Optical element, light guide element, and ar display device

Abstract

An optical element having a single cholesteric liquid crystal layer capable of reflecting red, green, and blue light is provided, along with a light guide element using the optical element and an AR display device. The optical element comprises a cholesteric liquid crystal layer containing a polymer of a polymerizable liquid crystal compound and a chiral agent. The cholesteric liquid crystal layer has, in-plane,: a first reflective region having a peak reflectivity in the wavelength range of 400–550 nm; and a second reflective region having a peak reflectivity different from that of the first reflective region in the wavelength range of 550–700 nm. The thickness of the first reflective region is thinner than the thickness of the second reflective region.

Description

Technical Field

[0001] The following disclosure relates to an optical element, a light guide element, and an AR display device. Background Technology

[0002] In recent years, research and development of augmented reality (AR) display devices that overlay images onto the real world have been progressing. For example, AR glasses have been proposed that project display light from a display onto one end of a light guide plate, where it propagates and exits from the other end, thereby overlaying the display image onto the scene actually seen by the user. These AR glasses sometimes incorporate diffraction elements utilizing a liquid crystal layer with added chiral agents. Specifically, cholesteric liquid crystal layers with liquid crystal alignment patterns that continuously rotate in at least one in-plane direction from the optical axis of the liquid crystal compound are known (see, for example, Patent Documents 1-3).

[0003] Existing technical documents Patent documents 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 Summary of the Invention The technical problem to be solved by the present invention Cholesteric liquid crystal layers have the property of selectively reflecting visible light. To improve the display quality of AR glasses, a diffraction element of a cholesteric liquid crystal layer is required that reflects all of the red (R), green (G), and blue (B) light contained in visible light. If cholesteric liquid crystal layers that selectively reflect light of different wavelengths are stacked, RGB light can be reflected. However, a method is needed that can reflect RGB light even when using a single layer of cholesteric liquid crystal layer.

[0004] The present invention was made in view of the above-mentioned situation, and its object is to provide an optical element, a light guide element using the optical element, and an AR display device, wherein the optical element has a single cholesteric liquid crystal layer capable of reflecting red, green and blue light.

[0005] Solution to the problem (1) One embodiment of the present invention is an optical element comprising a cholesteric liquid crystal layer containing a polymeric liquid crystal compound and a chiral agent, wherein the cholesteric liquid crystal layer has in-plane: a first reflective region having a peak reflectance in a wavelength range of 400-550 nm; and a second reflective region having a peak reflectance different from that of the first reflective region in a wavelength range of 550-700 nm, wherein the thickness of the first reflective region is thinner than the thickness of the second reflective region.

[0006] (2) In addition, in one embodiment of the present invention, based on the configuration described in (1) above, one of the first reflective region and the second reflective region is dispersedly arranged in a plurality of partial regions, and the other of the first reflective region and the second reflective region is arranged in such a way that it surrounds each of the partial regions in the plurality of partial regions.

[0007] (3) In addition, in one embodiment of the present invention, based on the above (2) configuration, 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.

[0008] (4) In addition, in a certain embodiment of the present invention, based on the above-described (1), (2) or (3), in the cholesteric liquid crystal layer, the reflectivity of the first reflective region at a wavelength of 450 nm is greater than the reflectivity of the second reflective region at a wavelength of 650 nm, and the area of ​​the first reflective region is smaller than the area of ​​the second reflective region.

[0009] (5) In addition, in a certain embodiment of the present invention, based on the above-described (1), (2) or (3), in the cholesteric liquid crystal layer, the reflectivity of the first reflective region at a wavelength of 450 nm is less than the reflectivity of the second reflective region at a wavelength of 650 nm, and the area of ​​the first reflective region is greater than the area of ​​the second reflective region.

[0010] (6) In addition, in a certain embodiment of the present invention, based on the above-described (1), (2), (3), (4) or (5), the cholesteric liquid crystal layer has a low-reflection region in the plane, and the visible light reflectance of the low-reflection region is less than that of the first reflective region and the second reflective region.

[0011] (7) In addition, in one embodiment of the present invention, based on the configuration described in (6) above, one of the first reflective region and the second reflective region is dispersedly disposed in a plurality of first partial regions, the low reflective region is dispersedly disposed in a plurality of second partial regions, and 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.

[0012] (8) In addition, one embodiment of the present invention is a light guide element, which includes: a light guide plate; an incident light-side optical element mounted on the incident light side of the light guide plate; and an exit light-side optical element mounted on the exit light side of the light guide plate, wherein at least one of the incident light-side optical element and the exit light-side optical element is an optical element of (1), (2), (3), (4), (5) or (6) above.

[0013] (9) In addition, in one embodiment of the present invention, based on the configuration described in (8) above, the light-emitting optical element includes a cholesteric liquid crystal layer, the cholesteric liquid crystal layer having a low-reflection region in-plane, the visible light reflectance of the low-reflection region being less than the visible light reflectance of the first reflection region and the second reflection region, the area ratio of the low-reflection region in the first region being greater than the area ratio of the low-reflection region in the second region, wherein the second region is farther from the light-incident side of the light guide plate than the first region.

[0014] (10) In addition, one embodiment of the present invention is an AR display device, which includes: the light guide element of (8) or (9) above; and a display module, which is arranged opposite to the light-incident optical element.

[0015] Invention Effects According to the present invention, it is possible to provide an optical element having 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. Attached Figure Description

[0016] Figure 1 This is a schematic cross-sectional view of the optical element involved in Embodiment 1.

[0017] Figure 2 This is a schematic perspective view of the optical element involved in Embodiment 1.

[0018] Figure 3 This is a graph showing the reflectance spectrum of a typical cholesteric liquid crystal layer consisting of one layer.

