Optical element

Abstract

The present invention addresses the problem of providing an optical element which is capable of diffracting incident light with high diffraction efficiency. The problem is solved by an optical element which has a first optically anisotropic layer that contains a calamitic liquid crystal compound and a second optically anisotropic layer that contains a discotic liquid crystal compound, wherein the first optically anisotropic layer and the second optically anisotropic layer have a first liquid crystal alignment pattern in which the orientation of an optical axis derived from a liquid crystal compound changes while continuously rotating in at least one direction, and have a region in which the orientation of the optical axis rotates by 180° with a period that is shorter than 0.5 μm.

Description

Optical elements

[0001] The present invention relates to an optical element used in a head-mounted display or the like.

[0002] Diffraction elements are optical elements that bend light to control its direction of travel, and are used in many optical devices and optical systems. As such optical elements, liquid crystal diffraction elements using liquid crystal compounds have been proposed.

[0003] For example, Patent Document 1 describes a liquid crystal diffraction element (optical element) comprising a plurality of stacked birefringent sublayers configured to change the direction of propagation of light passing therethrough in accordance with the Bragg condition, the stacked birefringent sublayers having local optical axes that vary along respective interface surfaces between adjacent stacked birefringent sublayers to define respective grating periods.

[0004] Specifically, the liquid crystal diffraction element described in Patent Document 1 has a liquid crystal orientation pattern in which the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. When circularly polarized light is incident on a liquid crystal diffraction element having such a liquid crystal orientation pattern, the incident light is diffracted along the direction in which the optical axis derived from the liquid crystal compound continuously rotates, depending on the rotation direction of the circularly polarized light and the rotation direction of the optical axis derived from the liquid crystal compound.

[0005] The liquid crystal diffraction element described in Patent Document 1 can be used in various optical devices and optical systems, such as a beam steering device that bends light in a desired direction.

[0006] Special table 2017-522601 publication

[0007] Recently, there has been a demand for smaller and thinner optical devices and optical systems, etc. For example, there is a demand for thinner head mounted displays (hereinafter also referred to as HMDs) that provide users with virtual reality (VR), augmented reality (AR), etc.

[0008] In order to make HMDs that use liquid crystal diffraction elements thinner, it is necessary to diffract light significantly using the liquid crystal diffraction element. However, with conventional liquid crystal diffraction elements, diffracting light significantly reduces the diffraction efficiency, resulting in a large amount of light that is not diffracted by the liquid crystal diffraction element and passes through as is, i.e., the zero-order light.

[0009] An object of the present invention is to solve the problems of the prior art and to provide an optical element that can diffract incident light with high diffraction efficiency.

[0010] In order to solve the above problems, the present invention has the following configuration: [1] An optical element comprising: a first optically anisotropic layer which is a cured layer of a liquid crystal composition containing a rod-shaped liquid crystal compound; and a second optically anisotropic layer which is a cured layer of a liquid crystal composition containing a discotic liquid crystal compound, wherein the first optically anisotropic layer has a liquid crystal orientation pattern in which rod-shaped liquid crystal compounds are aligned along at least one in-plane direction, a first liquid crystal orientation pattern in which the orientation of an optical axis derived from the rod-shaped liquid crystal compound changes while continuously rotating, and the first liquid crystal orientation pattern has a region in which the orientation of the optical axis of the rod-shaped liquid crystal compound rotates by 180° with a period shorter than 0.5 μm, and the second optically anisotropic layer has a liquid crystal orientation pattern in which discotic liquid crystal compounds are aligned along at least one in-plane direction, a second liquid crystal orientation pattern in which the orientation of an optical axis derived from the discotic liquid crystal compound changes while continuously rotating, and the second liquid crystal orientation pattern has a region in which the orientation of the optical axis of the discotic liquid crystal compound rotates by 180° with a period shorter than 0.5 μm. [2] The optical element according to [1], wherein in the first optically anisotropic layer, the rod-shaped liquid crystal compound is twistedly aligned in the thickness direction of the first optically anisotropic layer according to a first torsion. [3] The optical element according to [1] or [2], wherein in the second optically anisotropic layer, the discotic liquid crystal compound is twistedly aligned in the thickness direction of the second optically anisotropic layer according to a second torsion. [4] The optical element according to [2], wherein in the second optically anisotropic layer, the discotic liquid crystal compound is twistedly aligned in the thickness direction of the second optically anisotropic layer according to a second torsion, the first torsion and the second torsion are in the same direction, and the torsion of the optical axis of the rod-shaped liquid crystal compound and the torsion of the optical axis of the discotic liquid crystal compound are continuous torsion in the first optically anisotropic layer and the second optically anisotropic layer. [5] The optical element according to [2], wherein in the second optically anisotropic layer, the discotic liquid crystal compound is twistedly aligned in the thickness direction of the second optically anisotropic layer according to the second twist, and the first twist and the second twist are opposite in direction. [6] The optical element according to [1], wherein in the first optically anisotropic layer, the rod-shaped liquid crystal compound is cholesterically aligned in the thickness direction, and in the second optically anisotropic layer, the discotic liquid crystal compound is cholesterically aligned in the thickness direction.[7] The optical element according to [6], wherein the rod-shaped liquid crystal compound in the first optically anisotropic layer and the discotic liquid crystal compound in the second optically anisotropic layer are continuously cholesterically aligned in the thickness direction. [8] The optical element according to any one of [1] to [7], wherein the first optically anisotropic layer has a region in which the rod-shaped liquid crystal compound is tiltedly aligned in the plane of the optically anisotropic layer in the thickness direction of the first optically anisotropic layer. [9] The optical element according to any one of [1] to [8], wherein the second optically anisotropic layer has a region in which the discotic liquid crystal compound is tiltedly aligned in the plane of the optically anisotropic layer in the thickness direction of the second optically anisotropic layer.

[10] The optical element according to any one of [1] to [9], wherein an optically anisotropic layer which is a cured layer of a liquid crystal composition containing a rod-shaped liquid crystal compound and an optically anisotropic layer which is a cured layer of a liquid crystal composition containing a discotic liquid crystal compound are alternately laminated.

[11] A head-mounted display having the optical element according to any one of [1] to

[10] .

[0011] According to the optical element of the present invention, incident light can be diffracted with high diffraction efficiency.

[0012] FIG. 1 is a conceptual diagram showing one example of the optical element of the present invention. FIG. 2 is a conceptual diagram showing another example of the optical element of the present invention. FIG. 3 is a conceptual diagram showing another example of the optical element of the present invention. FIG. 4 is a conceptual front view showing a rod-shaped liquid crystal layer of the optical element shown in FIG. 1. FIG. 5 is a conceptual plan view showing a rod-shaped liquid crystal layer of the optical element shown in FIG. 1. FIG. 6 is a conceptual front view showing a discotic liquid crystal layer of the optical element shown in FIG. 1. FIG. 7 is a conceptual plan view showing a discotic liquid crystal layer of the optical element shown in FIG. 1. FIG. 8 is a conceptual diagram of an example of an exposure apparatus for exposing an alignment film. FIG. 9 is a conceptual diagram for explaining the function of the rod-shaped liquid crystal layer. FIG. 10 is a conceptual diagram for explaining the function of the rod-shaped liquid crystal layer. FIG. 11 is a conceptual plan view showing another example of the rod-shaped liquid crystal layer constituting the optical element of the present invention. FIG. 12 is a conceptual diagram of another example of an exposure apparatus for exposing an alignment film. FIG. 13 is a conceptual diagram showing another example of the optical element of the present invention. Fig. 14 is a conceptual diagram for explaining the action of the optical element shown in Fig. 13. Fig. 15 is a conceptual diagram showing an example of an HMD of the present invention. Fig. 16 is a conceptual diagram showing an example of an HMD of the present invention. Fig. 17 is a conceptual diagram showing an example of an HMD of the present invention. Fig. 18 is a conceptual diagram for explaining an evaluation method of an embodiment of the present invention. Fig. 19 is a conceptual diagram for explaining an evaluation method of another embodiment of the present invention.

[0013] The optical element of the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings.

[0014] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In this specification, "(meth)acrylate" is used to mean "either one or both of acrylate and methacrylate." In this specification, "same," "equal," etc. are intended to include a range of error generally accepted in the technical field.

[0015] [Optical Element] The optical element of the present invention is specifically a liquid crystal diffraction element, comprising: a first optically anisotropic layer which is a cured layer of a liquid crystal composition containing a rod-shaped liquid crystal compound; and a second optically anisotropic layer which is a cured layer of a liquid crystal composition containing a discotic liquid crystal compound; the first optically anisotropic layer has a liquid crystal orientation pattern in which rod-shaped liquid crystal compounds are aligned along at least one in-plane direction, a first liquid crystal orientation pattern in which the orientation of the optical axis derived from the rod-shaped liquid crystal compound changes while continuously rotating, and the first liquid crystal orientation pattern has a region in which the orientation of the optical axis of the rod-shaped liquid crystal compound rotates by 180° with a period shorter than 0.5 μm; and the second optically anisotropic layer has a liquid crystal orientation pattern in which discotic liquid crystal compounds are aligned along at least one in-plane direction, a second liquid crystal orientation pattern in which the orientation of the optical axis derived from the discotic liquid crystal compound changes while continuously rotating, and the second liquid crystal orientation pattern has a region in which the orientation of the optical axis of the discotic liquid crystal compound rotates by 180° with a period shorter than 0.5 μm.

[0016] Such optical elements of the present invention can be broadly divided into two types: transmission-type optical elements in which the liquid crystal compound in the optically anisotropic layer (liquid crystal layer) is not twistedly oriented by 360° or more in the thickness direction and diffracts and transmits incident light; and reflection-type optical elements in which the liquid crystal compound in the optically anisotropic layer is cholesterically oriented in the thickness direction and diffracts and reflects incident light.

[0017] Figure 1 conceptually shows an example of a transmission-type optical element of the present invention. The drawings shown below are conceptual or schematic diagrams for explaining the present invention. Therefore, the shapes, thicknesses, and sizes of each layer, the shapes and sizes of each member including the liquid crystal compound, and the positional relationships of each component shown in the drawings do not necessarily correspond to the actual ones.

[0018] The optical element 10 shown in FIG. 1 has a rod-shaped liquid crystal layer 42 and a discotic liquid crystal layer 44 stacked in the thickness direction. In the optical element 10 shown in FIG. 1, the rod-shaped liquid crystal layer 42 is a cured layer of a liquid crystal composition containing a rod-shaped liquid crystal compound and serves as the first optically anisotropic layer in the optical element of the present invention. The discotic liquid crystal layer 44 is a cured layer of a liquid crystal composition containing a discotic liquid crystal compound and serves as the second optically anisotropic layer in the optical element of the present invention. This also applies to the rod-shaped liquid crystal layers and discotic liquid crystal layers described below. Note that in FIG. 1, in order to simplify the drawing and clearly show the configuration of the optical element 10, only the liquid crystal compound (liquid crystal compound molecules) on the surface of the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44 are conceptually shown. However, the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44 each have a structure in which liquid crystal compounds are stacked in the thickness direction, as conceptually shown in FIGS. 4 and 6 . In the following description, when it is not necessary to distinguish between rod-shaped liquid crystal compounds and discotic liquid crystal compounds, both compounds are also collectively referred to as liquid crystal compounds.

[0019] As described above, the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44 are laminated in the thickness direction. The rod-shaped liquid crystal layer 42 is a layer in which rod-shaped liquid crystal compounds 40c are oriented in a liquid crystal orientation pattern in which the direction of the optical axis derived from the rod-shaped liquid crystal compounds 40c changes while continuously rotating along at least one direction in the plane. The discotic liquid crystal layer 44 is a layer in which discotic liquid crystal compounds 40d are oriented in a liquid crystal orientation pattern in which the direction of the optical axis derived from the discotic liquid crystal compounds 40d changes while continuously rotating along at least one direction in the plane. In the following description, the "optical axis derived from the rod-shaped liquid crystal compound" will also be referred to simply as the "optical axis of the rod-shaped liquid crystal compound." In the following description, the "optical axis derived from the discotic liquid crystal compound" will also be referred to simply as the "optical axis of the discotic liquid crystal compound." In the following description, the "optical axis derived from the liquid crystal compound" will also be referred to simply as the "optical axis."

