Image display unit and head-mounted display

Abstract

The present application provides a small, high light utilization efficiency, less image display unit and head-mounted display. The image display unit of the present application has: image display device; polarized light diffraction element, diffracting light emitted from the image display device; and polarizer, transmitting polarized light diffracted by the polarized light diffraction element, and absorbing light not diffracted by the polarized light diffraction element, the polarized light diffraction element is a polarized light diffraction lens with lens function, the focal length of the polarized light diffraction lens is set as f, the distance between the image display device and the polarized light diffraction lens is set as d, and d≤f is satisfied.

Description

Technical Field

[0001] This invention relates to an image display unit and a head-mounted display for VR (virtual reality) head-mounted display. Background Technology

[0002] There exists a head-mounted display (HUD) that, in order to provide an immersive virtual reality (VR) experience that prevents external light from passing through, guides images to the user's eyes when worn. In the HUD's image display unit, a lens is needed to focus light emitted from the image display device at the user's glasses. In the HUD's image display unit, by aligning the distance between the image display device and the lens close to the lens's focal distance, the user can visually recognize the image displayed on the image display device as a distant virtual image.

[0003] In image display units used in head-mounted displays, Fresnel lenses are typically used to achieve thinner and lighter designs. However, there are limitations in shortening the focal distance when using Fresnel lenses. Therefore, it is difficult to reduce the overall thickness of the image display unit (head-mounted display).

[0004] In contrast, as a structure for making the image display unit thinner, a structure has been proposed in which light emitted from the image display device is reflected once by a reflective polarizer or the like, and then reflected again by a mirror or the like to guide it to the user's eye. This allows for obtaining the optical path length from the image display device to the user's eye, and also enables the overall image display unit to be made thinner.

[0005] For example, Patent Document 1 describes a head-mounted display that, from the image display device side, sequentially includes a linear polarizer, a quarter-wave plate, a half-reflector, another quarter-wave plate, and a reflective polarizer. This head-mounted display can be used as an optical device for VR. In this optical element, light reciprocates between the half-reflector and the reflective polarizer to extend the optical path length.

[0006] Previous technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Publication No. 2019-526075 Summary of the Invention

[0009] The technical problem to be solved by the invention

[0010] As described above, in an image display unit that uses a semi-reflective mirror and a reflective polarizer to extend the optical path by having light traverse between the semi-reflective mirror and the reflective polarizer, the semi-reflective mirror transmits approximately 50% of the incident light, and subsequently reflects approximately 50% of the light transmitted through the semi-reflective mirror and reflected by the reflective polarizer, which then exits from the image display unit. Therefore, there is a problem that the light utilization efficiency relative to the amount of light emitted from the image display device is low, around 25%.

[0011] Furthermore, in image display units using Fresnel lenses, if the focal distance is shortened, there is a problem of scattering caused by the groove structure of the Fresnel lens or the visual recognition of light stripes caused by the groove structure, and there is a problem of reduced image quality.

[0012] The objective of this invention is to provide a small, light-efficient image display unit and a head-mounted display with minimal image quality degradation.

[0013] means for solving technical problems

[0014] To address this issue, the present invention has the following structure.

[0015] [1] An image display unit having:

[0016] Image display device;

[0017] A polarizing diffracting element that diffracts light emitted from an image display device; and

[0018] A polarizer transmits polarized light diffracted by a polarizing diffraction element and absorbs light not diffracted by the same element.

[0019] The polarizing diffraction element is a polarizing diffraction lens that functions as a lens.

[0020] When the focal distance of the polarizing diffraction lens is set as f, and the distance between the image display device and the polarizing diffraction lens is set as d, d≤f is satisfied.

[0021] [2] According to the image display unit described in [1], wherein,

[0022] The focal distance f of the polarizing diffraction lens is less than 40 mm.

[0023] [3] The image display unit according to [1] or [2], wherein,

[0024] Polarizing diffracting elements diffract circularly polarized light.

[0025] The polarizer is a circular polarizer.

[0026] [4] According to the image display unit described in [3], wherein,

[0027] The image display device emits linearly polarized light.

[0028] A phase difference plate is provided between the image display device and the polarization diffraction element.

[0029] [5] According to the image display unit described in [4], wherein,

[0030] The phase difference plate is a λ / 4 plate.

[0031] [6] According to the image display unit described in [3], wherein,

[0032] The image display device emits unpolarized light.

[0033] A circular polarizer is placed between the image display device and the polarizing diffraction element.

[0034] [7] The image display unit according to any one of [3] to [6], wherein,

[0035] A circular polarizer consists of a linear polarizer and a phase difference plate.

[0036] [8] The image display unit according to [7], wherein,

[0037] The phase difference plate is a λ / 4 plate.

[0038] [9] The image display unit according to any one of [1] to [8], wherein,

[0039] The polarization diffraction element is a liquid crystal diffraction element having a liquid crystal layer containing a liquid crystal compound.

[0040] The liquid crystal layer has a liquid crystal alignment pattern derived from the liquid crystal compound, in which the orientation of the optical axis changes continuously with rotation in at least one in-plane direction.

[0041] If the length of the orientation of the optical axis originating from the liquid crystal compound in the liquid crystal alignment pattern, rotated 180° in the in-plane direction, is defined as one period, then the liquid crystal layer has regions with different lengths of one period in the in-plane.

[0042]

[10] The image display unit according to [9], wherein,

[0043] One cycle of the liquid crystal layer gradually shortens from one side of the liquid crystal alignment pattern toward the other.

[0044]

[11] The image display unit according to [9] or

[10] , wherein,

[0045] The liquid crystal layer has a liquid crystal alignment pattern in one direction, with concentric circles from the inside to the outside.

[0046]

[12] The image display unit according to any one of [9] to

[11] , wherein,

[0047] In a cross-sectional image obtained by cutting along one direction in the thickness direction using a scanning electron microscope, the liquid crystal layer has bright and dark regions originating from the liquid crystal phase that are tilted relative to the main surface of the liquid crystal layer.

[0048]

[13] According to the image display unit described in

[12] , wherein,

[0049] Liquid crystal diffraction elements have two or more liquid crystal layers.

[0050] In a cross-sectional image obtained by cutting along one direction in the thickness direction of a liquid crystal layer with at least two layers using a scanning electron microscope, bright and dark areas originating from the optical axis were observed.

[0051] In a liquid crystal layer with at least two layers, the bright and dark areas are tilted at different angles relative to the main surface of the liquid crystal layer.

[0052]

[14] The image display unit according to any one of [9] to

[13] , wherein,

[0053] In a cross-sectional image obtained by cutting along one direction in the thickness direction using a scanning electron microscope, the liquid crystal layer has bright and dark areas extending from one surface to another, with the dark areas having more than two inflection points.

[0054] There are regions with different tilt directions in the thickness area, which are dark areas.

[0055]

[15] The image display unit according to

[14] , wherein,

[0056] The number of inflection points where the tilt direction of the dark area in the liquid crystal layer is reversed is odd.

[0057]

[16] The image display unit according to any one of

[12] to

[15] , wherein,

[0058] The average tilt angle of the dark areas in the liquid crystal layer gradually changes in one direction.

[0059]

[17] The image display unit according to any one of

[12] to

[16] , wherein,

[0060] The liquid crystal layer has regions whose bright and dark areas are asymmetrical with respect to the centerline of the thickness direction of the liquid crystal layer.

[0061]

[18] The image display unit according to any one of [9] to

[17] , wherein,

[0062] The refractive index difference Δn accompanying the refractive index anisotropy of the liquid crystal layer 550 It is above 0.2.

[0063]

[19] A head-mounted display having an image display unit as described in any one of [1] to

[18] .

[0064] Invention Effects

[0065] According to the present invention, a small image display unit and a head-mounted display with high light utilization efficiency and minimal image quality degradation can be provided. Attached Figure Description

[0066] Figure 1 This is a diagram that conceptually illustrates an example of the image display unit of the present invention.

[0067] Figure 2 It is magnification Figure 1 The image is a portion of the display unit.

[0068] Figure 3 It is used for explanation Figure 1 A conceptual diagram illustrating the function of the image display unit.

[0069] Figure 4 This is a partially enlarged view that conceptually represents another example of the image display unit of the present invention.

[0070] Figure 5 This is a plan view that conceptually represents an example of a liquid crystal layer in a liquid crystal diffraction element.

[0071] Figure 6 It is a conceptual representation Figure 5 The diagram shows the liquid crystal layer of the liquid crystal diffraction element.

[0072] Figure 7 It is an enlarged representation Figure 5 A plan view of a portion of the liquid crystal layer of the liquid crystal diffraction element shown.

[0073] Figure 8 It is a conceptual representation of the formation Figure 5 The figure shows an example of an exposure apparatus for exposing the alignment film of the liquid crystal layer.

[0074] Figure 9 This is a conceptual diagram used to illustrate the function of the liquid crystal layer.

[0075] Figure 10 This is a conceptual diagram used to illustrate the function of the liquid crystal layer.

[0076] Figure 11 It means Figure 5 A conceptual diagram illustrating the function of a liquid crystal diffraction element.

[0077] Figure 12 This is a diagram that conceptually represents an example of a SEM cross-section of a liquid crystal layer.

[0078] Figure 13 This is a conceptual diagram representing another example of a liquid crystal layer.

[0079] Figure 14 This is a conceptual diagram representing another example of a liquid crystal layer. Detailed Implementation

[0080] The present invention will now be described in detail. The description of the constituent elements described below is based on a representative embodiment of the present invention, but the present invention is not limited to this embodiment. Furthermore, in this specification, the numerical range indicated by "~" refers to the range encompassed by the values ​​before and after "~" as a lower and upper limit value. Moreover, the terms "orthogonal" and "parallel" for angles refer to a strict range of ±10°, and the terms "same" and "different" for angles can be determined based on whether their difference is less than 5°.

[0081] In this specification, "slow axis" refers to the direction with the highest in-plane refractive index.

[0082] In this specification, inverse wavelength dispersion refers to the property that the absolute value of the in-plane delay increases as the wavelength becomes longer. Specifically, it means that the in-plane delay values ​​Re(450) measured at a wavelength of 450 nm, Re(550) measured at a wavelength of 550 nm, and Re(650) measured at a wavelength of 650 nm satisfy the relationship Re(450)≤Re(550)≤Re(650).

[0083] [Image Display Unit]

[0084] The image display unit of the present invention has:

[0085] Image display device;

[0086] A polarizing diffracting element that diffracts light emitted from an image display device; and

[0087] A polarizer transmits polarized light diffracted by a polarizing diffraction element and absorbs light not diffracted by the same element.

[0088] The polarizing diffraction element is a polarizing diffraction lens that functions as a lens.

[0089] When the focal distance of the polarizing diffraction lens is set as f, and the distance between the image display device and the polarizing diffraction lens is set as d, d≤f is satisfied.

[0090] Figure 1This is a diagram that conceptually illustrates an example of the image display unit of the present invention. Figure 2 It is magnification Figure 1 The diagram shows a portion of the image display unit (the part surrounded by dashed lines), and is used to illustrate the function of the image display unit.

[0091] Figure 1 and Figure 2 The image display unit 10 shown includes an image display device 52, a first circular polarizer 16, a polarizing diffraction element 20, and a second circular polarizer 26. The first circular polarizer 16 includes a first linear polarizer 12 and a first phase retardation plate 14. Furthermore, the second circular polarizer 26 includes a second linear polarizer 24 and a second phase retardation plate 22. The second circular polarizer 26 is the polarizer of this invention.

[0092] exist Figure 1 In the example shown, the image display device 52 emits unpolarized light as an image. Furthermore, the first circular polarizer 16 allows circularly polarized light in a predetermined rotational direction to pass through and blocks another circularly polarized light. Figure 1 In the example shown, the first circular polarizer 16 allows a predetermined linearly polarized component of the incident light to pass through the first linear polarizer 12, and the first phase retardation plate 14 converts the linearly polarized light passing through the first linear polarizer 12 into circularly polarized light, thereby allowing circularly polarized light with a predetermined rotation direction to pass through. Furthermore, the polarizing diffraction element 20 diffracts the circularly polarized light passing through the first circular polarizer 16. At this time, the polarizing diffraction element 20 converts the circularly polarized light into circularly polarized light with the opposite rotation direction during conversion. Moreover, the polarizing diffraction element 20 is a polarizing diffraction lens that functions as a lens by converging light through diffraction of circularly polarized light. The second circular polarizer 26 allows the light diffracted by the polarizing diffraction element 20 to pass through and absorbs the undiffracted light. Figure 1 In the example shown, the second circular polarizer 26 uses the second phase retarder 22 to convert the circularly polarized light diffracted by the polarizing light diffraction element 20 into linearly polarized light. The second linear polarizer 24 allows the linearly polarized light converted by the second phase retarder 22 to pass through and absorbs other linearly polarized light components, thereby allowing the polarized light diffracted by the polarizing light diffraction element 20 to pass through and absorbing the undiffracted light.

[0093] And, as Figure 3 As shown, when the focal distance of the polarization diffraction element (polarization diffraction lens) 20 is set to f, and the distance between the image display device 52 and the polarization diffraction element 20 is set to d, the polarization diffraction element 20 and the image display device 52 are configured to satisfy d≤f.

[0094] In the image display unit 10, when light (image) is emitted from the image display device 52, the light passes through the first circular polarizer 16, the polarizing diffraction element 20, and the second circular polarizer 26 and is emitted towards the user U. At this time, the light emitted from the image display device 52 is focused by the polarizing diffraction element 20 to the position of the user U's eye. Figure 3 As shown, if the distance d between the polarization diffraction element 20 and the image display device 52 is less than or equal to the focal distance f of the polarization diffraction element 20, the image display unit 10 enables the user U to visually recognize the image as a distant virtual image VI.

[0095] The following uses Figure 2 Please explain the function of each component in detail. For example... Figure 2 As shown, unpolarized light emitted from the image display device 52 only transmits a predetermined linearly polarized light component through the first linear polarizer 12. As an example, in... Figure 2 In the example shown, the first linear polarizer 12 transmits and Figure 2 The linearly polarized light component perpendicular to the plane of the paper. The linearly polarized light transmitted through the first linear polarizer 12 is incident on the first phase retarder 14 and converted into right-hand circularly polarized light. The right-hand circularly polarized light converted by the first phase retarder 14 is incident on the polarization diffraction element 20 and diffracted. Furthermore, the right-hand circularly polarized light is converted into left-hand circularly polarized light during diffraction. The left-hand circularly polarized light diffracted by the polarization diffraction element 20 is converted into linearly polarized light in the vertical direction as shown in the figure by the second phase retarder 22. The linearly polarized light converted by the second phase retarder 22 is transmitted through the second linear polarizer 24 and then exits.

[0096] Here, since it is difficult to set the diffraction efficiency based on the polarization diffraction element 20 to 100%, therefore, as Figure 2 As indicated by the dashed arrow, a portion of the right-hand circularly polarized light incident on the polarization diffraction element 20 is not diffracted and is transmitted through the element. Without the second circular polarizer 26, the right-hand circularly polarized light not diffracted by the element 20 exits from the image display unit 10 and is perceived by the user U. Since the image based on this right-hand circularly polarized light is not focused, it is perceived as a real image. Therefore, because the user U perceives a real image superimposed on a virtual image, the image quality of the virtual image to be displayed is reduced.