[0019] Figure 4This is a graph showing the changes in the reflectance spectrum of the cholesteric liquid crystal layer with and without a coating solvent.

[0020] Figure 5 This is a schematic cross-sectional view of the light guide element according to Embodiment 2.

[0021] Figure 6 This diagram illustrates the uneven brightness that occurs when the reflectivity of the coupler element is uniform in-plane.

[0022] Figure 7 This is a schematic perspective view of the optical element involved in Embodiment 3.

[0023] Figure 8 This is a graph showing the reflectance of the cholesteric liquid crystal layer of Comparative Example 1.

[0024] Figure 9 This is a graph showing the reflectance of the cholesteric liquid crystal layer of Comparative Example 2.

[0025] Figure 10 A graph showing the reflectance of the cholesteric liquid crystal layers of Comparative Examples 1 and 3.

[0026] Figure 11 This is a flowchart illustrating the mechanism by which the reflection wavelength of a cholesteric liquid crystal layer shifts when a solvent is coated onto a semi-cured polymeric liquid crystal compound.

[0027] Figure 12 This is a graph showing the reflectance of the cholesteric phase liquid crystal layer of Comparative Example 4.

[0028] Figure 13 This is a diagram showing the curing process of the polymeric liquid crystal compound in Example 1.

[0029] Figure 14 This is a graph comparing the reflectance of the cholesteric liquid crystal layers of Example 1, Comparative Example 3, and Comparative Example 4. Detailed Implementation

[0030] Although the following embodiments are disclosed and the invention is described in more detail with reference to the accompanying drawings, the invention is not limited to these embodiments. Furthermore, the configurations of each embodiment can be appropriately combined and modified without departing from the spirit of the invention.

[0031] Furthermore, in the following description, the same reference numerals are used interchangeably between different figures for the same parts or parts that have the same function, and repeated descriptions are omitted where appropriate.

[0032] In this specification, “Re(λ)” represents the in-plane phase difference in wavelength λ.

[0033] (Implementation Method 1) Figure 1 This is a schematic cross-sectional view of the optical element involved in Embodiment 1. Figure 2 This is a schematic perspective view of the optical element according to Embodiment 1. As shown, the optical element according to Embodiment 1 has a structure in which an alignment film 20 and a cholesteric liquid crystal layer 30 are stacked on a support 10.

[0034] <Support Body> The support 10 only needs to support the alignment film 20 and the cholesteric liquid crystal layer 30, and is not particularly limited. For example, a glass substrate or a resin substrate can be used. When the optical element of this embodiment is used as a light guide element, the support 10 is preferably a light guide plate.

[0035] <Orientation film> The alignment film 20 is patterned by an in-plane alignment constraint force. Specifically, the alignment film 20 has an alignment constraint force that aligns the optical axis (or molecular orientation) of the polymeric liquid crystal compound 31 in the cholesteric liquid crystal layer 30 into a pattern that rotates periodically in the plane. The period P1 of the pattern is adjusted, for example, in the range of 200 to 600 nm.

[0036] As the material for the alignment film 20, materials commonly used in the field of liquid crystal panels, such as polymers having polyimide in the main chain, polymers having polyamic acid in the main chain, and polymers having polysiloxane in the main chain, can be used. 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.

[0037] The type of alignment film 20 is not particularly limited. It can be a friction alignment film that has been subjected to friction treatment as an alignment treatment, or a photoalignment film that has optical functional groups and has been subjected to optical alignment treatment as an alignment treatment. However, from the viewpoint of patterning the in-plane alignment constraint force into a complex pattern, a photoalignment film is preferred.

[0038] <Cholesteric phase liquid crystal layer> The aforementioned cholesteric liquid crystal layer 30 is obtained by polymerizing a polymerizable liquid crystal compound 31 containing a chiral agent (also called a chiral compound). Through the chiral agent, the molecules of the polymerizable liquid crystal compound 31 are continuously oriented in different directions along the thickness direction of the cholesteric liquid crystal layer 30, forming a helical molecular arrangement. Through polymerization, the helical molecular arrangement is immobilized. 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, in the range of 220 to 900 nm.

[0039] The aforementioned spiral axis is preferably inclined relative 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 set to 0 degrees and the direction of the normal to the surface is set to 90 degrees, the orientation (spiral axis tilt angle) of the spiral axis can be appropriately selected within the range of 0 to 90 degrees according to the function of the optical element of this embodiment. For example, when the optical element of this embodiment is used as a light guide element, it is preferably 40 degrees or more and less than 80 degrees.

[0040] Figure 3 This is a graph showing the reflectance spectrum of a typical single-layer cholesteric liquid crystal layer. As shown, a typical single-layer cholesteric liquid crystal layer is typically configured to have only one distinct peak of reflectance in the visible light wavelength region, with a peak of reflectance near wavelength 550 nm, which is the center of the visible light wavelength region. In contrast, in this embodiment, the cholesteric liquid crystal layer 30 has a first reflective region 37 with a peak of reflectance in the wavelength range of 400-550 nm and a second reflective region 36 with a peak of reflectance different from that of the first reflective region 37 in the wavelength range of 550-700 nm. By mixing the large amount of light containing wavelength components of 400-550 nm reflected by the first reflective region 37 and the large amount of light containing wavelength components of 550-700 nm reflected by the second reflective region 36, the reflectance of the cholesteric liquid crystal layer 30 can be made close to a constant value throughout the entire visible light wavelength region.

[0041] Here, "peak reflectance" refers to a maximum reflectance of 40% or more when the maximum reflectance in the wavelength range of 400 to 700 nm is set to 100% for normalization. Preferably, it is a maximum reflectance of 50% or more, more preferably a maximum reflectance of 60% or more, and even more preferably a maximum reflectance of 70% or more.

