Optical device and head-mounted display

Abstract

The present invention addresses the problem of providing an optical device with which stable image quality can be obtained regardless of focal distance when the focal distance of an image is changed in an HMD or the like, and an HMD using the same. The problem is solved by an optical device comprising: a switching element capable of performing switching between a first phase difference and a second phase difference, the difference between the first phase difference and the second phase difference being 275±20 nm at a wavelength of 550 nm; and a liquid crystal layer that is formed using a liquid crystal composition containing a reverse wavelength dispersible liquid crystal compound and has a liquid crystal orientation pattern in which the direction of an optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane.

Description

Optical devices and head-mounted displays

[0001] The present invention relates to an optical device used in a head-mounted display or the like, and to a head-mounted display having this optical device.

[0002] Head-mounted displays (HMDs) and the like are known as means for providing users with virtual reality (VR), augmented reality (AR), and mixed reality (MR). HMDs are relatively small and easy to carry and wear, and are expected to become multifunctional devices that can replace smartphones, tablets, and the like.

[0003] In such HMDs, for example, in a VR display device, a half mirror and a reflective polarizer are used to fold the optical path of light (image) emitted from the image display device so that the user can observe the image, thereby lengthening the optical path length and allowing the user to perceive the perspective of the image. Also, in this optical device, for example, the half mirror and the reflective polarizer are attached to a lens such as a convex lens, and the light is collected by the lens, thereby widening the FOV (Field of View).

[0004] Incidentally, Patent Document 1 describes that in such an HMD, a switchable half waveplate (SHWP) and a plurality of liquid crystal (LC) lenses are used to dynamically change the focal length of the optical system of the HMD and control the distance from the user to the observed image.

[0005] In the HMD described in Patent Document 1, for example, a switching unit having a switchable half-wave plate and a liquid crystal lens is disposed between an optical system constituting the HMD and a position where a user observes an image. The switchable half-wave plate is a half-wave plate that can be switched between an on state in which it acts as a half-wave plate and an off state in which it does not affect incident light and transmits it as is. As is well known, a liquid crystal lens is a liquid crystal diffraction grating that has a concentric (radial) liquid crystal orientation pattern in which the optical axis derived from the liquid crystal compound continuously rotates in one direction. The liquid crystal lens focuses or diverges incident light depending on whether the incident light is right-handed or left-handed circularly polarized light. Specifically, a liquid crystal lens that focuses right-handed circularly polarized light diverges left-handed circularly polarized light, and conversely, a liquid crystal lens that focuses left-handed circularly polarized light diverges right-handed circularly polarized light.

[0006] As an example, a case will be described in which an optical system immediately upstream of a switching unit in an HMD emits right-handed circularly polarized light and a liquid crystal lens in the switching unit focuses the right-handed circularly polarized light. In this configuration, when the switchable half-wave plate is off, i.e., does not function as a half-wave plate, the light remains right-handed circularly polarized and enters the liquid crystal lens, and the focal point of the image displayed by the HMD is at the position focused by the liquid crystal lens in the switching unit. In contrast, when the switchable half-wave plate in the switching unit is on, i.e., functions as a half-wave plate, the light transmitted through the switchable half-wave plate is converted to left-handed circularly polarized light. As described above, the liquid crystal lens in the switching unit focuses right-handed circularly polarized light, while diverging left-handed circularly polarized light. Therefore, in this case, the light is diverged by the switching unit (liquid crystal lens), and the focal length of the image displayed by the HMD is longer than when the switchable half-wave plate is off. In other words, in this state, the position of the displayed image is closer to the user's eyes.

[0007] Various liquid crystal lenses are known. For example, Non-Patent Document 1 discloses a liquid crystal lens that improves diffraction efficiency and broadens the wavelength range in which it functions as a lens by stacking two liquid crystal layers. The liquid crystal layer that constitutes this liquid crystal lens is a diffraction grating (PG) that has a liquid crystal orientation pattern in which the optical axis derived from the liquid crystal compound continuously rotates in one direction, similar to that of a liquid crystal lens, and the liquid crystal compound is helically twisted and oriented in the thickness direction (chiral PG). In the liquid crystal lens of Non-Patent Document 1, stacking liquid crystal layers in which the twist direction of the liquid crystal compound is reversed in the thickness direction improves diffraction efficiency and broadens the wavelength range in which it functions as a lens.

[0008] U.S. Pat. No. 1,037,9419

[0009] J.Escuti et al., Achromatic diffraction from polarization gratings with high efficiency, OPTICS LETTERS Vol.33, No.20, pp.2287-2289 (October 15, 2008)

[0010] As described in Patent Document 1, by combining an HMD with a switching unit having a switchable half-wave plate and a liquid crystal lens, it is possible to dynamically change the focal length of the HMD's optical system and control the distance from the user to the observed image. This allows the HMD user to shorten the convergence distance and accommodation distance of their eyes, enabling natural stereoscopic vision. As a result, VR sickness can be prevented.

[0011] However, according to the inventors' investigations, with a conventional switching unit using a switchable half-wave plate and a liquid crystal lens, when switching the focal length of an image, for example in an HMD, there may be inconveniences such as the image quality fluctuating depending on the focal length.

[0012] The object of the present invention is to solve the problems of the conventional technology, and to provide an optical device that can obtain images of stable image quality regardless of the focal length when the focal length of the displayed image is changed, for example, in an HMD, and an HMD that uses this optical device.

[0013] To achieve the above object, the present invention has the following configurations. [1] An optical device including a switching element and a liquid crystal layer, wherein the switching element is an element capable of switching between a first retardation and a second retardation, and the difference between the first retardation and the second retardation is 275±20 nm at a wavelength of 550 nm, and the liquid crystal layer is formed using a liquid crystal composition containing a liquid crystal compound with reverse wavelength dispersion, and the optical device has a liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. [2] The optical device according to [1], wherein the liquid crystal orientation pattern has regions in the plane where the length of one period of the direction of the optical axis derived from the liquid crystal compound is different, when the length of a 180° rotation in the plane is defined as one period. [3] The optical device according to [1] or [2], wherein the liquid crystal orientation pattern has a plurality of rings of different sizes, and larger rings sequentially enclose smaller rings in the plane. [4] The optical device according to [3], wherein the liquid crystal orientation pattern is concentric. [5] The optical device according to any one of [1] to [4], wherein the switching element is formed using a liquid crystal cell. [6] A head-mounted display having the optical device according to any one of [1] to [5]. [7] The head-mounted display according to [6], which is either a virtual reality image display device or an augmented reality image display device. [8] The head-mounted display according to [7], which is a virtual reality image display device having a condensing optical system, wherein the optical device is provided downstream of the condensing optical system. [9] The head-mounted display according to [7] or [8], which is an augmented reality image display device having a light guide plate, wherein the optical device is provided downstream of the light guide plate.

[0014] According to the present invention, when the focal length of a display image is changed in an HMD or the like, for example, an image with stable image quality can be obtained regardless of the focal length.

[0015] FIG. 1 is a diagram conceptually showing an example of a VR image display device of the present invention. FIG. 2 is a plan view conceptually showing an example of a liquid crystal lens. FIG. 3 is a partial cross-sectional view conceptually showing the liquid crystal lens shown in FIG. 2. FIG. 4 is a plan view for explaining the polarization diffraction element shown in FIG. 2. FIG. 5 is a conceptual diagram for explaining the function of the polarization diffraction element shown in FIG. 2. FIG. 6 is a conceptual diagram for explaining the function of the polarization diffraction element shown in FIG. 2. FIG. 7 is a diagram conceptually showing an exposure apparatus for forming a liquid crystal orientation pattern. FIG. 8 is a conceptual diagram for explaining the function of an optical device of the present invention. FIG. 9 is a plan view conceptually showing another example of a liquid crystal lens. FIG. 10 is a plan view conceptually showing another example of a liquid crystal lens. FIG. 11 is a diagram conceptually showing an example of an AR image display device of the present invention.

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical device and a head-mounted display (HMD) according to the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings.

[0017] The drawings shown below are conceptual diagrams for explaining the present invention, and the shape, thickness, size, and positional relationship of each component are not necessarily the same as those of an actual device. Furthermore, the examples shown below illustrate representative embodiments of the present invention. Therefore, the present invention is not limited to the embodiments shown below. In this specification, numerical ranges expressed using "to" refer to ranges that include the numerical values ​​before and after "to" as the lower and upper limits. Furthermore, although not limited thereto, light in the wavelength range of 420 to 490 nm is blue light (B light), light in the wavelength range of 495 to 570 nm is green light (G light), and light in the wavelength range of 580 to 700 nm is red light (R light).

[0018] FIG. 1 conceptually shows an example of a VR image display device, which is an HMD (head mounted display) of the present invention, that uses an example of an optical unit of the present invention.

[0019] The VR image display device 10 shown in Fig. 1 is an image display device that displays (projects) a virtual reality image (VR image) for a user O to observe. In the following description, the VR image display device 10 will also be simply referred to as "display device 10." As shown in Fig. 1, the display device 10 has a display 12, a circular polarizer 14, a half mirror 16, a lens 18, a circularly polarized reflective polarizer 24, a circular polarizer 26, and an optical device 30.

[0020] The half mirror 16, the lens 18, the circularly polarized reflective polarizer 24, and the circular polarizer 26 form a light-collecting optical system in the display device 10. The optical device 30 is an optical device of the present invention. In the illustrated example, the optical device 30 has a switching element 32 and a liquid crystal lens 34. The liquid crystal lens 34 has a liquid crystal layer 36 (see FIG. 3 ).

[0021] The display device 10 shown in FIG. 1 is basically the same as a VR image display device having a known folded optical system such as a pancake lens, except for the inclusion of an optical device 30, which is an optical device of the present invention. In the display device 10, an image (light) displayed on a display 12 is converted into, for example, right-handed circularly polarized light by a circular polarizer 14, and approximately half of the light passes through a half mirror 16 and a lens 18 to enter a circularly polarized reflective polarizer 24. The circularly polarized reflective polarizer 24 is, for example, a reflective polarizer that selectively reflects right-handed circularly polarized light and transmits left-handed circularly polarized light. Therefore, the right-handed circularly polarized image is reflected by the circularly polarized reflective polarizer 24 and again enters the half mirror 16, where approximately half of the light is reflected by the half mirror 16. The right-handed circularly polarized image reflected by the half mirror 16 is converted into left-handed circularly polarized light. The left-handed circularly polarized image reflected by the half mirror 16 is collected by a lens 18 and re-enters the circularly polarized reflective polarizer 24. As described above, the circularly polarized reflective polarizer 24 is a reflective polarizer that selectively reflects right-handed circularly polarized light and transmits left-handed circularly polarized light. Therefore, the left-handed circularly polarized image that re-enters the circularly polarized reflective polarizer 24 is transmitted through the circularly polarized reflective polarizer 24. The left-handed circularly polarized image that has transmitted through the circularly polarized reflective polarizer 24 is incident on the circular polarizer 26. The circular polarizer 26 blocks the right-handed circularly polarized light to prevent the unwanted right-handed circularly polarized light from becoming stray light (ghost) when the right-handed circularly polarized image first enters the circularly polarized reflective polarizer 24. In other words, the circular polarizer transmits left-handed circularly polarized light and blocks, preferably absorbs, right-handed circularly polarized light. Therefore, the left-handed circularly polarized image that has entered the circular polarizer 26 is transmitted through the circular polarizer 26.

[0022] The left-handed circularly polarized image transmitted through the circular polarizer 26 is then incident on and transmitted through the optical device 30 in a condensed state, and the focal length is adjusted so that the image is viewed as a virtual reality image by the user O. The optical device 30 will be described in detail later.

[0023] The VR image display device of the present invention is basically a known VR image display device except for having the optical device 30, which is the optical device of the present invention. Therefore, the VR image display device of the present invention is not limited to the configuration shown in Fig. 1, and various known VR image display devices can be used.

[0024] In the display device 10, various known displays (image display devices) can be used as the display 12. Examples of the display 12 include a liquid crystal display (LCD (Liquid Crystal Display)), an organic electroluminescence display (OLED (Organic Light Emitting Diode)), a CRT (Cathode-ray tube), a plasma display, an LED (Light Emitting Diode) display, a micro LED display, a laser display, a DLP (Digital Light Processing), and a MEMS (Micro-Electro-Mechanical Systems) display. In the present invention, the liquid crystal display device also includes LCOS (Liquid Crystal On Silicon) and the like.

[0025] In the display device 10, there are no limitations on the circular polarizer 14, and various known circular polarizers (circular polarizers) that convert the image (light) emitted from the display 12 into circularly polarized light in a predetermined rotation direction can be used. The circular polarizer 14 in the illustrated example is a circular polarizer that includes a linear polarizer 14a and a quarter-wave plate (λ / 4 plate) 14b. That is, the circular polarizer 14 converts the image emitted from the display 12 into linearly polarized light in a predetermined direction using the linear polarizer 14a, and then converts this linearly polarized light into circularly polarized light in a predetermined rotation direction using the quarter-wave plate 14b.