[0097] In contrast, the image display unit 10 of the present invention has a second circular polarizer 26. At this time, as... Figure 2 As shown, right-handed circularly polarized light (i.e., zero-order light) that is not diffracted by the polarization diffraction element 20 is incident on the second phase difference plate 22 of the second circular polarizer 26 and converted into light with the polarizer 20. Figure 2Linearly polarized light perpendicular to the plane of the paper is incident on the second linear polarizer 24 and absorbed. That is, right-hand circularly polarized light that is not diffracted by the polarization diffraction element 20 is absorbed by the second circular polarizer 26. Therefore, the user U can only visually perceive the virtual image based on left-hand circularly polarized light, and cannot visually perceive the undiffracted right-hand circularly polarized light. Therefore, the image quality degradation of the virtual image displayed by the image display unit 10 can be suppressed.

[0098] Furthermore, as mentioned above, in an image display unit using a Fresnel lens, if the focal distance is shortened, there is a problem of scattering caused by the groove structure of the Fresnel lens or visually recognizing light stripes caused by the groove structure.

[0099] In contrast, the image display unit 10 of the present invention uses a polarized light diffraction element 20 as a lens. Therefore, since the polarized light diffraction element 20 does not have a groove structure, it does not produce scattering and light fringes caused by the groove structure, nor does it cause a reduction in image quality.

[0100] Furthermore, as described above, in an image display unit that uses a semi-reflective mirror and a reflective polarizer to extend the optical path by having light traverse between the semi-reflective mirror and the reflective polarizer, the semi-reflective mirror transmits approximately 50% of the incident light, and subsequently reflects approximately 50% of the light transmitted through the semi-reflective mirror and reflected by the reflective polarizer, which then exits from the image display unit. Therefore, as an image display unit, there is a problem that the light utilization efficiency relative to the amount of light emitted from the image display device is low, at approximately 25%.

[0101] In contrast, the image display unit 10 of the present invention uses a polarizing diffraction element 20 for diffractive polarized light as a lens. Therefore, the light utilization efficiency relative to the amount of light emitted from the image display device 52 can be further improved.

[0102] Here, in Figure 1 In the example shown, the image display device 52 emits unpolarized light, and there is a structure with a first circular polarizer 16 between the image display device 52 and the polarized light diffraction element 20, but it is not limited to this.

[0103] Figure 3 This is a partial enlarged view of another example of the image display unit of the present invention, which is conceptually illustrated.

[0104] Figure 3 The image display unit 10b shown includes an image display device 52b, a first phase retardation plate 14, a polarizing diffraction element 20, and a second circular polarizer 26. The second circular polarizer 26 includes a second linear polarizer 24 and a second phase retardation plate 22. The second circular polarizer 26 is the polarizer of this invention.

[0105] exist Figure 3 In the example shown, the image display device 52b emits linearly polarized light as the image. Furthermore, the first phase retarder 14 converts the linearly polarized light emitted from the image display device 52b into circularly polarized light. The polarized light diffraction element 20 and the second circular polarizer 26 have the same polarization characteristics as... Figure 1 The image display unit 10 shown has the same structure as the polarization diffraction element 20 and the second circular polarizer 26. Furthermore, the polarization diffraction element 20 and the image display device 52 are configured to satisfy d ≤ f.

[0106] In the image display unit 10b, if linearly polarized light (image) is emitted from the image display device 52b, the light passes through the first phase retardation plate 14, the polarized light diffraction element 20, and the second circular polarizer 26 and is emitted towards the user U. At this time, the light emitted from the image display device 52b is focused by the polarized light diffraction element 20 to the position of the user U's eye. Since the distance d between the polarized light diffraction element 20 and the image display device 52b is less than or equal to the focal distance f of the polarized light diffraction element 20, the image display unit 10b enables the user U to visually recognize the image as a distant virtual image.

[0107] As an example, in Figure 3 In the example shown, the image display device 52b emits and Figure 3 Linearly polarized light perpendicular to the plane of the paper. Linearly polarized light emitted from the image display device 52b is incident on the first phase retarder 14 and converted into right-hand circularly polarized light. The right-hand circularly polarized light converted by the first phase retarder 14 is incident on the polarization diffraction element 20 and diffracted. Furthermore, the right-hand circularly polarized light is converted into left-hand circularly polarized light during diffraction. The left-hand circularly polarized light diffracted by the polarization diffraction element 20 is converted into linearly polarized light in the vertical direction as shown in the figure by the second phase retarder 22. The linearly polarized light converted by the second phase retarder 22 is transmitted through the second linear polarizer 24 and then emitted.

[0108] Furthermore, the right-hand circularly polarized light (i.e., zero-order light) that is not diffracted by the polarization diffraction element 20 is incident on the second phase difference plate 22 of the second circular polarizer 26 and converted into light with the polarizer 20. Figure 4 Linearly polarized light perpendicular to the plane of the paper is incident on the second linear polarizer 24 and absorbed. That is, right-hand circularly polarized light that is not diffracted by the polarization diffraction element 20 is absorbed by the second circular polarizer 26. Therefore, the user U can only visually perceive the virtual image based on left-hand circularly polarized light, and cannot visually perceive the undiffracted right-hand circularly polarized light. Therefore, the image quality degradation of the virtual image displayed by the image display unit 10 can be suppressed.

[0109] Here, in Figure 2 and Figure 4In the example shown, the polarizing diffraction element 20 diffracts circularly polarized light, but it is not limited to this. For example, the polarizing diffraction element can be a polarizing diffraction lens that diffracts linearly polarized light. When the polarizing diffraction element is a polarizing diffraction lens that diffracts linearly polarized light, instead of the second circular polarizer 26, a linear polarizer can be configured to transmit the linearly polarized light diffracted by the polarizing diffraction element and absorb the linearly polarized light that the polarizing diffraction element does not diffract. In this configuration, the linear polarizer corresponds to the polarizer in this invention.

[0110] Furthermore, when the polarizing diffraction element is a polarizing diffraction lens that diffracts linearly polarized light, if the image display device emits unpolarized light, a linear polarizer can be placed between the image display device and the polarizing diffraction element. If the image display device emits linearly polarized light, then a linear polarizer and phase difference plate are not required between the image display device and the polarizing diffraction element.

[0111] Furthermore, in Figure 2 and Figure 4 In the example shown, from the viewpoint of converting incident linearly polarized light into circularly polarized light, the first phase retarder 14 is preferably a λ / 4 plate. Since the image display device basically emits visible light, the first phase retarder 14 can be a λ / 4 plate relative to the wavelength of the visible light region. Furthermore, in cases where the light incident on the first phase retarder 14 is elliptically polarized light, the first phase retarder 14 can simply have a phase difference that converts the incident light into circularly polarized light.

[0112] Furthermore, in Figure 2 and Figure 4 In the example shown, from the viewpoint of converting incident circularly polarized light into linearly polarized light, the second phase retarder 22 is preferably a λ / 4 plate. The second phase retarder 22 can be a λ / 4 plate relative to the wavelength of the visible light region.

[0113] Furthermore, from the viewpoints of thinning the image display unit and viewing angle, the focal distance f of the polarization diffraction element (polarization diffraction lens) is preferably less than 40 mm, more preferably 1 mm or more and 30 mm or less, and even more preferably 3 mm or more and 15 mm or less.

[0114] Furthermore, from the viewpoint of displaying a virtual image, the distance d between the image display system and the polarization diffraction element only needs to be less than or equal to the focal distance f of the polarization diffraction element. From the viewpoint of displaying a virtual image at a distance, the ratio d / f of the distance d to the focal distance f is preferably in the range of 0.8 to 1, more preferably in the range of 0.9 to 1, and even more preferably in the range of 0.95 to 1.

[0115] The components of the image display system will be described below.

[0116] <Image display device>

[0117] An image display device illuminates an image (still image or moving image) displayed by an image display system.

[0118] There are no limitations on the image display device; for example, known displays used in various head-mounted displays can be utilized.

[0119] As examples of displays, liquid crystal displays (including LCOS: Liquid Crystal On Silicon), organic electroluminescent displays, and scanning displays using DLP (Digital Light Processing) or MEMS (Micro Electro Mechanical Systems) mirrors can be cited.

[0120] In addition, the image display device can be a monitor that displays monochrome images or a monitor that displays multicolor images.

[0121] As described above, in the image display unit of the present invention, the light irradiated by the image display device can be unpolarized light or linearly polarized light.

[0122] <Polarizer>

[0123] The first and second linear polarizers are not particularly limited as long as they are linear polarizers that can transmit linearly polarized light in one polarization direction and absorb linearly polarized light in another polarization direction; conventionally known linear polarizers can be used. The linear polarizer can be either an absorptive type or a reflective type.

[0124] As an absorptive linear polarizer, iodine-based polarizers, dye-based polarizers utilizing dichroic dyes, and polyene-based polarizers can be used. Iodine-based polarizers and dye-based polarizers include coated polarizers and stretched polarizers, and either type can be used. Among these, a polarizer made by adsorbing iodine or dichroic dye onto polyvinyl alcohol and then stretching it is preferred.

[0125] Furthermore, as a method for obtaining a polarizer by stretching and dyeing a laminated film in which a polyvinyl alcohol layer is formed on a substrate, examples include Japanese Patent No. 5048120, Japanese Patent No. 5143918, Japanese Patent No. 4691205, Japanese Patent No. 4751481, and Japanese Patent No. 4751486, and known techniques related to these polarizers can be preferred.

[0126] As an absorption-type polarizer, a polarizer that orients dichroic pigments by utilizing the orientation properties of liquid crystals without stretching is particularly preferred. This polarizer has many advantages, including: it can be made extremely thin, with a thickness of approximately 0.1 μm to 5 μm; as described in Japanese Patent Application Publication No. 2019-194685, it is less prone to cracking during bending and exhibits minimal thermal deformation; as described in Japanese Patent Publication No. 6483486, it also possesses excellent durability and thermoforming properties due to its high transmittance (over 50%).

[0127] Taking advantage of these advantages, it can be used for applications requiring high brightness or small and lightweight components, micro-optical systems, applications requiring curved surfaces, and applications in flexible parts. Furthermore, it can also be used by peeling off the support and transferring a polarizer.

[0128] However, it is also preferable to assemble absorptive polarizers in optical systems such as head-up displays, AR glasses, VR glasses, or optical sensors such as LiDAR, facial recognition systems, and polarization imagers, with the aim of suppressing stray light.

[0129] As described in Japanese Patent Application Publication No. 2011-053705, reflective linear polarizers can be made by stretching a thin film containing two polymers or using a wire grid polarizer. From a brightness perspective, a thin film stretched from a polymer-containing layer is preferred. Commercially available products include reflective polarizers (trade name APF) manufactured by 3M Company and wire grid polarizers (trade name WGF) manufactured by Asahi Kasei Corporation. Alternatively, a reflective linear polarizer composed of a cholesterol-type liquid crystal film and a λ / 4 plate can also be used.

[0130] The polarizer used in this invention preferably has a smooth surface. In particular, when the polarizer is applied to lenses or the like, minute surface irregularities can sometimes cause image distortion due to the magnification effect of the lens; therefore, a smooth surface is desirable. Specifically, the average arithmetic roughness Ra of the surface is preferably 50 nm or less, more preferably 30 nm or less, even more preferably 10 nm or less, and most preferably 5 nm or less. Furthermore, the height difference of surface irregularities within a 1 square millimeter area on the surface of the polarizer is preferably 100 nm or less, more preferably 50 nm or less, and most preferably 20 nm or less.

[0131] The roughness and average arithmetic roughness of a surface can be measured using a roughness gauge or interferometer. For example, the "vertscan" interferometer manufactured by Mitsubishi Chemical Systems, Inc. can be used for measurement.

[0132] (Phase difference plate)

[0133] The first and second phase retarders are phase retarders that convert the phase of the incident polarization. The phase retarders are configured to adjust the direction of the slow axis according to whether the incident polarized light is converted into near-linear polarization or near-circular polarization. Specifically, the phase retarders are configured such that the slow axis is +45° or -45° relative to the transmission axis of the adjacent linear polarizer.

[0134] The retardation plate used in this invention can be a single-layer type consisting of one optical anisotropic layer, or a multi-layer type consisting of two or more optical anisotropic layers each having multiple different slow axes. Examples of multi-layer retardation plates include WO13 / 137464, WO2016 / 158300, Japanese Patent Application Publication Nos. 2014-209219, 2014-209220, WO14 / 157079, 2019-215416, and WO2019 / 160044, but are not limited thereto.

[0135] From the viewpoint of converting linearly polarized light into circularly polarized light or vice versa, the phase difference plate is preferably a λ / 4 plate.

[0136] There are no restrictions on the λ / 4 plate; various known plates with λ / 4 functionality can be used. Specific examples of λ / 4 plates include those described in U.S. Patent Application Publication No. 2015 / 0277006.

[0137] For example, as a single-layer structure of the λ / 4 plate, examples include a stretchable polymer film and a phase retardation film on a support having an optical anisotropy layer with λ / 4 functionality. Furthermore, as a multi-layer structure of the λ / 4 plate, examples include a broadband λ / 4 plate formed by stacking λ / 4 plates and λ / 2 waveplates.

[0138] The thickness of the λ / 4 plate is not particularly limited, but is preferably 1 to 500 μm, more preferably 1 to 50 μm, and even more preferably 1 to 5 μm.

[0139] The phase difference plate used in this invention preferably has inverse wavelength dispersion. By having inverse wavelength dispersion, the phase change on the phase difference plate becomes ideal, and the conversion between linearly polarized light and circularly polarized light becomes ideal.

[0140] <Polarization diffraction element>

[0141] A polarizing light diffraction element is a polarizing light diffraction lens that functions as a lens to diffract and converge polarized light. As mentioned above, a polarizing light diffraction element can be an element that diffracts linearly polarized light or an element that diffracts circularly polarized light.

[0142] Examples of polarization diffraction elements that diffract linearly polarized light include volume holographic diffraction elements. Furthermore, since the polarization diffraction element is designed to converge the polarized light diffracted by the diffraction structure, it is configured, for example, such that the diffraction angle increases from the center of the polarization diffraction element outwards.

[0143] (Liquid crystal diffraction element)

[0144] Liquid crystal diffraction elements can be cited as examples of polarization diffraction elements that diffract circularly polarized light.

[0145] As an example, Figure 5 The diagram shows a concept of a positive lens using a liquid crystal diffraction element. Figure 5 It is a planar diagram that conceptually represents the liquid crystal layer of a liquid crystal diffraction element.

[0146] A liquid crystal diffraction element has a liquid crystal layer formed using a composition containing a liquid crystal compound, having a predetermined liquid crystal alignment pattern that rotates an optical axis derived from the liquid crystal compound. Figure 5 In the example shown, the liquid crystal alignment pattern of the liquid crystal layer 36 is a concentric circle pattern that changes in one direction from the inside to the outside while the orientation of the optical axis of the liquid crystal compound 40 rotates continuously. A concentric circle pattern is a pattern in which the lines connecting liquid crystal compounds with the same optical axis orientation are circular, and the circular line segments are concentric. In other words, Figure 5 The liquid crystal alignment pattern of the liquid crystal layer 36 shown is a liquid crystal alignment pattern that is radially arranged from the center of the liquid crystal layer 36, which changes as the optical axis of the liquid crystal compound 40 rotates continuously.

[0147] exist Figure 5 In the liquid crystal layer 36 shown, the optical axis of the liquid crystal compound 40 (not shown) is the direction of the long side of the liquid crystal compound 40.

[0148] In the liquid crystal layer 36, the orientation of the optical axis of the liquid crystal compound 40 changes as it rotates continuously along multiple directions from the center of the liquid crystal layer 36 outward, such as the direction indicated by arrow A1, the direction indicated by arrow A2, the direction indicated by arrow A3, etc. Arrows A1, A2, and A3 are arranged axes as described later.

[0149] Furthermore, the liquid crystal layer 36 of the liquid crystal diffraction element has a period Λ of liquid crystal alignment pattern in different regions within the plane. Here, a period Λ of the liquid crystal alignment pattern refers to the length (distance) of the optical axis of the liquid crystal compound 40 rotating 180° in a direction in which the orientation of the optical axis of the liquid crystal alignment pattern changes continuously by rotating within the plane.