[0020] 1 , the rod-shaped liquid crystal compound 40c and the discotic liquid crystal compound 40d that are present at the same position in the planar direction of the main surface of the optical element 10 are oriented so that the longitudinal direction of the rod-shaped liquid crystal compound 40c coincides with the longitudinal direction of the discotic liquid crystal compound 40d when projected onto the interface of the discotic liquid crystal layer 44. In the following description, the "longitudinal direction of the discotic liquid crystal compound 40d when projected onto the interface of the discotic liquid crystal layer 44" will also be simply referred to as the "longitudinal direction of the discotic liquid crystal compound 40d."

[0021] As will be described in detail later, when a liquid crystal layer using a liquid crystal compound has a liquid crystal orientation pattern in which the direction of the optical axis changes while continuously rotating along at least one direction in the plane, it can diffract transmitted light. That is, a liquid crystal layer (optically anisotropic layer) having such a liquid crystal orientation pattern functions as a liquid crystal diffraction element. The diffraction angle depends on one period Λ, where the length (length Λ) over which the direction of the optical axis derived from the liquid crystal compound rotates 180° in the plane in the liquid crystal orientation pattern is defined as one period Λ of the liquid crystal orientation pattern. That is, in a liquid crystal diffraction element, one period Λ over which the direction of this optical axis rotates 180° in the plane corresponds to one period of the periodic structure of the diffraction element. In a diffraction element, the shorter this period Λ, the larger the diffraction angle. Therefore, the diffraction angle can be adjusted by adjusting one period of the liquid crystal orientation pattern. In the optical element of the present invention, the rod-shaped liquid crystal layer 42 (first optically anisotropic layer) and the discotic liquid crystal layer 44 (second optically anisotropic layer) both have a period Λ shorter than 0.5 μm. That is, the optical element of the present invention has a region in which the orientation of the optical axis of the liquid crystal compound rotates 180° in a period shorter than 0.5 μm. Therefore, the optical element of the present invention has an extremely short period Λ and can diffract incident light at a large diffraction angle.

[0022] In addition, taking into consideration the accuracy of the liquid crystal alignment pattern, the difficulty of forming the liquid crystal layer, etc., in the optical element of the present invention, it is preferable that one period Λ in the rod-shaped liquid crystal layer (first optically anisotropic layer) and the discotic liquid crystal layer (second optically anisotropic layer) is 0.05 μm or more.

[0023] Furthermore, the direction of light diffraction in a liquid crystal diffraction element depends on the rotation direction of the optical axis in the liquid crystal orientation pattern, so the direction of diffraction can be adjusted by adjusting the rotation direction of the optical axis in the liquid crystal orientation pattern.

[0024] In the illustrated example, in a preferred embodiment, the rotation direction of the optical axis in the liquid crystal orientation pattern of the rod-shaped liquid crystal layer 42 is the same as the rotation direction of the optical axis in the liquid crystal orientation pattern of the discotic liquid crystal layer 44, and the length of one period of the liquid crystal orientation pattern of the rod-shaped liquid crystal layer 42 is the same as the length of one period of the liquid crystal orientation pattern of the discotic liquid crystal layer 44. Furthermore, at the interface between the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44, the rod-shaped liquid crystal compound 40c and the discotic liquid crystal compound 40d that are present at the same position in the in-plane direction are such that the longitudinal direction of the rod-shaped liquid crystal compound 40c coincides with the longitudinal direction of the shape of the discotic liquid crystal compound 40d projected onto the interface of the discotic liquid crystal layer 44. In the present invention, since the cycle and rotation direction of the liquid crystal orientation patterns of the stacked rod-shaped liquid crystal layer 42 and discotic liquid crystal layer 44 are the same, the stacked rod-shaped liquid crystal layer 42 and discotic liquid crystal layer 44 integrally exhibit optical effects as a single liquid crystal layer (optically anisotropic layer) having a predetermined liquid crystal orientation pattern.

[0025] Diffraction elements using liquid crystal compounds have a problem in that their diffraction performance, such as diffraction efficiency, depends on the incident angle, resulting in a decrease in diffraction efficiency as the incident angle of light increases. Specifically, for example, in the case of a single-layer liquid crystal layer in which rod-shaped liquid crystal compounds are oriented in a predetermined liquid crystal orientation pattern, when viewed perpendicular to the surface of the liquid crystal layer, the difference between the longitudinal and lateral lengths of the rod-shaped liquid crystal compounds is the same regardless of the orientation of the rod-shaped liquid crystal compounds. Therefore, the in-plane retardation Re is constant regardless of the position in the in-plane direction of the liquid crystal layer. In contrast, when viewed obliquely from the surface of the liquid crystal layer, the difference between the longitudinal and lateral lengths of the rod-shaped liquid crystal compounds varies depending on the orientation of the rod-shaped liquid crystal compounds. Therefore, the in-plane retardation Re varies depending on the position in the in-plane direction of the liquid crystal layer. Therefore, when light is incident obliquely on the surface of the liquid crystal layer, the optical function of the liquid crystal layer differs from that when light is incident perpendicular to the surface of the liquid crystal layer, resulting in a decrease in diffraction efficiency. This is also true for a single-layer liquid crystal layer in which discotic liquid crystal compounds are oriented in a predetermined liquid crystal orientation pattern. In this way, the in-plane retardation Re changes depending on the incident angle of light when the retardation in the thickness direction Rth of the liquid crystal layer is not zero.

[0026] As will be described in detail later, a transmissive liquid crystal diffraction element converts incident circularly polarized light into circularly polarized light with the opposite rotation direction. If the thickness retardation Rth of the liquid crystal diffraction element is not zero, the influence of the in-plane retardation Re on the light changes as the light changes direction while traveling through the liquid crystal diffraction element. Therefore, the circularly polarized light diffracted by the liquid crystal diffraction element does not become completely circularly polarized. This phenomenon can cause noise and inconvenience in applications where mixing of right-handed and left-handed circularly polarized light is undesirable.

[0027] In contrast, the present invention has a structure in which a rod-shaped liquid crystal layer 42 and a discotic liquid crystal layer 44, which have the same cycle and rotation direction of the liquid crystal alignment pattern, are laminated. Here, the rod-shaped liquid crystal compound 40c has positive birefringence, and the discotic liquid crystal compound 40d has negative birefringence. Therefore, by laminating the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44, the thickness retardation Rth of the liquid crystal layer formed by alternately laminating the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44 can be made close to zero. This suppresses the change in in-plane retardation Re depending on the incident angle of light, thereby reducing the change in in-plane retardation Re depending on the incident angle when light is incident obliquely on an optical element having this liquid crystal layer. This improves the incident angle dependency of the diffraction efficiency, thereby improving the diffraction efficiency.

[0028] Furthermore, in the optical element of the present invention, by laminating the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44, the thickness retardation Rth can be made close to zero, so that even if light changes direction while traveling through the liquid crystal diffraction element, the influence of retardation on the light is small. Therefore, circularly polarized light diffracted by the optical element is converted into completely circularly polarized light. Therefore, the optical element of the present invention can be preferably used in applications where mixing of right-handed circularly polarized light and left-handed circularly polarized light is undesirable.

[0029] The reason why the diffraction efficiency can be improved as described above is basically the same for the reflective optical element of the present invention, i.e., the reflective liquid crystal diffraction element, in which the liquid crystal compounds are cholesterically oriented in the thickness direction in the rod-shaped liquid crystal layer and discotic liquid crystal layer described below.

[0030] Here, it is preferable that the thickness of the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44, the combined thickness of the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44, is not too large compared to the wavelength of the incident light. When the thickness of the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44 is sufficiently large compared to the wavelength of the incident light, each layer exerts an optical effect (retardation) on the light as a single layer. In this case, as in the case of the single layer described above, the retardation changes depending on the angle of incidence of the light, and a large angle of incidence reduces the diffraction efficiency. From the above perspective, the thickness of the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44 may be appropriately set according to the wavelength of the diffracted light. When the diffracted light is visible light, the thickness is preferably 2.0 μm or less, more preferably 0.9 μm or less, more preferably 0.7 to 0.01 μm, and even more preferably 0.5 to 0.01 μm.

[0031] 1 shows a configuration including one rod-shaped liquid crystal layer 42 and one discotic liquid crystal layer 44, but the present invention is not limited to this. For example, the liquid crystal display may have a four-layer configuration including two alternating rod-shaped liquid crystal layers 42 and two alternating discotic liquid crystal layers 44, or a six-layer configuration including three or more alternating rod-shaped liquid crystal layers 42 and two discotic liquid crystal layers 44. Alternatively, the liquid crystal display may have a total of three layers, such as a configuration in which one discotic liquid crystal layer 44 is sandwiched between two rod-shaped liquid crystal layers 42, or a configuration in which one rod-shaped liquid crystal layer 42 is sandwiched between two discotic liquid crystal layers 44. Furthermore, the liquid crystal display may have a total of five or more rod-shaped liquid crystal layers 42 and discotic liquid crystal layers 44, as long as the rod-shaped liquid crystal layers 42 and the discotic liquid crystal layers 44 are alternately stacked. That is, the present invention is not limited to a configuration having the same number of rod-shaped liquid crystal layers 42 and discotic liquid crystal layers 44, and there may be one more layer in either the rod-shaped liquid crystal layer 42 or the discotic liquid crystal layer 44. The thickness of the rod-shaped liquid crystal layer and the thickness of the discotic liquid crystal layer, and the total thickness of the rod-shaped liquid crystal layers and the total thickness of the discotic liquid crystal layers may be the same or different.

[0032] 1, the rod-shaped liquid crystal compound 40c and the discotic liquid crystal compound 40d that are present at the same position in the plane direction are oriented such that the longitudinal direction of the rod-shaped liquid crystal compound 40c and the longitudinal direction of the discotic liquid crystal compound 40d coincide with each other. However, the transmission type optical element of the present invention is not limited to this.

[0033] Another example of the optical element of the present invention is shown in Figure 2. The optical element 10b shown in Figure 2 has a total of four layers, namely, rod-shaped liquid crystal layers 42b and discotic liquid crystal layers 44b, which are alternately stacked in the thickness direction. In Figure 2, in order to simplify the drawing and clearly show the configuration of the optical element 10b, only the liquid crystal compounds on the surfaces of the rod-shaped liquid crystal layers 42b and discotic liquid crystal layers 44b are conceptually shown. However, the rod-shaped liquid crystal layers 42b and discotic liquid crystal layers 44b have a structure in which liquid crystal compounds are stacked in the thickness direction.

[0034] The rod-shaped liquid crystal layer 42b is a layer in which rod-shaped liquid crystal compounds 40c are oriented in a liquid crystal orientation pattern in which the direction of the optical axis changes while continuously rotating along at least one in-plane direction. The discotic liquid crystal layer 44b is a layer in which discotic liquid crystal compounds 40d are oriented in a liquid crystal orientation pattern in which the direction of the optical axis changes while continuously rotating along at least one in-plane direction. The rotation direction of the optical axis in the liquid crystal orientation pattern of the rod-shaped liquid crystal layer 42b is the same as the rotation direction of the optical axis in the liquid crystal orientation pattern of the discotic liquid crystal layer 44b, and the length of one period of the liquid crystal orientation pattern of the rod-shaped liquid crystal layer 42b is the same as the length of one period of the liquid crystal orientation pattern of the discotic liquid crystal layer 44b. Furthermore, at the interface between the rod-shaped liquid crystal layer 42b and the discotic liquid crystal layer 44b, the rod-shaped liquid crystal compound 40c and the discotic liquid crystal compound 40d that are present at the same position in the planar direction have a longitudinal direction that coincides with the longitudinal direction of the rod-shaped liquid crystal compound 40c when projected onto the interface of the discotic liquid crystal layer 44b.