[0042] The peak reflectance of the first reflective region 37 is preferably in the wavelength range of 400-500 nm, more preferably in the wavelength range of 420-480 nm. The first reflective region 37 mainly reflects blue light. The peak reflectance of the second reflective region 36 is preferably in the wavelength range of 600-700 nm, more preferably in the wavelength range of 620-680 nm. The second reflective region 36 mainly reflects red light. Furthermore, the wavelength difference between the peak reflectance in the first reflective region 37 and the peak reflectance in the second reflective region 36 is preferably 50 nm or more, more preferably 100 nm or more.

[0043] In the cholesteric liquid crystal layer 30 described above, the helical pitch of the polymerizable liquid crystal compound 31 in the first reflective region 37 is different from that in the second reflective region 36, thereby enabling different peak wavelengths of reflectivity. The helical pitch in the first reflective region 37 is shorter than that in the second reflective region 36. The concentration of the chiral agent in the first reflective region 37 is higher than that in the second reflective region 36. The helical pitch of the polymerizable liquid crystal compound 31 in the first reflective region 37 is preferably 120 nm or more and 230 nm or less, and the helical pitch of the polymerizable liquid crystal compound 31 in the second reflective region 36 is preferably 170 nm or more and 290 nm or less.

[0044] The thickness of the first reflective region 37 of the cholesteric liquid crystal layer 30 is thinner than the thickness of the second reflective region 36. In order to form the first reflective region 37 and the second reflective region 36 in-plane, the inventors investigated a method for forming regions in-plane with different concentrations of the chiral agent of the polymerizable liquid crystal compound 31. As a result, they discovered a method for coating a solvent after forming regions in-plane with different degrees of curing of the cholesteric liquid crystal layer 30. Figure 4 This is a graph showing the change in reflectance spectrum when a solvent is applied to a cholesteric liquid crystal layer in a semi-cured state. As shown in the figure, when a solvent is applied to the cholesteric liquid crystal layer 30 in a semi-cured state, the peak reflectance shifts towards the shorter wavelength side. This is because when the solvent is applied to a region of the cholesteric liquid crystal layer 30 with low curing degree, a phenomenon occurs where the polymerizable liquid crystal compound 31 diffuses towards the solvent side, while the chiral agent diffuses towards the substrate side instead of the solvent side. If this phenomenon occurs, in the region with low curing degree, the concentration of the chiral agent becomes higher, the helical pitch becomes shorter, and the thickness of the cholesteric liquid crystal layer 30 becomes smaller. On the other hand, in the region with high curing degree, the concentration of the chiral agent does not change, therefore the helical pitch does not change, and the thickness of the cholesteric liquid crystal layer 30 does not change. Therefore, when forming the cholesteric liquid crystal layer 30, the helical pitch in the region with high curing degree is set to be longer, so that the peak reflectance appears at a shorter wavelength than the peak reflectance. Figure 3 The typical cholesteric liquid crystal layer 30 shown has a reflection spectrum closer to the longer wavelength side, serving as a second reflection region. Simultaneously, a solvent is applied to areas with low curing degree, shifting the peak reflectance towards the shorter wavelength side, thus creating a first reflection region 37. Therefore, a single cholesteric liquid crystal layer 30 can reflect RGB light.

[0045] Furthermore, the thinner thickness of the first reflective region 37 compared to the second reflective region 36 is advantageous in terms of achieving uniform reflectivity of RGB light. The reflectivity of the cholesteric liquid crystal layer 30 is determined by the number of cycles of the helical molecular arrangement of the polymeric liquid crystal compound 31 with added chiral agent in the normal direction of the cholesteric liquid crystal layer 30. Since a shorter wavelength of selectively reflected light corresponds to a shorter helical pitch, high reflectivity can be obtained even with a thin layer thickness. Therefore, during solvent coating, short-wavelength shift and film thickness reduction occur simultaneously, resulting in a tendency for uniform reflectivity of RGB light, which is an advantage.

[0046] Based on obtaining a cholesteric liquid crystal layer 30 with a wide bandgap in the wavelength range of reflectable light, and after fabricating regions of the cholesteric liquid crystal layer 30 with different degrees of curing within the plane, the solvent coating method only requires setting one cholesteric liquid crystal layer 30, and the orientation control is also limited to one layer, thus offering advantages in terms of operability and cost. On the other hand, when multiple cholesteric liquid crystal layers with different reflective wavelengths are stacked to achieve a wide bandgap, various polymerizable liquid crystal compounds are required, which can easily increase costs. Furthermore, compared to the first layer, it is difficult to control the orientation of the second and subsequent cholesteric liquid crystal layers. Consequently, when coating other polymerizable liquid crystal compounds onto the cholesteric liquid crystal layer, coating liquid repulsion can easily occur.

[0047] 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, such as propylene glycol monomethyl ether acetate (PGMEA). When a cholesteric liquid crystal layer 30 is formed by coating a composition containing the polymerizable liquid crystal compound 31 and the chiral agent onto the alignment film 20, the solvent of the above composition can be used.

[0048] 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. Figure 1 The cross-sectional view omits the illustration of the thickness difference between the first reflective region 37 and the second reflective region 36.

[0049] As shown in the figure, the first reflective region 37 is dispersedly arranged in multiple partial regions, and the second reflective region 36 is arranged to surround each of the multiple partial regions. Conversely, the second reflective region 36 may also be dispersedly arranged in multiple partial regions, and the first reflective region 37 may surround each of the multiple partial regions. In this embodiment, it is preferable that one of the first reflective region 37 and the second reflective region 36 is dispersedly arranged in multiple partial regions, and the other of the first reflective region 37 and the second reflective region 36 surrounds each of the multiple partial regions. With this arrangement, when white light is incident on the optical element, the light reflected by the first reflective region 37 and the light reflected by the second reflective region 36 will not be perceived as different colors by the observer, but can be perceived as white light. As shown in the figure, when one of the first reflective region 37 and the second reflective region 36 in the cholesteric liquid crystal layer 30 is dispersedly arranged in multiple partial regions, the area outside the multiple partial regions may also be the other of the first reflective region 37 and the second reflective region 36.