[0026] As described above, in the display device 10 of the illustrated example, the circular polarizer 14 converts the image output from the display 12 into right-handed circularly polarized light. However, the present invention is not limited to this, and the circular polarizer 14 may also convert the image output from the display 12 into left-handed circularly polarized light. In this case, the circularly polarized light reflective polarizer 24 described below selectively reflects left-handed circularly polarized light and transmits right-handed circularly polarized light. That is, in the display device of the present invention, there is no limitation on the rotation direction of the circularly polarized light of the image incident on the optical device 30 of the present invention. Therefore, in the display device of the present invention, it is sufficient to select the rotation direction of the circularly polarized light transmitted through the polarizer and, if necessary, use a half-wave plate or the like so that the set circularly polarized light is incident on the optical device.

[0027] The display device 10 is not limited to the linear polarizer 14a and the quarter-wave plate 14b, and various known polarizers can be used. Therefore, the linear polarizer 14a may be a reflective polarizer or an absorptive polarizer. Various known linear polarizers can be used, such as an iodine-based polarizer, a dye-based polarizer using a dichroic dye, a polyene-based polarizer, a wire-grid polarizer, and a film obtained by stretching a dielectric multilayer film as described in JP 2011-053705 A. Furthermore, the quarter-wave plate 14b can be a stretched polycarbonate film, a stretched norbornene-based polymer film, a transparent film containing and oriented inorganic particles having birefringence such as strontium carbonate, a thin film obtained by obliquely depositing an inorganic dielectric on a substrate, a film obtained by uniaxially aligning and fixing a polymerizable liquid crystal compound, and a film obtained by uniaxially aligning and fixing a liquid crystal compound. In this regard, the same is true for other linear polarizers and quarter wave plates.

[0028] In addition, if the display 12 is a device that emits linearly polarized light, such as a liquid crystal display device or an organic electroluminescent display device having an anti-reflection film, it is possible to use only the quarter-wave plate 14b without using the linear polarizer 14a.

[0029] In the display device 10 of the present invention, there is no limitation on the half mirror 16, and various known half mirrors can be used. Furthermore, there is no limitation on the lens 18 in the display device 10, and various known lenses (convex lenses) that focus incident light can be used. In the illustrated example, the lens 18 is, for example, a plano-convex lens.

[0030] In the display device 10 of the present invention, there is no limitation on the circularly polarized reflective polarizer 24, and various known reflective circular polarizers that selectively reflect right-handed or left-handed circularly polarized light and transmit circularly polarized light with the opposite rotation direction can be used. A preferred example of the circularly polarized reflective polarizer 24 is a cholesteric liquid crystal layer.

[0031] A cholesteric liquid crystal layer is a liquid crystal layer formed by fixing a liquid crystal phase (cholesteric liquid crystal phase) made of cholesterically oriented liquid crystal compounds. As is well known, a cholesteric liquid crystal layer has a helical structure in which liquid crystal compounds are spirally rotated and stacked, and the helical pitch (helical pitch) is defined as a configuration in which liquid crystal compounds are spirally rotated and stacked one turn (360° rotation). The helical pitch (helical pitch) is a structure in which helically rotated liquid crystal compounds are stacked at multiple pitches.

[0032] As is well known, a cholesteric liquid crystal layer selectively reflects right-handed or left-handed circularly polarized light in a specific wavelength range and transmits other light depending on the helical sense of the liquid crystal compound. Specifically, the cholesteric liquid crystal layer selectively reflects light in a specific wavelength range and transmits light in other wavelength ranges depending on the length of one helical pitch. The central wavelength λ of the selective reflection of the cholesteric liquid crystal layer (selective reflection central wavelength λ) depends on one helical pitch P of the helical structure in the cholesteric liquid crystal phase and follows the relationship λ = n × P with the average refractive index n of the cholesteric liquid crystal structure. One helical pitch P of the helical structure is the helical period, which is the length in the thickness direction over which the liquid crystal compound rotates 360°. Depending on the helical sense of the helical twist, the cholesteric liquid crystal layer reflects right-handed circularly polarized light and transmits left-handed circularly polarized light, or reflects left-handed circularly polarized light and transmits right-handed circularly polarized light. The rotation direction of the circularly polarized light reflected by the cholesteric liquid crystal layer corresponds to the sense of helix of the cholesteric liquid crystal phase.

[0033] The cholesteric liquid crystal layer may be any of various known cholesteric liquid crystal layers formed by fixing a cholesteric liquid crystal phase, or may be a cholesteric liquid crystal layer having a so-called pitch gradient structure (PG structure) in which the helical pitch varies in the thickness direction.

[0034] As described above, a cholesteric liquid crystal layer selectively reflects light in a specific wavelength range and transmits light in other wavelength ranges. Therefore, when the circularly polarized reflective polarizer 24 is composed of a cholesteric liquid crystal layer, the circularly polarized reflective polarizer 24 may have only one cholesteric liquid crystal layer or may have multiple cholesteric liquid crystal layers, depending on the image displayed by the display 12. For example, when the display 12 displays full-color images or black-and-white images, the circularly polarized reflective polarizer 24 may have three cholesteric liquid crystal layers: a cholesteric liquid crystal layer having a selective reflection center wavelength in the wavelength range of blue light, a cholesteric liquid crystal layer having a selective reflection center wavelength in the wavelength range of green light, and a cholesteric liquid crystal layer having a selective reflection center wavelength in the wavelength range of red light.

[0035] In the display device 10, various known circular polarizers 26 that block circularly polarized light of a predetermined rotation direction and transmit circularly polarized light of the other direction can be used. As described above, this circular polarizer 26 blocks right-handed circularly polarized light that is unnecessarily transmitted when a right-handed circularly polarized image is first incident on the circularly polarized reflective polarizer 24. One example of the circular polarizer 26 is one that has, in this order, a quarter-wave plate, a linear polarizer, and a quarter-wave plate. In this circular polarizer 26, the right-handed circularly polarized light that is unnecessarily transmitted through the circularly polarized reflective polarizer 24 is converted into linearly polarized light in the direction that the linear polarizer blocks by the upstream quarter-wave plate, thereby blocking the right-handed circularly polarized light that is unnecessarily transmitted through the circularly polarized reflective polarizer 24. In consideration of this point, an absorptive linear polarizer is preferable as the linear polarizer. On the other hand, when proper left-handed circularly polarized light that has passed through the circularly polarized reflective polarizer 24 enters the circular polarizer 26, the left-handed circularly polarized light is converted into linearly polarized light that is in the opposite direction to the right-handed circularly polarized light and can be transmitted through the linear polarizer. The linearly polarized light converted from this left-handed circularly polarized light is then converted back into left-handed circularly polarized light by the downstream quarter-wave plate.

[0036] The left-handed circularly polarized light image that has passed through the circular polarizer 26 then enters the optical device 30. As described above, the optical device 30 is an optical device of the present invention, and includes the switching element 32 and the liquid crystal lens 34. The optical device 30 extends or shortens the focal length of the display device 10 by switching using the switching element 32. In other words, by including the optical device 30, the display device 10 makes it possible to change the focal length of the image (projected video) observed by the user O.

[0037] The switching element 32 is an element capable of switching between a first phase difference and a second phase difference. The difference between the first phase difference and the second phase difference switched by the switching element 32 is 275±20 nm at a wavelength of 550 nm. As an example, the switching element 32 is an element capable of switching between a zero phase difference state and a half-wave (λ / 2) phase difference state. That is, the switching element 32 is an element capable of switching between a state in which incident light passes through as is and a state in which the switching element 32 acts as a half-wave plate for the incident light. Hereinafter, for convenience, the zero phase difference state will be referred to as "off," and the half-wave phase difference state in which the switching element 32 acts as a half-wave plate will be referred to as "on." As described above, in the display device 10, a left-handed circularly polarized image is incident on the optical device 30. Therefore, the switching element 32 is an element capable of switching between a state in which incident left-handed circularly polarized light is transmitted as left-handed circularly polarized light and a state in which incident left-handed circularly polarized light is converted into right-handed circularly polarized light and transmitted.

[0038] There are no limitations on the switching element 32, and various elements capable of switching between a first retardation and a second retardation, the difference between which is 275±20 nm at a wavelength of 550 nm, can be used. An example is a switching element configured using a liquid crystal cell. The liquid crystal cell is preferably in a VA (Vertical Alignment) mode.

[0039] 1, the optical device 30 has a liquid crystal lens 34 downstream of the switching element 32. Therefore, left-handed circularly polarized light that has passed through the switching element 32 or right-handed circularly polarized light that has been converted by the switching element 32 is incident on the liquid crystal lens 34.

[0040] An example of a liquid crystal lens 34 is conceptually shown in FIGS. 2 and 3 . FIG. 2 is a plan view of the liquid crystal lens 34, and FIG. 3 is a cross-sectional view in the thickness direction. As shown in FIGS. 2 and 3 , the liquid crystal lens 34 has a liquid crystal layer 36 formed using a liquid crystal composition containing a liquid crystal compound 38. In the present invention, a liquid crystal compound with reverse wavelength dispersion is used as the liquid crystal compound 38. This will be described in detail later. The liquid crystal layer 36 has a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound 38 changes while continuously rotating along at least one direction in the plane. Furthermore, in a preferred embodiment, the liquid crystal layer 36 has regions in the plane where the length of one period is different, where the length of one period is defined as the length of a 180° rotation of the orientation of the optical axis derived from the liquid crystal compound 38 in the plane.

[0041] 2 and 3, the liquid crystal lens 34 has a substrate 50, an alignment film 52, and a liquid crystal layer 36 (optically anisotropic layer). In the liquid crystal lens 34, the liquid crystal layer 36 acts as a liquid crystal lens, i.e., a liquid crystal diffraction element. Therefore, the liquid crystal lens 34 may be composed of only the liquid crystal layer 36, or may be composed of the alignment film 52 and the liquid crystal layer 36 after the substrate 50 has been peeled off, or may be composed of the liquid crystal layer 36 laminated on another substrate after the substrate 50 and alignment film 52 have been peeled off from the liquid crystal layer 36.

[0042] In the liquid crystal lens 34 shown in Figures 2 and 3, the liquid crystal layer 36 is a liquid crystal layer formed on an alignment film 52 using a composition containing a liquid crystal compound 38, and the liquid crystal compound 38 is aligned and fixed in the following liquid crystal alignment pattern. Specifically, the liquid crystal layer 36 has a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound 38 changes while continuously rotating in one direction, radially from the inside to the outside. That is, the liquid crystal alignment pattern of the liquid crystal layer 36 shown in Figures 2 and 3 is a pattern having multiple rings, and is a concentric pattern in which the orientation of the optical axis derived from the liquid crystal compound 38 changes while continuously rotating in one direction, concentrically from the inside to the outside.

[0043] 2 and 4 described later, in order to simplify the drawings and clearly show the configuration of the liquid crystal layer 36, only the liquid crystal compound 38 at the interface of the liquid crystal layer 36 on the alignment film 52 side is shown. However, as shown in Fig. 3, the liquid crystal layer 36 has a configuration in which liquid crystal compounds 38 are stacked in the thickness direction, similar to a liquid crystal layer formed using a composition containing a normal liquid crystal compound. Furthermore, since Figs. 2 and 3 illustrate a rod-shaped liquid crystal compound as the liquid crystal compound 38, the direction of the optical axis coincides with the longitudinal direction of the liquid crystal compound 38.

[0044] Specifically, in the liquid crystal layer 36, the direction of the optical axis of the liquid crystal compound 38 changes while continuously rotating in multiple directions, for example, the direction indicated by arrow A1, the direction indicated by arrow A2, the direction indicated by arrow A3, the direction indicated by arrow A4, etc., extending outward from the center, i.e., the optical axis, of the liquid crystal layer 36. Therefore, in the liquid crystal layer 36, the direction of rotation of the optical axis of the liquid crystal compound 38 is the same in all directions (one direction). In the illustrated example, the direction of rotation of the optical axis of the liquid crystal compound 38 is counterclockwise in all directions indicated by arrow A1, the direction indicated by arrow A2, the direction indicated by arrow A3, and the direction indicated by arrow A4. In other words, if arrows A1 and A4 are considered to be a single line, the direction of rotation of the optical axis of the liquid crystal compound 38 is reversed at the center of the liquid crystal layer 36 on this line. As an example, the line formed by arrows A1 and A4 is assumed to be directed rightward in the figure (the direction indicated by arrow A1). In this case, the optical axis of the liquid crystal compound 38 initially rotates clockwise from the outside toward the center of the liquid crystal layer 36, reverses its direction of rotation at the center of the liquid crystal layer 36, and then rotates counterclockwise from the center toward the outside of the liquid crystal layer 36. The center of the liquid crystal layer 36 is the optical axis of the liquid crystal lens 34.