[0035] In the example shown in Figure 2, the longitudinal direction of the liquid crystal compound in the layer is twisted in the thickness direction from the rod-shaped liquid crystal layer 42b at the bottom of the figure to the discotic liquid crystal layer 44b at the top of the figure. As a result, the two rod-shaped liquid crystal layers 42b and the two discotic liquid crystal layers 44b form a single liquid crystal layer, with the liquid crystal compound twisted in the thickness direction. In the example shown in Figure 2, the twist direction of the liquid crystal compound in the optical element 10b rotates counterclockwise from top to bottom in the figure. The twist angle of the liquid crystal compound in the optical element 10b in the thickness direction is less than 360°. In other words, both liquid crystal layers are twisted to such an extent that cholesteric alignment is not achieved.

[0036] In this way, when the optical element 10b has a structure in which the liquid crystal compound is twistedly aligned in the thickness direction, it is possible to increase the diffraction efficiency when the angle of incidence and the angle of emergence of light differ with respect to the optical element 10. Specifically, in a cross section parallel to the direction in which the orientation of the optical axis changes while continuously rotating (the direction of the array axis D, which will be described later), it is preferable that the angle formed by the direction of incidence of light and the angle formed by the direction of emergence of light with respect to a line segment connecting the liquid crystal compounds oriented in the same direction in the thickness direction be the same.

[0037] Alternatively, a configuration may be adopted in which a rod-shaped liquid crystal layer and a discotic liquid crystal layer are laminated as shown in FIG. 2, and two optically anisotropic layers are laminated in which the liquid crystal compound is twistedly aligned in the longitudinal direction, with the twist directions of the two optically anisotropic layers being opposite to each other.

[0038] Such a configuration in which the liquid crystal compound is twisted and aligned in the thickness direction can also be used in the two-layer optical element shown in FIG.

[0039] Another example of the optical element of the present invention is conceptually shown in Figure 3. The optical element 10c shown in Figure 3 has a first laminate 37b having four alternating rod-shaped liquid crystal layers 42b and discotic liquid crystal layers 44b, and a second laminate 37c having four alternating rod-shaped liquid crystal layers 42b and discotic liquid crystal layers 44b.

[0040] The rod-shaped liquid crystal layer 42b is a layer in which rod-shaped liquid crystal compounds 40c are oriented in a liquid crystal orientation pattern in which the direction of the optical axis changes while continuously rotating along at least one in-plane direction. The discotic liquid crystal layer 44b is a layer in which discotic liquid crystal compounds 40d are oriented in a liquid crystal orientation pattern in which the direction of the optical axis changes while continuously rotating along at least one in-plane direction. The rotation direction of the optical axis in the liquid crystal orientation pattern of the rod-shaped liquid crystal layer 42b is the same as the rotation direction of the optical axis in the liquid crystal orientation pattern of the discotic liquid crystal layer 44b, and the length of one period of the liquid crystal orientation pattern of the rod-shaped liquid crystal layer 42b is the same as the length of one period of the liquid crystal orientation pattern of the discotic liquid crystal layer 44b. That is, the direction of rotation of the optical axis and the length of one period in the liquid crystal orientation pattern of the rod-shaped liquid crystal layer 42b and the discotic liquid crystal layer 44b of the first laminate 37b are the same as the direction of rotation of the optical axis and the length of one period in the liquid crystal orientation pattern of the rod-shaped liquid crystal layer 42b and the discotic liquid crystal layer 44b of the second laminate 37c.

[0041] In the example shown in FIG. 3 , the first stack 37b has the liquid crystal compounds in the layers twisted in the thickness direction from the rod-shaped liquid crystal layer 42b at the bottom of the figure toward the discotic liquid crystal layer 44b at the top of the figure. Specifically, the twist direction of the liquid crystal compounds in the first stack 37b rotates counterclockwise from top to bottom in the figure. The bottom side of the first stack 37b in the figure is the side that contacts the second stack 37c. Meanwhile, the second stack 37c has the liquid crystal compounds in the layers twisted in the thickness direction from the discotic liquid crystal layer 44b at the bottom of the figure toward the rod-shaped liquid crystal layer 42b at the top of the figure. Specifically, the twist direction of the liquid crystal compounds in the second stack 37c rotates clockwise from top to bottom in the figure. The top side of the second stack 37c in the figure is the side that contacts the first stack 37b. That is, the twist direction of the liquid crystal compound in the first stack 37b is opposite to the twist direction of the liquid crystal compound in the second stack 37c.

[0042] In this way, by configuring the optical element 10c to have a laminate (optically anisotropic layer) in which the twist directions of the liquid crystal compound differ in the thickness direction, the angle dependence and wavelength dependence of the diffraction efficiency are further improved. In this case, the optimum values ​​of the twist angle (total twist angle in the thickness direction) and retardation Δn×d of each optically anisotropic layer change depending on the refractive index difference Δn of the liquid crystal compound. Therefore, it is sufficient to optimize the twist angle according to each optically anisotropic layer. The twist angle is preferably 30 to 180°. The twist alignment in the thickness direction can be achieved by adding a commonly used chiral agent.

[0043] Furthermore, it is preferable that the Δn of the liquid crystal compound is large, since this further improves the angle dependency and wavelength dependency.

[0044] In the example shown in FIG. 3, the optical element 10c has a two-layer structure consisting of laminates with different twist directions, but this is not limited thereto. The optical element may have three or more laminates with different twist directions. Alternatively, the optical element may have a laminate in which the liquid crystal compound is not twisted in the thickness direction between two laminates with different twist directions. This further improves the angle dependence and wavelength dependence of the diffraction efficiency. It is preferable that the optical axis direction of the non-twist-oriented laminate between the twist-oriented laminates is continuously connected (facing the same direction) at each in-plane location with the optical axis direction of the liquid crystal compound at the interface of the adjacent twist-oriented laminate. Such a configuration in which the optical axis direction of the liquid crystal compound is continuously connected between adjacent laminates can be produced by laminating and coating an upper liquid crystal layer on a lower liquid crystal layer.

[0045] When an optical element has optically anisotropic layers in which the twist directions of the liquid crystal compounds in the thickness direction are different, the twist angles per unit length in the thickness direction of each optically anisotropic layer may be the same or different.

[0046] The rod-shaped liquid crystal layer 42 will be described below with reference to Figures 4 and 5. As described above, the rod-shaped liquid crystal layer 42 is a rod-shaped liquid crystal layer formed by fixing a liquid crystal phase in which rod-shaped liquid crystal compounds are aligned, and has a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compounds changes while continuously rotating along at least one direction in the plane.

[0047] In the example shown in Fig. 4, the rod-shaped liquid crystal layer 42 is laminated on an alignment film 32 laminated on a support 30. In the rod-shaped liquid crystal layer 42 of the optical element 10 shown in Fig. 1, the rod-shaped liquid crystal layer 42 may be laminated on the support 30 and the alignment film 32. Alternatively, the rod-shaped liquid crystal layer 42 may be laminated in a state where the alignment film 32 and the rod-shaped liquid crystal layer 42 are laminated, with the support 30 peeled off. Alternatively, the rod-shaped liquid crystal layer 42 may be laminated in a state where the support 30 and the alignment film 32 are peeled off, with only the rod-shaped liquid crystal layer 42 being laminated. Furthermore, when a plurality of rod-shaped liquid crystal layers 42 and discotic liquid crystal layers 44 are alternately provided, the rod-shaped liquid crystal layer 42 laminated on the discotic liquid crystal layer 44 may be formed directly on the discotic liquid crystal layer 44 and laminated thereon, or may be formed on the support and then laminated on the discotic liquid crystal layer 44 after the support and alignment film are peeled off, as in the example of Fig. 4.

[0048] <Support> The support 30 supports the alignment film 32 and the rod-like liquid crystal layer 42. Various sheet-like materials (films, plates) can be used as the support 30, as long as they can support the alignment film 32 and the rod-like liquid crystal layer 42. The support 30 preferably has a transmittance of 50% or more to diffracted light, more preferably 70% or more, and even more preferably 85% or more.

[0049] There is no limitation on the thickness of the support 30, and it may be set appropriately to a thickness that can support the alignment film 32 and the rod-like liquid crystal layer 42 depending on the application of the optical element and the material forming the support 30. The thickness of the support 30 is preferably 1 to 1000 μm, more preferably 3 to 250 μm, and even more preferably 5 to 150 μm.

[0050] The support 30 may be a single layer or a multilayer. Examples of the single layer support 30 include support 30 made of glass, triacetyl cellulose (TAC), polyethylene terephthalate (PET), polycarbonate, polyvinyl chloride, acrylic, polyolefin, etc. Examples of the multilayer support 30 include one that includes any of the above-mentioned single layer supports as a substrate, with another layer provided on the surface of this substrate.

[0051] <Alignment Film> An alignment film 32 is formed on the surface of the support 30. The alignment film 32 is an alignment film for orienting the rod-shaped liquid crystal compounds 40c into a predetermined liquid crystal alignment pattern when forming the rod-shaped liquid crystal layer 42. As will be described later, in the present invention, the rod-shaped liquid crystal layer 42 has a liquid crystal alignment pattern in which the orientation of the optical axis 40A (see FIG. 5 ) derived from the rod-shaped liquid crystal compounds 40c changes while continuously rotating along one in-plane direction. Therefore, the alignment film 32 is formed so that the rod-shaped liquid crystal layer 42 can form this liquid crystal alignment pattern. In the following description, "the orientation of the optical axis 40A rotates" may also be simply referred to as "the optical axis 40A rotates."

[0052] Various known alignment films can be used for the alignment film 32. Examples include a rubbed film made of an organic compound such as a polymer, an obliquely evaporated film of an inorganic compound, a film with microgrooves, and a film formed by accumulating LB (Langmuir-Blodgett) films made by the Langmuir-Blodgett method using organic compounds such as ω-tricosanoic acid, dioctadecylmethylammonium chloride, and methyl stearate.

[0053] The alignment film 32 formed by rubbing treatment can be formed by rubbing the surface of the polymer layer several times in a certain direction with paper or cloth. Preferred materials for the alignment film 32 include polyimide, polyvinyl alcohol, polymers having polymerizable groups as described in JP-A-9-152509, and materials used to form alignment films 32 as described in JP-A-2005-97377, JP-A-2005-99228, and JP-A-2005-128503.

[0054] The alignment film 32 is preferably a so-called photo-alignment film obtained by irradiating a photo-alignable material with polarized or non-polarized light to form the alignment film 32. That is, a photo-alignment film formed by applying a photo-alignment material onto a support 30 is preferably used as the alignment film 32. Irradiation with polarized light can be performed vertically or obliquely to the photo-alignment film, and irradiation with non-polarized light can be performed obliquely to the photo-alignment film.

[0055] Examples of photo-alignment materials used in the alignment film that can be used in the present invention include those disclosed in JP-A-2006-285197, JP-A-2007-76839, JP-A-2007-138138, JP-A-2007-94071, JP-A-2007-121721, JP-A-2007-140465, JP-A-2007-156439, and JP-A-2007 azo compounds described in JP-A-133184, JP-A-2009-109831, Japanese Patent Nos. 3,883,848 and 4,151,746; aromatic ester compounds described in JP-A-2002-229039; maleimides having photo-orientable units described in JP-A-2002-265541 and JP-A-2002-317013; / or alkenyl-substituted nadimide compounds, photocrosslinkable silane derivatives described in Japanese Patent Nos. 4205195 and 4205198, photocrosslinkable polyimides, photocrosslinkable polyamides and photocrosslinkable polyesters described in JP-T-2003-520878, JP-T-2004-529220 and JP-T-4162850, and photodimerizable compounds described in JP-A-9-118717, JP-A-10-506420, JP-A-2003-505561, WO 2010 / 150748, JP-A-2013-177561 and JP-A-2014-12823, particularly cinnamate compounds, chalcone compounds and coumarin compounds are exemplified as preferred examples. Among these, azo compounds, photocrosslinkable polyimides, photocrosslinkable polyamides, photocrosslinkable polyesters, cinnamate compounds, and chalcone compounds are preferably used.

