P) in the cholesteric liquid crystal phase is 360 nm and that selectively reflects right-handed circularly polarized light of green (G) light. Except for using this composition A-2, G liquid crystal layer 1 was formed in the same manner as R liquid crystal layer 1. When measured in the same manner as R liquid crystal layer 1, the film thickness of G liquid crystal layer 1 was 4.6 um. In the liquid crystal alignment pattern of G liquid crystal layer 1, one period Λ in which the optical axis of the liquid crystal compound rotates by 180° was 0.39 μm.

[0133] The difference between the maximum and minimum film thicknesses in a 200 μm range at 10 cross sections of the fabricated G liquid crystal layer 1 was calculated arithmetically, in the same manner as for the R liquid crystal layer 1. As a result, the arithmetic average of the difference between the maximum and minimum film thicknesses of the G liquid crystal layer 1 was 0.04 μm. Therefore, this G liquid crystal layer 1 satisfies the above-mentioned film thickness distribution requirement.

[0134] (Formation and exposure of photo-alignment film for B liquid crystal layer 1) As with the R liquid crystal layer 1, a photo-alignment film was formed on the surface of a glass support. The photo-alignment film thus formed was exposed to light using the exposure apparatus shown in FIG. 8 in the same manner, except that the crossing angle (crossing angle α) of the two laser beams was set to 61.0°, thereby forming a photo-alignment film having an alignment pattern.

[0135] (Formation of B liquid crystal layer 1 (B entrance 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 one helical pitch (helical pitch P) in the cholesteric liquid crystal phase is 300 nm and that selectively reflects right-handed circularly polarized light of blue (B) light. Except for using this composition A-3, the B liquid crystal layer 1 was formed in the same manner as the R liquid crystal layer 1. When the thickness of the B liquid crystal layer 1 was measured in the same manner as the R liquid crystal layer, it was found to be 3.8 μm. In addition, in the liquid crystal alignment pattern of the B liquid crystal layer 1, one period Λ in which the optical axis of the liquid crystal compound rotates by 180° was 0.32 μm.

[0136] The difference between the maximum and minimum film thicknesses in a 200 μm range at 10 cross sections of the fabricated B liquid crystal layer 1 was arithmetically averaged in the same manner as for the R liquid crystal layer 1. As a result, the arithmetic average of the difference between the maximum and minimum film thicknesses of the B liquid crystal layer 1 was 0.04 μm. Therefore, this B liquid crystal layer 1 satisfies the above-mentioned film thickness distribution requirement.

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

[0138] (Peeling of B liquid crystal layer 1) Two sheets of B liquid crystal layer 1 were prepared for the incident liquid crystal layer and the outgoing liquid crystal layer. A temporary support with a weak adhesive layer for transfer (Panaprotect ST50, manufactured by Panac Corporation) was attached to B liquid crystal layer 1, and then peeled off at the interface between B liquid crystal layer 1 and the photoalignment film.

[0139] (Attachment of B liquid crystal layer 1 to glass) The surface of the peeled B liquid crystal layer 1 on the alignment film side is coated with SiO x A SiO layer was formed. x The layer was formed using a deposition device manufactured by ULVAC (model number ULEYES). 2Powder was used. The SiOx layer side of B liquid crystal layer 1, which serves as an incident liquid crystal layer and an outgoing liquid crystal layer, was attached to glass which serves as a light guide plate, and then the temporary support was peeled off.

[0140] (G Peeling off liquid crystal layer 1) Two sheets of G liquid crystal layer 1 were prepared for the incident liquid crystal layer and the outgoing liquid crystal layer. A temporary support with a weak adhesive layer for transfer (Panaprotect ST50, manufactured by Panac Corporation) was attached to the G liquid crystal layer 1 and peeled off at the interface between the G liquid crystal layer and the photoalignment film.