[0045] As is well known, a liquid crystal layer having a liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal compound 38 changes while continuously rotating in one direction acts as a transmissive liquid crystal diffraction element that diffracts incident circularly polarized light in one direction and the opposite direction of the rotation of the optical axis, depending on the rotation direction of the optical axis and the rotation direction of the incident circularly polarized light.

[0046] In a liquid crystal layer 36 having a liquid crystal orientation pattern in which the orientation of the optical axis of the liquid crystal compound 38 changes while continuously rotating in one direction, the diffraction direction (refraction direction) of transmitted light depends on the rotation direction of the optical axis of the liquid crystal compound 38. That is, in this liquid crystal orientation pattern, when the rotation direction of the optical axis of the liquid crystal compound 38 facing in one direction is reversed, the diffraction direction of transmitted light is opposite to the direction in which the optical axis rotates. Furthermore, in a liquid crystal layer 36 having a liquid crystal orientation pattern in which the orientation of the optical axis of the liquid crystal compound 38 changes while continuously rotating in one direction, the diffraction direction of transmitted light differs depending on the rotation direction of the incident circularly polarized light. That is, in this liquid crystal orientation pattern, the diffraction direction of transmitted light is reversed between when the incident light is right-handed circularly polarized light and when it is left-handed circularly polarized light.

[0047] Furthermore, when the in-plane retardation (retardation in the plane direction) of the liquid crystal layer 36 is set to λ / 2, the liquid crystal layer 36 functions as a typical half-wave plate, that is, it imparts a phase difference of half the wavelength, i.e., 180°, to the polarized light component incident on the liquid crystal layer. Therefore, the circularly polarized light incident on the liquid crystal layer 36 and diffracted therefrom has the opposite rotation direction. That is, right-handed circularly polarized light incident on the liquid crystal layer 36 and diffracted therefrom exits as left-handed circularly polarized light, and left-handed circularly polarized light exits as right-handed circularly polarized light.

[0048] In the liquid crystal layer 36 of the liquid crystal lens 34, when the length of a 180° rotation of the optical axis direction of the liquid crystal compound 38 in one direction in which the orientation of the optical axis of the liquid crystal compound 38 changes while continuously rotating is defined as one period, the length of one period gradually decreases from the inside to the outside. That is, the liquid crystal layer 36 in the illustrated example has regions in its plane in which the length of one period varies. Here, in a liquid crystal layer having a liquid crystal orientation pattern in which the orientation of the optical axis of the liquid crystal compound 38 changes while continuously rotating in one direction, the shorter the length of this period, the larger the diffraction angle. Therefore, in a liquid crystal layer 36 having a concentric liquid crystal orientation pattern, the diffraction angle gradually increases from the center of the concentric circle toward the outside.

[0049] Therefore, the liquid crystal layer 36 having a concentric liquid crystal orientation pattern, in which the optical axis derived from the liquid crystal compound changes by continuously rotating radially, can transmit incident light in a divergent or convergent manner depending on the rotation direction of the optical axis of the liquid crystal compound 38 and the rotation direction of the incident circularly polarized light. In other words, the liquid crystal lens 34 having such a liquid crystal layer 36 acts, for example, as a concave lens when right-handed circularly polarized light is incident and as a convex lens when left-handed circularly polarized light is incident, depending on the rotation direction of the incident circularly polarized light. Alternatively, the liquid crystal lens 34 acts as a convex lens when right-handed circularly polarized light is incident and as a concave lens when left-handed circularly polarized light is incident. In the illustrated example, for example, the liquid crystal layer 36 acts as a convex lens when left-handed circularly polarized light is incident and focuses light, and acts as a concave lens when right-handed circularly polarized light is incident.

[0050] To achieve natural stereoscopic vision with an HMD, it is preferable that the distance from the HMD user to the observation image can be adjusted from infinity to close to the user's hand. For example, it is preferable that the distance from the HMD user to the observation image can be adjusted from infinity to 25 cm.

[0051] As described above, the optical device 30 extends or shortens the focal length of the display device 10 by switching the switching element 32. The control range of the refractive power of the optical device 30, which can be controlled by switching the switching element 32, is preferably 1 to 5 diopters. For example, if the control range of the refractive power is 4 diopters, in one embodiment, the refractive power of the optical device 30 ranges from 0 to 4 diopters, and in another embodiment, the refractive power of the optical device 30 ranges from -2 to 2 diopters. Here, diopter is a unit of lens refractive power and is the reciprocal of the focal length expressed in meters. If the control range of the refractive power of the optical device 30 is 1 diopter or more, the user can experience an effect that approaches natural stereoscopic vision. Furthermore, by setting the control range of the refractive power of the optical device 30 to 4 diopters, the distance from the user of the HMD to the observed image can be adjusted from infinity to 25 cm.

[0052] In order for the optical device 30 to achieve the above-described control range of refractive power, the absolute value of the refractive power of the liquid crystal lens 34 is preferably 0.01 to 2.5 diopters. As described above, the liquid crystal lens 34 acts as a concave lens when right-handed circularly polarized light is incident, and as a convex lens when left-handed circularly polarized light is incident, depending on the rotation direction of the incident circularly polarized light. For example, a liquid crystal lens 34 with a 2.0 diopter for left-handed circularly polarized light becomes -2.0 diopter for right-handed circularly polarized light. In this case, the control range of the refractive power of the optical device 30 by switching the switching element 32 is 4 diopters. The absolute value of the refractive power of the liquid crystal lens 34 is more preferably 0.01 to 1.5 diopters, and even more preferably 0.5 to 1.0 diopters. By setting the absolute value of the refractive power of the liquid crystal lens 34 within this range, it is possible to prevent image quality from varying depending on the distance from the HMD user to the observed image.

[0053] The optical device 30 may have a multi-stage configuration in which multiple switching elements and multiple liquid crystal lenses are alternately arranged. This allows the refractive power of the optical device 30 to be controlled in stages. When one pair of switching elements and liquid crystal lenses is used, two different refractive powers can be achieved, whereas when two pairs of switching elements and liquid crystal lenses are used, four different refractive powers can be achieved. Furthermore, when four pairs of switching elements and liquid crystal lenses are used, 16 different refractive powers can be achieved. By precisely controlling the refractive power, a natural stereoscopic viewing experience can be provided to the user.

[0054] The liquid crystal lens 34 (liquid crystal layer 36) preferably has an orientation structure that exhibits the above-mentioned refractive power. One period in the liquid crystal layer 36 varies depending on the distance from the optical center. As an example, the minimum value of one period for a lens with a diameter of 5 cm and a refractive power of 1 diopter is approximately 20 μm.

[0055] 2, in order to simplify the drawing and clearly show the configuration of the liquid crystal lens 34, the liquid crystal layer 36 only shows the liquid crystal compounds 38 (liquid crystal compound molecules) on the surface of the alignment film 52. However, as conceptually shown in FIG. 3, the liquid crystal layer 36 has a structure in which aligned liquid crystal compounds 38 are stacked, similar to a liquid crystal layer formed using a composition containing a normal liquid crystal compound.

[0056] The function of this liquid crystal layer 36 will be described in more detail below with reference to a liquid crystal layer 36A having a liquid crystal orientation pattern in which an optical axis 38A derived from the liquid crystal compound 38 changes while continuously rotating in one direction indicated by arrow A, as conceptually shown in a plan view in Fig. 4. Even in the concentric liquid crystal orientation pattern shown in Fig. 2, in which the optical axis changes while continuously rotating in one direction radially from the inside to the outside, the same optical effect as the liquid crystal orientation pattern shown in Fig. 4 is exhibited with respect to the one direction in which the optical axis changes while continuously rotating. In the following description, the optical axis 38A derived from the liquid crystal compound 38 will also be referred to as the "optical axis 38A of the liquid crystal compound 38" or "optical axis 38A."

[0057] In the liquid crystal layer 36A, the liquid crystal compound 38 is two-dimensionally aligned in a plane parallel to one direction indicated by arrow A and the Y direction perpendicular to the direction of arrow A. In FIG. 3 and in FIGS. 5 and 6 described below, the Y direction is perpendicular to the paper surface. In the following description, the "one direction indicated by arrow A" will also be simply referred to as the "direction of arrow A." In the liquid crystal layer 36 shown in FIG. 2, the circumferential direction of the concentric circles in the concentric liquid crystal alignment pattern corresponds to the Y direction in FIG. 4.

[0058] The liquid crystal layer 36A has a liquid crystal orientation pattern in which the orientation of the optical axis 38A derived from the liquid crystal compound 38 changes while continuously rotating along the direction of the arrow A within the plane of the liquid crystal layer 36A. The orientation of the optical axis 38A of the liquid crystal compound 38 changes while continuously rotating in the direction of the arrow A (a predetermined direction), specifically, means that the angle formed between the optical axis 38A of the liquid crystal compound 38 aligned along the direction of the arrow A and the direction of the arrow A varies depending on the position in the direction of the arrow A, and the angle formed between the optical axis 38A and the direction of the arrow A changes sequentially from θ to θ+180° or θ−180° along the direction of the arrow A.

[0059] On the other hand, in the Y direction perpendicular to the direction of arrow A, i.e., the Y direction perpendicular to the direction in which the optical axes 38A continuously rotate, the liquid crystal compounds 38 forming the liquid crystal layer 36A are arranged at equal intervals, with the liquid crystal compounds 38 having the same orientation of the optical axes 38A. In other words, among the liquid crystal compounds 38 forming the liquid crystal layer 36, the angles formed by the orientation of the optical axes 38A and the direction of arrow A are equal among the liquid crystal compounds 38 arranged in the Y direction. In the liquid crystal layer 36 shown in FIG. 2, regions having the same orientation of the optical axes 38A are formed in the shape of rings whose centers coincide, forming a concentric liquid crystal orientation pattern.

[0060] As described above, in a liquid crystal orientation pattern in which the optical axis 38A continuously rotates in one direction, the length (distance) over which the optical axis 38A of the liquid crystal compound 38 rotates 180° is the length Λ of one period in the liquid crystal orientation pattern. That is, in the liquid crystal layer 36A shown in FIG. 4 , the length (distance) over which the optical axis 38A of the liquid crystal compound 38 rotates 180° in the direction of arrow A, in which the orientation of the optical axis 38A continuously rotates and changes in the plane, is defined as one period Λ in the liquid crystal orientation pattern. In other words, one period Λ in the liquid crystal orientation pattern is defined as the distance from the angle θ between the optical axis 38A of the liquid crystal compound 38 and the direction of arrow A to the angle θ + 180°. In other words, one period Λ is the distance between the centers of two liquid crystal compounds 38 that have the same angle with respect to the direction of arrow A. Specifically, as shown in FIG. 4 , one period Λ is the distance between the centers of two liquid crystal compounds 38 whose optical axes 38A coincide with the direction of arrow A. In the liquid crystal layer 36A (liquid crystal layer 36), the liquid crystal orientation pattern repeats this one period Λ in the direction of arrow A, i.e., in one direction in which the orientation of the optical axis 38A continuously rotates and changes. As described above, the liquid crystal layer 36A having such a liquid crystal orientation pattern is also a transmissive liquid crystal diffraction element, and this one period Λ is the period (one period) of the diffraction structure.

[0061] In the liquid crystal layer 36A, the liquid crystal compounds aligned in the Y direction have the same angle between their optical axes 38A and the direction of arrow A. A region in which the liquid crystal compounds 38, whose optical axes 38A and the direction of arrow A form the same angle, are arranged in the Y direction is referred to as region R. In this case, the in-plane retardation (Re) value in each region R is preferably half the wavelength, i.e., λ / 2. This in-plane retardation is calculated by the product of the refractive index difference Δn associated with the refractive index anisotropy of region R and the thickness of the liquid crystal layer. Here, the refractive index difference associated with the refractive index anisotropy of region R in the liquid crystal layer is the refractive index difference defined by the difference between the refractive index in the direction of the slow axis in the plane of region R and the refractive index in the direction perpendicular to the slow axis. In other words, the refractive index difference Δn associated with the refractive index anisotropy of region R is equal to the difference between the refractive index of the liquid crystal compound 38 in the direction of the optical axis 38A and the refractive index of the liquid crystal compound 38 in the direction perpendicular to the optical axis 38A in the plane of region R. In other words, the refractive index difference Δn is equal to the refractive index difference of the liquid crystal compound. In the liquid crystal lens 34 having a concentric liquid crystal orientation pattern in which the optical axis 38A is continuously rotated in one direction, the region formed in an annular shape with the same center and in which the optical axis 38A is oriented in the same direction corresponds to the region R in FIG.