[0056] There is no limitation on the thickness of the alignment film 32, and it may be set appropriately to a thickness that provides the necessary alignment function depending on the material forming the alignment film 32. The thickness of the alignment film 32 is preferably 0.01 to 5 μm, and more preferably 0.05 to 2 μm.

[0057] There is no limitation on the method for forming the alignment film 32, and various known methods can be used depending on the material for forming the alignment film 32. One example is a method in which the alignment film 32 is applied to the surface of the support 30, dried, and then exposed to laser light to form an alignment pattern.

[0058] 8 conceptually shows an example of an exposure device that exposes the alignment film 32 to light to form an alignment pattern. The exposure device 60 shown in FIG. 8 includes a light source 64 equipped with a laser 62, a λ / 2 plate 65 that changes the polarization direction of laser light M emitted by the laser 62, a polarizing beam splitter 68 that splits the laser light M emitted by the laser 62 into two beams MA and MB, mirrors 70A and 70B that are respectively arranged on the optical paths of the two split beams MA and MB, and λ / 4 plates 72A and 72B. The light source 64 emits linearly polarized light P0. The λ / 4 plate 72A converts the linearly polarized light P0 (beam MA) into right-handed circularly polarized light P R The λ / 4 plate 72B converts the linearly polarized light P0 (light beam MB) into left-handed circularly polarized light P L are converted to , respectively.

[0059] A support 30 having an alignment film 32 before an alignment pattern is formed is placed in an exposure unit, and two light beams MA and MB are caused to intersect and interfere on the alignment film 32, and the alignment film 32 is irradiated with the interference light for exposure. This interference causes the polarization state of the light irradiating the alignment film 32 to periodically change in the form of interference fringes. This results in an alignment film having an alignment pattern in which the alignment state periodically changes. In the following description, an alignment film having an alignment pattern is also referred to as a "pattern alignment film." In the exposure device 60, the period of the alignment pattern can be adjusted by changing the crossing angle α of the two light beams MA and MB. That is, in the exposure device 60, by adjusting the crossing angle α, the length of one period Λ in which the optical axis 40A rotates 180° in one direction of the rotation of the optical axis 40A can be adjusted in the liquid crystal alignment pattern in which the optical axis 40A continuously rotates along one direction. By forming an optically anisotropic layer on the alignment film 32 having such an alignment pattern in which the alignment state changes periodically, it is possible to form a rod-shaped liquid crystal layer 42 having a liquid crystal alignment pattern in which the optic axis 40A derived from the rod-shaped liquid crystal compound 40c changes while continuously rotating along one direction, as will be described later. In addition, by rotating the optic axes of the λ / 4 plates 72A and 72B by 90°, respectively, the rotation direction of the optic axis 40A can be reversed.

[0060] As described above, a patterned alignment film has an alignment pattern that orients liquid crystal compounds in a rod-shaped liquid crystal layer formed on the patterned alignment film, so that the orientation of the optical axis of the liquid crystal compound changes while continuously rotating along at least one in-plane direction. If the axis along which the patterned alignment film aligns the liquid crystal compound is defined as the alignment axis, the patterned alignment film can be said to have an orientation pattern in which the orientation of the alignment axis changes while continuously rotating along at least one in-plane direction. The alignment axis of a patterned alignment film can be detected by measuring absorption anisotropy. For example, when a patterned alignment film is irradiated with linearly polarized light while rotating and the amount of light transmitted through the patterned alignment film is measured, the direction in which the amount of light is maximized or minimized is observed to gradually change along one in-plane direction.

[0061] In one embodiment of the present invention, multiple alignment patterns may be formed on the same alignment film. The multiple alignment patterns may have alignment patterns in which the alignment state changes periodically, and further, the orientation of the optical axis 40A of the alignment patterns may be different. Examples of methods for achieving such alignment patterns include a method of rotating the substrate relative to the exposure device 60 and performing multiple exposures, and a method of providing an optical path that splits the laser light M into two beams MA and MB and two other beams MC and MD, and switching between each optical path to perform multiple exposures.

[0062] In the present invention, the alignment film 32 is provided as a preferred embodiment but is not an essential component. For example, by forming an alignment pattern on the support 30 by a method of rubbing the support 30 or a method of processing the support 30 with laser light or the like, it is possible to configure the rod-like liquid crystal layer 42 to have a liquid crystal alignment pattern in which the direction of the optical axis 40A derived from the rod-like liquid crystal compound 40c changes while continuously rotating along at least one direction in the plane. That is, in the present invention, the support 30 may function as an alignment film.

[0063] <Rod-shaped Liquid Crystal Layer> The rod-shaped liquid crystal layer 42 is formed on the surface of the alignment film 32. As described above, the rod-shaped liquid crystal layer 42 is a liquid crystal layer formed by fixing a liquid crystal phase in which rod-shaped liquid crystal compounds 40c are aligned, and has a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane.

[0064] As conceptually shown in Figure 4, in the rod-shaped liquid crystal layer 42, the rod-shaped liquid crystal compounds 40c are not twisted or rotated in the thickness direction, and the rod-shaped liquid crystal compounds 40c at the same position in the plane direction are oriented so that their optical axes 40A are oriented in the same direction.

[0065] <<Method for Forming a Rod-Shaped Liquid Crystal Layer>> A rod-shaped liquid crystal layer can be formed by fixing a liquid crystal phase aligned in a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one in-plane direction. The structure in which the liquid crystal phase is fixed may be any structure in which the orientation of the liquid crystal compound in the liquid crystal phase is maintained. Typically, a preferred structure is one in which a polymerizable liquid crystal compound is aligned along the liquid crystal orientation pattern, then polymerized and cured by ultraviolet irradiation, heating, or the like to form a non-fluid layer, and simultaneously changed to a state in which the orientation form is not changed by an external field or external force. It is sufficient for the structure in which the liquid crystal phase is fixed to maintain the optical properties of the liquid crystal phase; in the rod-shaped liquid crystal layer, the liquid crystal compound does not need to exhibit liquid crystallinity. For example, the polymerizable liquid crystal compound may be polymerized by a curing reaction and lose its liquid crystallinity. These points also apply to the discotic liquid crystal layer described below.

[0066] An example of a material used to form a rod-shaped liquid crystal layer formed by fixing a liquid crystal phase is a liquid crystal composition containing a liquid crystal compound. The liquid crystal compound is preferably a polymerizable liquid crystal compound. The liquid crystal composition used to form the rod-shaped liquid crystal layer may further contain a surfactant, a polymerization initiator, etc.

[0067] --Polymerizable Liquid Crystal Compound-- Examples of rod-shaped polymerizable liquid crystal compounds that form rod-shaped liquid crystal layers include rod-shaped nematic liquid crystal compounds. Preferred rod-shaped nematic liquid crystal compounds include azomethines, azoxy compounds, cyanobiphenyls, cyanophenyl esters, benzoates, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes, and alkenylcyclohexylbenzonitriles. Not only low-molecular-weight liquid crystal compounds but also high-molecular-weight liquid crystal compounds can be used.

[0068] A polymerizable liquid crystal compound can be obtained by introducing a polymerizable group into a liquid crystal compound. Examples of the polymerizable group include an unsaturated polymerizable group, an epoxy group, and an aziridinyl group, with an unsaturated polymerizable group being preferred and an ethylenically unsaturated polymerizable group being more preferred. The polymerizable group can be introduced into the molecule of the liquid crystal compound by various methods. The number of polymerizable groups in the polymerizable liquid crystal compound is preferably 1 to 6, more preferably 1 to 3. Examples of polymerizable liquid crystal compounds include those described in Makromol.Chem., Vol. 190, p. 2255 (1989), Advanced Materials, Vol. 5, p. 107 (1993), U.S. Pat. No. 4,683,327, U.S. Pat. No. 5,622,648, U.S. Pat. No. 5,770,107, WO 95 / 22586, WO 95 / 24455, WO 97 / 00600, WO 98 / 23580, WO 98 / 52905, JP-A Nos. 1-272551, 6-16616, 7-110469, 11-80081, and 2001-328973. Two or more polymerizable liquid crystal compounds may be used in combination. When two or more types of polymerizable liquid crystal compounds are used in combination, the alignment temperature can be lowered.

[0069] Other examples of polymerizable liquid crystal compounds that can be used include cyclic organopolysiloxane compounds having a cholesteric phase, such as those disclosed in JP-A-57-165480. Examples of the polymeric liquid crystal compounds that can be used include polymers having mesogen groups exhibiting liquid crystallinity introduced into the main chain, side chain, or both the main chain and side chain, polymeric cholesteric liquid crystals having cholesteryl groups introduced into the side chain, liquid crystalline polymers such as those disclosed in JP-A-9-133810, and liquid crystalline polymers such as those disclosed in JP-A-11-293252.

[0070] The amount of the polymerizable liquid crystal compound added to the liquid crystal composition is preferably 75 to 99.9 mass %, more preferably 80 to 99 mass %, and even more preferably 85 to 90 mass %, based on the solid content mass (mass excluding the solvent) of the liquid crystal composition.

[0071] --Surfactant-- The liquid crystal composition used to form the rod-shaped liquid crystal layer may contain a surfactant. The surfactant is preferably a compound that can function as an alignment control agent that contributes to the stable or rapid alignment of the liquid crystal compound. Examples of the surfactant include silicone surfactants and fluorine surfactants, with fluorine surfactants being preferred.

[0072] Specific examples of surfactants include the compounds described in paragraphs

[0082] to

[0090] of JP-A No. 2014-119605, the compounds described in paragraphs

[0031] to

[0034] of JP-A No. 2012-203237, the compounds exemplified in paragraphs

[0092] and

[0093] of JP-A No. 2005-99248, the compounds exemplified in paragraphs

[0076] to

[0078] and paragraphs

[0082] to

[0085] of JP-A No. 2002-129162, and fluorine (meth)acrylate polymers described in paragraphs

[0018] to

[0043] of JP-A No. 2007-272185, etc. One type of surfactant may be used alone, or two or more types may be used in combination. As the fluorine-based surfactant, the compounds described in paragraphs

[0082] to

[0090] of JP-A-2014-119605 are preferred.

[0073] The amount of the surfactant added in the liquid crystal composition is preferably 0.01 to 10% by mass, more preferably 0.01 to 5% by mass, and even more preferably 0.02 to 1% by mass, based on the total mass of the liquid crystal compound.

[0074] --Polymerization initiator-- When the liquid crystal composition contains a polymerizable compound, it preferably contains a polymerization initiator. In an embodiment in which the polymerization reaction is caused to proceed by ultraviolet irradiation, the polymerization initiator used is preferably a photopolymerization initiator that can initiate the polymerization reaction by ultraviolet irradiation. Examples of photopolymerization initiators include α-carbonyl compounds (described in U.S. Pat. Nos. 2,367,661 and 2,367,670), acyloin ethers (described in U.S. Pat. No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin compounds (described in U.S. Pat. No. 2,722,512), polynuclear quinone compounds (described in U.S. Pat. Nos. 3,046,127 and 2,951,758), combinations of triarylimidazole dimers and p-aminophenyl ketones (described in U.S. Pat. No. 3,549,367), acridine and phenazine compounds (described in JP-A No. 60-105,667 and U.S. Pat. No. 4,239,850), and oxadiazole compounds (described in U.S. Pat. No. 4,212,970). The content of the photopolymerization initiator in the liquid crystal composition is preferably 0.1 to 20% by mass, more preferably 0.5 to 12% by mass, based on the content of the liquid crystal compound.