[0150] Specifically, in Figure 5 In the example shown, the structure is as follows: in each direction in which the orientation of the optical axis of the liquid crystal compound 40 is continuously rotated and changed, one period Λ gradually becomes shorter as it moves from the center outward.

[0151] As will be explained in detail later, the diffraction angle of a liquid crystal diffraction element depends on one period Λ of the liquid crystal alignment pattern. The shorter the period Λ, the larger the diffraction angle.

[0152] The liquid crystal layer 36 has a liquid crystal alignment pattern that changes continuously as it rotates radially from the center of the liquid crystal layer 36, corresponding to the orientation of the optical axis of the liquid crystal compound 40. In each direction, the period Λ of the liquid crystal alignment pattern gradually shortens from the center outwards. Therefore, circularly polarized light incident on the liquid crystal layer 36 with this liquid crystal alignment pattern experiences changes in absolute phase in different local regions where the optical axis of the liquid crystal compound 40 is oriented. The amount of change in absolute phase varies depending on the orientation of the optical axis of the circularly polarized light incident on the liquid crystal compound 40. Furthermore, the diffraction angle varies according to one period within the region where the circularly polarized light is incident. The liquid crystal layer 36 can transmit incident light as converging light depending on the rotation direction of the optical axis of the liquid crystal compound 40 and the direction of the incident circularly polarized light. This liquid crystal layer 36 has a concentric liquid crystal alignment pattern, i.e., a liquid crystal alignment pattern that changes radially as the optical axis rotates continuously.

[0153] That is, by setting the liquid crystal alignment pattern of the liquid crystal layer to a concentric circle, the liquid crystal diffraction element can express its function, for example, as a convex lens.

[0154] The liquid crystal layer of a liquid crystal diffraction element will be described in detail below.

[0155] Figure 6 This is a conceptual diagram of a cross-section of the liquid crystal compound 40 along the optical axis 40A of the liquid crystal layer 36, which is rotated continuously while changing direction. Figure 7 for Figure 6 Floor plan.

[0156] Figure 6 The liquid crystal diffraction element shown has a support 30, an alignment film 32, and a liquid crystal layer (hereinafter also referred to as an optical anisotropy layer) 36.

[0157] As described above, the liquid crystal diffraction element has a liquid crystal layer formed using a composition containing a liquid crystal compound, having a predetermined liquid crystal alignment pattern that rotates the optical axis from the liquid crystal compound. Furthermore, as described later, the liquid crystal layer has one period Λ of the liquid crystal alignment pattern in different in-plane regions.

[0158] and, Figure 6 The liquid crystal diffraction element shown has a support 30, but the support 30 may not be provided.

[0159] For example, the optical element of the present invention can also be constructed according to the above structure by peeling off the support 30 and making only the alignment film and liquid crystal layer to form the optical element of the present invention, or by peeling off the alignment film and making only the liquid crystal layer to form the optical element of the present invention.

[0160] That is, any liquid crystal diffraction element can utilize various layer structures as long as the liquid crystal layer has a liquid crystal alignment pattern that rotates in one direction from the optical axis of the liquid crystal compound.

[0161] <<Support>>

[0162] In the liquid crystal diffraction element, the support 30 supports the alignment film 32 and the liquid crystal layer 36.

[0163] As long as it can support the alignment film and the liquid crystal layer, the support 30 can utilize various sheet-like materials (films, plates).

[0164] The support 30 is preferably a transparent support, and examples include polyacrylic resin films such as polymethyl methacrylate, cellulose resin films such as cellulose triacetate, cyclic olefin polymer films (e.g., those manufactured under the trade name "ARTON" by JSR Corporation, and those manufactured under the trade name "ZEONOR" by Zeon Corporation), polyethylene terephthalate (PET), polycarbonate, and polyvinyl chloride. The support is not limited to flexible films and can be a non-flexible substrate such as a glass substrate.

[0165] Furthermore, the support 30 can be a multi-layered support, including any of the aforementioned supports as a substrate, and other support layers are disposed on the surface of the substrate.

[0166] There is no limitation on the thickness of the support 30, as long as it is appropriately set according to the application of the liquid crystal diffraction element and the forming material of the support 30 to maintain the thickness of the alignment film and the liquid crystal layer.

[0167] The thickness of the support 30 is preferably 1 to 1000 μm, more preferably 3 to 500 μm, and even more preferably 5 to 250 μm.

[0168] <<Orientation Membrane>>

[0169] In a liquid crystal diffraction element, an alignment film 32 is formed on the surface of a support 30.

[0170] The alignment film 32 is an alignment film used to align the liquid crystal compound 40 into a predetermined liquid crystal alignment pattern when forming the liquid crystal layer 36 of the liquid crystal diffraction element.

[0171] As described later, in a liquid crystal diffraction element, the liquid crystal layer has an optical axis 40A derived from the liquid crystal compound 40 (reference). Figure 7 The orientation of the liquid crystal diffraction element changes as it rotates continuously in one in-plane direction (the alignment axis D direction described later). Therefore, the alignment film of the liquid crystal diffraction element can be formed into a liquid crystal layer to form this liquid crystal alignment pattern.

[0172] Furthermore, in one direction where the orientation of the optical axis 40A changes continuously as it rotates in the liquid crystal alignment pattern, the length of 180° rotation of the orientation of the optical axis 40A is defined as one cycle Λ (rotation cycle of the optical axis).

[0173] In the following description, "orientation rotation of optical axis 40A" will also be referred to as "rotation of optical axis 40A".

[0174] Orientation films can utilize a variety of known orientation films.

[0175] Examples include triboelectric films formed from organic compounds such as polymers, tilted vapor-deposited films of inorganic compounds, films with microgrooves, and films formed by accumulating organic compounds such as ω-trisanoic acid, dioctadecylmethylammonium chloride, and methyl stearate using the Langmuir-Blodgett process.

[0176] The alignment film based on friction treatment can be formed by repeatedly rubbing the surface of the polymer layer with paper or cloth in a specified direction. Preferred materials used in the alignment film include polyimide, polyvinyl alcohol, polymers with polymerizable groups as described in Japanese Patent Application Publication No. 9-152509, and alignment films as described in Japanese Patent Application Publication Nos. 2005-97377, 2005-99228, and 2005-128503.

[0177] In liquid crystal diffraction elements, the alignment film is preferably a so-called photoalignment film formed by irradiating polarized or unpolarized light with a light-oriented raw material. That is, in liquid crystal diffraction elements, as the alignment film, a photoalignment film formed by coating a light-oriented material on a support 30 is preferred.

[0178] Regarding the irradiation of polarized light, it can be performed from a direction perpendicular to or inclined relative to the photo-alignment film; regarding the irradiation of unpolarized light, it can be performed from a direction inclined relative to the photo-alignment film.

[0179] Examples of photoalignment materials that can be used in the photoalignment film of the present invention include Japanese Patent Application Publication Nos. 2006-285197, 2007-76839, 2007-138138, 2007-94071, 2007-121721, 2007-140465, and 2007-156. The azo compounds described in Japanese Patent Publication No. 439, Japanese Patent Application Publication No. 2007-133184, Japanese Patent Application Publication No. 2009-109831, Japanese Patent Publication No. 3883848 and Japanese Patent Publication No. 4151746, the aromatic ester compounds described in Japanese Patent Application Publication No. 2002-229039, and Japanese Patent Application Publication No. 2002-265541 and Japanese Patent Application Publication No. 2002-317013 The described maleimide and / or alkenyl-substituted nadicimide compounds having photooriented units, the photocrosslinkable silane derivatives described in Japanese Patent Nos. 4205195 and 4205198, the photocrosslinkable polyimides, photocrosslinkable polyamides and photocrosslinkable polyamides described in Japanese Patent Nos. 2003-520878, 2004-529220 and 4162850, are all examples of such compounds. Esters and photodimerizable compounds, particularly cinnamic acid esters, chalcone compounds and coumarin compounds, as described in Japanese Patent Application Publication Nos. 9-118717, 10-506420, 2003-505561, International Publication No. 2010 / 150748, 2013-177561 and 2014-12823, are preferred examples.

[0180] Among them, azo compounds, photocrosslinked polyimides, photocrosslinked polyamides, photocrosslinked esters, cinnamic acid ester compounds and chalcone compounds are preferred.

[0181] There is no limit to the thickness of the alignment film; as long as the thickness is appropriately set according to the forming material of the alignment film, the required alignment function can be obtained.

[0182] The thickness of the alignment film is preferably 0.01 to 5 μm, more preferably 0.05 to 2 μm.

[0183] There are no limitations on the method of forming the alignment film, and various known methods corresponding to the materials used to form the alignment film can be used. As an example, a method can be illustrated by coating the alignment film onto the surface of the support 30 and drying it, and then exposing the alignment film with a laser beam to form an alignment pattern.

[0184] Figure 8 This is an example of an exposure apparatus that conceptually represents an alignment film forming a concentric circle alignment pattern.

[0185] The exposure apparatus 80 includes a light source 84 with a laser 82, a polarization beam splitter 86 that splits the laser beam M from the laser 82 into S-polarized MS and P-polarized MP, a reflector 90A disposed in the optical path of P-polarized MP and a reflector 90B disposed in the optical path of S-polarized MS, a lens 92 disposed in the optical path of S-polarized MS, a polarization beam splitter 94, and a λ / 4 plate 96.

[0186] The P-polarized MP, separated by polarization beam splitter 86, is reflected by mirror 90A and incident on polarization beam splitter 94. On the other hand, the S-polarized MS, separated by polarization beam splitter 86, is reflected by mirror 90B, converged by lens 92, and incident on polarization beam splitter 94.

[0187] P-polarized MP and S-polarized MS are combined by polarization beam splitter 94, and then passed through λ / 4 plate 96 to become right-hand circularly polarized light and left-hand circularly polarized light corresponding to the polarization direction, and then incident on the alignment film 32 on the support 30.

[0188] Here, through the interference of right-handed and left-handed circularly polarized light, the polarization state of the light illuminating the alignment film changes periodically in the form of interference fringes. Since the cross angle between the left-handed and right-handed circularly polarized light changes from the inside to the outside of the concentric circles, an exposure pattern in which the pitch changes from the inside to the outside can be obtained. Thus, a concentric circular alignment pattern in the alignment film with a periodically changing alignment state can be obtained.

[0189] In this exposure apparatus 80, one cycle Λ of the liquid crystal alignment pattern in which the optical axis of the liquid crystal compound 40 rotates continuously by 180° in one direction can be controlled by changing the refractive power (F-value of the lens 92), the focal distance of the lens 92, and the distance between the lens 92 and the alignment film 32.

[0190] Furthermore, by adjusting the refractive power of lens 92 (F-value of lens 92), the length Λ of one cycle of the liquid crystal orientation pattern can be changed in one direction of continuous rotation of the optical axis.

[0191] Specifically, by adjusting the expansion angle of the light extended by lens 92 that interferes with parallel light, the length Λ of one cycle of the liquid crystal alignment pattern can be changed in one direction of continuous rotation of the optical axis. More specifically, if the refractive power of lens 92 is reduced, the light approaches parallelism, and therefore the length Λ of one cycle of the liquid crystal alignment pattern gradually shortens from the inside to the outside, resulting in a larger F-value. Conversely, when the refractive power of lens 92 is increased, the length Λ of one cycle of the liquid crystal alignment pattern suddenly shortens from the inside to the outside, resulting in a smaller F-value.

[0192] As described above, an alignment film (hereinafter also referred to as a patterned alignment film) having an exposed pattern has an alignment pattern that aligns the liquid crystal compound to form a liquid crystal alignment pattern in which the orientation of the optical axis of the liquid crystal compound in the liquid crystal layer formed on the patterned alignment film changes while continuously rotating in at least one in-plane direction. If the axis along which the liquid crystal compound is aligned is defined as the alignment axis, then it can be said that the patterned alignment film has an alignment pattern in which the orientation of the alignment axis changes while continuously rotating in at least one in-plane direction. The alignment axis of the patterned alignment film can be detected by measuring absorption anisotropy. For example, when linearly polarized light is irradiated onto the patterned alignment film while rotating, and the amount of light transmitted through the patterned alignment film is measured, it is observed that the direction in which the light amount becomes maximum or minimum gradually changes in one in-plane direction.

[0193] Furthermore, in liquid crystal diffraction elements, the alignment film is preferably arranged, but it is not a necessary component.

[0194] For example, an orientation pattern can be formed on the support 30 by a method of rubbing the support 30 or by processing the support 30 with a laser beam, etc., so that the liquid crystal layer 36 or the like can be configured to have a liquid crystal orientation pattern that changes as the orientation of the optical axis 40A of the liquid crystal compound 40 rotates continuously in at least one direction in the plane.

[0195] <<Liquid Crystal Layer>>

[0196] In a liquid crystal diffraction element, a liquid crystal layer 36 is formed on the surface of an alignment film 32.

[0197] As will be discussed later Figure 9 and Figure 10 In the diagram, only the liquid crystal compound 40 (liquid crystal compound molecules) on the surface of the alignment film is shown in the liquid crystal layer 36 to simplify the figures and clearly illustrate the structure of the liquid crystal diffraction element. However, as in Figure 6 The liquid crystal layer 36 is illustrated and conceptually represented in the diagram. The liquid crystal layer 36 has a structure in which liquid crystal compounds 40 are stacked and oriented along the thickness direction in the same manner as liquid crystal layers formed using compositions containing conventional liquid crystal compounds.

[0198] As described above, in the liquid crystal diffraction element, the liquid crystal layer 36 is formed using a composition containing a liquid crystal compound.

[0199] When the in-plane delay is set to λ / 2, the liquid crystal layer functions as a general λ / 2 plate, that is, it imparts a half-wavelength, or 180°, phase difference to the two orthogonal linearly polarized light components contained in the light incident on the liquid crystal layer.

[0200] Here, because the liquid crystal compound rotates and aligns in the planar direction, the liquid crystal layer refracts (diffracts) the incident circularly polarized light in the direction in which the optical axis rotates continuously, thus transmitting it. The direction of diffraction varies depending on the rotation direction of the incident circularly polarized light.

[0201] That is, the liquid crystal layer transmits circularly polarized light and diffracts the transmitted light.

[0202] Furthermore, the liquid crystal layer reverses the rotation direction of the transmitted circularly polarized light.

[0203] The liquid crystal layer has a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound changes as it rotates continuously within the plane of the liquid crystal layer in a direction represented by the alignment axis D.

[0204] Furthermore, the optical axis 40A originating from the liquid crystal compound 40 is the axis with the highest refractive index in the liquid crystal compound 40, also known as the slow axis. For example, in the case where the liquid crystal compound 40 is a rod-shaped liquid crystal compound, the optical axis 40A is along the long axis direction of the rod shape.

[0205] In the following description, "a direction represented by the arrangement axis D" will also be simply referred to as "the direction of the arrangement axis D". Furthermore, in the following description, the optical axis 40A derived from the liquid crystal compound 40 will also be referred to as "the optical axis 40A of the liquid crystal compound 40" or "optical axis 40A".

[0206] In the liquid crystal layer, the liquid crystal compound 40 is oriented in two dimensions in-plane, parallel to both the alignment axis D and the Y direction orthogonal to the alignment axis D. Furthermore, in Figure 6 , and so forth Figures 9-13 In this case, the Y direction becomes the direction perpendicular to the plane of the paper.

[0207] Figure 7 The diagram below is a conceptual representation of the liquid crystal layer 36.