[0062] When circularly polarized light enters such a liquid crystal layer 36A, the light is diffracted and the direction of the circularly polarized light is changed. This effect is conceptually shown in Figures 5 and 6. The liquid crystal layer 36A is assumed to have a value of λ / 2, where the product of the refractive index difference of the liquid crystal compound and the thickness of the liquid crystal layer is λ / 2. As mentioned above, this effect is exactly the same in the liquid crystal lens 34 having a concentric liquid crystal orientation pattern in which the optical axis 38A has a radial liquid crystal orientation pattern that continuously rotates in one direction.

[0063] 5, when the product of the refractive index difference between the liquid crystal compounds in the liquid crystal layer 36 and the thickness of the liquid crystal layer is λ / 2, left-handed circularly polarized incident light L1 enters the liquid crystal layer 36. The incident light L1 is given a phase difference of 180° as it passes through the liquid crystal layer 36A, and the transmitted light L2 is converted into right-handed circularly polarized light. Furthermore, because the liquid crystal orientation pattern formed in the liquid crystal layer 36 is a periodic pattern in the direction of arrow A, the transmitted light L2 travels in a direction different from the traveling direction of the incident light L1. In this way, the left-handed circularly polarized incident light L1 is converted into right-handed circularly polarized transmitted light L2, which is tilted at a certain angle in the direction of arrow A relative to the incident direction.

[0064] On the other hand, as conceptually shown in Figure 6, when the product of the refractive index difference between the liquid crystal compounds in the liquid crystal layer 36A and the thickness of the liquid crystal layer is λ / 2, when right-handed circularly polarized incident light L4 enters the liquid crystal layer 36A, the incident light L4 is given a phase difference of 180° as it passes through the liquid crystal layer 36A and is converted into left-handed circularly polarized transmitted light L5. Furthermore, because the liquid crystal orientation pattern formed in the liquid crystal layer 36A is a periodic pattern in the direction of arrow A, the transmitted light L5 travels in a direction different from the traveling direction of the incident light L4. At this time, the transmitted light L5 travels in a different direction from the transmitted light L2, i.e., in the opposite direction from the direction of arrow A relative to the incident direction. In this way, the incident light L4 is converted into left-handed circularly polarized transmitted light L5 that is tilted at a certain angle in the direction of arrow A relative to the incident direction.

[0065] In the liquid crystal layer 36A, the in-plane retardation value of the plurality of regions R is preferably a half wavelength. The in-plane retardation Re(550) of the plurality of regions R of the liquid crystal layer 36A for incident light having a wavelength of 550 nm is Re(550)=Δn 550 ×d is preferably within the range defined by the following formula (1): 550 is the refractive index difference due to the refractive index anisotropy of the region R when the wavelength of the incident light is 550 nm, and d is the thickness of the liquid crystal layer 36A. 550 ×d≦350 nm (1) That is, the in-plane retardation Re(550) of the plurality of regions R of the liquid crystal layer 36A=Δn 550If ×d satisfies the formula (1), a sufficient amount of the circularly polarized component of the light incident on the liquid crystal layer 36A can be converted into circularly polarized light traveling in a direction inclined forward or backward with respect to the direction of arrow A. In-plane retardation Re(550)=Δn 550 ×d is 225 nm≦Δn 550 ×d≦340 nm is more preferable, and 250 nm≦Δn 550 It is more preferable that ×d≦330 nm. The above formula (1) is a range for incident light having a wavelength of 550 nm, but the in-plane retardation Re(λ) of the plurality of regions R of the liquid crystal layer for incident light having a wavelength of λ nm is λ ×d is preferably within the range defined by the following formula (1-2), and can be set appropriately: 0.7×(λ / 2) nm≦Δn λ ×d≦1.3×(λ / 2)nm...(1-2)

[0066] In addition, the in-plane retardation values ​​of the regions R in the liquid crystal layer 36A may be outside the range of the above formula (1). 550 ×d<200 nm or 350 nm<Δn 550 ×d, it is possible to separate light into light traveling in the same direction as the incident light and light traveling in a direction different from the incident light. 550 When ×d approaches 0 nm or 550 nm, the component of light traveling in the same direction as the incident light increases, and the component of light traveling in a direction different from the incident light decreases.

[0067] As described above, the liquid crystal layer 36A can adjust the diffraction angle of the transmitted light L2 and L5 by changing the period Λ of the formed liquid crystal orientation pattern. Specifically, the shorter the period Λ of the liquid crystal orientation pattern, the stronger the interference between the lights passing through adjacent liquid crystal compounds 38, resulting in greater diffraction of the transmitted light L2 and L5. Furthermore, the liquid crystal layer 36A can reverse the direction of diffraction of the transmitted light by reversing the rotation direction of the optical axis 38A of the liquid crystal compounds 38, which rotates along the direction of arrow A. Furthermore, as described above, the liquid crystal layer 36A reverses the direction of diffraction of the transmitted light depending on the rotation direction of the incident circularly polarized light. That is, the liquid crystal layer 36A diffracts the transmitted light in opposite directions for right-handed and left-handed circularly polarized light. As described above, the above points are similar to those of the liquid crystal layer 36 having a concentric liquid crystal orientation pattern.

[0068] When a liquid crystal having reverse wavelength dispersion is used, it is preferable that the product of the refractive index difference between the liquid crystal compounds in the liquid crystal layer 36A and the thickness of the liquid crystal layer is greater than λ / 2. Specifically, it is particularly preferable that the thickness of the liquid crystal layer in the present invention satisfies the following formula (1-3): 275 nm<Δn 550 × d≦310 nm (1-3)

[0069] The twist angle of the liquid crystal layer is preferably 0° to 30°, more preferably 3° to 20°, and even more preferably 3° to 10°. By doing so, high diffraction efficiency can be obtained for light incident on the liquid crystal layer at an angle.

[0070] The liquid crystal layer 36 is formed using a liquid crystal composition containing a liquid crystal compound, and has a liquid crystal orientation pattern in which the optical axes of the liquid crystal compound are aligned as described above. An alignment film 52 having an orientation pattern corresponding to the above-described liquid crystal orientation pattern is formed on a substrate 50, and a liquid crystal composition is applied to the alignment film 52 and cured, thereby forming the liquid crystal layer 36 consisting of a cured layer of the liquid crystal composition. The liquid crystal composition for forming the liquid crystal layer 36 contains the liquid crystal compound, and may further contain other components such as a leveling agent, an alignment control agent, a polymerization initiator, and an alignment aid.

[0071] In the present invention, the liquid crystal compound 38 constituting the liquid crystal layer 36 is a liquid crystal compound with reverse wavelength dispersion. That is, the liquid crystal layer 36 is formed using a liquid crystal composition containing the liquid crystal compound 38 with reverse wavelength dispersion. The optical device of the present invention has the liquid crystal layer 36 using the liquid crystal compound with reverse wavelength dispersion, and thereby makes it possible to obtain images with stable image quality regardless of the focal length when the focal length of the display device 10 is changed.

[0072] The reverse wavelength dispersion liquid crystal compound refers to a liquid crystal compound that, when the in-plane retardation (Re) value of a retardation film produced by aligning (horizontally aligning) this liquid crystal compound at a specific wavelength (visible light range) is measured, the Re value or Rth value increases as the measured wavelength increases in the range of 450 to 650 nm.

[0073] The ratio Re450 / Re550 of the retardation value Re450 at a wavelength of 450 nm to the retardation value Re550 at a wavelength of 550 nm is preferably 0.6 or more and less than 1.0, more preferably 0.6 or more and less than 0.9, and even more preferably 0.7 or more and less than 0.8.

[0074] The ratio Re650 / Re550 of the retardation value Re650 at a wavelength of 650 nm to the retardation value Re550 at a wavelength of 550 nm is preferably 1.0 or more and less than 1.3.

[0075] Δn of the liquid crystal layer 36 550 is preferably 0.01 or more and less than 0.3, more preferably 0.01 or more and less than 0.15, even more preferably 0.03 or more and less than 0.1, and particularly preferably 0.03 or more and less than 0.06. 550 By controlling the wavelength dispersion coefficient to fall within this range, it is possible to obtain desirable optical characteristics of reverse wavelength dispersion.

[0076] The reverse wavelength dispersion liquid crystal compound is preferably a polymerizable liquid crystal compound having a partial structure represented by the following formula (I): *-D １ -Ar-D ２ - * ... (I)

[0077] In the above formula (I), D １ and D ２ each independently represents a single bond, —O—, —CO—, —CO—O—, —C(═S)O—, or —CR １ R ２ -, -CR １ R ２ -CR ３ R ４ -, -O-CR １ R ２ -, -CR １ R ２ -O-CR ３ R ４ -, -CO-O-CR １ R ２ -, -O-CO-CR １ R ２ -, -CR １ R ２ -CR ３ R ４ -O-CO-, -CR １ R ２ -O-CO-CR ３ R ４ -, -CR １ R ２ -CO-O-CR ３ R ４ -, -NR １ -CR ２ R ３ -, or -CO-NR １ - represents. １ , R ２ , R ３ and R ４ R each independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 4 carbon atoms. １ , R ２ , R ３ and R ４ When there are multiple R １ , multiple R ２ , multiple R ３ and multiple R ４ may be the same or different. Ar represents an aromatic ring selected from the group consisting of groups represented by formulas (Ar-1) to (Ar-7). In the following formulas (Ar-1) to (Ar-7), * represents D １ or D２ The symbols in the following formulae (Ar-1) to (Ar-7) are the same as those explained for Ar in formula (II) below.

[0078]

[0079] As the polymerizable liquid crystal compound having the partial structure represented by the above formula (I), a polymerizable liquid crystal compound represented by the following formula (II) is preferred. The polymerizable liquid crystal compound represented by the following formula (II) is a compound that exhibits liquid crystallinity. １ -G １ -D １ -Ar-D ２ -G ２ -L ２ ... (II)

[0080] In the above formula (II), D １ and D ２ each independently represents a single bond, —O—, —CO—, —CO—O—, —C(═S)O—, or —CR １ R ２ -, -CR １ R ２ -CR ３ R ４ -, -O-CR １ R ２ -, -CR １ R ２ -O-CR ３ R ４ -, -CO-O-CR １ R ２ -, -O-CO-CR １ R ２ -, -CR １ R ２ -CR ３ R ４ -O-CO-, -CR １ R ２ -O-CO-CR ３ R ４ -, -CR １ R ２ -CO-O-CR ３ R ４ -, -NR １ -CR ２ R ３ -, or -CO-NR １ - represents.１ , R ２ , R ３ and R ４ R each independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 4 carbon atoms. １ , R ２ , R ３ and R ４ When there are multiple R １ , multiple R ２ , multiple R ３ and multiple R ４ may be the same or different from each other. １ and G ２ each independently represents a divalent alicyclic hydrocarbon group or aromatic hydrocarbon group having 5 to 8 carbon atoms, and a methylene group contained in the alicyclic hydrocarbon group may be substituted with —O—, —S—, or —NH—. １ and L ２ each independently represents a monovalent organic group; L １ and L ２ At least one selected from the group consisting of represents a monovalent group having a polymerizable group. Ar represents an aromatic ring selected from the group consisting of groups represented by formulas (Ar-1) to (Ar-7). In the following formulas (Ar-1) to (Ar-7), * represents D １ or D ２ represents the bonding position with

[0081]

[0082] In the above formula (Ar-1), Q １ represents N or CH, and Q ２ is -S-, -O-, or -N(R ７ )-, R ７ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; Y １ represents an aromatic hydrocarbon group having 6 to 12 carbon atoms or an aromatic heterocyclic group having 3 to 12 carbon atoms, which may have a substituent. ７Examples of the alkyl group having 1 to 6 carbon atoms represented by Y include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, and an n-hexyl group. １ Examples of the aromatic hydrocarbon group having 6 to 12 carbon atoms represented by Y include aryl groups such as a phenyl group, a 2,6-diethylphenyl group, and a naphthyl group. １ Examples of the aromatic heterocyclic group having 3 to 12 carbon atoms represented by Y include heteroaryl groups such as a thienyl group, a thiazolyl group, a furyl group, and a pyridyl group. １ Examples of the substituent that may be possessed by the alkyl group include an alkyl group, an alkoxy group, and a halogen atom. As the alkyl group, an alkyl group having 1 to 18 carbon atoms is preferred, an alkyl group having 1 to 8 carbon atoms is more preferred, an alkyl group having 1 to 4 carbon atoms is even more preferred, and a methyl group or an ethyl group is particularly preferred. The alkyl group may be linear, branched, or cyclic. As the alkoxy group, for example, an alkoxy group having 1 to 18 carbon atoms is preferred, an alkoxy group having 1 to 8 carbon atoms is more preferred, an alkoxy group having 1 to 4 carbon atoms is even more preferred, and a methoxy group or an ethoxy group is particularly preferred. As the halogen atom, for example, a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom are mentioned, and among these, a fluorine atom or a chlorine atom is preferred.