[0075] Crosslinking Agent The liquid crystal composition may optionally contain a crosslinking agent to improve the film strength and durability after curing. Suitable crosslinking agents are those that cure under ultraviolet light, heat, moisture, or the like. The crosslinking agent is not particularly limited and can be appropriately selected depending on the purpose. Examples include polyfunctional acrylate compounds such as trimethylolpropane tri(meth)acrylate and pentaerythritol tri(meth)acrylate; epoxy compounds such as glycidyl (meth)acrylate and ethylene glycol diglycidyl ether; aziridine compounds such as 2,2-bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate] and 4,4-bis(ethyleneiminocarbonylamino)diphenylmethane; isocyanate compounds such as hexamethylene diisocyanate and biuret-type isocyanate; polyoxazoline compounds having an oxazoline group in the side chain; and alkoxysilane compounds such as vinyltrimethoxysilane and N-(2-aminoethyl)3-aminopropyltrimethoxysilane. Furthermore, known catalysts can be used depending on the reactivity of the crosslinking agent, which can improve productivity in addition to improving film strength and durability. These may be used alone or in combination of two or more. The content of the crosslinking agent is preferably 3 to 20% by mass, more preferably 5 to 15% by mass, based on the mass of the solid content of the liquid crystal composition. When the content of the crosslinking agent is within the above range, the effect of improving the crosslink density is easily obtained, and the stability of the liquid crystal phase is further improved.

[0076] --Other Additives-- If necessary, polymerization inhibitors, antioxidants, ultraviolet absorbers, light stabilizers, colorants, metal oxide fine particles, and the like may be added to the liquid crystal composition within a range that does not impair optical performance, etc.

[0077] The liquid crystal composition is preferably used as a liquid when forming a rod-shaped liquid crystal layer. The liquid crystal composition may contain a solvent. The solvent is not limited and can be appropriately selected depending on the purpose, but organic solvents are preferred. The organic solvent is not limited and can be appropriately selected depending on the purpose, and examples thereof include ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. These may be used alone or in combination of two or more. Among these, ketones are preferred when considering the environmental impact.

[0078] When forming a rod-shaped liquid crystal layer, it is preferable to apply a liquid crystal composition to the surface on which the rod-shaped liquid crystal layer is to be formed, align the liquid crystal compound into a liquid crystal phase oriented in a predetermined liquid crystal orientation pattern, and then harden the liquid crystal compound to form a rod-shaped liquid crystal layer. That is, when forming a rod-shaped liquid crystal layer on the alignment film 32, it is preferable to apply a liquid crystal composition to the alignment film 32, align the liquid crystal compound into a predetermined liquid crystal orientation pattern, and then harden the liquid crystal compound to fix the liquid crystal phase, thereby forming a rod-shaped liquid crystal layer. On the other hand, when forming a rod-shaped liquid crystal layer on a discotic liquid crystal layer, it is preferable to apply a liquid crystal composition to the discotic liquid crystal layer, align the liquid crystal compound into a predetermined liquid crystal orientation pattern, and then harden the liquid crystal compound to fix the liquid crystal phase, thereby forming a rod-shaped liquid crystal layer. The liquid crystal composition can be applied by any known method capable of uniformly applying a liquid to a sheet-like material, including printing methods such as inkjet printing and scroll printing, as well as spin coating, bar coating, and spray coating.

[0079] The applied liquid crystal composition is dried and / or heated as necessary, and then cured to form a rod-shaped liquid crystal layer. In this drying and / or heating process, the liquid crystal compounds in the liquid crystal composition may be oriented in a predetermined liquid crystal orientation pattern. When heating is performed, the heating temperature is preferably 200° C. or less, and more preferably 130° C. or less.

[0080] The aligned liquid crystal compound is further polymerized as needed. The polymerization may be either thermal polymerization or photopolymerization by light irradiation, but photopolymerization is preferred. The light irradiation is preferably performed using ultraviolet light. The irradiation energy is 20 mJ / cm. 2 ~50 J / cm 2 is preferred, and 50 to 1500 mJ / cm 2 In order to promote the photopolymerization reaction, the irradiation may be carried out under heated conditions or in a nitrogen atmosphere. The wavelength of the ultraviolet light to be irradiated is preferably 250 to 430 nm.

[0081] <<Liquid Crystal Alignment Pattern of Rod-Shaped Liquid Crystal Layer>> As described above, the rod-shaped liquid crystal layer has a liquid crystal alignment pattern in which the direction of the optical axis 40A derived from the rod-shaped liquid crystal compound 40c changes while continuously rotating in one direction within the plane of the optically anisotropic layer. The optical axis 40A derived from the rod-shaped liquid crystal compound 40c is the axis along which the refractive index of the rod-shaped liquid crystal compound 40c is highest, that is, the so-called slow axis. In the rod-shaped liquid crystal compound 40c, the optical axis 40A is aligned with the long axis direction of the rod shape.

[0082] Fig. 5 conceptually shows a plan view of the rod-shaped liquid crystal layer 42. Note that the plan view is a view of the rod-shaped liquid crystal layer in Fig. 4 as seen from above, i.e., a view as seen from the thickness direction of the optical element (i.e., the lamination direction of each layer (film)). In Fig. 5, in order to clearly show the configuration of the rod-shaped liquid crystal layer, only the rod-shaped liquid crystal compounds 40c on the surface of the alignment film 32 are shown.

[0083] As shown in FIG. 5 , on the surface of the alignment film 32, the rod-shaped liquid crystal compounds 40c constituting the rod-shaped liquid crystal layer 42 have a liquid crystal orientation pattern in which the orientation of the optic axis 40A changes while continuously rotating along a predetermined direction indicated by arrow D (hereinafter referred to as alignment axis D) within the plane of the rod-shaped liquid crystal layer 42, in accordance with the orientation pattern formed on the underlying alignment film 32. In the illustrated example, the liquid crystal orientation pattern is such that the optic axis 40A of the rod-shaped liquid crystal compounds 40c changes while continuously rotating clockwise along the alignment axis D. The rod-shaped liquid crystal compounds 40c constituting the rod-shaped liquid crystal layer 42 are two-dimensionally aligned along the alignment axis D and a direction perpendicular to this direction (the alignment axis D direction). In the following description, the direction perpendicular to the alignment axis D direction will be referred to as the Y direction for convenience. That is, the arrow Y direction is a direction perpendicular to the direction in which the orientation of the optic axis 40A of the rod-shaped liquid crystal compounds 40c changes while continuously rotating within the plane of the rod-shaped liquid crystal layer 42. Therefore, in FIGS. 1 to 4 and FIG. 6 described later, the Y direction is a direction perpendicular to the paper surface.

[0084] The expression "the orientation of the optical axis 40A of the rod-shaped liquid crystal compounds 40c changes while continuously rotating in the direction of the alignment axis D (a predetermined direction)" specifically means that the angle formed between the optical axis 40A of the rod-shaped liquid crystal compounds 40c aligned along the alignment axis D and the alignment axis D direction varies depending on the position in the alignment axis D direction, and the angle formed between the optical axis 40A and the alignment axis D direction sequentially changes from θ to θ+180° or θ−180° along the alignment axis D direction. The difference in angle between the optical axes 40A of the rod-shaped liquid crystal compounds 40c adjacent to each other in the alignment axis D direction is preferably 45° or less, more preferably 15° or less, and even more preferably a smaller angle.

[0085] In the present invention, the liquid crystal compounds are rotated in a direction such that the angle formed by the optical axes 40A of the rod-shaped liquid crystal compounds 40c adjacent to each other in the direction of the alignment axis D becomes smaller. Therefore, in the rod-shaped liquid crystal layer 42 shown in Figures 4 and 5, the optical axes 40A of the rod-shaped liquid crystal compounds 40c rotate rightward (clockwise) along the direction of the arrow of the alignment axis D.

[0086] On the other hand, the rod-shaped liquid crystal compounds 40c forming the rod-shaped liquid crystal layer 42 have the same orientation of the optic axes 40A in the Y direction perpendicular to the direction of the alignment axis D, i.e., the Y direction perpendicular to the direction in which the optic axes 40A change while continuously rotating. In other words, the rod-shaped liquid crystal compounds 40c forming the rod-shaped liquid crystal layer 42 have the same angle between the optic axes 40A of the rod-shaped liquid crystal compounds 40c and the direction of the alignment axis D in the Y direction.

[0087] In the rod-shaped liquid crystal layer 42, the liquid crystal compounds aligned in the Y direction have the same angle between their optical axes 40A and the alignment axis D. The alignment axis D is a direction in which the orientations of the optical axes of the rod-shaped liquid crystal compounds 40c change while continuously rotating. A region R is defined as a region in which the rod-shaped liquid crystal compounds 40c, in which the angle between their optical axes 40A and the alignment axis D is the same, are arranged in the Y direction.

[0088] As described above, in the rod-shaped liquid crystal layer 42, in the liquid crystal orientation pattern of the rod-shaped liquid crystal compounds 40c, the length (length Λ (distance)) over which the optical axis 40A of the rod-shaped liquid crystal compounds 40c rotates 180° in the direction of the alignment axis D, in which the optical axis 40A continuously rotates and changes in the plane, is defined as one period Λ in the liquid crystal orientation pattern. That is, one period Λ is defined as the distance between the centers in the direction of the alignment axis D of two rod-shaped liquid crystal compounds 40c that are at the same angle with respect to the direction of the alignment axis D. Specifically, as shown in FIG. 5 , one period Λ is defined as the distance between the centers in the direction of the alignment axis D of two rod-shaped liquid crystal compounds 40c whose alignment axis D and the direction of the optical axis 40A coincide. In the liquid crystal orientation pattern of the rod-shaped liquid crystal layer 42, this one period Λ is repeated in one direction along the alignment axis D, i.e., in which the orientation of the optical axis 40A continuously rotates and changes.

[0089] In the optical element of the present invention, this period Λ is shorter than 0.5 μm. That is, in the present invention, the optical axis 40A repeatedly rotates by 180° along the alignment axis D at a period shorter than 0.5 μm. This also applies to the discotic liquid crystal layer 44.

[0090] 4, the rod-shaped liquid crystal compounds 40c present at the same in-plane position in the thickness direction are configured so that their optic axes 40A are aligned in the same direction. However, in the example shown in FIG. 2, when the longitudinal directions of the liquid crystal compounds are twisted in the thickness direction in the alternately stacked rod-shaped liquid crystal layers 42b and discotic liquid crystal layers 44b, the optic axes 40A of the rod-shaped liquid crystal compounds 40c are twisted in the thickness direction in each layer. This also applies to the discotic liquid crystal layer.

[0091] <Disc-Shaped Liquid Crystal Layer> The disc-shaped liquid crystal layer 44 will be described below with reference to FIGS. 6 and 7. FIG.

[0092] The examples shown in Figures 6 and 7 are discotic liquid crystal layers formed by fixing a liquid crystal phase in which discotic liquid crystal compounds are aligned, and have a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compounds changes while continuously rotating along at least one direction in the plane.

[0093] When the discotic liquid crystal layer 44 is laminated on the rod-shaped liquid crystal layer 42, like the discotic liquid crystal layer 44 of the optical element 10 in Figure 1, the discotic liquid crystal layer 44 may be formed directly on the rod-shaped liquid crystal layer 42 and laminated thereon, or may be formed on a support and an alignment film, like the rod-shaped liquid crystal layer 42 in Figure 4, and then the support and alignment film may be peeled off and the discotic liquid crystal layer 44 may be laminated on the rod-shaped liquid crystal layer 42.

[0094] As described above, the discotic liquid crystal layer 44 is a liquid crystal layer formed by fixing a liquid crystal phase in which the discotic liquid crystal compound 40d is aligned, and has a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. The optical axis of the discotic liquid crystal compound 40d is oriented in a direction perpendicular to the disc surface. Therefore, in the discotic liquid crystal layer 44, the discotic liquid crystal compound 40d is aligned so that the disc surface is perpendicular to the interface (surface) of the discotic liquid crystal layer 44.

[0095] As conceptually shown in Figure 6, in the discotic liquid crystal layer 44, the discotic liquid crystal compounds 40d are not twisted or rotated in the thickness direction, and the discotic liquid crystal compounds 40d at the same position in the surface direction are oriented so that their optical axes 40A are oriented in the same direction.