[0050] The configuration density of the aforementioned multiple areas is not specifically limited, for example, it can be 10 units / mm. 2 More than 100 pieces / mm 2 the following.

[0051] The size of each of the aforementioned regions is not specifically limited; for example, it could be 0.005 mm. 2 Above and 0.05mm 2 the following.

[0052] The shapes of the aforementioned regions are not particularly limited; for example, circles and squares can be included.

[0053] As a preferred embodiment of the above-mentioned cholesteric liquid crystal layer 30, the following embodiments are provided: (1) the reflectivity of the first reflective region 37 at a wavelength of 450 nm is greater than the reflectivity of the second reflective region 36 at a wavelength of 650 nm, and the area of ​​the first reflective region 37 (the total area of ​​the first reflective region 37 included in the cholesteric liquid crystal layer 30 when viewed from above) is smaller than the area of ​​the second reflective region 36 (the total area of ​​the second reflective region 36 included in the cholesteric liquid crystal layer 30 when viewed from above); (2) the reflectivity of the first reflective region 37 at a wavelength of 450 nm is smaller than the reflectivity of the second reflective region 36 at a wavelength of 650 nm, and the area of ​​the first reflective region 37 (the total area of ​​the first reflective region 37 included in the cholesteric liquid crystal layer 30 when viewed from above) is larger than the area of ​​the second reflective region 36 (the total area of ​​the second reflective region 36 included in the cholesteric liquid crystal layer 30 when viewed from above). In these methods, because the area of ​​regions with high reflectivity is reduced, it is easier to make the reflectivity uniform in the wavelength region of visible light.

[0054] The type of polymerizable liquid crystal compound 31 is not particularly limited, and conventionally known polymerizable liquid crystal compounds can be used, preferably substances that are polymerized and cured by ultraviolet (UV) irradiation. The polymerizable liquid crystal compound 31 is also known as reactive mesogen (RM).

[0055] Examples of polymerizable liquid crystal compounds 31 include polymers having side chains with liquid crystal building blocks such as biphenyl, terphenyl, naphthyl, phenylbenzoate, azophenyl, and their derivatives, as well as photoreactive groups such as cinnamyl, chalcone, cinnamylene, β-(2-phenyl)acryloyl, cinnamic acid, and their derivatives, and a main chain with structures such as acrylate, methacrylate, maleimide, N-phenylmaleimide, and siloxane.

[0056] The aforementioned polymerizable liquid crystal compound 31 can be a homopolymer composed of a single repeating unit, or a copolymer composed of two or more repeating units with different side chain structures. The copolymers include any type of copolymer, such as alternating, random, or grafted copolymers.

[0057] There are no particular limitations on the types of chiral agents mentioned above; any chiral agent known in the art may be used. For example, S-811 (manufactured by Merck) may be used as a chiral agent.

[0058] The optical element according to Embodiment 1 includes an alignment film 20 with in-plane alignment constraint patterning and a cholesteric liquid crystal layer 30 oriented through the alignment film 20, and is therefore classified as an element called a polarization volume hologram (PVH). In applications using light guide plates, PVHs 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, it is preferable that the optical element according to Embodiment 1 can be used as a diffraction grating, and is a diffraction element having an inclined Bragg plane.

[0059] (Implementation Method 2) Figure 5 This is a schematic cross-sectional view of the light guide element according to Embodiment 2. As shown, the light guide element according to Embodiment 2 includes: a light guide plate 50; an incident optical element (first coupling element) 60, which is mounted on the incident side of the light guide plate 50; and an emitting optical element (second coupling element) 70, which is mounted on the emitting side of the light guide plate. For example, when... Figure 5 When the length of the light guide plate 50 in the left-right direction is set to 70mm, at the end of the light guide plate 50 ( Figure 5 An incident optical element 60 is positioned 10mm to 15mm from the left end of the light guide plate 50. Figure 5 An optical element 70 for emitting light is arranged at a position of 40mm to 60mm on the left side. Figure 5 The arrows in the diagram indicate the path of the light incident on the guide vane.

[0060] The light guide plate 50 described above can be a light guide plate 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-incident optical element 60 and the light-exiting optical element 70 is the optical element according to Embodiment 1, wherein the light-exiting optical element 70 is preferably the optical element according to Embodiment 1.

[0061] The light guide element described in Embodiment 2 is preferably used in augmented reality (AR) display devices. When the light guide element described in Embodiment 2 is assembled within an AR display device, a display module is positioned opposite the incident light-side optical element 60, serving as a light source 80. The display module (light source 80) can be configured as follows: Figure 5As shown, the light guide plate 50 faces the light-incident optical element 60, or it can face the light-incident optical element 60 directly without the light guide plate 50 (that is, the display module (light source 80) can be positioned on the side opposite to the light guide plate 50 relative to the light-incident optical element 60). The display module is not particularly limited as long as it displays content corresponding to AR technology; for example, a thin display such as a liquid crystal display module or an organic EL display module can be used.

[0062] An AR display device equipped with the light guide element according to Embodiment 2 is preferably an AR glasses-shaped device. In the AR glasses, light from the display module is incident on the light guide plate 50 and guided to a direction designed by the light-incident optical element (inner coupler element) 60 mounted on the light-incident side of the light guide plate 50. Then, while the light is repeatedly reflected at the interface between the light guide plate 50 and the air layer, it travels inside the light guide plate 50 from one end (the end where the light-incident optical element 60 is disposed) to the other end (the end where the light-emitting optical element 70 is disposed). The light reaching the light-emitting side of the light guide plate 50 is reflected by the light-emitting optical element (outer coupler element) 70 and incident on the observer's (user's) eyeball, thereby enabling the observer to visually recognize the image of the display module.