[0083] In addition, in the above formulas (Ar-1) to (Ar-7), Z １ , Z ２ and Z ３ each independently represents a hydrogen atom, a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, a monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms, a halogen atom, a cyano group, a nitro group, -OR ８ , -NR ９ R １０ , or -SR １１ represents R ８ ~R １１ each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; Z １ and Z ２may be bonded to each other to form an aromatic ring. As the monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, an alkyl group having 1 to 15 carbon atoms is preferred, an alkyl group having 1 to 8 carbon atoms is more preferred, a methyl group, an ethyl group, an isopropyl group, a tert-pentyl group (1,1-dimethylpropyl group), a tert-butyl group, or a 1,1-dimethyl-3,3-dimethyl-butyl group is even more preferred, and a methyl group, an ethyl group, or a tert-butyl group is particularly preferred. Examples of the monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms include monocyclic saturated hydrocarbon groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclodecyl, methylcyclohexyl, and ethylcyclohexyl; monocyclic unsaturated hydrocarbon groups such as cyclobutenyl, cyclopentenyl, cyclohexenyl, cycloheptenyl, cyclooctenyl, cyclodecenyl, cyclopentadienyl, cyclohexadienyl, cyclooctadienyl, and cyclodecadiene; bicyclo[2.2.1]heptyl, bicyclo[2.2.2]octyl, tricyclo[5.2.1.0]dienyl; ２，６ ]decyl group, tricyclo[3.3.1.1 ３，７ ]decyl group, tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] polycyclic saturated hydrocarbon groups such as a dodecyl group and an adamantyl group; etc. Examples of the monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms include a phenyl group, a 2,6-diethylphenyl group, a naphthyl group, and a biphenyl group, with an aryl group having 6 to 12 carbon atoms (particularly a phenyl group) being preferred. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, with a fluorine atom, a chlorine atom, or a bromine atom being preferred.

[0084] In addition, in the above formulas (Ar-2) and (Ar-3), A １ and A ２ are each independently —O—, —N(R １２ represents a group selected from the group consisting of —, —S—, and —CO—; R １２ represents a hydrogen atom or a substituent. １２The substituent represented by the formula (Ar-1) is preferably Y １ Examples of the substituents include the same as those that may be possessed by the group.

[0085] In the formula (Ar-2), X represents a nonmetallic atom of Groups 14 to 16 which may have a substituent bonded thereto. Examples of the nonmetallic atom of Groups 14 to 16 represented by X include an oxygen atom, a sulfur atom, a hydrogen atom, or a nitrogen atom bonded to a substituent [═N—R Ｎ１ , R Ｎ１ represents a hydrogen atom or a substituent.], a carbon atom to which a hydrogen atom or a substituent is bonded [═C—(R Ｃ１ ) ２ , R Ｃ１ represents a hydrogen atom or a substituent. Ｎ１ or R Ｃ１ The substituent of is preferably CN.

[0086] In addition, in the above formula (Ar-3), D ４ and D ５ each independently represents a single bond, or —CO—, —O—, —S—, —C(═S)—, or —CR １ａ R ２ａ -, -CR ３ａ =CR ４ａ -, -NR ５ａ -, or a divalent linking group formed by a combination of two or more thereof, R １ａ ~R ５ａ each independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 4 carbon atoms. Examples of the divalent linking group include -CO-, -O-, -CO-O-, -C(=S)O-, and -CR １ｂ R ２ｂ -, -CR １ｂ R ２ｂ -CR １ｂ R ２ｂ -, -O-CR １ｂ R ２ｂ -, -CR １ｂ R ２ｂ -O-CR １ｂ R ２ｂ -, -CO-O-CR １ｂ R ２ｂ -, -O-CO-CR １ｂ R ２ｂ -, -CR１ｂ R ２ｂ -O-CO-CR １ｂ R ２ｂ -, -CR １ｂ R ２ｂ -CO-O-CR １ｂ R ２ｂ -, -NR ３ｂ -CR １ｂ R ２ｂ - and -CO-NR ３ｂ - is mentioned. １ｂ , R ２ｂ and R ３ｂ each independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 4 carbon atoms.

[0087] In addition, in the above formula (Ar-3), SP １ and SP ２ are each independently a single bond, a linear or branched alkylene group having 1 to 12 carbon atoms, or a —CH ２ represents a divalent linking group in which one or more - is substituted with -O-, -S-, -NH-, -N(Q)-, or -CO-, and Q represents a substituent. １ Examples of the substituents include the same as those that may be possessed by the group.

[0088] In addition, in the above formula (Ar-3), L ３ and L ４Each independently represents a monovalent organic group. Examples of the monovalent organic group include an alkyl group, an aryl group, and a heteroaryl group. The alkyl group may be linear, branched, or cyclic, but is preferably linear. The alkyl group preferably has 1 to 30 carbon atoms, more preferably 1 to 20, and even more preferably 1 to 10. The aryl group may be monocyclic or polycyclic, but is preferably monocyclic. The aryl group preferably has 6 to 25 carbon atoms, more preferably 6 to 10. The heteroaryl group may be monocyclic or polycyclic. The number of heteroatoms constituting the heteroaryl group is preferably 1 to 3. The heteroatoms constituting the heteroaryl group are preferably nitrogen atoms, sulfur atoms, or oxygen atoms. The heteroaryl group preferably has 6 to 18 carbon atoms, more preferably 6 to 12. The alkyl group, aryl group, and heteroaryl group may be unsubstituted or may have a substituent. Examples of the substituent include Y in the above formula (Ar-1). １ Examples of the substituents include the same as those that may be possessed by the group.

[0089] In the above formulae (Ar-4) to (Ar-7), Ax represents an organic group having 2 to 30 carbon atoms and having at least one aromatic ring selected from the group consisting of aromatic hydrocarbon rings and aromatic heterocycles. In the above formulae (Ar-4) to (Ar-7), Ay represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms which may have a substituent, or an organic group having 2 to 30 carbon atoms and having at least one aromatic ring selected from the group consisting of aromatic hydrocarbon rings and aromatic heterocycles. Here, the aromatic rings in Ax and Ay may have a substituent, and Ax and Ay may be bonded to form a ring. In addition, Q ３ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms which may have a substituent. Examples of Ax and Ay include those described in paragraphs

[0039] to

[0095] of Patent Document 1 (WO 2014 / 010325). ３Specific examples of the alkyl group having 1 to 6 carbon atoms represented by include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, and an n-hexyl group. １ Examples of the substituents include the same as those that may be possessed by the group.

[0090] The definition and preferred range of each substituent of the liquid crystal compound represented by formula (II) are described in D relating to compound (A) in JP-A-2012-021068. １ , D ２ , G １ , G ２ , L １ , L ２ , R ４ , R ５ , R ６ , R ７ , X １ , Y １ , Q １ , Q ２ The description regarding D １ , D ２ , G １ , G ２ , L １ , L ２ , R １ , R ２ , R ３ , R ４ , Q １ , Y １ , Z １ , and Z ２ and the A of the compound represented by general formula (I) described in JP-A-2008-107767. １ , A ２ , and the description of X are A １ , A ２ and X, and Ax, Ay, Q for the compound represented by general formula (I) described in WO 2013 / 018526 can be referred to. １ The descriptions for Ax, Ay, and Q are ２ You can refer to Z. ３ Regarding the compound (A) described in JP-A-2012-21068, １Please refer to the description below.

[0091] In particular, L １ and L ２ The organic group represented by the formula: ３ -G ３ -Sp-P ３ It is preferable that the group is a group represented by the following formula: ３ is D １ It is synonymous with G. ３ represents a single bond, a divalent aromatic or heterocyclic group having 6 to 12 carbon atoms, or a divalent alicyclic hydrocarbon group having 5 to 8 carbon atoms, and the methylene group contained in the alicyclic hydrocarbon group is -O-, -S-, or -NR ７ -, where R ７ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. Sp represents a single bond, -(CH ２ ) ｎ -, -(CH ２ ) ｎ -O-, -(CH ２ -O-) ｎ -, -(CH ２ CH ２ -O-) ｍ , —O—(CH ２ ) ｎ -, -O-(CH ２ ) ｎ -O-, -O-(CH ２ -O-) ｎ -, -O-(CH ２ CH ２ -O-) ｍ , -C(=O)-O-(CH ２ ) ｎ -, -C(=O)-O-(CH ２ ) ｎ -O-, -C(=O)-O-(CH ２ -O-) ｎ -, -C(=O)-O-(CH ２ CH ２ -O-) ｍ , -C(=O)-N(R ８ )-(CH ２ ) ｎ -, -C(=O)-N(R ８ )-(CH ２ ) ｎ-O-, -C(=O)-N(R ８ )-(CH ２ -O-) ｎ -, -C(=O)-N(R ８ )-(CH ２ CH ２ -O-) ｍ , or -(CH ２ ) ｎ -O-(C=O)-(CH ２ ) ｎ -C(=O)-O-(CH ２ ) ｎ -, where n is an integer of 2 to 12, m is an integer of 2 to 6, and R ８ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. ２ The hydrogen atom of - may be substituted with a methyl group. ３ represents a polymerizable group.

[0092] The polymerizable group is not particularly limited, but a polymerizable group capable of radical polymerization or cation polymerization is preferred. Examples of the radical polymerizable group include known radical polymerizable groups, with an acryloyl group or a methacryloyl group being preferred. It is known that the polymerization rate of an acryloyl group is generally fast, and an acryloyl group is preferred from the viewpoint of improving productivity, but a methacryloyl group can also be used as a polymerizable group for a highly birefringent liquid crystal. Examples of the cation polymerizable group include known cation polymerizable groups, such as an alicyclic ether group, a cyclic acetal group, a cyclic lactone group, a cyclic thioether group, a spiro orthoester group, and a vinyloxy group. Among these, an alicyclic ether group or a vinyloxy group is preferred, with an epoxy group, an oxetanyl group, or a vinyloxy group being more preferred.

[0093] As described above, the liquid crystal lens 34 includes a substrate 50, an alignment film 52, and the liquid crystal layer 36. The substrate 50 constituting the liquid crystal lens 34 can be made of various sheet-like materials as long as it can support the alignment film 52 and the liquid crystal layer 36 (described later). Transparent substrates are preferred for the substrate 50, and examples of such materials include polyacrylic resin films such as polymethyl methacrylate, cellulose resin films such as cellulose triacetate, cycloolefin polymer films, polyethylene terephthalate (PET), polycarbonate, and polyvinyl chloride. Examples of cycloolefin polymer films include those sold under the trade name "Arton" by JSR Corporation and "Zeonor" by Zeon Corporation. A glass substrate can also be suitably used for the substrate 50.

[0094] An alignment film 52 is formed on the surface of such a substrate 50. The liquid crystal alignment pattern in the liquid crystal layer 36 follows the alignment pattern formed on the alignment film 52. Therefore, the alignment film 52 for forming a liquid crystal layer having such a liquid crystal alignment pattern has the same alignment pattern as the liquid crystal alignment pattern in the liquid crystal layer 36 formed thereon.

[0095] 7 conceptually shows an example of an exposure device that exposes a coating film that will become the alignment film 52 (photo-alignment film) for forming the liquid crystal layer 36 to light to form an alignment pattern corresponding to a concentric liquid crystal alignment pattern in which the optical axis changes radially and continuously rotates. The exposure device 80 shown in FIG. 7 includes a light source 84 equipped with a laser 82, a polarizing beam splitter 86 that splits laser light M from the laser 82 into S-polarized light MS and P-polarized light MP, a mirror 90A arranged in the optical path of the P-polarized light MP, a mirror 90B arranged in the optical path of the S-polarized light MS, a lens 92 arranged in the optical path of the S-polarized light MS, a beam splitter 94, and a quarter-wave plate 96.

[0096] The P-polarized light MP split by the polarizing beam splitter 86 is reflected by a mirror 90A and enters a beam splitter 94. On the other hand, the S-polarized light MS split by the polarizing beam splitter 86 is reflected by a mirror 90B, collected by a lens 92, and enters the beam splitter 94. The P-polarized light MP and the S-polarized light MS are combined by the beam splitter 94 and converted into right- and left-circularly polarized light according to the polarization direction by a quarter-wave plate 96. The combined light then enters the alignment film 52 on the substrate 50. Here, due to interference between the right- and left-circularly polarized light, the polarization state of the light irradiated onto the alignment film 52 changes periodically, like an interference fringe. Because the crossing angle between the left- and right-circularly polarized light changes from the inside to the outside of the concentric circles, an exposure pattern is obtained in which the pitch (one period) gradually decreases from the inside to the outside. This results in a concentric (radial) alignment pattern in the alignment film 52 in which the alignment state changes periodically.