[0096] <<Method for forming a discotic liquid crystal layer>> A discotic liquid crystal layer can be formed by fixing a liquid crystal phase oriented in a layer form in a liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane.

[0097] An example of a material used to form a discotic liquid crystal layer formed by fixing a liquid crystal phase is a liquid crystal composition containing a liquid crystal compound. The liquid crystal compound is preferably a polymerizable liquid crystal compound. Similar to the liquid crystal composition used to form a rod-shaped liquid crystal layer, the liquid crystal composition used to form a discotic liquid crystal layer may further contain additives such as a surfactant and a polymerization initiator, as well as a solvent. The additives such as the surfactant and the polymerization initiator, as well as the solvent, are as described above.

[0098] --Discotic Liquid Crystal Compound-- As the discotic liquid crystal compound, for example, those described in JP-A Nos. 2007-108732 and 2010-244038 can be preferably used.

[0099] When forming a discotic liquid crystal layer, it is preferable to apply a liquid crystal composition to the surface on which the discotic liquid crystal layer is formed, align the liquid crystal compound into a liquid crystal phase oriented in a predetermined liquid crystal orientation pattern, and then harden the liquid crystal compound to form a discotic liquid crystal layer. That is, when forming a discotic liquid crystal layer on an alignment film, it is preferable to apply a liquid crystal composition to the alignment film, align the liquid crystal compound into a predetermined liquid crystal orientation pattern, and then harden the liquid crystal compound to fix the liquid crystal phase, thereby forming a discotic liquid crystal layer. Also, when forming a discotic liquid crystal layer on a rod-shaped liquid crystal layer, it is preferable to apply a liquid crystal composition to the rod-shaped liquid crystal layer, align the liquid crystal compound into a predetermined liquid crystal orientation pattern, and then harden the liquid crystal compound to fix the liquid crystal phase, thereby forming a discotic liquid crystal layer. However, the present invention is not limited thereto, and an alignment film or a support for forming the discotic liquid crystal layer 44 may be provided between the discotic liquid crystal layer 44 and the rod-shaped liquid crystal layer 42, as with the rod-shaped liquid crystal layer 42 described above.

[0100] The method of applying the liquid crystal composition, the method of drying and heating after application, and the method of polymerization are as described above. When a liquid crystal layer is formed on another liquid crystal layer by the application method, the upper liquid crystal layer basically follows the alignment state of the liquid crystal compound on the surface (interface) of the lower liquid crystal layer.

[0101] <<Liquid Crystal Alignment Pattern of Discotic Liquid Crystal Layer>> As described above, the discotic liquid crystal layer has a liquid crystal alignment pattern in which the direction of the optic axis 40A derived from the discotic liquid crystal compound 40d changes while continuously rotating in one direction within the plane of the optically anisotropic layer. Note that the optic axis 40A derived from the discotic liquid crystal compound 40d is an axis perpendicular to the disc surface of the discotic liquid crystal compound 40d.

[0102] Fig. 7 conceptually shows a plan view of the discotic liquid crystal layer 44. The plan view is a view of the discotic liquid crystal layer in Fig. 6 viewed from above, i.e., a view viewed from the thickness direction of the optical element (i.e., the stacking direction of each layer (film)). In Fig. 7, in order to clearly show the configuration of the discotic liquid crystal layer, only the discotic liquid crystal compound 40d on the surface (interface) of the discotic liquid crystal layer 44 is shown.

[0103] 7 , the discotic liquid crystal compound 40d constituting the discotic liquid crystal layer 44 has a liquid crystal orientation pattern in which the orientation of the optic axis 40A changes while continuously rotating along a predetermined direction indicated by the alignment axis D within the plane of the discotic liquid crystal layer 44. In the illustrated example, the discotic liquid crystal compound 40d has a liquid crystal orientation pattern in which the optic axis 40A changes while continuously rotating clockwise along the alignment axis D. The discotic liquid crystal compound 40d constituting the discotic liquid crystal layer 44 is two-dimensionally aligned along the alignment axis D and the Y direction perpendicular to the alignment axis D.

[0104] In the discotic liquid crystal layer 44, the liquid crystal compounds aligned in the Y direction have the same angle between their optical axes 40A and the alignment axis D. A region R is defined as a region where discotic liquid crystal compounds 40d aligned in the Y direction have the same angle between their optical axes 40A and the alignment axis D.

[0105] As in the rod-like liquid crystal layer 42, in the discotic liquid crystal layer 44, in the liquid crystal orientation pattern of the discotic liquid crystal compounds 40d, the length (length Λ (distance)) over which the optical axis 40A of the discotic liquid crystal compounds 40d rotates 180° in the direction of the alignment axis D, in which the optical axis 40A continuously rotates and changes in the plane, is defined as one period Λ in the liquid crystal orientation pattern. That is, one period Λ is defined as the distance between the centers of two discotic liquid crystal compounds 40d that are at the same angle with respect to the alignment axis D, in the direction of the alignment axis D. Specifically, as shown in FIG. 7 , the length Λ of one period is defined as the distance between the centers of two discotic liquid crystal compounds 40d whose alignment axis D and the direction of the optical axis 40A are the same. In the liquid crystal orientation pattern of the discotic liquid crystal layer 44, this one period Λ is repeated in the direction of the alignment axis D, i.e., in one direction in which the orientation of the optical axis 40A continuously rotates and changes.

[0106] As described above, in the optical element of the present invention, this period Λ is shorter than 0.5 μm. That is, in the present invention, the optical axis 40A of the discotic liquid crystal layer 44 also repeatedly rotates by 180° along the alignment axis D at a period shorter than 0.5 μm.

[0107] As described above, the rod-shaped liquid crystal compound 40c and the discotic liquid crystal compound 40d present at the same position in the in-plane direction at the interface between the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44 have their longitudinal directions aligned with the longitudinal directions of the discotic liquid crystal compound 40d projected onto the interface of the discotic liquid crystal layer 44. Therefore, in the rod-shaped liquid crystal layer 42b and the discotic liquid crystal layer 44b stacked as shown in Figure 1, the rod-shaped liquid crystal compound 40c and the discotic liquid crystal compound 40d at the same position in the in-plane direction are aligned so that their longitudinal directions are in the same direction throughout the thickness direction.

[0108] In the optical element 10 in which rod-shaped liquid crystal layers 42 and discotic liquid crystal layers 44 are alternately laminated, the in-plane retardation (Re) value in each region R is preferably a half wavelength, i.e., λ / 2. This in-plane retardation is calculated by the product of the refractive index difference Δn associated with the refractive index anisotropy of the region R and the thickness of the optical element 10. Here, the refractive index difference associated with the refractive index anisotropy of the region R in the optical element 10 depends on the difference between the refractive index of the rod-shaped liquid crystal compound 40c in the longitudinal direction and the refractive index in the direction perpendicular to the longitudinal direction (the refractive index difference of the rod-shaped liquid crystal compound 40c), and the difference between the refractive index of the discotic liquid crystal compound 40d in the longitudinal direction and the refractive index in the direction perpendicular to the longitudinal direction (the refractive index difference of the discotic liquid crystal compound 40d). Therefore, the in-plane retardation in region R of the optical element 10 is determined depending on the refractive index difference of the rod-shaped liquid crystal compound 40c, the refractive index difference of the discotic liquid crystal compound 40d, the thickness of the rod-shaped liquid crystal compound 40c, and the thickness of the discotic liquid crystal compound 40d, etc.

[0109] Such an optical element 10 refracts incident circularly polarized light and converts the polarization direction of the circularly polarized light. The operation of the optical element 10 will be explained using the conceptual diagrams in FIGS. 9 and 10 . It is assumed that the product of the refractive index difference of the liquid crystal compounds and the thickness of the optical element is λ / 2. In addition, although FIGS. 9 and 10 only show the rod-shaped liquid crystal compounds 40c on the surface in order to show the rotation direction of the optical axis in the liquid crystal orientation pattern of the optical element 10, the optical element 10 has a layered rod-shaped liquid crystal layer 42 and a discotic liquid crystal layer 44, as in the example shown in FIG. 1 .

[0110] As shown in Figure 9, when the product of the refractive index difference of the liquid crystal compound of the optical element 10 and the thickness of the optical element 10 is λ / 2, when left-handed circularly polarized incident light L1 is incident on the optical element 10, the incident light L1 is given a phase difference of 180° as it passes through the optical element 10, and the transmitted light L2 is converted to right-handed circularly polarized light. Furthermore, because the liquid crystal orientation pattern formed on the optical element 10 is a periodic pattern in the direction of the alignment axis D, the transmitted light L2 travels in a direction different from the traveling direction of the incident light L1. In this way, the left-handed circularly polarized incident light L1 is converted to right-handed circularly polarized transmitted light L2 that is tilted at a certain angle toward the alignment axis D with respect to the incident direction. In the example shown in Figure 9, the transmitted light L2 is diffracted to travel in a downward and rightward direction.

[0111] On the other hand, as shown in FIG. 10 , when the product of the refractive index difference between the liquid crystal compounds of the optical element 10 and the thickness of the rod-shaped liquid crystal layer 42 is λ / 2, when right-handed circularly polarized incident light L4 is incident on the optical element 10, the incident light L4 is given a phase difference of 180° as it passes through the optical element 10 and is converted into left-handed circularly polarized transmitted light L5. Furthermore, because the liquid crystal orientation pattern formed on the optical element 10 is a periodic pattern in the direction of the alignment axis D, the transmitted light L5 travels in a direction different from the traveling direction of the incident light L4. At this time, the transmitted light L5 travels in a different direction from the transmitted light L2, that is, in the direction opposite to the direction of the arrow of the alignment axis D with respect to the incident direction. In this way, the incident light L4 is converted into left-handed circularly polarized transmitted light L5 that is tilted at a certain angle in the direction opposite to the direction of the alignment axis D with respect to the incident direction. In the example shown in FIG. 10 , the transmitted light L5 is diffracted to travel in a downward and leftward direction.

[0112] As described above, the optical element 10 can adjust the refraction angles of the transmitted light L2 and L5 by adjusting the length of one period Λ of the formed liquid crystal orientation pattern. Specifically, the shorter the period Λ of the liquid crystal orientation pattern, the stronger the interference between the lights that have passed through adjacent liquid crystal compounds, and therefore the greater the refraction of the transmitted light L2 and L5.

[0113] In the optical element 10 of the present invention, the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44 both have a period Λ shorter than 0.5 μm. That is, the optical element 10 of the present invention can diffract (refract) transmitted light at a large diffraction angle with respect to incident light. Moreover, as described above, the optical element 10 of the present invention has a configuration in which the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44, which have similar liquid crystal orientation patterns, are laminated together directly or via a support 30 or the like. Therefore, the optical element 10 of the present invention can diffract incident light with high diffraction efficiency and little zero-order light. That is, the optical element of the present invention can diffract (refract) incident light at a large diffraction angle with high diffraction efficiency.

[0114] Furthermore, by reversing the direction of rotation of the optical axis 40A of the liquid crystal compound, which rotates along the direction of the alignment axis D, the direction of refraction of transmitted light can be reversed. That is, in the example shown in FIGS. 9 and 10 , the rotation direction of the optical axis 40A pointing toward the direction of the alignment axis D is clockwise, but by changing this rotation direction to counterclockwise, the direction of refraction of transmitted light can be reversed. Specifically, in FIGS. 9 and 10 , when the rotation direction of the optical axis 40A pointing toward the direction of the alignment axis D is counterclockwise, left-handed circularly polarized light incident on the optical element 10 from above in the figure passes through the optical element 10, and the transmitted light is converted to right-handed circularly polarized light, and is diffracted to travel in the lower left direction in the figure. Similarly, right-handed circularly polarized light incident on the optical element 10 from above in the figure passes through the optical element 10, and the transmitted light is converted to left-handed circularly polarized light, and is diffracted to travel in the lower right direction in the figure.

