Optical elements, light guide elements, and AR display devices

Abstract

The present invention provides an optical element comprising a single cholesteric liquid crystal layer capable of reflecting red, green, and blue light, a light guide element using the optical element, and an AR display device. [Solution] An optical element comprising a cholesteric liquid crystal layer containing a polymerizable liquid crystal compound and a chiral agent, wherein the cholesteric liquid crystal layer has, in its plane, a first reflective region having a reflectance peak in the wavelength range of 400 to 550 nm, and a second reflective region having a reflectance peak different from that of the first reflective region in the wavelength range of 550 to 700 nm, wherein the thickness of the first reflective region of the cholesteric liquid crystal layer is thinner than the thickness of the second reflective region.

Description

[Technical Field]

[0001] The following disclosure relates to optical elements, light guide elements, and AR display devices. [Background technology]

[0002] In recent years, research and development of augmented reality (AR) display devices that superimpose images onto the real world have progressed. For example, AR glasses have been proposed that superimpose the display image onto the scene the user is actually seeing by having the display light incident on one end of a light guide plate, propagating through it, and exiting from the other end. Such AR glasses sometimes incorporate a diffraction element using a liquid crystal layer doped with a chiral agent. Specifically, it has been known to utilize a cholesteric liquid crystal layer having a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound rotates continuously along at least one direction in the plane (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] U.S. Patent Application Publication No. 2021 / 0397008 [Patent Document 2] International Publication No. 2019 / 189852 [Patent Document 3] International Publication No. 2020 / 122119 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Cholesteric liquid crystal layers have the property of selectively reflecting visible light. However, to improve the display quality of AR glasses, there was a need for a diffraction element equipped with a cholesteric liquid crystal layer that reflects all of the red (R), green (G), and blue (B) light contained in visible light. While it is possible to reflect RGB light by stacking cholesteric liquid crystal layers that selectively reflect light of different wavelengths, there was a need for a method that could reflect RGB light even with a single layer of cholesteric liquid crystal.

[0005] The present invention has been made in view of the above-mentioned circumstances, and aims to provide an optical element comprising a single cholesteric liquid crystal layer capable of reflecting red, green, and blue light, a light guide element using the optical element, and an AR display device. [Means for solving the problem]

[0006] (1) One embodiment of the present invention is an optical element comprising a cholesteric liquid crystal layer containing a polymerizable liquid crystal compound and a chiral agent, wherein the cholesteric liquid crystal layer has, in its plane, a first reflective region having a reflectance peak in the wavelength range of 400 to 550 nm, and a second reflective region having a reflectance peak different from that of the first reflective region in the wavelength range of 550 to 700 nm, and the thickness of the first reflective region of the cholesteric liquid crystal layer is thinner than the thickness of the second reflective region.

[0007] (2) In addition, one embodiment of the present invention is an optical element in which, in addition to the configuration of (1) above, one of the first reflection region and the second reflection region is distributed and arranged in a plurality of partial regions, and the other of the first reflection region and the second reflection region is arranged surrounding each of the plurality of partial regions.

[0008] (3) In addition, one embodiment of the present invention is an optical element in which, in addition to the configuration of (2) above, the region of the cholesteric liquid crystal layer other than the plurality of partial regions is the other of the first reflective region and the second reflective region.

[0009] (4) In addition, one embodiment of the present invention is an optical element in which, in addition to the configuration of (1), (2) or (3) above, the cholesteric liquid crystal layer has a reflectance at a wavelength of 450 nm in the first reflection region that is greater than the reflectance at a wavelength of 650 nm in the second reflection region, and the area of ​​the first reflection region is smaller than the area of ​​the second reflection region.

[0010] (5) In addition, one embodiment of the present invention is an optical element in which, in addition to the configuration of (1), (2) or (3) above, the cholesteric liquid crystal layer has a reflectance at a wavelength of 450 nm in the first reflection region that is smaller than the reflectance at a wavelength of 650 nm in the second reflection region, and the area of ​​the first reflection region is larger than the area of ​​the second reflection region.

[0011] (6) In addition, one embodiment of the present invention is an optical element in which, in addition to the configuration of (1), (2), (3), (4) or (5) above, the cholesteric liquid crystal layer has a low-reflectance region in its plane that has a visible light reflectance smaller than the first reflective region and the second reflective region.

[0012] (7) In addition, one embodiment of the present invention is an optical element in which, in addition to the configuration of (6) above, one of the first reflective region and the second reflective region is distributed and arranged in a plurality of first partial regions, the low reflective region is distributed and arranged in a plurality of second partial regions, and the region of the cholesteric liquid crystal layer other than the plurality of first partial regions and the plurality of second partial regions is the other of the first reflective region and the second reflective region.

[0013] (8) Another embodiment of the present invention is a light guide element comprising a light guide plate, a light-receiving optical element attached to the light-receiving side of the light guide plate, and a light-emitting optical element attached to the light-emitting side of the light guide plate, wherein at least one of the light-receiving optical element and the light-emitting optical element is the optical element of (1), (2), (3), (4), (5), (6) or (7) above.

[0014] (9) Further, in a certain embodiment of the present invention, in addition to the configuration of (8) above, the light-emitting side optical element includes the cholesteric liquid crystal layer having a low reflection region in the plane with a visible light reflectance smaller than that of the first reflection region and the second reflection region, and in the cholesteric liquid crystal layer, the area ratio of the low reflection region in the first region is larger than the area ratio of the low reflection region in the second region, which is farther from the light-incident side of the light guide plate than the first region.

[0015] (10) Further, a certain embodiment of the present invention includes the light guide element according to (8) or (9) above, and a display module disposed opposite to the light-incident side optical element through the light guide plate.

Advantages of the Invention

[0016] According to the present invention, it is possible to provide an optical element including a single cholesteric liquid crystal layer capable of reflecting red, green, and blue light, a light guide element using the optical element, and an AR display device.