[0208] Floor plan Figure 6 The middle image is a view of the liquid crystal diffraction element from above, that is, a view of the liquid crystal diffraction element viewed from the thickness direction (= the stacking direction of each layer (film)). In other words, it is a view of the liquid crystal layer 36 viewed from a direction orthogonal to the main surface.

[0209] Furthermore, in Figure 7 In this diagram, only the liquid crystal compound 40 on the surface of the alignment film 32 is shown to clearly illustrate the structure of the liquid crystal diffraction element. However, as... Figure 6 As shown, the liquid crystal layer 36 has a structure in the thickness direction formed by stacking liquid crystal compounds 40 from the surface of the alignment film 32, as described above.

[0210] In addition, Figure 6 and Figure 7 In this example, a portion of the liquid crystal layer 36 is used as a representative example. However, in each region of the liquid crystal layer, except for the length of one cycle (one cycle Λ) of the liquid crystal alignment pattern, they basically have the same structure and function.

[0211] The liquid crystal layer 36 has a liquid crystal alignment pattern in which the orientation of the optical axis 40A from the liquid crystal compound 40 changes as it rotates continuously in the plane of the liquid crystal layer 36 along the alignment axis D.

[0212] The orientation of the optical axis 40A of the liquid crystal compound 40 changes as it rotates continuously along the arrangement axis D (a specified direction). Specifically, the angle between the optical axis 40A of the liquid crystal compound 40 arranged along the arrangement axis D and the arrangement axis D varies depending on the position of the arrangement axis D. Along the arrangement axis D, the angle between the optical axis 40A and the arrangement axis D changes sequentially from θ to θ+180° or θ-180°.

[0213] Furthermore, the angle difference between the optical axes 40A of the liquid crystal compounds 40 that are adjacent to each other in the direction of the arrangement axis D is preferably 45° or less, more preferably 15° or less, and even more preferably a smaller angle.

[0214] On the other hand, in the liquid crystal compound 40 forming the liquid crystal layer 36, liquid crystal compounds 40 with the same orientation of the optical axis 40A are arranged at equal intervals in the Y direction orthogonal to the arrangement axis D direction, that is, in the Y direction orthogonal to a direction in which the optical axis 40A rotates continuously.

[0215] In other words, in the liquid crystal compound 40 that forms the liquid crystal layer 36, the orientation of the optical axis 40A of the liquid crystal compounds 40 arranged in the Y direction is equal to the angle formed by the direction of the arrangement axis D.

[0216] In a liquid crystal diffraction element, in the liquid crystal alignment pattern of this liquid crystal compound 40, the length (distance) by which the optical axis 40A of the liquid crystal compound 40 is rotated 180° along the alignment axis D direction, where the orientation of the in-plane optical axis 40A changes with continuous rotation, is defined as the length Λ of one cycle in the liquid crystal alignment pattern. In other words, the length of one cycle in the liquid crystal alignment pattern is defined by the distance from θ to θ+180° between the angle formed by the optical axis 40A of the liquid crystal compound 40 and the alignment axis D direction.

[0217] That is, the distance between the centers of two liquid crystal compounds 40 with equal angles relative to the alignment axis D along the alignment axis D is defined as the length Λ of one period. Specifically, as... Figure 7 As shown, the distance between the centers of two liquid crystal compounds 40 whose alignment axis D is aligned with the optical axis 40A is defined as the length Λ of one period. In the following description, the length Λ of one period will also be referred to as "one period Λ".

[0218] In a liquid crystal diffraction element, the liquid crystal alignment pattern of the liquid crystal layer repeats one cycle Λ in a direction that changes as the orientation of the alignment axis D, i.e., the optical axis 40A, rotates continuously.

[0219] As described above, in the liquid crystal layer, among the liquid crystal compounds arranged in the Y direction, the angle formed by the optical axis 40A and the arrangement axis D direction (a direction in which the optical axis of the liquid crystal compound 40 is rotated) is equal. The region in the Y direction where the liquid crystal compound 40 with the angle formed by the optical axis 40A and the arrangement axis D direction is equal is designated as region R.

[0220] In this case, the preferred value of the in-plane retardation (Re) in each region R is half the wavelength, i.e., λ / 2. These in-plane retardations are calculated by multiplying the refractive index difference Δn associated with the refractive index anisotropy of region R by the thickness of the liquid crystal layer. The refractive index difference associated with the refractive index anisotropy of region R in the liquid crystal layer is defined as the difference between the refractive index in the direction passing through the slow axis within the plane of region R and the refractive index in the direction orthogonal to the slow axis. That is, 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 40 in the direction of the optical axis 40A and the refractive index of the liquid crystal compound 40 in the direction perpendicular to the optical axis 40A within the plane of region R. In other words, the aforementioned refractive index difference Δn is equal to the refractive index difference of the liquid crystal compound.

[0221] If circularly polarized light is incident on this liquid crystal layer 36, the light is refracted and the direction of the circularly polarized light is reversed.

[0222] exist Figure 9 and Figure 10This effect is conceptually represented in the text. Furthermore, the product of the refractive index difference of the liquid crystal compound in liquid crystal layer 36 and the thickness of liquid crystal layer 36 is λ / 2.

[0223] like Figure 9 As shown, when the product of the refractive index difference of the liquid crystal compound in the liquid crystal layer 36 and the thickness of the liquid crystal layer 36 is λ / 2, if the incident light L1, which is left-handed circularly polarized light, is incident on the liquid crystal layer 36, the incident light L1 imparts a phase difference of 180° by passing through the liquid crystal layer 36, and the transmitted light L2 is converted into right-handed circularly polarized light.

[0224] Furthermore, the liquid crystal alignment pattern formed on the liquid crystal layer 36 is a periodic pattern along the alignment axis D, so the transmitted light L2 travels in a direction different from the direction of travel of the incident light L1. In this way, the incident light L1 of left-handed circularly polarized light is converted into the transmitted light L2 of right-handed circularly polarized light that is tilted at a predetermined angle relative to the incident direction along the alignment axis D.

[0225] On the other hand, such as Figure 10 As shown, when the product of the refractive index difference of the liquid crystal compound in the liquid crystal layer 36 and the thickness of the liquid crystal layer 36 is λ / 2, if the incident light L4 of right-hand circularly polarized light is incident on the liquid crystal layer 36, the incident light L4 will be converted into the transmitted light L5 of left-hand circularly polarized light by passing through the liquid crystal layer 36 and thus imparting a phase difference of 180°.

[0226] Furthermore, the liquid crystal alignment pattern formed on the liquid crystal layer 36 is a periodic pattern along the alignment axis D, so the transmitted light L5 travels in a direction different from the direction of travel of the incident light L4. At this time, the transmitted light L5 travels in a direction different from the transmitted light L2, that is, in a direction opposite to the direction of the alignment axis D relative to the incident direction. In this way, the incident light L4 is converted into the transmitted light L5, which is left-handed circularly polarized light tilted at a predetermined angle relative to the direction of the alignment axis D relative to the incident direction.

[0227] The liquid crystal layer 36 can adjust the refraction angles of transmitted light L2 and L5 by changing one period Λ of the formed liquid crystal alignment pattern. Specifically, in the liquid crystal layer 36, the shorter one period Λ of the liquid crystal alignment pattern, the stronger the interference between the light passing through adjacent liquid crystal compounds 40, thus enabling the transmitted light L2 and L5 to be refracted more.

[0228] Furthermore, by reversing the rotation direction of the optical axis 40A of the liquid crystal compound 40, which rotates along the alignment axis D, the direction of refraction of transmitted light can be reversed. That is, in Figures 9-10 In the example shown, the optical axis 40A, which is oriented toward the alignment axis D, rotates clockwise. However, by setting the rotation direction to counterclockwise, the direction of refraction of the transmitted light can be reversed.

[0229] In the liquid crystal layer 36, the in-plane retardation value of the plurality of regions R is preferably half a wavelength, but more preferably the in-plane retardation Re(550) = Δn of the plurality of regions R of the liquid crystal layer 36 relative to incident light with a wavelength of 550 nm. 550 ×d is within the range specified in equation (1) below. Here, Δn 550 d is the refractive index difference caused by the anisotropy of the refractive index in region R when the wavelength of the incident light is 550nm, and d is the thickness of the liquid crystal layer 36.

[0230] 200nm≤Δn 550 ×d≤350nm……(1)

[0231] That is, if the in-plane retardation Re(550) of multiple regions R of the liquid crystal layer 36 is Δn 550 If ×d satisfies equation (1), then a sufficient amount of circularly polarized light components incident on the liquid crystal layer 36 can be converted into circularly polarized light traveling in a direction inclined in the positive or negative direction relative to the arrangement axis D. In-plane retardation Re(550)=Δn 550 ×d is more preferably 225nm≤Δn 550 ×d≤340nm, more preferably 250nm≤Δn 550 ×d≤330nm.

[0232] Equation (1) above represents the in-plane retardation Re(λ) = Δn for multiple regions R of the liquid crystal layer relative to incident light with a wavelength of 550 nm and an incident light with a wavelength of λ nm. λ ×d is preferably set appropriately within the range specified in the following formula (1-2).

[0233] 0.7×(λ / 2)nm≤Δn λ ×d≤1.3×(λ / 2)nm……(1-2)

[0234] Furthermore, the in-plane retardation Re(450) = Δn of region R of liquid crystal layer 36 relative to incident light with a wavelength of 450 nm is... 450 ×d, the in-plane retardation Re(550)=Δn of region R of liquid crystal layer 36 relative to incident light with wavelength of 550nm. 550 ×d preferably satisfies the following equation (2). Here, Δn 450 It is the refractive index difference caused by the anisotropy of the refractive index in region R when the wavelength of the incident light is 450nm.

[0235] (Δn 450 ×d) / (Δn 550 ×d)<1.0……(2)

[0236] Equation (2) indicates that the liquid crystal compound 40 contained in the liquid crystal layer 36 has reverse dispersion. That is, by satisfying equation (2), the liquid crystal layer 36 can correspond to incident light with a wide bandwidth wavelength.

[0237] The liquid crystal layer is composed of a cured layer of a liquid crystal composition containing rod-shaped liquid crystal compounds or disk-shaped liquid crystal compounds, and has a liquid crystal alignment pattern with optical axes of rod-shaped liquid crystal compounds or disk-shaped liquid crystal compounds as described above.

[0238] By forming an alignment film on a support, coating the alignment film with a liquid crystal composition, and curing it, a liquid crystal layer composed of a cured layer of the liquid crystal composition can be obtained. Furthermore, while the liquid crystal layer functions as a so-called λ / 2 plate, this invention includes a laminate integrally comprising a support and an alignment film that functions as a λ / 2 plate.

[0239] Furthermore, the liquid crystal composition used to form the liquid crystal layer contains rod-shaped or disc-shaped liquid crystal compounds, and may contain other components such as leveling agents, orientation control agents, polymerization initiators, and orientation aids.

[0240] Furthermore, the liquid crystal layer preferably has a wide bandwidth relative to the wavelength of the incident light, and it is preferably constructed using a liquid crystal material with an inversely dispersed birefringence. It is also preferable to impart a twisting component to the liquid crystal composition and to stack different phase difference layers, so that the liquid crystal layer becomes substantially wide bandwidth relative to the wavelength of the incident light. For example, a method for achieving a wide bandwidth patterned λ / 2 plate by stacking two liquid crystal layers with different twisting directions in the liquid crystal layer is shown in Japanese Patent Application Publication No. 2014-089476, etc., and can preferably be used in this invention.

[0241] -Rod-shaped liquid crystal compounds-

[0242] As rod-shaped liquid crystal compounds, preferably used are methylimine derivatives, azo derivatives, cyanobiphenyl derivatives, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexane derivatives, cyano-substituted phenylpyrimidine derivatives, alkoxy-substituted phenylpyrimidine derivatives, phenyl dioxane derivatives, diphenylacetylene derivatives, and alkenylcyclohexylbenzonitrile derivatives. Not only can low-molecular-weight liquid crystal molecules like those mentioned above be used, but high-molecular-weight liquid crystal molecules can also be used.

[0243] More preferably, the orientation of the rod-shaped liquid crystal compound is fixed by polymerization. As a polymerizable rod-shaped liquid crystal compound, it can be used in Makromol. Chem., Vol. 190, pp. 2255 (1989), Advanced Materials. Compounds described in 5 volumes, 107 pages (1993), U.S. Patent No. 4,683,327, U.S. Patent No. 5,622,648, U.S. Patent No. 5,770,107, International Publication No. 95 / 22586, International Publication No. 95 / 24455, International Publication No. 97 / 00600, International Publication No. 98 / 23580, International Publication No. 98 / 52905, Japanese Patent Application Publication No. 1-272,551, Japanese Patent Application Publication No. 6-16616, Japanese Patent Application Publication No. 7-110,469, Japanese Patent Application Publication No. 11-80081, and Japanese Patent Application Publication No. 2001-64627. Furthermore, as rod-shaped liquid crystal compounds, compounds described in Japanese Patent Application Publication No. 11-513019 and Japanese Patent Application Publication No. 2007-279688 are preferred.

[0244] -Disc-shaped liquid crystal compound-

[0245] As a disc-shaped liquid crystal compound, the disc-shaped liquid crystal compound described in Japanese Patent Application Publication No. 2007-108732 and Japanese Patent Application Publication No. 2010-244038 is preferred.

[0246] Furthermore, when a disk-shaped liquid crystal compound is used in the liquid crystal layer, the liquid crystal compound 40 rises in the thickness direction in the liquid crystal layer, and the optical axis 40A from the liquid crystal compound is defined as an axis perpendicular to the disk surface, the so-called fast axis.

[0247] To obtain high diffraction efficiency, liquid crystal compounds with high refractive index anisotropy Δn are preferred. By increasing the refractive index anisotropy, the diffraction efficiency can be maintained at a relatively high level when the incident angle changes. There are no particular limitations on the liquid crystal compound with high refractive index anisotropy Δn, but compounds exemplified in WO2019 / 182129A1 and compounds represented by the following general formula (I) are preferred.

[0248] [Chemical Formula 1]

[0249]

[0250] In general formula (I),

[0251] P 1 and P 2 Each can be used independently to represent a hydrogen atom, -CN, -NCS, or a polymeric group.

[0252] Sp 1 and Sp 2 Each can independently represent a single bond or a divalent linker. Where Sp 1 and Sp 2 It does not mean that it contains a divalent linker consisting of at least one group selected from the group consisting of aromatic hydrocarbon cyclic groups, aromatic heterocyclic groups and aliphatic hydrocarbon cyclic groups.

[0253] Z 1 Z 2 and Z 3 These characters independently represent single bonds, -O-, -S-, -CHR-, -CHRCHR-, -OCHR-, -CHRO-, -SO-, -SO2-, -COO-, -OCO-, -CO-S-, -S-CO-, -O-CO-O-, -CO-NR-, -NR-CO-, -SCHR-, -CHRS-, -SO-CHR-, -CHR-SO-, -SO2-CHR-, -CHR-SO2-, -CF2O-, -OCF2-, -CF2S-, -SCF2-, -OCHRCHRO-, -SCHRCHRS-, and -SO-CHR. CHR-SO-, -SO2-CHRCHR-SO2-, -CH=CH-COO-, -CH=CH-OCO-, -COO-CH=CH-, -OCO-CH=CH-, -COO-CHRCHR-, -OCO-CHRCHR-, -CHRCHR-COO-, -CHRCHR-OCO-, -COO-CHR-, -OCO-CHR-, -CHR-COO-, -CHR-OCO-, -CR=CR-, -CR=N-, -N=CR-, -N=N-, -CR=NN=CR-, -CF=CF-, or -C≡C-. R represents a hydrogen atom or an alkyl group with 1 to 10 carbon atoms. When multiple Rs exist, they can be the same or different. When Z 1 and Z 2 When multiple Z exist, they can be the same or different. 3 They can be the same or different. Among them, those connected to Sp... 2 Z 3 Indicates a single key.