[0063] When the external coupler element 70 is applied to AR glasses, it is preferably larger than the human eye's light-receiving area, and the horizontal dimension of the external coupler element 70 is, for example, 20 mm. Furthermore, by making the reflectivity of the external coupler element 70 less than 100%, the light incident on the external coupler element 70 is divided into a component for the observer's visual recognition and a component for continuous light guiding. As a result, the light incident from the external coupler element 70 to the observer can be dispersed at multiple locations within the surface. Thus, the image can be seen even when the observer's eye moves. The area where the image can be seen even with eye movement is called the "eye box." Preferably, more than 95% of the light from the light source exits into the eye box, for example, by adjusting the horizontal dimension and reflectivity of the external coupler element 70.

[0064] Furthermore, in applications such as AR glasses, for example, the thickness of the light guide plate 50 is set to 1 mm, and the diffraction angle (e.g., the diffraction angle for light with a wavelength of 550 nm) between the inner coupler element 60 and the outer coupler element 70 is set to 45°. The diffraction angle between the inner coupler element 60 and the outer coupler element 70 is determined by the period P1 (refer to...). Figure 1 (This is determined.) In this case, light incident from the normal direction of the main surface of the light guide plate 50 undergoes total internal reflection through the coupler element 60 at an angle of 45° with the interior of the light guide plate 50, and is then emitted in the normal direction through the outer coupler element 70. Furthermore, by adjusting the reflectivity of the outer coupler element 70 to 30%, more than 95% of the light from the light source is emitted into the eye box.

[0065] To improve the display quality of AR glasses, the coupler element needs to function for RGB light. However, since the reflection spectrum of PVH has a constant width, similar to the selective reflection of typical cholesteric liquid crystals, it cannot reflect light across all wavelength regions of RGB. Therefore, the inventors investigated methods for stacking PVHs with different chiral pitches, but found problems such as orientation disorder of the polymeric liquid crystal compound after the second layer, coating repulsion, control of chiral pitch, increased processing time, and increased cost. In contrast, the inventors discovered that if the polymeric liquid crystal compound is in contact with the solvent in a semi-cured state, the reflected wavelength shifts to the shorter wavelength side, thereby reducing the film thickness. Based on this discovery, the inventors fabricated semi-cured and fully cured regions in-plane before coating with solvent, thereby achieving a one-layer PVH structure that enables uniform reflectivity across all wavelength regions of RGB.

[0066] (Implementation Method 3) Figure 6 This diagram illustrates the uneven brightness that occurs when the reflectivity of the coupler element is uniform in-plane. Figure 7 This is a schematic perspective view of the optical element according to Embodiment 3. The optical element according to Embodiment 3 has the same structure 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 with a visible light reflectance smaller than that of the first reflective region 37 and the second reflective region 36. By providing the low-reflection region 38, additional functions can be added to the optical element. For example, in the case of an optical element used in combination with a light guide plate 50, the closer the distance to the light incident portion, the larger the area of ​​the low-reflection region 38, thereby enabling a more uniform brightness distribution of the emitted light. One of the first reflective region 37 and the second reflective region 36 (in...) Figure 7 In the case of a first reflective region 37, the low reflective regions 38 are dispersedly disposed in a plurality of first partial regions, and the regions in the cholesteric liquid crystal layer other than the plurality of first partial regions and the plurality of second partial regions can also be the other of the first reflective regions 37 and the second reflective regions 36 (in the case of a first reflective region 37). Figure 7 In the case of the second reflection region 36).

[0067] The aforementioned low-reflection region 38 can be formed, for example, by forming a region (e.g., an uncured region) with a lower degree of curing of the polymeric liquid crystal compound compared to the first reflective region 37 and then coating it with a solvent. This is because, in the region where the degree of curing of the polymeric liquid crystal compound is lower than that of the first reflective region 37, the aforementioned helical pitch is shorter than that of the first reflective region 37, and the peak reflectance is less than 400 nm.

[0068] Furthermore, the aforementioned visible light reflectance is the average reflectance in the wavelength range of 400~700nm.

[0069] The optical element described in Embodiment 3 can also be applied to the light-emitting side optical element 70 in the light guide element described in Embodiment 2. Therefore, the light-emitting side optical element 70 includes a cholesteric liquid crystal layer 30 with 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 (which is the region closer to the light-incident side of the light guide plate 50, for example, including the region of the cholesteric liquid crystal layer 30 closest to the light-incident 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 farther from the light-incident side of the light guide plate 50 than the first region, for example, including the region of the cholesteric liquid crystal layer 30 farthest from the light-incident side of the light guide plate 50). With this configuration, the display quality of AR glasses can be improved.

[0070] To improve the display quality of AR glasses, it is preferable to ensure that the image of the display module can be seen even when the observer's eye moves. While it is possible to expand the visible image range (eye box) by illuminating multiple parts of the coupler element, however... Figure 6 As shown, if the reflectivity of the coupler element is uniform in the plane, the intensity of light emitted from the light guide plate 50 increases the closer it is to the light source, which may result in uneven brightness in the plane. In contrast, when the optical element (coupler element) according to Embodiment 3 is used in AR glasses, uniform brightness can be achieved within the eye box in the visible light region of 400~700nm.

[0071] Examples and Comparative Examples The effects of the present invention will be illustrated below with examples and comparative examples, but the present invention is not limited to these examples.

[0072] <Comparative Example 1> In Comparative Example 1, the selective reflection wavelength of a polymeric liquid crystal compound with added chiral agent when formed into a single layer was evaluated. Samples were prepared according to the following steps.