Brief Description of the Drawings

[0017] [Figure 1] It is a cross-sectional view schematically showing the optical element according to Embodiment 1. [Figure 2] It is a perspective view schematically showing the optical element according to Embodiment 1. [Figure 3] It is a graph showing the reflection spectrum of a normal single-layer cholesteric liquid crystal layer. [Figure 4] It is a graph showing the change in the reflection spectrum of the cholesteric liquid crystal layer depending on the presence or absence of solvent coating. [Figure 5] It is a cross-sectional view schematically showing the light guide element according to Embodiment 2. [Figure 6] It is a diagram explaining the occurrence of luminance unevenness when the reflectance of the coupler element is uniform in the plane. [Figure 7] It is a perspective view schematically showing the optical element according to Embodiment 3. [Figure 8] It is a graph showing the reflectance of the cholesteric liquid crystal layer of Comparative Example 1. [Figure 9] This graph shows the reflectance of the cholesteric liquid crystal layer in Comparative Example 2. [Figure 10] This graph shows the reflectance of the cholesteric liquid crystal layers in Comparative Examples 1 and 3. [Figure 11] This flowchart illustrates the mechanism by which the reflection wavelength of the cholesteric liquid crystal layer shifts when a solvent is applied to a partially cured polymerizable liquid crystal compound. [Figure 12] This graph shows the reflectance of the cholesteric liquid crystal layer in Comparative Example 4. [Figure 13] This figure shows the curing treatment of the polymerizable liquid crystal compound in Example 1. [Figure 14] This graph compares the reflectance of the cholesteric liquid crystal layers in Example 1, Comparative Example 3, and Comparative Example 4. [Modes for carrying out the invention]

[0018] The present invention will be described in more detail below with reference to the drawings, with the following examples of embodiments, but the present invention is not limited to these embodiments. Furthermore, the configurations of each embodiment may be combined or modified as appropriate without departing from the spirit of the present invention. In the following explanation, the same reference numerals will be used across different drawings to represent identical parts or parts with similar functions, and repeated explanations will be omitted as appropriate.

[0019] In this specification, "Re(λ)" represents the in-plane phase difference at wavelength λ.

[0020] (Embodiment 1) Figure 1 is a schematic cross-sectional view showing an optical element according to Embodiment 1. Figure 2 is a schematic perspective view showing an optical element according to Embodiment 1. As shown in the figures, the optical element according to Embodiment 1 has a configuration in which an alignment film 20 and a cholesteric liquid crystal layer 30 are laminated on a support 10.

[0021] <Support> The support 10 is not particularly limited as long as it supports the alignment film 20 and the cholesteric liquid crystal layer 30, and for example, a glass substrate, a resin substrate, etc., can be used. When the optical element of this embodiment is applied to a light guide element, the support 10 is preferably a light guide plate.

[0022] <Orientation film> The alignment film 20 is patterned with an in-plane orientation restricting force. Specifically, the alignment film 20 has an orientation restricting force that aligns the slow axis of the polymerizable liquid crystal compound 31 in the cholesteric liquid crystal layer 30 to a pattern in which it rotates periodically in the plane. The period P1 of the above pattern is adjusted, for example, within the range of 200 to 600 nm.

[0023] As the material for the alignment film 20, materials commonly used in the field of liquid crystal panels can be used, such as polymers having polyimide as the main chain, polymers having polyamic acid as the main chain, and polymers having polysiloxane as the main chain. The alignment film 20 can be formed by coating the alignment film material onto the support 10. The coating method is not particularly limited, and for example, flexographic printing, inkjet coating, etc., can be used.

[0024] The type of alignment film 20 is not particularly limited. It may be a rubbing alignment film that has undergone a rubbing treatment as an alignment treatment, or a photo-alignment film that has photo-functional groups and has undergone a photo-alignment treatment as an alignment treatment. However, from the viewpoint of patterning the in-plane alignment restricting force into a complex pattern, a photo-alignment film is preferred.

[0025] <Cholesteric liquid crystal layer> The cholesteric liquid crystal layer 30 described above is obtained by polymerizing a polymerizable liquid crystal compound 31 containing a chiral agent (also called a chiral agent). The chiral agent causes the molecules of the polymerizable liquid crystal compound 31 to be continuously oriented in different directions along the thickness direction of the cholesteric liquid crystal layer 30, forming a helical molecular arrangement. The helical molecular arrangement is fixed by polymerization. In this specification, the period of one rotation in the helical molecular arrangement is also referred to as the "helical pitch" or "chiral period". Specifically, the helical pitch P2 is the length of the helical axis corresponding to a 180° rotation of the orientation of the molecules of the polymerizable liquid crystal compound 31. The helical pitch P2 is adjusted, for example, within the range of 220 to 900 nm.

[0026] The helical axis described above is preferably inclined with respect to the normal to the surface of the cholesteric liquid crystal layer 30. That is, when the direction parallel to the surface of the cholesteric liquid crystal layer 30 is defined as 0 degrees and the direction of the normal to the surface is defined as 90 degrees, the orientation of the helical axis (helical axis inclination angle) can be appropriately selected within the range of 0 to 90 degrees depending on the function of the optical element of this embodiment. For example, when the optical element of this embodiment is applied to a light guide element, it is preferably 40 degrees or more and less than 80 degrees.

[0027] Figure 3 is a graph showing the reflection spectrum of a typical single-layer cholesteric liquid crystal layer. As shown in the figure, a typical single-layer cholesteric liquid crystal layer has only one clear reflectance peak in the visible light wavelength range, and is often set to have a reflectance peak around 550 nm, which is the center of the visible light wavelength range. In contrast, in this embodiment, the cholesteric liquid crystal layer 30 has a first reflection region 37 in the plane that has a reflectance peak in the wavelength range of 400 to 550 nm, and a second reflection region 36 that has a reflectance peak in the wavelength range of 550 to 700 nm, which is different from that of the first reflection region 37. By mixing the light containing a large amount of wavelength components in the 400 to 550 nm range reflected by the first reflection region 37 and the light containing a large amount of wavelength components in the 550 to 700 nm range reflected by the second reflection region 36, the reflectance of the cholesteric liquid crystal layer 30 across the entire visible light wavelength range can be brought closer to a constant value. Here, "reflectance peak" refers to the maximum value where the reflectance is 40% or higher when the maximum reflectance within the wavelength range of 400 to 700 nm is normalized to 100%, preferably a maximum value where the reflectance is 50% or higher, more preferably a maximum value where the reflectance is 60% or higher, and even more preferably a maximum value where the reflectance is 70% or higher.