[0254] X 1 and X 2 Each can independently represent a single bond or -S-. Multiple X's exist. 1 and X 2 They can be the same or different. There are multiple X's. 1 And there are multiple X 2 In the above, at least one of them represents -S-.

[0255] k represents an integer from 2 to 4.

[0256] m and n each independently represent an integer from 0 to 3. There can be multiple m values, which can be the same or different.

[0257] A 1 A 2 A 3 and A 4 Each of the following formulas (B-1) to (B-7) can independently represent a group formed by linking two or three groups represented by any one of the following formulas (B-1) to (B-7). Multiple A's exist. 2 and A 3 They can be the same or different. When A 1 and A 4 When multiple instances exist, they can be the same or different.

[0258] [Chemical Formula 2]

[0259]

[0260] In general formulas (B-1) to (B-7),

[0261] W 1 ~W 18 CR are represented independently. 1 Or N, R 1 L represents a hydrogen atom or the following substituent.

[0262] Y 1 ~Y 6 NR are represented independently. 2 O or S, R 2 L represents a hydrogen atom or the following substituent.

[0263] G 1 ~G 4 CR are represented independently. 3 R 4 NR 5 O or S, R 3 ~R 5 Each can be represented independently by a hydrogen atom or a substituent L as described below.

[0264] M 1 and M 2 CR are represented independently. 6 Or N, R 6 L represents a hydrogen atom or the following substituent.

[0265] * indicates the bonding location.

[0266] Substituent L is an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkanoyl group having 1 to 10 carbon atoms, an alkanoyloxy group having 1 to 10 carbon atoms, an alkanoylamino group having 1 to 10 carbon atoms, an alkanoylthio group having 1 to 10 carbon atoms, an alkoxycarbonyl group having 2 to 10 carbon atoms, an alkylaminocarbonyl group having 2 to 10 carbon atoms, an alkanothiocarbonyl group having 2 to 10 carbon atoms, a hydroxyl group, an amino group, a mercapto group, a carboxyl group, a sulfonyl group, an amide group, a cyano group, a nitro group, a halogen atom, or a polymerizable group. Wherein, if the group described as substituent L has -CH2-, a group formed by replacing at least one of the -CH2- groups with -O-, -CO-, -CH=CH-, or -C≡C- is also included in substituent L. Furthermore, when the group described as substituent L has hydrogen atoms, a group formed by replacing at least one of the hydrogen atoms contained in the group with at least one selected from the group consisting of fluorine atoms and polymerizable groups is also included in substituent L.

[0267] To maintain high diffraction efficiency with varying incident angles, the refractive index anisotropy Δn of the liquid crystal compound is... 550 Preferably, it is 0.15 or more, more preferably 0.2 or more, even more preferably 0.25 or more, and most preferably 0.3 or more.

[0268] <The function of liquid crystal diffraction elements>

[0269] As described above, a liquid crystal layer formed using a composition containing a liquid crystal compound, having a liquid crystal alignment pattern with an optical axis 40A rotating along the alignment axis D, refracts circularly polarized light. However, the smaller the period Λ of the liquid crystal alignment pattern, the larger the angle of refraction.

[0270] Therefore, when patterns are formed in different regions of the plane in a manner that is different from one cycle Λ of the liquid crystal alignment pattern, the light incident on different regions of the plane is refracted at different angles.

[0271] The following is for reference. Figure 11 The conceptual diagram illustrates the function of the liquid crystal diffraction element in detail. Figure 11 This is a conceptual diagram showing a portion of a cross-section of a direction along which the orientation of the optical axis 40A of the liquid crystal compound 40 of the liquid crystal layer 36 changes as it rotates continuously.

[0272] In liquid crystal diffraction elements, the optical effect is essentially expressed only by the liquid crystal layer. Therefore, in Figure 11 In the figure, only the liquid crystal layer 36 is shown as the liquid crystal diffraction element to simplify the figure and clearly show the structure and function.

[0273] As described above, the liquid crystal diffraction element has a liquid crystal layer 36.

[0274] Liquid crystal diffraction elements, as an example, refract and transmit incident light in a predetermined direction using circularly polarized light. Figure 11 In this case, the incident light is set as left-handed circularly polarized light.

[0275] exist Figure 11 In the portion shown, liquid crystal layer 36 from Figure 11 Starting from the left side, there are three regions A0, A1, and A2, with a different length Λ for one cycle in each region. Specifically, the length Λ of one cycle decreases in the order of regions A0, A1, and A2. Furthermore, regions A1 and A2 have a structure in which the optical axis is twisted and rotated in the thickness direction of the liquid crystal layer (hereinafter also referred to as a twist structure). The twist angle of each region can be the same or different, and can be appropriately set according to the required performance. Figure 11 A0 is an example of a region where the torsion angle in the thickness direction of region A1 is smaller than that in region A2, and region A0 is a region without a torsion structure (i.e., the torsion angle is 0°).

[0276] The twist angle is the twist angle along the entire thickness direction.

[0277] When the liquid crystal layer has a twisted structure, such as Figure 12 As shown, in a cross-section observed using a SEM (Scanning Electron Microscope), the bright portion 42 and the dark portion 44 are tilted relative to the main surface of the liquid crystal layer 36.

[0278] In a liquid crystal diffraction element, when left-handed circularly polarized light LC1 is incident on region A1 within the plane of the liquid crystal layer 36, as described above, it is refracted and transmitted at a predetermined angle relative to the incident direction along the alignment axis D—that is, a direction in which the orientation of the optical axis of the liquid crystal compound changes continuously with rotation. Similarly, when left-handed circularly polarized light LC2 is incident on region A2 within the plane of the liquid crystal layer 36, it is refracted and transmitted at a predetermined angle relative to the incident direction along the alignment axis D. Similarly, when left-handed circularly polarized light LC0 is incident on region A0 within the plane of the liquid crystal layer 36, it is refracted and transmitted at a predetermined angle relative to the incident direction along the alignment axis D.

[0279] Here, regarding the angle of refraction based on liquid crystal layer 36, one period Λ of the liquid crystal alignment pattern in region A2 is... A2 Compared to one period Λ of the liquid crystal alignment pattern in region A1 A1 Short, therefore, as Figure 11 As shown, the angle θ of the transmitted light in region A2 is relative to the angle of refraction of the incident light. A2 The angle θ of the transmitted light is greater than that of region A1 A1Furthermore, one period Λ of the liquid crystal alignment pattern in region A0 A0 Compared to one period Λ of the liquid crystal alignment pattern in region A1 A1 Long, therefore, as Figure 11 As shown, the angle θ of the transmitted light in region A0 is related to the angle of refraction relative to the incident light. A0 The angle θ of the transmitted light is smaller than that of region A1 A1 .

[0280] By using a liquid crystal alignment pattern Λ that shortens the region from the center side to the end side of the liquid crystal diffraction element, light incident on the more end side can be refracted more than light incident near the center of the liquid crystal diffraction element, and can function as a positive lens that converges light.

[0281] Here, in the diffraction of light from a liquid crystal layer with a liquid crystal alignment pattern that changes as the orientation of the optical axis of the in-plane liquid crystal compound rotates continuously, the diffraction angle increases and the diffraction efficiency may decrease.

[0282] Therefore, when the liquid crystal layer is configured such that the orientation of the optical axis of the liquid crystal compound varies within a period of 180° rotation within the plane, the amount of diffracted light may differ depending on the incident position of the light, since the diffraction angle varies depending on the incident position within the plane. That is, depending on the incident position within the plane, regions where the transmitted and diffracted light are darker may occur.

[0283] In contrast, when a liquid crystal diffraction element has a region in which the liquid crystal layer is twisted and rotated in the thickness direction, the reduction in the diffraction efficiency of the refracted light can be suppressed. Therefore, a liquid crystal diffraction element having a region in which the liquid crystal layer is twisted and rotated in the thickness direction is preferable to having a region with different twist angles in the thickness direction.

[0284] Specifically, the shorter the period Λ of the liquid crystal alignment pattern, the greater the twist angle in the thickness direction, so that the amount of transmitted light can be made uniform regardless of the incident position in the plane.

[0285] Furthermore, in a liquid crystal diffraction element, it is preferable to have a region with a twist angle in the thickness direction of 10° to 360°.

[0286] In a liquid crystal diffraction element, the twist angle in the thickness direction can be appropriately set according to one period Λ of the liquid crystal alignment pattern in the plane.

[0287] Here, in Figure 6 In the example shown, the liquid crystal diffraction element is configured to have a structure with one liquid crystal layer, but it is not limited to this and may also have two or more liquid crystal layers.

[0288] Furthermore, when a liquid crystal diffraction element has two or more liquid crystal layers, it can further have liquid crystal layers that are twisted and rotated in different directions (or the direction of the twist angle) in the thickness direction.

[0289] For example, a liquid crystal layer can be stacked as follows: a liquid crystal alignment pattern having an optical axis from a liquid crystal compound that rotates in one direction, and further having a region where the optical axis is twisted and rotated in the thickness direction of the liquid crystal layer, and having regions where the rotation angles are different in the plane, and liquid crystal layers that are twisted and rotated in different directions in the thickness direction.

[0290] Thus, by further having liquid crystal layers with different directions of twisting and rotating in the thickness direction, incident light with respect to various polarization states can be effectively refracted in regions with twist angles in the thickness direction.

[0291] Here, when liquid crystal layers have different directions of twisting and rotating in the thickness direction, it is preferable that the twist angle in the thickness direction is the same in each region in the plane.

[0292] However, the present invention is not limited thereto. In liquid crystal diffraction elements, there is no limitation on the torsion angle in the thickness direction. It can be set appropriately according to the application of the optical element.

[0293] Furthermore, in liquid crystal layers that are twisted and rotated in different directions along their thickness, the in-plane retardation Re(λ) = Δn for multiple regions R of the liquid crystal layer with respect to incident light of wavelength λnm is... λ ×d is preferred to be the same.

[0294] However, the present invention is not limited thereto. In a liquid crystal diffraction element, the in-plane retardation Re(λ) = Δn for multiple regions R of the liquid crystal layer with respect to incident light of wavelength λnm is... λ There are no restrictions on ×d; it can be set appropriately according to the application of the optical element.

[0295] In liquid crystal diffraction elements, there is no restriction on one period Λ in the alignment pattern of the liquid crystal layer; it can be set appropriately according to the application of the optical element.

[0296] (Methods for forming regions with different torsion angles in a torsion structure)

[0297] In a liquid crystal layer, a structure with different twist angles in regions having a twisted structure can be formed by the following method: using a chiral reagent whose helical twisting power (HTP) changes due to reverse isomerization, dimerization, and isomerization and dimerization by irradiation light, before or during the curing of the liquid crystal composition forming the liquid crystal layer, the wavelength of light that changes the HTP of the chiral reagent is irradiated by changing the irradiation amount of each region.

[0298] For example, by using a chiral reagent whose HTP decreases upon light irradiation, the HTP of the chiral reagent is reduced by light irradiation. Here, by varying the amount of light irradiation in each region, for example, in regions with high irradiation, HTP decreases significantly, the helical induction decreases, and therefore the torsion angle of the torsion structure decreases. On the other hand, in regions with low irradiation, the reduction in HTP is less, and therefore the torsion angle of the torsion structure increases.

[0299] There are no particular limitations on the method of changing the amount of light irradiation in each area. Methods such as irradiating light through a gradient mask, changing the irradiation time in each area, or changing the irradiation intensity in each area can be used.

[0300] A gradient mask is a mask whose transmittance changes in-plane relative to the illumination light.

[0301] In this invention, when the liquid crystal diffraction element functions as a convex lens, it is preferable to satisfy the following formula.

[0302] Φ(r)=(π / λ)[(r 2 +f 2 ) 1 / 2 -f]

[0303] Here, r is the distance from the center of the concentric circles, as given by the equation r = (x 2 +y 2 ) 1 / 2 Let x and y represent the positions within the plane, and (x, y) = (0, 0) represent the center of the concentric circles. Φ(r) represents the angle of the optical axis at a distance r from the center, λ represents the wavelength, and f represents the target focal distance.

[0304] Furthermore, in this invention, for example, when it is necessary to set the light intensity distribution of transmitted light, depending on the application of the liquid crystal diffraction element, a structure can be used that does not gradually change one period Λ in one direction of continuous rotation toward the optical axis, but rather has regions that partially have one period Λ different in one direction of continuous rotation toward the optical axis. For example, as a method of locally changing one period Λ, a method of patterning the photo-alignment film by scanning and exposing while arbitrarily changing the polarization direction of the focused laser beam can be used.

[0305] Furthermore, liquid crystal diffraction elements can have a liquid crystal layer that is completely uniform within one period Λ and a liquid crystal layer that has different regions within one period Λ.

[0306] Here, in Figure 5 In the example shown, the liquid crystal alignment pattern of the liquid crystal layer is set as a concentric circle pattern that radiates from the center of the liquid crystal layer and changes direction as it rotates continuously. However, it is not limited to this as long as it can converge the incident polarized light.

[0307] For example, the liquid crystal alignment pattern of the liquid crystal layer can be a concentric circle pattern in which the direction of the optical axis of the liquid crystal compound changes as it rotates continuously. That is, it can also be a concentric circle pattern in which the lines formed by connecting liquid crystal compounds with the optical axes pointing in the same direction are elliptical. Alternatively, it can be a pattern that is a deformation of the concentric circle pattern, as long as it can converge the incident polarized light.

[0308] As described above, a liquid crystal diffraction element can have two or more liquid crystal layers. In this case, when at least two liquid crystal layers are scanned using a scanning electron microscope to obtain a cross-sectional image of a section cut along the thickness direction in a direction that changes continuously while rotating along the optical axis of the liquid crystal compound, bright and dark areas originating from the optical axis are observed. In the at least two liquid crystal layers, the tilt angles of the bright and dark areas relative to the main surface of the liquid crystal layer are preferably different from each other. Furthermore, the tilt directions of the bright and dark areas are preferably different from each other.

[0309] exist Figure 13 An example of such a liquid crystal diffraction element is shown in the figure.

[0310] Figure 13 The liquid crystal diffraction element shown has a structure formed by sequentially stacking a first liquid crystal layer 217, a second liquid crystal layer 219, and a third liquid crystal layer 218.

[0311] The first liquid crystal layer 217 and the third liquid crystal layer 218 have liquid crystal alignment patterns that change as the orientation of the optical axis derived from the liquid crystal compound rotates continuously in at least one direction within the plane, and are twisted along the thickness direction.

[0312] "Optical axis twist orientation along the thickness direction" refers to a state in which the orientation of optical axes arranged along the thickness direction from one main surface of the liquid crystal layer to another is relatively changed and twisted in one direction. Twist can be right-handed or left-handed, but it can be applied according to the desired diffraction direction. Furthermore, the twist of the optical axis in the thickness direction is less than one turn, i.e., the twist angle is less than 360°. The twist angle of the liquid crystal compound in the thickness direction is preferably about 10° to 200°, more preferably about 20° to 180°. In the case of a cholesterol-type orientation, selective reflectivity is achieved, reflecting a twist angle of 360° or more and specific circularly polarized light in a specific wavelength region. The "twist orientation" in this specification does not include cholesterol-type orientation, and selective reflectivity is not produced in liquid crystal layers with a twist orientation.

[0313] When observing the cross-section of a liquid crystal layer with this liquid crystal alignment pattern using SEM, it was observed that... Figure 13 The visible and hidden lines are shown. For example... Figure 13 The liquid crystal alignment pattern is displayed by overlapping bright and dark lines, and the period of the bright and dark lines is consistent with the period of the liquid crystal alignment pattern.