[0141] (Laminating G liquid crystal layer 1 onto B liquid crystal layer 1) The surface of the alignment film side of the peeled G liquid crystal layer 1 is then coated with SiO x A SiO layer was formed. x The layer was formed using a deposition device manufactured by ULVAC (model number ULEYES). 2 The surface of the B liquid crystal layer 1 attached to the light guide plate was also coated with SiO x A layer was formed. On the B liquid crystal layer 1 bonded to the light guide plate, the SiO x After the layer sides were laminated, the temporary support was peeled off.

[0142] (Peeling of R liquid crystal layer 1) Two R liquid crystal layers 1 were prepared, one for incidence and one for emission. A temporary support with a weak adhesive layer for transfer (Panaprotect ST50, manufactured by Panac Corporation) was attached 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] (Laminating R liquid crystal layer 1 onto G liquid crystal layer 1 (production of optical element)) The surface of the peeled R liquid crystal layer 1 on the alignment film side is coated with SiO x A SiO layer was formed. x The layer was formed using a deposition device manufactured by ULVAC (model number ULEYES). 2 The surface of the G liquid crystal layer 1 attached to the light guide plate was also coated with SiO x A layer was formed. On the G liquid crystal layer 1 bonded to the light guide plate, the SiO x After the layer sides were laminated, the temporary support was peeled off. This resulted in the fabrication of optical element 1 as shown in Fig. 1, in which an entrance section in which a B-incident liquid crystal layer, a G-incident liquid crystal layer, and an R-incident liquid crystal layer were laminated, and an exit section in which a B-exiting liquid crystal layer, a G-exiting liquid crystal layer, and an R-exiting liquid crystal layer were laminated, on the main surface of the light guide plate. In this example, all of the liquid crystal layers satisfy the above-mentioned film thickness distribution requirements.

[0144] The periodic direction (direction of the alignment axis) of the liquid crystal compound in each liquid crystal layer was determined by attaching marks indicating the periodic direction in advance to the cholesteric liquid crystal layer on the side to be laminated and to the temporary support on the side to be laminated, and using these as marks when laminating the layers.

[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 one helical pitch (helical pitch P) in the cholesteric liquid crystal phase is 410 nm and that selectively reflects right-handed circularly polarized red (R) light. Using this 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 70° C. When the film thickness of R liquid crystal layer 2 was measured in the same manner as R liquid crystal layer 1, it was found to be 5.2 μm. In addition, in the liquid crystal alignment pattern of R liquid crystal layer 2, one 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 difference between the maximum and minimum film thicknesses in a 200 μm range at 10 cross sections was calculated arithmetically, in the same manner as for the R liquid crystal layer 1. As a result, the arithmetic mean of the difference between the maximum and minimum film thicknesses of the R liquid crystal layer 2 was 0.20 μm. Therefore, this R liquid crystal layer 2 does not satisfy the above-mentioned film thickness distribution requirement.

[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 one helical pitch (helical pitch P) in the cholesteric liquid crystal phase is 360 nm and that selectively reflects right-handed circularly polarized light of green (G) light. G liquid crystal layer 2 was formed in the same manner as R liquid crystal layer 1, except that composition A-5 was used and the heating temperature of the coating was 70° C. The thickness of G liquid crystal layer 2 was 4.6 μm, as measured in the same manner as R liquid crystal layer 1. In the liquid crystal alignment pattern of G liquid crystal layer 2, one period Λ in which the optical axis of the liquid crystal compound rotates 180° was 0.39 μm.

[0149] The difference between the maximum and minimum thicknesses of the fabricated G liquid crystal layer 2 in a 200 μm range was calculated arithmetically in ten cross sections in the same manner as for the R liquid crystal layer 1. As a result, the arithmetic average of the difference between the maximum and minimum thicknesses of the G liquid crystal layer 2 was 0.16 μm. Therefore, this G liquid crystal layer 2 does not satisfy the above-mentioned thickness distribution requirement.