[0028] The reflectance peak in the first reflection region 37 is preferably in the wavelength range of 400 to 500 nm, and more preferably in the wavelength range of 420 to 480 nm. The first reflection region 37 mainly reflects blue light. The reflectance peak in the second reflection region 36 is preferably in the wavelength range of 600 to 700 nm, and more preferably in the wavelength range of 620 to 680 nm. The second reflection region 36 mainly reflects red light. Furthermore, the difference in wavelength between the reflectance peak in the first reflection region 37 and the reflectance peak in the second reflection region 36 is preferably 50 nm or more, and more preferably 100 nm or more.

[0029] In the cholesteric liquid crystal layer 30 described above, the peak wavelength of reflectance can be made different by having different helical pitches in the first reflection region 37 and the second reflection region 36 of the polymerizable liquid crystal compound 31. The helical pitch in the first reflection region 37 is shorter than the helical pitch in the second reflection region 36. The concentration of the chiral agent in the first reflection region 37 is higher than the concentration of the chiral agent in the second reflection region 36. Preferably, the helical pitch in the first reflection region 37 of the polymerizable liquid crystal compound 31 is 120 nm or more and 230 nm or less, and preferably the helical pitch in the second reflection region 36 is 170 nm or more and 290 nm or less.

[0030] In the cholesteric liquid crystal layer 30 described above, the thickness of the first reflection region 37 is thinner than the thickness of the second reflection region 36. The inventors investigated a method for forming regions with different concentrations of the chiral agent in the polymerizable liquid crystal compound 31 within a plane in order to form the first reflection region 37 and the second reflection region 36 within the plane. As a result, they found a method in which regions with different degrees of curing of the cholesteric liquid crystal layer 30 are created within the plane, and then a solvent is applied. Figure 4 is a graph showing the change in the reflection spectrum when a solvent is applied to a semi-cured cholesteric liquid crystal layer. As shown in the figure, it can be seen that when a solvent is applied to a semi-cured cholesteric liquid crystal layer 30, the reflectance peak shifts to the shorter wavelength side. This is thought to be because when the solvent is applied to a region of the cholesteric liquid crystal layer 30 with a low degree of curing, the polymerizable liquid crystal compound 31 diffuses towards the solvent side, while the chiral agent does not diffuse towards the solvent side but diffuses towards the substrate side. When this phenomenon occurs, in the low-hardness region, the concentration of the chiral agent increases, shortening the helical pitch and reducing the thickness of the cholesteric liquid crystal layer 30. On the other hand, in the high-hardness region, the concentration of the chiral agent does not change, so the helical pitch remains unchanged, and the thickness of the cholesteric liquid crystal layer 30 also remains unchanged. Therefore, when forming the cholesteric liquid crystal layer 30, the high-hardness region is designated as a second reflection region by setting the helical pitch longer so that the reflectance peak appears on the longer wavelength side than the reflection spectrum of a normal cholesteric liquid crystal layer 30 shown in Figure 3, while the low-hardness region is designated as a first reflection region 37 by applying a solvent to shift the reflectance peak to the shorter wavelength side. This makes it possible to reflect RGB light with a single cholesteric liquid crystal layer 30.

[0031] Furthermore, the fact that the thickness of the first reflection region 37 is thinner than the thickness of the second reflection region 36 is advantageous in terms of making the reflectance of RGB light uniform. The reflectance of the polymerizable liquid crystal compound 31 containing the chiral agent is determined by the number of rotations of the helical molecular arrangement in the normal direction of the cholesteric liquid crystal layer 30. The shorter the wavelength of the light that is selectively reflected, the shorter the corresponding helical pitch, and therefore a high reflectance can be obtained even with a thin layer thickness. Thus, when the solvent is applied, the simultaneous occurrence of a short-wavelength shift and a decrease in film thickness is advantageous because it tends to make the reflectance of RGB light uniform.

[0032] In obtaining a cholesteric liquid crystal layer 30 with a broadband range of reflective light wavelengths, the method of creating regions with different curing degrees within the cholesteric liquid crystal layer 30 and then applying a solvent is superior in terms of workability and cost because it only requires one layer of cholesteric liquid crystal layer 30, and orientation control is only required for one layer. On the other hand, when stacking multiple cholesteric liquid crystal layers with different reflection wavelengths to broaden the bandwidth, multiple types of polymerizable liquid crystal compounds are required, which tends to increase costs. Furthermore, orientation control of cholesteric liquid crystal layers from the second layer onwards is more difficult than that of the first layer. In addition, when applying another polymerizable liquid crystal compound on top of the cholesteric liquid crystal layer, repulsion of the coating liquid is likely to occur.

[0033] The type of solvent is not particularly limited, and any solvent capable of dissolving the polymerizable liquid crystal compound 31 and the chiral agent can be used, for example, propylene glycol monomethyl ether acetate (PGMEA). When forming a cholesteric liquid crystal layer 30 by coating the alignment film 20 with a composition containing the polymerizable liquid crystal compound 31 and the chiral agent, the solvent of the above composition may be used.

[0034] The difference between the thickness of the first reflective region 37 and the thickness of the second reflective region 36 of the cholesteric liquid crystal layer 30 is, for example, 0.1 μm or more and 0.5 μm or less, preferably 0.2 μm or more and 0.4 μm or less. In the cross-sectional view of Figure 1, the difference in thickness between the first reflective region 37 and the second reflective region 36 is not shown.