[0314] like Figure 13 As shown, in the first liquid crystal layer 217 and the third liquid crystal layer 218, the bright lines and dark lines have the same tilt angle relative to the main surface of the liquid crystal layer, but their tilt directions are different. Therefore, in the first liquid crystal layer 217 and the third liquid crystal layer 218, the bright lines and dark lines are symmetrical vertically (symmetrical with respect to the center line in the thickness direction).

[0315] Furthermore, the second liquid crystal layer 219 disposed between the first liquid crystal layer 217 and the third liquid crystal layer 218 has a liquid crystal alignment pattern that changes as the orientation of the optical axis originating from the liquid crystal compound rotates continuously in at least one direction within the plane, and is not twisted along the thickness direction. Therefore, the bright and dark lines of the second liquid crystal layer 219 are along the normal to the interface of the second liquid crystal layer 219 and are not tilted.

[0316] One period of the liquid crystal alignment pattern of the first liquid crystal layer 217, the second liquid crystal layer 219 and the third liquid crystal layer 218 is different in each region of the plane, but one period of the liquid crystal alignment pattern of the first liquid crystal layer 217, the second liquid crystal layer 219 and the third liquid crystal layer 218 at the same position in the plane is equal.

[0317] Therefore, in the liquid crystal diffraction element having a first liquid crystal layer 217, a second liquid crystal layer 219 and a third liquid crystal layer 218, the bright lines and dark lines are symmetrical vertically.

[0318] When the second liquid crystal layer 219 is aligned without twisting along the thickness direction, the diffraction efficiency is high for light incident from the normal direction, but low for light incident from the oblique direction. On the other hand, the diffraction efficiency for light incident from the oblique direction can be improved in the first liquid crystal layer 217 and the third liquid crystal layer 218.

[0319] Therefore, liquid crystal diffraction elements formed by stacking these liquid crystal layers can reduce the change in diffraction efficiency caused by the incident angle and improve the average diffraction efficiency.

[0320] In addition, Figure 13 In the example shown, the liquid crystal diffraction element is designed with a symmetrical structure between the bright and dark lines, but it is not limited to this.

[0321] For example, in the first liquid crystal layer 217, the second liquid crystal layer 219, and the third liquid crystal layer 218, by varying the torsion angle in the thickness direction that changes along the direction from the optical axis of the liquid crystal compound, the bright and dark parts on the center side of the liquid crystal diffraction element can be configured to be vertically symmetrical, and vertically asymmetrical, on the center side of the liquid crystal diffraction element.

[0322] And, as Figure 14 The example shown can also be configured as an asymmetrical structure in which the bright and dark parts of the first liquid crystal layer 37a, the second liquid crystal layer 37b, and the third liquid crystal layer 37c are tilted to each other at different angles.

[0323] Here, in this invention, as Figure 13 and Figure 14 As shown, the liquid crystal layer can preferably be used in SEM images to have bright and dark areas extending from one surface to another, with the dark areas having two or more inflection points, and regions with different tilt directions of the dark areas in the thickness direction.

[0324] exist Figure 13 and Figure 14 In the example shown, the liquid crystal layer has a stripe pattern with bright and dark areas. Each dark area is located at two positions along the thickness direction, with varying tilt angles relative to the surface. That is, each dark area has two inflection points. Furthermore, within any dark area, the tilt direction in the upper region of the figure is opposite to the tilt direction in the lower region. In other words, each dark area has regions with different tilt directions.

[0325] Furthermore, the number of inflection points where the tilt direction of the dark areas in the liquid crystal layer is reversed is preferably odd. Figure 14 In the example shown, the number of inflection points where the tilt direction of the dark area is reversed is 1.

[0326] The average tilt angle of the dark areas in the liquid crystal layer preferably changes gradually in one direction. The average tilt angle of the dark areas is the angle of the line segment connecting a point on one surface of a dark area to a point on another surface relative to the main surface of the liquid crystal layer.

[0327] Furthermore, the refractive index difference Δn, which accompanies the anisotropy of the refractive index of the liquid crystal layer, 550 The preferred value is 0.2 or higher.

[0328] Another example of a liquid crystal diffraction element having two or more liquid crystal layers, with the bright and dark portions of at least two liquid crystal layers having different tilt angles, is described in International Publication No. 2020 / 066429.

[0329] The image display unit of the present invention described above is preferably used as an image display unit for a head-mounted display.

[0330] Example

[0331] The following examples and comparative examples further illustrate the features of the present invention. The materials, amounts, proportions, processing contents, processing steps, etc., shown in the following examples can be appropriately modified without departing from the spirit of the invention. Therefore, the scope of the present invention should not be limited by the specific examples shown below.

[0332] [Example 1]

[0333] <Fabrication of Polarizing Diffraction Elements>

[0334] (Support structure)

[0335] Glass was prepared as a support.

[0336] (Formation of the orientation film)

[0337] The following alignment film forming coating solution is continuously applied to a support by spin coating. The support with the coating solution is then dried on a hot plate at 60°C for 60 seconds to form an alignment film.

[0338] Coating solution for oriented film formation

[0339]

[0340] -Raw material A for photoorientation-

[0341] [Chemical Formula 3]

[0342]

[0343] (Exposure of the alignment film)

[0344] use Figure 8The exposure apparatus shown exposes the alignment film, thereby forming an alignment film P-1 with an alignment pattern.

[0345] In the exposure apparatus, a device using a laser beam with an output wavelength of 325 nm is used as the laser. The exposure dose based on interference light is set to 1000 mJ / cm². 2 By using Figure 8 The exposure apparatus shown causes one cycle of the orientation pattern to gradually shorten in the outward direction.

[0346] (Formation of the liquid crystal layer)

[0347] As a liquid crystal composition for forming the first liquid crystal layer, the following composition A-1 was prepared.

[0348] Composition A-1

[0349]

[0350] Liquid crystal compound L-1

[0351] [Chemical Formula 4]

[0352]

[0353] Chiral reagent M-1

[0354] [Chemical Formula 5]

[0355]

[0356] Leveling agent T-1

[0357] [Chemical Formula 6]

[0358]

[0359] The liquid crystal layer is formed by multilayer coating of composition A-1 onto an alignment film P-1. Multilayer coating refers to the following process: first, a first layer of composition A-1 is coated onto the alignment film, followed by heating, cooling, and UV curing to create a liquid crystal immobilization layer; then, subsequent layers are overlapped onto this liquid crystal immobilization layer, and the same heating, cooling, and UV curing processes are performed. Through multilayer coating, even as the total thickness of the liquid crystal layer increases, the alignment direction of the alignment film is reflected from the bottom to the top of the liquid crystal layer.

[0360] First, in the first layer, the following composition A-1 is coated onto the alignment film P-1. The coating is heated to 80°C on a hot plate, and then subjected to high-pressure mercury lamp at 300 mJ / cm under nitrogen atmosphere. 2 The irradiation dose is 365nm ultraviolet light applied to the coating to fix the orientation of the liquid crystal compound.

[0361] After the second layer, the liquid crystal layer is overlapped and coated again. Under the same conditions as above, it is heated, cooled, and then cured with ultraviolet light to create a liquid crystal immobilization layer. This process of overlapping coating is repeated until the total thickness reaches the desired film thickness, thus forming the first liquid crystal layer.

[0362] The birefringence Δn of the cured layer of liquid crystal composition A1 was determined by measuring the retardation value and film thickness of the liquid crystal immobilized layer (cured layer) obtained by coating liquid crystal composition A1 onto a separately prepared support with an alignment film for retardation measurement, ensuring the liquid crystal compound is horizontally aligned on the substrate, and then immobilizing it by irradiation with ultraviolet light. Δn can be calculated by dividing the retardation value by the film thickness. The retardation value was measured at the target wavelength using an Axometrix Axoscan, and the film thickness was measured using a scanning electron microscope (SEM).

[0363] In the first liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 160nm, and becomes as Figure 5 The concentric (radial) periodic alignment surfaces are shown. Furthermore, the liquid crystal alignment pattern of this first liquid crystal layer is a liquid crystal alignment pattern whose period shortens outwards. Also, the torsion angle in the thickness direction of the first liquid crystal layer is 80° to the right in-plane. Hereinafter, unless otherwise stated, "Δn" will be used in the same manner. 550 The determination of ×d”, etc.

[0364] As a liquid crystal composition for forming the second liquid crystal layer, the following composition A-2 was prepared.

[0365] Composition A-2

[0366]

[0367]

[0368] Except for adjusting the film thickness of the liquid crystal layer using composition A-2, a second liquid crystal layer is formed on the first liquid crystal layer in the same manner as the first liquid crystal layer.

[0369] In the second liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 330nm, and becomes as Figure 5 The second liquid crystal layer exhibits a concentric (radial) periodic alignment surface. Furthermore, the liquid crystal alignment pattern of this second liquid crystal layer is a pattern whose period shortens outwards. Additionally, the twist angle in the thickness direction of the second liquid crystal layer is 0° in-plane.

[0370] As a liquid crystal composition for forming the third liquid crystal layer, the following composition A-3 was prepared.

[0371] Composition A-3

[0372]

[0373] Chiral reagent H-1

[0374] [Chemical Formula 7]

[0375]

[0376] Except for adjusting the film thickness of the liquid crystal layer using composition A-3, a third liquid crystal layer was formed on the second liquid crystal layer in the same manner as the first liquid crystal layer.

[0377] In the third liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 160nm, and becomes as Figure 5 The concentric (radial) periodic alignment surfaces are shown. Furthermore, the liquid crystal alignment pattern of this third liquid crystal layer is a liquid crystal alignment pattern whose period shortens outwards. Also, the torsion angle in the thickness direction of the liquid crystal layer is 80° to the left in-plane.

[0378] Parallel light was incident on a liquid crystal diffraction element having 1 to 3 liquid crystal layers, and the focal distance of the converged outgoing light was measured. The focal distance was 30 mm.

[0379] <Preparation of Phase Contrast Plates>

[0380] A cellulose acylated film, an orientation film, and a film having an optically anisotropic layer C were obtained by means of the same method as that described in paragraphs 0102 to 0126 of Japanese Patent Application Publication No. 2019-215416 for the positive A plate.

[0381] The optical anisotropy layer C is a positive A plate (phase retardation plate), and the thickness of the positive A plate is controlled so that Re(550) is 138nm.

[0382] <Production of Image Display Unit>

[0383] An image display unit was fabricated using a first linear polarizer, a first phase retardation plate (λ / 4 plate), a liquid crystal diffraction element, a second phase retardation plate (λ / 4 plate), and a linear polarizer (reference). Figure 1The Oculus Rift S, a commercially available head-mounted display from Oculus Corporation, was disassembled. The display itself was used as the image display device, and linear polarizers were attached to its surface as the first and second linear polarizers. On the image display device side, the first linear polarizer was configured such that the absorption axis angle was 90°. The first phasor was configured such that the slow axis angle was 45°. The second phasor was configured such that the slow axis angle was -45°. The second linear polarizer was configured such that the absorption axis angle was 0°. Furthermore, the described axis angles are based on the horizontal direction of the head-mounted display (0°), and are set to positive clockwise when viewing the image display unit from the visual recognition side.

[0384] Furthermore, the distance between the image display device and the liquid crystal diffraction element is set to 30mm.

[0385] [Example 2]

[0386] In the fabrication of the liquid crystal diffraction element, the alignment pattern formed as alignment film P-1 was changed, the focal distance was set to 15mm, and the distance between the image display device and the liquid crystal diffraction element was set to 15mm. Otherwise, the image display unit was fabricated in the same manner as in Example 1.

[0387] [Example 3]

[0388] In the fabrication of the liquid crystal diffraction element, the alignment pattern formed as alignment film P-1 was changed, the focal distance was set to 10 mm, and the distance between the image display device and the liquid crystal diffraction element was set to 10 mm. Otherwise, the image display unit was fabricated in the same manner as in Example 1.

[0389] [Comparative Example 1]

[0390] An image display unit is fabricated by placing a Fresnel lens on the display surface side of the image display device. The focal distance of the Fresnel lens is 40mm. The distance between the image display device and the Fresnel lens is set to 40mm.

[0391] The Fresnel lens uses the lens that comes with the Oculus Rift S.

[0392] [Comparative Example 2]

[0393] Optical elements were fabricated using a first absorptive linear polarizer, a first retardation plate (λ / 4 plate), a partial reflector, a second retardation plate (λ / 4 plate), a reflective linear polarizer, and a second absorptive linear polarizer, and an image display unit as a head-mounted display was fabricated. The Oculus Rift S, a commercially available head-mounted display from Oculus Corporation, was disassembled. Using the display and the absorptive linear polarizer attached to its surface, the absorption axis angle of the first absorptive linear polarizer was configured to be 90°. As a partial reflector, an aluminum film was formed by sputtering onto the convex surface of a lens with a diameter of 5 cm and a radius of curvature of 10 cm, resulting in a transmittance of 50% and a reflectance of 50%. That is, the partial reflector was curved. A 3M Company DBEF was used as the second reflective linear polarizer, configured with a transmission axis angle of 90°. On the visual recognition side of the second reflective linear polarizer, the second absorptive linear polarizer was configured with an absorption axis angle of 0°. Furthermore, the first phase difference plate and the second phase difference plate are configured with slow axes of 45° and -45°, respectively.

[0394] Set the dot distance of some of the reflectors to 20mm. Set the distance between the image display device and some of the reflectors to 20mm.

[0395] [Comparative Example 3]

[0396] The image display unit was fabricated in the same manner as in Example 1, except that it did not have the second phase difference plate and the second linear polarizer.

[0397] [evaluate]

[0398] <Evaluation of the light utilization efficiency of the image display unit>

[0399] The display in the image display unit was removed, and an evaluation light source was configured. A laser pointer (wavelength 532nm) was used as the evaluation light source. Using the laser pointer, incident light was incident from the first linear polarizer side, and the intensity of the outgoing light was measured using a power meter. The intensity ratio to the incident light intensity was calculated, and the evaluation was performed based on the following criteria.

[0400] A: Strength ratio of 0.7 or higher

[0401] B: Strength ratio greater than 0.5 and less than 0.7

[0402] C: Strength ratio less than 0.5

[0403] <Image Quality Rating 1>

[0404] Similar to the evaluation of light utilization efficiency mentioned above, light was incident from the side of the first linear polarizer using a laser pointer, and the light displayed on the paper was observed at a focal distance. The evaluation was conducted according to the following criteria.

[0405] A: The point of light observed at a focal point.

[0406] B: Light is also observed at locations outside the focal point.

[0407] <Image Quality Rating 2>

[0408] The display in the image display unit was turned on, and the displayed image was observed and evaluated according to the following benchmarks.

[0409] A: No light fringes were observed.

[0410] B: Observe the stripes of light.

[0411] The results are shown in Table 1.

[0412] [Table 1]

[0413]

[0414] As shown in Table 1, compared with the comparative example, the light utilization efficiency of Examples 1 to 3 of the present invention is higher, and the image quality of the displayed image is also higher.

[0415] In Comparative Example 1, the image quality is poor due to light stripes caused by the groove structure of the Fresnel lens.

[0416] Comparative Example 2 has low light utilization efficiency.

[0417] In Comparative Example 3, the image quality is reduced because the emitted light is not diffracted by the liquid crystal diffraction element.

[0418] [Example 1-A2]

[0419] In Example 1, liquid crystal compound L-1 was changed to liquid crystal compound L-2, the amount of chiral reagent M-1 and chiral reagent H-1 was adjusted, and the film thickness of the liquid crystal layer was adjusted. Otherwise, the liquid crystal diffraction element was fabricated in the same manner, and the image display unit of Example 1-A2 was fabricated.