[0097] In this exposure device 80, the period Λ of the liquid crystal orientation pattern in which the optical axis of the liquid crystal compound 38 continuously rotates 180° along one direction can be controlled by changing the refractive power of the lens 92, the focal length of the lens 92, and the distance between the lens 92 and the orientation film 52. Furthermore, by adjusting the refractive power (F-number) of the lens 92, the length of one period of the liquid crystal orientation pattern in one direction in which the optical axis continuously rotates can be changed. Specifically, the length of one period of the liquid crystal orientation pattern in one direction in which the optical axis continuously rotates can be changed by adjusting the spread angle of the light expanded by the lens 92, which interferes with the parallel light. More specifically, when the refractive power of the lens 92 is weakened, the light approaches parallel light, and the length Λ of one period of the liquid crystal orientation pattern gradually shortens from the inside to the outside. Conversely, when the refractive power of the lens 92 is strengthened, the length Λ of one period of the liquid crystal orientation pattern suddenly shortens from the inside to the outside. That is, by adjusting the refractive index of the lens 92, it is possible to adjust the refractive index of the liquid crystal lens 34 (liquid crystal layer 36) which acts as a concave or convex lens depending on the rotation direction of the incident circularly polarized light.

[0098] A liquid crystal composition containing a liquid crystal compound for forming the above-described liquid crystal layer 36 is applied to the exposed alignment film 52 thus formed, dried, and further cured by ultraviolet irradiation, etc., as necessary. This forms the liquid crystal layer 36 having the above-described concentric liquid crystal alignment pattern, in which one period gradually becomes shorter from the center outward, and allows the production of the liquid crystal lens 34 as shown in Figures 2 and 3.

[0099] Compounds having a photo-alignment group, that is, photo-alignment materials used in photo-alignment films, include those disclosed in, for example, JP-A Nos. 2006-285197, 2007-76839, 2007-138138, 2007-94071, 2007-121721, 2007-140465, and 2007-156439. azo compounds described in JP-A-2007-133184, JP-A-2009-109831, Japanese Patent No. 3883848 and Japanese Patent No. 4151746; aromatic ester compounds described in JP-A-2002-229039; maleic anhydrides having a photo-alignable unit described in JP-A-2002-265541 and JP-A-2002-317013; Preferred examples include imide and / or alkenyl-substituted nadimide compounds, photocrosslinkable silane derivatives described in Japanese Patent Nos. 4205195 and 4205198, photocrosslinkable polyimides, photocrosslinkable polyamides, and photocrosslinkable esters described in JP-T-2003-520878, JP-T-2004-529220, and JP-T-4162850, and photodimerizable compounds described in JP-A-9-118717, JP-A-10-506420, JP-A-2003-505561, WO 2010 / 150748, JP-A-2013-177561, and JP-A-2014-12823, particularly cinnamate compounds, chalcone compounds, and coumarin compounds. Among these, azo compounds, photocrosslinkable polyimides, photocrosslinkable polyamides, photocrosslinkable esters, cinnamate compounds, and chalcone compounds are preferably used.

[0100] The display device 10 will be described in more detail below by explaining the operation of the optical device 30 with reference to the conceptual diagram in Fig. 8. As described above, the image emitted from the light-collecting optical system of the display device 10, which is configured to include the half mirror 16, the lens 18, the circularly polarized reflective polarizer 24, and the circular polarizer 26, is a left-handed circularly polarized image. Furthermore, this left-handed circularly polarized image is incident on the optical device 30, i.e., the switching element 32 and the liquid crystal lens 34, in a state where it is collected by the light-collecting optical system (lens 18).

[0101] In the optical device 30, the switching element 32 is an element that switches between an off state in which the phase difference is zero and an on state in which the phase difference is half the wavelength and the element acts as a half-wave plate. Furthermore, the liquid crystal lens 34 (liquid crystal layer 36), for example, acts as a convex lens for left-handed circularly polarized light to focus the light, and acts as a concave lens for right-handed circularly polarized light to diverge the light. However, the present invention is not limited to this, and the liquid crystal lens 34 (liquid crystal layer 36) may also diverge left-handed circularly polarized light and diverge right-handed circularly polarized light.

[0102] In Figure 8, the dashed line indicates the state of focusing of a left-handed circularly polarized image by the focusing optical system consisting of the half mirror 16, lens 18, circularly polarized reflective polarizer 24, and circular polarizer 26. The focal point, i.e., the focal point of the lens 18, is designated as FO. The image output from the focusing optical system (circular polarizer 26) is a left-handed circularly polarized image. Therefore, when the switching element 32 is in the off state, the left-handed circularly polarized image passes through the switching element 32 as is and enters the liquid crystal lens 34 as left-handed circularly polarized light. The liquid crystal lens 34 (liquid crystal layer 36) focuses left-handed circularly polarized light and diverges right-handed circularly polarized light. Therefore, in this state, the left-handed circularly polarized image that is focused by the focusing optical system and enters the liquid crystal lens 34 is further focused and converted to right-handed circularly polarized light by the liquid crystal lens 34, as shown by the dashed line in Figure 8. As a result, this right-handed circularly polarized image is focused at a focal point FL, which has a shorter focal length than the focal point FP.

[0103] On the other hand, when the switching element 32 is in the on state, the left-handed circularly polarized image is converted to right-handed circularly polarized light by the switching element 32, which acts as a half-wave plate, and enters the liquid crystal lens 34. The liquid crystal lens 34 (liquid crystal layer 36) focuses left-handed circularly polarized light and diverges right-handed circularly polarized light. Therefore, in this state, the right-handed circularly polarized image that is focused by the focusing optical system and enters the liquid crystal lens 34 is diverged by the liquid crystal lens 34 while maintaining the focused state, as shown by the two-dot chain line in FIG. 8, and is converted to left-handed circularly polarized light. In other words, the right-handed circularly polarized image that is focused by the focusing optical system and enters the liquid crystal lens 34 is focused less by the liquid crystal lens 34, as shown by the two-dot chain line in FIG. 8, and is converted to left-handed circularly polarized light. As a result, this left-handed circularly polarized image is focused at the focal point FR, which has a longer focal length than the focal point FP.

[0104] In this way, the display device 10 using the optical device of the present invention can change the focal length of the image observed by the user O by switching the phase difference using the switching element 32, thereby making it possible to change the sense of depth of the virtual reality image, etc. Here, the display device 10 using the optical device 30 of the present invention can display (project) an image with stable image quality regardless of the focus, even when the focus of the image observed by the user O is changed.

[0105] As described in Patent Document 1, the focal length of an observed image in an HMD can be switched by using a switchable half-wave plate (SHWP) and a liquid crystal lens. However, according to the inventor's investigations, in a conventional HMD, when the focal length is switched using a switchable half-wave plate and a liquid crystal lens, an appropriate image can be displayed at a certain focal length, but at another focal length, ghost images caused by light leakage or the like increase. In the case of a full-color image, changing the focal length can cause problems such as deterioration in the image quality of any of the red, green, and blue images, resulting in unstable image quality depending on the focal length.

[0106] In contrast, the optical device 30 of the present invention is an optical device having a switching element capable of switching the phase difference and a liquid crystal layer, and uses a liquid crystal layer 36 formed using a liquid crystal composition containing a liquid crystal compound with reverse wavelength dispersion. That is, the optical device of the present invention has a liquid crystal layer 36 formed using a liquid crystal compound with reverse wavelength dispersion. Therefore, as will be shown in the examples later, the optical device of the present invention exhibits little change in image quality when the focal length of an HMD or the like is switched, and stable image quality can be obtained for all red, green, and blue images regardless of the focal length. Furthermore, when changing the focal length of an HMD or the like using the optical device of the present invention, it is sufficient to slightly focus or diverge the focused light.

[0107] 1 and 8 , the display device 10 includes only one optical device 30 of the present invention, but the present invention is not limited to this. That is, a display device such as an HMD that uses the optical device of the present invention may include multiple optical devices 30 of the present invention, each of which is composed of a switching element and a liquid crystal layer. Furthermore, when a display device includes multiple optical devices 30, it is preferable that the liquid crystal layer 36 of at least one optical device has a different period Λ from the liquid crystal layers 36 of the other optical devices 30. Furthermore, when a display device includes multiple optical devices 30, it is more preferable that the liquid crystal layers 36 of all optical devices have different periods Λ.

[0108] As shown in FIGS. 1 and 8 , when a display device has only one optical device 30, the focal length can be switched between two. In contrast, when a display device has multiple optical devices 30, the focal length of the display device can be switched between three or more, depending on the number of optical devices 30. In particular, by varying the period Λ of the liquid crystal layer 36 of the optical device 30, the focal length of the display device can be switched between a greater number of focal lengths. For example, when a display device has two optical devices, a first and a second, and the periods Λ of the liquid crystal layers of both optical devices are equal, three focal lengths are possible: first device on / second device on, first device off / second device off, and first device on / second device off. Note that the on / off state of each device here refers to the on / off state of the switching element of the optical device. Note that the focal lengths of the first device on / second device off and the first device off / second device on are the same. In contrast, when a display device has two optical devices, a first and a second, and the periods Λ of the liquid crystal layers of the two optical devices are different, four focal lengths are possible: first device on / second device on, first device off / second device off, first device on / second device off, and first device off / second device on. In this case, having three or more optical devices enables switching between more focal lengths by switching each device on and off.

[0109] 1 , in a preferred embodiment, the optical device of the present invention is disposed downstream of the focusing optical system. However, the present invention is not limited to this configuration, and the optical device of the present invention may be disposed upstream of the focusing optical system or within the focusing optical system. However, in this configuration, it may be necessary to add a quarter-wave plate to rotate the circularly polarized light emitted from the focusing optical system in a predetermined direction, and control of the focal length may become complicated.

[0110] Although the liquid crystal layer shown in FIG. 2 has a concentric circular liquid crystal orientation pattern, the present invention is not limited thereto, and various liquid crystal orientation patterns can be used. One example is a liquid crystal orientation pattern conceptually shown in FIG. 9, in which circular patterns of different sizes are arranged with larger circles sequentially enclosing smaller circles and with their centers shifted. Furthermore, the liquid crystal orientation pattern is not limited to a circular pattern, and may be an elliptical or oval pattern conceptually shown in FIG. 10. That is, the present invention can use various liquid crystal orientation patterns having multiple rings of different sizes, in which larger rings sequentially enclose smaller rings in a plane. In the present invention, the term "ring" refers to a shape without edges, such as a circle, an ellipse, or a rectangle.

[0111] Furthermore, in the present invention, the liquid crystal orientation pattern in the liquid crystal layer is not limited to one having multiple rings. For example, it may be a linear liquid crystal orientation pattern, as shown in FIG. 4, in which the orientation of the optical axis derived from the liquid crystal compound continuously changes in only one direction. A liquid crystal layer having a linear liquid crystal orientation pattern refracts circularly polarized light in the direction of rotation of the optical axis, i.e., the direction of arrow A or the direction opposite to the direction of arrow A, depending on the rotation direction of the incident circularly polarized light, as shown in FIGS. 5 and 6. In other words, by using a liquid crystal layer having a linear liquid crystal orientation pattern, the traveling direction of light can be changed to two (or more) types. For example, by using an optical device having such a liquid crystal layer in an image display device, the display position of an image can be changed. Such a linear liquid crystal orientation pattern can be formed by exposing an alignment film 52 using an exposure apparatus such as that shown in FIG. 7 of JP 2022-36995 A.

[0112] It should be noted that, in these various liquid crystal alignment patterns, it is preferable to have regions with different periods in the plane, just as in the case of the concentric circular liquid crystal alignment pattern.

[0113] The number of optical devices included in the display device, the positions of the optical devices, and the liquid crystal orientation patterns of the liquid crystal layers included in the optical devices described above are similar to those of the AR glasses and the like described below.

[0114] The above example is an example in which the optical device 30 of the present invention is used in the VR image display device 10 as an HMD, but the present invention is not limited to this. As an example, the optical device 30 of the present invention can also be used in an AR image display device (AR glasses) that is an HMD.

[0115] An example of such a configuration is conceptually shown in FIG. 11 . The AR glasses 60 shown in FIG. 11 use multiple components identical to those of the display device 10 described above, and therefore the same components are denoted by the same reference numerals, and the following description will focus mainly on the different components. The AR glasses 60 shown in FIG. 11 are worn, for example, as eyeglasses, and allow a user O to observe an image displayed on the display 12 superimposed on a background, a so-called augmented reality (AVR). In the AR glasses 60, an image displayed on the display 12 is focused by a lens 62, transmitted through a light guide plate 68, and incident on an incident diffraction element 64. The incident diffraction element 64 is a reflective diffraction element that diffracts and reflects an image that has passed through the light guide plate 68 and is incident on the light guide plate 68 at an angle at which the image is totally reflected and propagated within the light guide plate 68.

[0116] The image that has propagated through the light guide plate 68 then enters the output diffraction element 70. The output diffraction element 70 is a reflective diffraction element that diffracts and reflects the image that has propagated through the light guide plate 68 by total reflection, causing it to exit the light guide plate 68.