[0035] As shown in the figure, the first reflection region 37 is distributed across multiple sub-regions, and the second reflection region 36 is arranged surrounding each of the multiple sub-regions. Conversely, the second reflection region 36 may be distributed across multiple sub-regions, and the first reflection region 37 may be arranged surrounding each of the multiple sub-regions. In this embodiment, it is preferable that one of the first reflection region 37 and the second reflection region 36 is distributed across multiple sub-regions, and the other of the first reflection region 37 and the second reflection region 36 is arranged surrounding each of the multiple sub-regions. With such an arrangement, when white light is incident on the optical element, the light reflected by the first reflection region 37 and the light reflected by the second reflection region 36 are not perceived by the observer as separate colored lights, but rather as white light. As shown in the figure, if one of the first reflective region 37 and the second reflective region 36 in the cholesteric liquid crystal layer 30 is distributed across multiple subregions, the regions other than the multiple subregions may be the other of the first reflective region 37 and the second reflective region 36.

[0036] The arrangement density of the above-mentioned sub-regions is not particularly limited; for example, 10 units / mm 2 More than 100 pieces / mm 2 The following applies: The size of each of the above sub-regions is not particularly limited; for example, 0.005 mm 2 Above, 0.05mm 2 The following applies: The shape of each of the above-mentioned sub-regions is not particularly limited and may be a circle, a square, etc.

[0037] Preferred embodiments of the cholesteric liquid crystal layer 30 include: (1) an embodiment in which the reflectance at a wavelength of 450 nm in the first reflection region 37 is greater than the reflectance at a wavelength of 650 nm in the second reflection region 36, and the area of ​​the first reflection region 37 (the total area of ​​the first reflection region 37 included in the cholesteric liquid crystal layer 30 in a plan view) is smaller than the area of ​​the second reflection region 36 (the total area of ​​the second reflection region 36 included in the cholesteric liquid crystal layer 30 in a plan view); and (2) an embodiment in which the reflectance at a wavelength of 450 nm in the first reflection region 37 is less than the reflectance at a wavelength of 650 nm in the second reflection region 36, and the area of ​​the first reflection region 37 (the total area of ​​the first reflection region 37 included in the cholesteric liquid crystal layer 30 in a plan view) is larger than the area of ​​the second reflection region 36 (the total area of ​​the second reflection region 36 included in the cholesteric liquid crystal layer 30 in a plan view). In these embodiments, the area of ​​the region with higher reflectivity is reduced, making it easier to achieve uniform reflectivity in the visible light wavelength range.

[0038] The type of polymerizable liquid crystal compound 31 is not particularly limited, and conventionally known polymerizable liquid crystal compounds can be used. Those that polymerize and harden upon ultraviolet (UV) irradiation are preferably used. Polymerizable liquid crystal compound 31 is also called reactive methogen (RM).

[0039] Examples of polymerizable liquid crystal compounds 31 include polymers having a side chain structure that combines a mesogenic group such as a biphenyl group, terphenyl group, naphthalene group, phenylbenzoate group, azobenzene group, or derivatives thereof, and a photoreactive group such as a cinnamoyl group, chalcone group, cinnamyridene group, β-(2-phenyl)acryloyl group, cinnamic acid group, or derivatives thereof, and having a main chain structure such as an acrylate, methacrylate, maleimide, N-phenylmaleimide, or siloxane.

[0040] The polymerizable liquid crystal compound 31 described above may be a homopolymer consisting of a single repeating unit, or a copolymer consisting of two or more repeating units with different side chain structures. The copolymer may include alternating, random, or graft types.

[0041] The type of chiral agent used is not particularly limited, and conventionally known chiral agents can be used. For example, S-811 (manufactured by Merck) can be used as a chiral agent.

[0042] The optical element according to Embodiment 1 is classified as a polarization volume hologram (PVH) because it comprises an alignment film 20 with patterned in-plane orientation restricting force and a cholesteric liquid crystal layer 30 oriented by that film. PVHs used in applications such as light guide plates are called coupling elements or coupler elements. The optical element according to Embodiment 1 is used as a coupling element in applications such as AR glasses. Furthermore, the optical element according to Embodiment 1 can be used as a diffraction grating, and it is preferable that it is a diffraction element having an inclined Bragg surface.

[0043] (Embodiment 2) Figure 5 is a schematic cross-sectional view of a light guide element according to Embodiment 2. As shown in the figure, the light guide element according to Embodiment 2 comprises a light guide plate 50, a light-ingress optical element (first coupling element) 60 attached to the light-ingress side of the light guide plate 50, and a light-discharge optical element (second coupling element) 70 attached to the light-discharge side of the light guide plate. For example, if the length of the light guide plate 50 in the left-right direction of Figure 5 is 70 mm, the light-ingress optical element 60 is positioned 10 mm to 15 mm from the end of the light guide plate 50 (left end of Figure 5), and the light-discharge optical element 70 is positioned 40 mm to 60 mm from the end of the light guide plate 50 (left end of Figure 5). The arrows in Figure 5 indicate the path of light incident on the light guide plate.

[0044] The light guide plate 50 described above can be one that is conventionally known in the field of liquid crystal display devices. In the light guide element according to Embodiment 2, at least one of the light-receiving optical element 60 and the light-emitting optical element 70 is an optical element according to Embodiment 1, and it is preferable that the light-emitting optical element 70 is an optical element according to Embodiment 1.

[0045] The light guide element according to Embodiment 2 is suitably used in augmented reality (AR) displays. When the light guide element according to Embodiment 2 is incorporated into an AR display device, a display module is positioned as a light source 80 facing the light-receiving optical element 60 via the light guide plate 50. The display module is not particularly limited as long as it displays content compatible with AR technology, and for example, a thin display such as a liquid crystal display module or an organic EL display module can be used.

[0046] The AR display device equipped with the light guide element according to Embodiment 2 is preferably an AR glasses having the shape of eyeglasses. In the AR glasses, light from the display module enters the light guide plate 50 and is guided in the designed direction by the light-ingress optical element (in-coupler element) 60 attached to the light-ingress side of the light guide plate 50. Subsequently, the light travels through the inside of the light guide plate 50 from one end (the end where the light-ingress optical element 60 is located) to the other end (the end where the light-emitting optical element 70 is located), while repeatedly reflecting at the interface between the light guide plate 50 and the air layer. The light that reaches the light-emitting side of the light guide plate 50 is reflected by the light-emitting optical element (out-coupler element) 70 and enters the observer's (user's) eyeball, allowing the observer to see the image from the display module.