[0073] (1) A photoisomerization-type photoalignment film is coated on a glass substrate.

[0074] (2) For the photo-alignment film, apply 100 mJ / cm 2 The photo-aligned film was irradiated with polarized ultraviolet (UV) light at a wavelength of 365 nm, and then baked in an oven at 160 °C for 20 minutes.

[0075] (3) A polymeric liquid crystal compound with a chiral agent was coated onto the photoalignment film using a spin coater rotating at 1000 rpm. The concentration of the chiral agent was adjusted to select a reflection wavelength of 650 nm. The wavelength dispersion of the polymeric liquid crystal compound was positive, with Re(450 nm) / Re(550 nm) ≈ 1.14 and Re(650 nm) / Re(550 nm) ≈ 0.94.

[0076] (4) Apply 3J / cm to the coated polymeric liquid crystal compound. 2 Irradiation with unpolarized UV light at a wavelength of 365 nm solidifies the polymeric liquid crystal compound, completing the sample preparation.

[0077] The completed sample has a structure consisting of a photoalignment film and a cholesteric liquid crystal layer stacked on a glass substrate. The cholesteric liquid crystal layer contains a polymer of a polymerizable liquid crystal compound and a chiral agent.

[0078] (evaluate) The thickness of the cholesteric liquid crystal layer was measured using the "NH-3MA," a non-contact three-dimensional measuring instrument manufactured by Mitaka Koki Co., Ltd. The measured thickness was 1.5 μm.

[0079] The transmittance Tmax and Tmin of the cholesteric liquid crystal layer were measured using an Axoscan instrument manufactured by Axometrics, and the reflectance R of the cholesteric liquid crystal layer was calculated using the following formula.

[0080] R(%)=(1-Tmin÷Tmax)×100 Tmax is the transmittance that maximizes the transmittance when the polarization state of the incident light source is maximized. Tmin is the transmittance that minimizes the transmittance when the polarization state of the incident light source is minimized. The cholesteric liquid crystal layer has the highest transmittance when the incident light is right-handed circularly polarized and the lowest transmittance when the incident light is left-handed circularly polarized.

[0081] Figure 8 This is a graph showing the reflectance of the cholesteric liquid crystal layer in Comparative Example 1. Figure 8 In this study, the maximum reflectance was normalized to 100%, and a reflection wavelength of 650 nm was chosen. The maximum reflectance before normalization (reflectance at a wavelength of 650 nm) was 82%.

[0082] <Comparative Example 2> In Comparative Example 2, except that the concentration of the chiral agent was adjusted to a selective reflection wavelength of 550 nm, the selective reflection wavelength was evaluated when a single layer of a polymeric liquid crystal compound containing a chiral agent was formed, just as in Comparative Example 1.

[0083] Figure 9This is a graph showing the reflectance of the cholesteric liquid crystal layer in Comparative Example 2. Figure 9 In this study, the maximum reflectivity was normalized to 100%, and the reflection wavelength was chosen to be 550 nm.

[0084] <Comparative Example 3> In Comparative Example 3, a single layer of a polymeric liquid crystal compound containing a chiral agent was prepared, and the selective reflection wavelength during solvent application was evaluated. Samples were prepared according to the following steps.

[0085] (1) A photoisomerization-type photoalignment film is coated on a glass substrate.

[0086] (2) For the photo-alignment film, apply 100 mJ / cm 2 The photo-aligned film was irradiated with polarized ultraviolet (UV) light at a wavelength of 365 nm, and then baked in an oven at 160 °C for 20 minutes.

[0087] (3) A polymeric liquid crystal compound with a chiral agent was coated onto the photoalignment 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 polymeric liquid crystal compound was positive, with Re(450 nm) / Re(550 nm) ≈ 1.14 and Re(650 nm) / Re(550 nm) ≈ 0.94.

[0088] (4) Apply 1 J / cm to the coated polymeric liquid crystal compound. 2 The polymeric liquid crystal compound was cured by irradiation with unpolarized UV light at a wavelength of 365 nm. The irradiation energy of the unpolarized UV light in Comparative Example 3 was less than that in Comparative Example 1. At this point, the polymeric liquid crystal compound was not completely cured, and this state was referred to as the "semi-cured state".

[0089] (5) Apply propylene glycol monomethyl ether acetate (PGMEA) as a solvent to the semi-cured polymeric liquid crystal compound. The contact time between the polymeric liquid crystal compound and the solvent is 5 seconds. After 5 seconds, the solvent is blown off with nitrogen. The sample is completed through the above steps.

[0090] The completed sample has a structure consisting of a photoalignment film and a cholesteric liquid crystal layer stacked on a glass substrate. The cholesteric liquid crystal layer contains a polymer of a polymerizable liquid crystal compound and a chiral agent.

[0091] The thickness of the cholesteric liquid crystal layer was measured using the non-contact three-dimensional measuring instrument "NH-3MA" manufactured by Mitaka Optical Co., Ltd. The result showed that the thickness of the cholesteric liquid crystal layer was 1.2 μm, which is thinner than that of Comparative Example 1.

[0092] The transmittance Tmax and Tmin of the cholesteric liquid crystal layer were measured using an "Axoscan" manufactured by Axometrics, and the reflectance R of the cholesteric liquid crystal layer was calculated. Figure 10 A graph showing the reflectance of the cholesteric liquid crystal layers in Comparative Examples 1 and 3 is provided. Figure 10 In Comparative Examples 1 and 3, the maximum reflectance values ​​were normalized to 100%. In Comparative Example 3, the selective reflection wavelength of the cholesteric liquid crystal layer was around 450 nm. The maximum reflectance value before normalization of Comparative Example 1 (reflectance at a wavelength of 650 nm) was 82%, and the maximum reflectance value before normalization of Comparative Example 3 (reflectance at a wavelength of 450 nm) was 78%.