[0420] Liquid crystal compound L-2

[0421] [Chemical Formula 8]

[0422]

[0423] In the first liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 160nm, and becomes as Figure 5The first liquid crystal layer has a concentric (radial) periodic alignment surface. Furthermore, the liquid crystal alignment pattern of this first liquid crystal layer is a liquid crystal alignment pattern whose period shortens outwards. Also, the torsion angle in the thickness direction of the first liquid crystal layer is 80° to the right in-plane.

[0424] In the second liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 330nm, and becomes as Figure 5 The second liquid crystal layer exhibits a concentric (radial) periodic alignment surface. Furthermore, the liquid crystal alignment pattern of this second liquid crystal layer is a pattern whose period shortens outwards. Additionally, the twist angle in the thickness direction of the second liquid crystal layer is 0° in-plane.

[0425] In the third liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 160nm, and becomes as Figure 5 The concentric (radial) periodic alignment surfaces are shown. Furthermore, the liquid crystal alignment pattern of this third liquid crystal layer is a liquid crystal alignment pattern whose period shortens outwards. Also, the torsion angle in the thickness direction of the liquid crystal layer is 80° to the left in-plane.

[0426] Parallel light was incident on a liquid crystal diffraction element having 1 to 3 liquid crystal layers, and the focal distance of the converged outgoing light was measured. The focal distance was 30 mm.

[0427] [Example 2-A2]

[0428] In the fabrication of the liquid crystal diffraction element, the alignment pattern formed as alignment film P-1 was changed, the focal distance was set to 15mm, and the distance between the image display device and the liquid crystal diffraction element was set to 15mm. Otherwise, the image display unit was fabricated in the same manner as in Example 1-A2.

[0429] [Example 3-A2]

[0430] In the fabrication of the liquid crystal diffraction element, the alignment pattern formed as alignment film P-1 was changed, the focal distance was set to 10 mm, and the distance between the image display device and the liquid crystal diffraction element was set to 10 mm. Otherwise, the image display unit was fabricated in the same manner as in Example 1-A2.

[0431] [Example 1-A3]

[0432] In Example 1, liquid crystal compound L-1 was changed to liquid crystal compound L-3, the amount of chiral reagent M-1 and chiral reagent H-1 was adjusted, the heating temperature of the coating during liquid crystal layer formation was changed to 55°C, and the film thickness of the liquid crystal layer was adjusted. Otherwise, the liquid crystal diffraction element was manufactured in the same manner, and the image display unit of Example 1-A3 was produced.

[0433] Liquid crystal compound L-3

[0434] [Chemical Formula 9]

[0435]

[0436] In the first liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 160nm, and becomes as Figure 5 The first liquid crystal layer has a concentric (radial) periodic alignment surface. Furthermore, the liquid crystal alignment pattern of this first liquid crystal layer is a liquid crystal alignment pattern whose period shortens outwards. Also, the torsion angle in the thickness direction of the first liquid crystal layer is 80° to the right in-plane.

[0437] In the second liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 330nm, and becomes as Figure 5 The second liquid crystal layer exhibits a concentric (radial) periodic alignment surface. Furthermore, the liquid crystal alignment pattern of this second liquid crystal layer is a pattern whose period shortens outwards. Additionally, the twist angle in the thickness direction of the second liquid crystal layer is 0° in-plane.

[0438] In the third liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 160nm, and becomes as Figure 5 The concentric (radial) periodic alignment surfaces are shown. Furthermore, the liquid crystal alignment pattern of this third liquid crystal layer is a liquid crystal alignment pattern whose period shortens outwards. Also, the torsion angle in the thickness direction of the liquid crystal layer is 80° to the left in-plane.

[0439] Parallel light was incident on a liquid crystal diffraction element having 1 to 3 liquid crystal layers, and the focal distance of the converged outgoing light was measured. The focal distance was 30 mm.

[0440] [Example 2-A3]

[0441] In the fabrication of the liquid crystal diffraction element, the alignment pattern formed as alignment film P-1 was changed, the focal distance was set to 15mm, and the distance between the image display device and the liquid crystal diffraction element was set to 15mm. Otherwise, the image display unit was fabricated in the same manner as in Example 1-A3.

[0442] [Example 3-A3]

[0443] In the fabrication of the liquid crystal diffraction element, the alignment pattern formed as alignment film P-1 was changed, the focal distance was set to 10 mm, and the distance between the image display device and the liquid crystal diffraction element was set to 10 mm. Otherwise, the image display unit was fabricated in the same manner as in Example 1-A3.

[0444] In addition, the Δn of the liquid crystal layer (liquid crystal compound) in Examples 1 to 3 550 The Δn of the liquid crystal layer in Examples 1-A2 to 3-A2 is 0.15. 550 The Δn of the liquid crystal layer in Examples 1-A3 to 3-A3 is 0.25. 550 It is 0.32.

[0445] [evaluate]

[0446] <Evaluation of the light utilization efficiency of the image display unit>

[0447] The display in the image display unit was removed, and an evaluation light source was configured. A laser pointer (wavelength 532nm) was used as the evaluation light source. Using the laser pointer, incident light was incident from the first linear polarizer side, and the intensity of the outgoing light was measured using a power meter. The intensity ratio to the incident light intensity was calculated.

[0448] The incident angle was measured at positions 5 mm and 15 mm from the center of the concentric circles of the fabricated liquid crystal diffraction element, changing by ±40° (10° scale) from the normal direction (0°) of the liquid crystal diffraction element.

[0449] The average intensity ratio (light utilization efficiency) measured at different incident angles was calculated, and comparisons were made between Examples 1 to 3, Examples 1-A2 to 3-A2, and Examples 1-A3 to 3-A3.

[0450] The evaluation results show that, compared with Example 1, the light utilization efficiency (average value) of Example 1-A2 is improved, and the light utilization efficiency (average value) of Example 1-A3 is further improved.

[0451] Similarly, compared to Example 2, the light utilization efficiency (average value) of Example 2-A2 is improved, and the light utilization efficiency (average value) of Example 2-A3 is further improved.

[0452] Compared to Example 3, the light utilization efficiency (average value) of Example 3-A2 is improved, and the light utilization efficiency (average value) of Example 3-A3 is further improved.

[0453] As can be seen from the above, the refractive index difference Δn of the liquid crystal layer in the liquid crystal diffraction element 550 The higher the angle, the more efficient the utilization of light relative to different incident angles.

[0454] [Example 1-B1]

[0455] (Formation of the liquid crystal layer)

[0456] As a liquid crystal composition for forming the first liquid crystal layer, the following composition B-1 was prepared.

[0457] Composition B-1

[0458]

[0459] Chiral reagent C-3

[0460] [Chemical Formula 10]

[0461]

[0462] Chiral reagent C-4

[0463] [Chemical Formula 11]

[0464]

[0465] As a liquid crystal composition for forming the second liquid crystal layer, in composition B-1 of Example 1-B1, chiral reagent C-3 was changed to 0.54 parts by mass and chiral reagent C-4 was changed to 0.62 parts by mass, thereby preparing composition B-2.

[0466] As a liquid crystal composition for forming the third liquid crystal layer, in composition B-1 of Example 1-B1, the chiral reagent C-3 was changed to 0.48 parts by mass, and the chiral reagent C-4 was changed to be omitted, thereby preparing composition B-3.

[0467] First, a first liquid crystal layer is formed by multilayer coating of composition B-1 onto alignment film P-1.

[0468] First, for the first layer, the above-mentioned composition B-1 is coated onto the alignment film P-1. The coating is heated to 80°C on a hot plate, and then ultraviolet light with a wavelength of 365nm from an LED-UV exposure machine is irradiated onto the coating. At this time, the amount of ultraviolet light irradiated is varied in-plane and applied to the coating. Specifically, the irradiation amount is varied in-plane by increasing from the center towards the ends, and the coating is then irradiated. Next, the coating heated to 80°C on the hot plate is subjected to a high-pressure mercury lamp at 300mJ / cm² under a nitrogen atmosphere. 2 The irradiation dose is 365nm ultraviolet light applied to the coating to fix the orientation of the liquid crystal compound.

[0469] After the second layer, it is overlapped and coated onto the liquid crystal immobilization layer, and the liquid crystal immobilization layer is fabricated under the same conditions as described above. In this way, the overlapping coating is repeated until the total thickness reaches the desired film thickness, thereby forming the first liquid crystal layer.

[0470] In the first liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 160nm, and becomes as Figure 5 The liquid crystal layer exhibits a concentric (radial) periodic alignment surface. Furthermore, the liquid crystal alignment pattern has a period that shortens outwards. Additionally, the twist angle in the thickness direction of the liquid crystal layer is as follows: approximately 5 mm from the center, the twist angle is 80° (-80°) to the left; one cycle at a distance of 15 mm from the center is 115° (-115°) to the left; and the twist angle increases outwards.

[0471] As described above, a liquid crystal layer with an in-plane twist angle that changes is formed.

[0472] Next, a second liquid crystal layer was formed by multilayer coating of composition B-2 onto the first liquid crystal layer.

[0473] In the first liquid crystal layer of Example 1-B1, which is prepared by coating composition B-2 on the first liquid crystal layer, the amount of ultraviolet light irradiating the coating from the center toward the end is changed (the amount of irradiation is increased from the center toward the end), and the total thickness is changed to the desired film thickness. Otherwise, the liquid crystal layer is formed in the same manner.

[0474] After the second layer, it is overlapped and coated onto the liquid crystal immobilization layer, and the liquid crystal immobilization layer is fabricated under the same conditions as described above. In this way, the overlapping coating is repeated until the total thickness reaches the desired film thickness, thereby forming the second liquid crystal layer.

[0475] In this second liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 330nm, and becomes as Figure 5 The liquid crystal layer exhibits a concentric (radial) periodic alignment surface. Furthermore, the liquid crystal layer has a liquid crystal alignment pattern with periods decreasing in the outward direction. Additionally, the twist angle in the thickness direction of the liquid crystal layer is as follows: approximately 5 mm from the center, the twist angle is 6° (-6°) to the left; one cycle at a distance of 15 mm from the center is 76° (-76°) to the left; and the twist angle increases in the outward direction.

[0476] As described above, a liquid crystal layer with an in-plane twist angle that changes is formed.

[0477] Next, a third liquid crystal layer was formed by multilayer coating of composition B-3 onto the second liquid crystal layer.

[0478] In the first liquid crystal layer of Example 1-B1, which is prepared by coating composition B-3 on the second liquid crystal layer, the amount of ultraviolet light irradiating the coating from the center toward the end is changed (the amount of irradiation is increased from the center toward the end), and the total thickness is changed to the desired film thickness. Otherwise, the liquid crystal layer is formed in the same manner.

[0479] After the second layer, it is overlapped and coated onto the liquid crystal immobilization layer, and the liquid crystal immobilization layer is fabricated under the same conditions as above. In this way, the overlapping coating is repeated until the total thickness reaches the desired film thickness, thereby forming the third liquid crystal layer.

[0480] In this third liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 160nm, and becomes as Figure 5 The liquid crystal layer exhibits a concentric (radial) periodic alignment surface. Furthermore, the liquid crystal layer has a liquid crystal alignment pattern where the period shortens outwards. Additionally, the twist angle in the thickness direction of the liquid crystal layer is as follows: approximately 5 mm from the center, the twist angle is 80° to the right; one cycle at a distance of 15 mm from the center is 48° to the right; and the twist angle decreases outwards.

[0481] As described above, a liquid crystal layer having a third liquid crystal layer is formed from the first liquid crystal layer.

[0482] The results of SEM observation of the cross-section of the fabricated optical anisotropic layer show that the shape of the bright and dark parts is such that the dark part has two inflection points and the average tilt angle increases from the center outwards.

[0483] Furthermore, parallel light was incident on a liquid crystal diffraction element having 1 to 3 liquid crystal layers, and the focal distance of the converged outgoing light was measured. The focal distance was 30 mm.

[0484] [Example 2-B1]

[0485] In the fabrication of the liquid crystal diffraction element, the alignment pattern formed as alignment film P-1 was changed, the focal distance was set to 15mm, and the distance between the image display device and the liquid crystal diffraction element was set to 15mm. Otherwise, the image display unit was fabricated in the same manner as in Example 1-B1.

[0486] [Example 3-B1]

[0487] In the fabrication of the liquid crystal diffraction element, the alignment pattern formed as alignment film P-1 was changed, the focal distance was set to 10 mm, and the distance between the image display device and the liquid crystal diffraction element was set to 10 mm. Otherwise, the image display unit was fabricated in the same manner as in Example 1-B1.

[0488] [Example 1-B2]

[0489] In Example 1-B1, liquid crystal compound L-1 was changed to liquid crystal compound L-2, and the amounts of chiral reagent C-3 and chiral reagent C-4 were adjusted. In the fabrication of the liquid crystal layer, the amount of ultraviolet light irradiating the coating from the center toward the ends was adjusted, and the film thickness of the liquid crystal layer was adjusted. Otherwise, the liquid crystal diffraction element was fabricated in the same manner, and the image display unit of Example 1-B2 was fabricated.

[0490] In the first liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 160nm, and becomes as Figure 5 The liquid crystal layer exhibits a concentric (radial) periodic alignment surface. Furthermore, the liquid crystal alignment pattern has a period that shortens outwards. Additionally, the twist angle in the thickness direction of the liquid crystal layer is as follows: approximately 5 mm from the center, the twist angle is 80° (-80°) to the left; one cycle at a distance of 15 mm from the center is 115° (-115°) to the left; and the twist angle increases outwards.

[0491] As described above, a liquid crystal layer with an in-plane twist angle that changes is formed.

[0492] In the second liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 330nm, and becomes as Figure 5 The liquid crystal layer exhibits a concentric (radial) periodic alignment surface. Furthermore, the liquid crystal layer has a liquid crystal alignment pattern with periods decreasing in the outward direction. Additionally, the twist angle in the thickness direction of the liquid crystal layer is as follows: approximately 5 mm from the center, the twist angle is 6° (-6°) to the left; one cycle at a distance of 15 mm from the center is 76° (-76°) to the left; and the twist angle increases in the outward direction.

[0493] As described above, a liquid crystal layer with an in-plane twist angle that changes is formed.

[0494] In the third liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 160nm, and becomes as Figure 5 The liquid crystal layer exhibits a concentric (radial) periodic alignment surface. Furthermore, the liquid crystal layer has a liquid crystal alignment pattern where the period shortens outwards. Additionally, the twist angle in the thickness direction of the liquid crystal layer is as follows: approximately 5 mm from the center, the twist angle is 80° to the right; one cycle at a distance of 15 mm from the center is 48° to the right; and the twist angle decreases outwards.

[0495] As described above, a liquid crystal layer having a third liquid crystal layer is formed from the first liquid crystal layer.

[0496] The results of SEM observation of the cross-section of the fabricated optical anisotropic layer show that the shape of the bright and dark parts is such that the dark part has two inflection points and the average tilt angle increases from the center outwards.

[0497] Furthermore, parallel light was incident on a liquid crystal diffraction element having 1 to 3 liquid crystal layers, and the focal distance of the converged outgoing light was measured. The focal distance was 30 mm.

[0498] [Example 2-B2]

[0499] In the fabrication of the liquid crystal diffraction element, the alignment pattern formed as alignment film P-1 was changed, the focal distance was set to 15mm, and the distance between the image display device and the liquid crystal diffraction element was set to 15mm. Otherwise, the image display unit was fabricated in the same manner as in Example 1-B2.

[0500] [Example 3-B2]

[0501] In the fabrication of the liquid crystal diffraction element, the alignment pattern formed as alignment film P-1 was changed, the focal distance was set to 10 mm, and the distance between the image display device and the liquid crystal diffraction element was set to 10 mm. Otherwise, the image display unit was fabricated in the same manner as in Example 1-B2.