[0047] When applied to AR glasses, the outcoupler element 70 is preferably larger than the light-receiving area of ​​the human eye, and the horizontal size of the outcoupler element 70 is, for example, 20 mm. Furthermore, by having a reflectivity of less than 100% in the outcoupler element 70, the light incident on the outcoupler element 70 is divided into a component that is visible to the observer and a component that continues to guide the light. As a result, the light incident on the observer from the outcoupler element 70 can be dispersed to multiple positions in the plane. This makes it possible to see the image even when the observer's eyeballs move. The area where the image is visible even when the eyeballs move is called the "eye box". It is preferable that 95% or more of the light from the light source is emitted into the eye box, and this is adjusted, for example, by the horizontal size and reflectivity of the outcoupler element 70.

[0048] Furthermore, when applied to AR glasses, for example, the thickness of the light guide plate 50 is set to 1 mm, and the diffraction angles of the in-coupler element 60 and out-coupler element 70 (for example, the diffraction angle for light with a wavelength of 550 nm) are set to 45°. The diffraction angles of the in-coupler element 60 and out-coupler element 70 are determined by the period P1 (see Figure 1). In this case, light incident from the direction normal to the main surface of the light guide plate 50 is totally internalized by the in-coupler element 60 at an angle of 45° within the light guide plate 50, and is emitted in the normal direction by the out-coupler element 70. In addition, by adjusting the reflectivity of the out-coupler element 70 to 30%, more than 95% of the light from the light source is emitted into the eye box.

[0049] To improve the display quality of AR glasses, coupler elements need to function for RGB light. However, since the reflection spectrum of PVH has a certain width, similar to the selective reflection of ordinary cholesteric liquid crystals, it cannot reflect light across the entire RGB wavelength range. Therefore, the inventors investigated a method of stacking PVH with different chiral pitches, but found that orientation disorder of the polymerizable liquid crystal compound and repulsion of the coating liquid occurred in the second and subsequent layers, leading to problems such as difficulty in controlling the chiral pitch, increased process steps, and increased costs. In response, the inventors discovered that when a polymerizable liquid crystal compound comes into contact with a solvent in a semi-cured state, the reflection wavelength shifts to the shorter wavelength side, and furthermore, the film thickness decreases. Based on this discovery, the inventors realized a single-layer PVH that can achieve uniform reflectivity for light across the entire RGB wavelength range by creating a semi-cured region and a fully cured region within the surface and then applying a solvent.

[0050] (Embodiment 3) Figure 6 illustrates how brightness unevenness occurs when the reflectance of the coupler element is uniform in the plane. Figure 7 is a schematic perspective view of the optical element according to Embodiment 3. The optical element according to Embodiment 3 has the same configuration as the optical element according to Embodiment 1, except that it has a low-reflection region 38 in the plane of the cholesteric liquid crystal layer 30, where the visible light reflectance is smaller than that of the first reflection region 37 and the second reflection region 36. By providing the low-reflection region 38, it is possible to add functionality to the optical element. For example, in the case of an optical element used in combination with a light guide plate 50, the brightness distribution of the emitted light can be made uniform by increasing the area of ​​the low-reflection region 38 as the distance from the light-receiving part decreases. One of the first reflective region 37 and the second reflective region 36 (in the case of Figure 7, the first reflective region 37) is distributed across a plurality of first subregions, and the low reflective region 38 is distributed across a plurality of second subregions. The region in the cholesteric liquid crystal layer other than the plurality of first subregions and the plurality of second subregions may be the other of the first reflective region 37 and the second reflective region 36 (in the case of Figure 7, the second reflective region 36).

[0051] The low-reflectivity region 38 can be formed, for example, by creating a region (e.g., an uncured region) where the degree of curing of the polymerizable liquid crystal compound is lower than that of the first reflectivity region 37, and then applying a solvent. This is because in the region where the degree of curing of the polymerizable liquid crystal compound is lower than that of the first reflectivity region 37, the helical pitch becomes shorter than that of the first reflectivity region 37, and the reflectivity peak becomes less than 400 nm. The visible light reflectance mentioned above is the average reflectance in the wavelength range of 400 to 700 nm.

[0052] The optical element according to Embodiment 3 may be applied to the light-emitting optical element 70 in the light guide element according to Embodiment 2. This provides a configuration in which the light-emitting optical element 70 comprises a cholesteric liquid crystal layer 30 having a low-reflection region 38, and the area ratio of the low-reflection region 38 in the first region of the cholesteric liquid crystal layer 30 (a region closer to the light-receiving side of the light guide plate 50, for example, a region including the edge of the cholesteric liquid crystal layer 30 closest to the light-receiving side of the light guide plate 50) is larger than the area ratio of the low-reflection region 38 in the second region of the cholesteric liquid crystal layer 30 which is further from the light-receiving side of the light guide plate 50 than the first region (for example, a region including the edge of the cholesteric liquid crystal layer 30 furthest from the light-receiving side of the light guide plate 50). With such a configuration, the display quality of AR glasses can be improved. To improve the display quality of AR glasses, it is desirable that the image on the display module be visible even when the observer's eyes move. By shining light on multiple points on the coupler element, it is possible to widen the visible range (eye box) of the display module's image. However, as shown in Figure 6, if the reflectivity of the coupler element is uniform across the plane, the light intensity emitted from the light guide plate 50 increases closer to the light source, which may cause uneven brightness across the plane. In contrast, when the optical element (coupler element) according to Embodiment 3 is used in AR glasses, the brightness within the eye box can be made uniform in the visible light region of 400 to 700 nm.