[0093] Depend on Figure 10 As shown in the diagram, if a solvent is applied to a semi-cured polymeric liquid crystal compound, the thickness of the cholesteric phase liquid crystal layer decreases, and the reflected wavelength shifts to shorter wavelengths. This is caused by the diffusion phenomenon of the polymer.

[0094] Figure 11 This is a flowchart illustrating the mechanism by which the reflection wavelength of a cholesteric liquid crystal layer shifts when a solvent is coated onto a semi-cured polymeric liquid crystal compound.

[0095] When the polymeric liquid crystal compound 31 is irradiated with UV light, and a solvent 48 such as propylene glycol monomethyl ether acetate (PGMEA) is applied to the resulting polymeric liquid crystal compound film 34 (semi-cured film), the uncured portion of the polymeric liquid crystal compound 31 diffuses towards the solvent 48 side. On the other hand, the chiral agent 32 does not diffuse towards the solvent 48 side, but diffuses towards the substrate direction (alignment film 20 side). That is, it has been confirmed that if the solvent 48 is washed away, the remaining cholesteric liquid crystal layer 30 is a layer with a higher concentration of chiral agent 32, selectively reflecting wavelengths towards shorter wavelengths, or the flowing solvent 48 contains a large amount of polymeric liquid crystal compound 31 and a small amount of chiral agent 32. In addition, the thickness of the cholesteric liquid crystal layer 30 is thinner than the amount of polymeric liquid crystal compound 31 flowing from the solvent 48. This mechanism is believed to be due to the difference in solubility of polymeric liquid crystal compound 31 and chiral agent 32 in solvent 48.

[0096] <Comparative Example 4> In Comparative Example 4, a single layer of a polymeric liquid crystal compound containing a chiral agent was prepared, and the selective reflection wavelength during solvent application was evaluated. Samples were prepared according to the following steps.

[0097] (1) A photoisomerization-type photoalignment film is coated on a glass substrate.

[0098] (2) For the photo-alignment film, apply 100 mJ / cm 2The photo-aligned film was irradiated with polarized ultraviolet (UV) light at a wavelength of 365 nm, and then baked in an oven at 160 °C for 20 minutes.

[0099] (3) A polymeric liquid crystal compound with a chiral agent was coated onto the photoalignment 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 polymeric liquid crystal compound was positive, with Re(450 nm) / Re(550 nm) ≈ 1.14 and Re(650 nm) / Re(550 nm) ≈ 0.94.

[0100] (4) Apply 3J / cm to the coated polymeric liquid crystal compound. 2 The polymeric liquid crystal compound was cured by irradiation with unpolarized UV light at a wavelength of 365 nm. The irradiation energy of the unpolarized UV light in Comparative Example 4 was greater than that in Comparative Example 3, but the same as that in Comparative Example 1. At this point, the polymeric liquid crystal compound was completely cured.

[0101] (5) Apply propylene glycol monomethyl ether acetate (PGMEA) as a solvent to the cured polymeric liquid crystal compound. The contact time between the polymeric liquid crystal compound and the solvent is 5 seconds. After 5 seconds, the solvent is blown off with nitrogen. The sample is completed through the above steps.

[0102] The completed sample has a structure consisting of a photoalignment film and a cholesteric liquid crystal layer stacked on a glass substrate. The cholesteric liquid crystal layer contains a polymer of a polymerizable liquid crystal compound and a chiral agent.

[0103] The thickness of the cholesteric liquid crystal layer was measured using the non-contact three-dimensional measuring instrument "NH-3MA" manufactured by Mitaka Koki Co., Ltd. The result showed that the thickness of the cholesteric liquid crystal layer was 1.5 μm, the same as in Comparative Example 1.

[0104] The transmittance Tmax and Tmin of the cholesteric liquid crystal layer were measured using an "Axoscan" manufactured by Axometrics, and the reflectance R of the cholesteric liquid crystal layer was calculated. Figure 12 This is a graph showing the reflectance of the cholesteric liquid crystal layer in Comparative Example 4. Figure 12 In this study, the maximum reflectance of Comparative Example 4 was normalized to 100%. In Comparative Example 4, the selective reflection wavelength of the cholesteric liquid crystal layer was 650 nm, the same as that of Comparative Example 1.

[0105] <Example 1> In Example 1, a semi-cured region and a fully cured region of a polymeric liquid crystal compound were formed on a substrate, and the selective reflection wavelength during solvent application was evaluated. The sample in Example 1 was prepared according to the following steps.

[0106] (1) A photoisomerization-type photoalignment film is coated on a glass substrate.

[0107] (2) For the photo-alignment film, apply 100 mJ / cm 2 The photo-aligned film was irradiated with polarized ultraviolet (UV) light at a wavelength of 365 nm, and then baked in an oven at 160 °C for 20 minutes.

[0108] (3) A polymeric liquid crystal compound with a chiral agent was coated onto the photoalignment 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 polymeric liquid crystal compound was positive, with Re(450 nm) / Re(550 nm) ≈ 1.14 and Re(650 nm) / Re(550 nm) ≈ 0.94.

[0109] (4) For the coated polymeric liquid crystal compound, through a halftone mask, at 3J / cm 2 Irradiation with unpolarized UV light at a wavelength of 365 nm solidifies the polymeric liquid crystal compound. Figure 13 This diagram illustrates the curing process of the polymeric liquid crystal compound in Example 1. As shown, the halftone mask 45 used in Example 1 is a photomask having regions 46 with a transmittance of 30% and regions with a transmittance of 100%. The regions 46 with a transmittance of 30% are dispersed in multiple partial regions, and the regions with a transmittance of 100% surround each of the aforementioned partial regions. The area ratio of the regions 46 with a transmittance of 30% to the regions with a transmittance of 100% is 1:1. As a result of UV irradiating the polymeric liquid crystal compound film 34 (uncured film) through the halftone mask 45, the regions irradiated with UV light through the regions 46 with a transmittance of 30% become regions composed of the polymeric liquid crystal compound in a semi-cured state, and the regions irradiated with UV light through the regions with a transmittance of 100% become regions composed of the polymeric liquid crystal compound in a fully cured state.