[0502] [Example 1-B3]

[0503] In Example 1-B1, liquid crystal compound L-1 was changed to liquid crystal compound L-3, the amount of chiral reagent C-3 and chiral reagent C-4 added was adjusted, the amount of ultraviolet light irradiating the coating from the center to the end was adjusted during the fabrication of the liquid crystal layer, the heating temperature of the coating during the formation of the liquid crystal layer was changed to 55°C, and the thickness of the liquid crystal layer was adjusted. Otherwise, the liquid crystal diffraction element was fabricated in the same manner, and the image display unit of Example 1-B2 was fabricated.

[0504] In the first liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 160nm, and becomes as Figure 5 The liquid crystal layer exhibits a concentric (radial) periodic alignment surface. Furthermore, the liquid crystal alignment pattern has a period that shortens outwards. Additionally, the twist angle in the thickness direction of the liquid crystal layer is as follows: approximately 5 mm from the center, the twist angle is 80° (-80°) to the left; one cycle at a distance of 15 mm from the center is 115° (-115°) to the left; and the twist angle increases outwards.

[0505] As described above, a liquid crystal layer with an in-plane twist angle that changes is formed.

[0506] In the second liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 330nm, and becomes as Figure 5 The liquid crystal layer exhibits a concentric (radial) periodic alignment surface. Furthermore, the liquid crystal layer has a liquid crystal alignment pattern with periods decreasing in the outward direction. Additionally, the twist angle in the thickness direction of the liquid crystal layer is as follows: approximately 5 mm from the center, the twist angle is 6° (-6°) to the left; one cycle at a distance of 15 mm from the center is 76° (-76°) to the left; and the twist angle increases in the outward direction.

[0507] As described above, a liquid crystal layer with an in-plane twist angle that changes is formed.

[0508] In the third liquid crystal layer, the Δn of the liquid crystal was confirmed using a polarization microscope. 550 The thickness (Re(550)) eventually becomes 160nm, and becomes as Figure 5 The liquid crystal layer exhibits a concentric (radial) periodic alignment surface. Furthermore, the liquid crystal layer has a liquid crystal alignment pattern where the period shortens outwards. Additionally, the twist angle in the thickness direction of the liquid crystal layer is as follows: approximately 5 mm from the center, the twist angle is 80° to the right; one cycle at a distance of 15 mm from the center is 48° to the right; and the twist angle decreases outwards.

[0509] As described above, a liquid crystal layer having a third liquid crystal layer is formed from the first liquid crystal layer.

[0510] The results of SEM observation of the cross-section of the fabricated optical anisotropic layer show that the shape of the bright and dark parts is such that the dark part has two inflection points and the average tilt angle increases from the center outwards.

[0511] Furthermore, parallel light was incident on a liquid crystal diffraction element having 1 to 3 liquid crystal layers, and the focal distance of the converged outgoing light was measured. The focal distance was 30 mm.

[0512] [Example 2-B3]

[0513] In the fabrication of the liquid crystal diffraction element, the alignment pattern formed as alignment film P-1 was changed, the focal distance was set to 15mm, and the distance between the image display device and the liquid crystal diffraction element was set to 15mm. Otherwise, the image display unit was fabricated in the same manner as in Example 1-B3.

[0514] [Example 3-B3]

[0515] In the fabrication of the liquid crystal diffraction element, the alignment pattern formed as alignment film P-1 was changed, the focal distance was set to 10 mm, and the distance between the image display device and the liquid crystal diffraction element was set to 10 mm. Otherwise, the image display unit was fabricated in the same manner as in Example 1-B3.

[0516] [evaluate]

[0517] <Evaluation of the light utilization efficiency of the image display unit>

[0518] The display in the image display unit was removed, and an evaluation light source was configured. A laser pointer (wavelength 532nm) was used as the evaluation light source. Using the laser pointer, incident light was incident from the first linear polarizer side, and the intensity of the outgoing light was measured using a power meter. The intensity ratio to the incident light intensity was calculated.

[0519] The distance from the center of the concentric circles of the fabricated liquid crystal diffraction element was measured from the normal direction (0°) of the liquid crystal diffraction element at positions 5 mm and 15 mm away.

[0520] Using the measured intensity ratio (light utilization efficiency), comparisons were made between Examples 1 to 3 and Examples 1-B1 to 3-B1.

[0521] The evaluation results show that, compared with Example 1, the light utilization efficiency of Example 1-B1 is the same at a position 5 mm away from the center of the concentric circles of the liquid crystal diffraction element, but the utilization rate is improved at a position of 15 mm.

[0522] Similarly, compared to Example 2, the light utilization efficiency of Example 2-B1 is the same at a position 5 mm from the center of the concentric circles of the liquid crystal diffraction element, but the utilization rate is improved at a position of 15 mm.

[0523] Compared to Example 3, the light utilization efficiency of Example 3-B1 is the same at a position 5 mm from the center of the concentric circles of the liquid crystal diffraction element, but the utilization rate is improved at a position of 15 mm.

[0524] As can be seen from the above, the liquid crystal layer of the liquid crystal diffraction element has regions with different twist angles in the thickness direction. The shorter the period Λ of the liquid crystal alignment pattern, the higher the light utilization efficiency in the region where the diffraction angle increases (increases the average tilt angle of the dark area) by increasing the twist angle in the thickness direction of the liquid crystal layer.

[0525] [evaluate]

[0526] <Evaluation of the light utilization efficiency of the image display unit>

[0527] The display in the image display unit was removed, and an evaluation light source was configured. A laser pointer (wavelength 532nm) was used as the evaluation light source. Using the laser pointer, incident light was incident from the first linear polarizer side, and the intensity of the outgoing light was measured using a power meter. The intensity ratio to the incident light intensity was calculated.

[0528] The incident angle was measured at positions 5 mm and 15 mm from the center of the concentric circles of the fabricated liquid crystal diffraction element, changing by ±40° (10° scale) from the normal direction (0°) of the liquid crystal diffraction element.

[0529] The average intensity ratio (light utilization efficiency) measured at different incident angles was calculated, and comparisons were made between Examples 1-B1 to 3-B1, Examples 1-B2 to 3-B2, and Examples 1-B3 to 3-B3.

[0530] The evaluation results show that, compared with Examples 1-B1, the light utilization efficiency (average value) of Examples 1-B2 is improved, and the light utilization efficiency (average value) of Examples 1-B3 is further improved.

[0531] Similarly, compared to Example 2-B1, the light utilization efficiency (average value) of Example 2-B2 is improved, and the light utilization efficiency (average value) of Example 2-B3 is further improved.

[0532] Compared to Example 3-B1, the light utilization efficiency (average value) of Example 3-B2 is improved, and the light utilization efficiency (average value) of Example 3-B3 is further improved.

[0533] As can be seen from the above, the refractive index difference Δn of the liquid crystal layer in the liquid crystal diffraction element 550 The higher the angle, the more efficient the utilization of light relative to different incident angles.

[0534] [Examples 4-6]

[0535] In the image unit fabrication of Examples 1 to 3, the linear polarizer (polyvinyl alcohol layer type) was replaced with an absorptive polarizer fabricated as described later, and the image unit was fabricated in the same manner otherwise.

[0536] [Fabrication of an Absorption-Type Polarizer]

[0537] <Fabrication of Transparent Support>

[0538] The coating solution PA1, used for forming the orientation layer (described later), was continuously coated onto a cellulose acylate film (40 μm thick TAC substrate; TG40 FUJIFILM Corporation) using a wire rod. The coated support was dried with warm air at 140°C for 120 seconds, followed by polarized ultraviolet irradiation (10 mJ / cm²). 2 A photo-alignment layer PA1 was formed using an ultra-high pressure mercury lamp, thus obtaining a TAC thin film with a photo-alignment layer.

[0539] The film thickness is 0.3 μm.

[0540]

[0541] Polymer PA-1

[0542] [Chemical Formula 12]

[0543]

[0544] Acid-producing agent PAG-1

[0545] [Chemical Formula 13]

[0546]

[0547] Acid-producing agent CPI-110F

[0548] [Chemical Formula 14]

[0549]

[0550] <Formation of the light-absorbing anisotropic layer P1>

[0551] The following light-absorbing anisotropic layer forming composition P1 is continuously coated onto the obtained orientation layer PA1 using a wire rod, thereby forming the coating layer P1.

[0552] Next, the coating layer P1 was heated at 140°C for 30 seconds and then cooled to room temperature (23°C).

[0553] Next, heat at 90°C for 60 seconds, and then cool again to room temperature.

[0554] Then, using an LED light (center wavelength 365nm) at an illuminance of 200mW / cm² 2 Irradiation was performed for 2 seconds under the specified irradiation conditions, thereby creating an anisotropic light-absorbing layer P1 on the orientation layer PA1.

[0555] The film thickness is 1.6 μm.

[0556] It is designated as layer 1B.

[0557]

[0558] D-1

[0559] [Chemical Formula 15]

[0560]

[0561] D-2

[0562] [Chemical Formula 16]

[0563]

[0564] D-3

[0565] [Chemical Formula 17]

[0566]

[0567] P-1, a polymeric liquid crystal compound

[0568] [Chemical Formula 18]

[0569]

[0570] Low molecular weight liquid crystal compound M-1

[0571] [Chemical Formula 19]

[0572]

[0573] Surfactant F-1

[0574] [Chemical Formula 20]

[0575]

[0576] <Preparation of UV Adhesive>

[0577] The following UV adhesive composition was prepared.

[0578]

[0579] CPI-100P

[0580] [Chemical Formula 21]

[0581]

[0582] <Fabrication of Absorption Polarizing Films>

[0583] Using the aforementioned UV adhesive, TECHNOLLOY S001G (50 μm thick methacrylic resin, tanδ peak temperature 128 °C, SUMIKA ACRYL CO.,LTD.) was bonded to the surface of the light-absorbing anisotropic layer of laminate 1B as the resin substrate S1. Then, by peeling off only the cellulose acylate film, an absorption-type polarizing film was fabricated, consisting of a resin substrate, an adhesive layer, a light-absorbing anisotropic layer, and an orientation layer arranged sequentially. The thickness of the UV adhesive layer was 2 μm.

[0584] The average arithmetic roughness Ra of the obtained absorption polarizing film is less than 10 nm. On the other hand, the average arithmetic roughness Ra of the linear polarizer (polyvinyl alcohol layer type) is more than 20 nm.

[0585] Therefore, the absorptive polarizing film produced can suppress the distortion of the displayed image.

[0586] In addition, the average arithmetic roughness Ra was measured using an interferometer "vertscan" manufactured by Mitsubishi Chemical Systems, Inc.

[0587] [evaluate]

[0588] The light utilization efficiency, image quality evaluation 1, and image quality evaluation 2 of the image display unit were all rated A.

[0589] Based on the above, the effects of the present invention can be clearly understood.

[0590] Symbol Explanation

[0591] 10a, 10b - Image display unit; 12 - First linear polarizer; 14 - First phase retardation plate; 16 - First circular polarizer; 20 - Polarizing diffraction element (polarizing diffraction lens); 22 - Second phase retardation plate; 24 - Second linear polarizer; 26 - Second circular polarizer; 30 - Support; 32 - Alignment film; 36 - Liquid crystal layer; 40 - Liquid crystal compound; 40A - Optical axis; 42 - Bright area; 44 - Dark area; 52, 52b - Image display device; 80 - Exposure apparatus, 82-laser, 84-light source, 86, 94-polarization beam splitter, 90A, 90B-reflector, 96-λ / 4 plate, 92-lens, D, A1~A3-arrangement axis, Λ-1 cycle, U-user, M-laser beam, MP-P polarization, MS-S polarization, R-region, L1, L2, L4, L5-light, VI-virtual image, d-distance between image display device and polarization diffraction lens, f-focal distance of polarization diffraction lens.

Claims

1. An image display unit, comprising: Image display device; A polarizing diffraction element diffracts light emitted from the image display device; and A polarizer transmits polarized light diffracted by the polarizing diffraction element and absorbs light emitted from the image display device, transmitted from the polarizing diffraction element, and not diffracted by the polarizing diffraction element. The polarizing diffraction element is a polarizing diffraction lens with lens function. When the focal distance of the polarizing diffraction lens is set as f, and the distance between the image display device and the polarizing diffraction lens is set as d, d≤f is satisfied.

2. The image display unit according to claim 1, wherein, The focal distance f of the polarizing diffraction lens is less than 40 mm.

3. The image display unit according to claim 1, wherein, The polarization diffraction element diffracts circularly polarized light. The polarizer is a circular polarizer.

4. The image display unit according to claim 3, wherein, The image display device emits linearly polarized light. A phase difference plate is provided between the image display device and the polarization diffraction element.

5. The image display unit according to claim 4, wherein, The phase difference plate is a λ / 4 plate.

6. The image display unit according to claim 3, wherein, The image display device emits unpolarized light. The circular polarizer is located between the image display device and the polarizing diffraction element.

7. The image display unit according to any one of claims 3 to 6, wherein, The circular polarizer is composed of a linear polarizer and a phase difference plate.

8. The image display unit according to claim 7, wherein, The phase difference plate is a λ / 4 plate.

9. The image display unit according to claim 1 or 2, wherein, The polarizing diffraction element is a liquid crystal diffraction element having a liquid crystal layer containing a liquid crystal compound. The liquid crystal layer has a liquid crystal alignment pattern that changes as the orientation of the optical axis derived from the liquid crystal compound rotates continuously in at least one in-plane direction. If the length of the orientation of the optical axis originating from the liquid crystal compound in the liquid crystal alignment pattern, rotated 180° in the in-plane direction, is defined as one period, then the liquid crystal layer has regions in the plane with different lengths of the one period.

10. The image display unit according to claim 9, wherein, The period of the liquid crystal layer gradually shortens from one side of the liquid crystal alignment pattern toward the other.

11. The image display unit according to claim 9, wherein, The liquid crystal layer has the liquid crystal alignment pattern in one direction in a concentric circle shape from the inside to the outside.

12. The image display unit according to claim 9, wherein, The liquid crystal layer, when viewed in a cross-sectional image obtained by cutting along the thickness direction using a scanning electron microscope, has bright and dark regions originating from the liquid crystal phase that are inclined relative to the main surface of the liquid crystal layer.

13. The image display unit according to claim 12, wherein, The liquid crystal diffraction element has two or more liquid crystal layers. In a cross-sectional image obtained by cutting along the thickness direction in the at least two layers of the liquid crystal layer using a scanning electron microscope, bright and dark areas originating from the optical axis were observed. In the at least two liquid crystal layers, the bright portion and the dark portion have different tilt angles relative to the main surface of the liquid crystal layer.

14. The image display unit according to claim 9, wherein, In a cross-sectional image obtained by cutting along one direction in the thickness direction using a scanning electron microscope, the liquid crystal layer has bright and dark areas extending from one surface to another, with the dark areas having more than two inflection points. The region has different tilt directions in the thickness area of ​​the dark area.

15. The image display unit according to claim 14, wherein, The number of inflection points where the tilt direction of the dark portion in the liquid crystal layer is reversed is odd.

16. The image display unit according to claim 12, wherein, The average tilt angle of the dark portion in the liquid crystal layer gradually changes in one direction.

17. The image display unit according to claim 12, wherein, The liquid crystal layer has regions where the shapes of the bright and dark portions are asymmetrical with respect to the centerline of the thickness direction of the liquid crystal layer.

18. The image display unit according to claim 9, wherein, The refractive index difference Δn accompanying the refractive index anisotropy of the liquid crystal layer 550 It is above 0.

2.

19. A head-mounted display having an image display unit according to any one of claims 1 to 18.

Images