[0053] <<Examples and Comparative Examples>> The effects of the present invention will be explained below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0054] <Comparative Example 1> In Comparative Example 1, the selective reflection wavelength was evaluated when a single layer of polymerizable liquid crystal compound containing a chiral agent was deposited. Samples were prepared using the following procedure. (1) A photoisomerized photoalignment film was coated onto a glass substrate. (2) Apply polarized ultraviolet (UV) light with a wavelength of 365 nm to the photoalignment film at a rate of 100 mJ / cm². 2 The photo-alignment film was irradiated and then baked in a 160°C oven for 20 minutes. (3) A polymerizable liquid crystal compound containing a chiral agent was coated onto the photo-alignment film using a spin coater rotating at 1000 rpm. The concentration of the chiral agent was adjusted so that the selective reflection wavelength was 650 nm. The wavelength dispersion of the polymerizable liquid crystal compound was positive, with Re(450 nm) / Re(550 nm) ≈ 1.14 and Re(650 nm) / Re(550 nm) ≈ 0.94. (4) Apply 365 nm unpolarized UV light at 3 J / cm² to the polymerizable liquid crystal compound after coating. 2 The polymerizable liquid crystal compound was cured by irradiation, and the sample was completed. The completed sample has a structure in which a photoalignment film and a cholesteric liquid crystal layer are laminated on a glass substrate, and the cholesteric liquid crystal layer contains a polymerizable liquid crystal compound and a chiral agent.

[0055] (evaluation) The thickness of the cholesteric liquid crystal layer was measured using the "NH-3MA" non-contact 3D measuring instrument manufactured by Mitaka Kohki Co., Ltd. The measurement results showed that the thickness of the cholesteric liquid crystal layer was 1.5 μm.

[0056] The transmittance Tmax and Tmin of the cholesteric liquid crystal layer were measured using "Axoscan" manufactured by Axometrics, and the reflectance R of the cholesteric liquid crystal layer was calculated using the following formula. R(%) = (1 - Tmin ÷ Tmax) × 100 Tmax is the transmittance when the polarization state of the incident light source is optimized to maximize transmittance. Tmin is the transmittance when the polarization state of the incident light source is optimized to minimize transmittance. The cholesteric liquid crystal layer exhibits maximum transmittance when the incident light is right-circularly polarized and minimum transmittance when the incident light is left-circularly polarized.

[0057] Figure 8 is a graph showing the reflectance of the cholesteric liquid crystal layer of Comparative Example 1. In Figure 8, the maximum reflectance is normalized to 100%, and the selective reflection wavelength was 650 nm. The maximum reflectance before normalization (reflectance at a wavelength of 650 nm) was 82%.

[0058] <Comparative Example 2> In Comparative Example 2, the selective reflection wavelength was evaluated when a single layer of polymerizable liquid crystal compound containing a chiral agent was fabricated, in the same manner as in Comparative Example 1, except that the concentration of the chiral agent was adjusted so that the selective reflection wavelength was 550 nm.

[0059] Figure 9 is a graph showing the reflectance of the cholesteric liquid crystal layer of Comparative Example 2. In Figure 9, the maximum reflectance value is normalized to 100%, and the selective reflection wavelength was 550 nm.

[0060] <Comparative Example 3> In Comparative Example 3, a single layer of polymerizable liquid crystal compound containing a chiral agent was fabricated, and the selective reflection wavelength was evaluated when a solvent was applied. Samples were prepared using the following procedure. (1) A photoisomerized photoalignment film was coated onto a glass substrate. (2) Apply polarized ultraviolet (UV) light with a wavelength of 365 nm to the photoalignment film at a rate of 100 mJ / cm². 2 The photo-alignment film was irradiated and then baked in a 160°C oven for 20 minutes. (3) A polymerizable liquid crystal compound containing a chiral agent was coated onto the photo-alignment film using a spin coater rotating at 1000 rpm. The concentration of the chiral agent was the same as in Comparative Example 1. The wavelength dispersion of the polymerizable liquid crystal compound was positive, with Re(450nm) / Re(550nm) ≈ 1.14 and Re(650nm) / Re(550nm) ≈ 0.94. (4) Apply 1 J / cm of unpolarized UV light with a wavelength of 365 nm to the polymerizable liquid crystal compound after coating. 2 The polymerizable liquid crystal compound was cured by irradiation. The irradiation energy of unpolarized UV in Comparative Example 3 was lower than that in Comparative Example 1, and at this point the polymerizable liquid crystal compound was not completely cured; this state is referred to as the "semi-cured state." (5) Propylene glycol monomethyl ether acetate (PGMEA) was applied as a solvent to the partially cured polymerizable liquid crystal compound. The contact time between the polymerizable liquid crystal compound and the solvent was 5 seconds, and after 5 seconds, the solvent was removed by nitrogen blowing. The sample was completed by the above process. The completed sample has a structure in which a photoalignment film and a cholesteric liquid crystal layer are laminated on a glass substrate, and the cholesteric liquid crystal layer contains a polymerizable liquid crystal compound and a chiral agent.

[0061] The thickness of the cholesteric liquid crystal layer was measured using the non-contact 3D measuring instrument "NH-3MA" manufactured by Mitaka Kohki Co., Ltd. The result showed that the thickness of the cholesteric liquid crystal layer was 1.2 μm, which was thinner than that of Comparative Example 1.

[0062] The transmittance Tmax and Tmin of the cholesteric liquid crystal layer were measured using "Axoscan" manufactured by Axometrics, and the reflectance R of the cholesteric liquid crystal layer was calculated. Figure 10 is a graph showing the reflectance of the cholesteric liquid crystal layers of Comparative Examples 1 and 3. In Figure 10, the maximum reflectance values ​​of Comparative Examples 1 and 3 were normalized to 100%, and in Comparative Example 3, the selective reflection wavelength of the cholesteric liquid crystal layer was around 450 nm. The maximum reflectance value of Comparative Example 1 before normalization (reflectance at a wavelength of 650 nm) was 82%, and the maximum reflectance value of Comparative Example 3 before normalization (reflectance at a wavelength of 450 nm) was 78%.