[0117] The lens 62 (condensing lens) and the light guide plate 68 can be any of various known types used in AR glasses. The input diffraction element 64 and output diffraction element 70 can also be any of various known reflective diffraction elements (diffraction gratings), such as a surface relief diffraction element, a holographic diffraction element, and a reflective liquid crystal diffraction element. While the illustrated AR glasses 60 use a reflective diffraction element to input and output images to the light guide plate 68, the present invention is not limited to this. A transmissive diffraction element may also be used to input and output images to the light guide plate 68. In this case, the transmissive diffraction element can also be any known diffraction element, such as a transmissive liquid crystal diffraction element.

[0118] The image emitted from the light guide plate 68 is converted into, for example, left-handed circularly polarized light by the circular polarizer 14 and then enters the optical device 30 of the present invention. As explained with reference to FIG. 8 , in the AR glasses 60, the switching element 32 of the optical device 30 is turned off and left-handed circularly polarized light is incident on the liquid crystal lens 34 (liquid crystal layer 36) as left-handed circularly polarized light, thereby focusing the image at the focal point FL with a short focal length. Furthermore, the switching element 32 of the optical device 30 is turned on and left-handed circularly polarized light is converted into right-handed circularly polarized light and incident on the liquid crystal lens 34, thereby focusing the image at the focal point FR with a long focal length. Even in this case, the AR glasses using the optical device 30 of the present invention experience little change in image quality when the focal length is switched, and stable image quality can be obtained for all red, green, and blue images regardless of the focal length.

[0119] The above examples show the optical device of the present invention being used in a VR image display device and AR glasses, but the present invention is not limited thereto. That is, the optical device of the present invention can be used for various purposes. One example is a handling device that changes the direction of propagation of electromagnetic waves in communication applications.

[0120] The optical device and head-mounted display of the present invention have been described in detail above, but the present invention is not limited to the above-described examples, and various improvements and modifications may be made without departing from the spirit of the present invention.

[0121] The features of the present invention will be explained in more detail below with reference to examples. The materials, reagents, amounts used, amounts of substances, ratios, treatment details, and treatment procedures shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0122] <Preparation of Liquid Crystal Layer (Liquid Crystal Lens)> [Comparative Example 1] (Support) A glass substrate was prepared as a support.

[0123] (Formation of Orientation Film) The following coating solution for forming an alignment film was applied to a support by spin coating. The support on which the coating film of the coating solution for forming an alignment film had been formed was dried on a hot plate at 60° C. for 60 seconds to form an alignment film.

[0124] Coating liquid for forming alignment film ----------------------------------- Photoalignment material A 1.00 parts by mass Water 16.00 parts by mass Butoxyethanol 42.00 parts by mass Propylene glycol monomethyl ether 42.00 parts by mass ---------------------------------------------------

[0125] -Photo alignment material A-

[0126] (Exposure of Alignment Film) The formed alignment film was exposed using an exposure device 80 shown in FIG. 7 to form an alignment film P-1 having a concentric (radial) alignment pattern in which short straight lines (short lines) change while continuously rotating in one direction, as shown in FIG. 2. The period Λ of the alignment pattern of the alignment film varies within the plane, but its minimum value was set to 10 μm. The period Λ of the alignment pattern was adjusted by the focal length of the lens 92 used in the exposure device 80 shown in FIG. 7. A light source emitting laser light with a wavelength of 355 nm was used. The exposure dose by interference light was 1000 mJ / cm. 2 It was decided.

[0127] (Formation of Liquid Crystal Layer) The following liquid crystal composition A-1 was prepared as a liquid crystal composition for forming the liquid crystal layer A-1. The following liquid crystal compound L-1 is a liquid crystal compound with forward wavelength dispersion. Liquid Crystal Composition A-1 ----------------------------------- Liquid Crystal Compound L-1 100.00 parts by mass Polymerization initiator (Irgacure OXE01, manufactured by BASF) 1.00 part by mass Leveling agent T-1 0.08 part by mass Methyl ethyl ketone 1050.00 parts by mass -----------------------------------

[0128] Liquid crystal compound L-1

[0129] Leveling agent T-1

[0130] The liquid crystal layer was formed by applying liquid crystal composition A-1 in multiple layers on the alignment film P-1. Multilayer application refers to the process of first applying liquid crystal composition A-1 as a first layer on the alignment film, heating it, and then curing it with ultraviolet light to form a liquid crystal fixation layer, and then repeatedly applying layers from the second layer onwards to the liquid crystal fixation layer, and similarly heating it and curing it with ultraviolet light. By forming the liquid crystal layer by multilayer application, the alignment direction of the alignment film is reflected from the bottom surface to the top surface of the liquid crystal layer, even when the total thickness of the liquid crystal layer is large.

[0131] First, the first layer was formed by applying the liquid crystal composition A-1 to the alignment film P-1, heating the coating to 80°C on a hot plate, and then irradiating the coating with ultraviolet light of 365 nm wavelength at 300 mJ / cm using a high-pressure mercury lamp in a nitrogen atmosphere. 2 The orientation of the liquid crystal compound was fixed by irradiating the coating film with an irradiation amount of 1000 nm. From the second layer onwards, this liquid crystal fixing layer was recoated, and heated under the same conditions as above, followed by UV curing to produce a liquid crystal fixing layer. In this way, recoating was repeated until the desired total thickness was reached, and a liquid crystal layer A-1 (transmission type liquid crystal lens (liquid crystal diffraction element)) was produced.

[0132] The refractive index difference Δn of the cured layer of liquid crystal composition A-1 was determined by measuring the retardation value and film thickness of the liquid crystal fixed layer (cured layer) obtained by applying liquid crystal composition A-1 to a separately prepared support with an alignment film for retardation measurement, aligning the director of the liquid crystal compound horizontally to the substrate, and then irradiating with ultraviolet light to fix the layer. Δn can be calculated by dividing the retardation value by the film thickness. The retardation value was measured at the desired wavelength using an Axometrix Axoscan, and the film thickness was measured using a scanning electron microscope (SEM).

[0133] The liquid crystal layer A-1 finally has a Δn 550 It was confirmed by a polarizing microscope that the thickness (=Re(550)) of the liquid crystal layer A-1 was 275 nm, and that the liquid crystal layer A-1 had a concentric circular liquid crystal orientation pattern as shown in FIG. 2. In the liquid crystal orientation pattern of the liquid crystal layer A-1, the optical axis of the liquid crystal compound rotated 180° over one period of 53 μm at a distance of approximately 10 mm from the center, 27 μm at a distance of 20 mm from the center, and 10.7 μm at a distance of 25 mm from the center, resulting in a liquid crystal orientation pattern in which the period became shorter outward. In addition, in the liquid crystal layer A-1, the twist angle of the liquid crystal compound in the thickness direction was 0° in-plane.

[0134] The liquid crystal layer A-1 thus obtained had the property of diverging incident light when right-handed circularly polarized light was incident thereon and converging incident light when left-handed circularly polarized light was incident thereon. The liquid crystal layer A-1 also had an effective diameter of 50 mm and a refractive power of 2D.

[0135] Comparative Example 2 As a liquid crystal composition for forming the first region of the liquid crystal layer B-1, 0.33 parts by mass of the following chiral dopant C-2 was added to the liquid crystal composition A-1 to obtain a liquid crystal composition B-1.

[0136] Chiral agent C-2

[0137] A first region of the liquid crystal layer B-1 was formed in the same manner as the liquid crystal layer A-2, except that the liquid crystal composition B-1 was used instead of the liquid crystal composition A-1 and the thickness of the liquid crystal layer was adjusted.

[0138] The first region finally becomes the Δn 550 It was confirmed using a polarizing microscope that the thickness (=Re(550)) of the first region was 180 nm and that it had a concentric liquid crystal orientation pattern as shown in Figure 2. In the liquid crystal orientation pattern of the first region, the period in which the optical axis of the liquid crystal compound rotates by 180° was 53 μm at a distance of approximately 10 mm from the center, 27 μm at a distance of 20 mm from the center, and 10.7 μm at a distance of 25 mm from the center, resulting in a liquid crystal orientation pattern in which the period became shorter toward the outside. In addition, in the first region, the twist angle of the liquid crystal compound in the thickness direction was 80° in-plane.

[0139] Subsequently, a second region of the liquid crystal layer B-1 was formed on the first region of the liquid crystal layer B-1 by the same procedure as above, except that the liquid crystal composition A-1 was used and the thickness of the liquid crystal layer was adjusted.

[0140] The second region finally becomes the Δn 550 It was confirmed by a polarizing microscope that the thickness (=Re(550)) of the second region was 365 nm and that the liquid crystal layer had a concentric circular liquid crystal orientation pattern as shown in Figure 2. In the liquid crystal orientation pattern of the second region, the optical axis of the liquid crystal compound rotated 180° over one period of 53 μm at a distance of approximately 10 mm from the center, 27 μm at a distance of 20 mm from the center, and 10.7 μm at a distance of 25 mm from the center, resulting in a liquid crystal orientation pattern in which the period became shorter outward. In addition, in the second region of the liquid crystal layer B-1, the twist angle of the liquid crystal compound in the thickness direction was 0° in-plane.

[0141] A liquid crystal composition C-1 was obtained by adding 0.54 parts by mass of the following chiral dopant C-1 to the liquid crystal composition A-1.

[0142] Chiral agent C-1

[0143] A third region of the liquid crystal layer was formed on the second region in the same manner as the first region, except that liquid crystal composition C-1 was used, to prepare a liquid crystal layer B-1 (transmissive liquid crystal lens) consisting of the first region, the second region, and the third region.

[0144] The third region finally becomes the Δn 550It was confirmed by a polarizing microscope that the thickness (=Re(550)) of the first region was 180 nm and that the film had a concentric liquid crystal orientation pattern as shown in Figure 7. In the liquid crystal orientation pattern of the first region, the period in which the optical axis of the liquid crystal compound rotated by 180° was 53 μm at a distance of approximately 10 mm from the center, 27 μm at a distance of 20 mm from the center, and 10.7 μm at a distance of 25 mm from the center, resulting in a liquid crystal orientation pattern in which the period became shorter outward. In addition, in the third region, the twist angle of the liquid crystal compound in the thickness direction was -80° in-plane.

[0145] The liquid crystal layer B-1 thus obtained had the property of diverging incident light when right-handed circularly polarized light was incident thereon and converging incident light when left-handed circularly polarized light was incident thereon. The liquid crystal layer B-1 also had an effective diameter of 50 mm and a refractive power of 2D.

[0146] Example 1 Liquid crystal composition A-2 was prepared in the same manner as liquid crystal composition A-1, except that liquid crystal compound L-1 was replaced with liquid crystal compound L-2 and 0.02 parts by mass of chiral dopant C-2 was added. This liquid crystal compound L-2 is a liquid crystal compound with reverse wavelength dispersion.

[0147] Liquid crystal compound L-2

[0148] A liquid crystal layer A-2 (transmission type liquid crystal lens) was prepared in the same manner as for the liquid crystal layer A-1, except that the liquid crystal composition A-2 was used instead of the liquid crystal composition A-1.

[0149] The liquid crystal layer A-2 finally has a Δn 550 It was confirmed by a polarizing microscope that the thickness (=Re(550)) of the liquid crystal layer A-2 was 275 nm and that it had a concentric liquid crystal orientation pattern as shown in FIG. 2. In the liquid crystal orientation pattern of the liquid crystal layer A-2, the optical axis of the liquid crystal compound rotated 180° over one period of 53 μm at a distance of approximately 10 mm from the center, 27 μm at a distance of 20 mm from the center, and 10.7 μm at a distance of 25 mm from the center, resulting in a liquid crystal orientation pattern in which the period became shorter outward. In addition, in the liquid crystal layer A-2, the twist angle of the liquid crystal compound in the thickness direction was 7° in-plane.

[0150] The liquid crystal layer A-2 thus obtained had the property of diverging incident light when right-handed circularly polarized light was incident thereon and converging incident light when left-handed circularly polarized light was incident thereon. The liquid crystal layer A-2 also had an effective diameter of 50 mm and a refractive power of 2D.

[0151] Example 1-2 A liquid crystal layer A-3 (transmissive liquid crystal lens) was produced in the same manner as the liquid crystal layer A-2, except that the focal length of the lens 92 in the exposure device 80 shown in Figure 7 was adjusted during exposure of the alignment film. In the liquid crystal alignment pattern of the liquid crystal layer A-3, the optical axis of the liquid crystal compound rotated 180° over one period of 107 μm at a distance of approximately 10 mm from the center, 53 μm at a distance of 20 mm from the center, and 21.3 μm at a distance of 25 mm from the center, resulting in a liquid crystal alignment pattern in which the period became shorter outward. The liquid crystal layer A-3 had an effective diameter of 50 mm and a refractive power of 1 D.