[0110] (5) The polymerizable liquid crystal compound after UV irradiation is coated with propylene glycol monomethyl ether acetate (PGMEA) as a solvent. The contact time between the polymerizable liquid crystal compound and the solvent is 5 seconds. After 5 seconds, the solvent is blown off with nitrogen. The sample is completed through the above steps.

[0111] The completed sample has a structure consisting of a photoalignment film and a cholesteric liquid crystal layer stacked on a glass substrate. The cholesteric liquid crystal layer contains a polymer of a polymerizable liquid crystal compound and a chiral agent.

[0112] The thickness of the cholesteric liquid crystal layer was measured using the non-contact 3D measuring instrument "NH-3MA" manufactured by Mitaka Koki Co., Ltd. The results showed that the thickness of the cholesteric liquid crystal layer in the semi-cured region after UV irradiation was 1.2 μm, and the thickness of the cholesteric liquid crystal layer in the fully cured region after UV irradiation was 1.5 μm.

[0113] The transmittance Tmax and Tmin of the cholesteric liquid crystal layer were measured using an "Axoscan" manufactured by Axometrics, and the reflectance R of the cholesteric liquid crystal layer was calculated. Figure 14 This is a graph comparing the reflectance of the cholesteric liquid crystal layers of Example 1, Comparative Example 3, and Comparative Example 4. Figure 14 In this study, the maximum reflectance values ​​of Examples 1, 3, and 4 were normalized to 100%. The cholesteric liquid crystal layer of Example 1 exhibited a first reflective region with a reflectance peak (selective reflection wavelength) in the wavelength range of 400-550 nm, and a second reflective region with a reflectance peak (selective reflection wavelength) different from the first reflective region in the wavelength range of 550-700 nm. Compared with the reflectance spectra of the cholesteric liquid crystal layers of Comparative Examples 3 and 4, it was found that it exhibited uniform reflectance in RGB. Here, the regions that were in a semi-cured state after UV irradiation and had a thin cholesteric liquid crystal layer corresponded to the first reflective region, and the regions that were in a fully cured state after UV irradiation and had a thick cholesteric liquid crystal layer corresponded to the second reflective region. Therefore, the first reflective regions were dispersed in multiple partial regions, and the second reflective regions were arranged to surround each of the multiple partial regions.

[0114] As demonstrated by the results of Example 1, a broadband diffraction element can be fabricated using a single-layer cholesteric liquid crystal layer. Furthermore, in Example 1, the first and second reflective regions were fabricated with a 1:1 area ratio, but this can be varied depending on the material. It is preferable to adjust the area ratio to make the RGB reflectances uniformly close.

[0115] Explanation of reference numerals in the attached figures 10: Support body 20: Orientation film 30: Cholesteric phase liquid crystal layer 31: Polymerizable liquid crystal compounds 32: Chiral agent 34: Films of polymeric liquid crystal compounds 36: Second Reflection Area 37: First Reflection Area 38: Low-reflection area 45: Halftone Mask 46: Area with a transmittance of 30% 48: Solvent 50: Light guide plate 60: Optical elements on the light-incident side (internal coupler elements) 70: Optical elements on the light-emitting side (external coupler elements) 80: Light source.

Claims

1. An optical element, characterized in that, Includes a cholesteric liquid crystal layer containing a polymer of a polymerizable liquid crystal compound; and a chiral agent. The cholesteric liquid crystal layer has the following in-plane characteristics: The first reflection region has a peak reflectivity in the wavelength range of 400~550nm; as well as The second reflective region has a different peak reflectivity than the first reflective region in the wavelength range of 550~700nm. The thickness of the first reflective region is thinner than the thickness of the second reflective region.

2. The optical element according to claim 1, characterized in that, One of the first reflective region and the second reflective region is distributed in a plurality of partial regions, and the other of the first reflective region and the second reflective region is arranged in such a way that they surround the respective partial regions of the plurality of partial regions.

3. The optical element according to claim 2, characterized in that, 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.

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

5. The optical element according to claim 1, characterized in that, In the cholesteric liquid crystal layer, the reflectivity of the first reflective region at a wavelength of 450 nm is less than that of the second reflective region at a wavelength of 650 nm, and the area of ​​the first reflective region is greater than that of the second reflective region.

6. The optical element according to any one of claims 1 to 5, characterized in that, The cholesteric liquid crystal layer has a low-reflection region in-plane, and the visible light reflectance of the low-reflection region is less than that of the first reflective region and the second reflective region.

7. The optical element according to claim 6, characterized in that, One of the first reflective region and the second reflective region is distributed dispersedly in multiple first partial regions. The low-reflection regions are dispersed across multiple second-part regions. 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.

8. A light guide element, characterized in that, include: Light guide plate; An incident optical element is mounted on the incident side of the light guide plate; as well as The light-emitting optical element is mounted on the light-emitting side of the light guide plate. At least one of the light-incident optical element and the light-outcident optical element is an optical element according to any one of claims 1 to 7.

9. The light guide element according to claim 8, characterized in that, The light-emitting optical element includes a cholesteric liquid crystal layer, which has an in-plane low-reflection region. The visible light reflectance of the low-reflection region is less than that of the first and second reflective regions. 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, wherein the second region is farther from the light-incident side of the light guide plate than the first region.

10. An AR display device, characterized in that, include: The light guide element according to claim 8 or 9; as well as The display module is configured opposite to the light-incident optical element.

Images