[0063] As shown in Figure 10, when a solvent is applied to a partially cured polymerizable liquid crystal compound, the thickness of the cholesteric liquid crystal layer decreases, and the reflected wavelength shifts to the shorter wavelength side. This is due to the diffusion phenomenon of the polymer. FIG. 11 is a flow chart explaining the mechanism by which the reflection wavelength of a cholesteric liquid crystal layer shifts when a solvent is applied to a semi-cured polymeric liquid crystal compound. When the polymeric liquid crystal compound 31 is irradiated with UV and a solvent 48 such as propylene glycol monomethyl ether acetate (PGMEA) is applied to the obtained film 34 (semi-cured film) of the polymeric liquid crystal compound, the polymeric liquid crystal compound 31 diffuses toward the solvent 48 side by the amount that has not been cured. On the other hand, the chiral agent 32 does not diffuse toward the solvent 48 side but diffuses toward the substrate side (the alignment film 20 side). That is, when the solvent 48 is washed away, the remaining cholesteric liquid crystal layer 30 becomes a layer with a higher concentration of the chiral agent 32, and it has been confirmed that the selective reflection wavelength shifts to the short wavelength side, that the flowing solvent 48 contains a large amount of the polymeric liquid crystal compound 31 and a small amount of the chiral agent 32. Also, the thickness of the cholesteric liquid crystal layer 30 decreases by the amount of the polymeric liquid crystal compound 31 washed away by the solvent 48. Such a mechanism is considered to occur because the solubility in the solvent 48 is different between the polymeric liquid crystal compound 31 and the chiral agent 32.

[0064] <Comparative Example 4> In Comparative Example 4, the selective reflection wavelength when a solvent was further applied after forming a single layer of a polymeric liquid crystal compound containing a chiral agent was evaluated. Samples were prepared according to the following procedure. (1) A photo-isomerization type photo-alignment film was applied onto a glass substrate. (2) The photo-alignment film was irradiated with polarized ultraviolet light (UV) having a wavelength of 365 nm at 100 mJ / cm 2 and then baked in an oven at 160° C. for 20 minutes. (3) A polymeric liquid crystal compound containing a chiral agent was applied onto the photo-alignment film using a spin coater rotating at 1000 rpm. The concentration of the chiral agent was made the same as in Comparative Example 1. The wavelength dispersion of the polymeric liquid crystal compound was positive, and Re(450 nm) / Re(550 nm)≈1.14, Re(650 nm) / Re(550 nm)≈0.94. (4) The polymeric liquid crystal compound after coating was irradiated with non-polarized UV having a wavelength of 365 nm at 3 J / cm 2The polymerizable liquid crystal compound was cured by irradiation. The irradiation energy of unpolarized UV in Comparative Example 4 was greater than that in Comparative Example 3 and the same as that in Comparative Example 1. At this point, the polymerizable liquid crystal compound was completely cured. (5) Propylene glycol monomethyl ether acetate (PGMEA) was applied as a solvent to the cured polymerizable liquid crystal compound. The contact time between the polymerizable liquid crystal compound and the solvent was 5 seconds, and after 5 seconds, the solvent was removed by nitrogen blowing. The sample was completed by the above process. The completed sample has a structure in which a photoalignment film and a cholesteric liquid crystal layer are laminated on a glass substrate, and the cholesteric liquid crystal layer contains a polymerizable liquid crystal compound and a chiral agent.

[0065] The thickness of the cholesteric liquid crystal layer was measured using the non-contact 3D measuring instrument "NH-3MA" manufactured by Mitaka Kohki Co., Ltd. The result showed that the thickness of the cholesteric liquid crystal layer was 1.5 μm, which was the same as in Comparative Example 1.

[0066] The transmittance Tmax and Tmin of the cholesteric liquid crystal layer were measured using "Axoscan" manufactured by Axometrics, and the reflectance R of the cholesteric liquid crystal layer was calculated. Figure 12 is a graph showing the reflectance of the cholesteric liquid crystal layer of Comparative Example 4. In Figure 12, the maximum reflectance value of Comparative Example 4 is normalized to 100%, and the selective reflection wavelength of the cholesteric liquid crystal layer in Comparative Example 4 was 650 nm, the same as in Comparative Example 1.

[0067] <Example 1> In Example 1, a polymerizable liquid crystal compound was formed on a single substrate, creating both a semi-cured region and a fully cured region. The selective reflection wavelength was then evaluated after applying a solvent. The sample in Example 1 was prepared using the following procedure. (1) A photoisomerized photoalignment film was coated onto a glass substrate. (2) Apply polarized ultraviolet (UV) light with a wavelength of 365 nm to the photoalignment film at a rate of 100 mJ / cm². 2 The photo-alignment film was irradiated and then baked in a 160°C oven for 20 minutes. (3) A polymerizable liquid crystal compound containing a chiral agent was coated onto the photo-alignment film using a spin coater rotating at 1000 rpm. The concentration of the chiral agent was the same as in Comparative Example 1. The wavelength dispersion of the polymerizable liquid crystal compound was positive, with Re(450nm) / Re(550nm) ≈ 1.14 and Re(650nm) / Re(550nm) ≈ 0.94. (4) Apply 365 nm wavelength unpolarized UV light at 3 J / cm² to the polymerizable liquid crystal compound after coating, through a halftone mask. 2 The polymerizable liquid crystal compound was cured by irradiation. Figure 13 shows the curing treatment of the polymerizable liquid crystal compound in Example 1. As shown in the figure, the halftone mask 45 used in Example 1 is a photomask having a region 46 with a transmittance of 30% and a region with a transmittance of 100%. The region 46 with a transmittance of 30% is distributed across multiple subregions, and the region with a transmittance of 100% surrounds each of the above subregions. The area ratio of the region 46 with a transmittance of 30% to the region with a transmittance of 100% was 1:1. As a result of UV irradiation of the polymerizable liquid crystal compound film 34 (uncured film) through the halftone mask 45, the region irradiated with UV through the region 46 with a transmittance of 30% of the halftone mask 45 became a region consisting of a semi-cured polymerizable liquid crystal compound, and the region irradiated with UV through the region with a transmittance of 100% became a region consisting of a fully cured polymerizable liquid crystal compound. (5) Propylene glycol monomethyl ether acetate (PGMEA) was applied as a solvent to the polymerizable liquid crystal compound after UV irradiation. The contact time between the polymerizable liquid crystal compound and the solvent was 5 seconds, and after 5 seconds, the solvent was removed by nitrogen blowing. The sample was completed by the above process. The completed sample has a structure in which a photoalignment film and a cholesteric liquid crystal layer are laminated on a glass substrate, and the cholesteric liquid crystal layer contains a polymerizable liquid crystal compound and a chiral agent.