[0152] Example 1-3 A liquid crystal layer A-4 (transmissive liquid crystal lens) was produced in the same manner as the liquid crystal layer A-2, except that the focal length of the lens 92 in the exposure device 80 shown in Figure 7 was adjusted during exposure of the alignment film. In the liquid crystal alignment pattern of the liquid crystal layer A-4, the optical axis of the liquid crystal compound rotated 180° over one period of 213 μm at a distance of approximately 10 mm from the center, 107 μm at a distance of 20 mm from the center, and 42.6 μm at a distance of 25 mm from the center, resulting in a liquid crystal alignment pattern in which the period became shorter outward. The liquid crystal layer A-4 had an effective diameter of 50 mm and a refractive power of 0.5 D.

[0153] Example 1-4 A liquid crystal layer A-5 (transmissive liquid crystal lens) was produced in the same manner as the liquid crystal layer A-2, except that the focal length of the lens 92 in the exposure device 80 shown in Figure 7 was adjusted during exposure of the alignment film. In the liquid crystal alignment pattern of the liquid crystal layer A-5, the optical axis of the liquid crystal compound rotated 180° over one period of 426 μm at a distance of approximately 10 mm from the center, 213 μm at a distance of 20 mm from the center, and 85 μm at a distance of 25 mm from the center, resulting in a liquid crystal alignment pattern in which the period became shorter outward. The liquid crystal layer A-5 had an effective diameter of 50 mm and a refractive power of 0.25 D.

[0154] Example 2 Liquid crystal composition A-6 was prepared in the same manner as liquid crystal composition A-2, except that liquid crystal compound L-1 was replaced with liquid crystal compound L-3, which is a liquid crystal compound with reverse wavelength dispersion.

[0155] Liquid crystal compound L-3

[0156] A liquid crystal layer A-6 (transmission type liquid crystal lens) was prepared in the same manner as for the liquid crystal layer A-2, except that the liquid crystal composition A-6 was used instead of the liquid crystal composition A-2. In the liquid crystal layer A-6, the twist angle of the liquid crystal compound in the thickness direction was 7° in-plane.

[0157] [Example 3] The following liquid crystal composition A-7 was prepared as a liquid crystal composition for forming a liquid crystal layer A-7. Note that the following liquid crystal compounds L-3 and L-4 are liquid crystal compounds with reverse wavelength dispersion, and liquid crystal compounds L-1 and L-5 are liquid crystal compounds with normal wavelength dispersion, but the composition as a whole exhibits reverse wavelength dispersion.

[0158] Liquid crystal composition A-7 ----------------------------------- Liquid crystal compound L-1 10.34 parts by mass Liquid crystal compound L-3 43.10 parts by mass Liquid crystal compound L-4 20.75 parts by mass Liquid crystal compound L-5 4.95 parts by mass Polymerization initiator (Irgacure OXE01, manufactured by BASF) 1.00 part by mass Leveling agent T-1 0.08 part by mass Methyl ethyl ketone 805.00 parts by mass Cyclopentanone 245.00 parts by mass ---------------------------------------------------

[0159] Liquid crystal compound L-4

[0160] Liquid crystal composition L-5

[0161] A liquid crystal layer A-7 (transmission type liquid crystal lens) was prepared in the same manner as for the liquid crystal layer A-2, except that liquid crystal composition A-7 was used instead of liquid crystal composition A-2. In the liquid crystal layer A-7, the twist angle of the liquid crystal compound in the thickness direction was 7° in-plane.

[0162] Example 4 The thickness of the liquid crystal layer A-2 was changed to finally 550 A liquid crystal layer A-8 (transmission type liquid crystal lens) was prepared in the same manner as for the liquid crystal layer A-2, except that the thickness (= Re(550)) was set to 300 nm. In the liquid crystal layer A-8, the twist angle of the liquid crystal compound in the thickness direction was 7° in-plane.

[0163] (Evaluation of Liquid Crystal Layer) The prepared liquid crystal layer (liquid crystal lens) was evaluated according to the following criteria. The evaluation coordinate was the position where the length of one period was 40 μm, where the length of the 180° rotation of the optical axis direction of the liquid crystal compound in one direction, in which the orientation of the optical axis of the liquid crystal compound changes while continuously rotating, was defined as one period. Blue (450 nm), green (532 nm), and red (650 nm) laser light was incident on the liquid crystal layer at an oblique angle of 40° at the evaluation coordinate. The laser light was incident perpendicularly onto a circular polarizer corresponding to the wavelength of the laser light to convert it into left-handed circularly polarized light and right-handed circularly polarized light, and then incident on the prepared liquid crystal diffraction element. Under a total of six conditions, combining two conditions for left-handed circular polarization and three conditions for the wavelength of the incident light, the maximum value of zero-order leakage light (maximum transmittance of the linear component) that was transmitted through the liquid crystal diffraction element and not diffracted was used as the evaluation value. A+: The maximum value of zero-order leakage light is less than 1.6%. A: The maximum value of zero-order leakage light is 1.6% or more and less than 2%. B: The maximum value of zero-order leakage light is 2% or more and less than 5%. C: The maximum value of zero-order leakage light is 5% or more and less than 8%. D: The maximum value of zero-order leakage light is 8% or more.

[0164] The results are shown in Table 1 below. Table 1 also lists the Δn(550) of the liquid crystal layer at 550 nm, the dispersibility on the short wavelength side, the dispersibility on the long wavelength side, the minimum period (minimum pitch width) in the liquid crystal alignment pattern, and the refractive power.

[0165]

[0166] <Fabrication of Optical Device 101> A VA-mode liquid crystal cell was prepared as the switching element 51. This switching element had a phase difference of 275 nm in the voltage-on state and a phase difference of 5 nm or less in the voltage-off state. Both phase differences were measured at a wavelength of 550 nm. When right-handed circularly polarized light was incident on the switching element in the voltage-on state, the transmitted light was left-handed circularly polarized, and when right-handed circularly polarized light was incident on the switching element in the voltage-off state, the transmitted light was right-handed circularly polarized.

[0167] The liquid crystal layer A-2 was peeled off from the support and attached to one side of the switching element 51 via an adhesive, thereby obtaining an optical device 101 having the switching element 51, adhesive, and liquid crystal layer A-2 in this order.

[0168] When right-handed circularly polarized light was incident from the switching element 51 side of the optical device 101, if the voltage to the switching element 51 was turned ON, the optical device 101 functioned as a condensing lens with a refractive power of 2D. Furthermore, if the voltage to the switching element 51 was turned OFF, the optical device 101 functioned as a diverging lens with a refractive power of -2D. It was confirmed that the refractive power could be switched between two levels by switching the voltage of the switching element 51 between ON and OFF.

[0169] <Fabrication of Optical Devices 102 to 105> Optical devices 102 to 105 were obtained in the same manner as optical device 101, except that liquid crystal layers A-6 and A-7, and liquid crystal layers A-1 and B-1 were used instead of liquid crystal layer A-2.

[0170] <Fabrication of Optical Device 111> The liquid crystal layer A-3 was peeled from the support and attached to one surface of the first switching element 51 via an adhesive. Furthermore, the second switching element 51 was attached to the other surface of the liquid crystal layer A-3 via an adhesive. Furthermore, the second liquid crystal layer A-3 was attached via an adhesive. In this way, an optical device 111 was obtained which had, in this order, the first switching element 51, adhesive, the first liquid crystal layer A-3, adhesive, the second switching element 51, adhesive, and the second liquid crystal layer A-3.

[0171] Because the optical device 111 includes the first and second switching elements 51, there are four voltage application states. When right-handed circularly polarized light is incident from the first switching element 51 side of the optical device 111, the optical device 111 functions as a condensing lens with a refractive power of 2D when the voltage of the first switching element is ON and the voltage of the second switching element is OFF. Furthermore, when the voltage of the first switching element is OFF and the voltage of the second switching element is ON, the optical device 111 functions as a diverging lens with a refractive power of -2D. Furthermore, when the voltage of the first switching element is OFF and the voltage of the second switching element is ON, and when the voltage of the first switching element is ON and the voltage of the second switching element is OFF, the refractive power is 0, i.e., the optical device 111 does not function as a lens. From the above, it was confirmed that the optical device 111 can switch between three refractive powers.

[0172] <Fabrication of Optical Device 112> By repeating the same procedure as for optical device 111, optical device 112 was obtained, which had, in this order, a first switching element 51, an adhesive, a first liquid crystal layer A-3, an adhesive, a second switching element 51, an adhesive, a second liquid crystal layer A-4, an adhesive, a third switching element 51, an adhesive, and a third liquid crystal layer A-4. Because optical device 112 includes first, second, and third switching elements 51, there are eight different voltage application states. It was confirmed that by switching the voltage application state, the refractive power could be switched among a total of five states: 2D, 1D, 0, -1D, and -2D.

[0173] <Fabrication of Optical Device 113> By repeating the same procedure as for optical device 111, optical device 113 was obtained, which had, in this order, a first switching element 51, an adhesive, a first liquid crystal layer A-3, an adhesive, a second switching element 51, an adhesive, a second liquid crystal layer A-4, an adhesive, a third switching element 51, an adhesive, a third liquid crystal layer A-5, an adhesive, a fourth switching element 51, an adhesive, and a fourth liquid crystal layer A-5. Because optical device 112 includes first, second, third, and fourth switching elements 51, there are 16 different voltage application states. It was confirmed that by switching the voltage application state, the refractive power could be switched among a total of nine different states: 2D, 1.5D, 1D, 0.5D, 0, -0.5D, -1D, -1.5D, and -2D.

[0174] <Fabrication of a virtual reality image display device> A commercially available microdisplay (manufactured by SeeYa, screen size 0.49 inches) was prepared, and a plano-convex lens (manufactured by Thorlab, LA1145-A) was placed in front of it. When an observer looked at the microdisplay through the plano-convex lens, they were able to observe a virtual image of the image displayed on the microdisplay, confirming that it functioned as a virtual reality image display device.

[0175] By further arranging optical devices 101 to 105 on the observer side of the plano-convex lens, virtual reality image display devices 101 to 105 are obtained. By switching the state of applied voltage, the position of the virtual image displayed on the microdisplay can be switched.

[0176] The virtual reality display devices 101 to 105 were compared in terms of the amount of ghosting observed when an observer viewed a virtual image displayed on a microdisplay. While ghosting was clearly observed with the virtual reality display devices 104 and 105, the virtual reality display devices 101 to 103, which correspond to the HMD (head-mounted display) of the present invention, showed only minor ghosting and were favorable. Furthermore, the virtual reality display device 101 was even more favorable than the virtual reality display devices 102 and 103, with ghosting being less visible.

[0177] By further arranging optical devices 111 to 113 on the observer side of the plano-convex lens, virtual reality image display devices 111 to 113 corresponding to the HMD of the present invention were obtained. It was confirmed that the position of the virtual image displayed on the microdisplay can be switched in multiple stages by switching the state of applied voltage.

[0178] The present invention can be suitably used in HMDs such as VR image display devices.

[0179] REFERENCE SIGNS LIST 10 (VR image) display device 12 Display 14, 26 Circular polarizer 14a Linear polarizer 14b 1 / 4 wavelength plate 16 Half mirror 18, 62 Lens 24 Circularly polarized reflective polarizer 30 Optical device 32 Switching element 34 Liquid crystal lens 36, 36A Liquid crystal layer 38 Liquid crystal compound 50 Substrate 52 Alignment film 60 AR glass 64 Incident diffraction element 68 Light guide plate 70 Outgoing diffraction element

Claims

1. An optical device comprising a switching element and a liquid crystal layer, wherein the switching element is an element capable of switching between a first phase difference and a second phase difference, and the difference between the first phase difference and the second phase difference is 275±20 nm at a wavelength of 550 nm, and the liquid crystal layer is formed using a liquid crystal composition containing a liquid crystal compound with reverse wavelength dispersion, and has a liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal compound changes while rotating continuously along at least one direction in the plane.

2. The optical device of claim 1, wherein the liquid crystal orientation pattern has regions in the plane where the length of one period varies when the length of a 180° rotation of the orientation of the optical axis originating from the liquid crystal compound in the plane is taken as one period.

3. The optical device of claim 1, wherein the liquid crystal orientation pattern has a plurality of rings of different sizes, with larger rings sequentially enclosing smaller rings in the plane.

4. The optical device of claim 3, wherein the liquid crystal orientation pattern is concentric.

5. The optical device according to claim 1, wherein the switching element is constructed using a liquid crystal cell.

6. A head-mounted display comprising an optical device according to any one of claims 1 to 5.

7. The head mounted display according to claim 6, which is either a virtual reality image display device or an augmented reality image display device.

8. The head mounted display according to claim 7, which is a virtual reality image display device having a focusing optical system, and the optical device is provided downstream of the focusing optical system.

9. The head mounted display according to claim 7, which is an augmented reality image display device having a light guide plate, and the optical device is provided downstream of the light guide plate.

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