[0115] <<Method of Manufacturing Optical Element>> An optical element can be manufactured by forming a rod-shaped liquid crystal layer and a discotic liquid crystal layer using the methods described above. That is, for example, first, a patterned alignment film is formed on a support, and then a liquid crystal composition that will become the rod-shaped liquid crystal layer is applied to the patterned alignment film, dried, heated, and cured to form the rod-shaped liquid crystal layer 42. Next, a liquid crystal composition that will become the discotic liquid crystal layer is applied to the rod-shaped liquid crystal layer 42, dried, heated, and cured to form the discotic liquid crystal layer 44. As described above, when a liquid crystal layer is formed on top of another liquid crystal layer by a coating method, the upper liquid crystal layer basically follows the orientation state of the liquid crystal compound at the surface (interface) of the lower liquid crystal layer. To manufacture an optical element having multiple layers of alternating rod-shaped and discotic liquid crystal layers, the formation of such rod-shaped liquid crystal layers 42 and discotic liquid crystal layers 44 can be repeated alternately.

[0116] In the above example, the rod-shaped liquid crystal layer is formed on a patterned alignment film on a support, but this is not limiting. A discotic liquid crystal layer may be formed on a patterned alignment film on a support, and then a rod-shaped liquid crystal layer may be formed. Furthermore, the support and patterned alignment film may be peeled off after the optical element is fabricated. Alternatively, the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44 may be fabricated separately, and then the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44 may be attached to each other using an adhesive layer to fabricate the optical element of the present invention. In this case, an alignment film or even a support may be provided between the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44.

[0117] As described above, in order to form the rod-shaped liquid crystal layer and the discotic liquid crystal layer in such a manner that the liquid crystal compound is twistedly aligned in the thickness direction, a chiral agent may be added to the liquid crystal composition for forming the rod-shaped liquid crystal layer and the discotic liquid crystal layer.

[0118] --Chiral Agents (Optically Active Compounds)--Chiral agents have the function of inducing a helical structure in a liquid crystal phase. Chiral agents can be selected according to the purpose, as the direction of helical twist and helical twisting power (HTP) they induce vary depending on the compound. There are no particular limitations on the chiral agent, and known compounds (e.g., those described in "Liquid Crystal Device Handbook," Chapter 3, Section 4-3, Chiral Agents for TN (Twisted Nematic) and STN (Super Twisted Nematic)," p. 199, edited by the 142nd Committee of the Japan Society for the Promotion of Science, 1989), isosorbide, and isomannide derivatives can be used. Chiral agents generally contain an asymmetric carbon atom, but axially asymmetric or planar asymmetric compounds without an asymmetric carbon atom can also be used as chiral agents. Examples of axially asymmetric or planar asymmetric compounds include binaphthyl, helicene, paracyclophane, and their derivatives. The chiral agent may have a polymerizable group. When both the chiral agent and the liquid crystal compound have a polymerizable group, a polymer having a repeating unit derived from the polymerizable liquid crystal compound and a repeating unit derived from the chiral agent can be formed by a polymerization reaction between the polymerizable chiral agent and the polymerizable liquid crystal compound. In this embodiment, the polymerizable group of the polymerizable chiral agent is preferably the same type of group as the polymerizable group of the polymerizable liquid crystal compound. Therefore, the polymerizable group of the chiral agent is also preferably an unsaturated polymerizable group, an epoxy group, or an aziridinyl group, more preferably an unsaturated polymerizable group, and even more preferably an ethylenically unsaturated polymerizable group. The chiral agent may also be a liquid crystal compound.

[0119] When the chiral agent has a photoisomerizable group, it is possible to form a desired twisted alignment corresponding to the emission wavelength by irradiating the chiral agent with actinic rays or the like through a photomask after coating and alignment. The photoisomerizable group is preferably an isomerization site of a compound exhibiting photochromic properties, an azo group, an azoxy group, or a cinnamoyl group. Specific compounds that can be used include those described in JP-A-2002-80478, JP-A-2002-80851, JP-A-2002-179668, JP-A-2002-179669, JP-A-2002-179670, JP-A-2002-179681, JP-A-2002-179682, JP-A-2002-338575, JP-A-2002-338668, JP-A-2003-313189, and JP-A-2003-313292.

[0120] The content of the chiral dopant in the liquid crystal composition is preferably 0.01 to 200 mol %, more preferably 1 to 30 mol %, based on the molar amount of the liquid crystal compound.

[0121] 1 shows a configuration in which the optical axis of the liquid crystal compound is parallel to the principal plane of the optically anisotropic layer, but the present invention is not limited to this. In the optical element, the optical axis of the liquid crystal compound may be inclined to the principal plane of the optical element (liquid crystal layer).

[0122] In addition, the optical axis 40A of the liquid crystal compound in the liquid crystal alignment pattern of the rod-shaped liquid crystal layer 42 shown in Fig. 5 and the discotic liquid crystal layer 44 shown in Fig. 7 rotates continuously only along the direction of the alignment axis D. However, the present invention is not limited to this, and various configurations can be used in the rod-shaped liquid crystal layer 42 and the discotic liquid crystal layer 44 as long as the optical axis 40A of the liquid crystal compound changes while rotating continuously along one direction.

[0123] An example is shown in Figure 11. Figure 11 is a plan view of a rod-shaped liquid crystal layer 46. Note that while Figure 11 only shows the rod-shaped liquid crystal layer 46, in the optical element of the present invention, as in the above-mentioned examples, a discotic liquid crystal layer having a similar liquid crystal orientation pattern is laminated on the rod-shaped liquid crystal layer 46. Also, as in the above-mentioned examples, the action and effect as a liquid crystal diffraction element are similar between the rod-shaped liquid crystal layer and the discotic liquid crystal layer. Also, while Figure 11 only shows the orientation state of the rod-shaped liquid crystal compounds on the surface (lower layer interface side) of the alignment film, as shown in Figure 4, the structure in which rod-shaped liquid crystal compounds 40c are stacked from the rod-shaped liquid crystal compound 40c on the surface of this alignment film is the same as in the above-mentioned examples.

[0124] The rod-shaped liquid crystal layer 46 shown in Fig. 11 has a liquid crystal orientation pattern in which the direction of the optical axis derived from the rod-shaped liquid crystal compounds 44c changes while continuously rotating in one direction, radially from the inside to the outside. That is, the liquid crystal orientation pattern of the rod-shaped liquid crystal layer 46 shown in Fig. 11 is a concentric pattern in which the direction of the optical axis derived from the rod-shaped liquid crystal compounds 44c changes while continuously rotating in one direction, concentrically from the inside to the outside. As described above, the direction of the optical axis of the rod-shaped liquid crystal compounds 44c coincides with the longitudinal direction of the rod-shaped liquid crystal compounds 44c.

[0125] Specifically, in the rod-shaped liquid crystal layer 46, the direction of the optical axis of the rod-shaped liquid crystal compound 44c changes while continuously rotating along multiple directions radially outward from the center of the rod-shaped liquid crystal layer 46, such as the direction indicated by arrow D1, the direction indicated by arrow D2, the direction indicated by arrow D3, the direction indicated by arrow D4, etc. In the rod-shaped liquid crystal layer 46, the rotation direction of the optical axis of the rod-shaped liquid crystal compound 44c is the same in all directions, i.e., in all directions. In the illustrated example, the rotation direction of the optical axis of the rod-shaped liquid crystal compound 44c is counterclockwise in all directions indicated by arrow D1, the direction indicated by arrow D2, the direction indicated by arrow D3, and the direction indicated by arrow D4. In other words, if arrow D1 and arrow D4 are regarded as a straight line, the rotation direction of the optical axis of the rod-shaped liquid crystal compound 44c is reversed at the center of the rod-shaped liquid crystal layer 46 on this straight line. As an example, if the line formed by the arrows D1 and D4 points to the right in the figure (the direction of the arrow D1), the optical axis of the rod-shaped liquid crystal compound 44c will initially rotate clockwise from the outside of the rod-shaped liquid crystal layer 46 toward the center, reverse the direction of rotation at the center of the rod-shaped liquid crystal layer 46, and then rotate counterclockwise from the center of the rod-shaped liquid crystal layer 46 toward the outside.

[0126] The rod-shaped liquid crystal layer 46 has a liquid crystal orientation pattern in which one period Λ gradually shortens from the inside to the outside of the concentric circles. As in the above example, the rod-shaped liquid crystal layer 46 also has one period Λ of the liquid crystal orientation pattern shorter than 0.5 μm.

[0127] In a rod-shaped liquid crystal layer 46 having a concentric liquid crystal orientation pattern as shown in Fig. 11, the direction of arrows D1, D2... pointing from the center outward corresponds to the alignment axis D in Fig. 5 etc., and the direction of each concentric circle corresponds to the direction of arrow Y in Fig. 5 etc. Therefore, in the rod-shaped liquid crystal layer 46 having a concentric liquid crystal orientation pattern, the longitudinal direction of the rod-shaped liquid crystal compounds 40c, i.e., the direction of the optical axis, is the same in each of the concentric circles. The rod-shaped liquid crystal layer 46 having a concentric liquid crystal orientation pattern as shown in Fig. 11 also diffracts incident light with respect to the direction of arrow D, similar to the rod-shaped liquid crystal layer 42 having a liquid crystal orientation pattern in which the optical axis changes while rotating in one direction as described above.

[0128] Therefore, a rod-shaped liquid crystal layer 46 having a concentric liquid crystal orientation pattern as shown in Figure 11 diffracts incident light toward the center of the concentric circle or diffracts incident light outward from the center of the concentric circle. Here, as described above, the period Λ of the liquid crystal orientation pattern of the rod-shaped liquid crystal layer 46 gradually shortens from the inside to the outside of the concentric circle. Therefore, the rod-shaped liquid crystal layer 46 focuses transmitted light toward the center of the concentric circle or diverges transmitted light from the center to the outside of the concentric circle. In other words, the rod-shaped liquid crystal layer 46 acts like a convex lens that focuses light or a concave lens that diverges light, depending on the rotation direction of the incident circularly polarized light.

[0129] As mentioned above, the same effect can be obtained with a discotic liquid crystal layer having the same liquid crystal orientation pattern. Therefore, as shown in Figure 11, the optical element of the present invention, which is composed of a rod-shaped liquid crystal layer and a discotic liquid crystal layer, each having a concentric circular liquid crystal orientation pattern, stacked together, functions as a liquid crystal lens that focuses or greatly diverges incident light with high diffraction efficiency and a short focal length.

[0130] 12 conceptually shows an example of an exposure device for forming such a concentric alignment pattern on an alignment film. The exposure device 80 includes a light source 84 equipped with a laser 82, a polarizing beam splitter 86 that splits laser light M from the laser 82 into S-polarized light MS and P-polarized light MP, a mirror 90A arranged in the optical path of the P-polarized light MP, a mirror 90B arranged in the optical path of the S-polarized light MS, a lens 92 arranged in the optical path of the S-polarized light MS, a polarizing beam splitter 94, and a λ / 4 plate 96.

[0131] The P-polarized light MP split by the polarizing beam splitter 86 is reflected by a mirror 90A and enters a polarizing beam splitter 94. On the other hand, the S-polarized light MS split by the polarizing beam splitter 86 is reflected by a mirror 90B, collected by a lens 92, and enters the polarizing beam splitter 94. The P-polarized light MP and the S-polarized light MS are combined by the polarizing beam splitter 94 and converted into right- and left-circularly polarized light according to the polarization direction by a λ / 4 plate 96, and then enter the alignment film 24 on the support 20. Here, due to interference between the right- and left-circularly polarized light, the polarization state of the light irradiated onto the alignment film 24 changes periodically in the form of interference fringes. Because the crossing angle between the left- and right-circularly polarized light changes from the inside to the outside of the concentric circles, an exposure pattern whose pitch changes from the inside to the outside is obtained. This results in a concentric alignment pattern in the alignment film 24 in which the alignment state changes periodically.