[0150] (Formation of B 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 one helical pitch (helical pitch P) in the cholesteric liquid crystal phase is 300 nm and that selectively reflects right-handed circularly polarized light of blue (B) light. Using this composition A-5, B 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 70° C. When measured in the same manner as R liquid crystal layer 1, the film thickness of B liquid crystal layer 2 was 3.8 μm. In addition, in the liquid crystal alignment pattern of B liquid crystal layer 2, one period Λ in which the optical axis of the liquid crystal compound rotates by 180° was 0.32 μm.

[0151] The difference between the maximum and minimum thicknesses of the fabricated B liquid crystal layer 2 in a 200 μm range was calculated as an arithmetic average in ten cross sections in the same manner as for the R liquid crystal layer 1. As a result, the arithmetic average of the difference between the maximum and minimum thicknesses of the B liquid crystal layer 2 was 0.14 μm. Therefore, this R liquid crystal layer 2 does not satisfy the above-mentioned thickness distribution requirement. [Fabrication of optical element 2]

[0152] Optical element 2 having an entrance portion and an exit portion in a light guide plate 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. In this example, none of the liquid crystal layers satisfied the above-mentioned film thickness distribution requirement.

[0153] [evaluation] Using the manufactured optical element, an image consisting of a red image R, a green image G, and a blue image B was projected at the entrance part using an LCOS type projector as shown in Figure 1, and visual evaluation was performed at the observation position by a user U. As a result, when the optical element 1 of the embodiment, in which all the liquid crystal layers satisfied the above-mentioned thickness distribution requirements, was used, the image was clear and the characters were clearly readable. In contrast, when the optical element of the comparative example 1, in which all the liquid crystal layers did not satisfy the above-mentioned thickness distribution requirements, was used, the image was blurred and it was somewhat difficult to read the characters. From the above results, the effects of the present invention are clear. [Industrial Applicability]

[0154] The present invention can be suitably used for various applications in which light is refracted in optical devices, such as a diffraction element that causes 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. Emitter 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 Laser 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-handed circular polarization of red light M Laser light MA,MB rays P O Linearly polarized P R Right circular polarization P L Left circular polarization U user D Array axis Λ 1 period (period of the diffractive structure) Pitch

Claims

1. A substrate and a laminate including a plurality of liquid crystal layers formed by aligning a liquid crystal compound and provided on the substrate, the liquid crystal layer constituting the laminate has a liquid crystal orientation 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 a plane; An optical element, wherein at least one of the liquid crystal layers constituting the laminate satisfies the following film thickness distribution requirement. Film thickness distribution requirements A cross-section of the thickness direction of the liquid crystal layer is observed at 10,000 times magnification using a scanning electron microscope, and the observation position is moved continuously in the in-plane direction of the liquid crystal layer at 20 locations to obtain images of a range of 200 μm in the in-plane direction of the liquid crystal layer. This operation is performed on any 10 cross-sections of the liquid crystal layer to obtain the difference between the maximum film thickness and the minimum film thickness within the obtained range of 200 μm in the in-plane direction of the liquid crystal layer, and the arithmetic average 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. The optical element according to claim 1 , wherein the liquid crystal layer located at an end in a stacking direction among the liquid crystal layers constituting 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 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 layer other than the liquid crystal layer furthest from the substrate satisfies the film thickness distribution requirement.

5. 5. The optical element according to claim 1, wherein all of the liquid crystal layers constituting the laminate satisfy the thickness distribution requirement.

6. 6. The optical element according to claim 1, wherein the liquid crystal layer constituting the laminate is a cholesteric liquid crystal layer having a fixed cholesteric liquid crystal phase.

7. the substrate is a light guide plate having an incident portion through which light is incident to the light guide plate and an exit portion through which light is emitted from the light guide plate; 7. The optical element according to claim 1, wherein at least one of the entrance portion and the exit portion is formed using the laminate.

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

9. The optical element according to claim 8 , wherein the emission section is formed using the laminate.

Images