[0068] Using the non-contact 3D measuring instrument "NH-3MA" manufactured by Mitaka Kohki Co., Ltd., the thickness of the cholesteric liquid crystal layer was measured. The thickness of the cholesteric liquid crystal layer in the area that was semi-cured after UV irradiation was 1.2 μm, and the thickness of the cholesteric liquid crystal layer in the area that was fully cured after UV irradiation was 1.5 μm.

[0069] The transmittance Tmax and Tmin of the cholesteric liquid crystal layer were measured using "Axoscan" manufactured by Axometrics, and the reflectance R of the cholesteric liquid crystal layer was calculated. Figure 14 is a graph comparing the reflectances of the cholesteric liquid crystal layers of Example 1, Comparative Example 3, and Comparative Example 4. In Figure 14, the maximum reflectance values ​​of Example 1, Comparative Example 3, and Comparative Example 4 are normalized to 100%. The reflection spectrum of the cholesteric liquid crystal layer of Example 1 has a first reflection region with a reflectance peak (selective reflection wavelength) in the wavelength range of 400 to 550 nm, and a second reflection region with a reflectance peak (selective reflection wavelength) different from that of the first reflection region in the wavelength range of 550 to 700 nm. Compared with the reflection spectra of the cholesteric liquid crystal layers of Comparative Examples 3 and 4, it was found to exhibit a uniform reflectance in RGB. Here, the region where the cholesteric liquid crystal layer is thin and in a semi-cured state after UV irradiation corresponds to the first reflection region, and the region where the cholesteric liquid crystal layer is thick and in a fully cured state after UV irradiation corresponds to the second reflection region. Therefore, the first reflection region is distributed across multiple subregions, and the second reflection region is arranged surrounding each of the above subregions.

[0070] The results from Example 1 showed that a broadband diffraction element can be fabricated using a single-layer cholesteric liquid crystal layer. In Example 1, the first and second reflection regions were fabricated with a 1:1 area ratio, but this can be changed depending on the material. It is preferable to adjust the area ratio to make the RGB reflectances closer to uniform. [Explanation of Symbols]

[0071] 10:Support 20: Alignment film 30: Cholesteric liquid crystal layer 31: Polymerizable liquid crystal compound 32: Chiral agents 34: Film of polymerizable liquid crystal compound 36:Second reflective area 37: 1st reflection area 38: Low reflection area 45: Halftone Mask 46: Area with a transmittance of 30% 48: Solvent 50: Light guide plate 60: Light-receiving optical element (in-coupler element) 70: Idemitsu-side optical element (outcoupler element) 80:Light source

Claims

1. The cholesteric liquid crystal layer comprises a polymerizable liquid crystal compound and a chiral agent, The cholesteric liquid crystal layer has, in its plane, a first reflective region having a reflectance peak in the wavelength range of 400 to 550 nm, and a second reflective region having a reflectance peak different from that of the first reflective region in the wavelength range of 550 to 700 nm. The cholesteric liquid crystal layer has a thickness in the first reflective region that is thinner than the thickness in the second reflective region. Optical element.

2. The first reflective region and the second reflective region are distributed across a plurality of subregions, and the other of the first reflective region and the second reflective region is arranged to surround each of the plurality of subregions. The optical element according to claim 1.

3. The region in the cholesteric liquid crystal layer other than the plurality of partial regions is the other of the first reflective region and the second reflective region. The optical element according to claim 2.

4. The cholesteric liquid crystal layer has a reflectance at a wavelength of 450 nm in the first reflection region that is greater than the reflectance at a wavelength of 650 nm in the second reflection region, and the area of ​​the first reflection region is smaller than the area of ​​the second reflection region. The optical element according to claim 1.

5. The cholesteric liquid crystal layer has a reflectance at a wavelength of 450 nm in the first reflection region that is lower than the reflectance at a wavelength of 650 nm in the second reflection region, and the area of ​​the first reflection region is larger than the area of ​​the second reflection region. The optical element according to claim 1.

6. The cholesteric liquid crystal layer has a low-reflectivity region within its plane, which has a lower visible light reflectivity than the first and second reflective regions. The optical element according to claim 1.

7. One of the first reflection region and the second reflection region is distributed and arranged in a plurality of first subregions. The low-reflection regions are distributed and arranged in a plurality of second subregions. The region in the cholesteric liquid crystal layer other than the plurality of first partial regions and the plurality of second partial regions is the other of the first reflective region and the second reflective region. The optical element according to claim 6.

8. Light guide plate and The light-receiving optical element attached to the light-receiving side of the light guide plate, The light guide plate comprises a light-emitting optical element attached to the light-emitting side, At least one of the light-receiving optical element and the light-emitting optical element is an optical element according to any one of claims 1 to 7. Light guide element.

9. The light-emitting optical element comprises a cholesteric liquid crystal layer having a low-reflectance region in its plane that has a visible light reflectance lower than that of the first reflective region and the second reflective region. In the cholesteric liquid crystal layer, the area ratio of the low-reflection region in the first region is greater than the area ratio of the low-reflection region in the second region, which is further from the light-receiving side of the light guide plate than the first region. The light guide element according to claim 8.

10. The light guide element according to claim 8, The system comprises a display module positioned opposite the light-receiving optical element via the light guide plate. AR display device.

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