[0132] In this exposure device 80, the length Λ of one period of the liquid crystal orientation pattern, in which the optical axis of the rod-shaped liquid crystal compound 40c changes while continuously rotating 180°, can be controlled by changing the refractive power of the lens 92 (the F-number of the lens 92), the focal length of the lens 92, and the distance between the lens 92 and the alignment film 24. Furthermore, by adjusting the refractive power of the lens 92 (the F-number of the lens 92), the length Λ of one period of the liquid crystal orientation pattern can be changed in one direction in which the optical axis changes while continuously rotating. Specifically, the length Λ of one period of the liquid crystal orientation pattern can be changed in one direction in which the optical axis continuously rotates by adjusting the spread angle of the light expanded by the lens 92, which interferes with the parallel light. More specifically, when the refractive power of the lens 92 is weakened, the light approaches parallel light, so the length Λ of one period of the liquid crystal orientation pattern gradually shortens from the inside to the outside, and the F-number increases. Conversely, when the refractive power of the lens 92 is increased, the length Λ of one period of the liquid crystal alignment pattern suddenly decreases from the inside to the outside, and the F-number decreases.

[0133] The optical element of the present invention described above is a transmission-type optical element (transmission-type liquid crystal diffraction element) that diffracts and transmits incident light, but the present invention is not limited to this. In other words, the optical element of the present invention may be a reflection-type liquid crystal diffraction element that diffracts and reflects incident light.

[0134] An example is conceptually shown in Figure 13. The optical element 100 of the present invention shown in Figure 13 has a rod-shaped liquid crystal layer 102 and a discotic liquid crystal layer 104. Both the rod-shaped liquid crystal layer 102 and the discotic liquid crystal layer 104 are cholesteric liquid crystal layers formed by fixing a cholesteric liquid crystal phase. Specifically, the rod-shaped liquid crystal layer 102 is formed by cholesterically aligning rod-shaped liquid crystal compounds 40c in a helical twisted orientation of 360° or more in the thickness direction. That is, the rod-shaped liquid crystal layer 102 is a cholesteric liquid crystal layer having a helical structure in which rod-shaped liquid crystal compounds 40c are stacked helically, with one helical pitch (helical pitch P) being one helical rotation (360° rotation) of the rod-shaped liquid crystal compounds 40c stacked helically, and having a structure in which the rod-shaped liquid crystal compounds 40c are stacked helically at multiple pitches. On the other hand, the discotic liquid crystal layer 104 is a cholesterically oriented layer in which the discotic liquid crystal compounds 40d are helically twisted and aligned by 360° or more in the thickness direction. That is, the discotic liquid crystal layer 104 is a cholesteric liquid crystal layer having a helical structure in which the discotic liquid crystal compounds 40d are stacked in a helical shape, and in which the helical pitch is defined as one helical rotation of the rod-shaped liquid crystal compounds 40c, and the discotic liquid crystal compounds 40d are stacked in a helical shape at multiple pitches.

[0135] As is well known, a cholesteric liquid crystal layer selectively reflects specific circularly polarized light in a specific wavelength range and transmits the rest. In a cholesteric liquid crystal layer, the wavelength range exhibiting selective reflectivity, i.e., the central wavelength of selective reflection (selective reflection central wavelength λ), depends on the length of one helical pitch in the cholesteric liquid crystal phase and follows the relationship λ = n × P with the average refractive index n of the cholesteric liquid crystal phase. Therefore, by adjusting this helical pitch, the selective reflection central wavelength, i.e., the selective reflection wavelength range, can be adjusted. The longer the helical pitch P, the longer the selective reflection central wavelength of the cholesteric liquid crystal phase.

[0136] The helical pitch of a cholesteric liquid crystal phase depends on the type and concentration of the chiral dopant used together with the liquid crystal compound when forming the cholesteric liquid crystal layer. Therefore, the desired helical pitch can be obtained by adjusting these factors. Details on pitch adjustment are provided in Fujifilm Research Report No. 50 (2005), pp. 60-63. Methods for measuring the helical sense and pitch can be found in "Introduction to Liquid Crystal Chemistry Experiments," edited by the Japanese Liquid Crystal Society, published by Sigma Publishing in 2007, p. 46, and "Liquid Crystal Handbook," published by the Liquid Crystal Handbook Editorial Committee, Maruzen, p. 196.

[0137] Furthermore, the half-width Δλ (nm) of the wavelength range exhibiting selective reflection (circularly polarized light reflection wavelength range) depends on the Δn of the cholesteric liquid crystal phase and the helical pitch P, and follows the relationship Δλ = Δn × P. Therefore, the width of the selective reflection wavelength range can be controlled by adjusting Δn. Δn can be adjusted by the type and mixing ratio of the liquid crystal compounds forming the cholesteric liquid crystal layer, as well as the temperature during alignment fixation.

[0138] As is well known, cholesteric liquid crystal phases exhibit selective reflection for either left- or right-handed circularly polarized light in a specific wavelength range. Whether the reflected light is right-handed or left-handed circularly polarized light depends on the twist direction (sense) of the helix of the cholesteric liquid crystal phase. When the twist direction of the helix of the cholesteric liquid crystal phase is right-handed, right-handed circularly polarized light is reflected, and when the twist direction of the helix is ​​left-handed, left-handed circularly polarized light is reflected. The direction of rotation of the cholesteric liquid crystal phase can be adjusted by the type of liquid crystal compound forming the cholesteric liquid crystal layer and / or the type of chiral agent added.

[0139] Here, in the optical element of the present invention, the rod-shaped liquid crystal layer 102 has a liquid crystal orientation pattern in which the optical axis changes while continuously rotating along one direction (alignment axis D), as shown in Fig. 5, similar to the rod-shaped liquid crystal layer 42 described above. Also, similar to the above example, in the rod-shaped liquid crystal layer 102, one period Λ in the liquid crystal orientation pattern is 0.5 µm or less. On the other hand, the discotic liquid crystal layer 104 has a liquid crystal orientation pattern in which the optical axis changes while continuously rotating along one direction (alignment axis D), as shown in Fig. 7, similar to the above example. Also, similar to the above example, in the discotic liquid crystal layer 104, one period Λ in the liquid crystal orientation pattern is 0.5 µm or less.

[0140] A cholesteric liquid crystal layer having such a liquid crystal orientation pattern reflects incident light at an angle toward the alignment axis D relative to specular reflection. This effect will be explained below using the rod-shaped liquid crystal layer 102 shown in Figure 14 as an example. Note that, like the transmissive liquid crystal layer described above, the discotic liquid crystal layer 104 also has this effect.

[0141] As an example, the rod-shaped liquid crystal layer 102 is configured to polarize red light right-handed circularly polarized R R Therefore, when light is incident on the rod-shaped liquid crystal layer 102, the rod-shaped liquid crystal layer 102 selectively reflects right-handed circularly polarized red light R R It reflects only light and transmits all other light.

[0142] In the rod-shaped liquid crystal layer 102, the optical axes 40A of the rod-shaped liquid crystal compounds 40c change while rotating along the direction of the alignment axis D (one direction). The liquid crystal alignment pattern formed in the rod-shaped liquid crystal layer 102 is a periodic pattern along the direction of the alignment axis D. Therefore, the right-handed circularly polarized light R of red light incident on the rod-shaped liquid crystal layer 102 is R As conceptually shown in Figure 14, the light is not specularly reflected, but is diffracted in a direction according to the period of the liquid crystal orientation pattern, and is reflected by being diffracted in a direction tilted toward the alignment axis D with respect to the XY plane (the main surface of the cholesteric liquid crystal layer).

[0143] In the rod-shaped liquid crystal layer 102, the direction of the alignment axis D, which is one direction along which the optical axis 40A changes while rotating, can be appropriately set to adjust the diffraction direction of light, that is, the reflection direction.

[0144] Furthermore, when circularly polarized light of the same wavelength and the same rotation direction is reflected, the reflection direction of the circularly polarized light can be reversed by reversing the rotation direction of the optical axis 40A of the rod-shaped liquid crystal compound 40c facing the alignment axis D. For example, in Fig. 14, the rotation direction of the optical axis 40A facing the alignment axis D is clockwise, and some circularly polarized light is reflected with an inclination toward the alignment axis D. However, by changing this to counterclockwise, some circularly polarized light is reflected with an inclination in the opposite direction to the alignment axis D.

[0145] Furthermore, in liquid crystal layers having the same liquid crystal orientation pattern, the reflection direction is reversed depending on the helical gyration direction of the rod-shaped liquid crystal compounds 40c, i.e., the gyration direction of the reflected circularly polarized light. For example, if the helical gyration direction is right-handed, right-handed circularly polarized light is selectively reflected, and a liquid crystal layer having a liquid crystal orientation pattern in which the optical axis 40A changes while rotating clockwise along the alignment axis D direction reflects right-handed circularly polarized light with a tilt toward the alignment axis D direction. Also, for example, if the helical gyration direction is left-handed, left-handed circularly polarized light is selectively reflected, and a liquid crystal layer having a liquid crystal orientation pattern in which the optical axis 40A changes while rotating clockwise along the alignment axis D direction reflects left-handed circularly polarized light with a tilt toward the opposite direction to the alignment axis D direction.

[0146] In a cholesteric liquid crystal layer having a liquid crystal orientation pattern in which the optical axis changes while continuously rotating along at least one direction, the shorter the period Λ, the larger the diffraction angle of reflected light. For example, when light is incident on the cholesteric liquid crystal layer from the normal direction, the shorter the period Λ, the larger the angle between the reflected light and the normal direction, which is the specular reflection. As described above, in the optical element of the present invention, both the rod-shaped liquid crystal layer 102 and the discotic liquid crystal layer 104 have a period Λ shorter than 0.5 μm. Furthermore, in the optical element of the present invention, similar to a transmissive optical element, incident light can be reflected with high diffraction efficiency by stacking a cholesterically aligned rod-shaped liquid crystal layer and a cholesterically aligned discotic liquid crystal layer having the same liquid crystal orientation pattern. Therefore, the reflective optical element of the present invention can reflect incident light with high diffraction efficiency and a large diffraction angle.

[0147] The rod-shaped liquid crystal layer 102 and the discotic liquid crystal layer 104 shown in Figures 13 and 14 each have a liquid crystal orientation pattern in which the optical axis derived from the liquid crystal compound changes while continuously rotating along one direction, as shown in Figures 4 to 7 , but the reflective optical element of the present invention is not limited to this. That is, in the reflective optical element of the present invention, the rod-shaped liquid crystal layer and the discotic liquid crystal layer may have a concentric liquid crystal orientation pattern as shown in Figure 11. Here, in a cholesteric liquid crystal layer having a concentric liquid crystal orientation pattern as shown in Figure 11, the direction of arrows D1, D2... pointing from the center outward corresponds to the alignment axis D in Figure 5 etc., and the direction of each concentric circle corresponds to the direction of arrow Y in Figure 5 etc. Therefore, a reflective optical element of the present invention using a rod-shaped liquid crystal layer and a discotic liquid crystal layer, which are cholesteric liquid crystal layers having a concentric liquid crystal orientation pattern, acts like a concave mirror that focuses light or a convex mirror that diverges light, depending on the rotation direction of incident circularly polarized light.

[0148] The reflective rod-shaped liquid crystal layer 102 and discotic liquid crystal layer 104, which are cholesteric liquid crystal layers in which the liquid crystal compound is cholesterically aligned, can basically be formed in the same manner as the above-mentioned transmissive liquid crystal layer in which the liquid crystal compound is twistedly aligned by 360° or less in the thickness direction. However, because the reflective rod-shaped liquid crystal layer 102 and discotic liquid crystal layer 104 are cholesterically aligned liquid crystal compounds, the amount of chiral dopant added to the liquid crystal composition forming the liquid crystal layer must be increased compared to that of the transmissive liquid crystal layer.

[0149] The reflective optical element of the present invention is not limited to a configuration having one rod-shaped liquid crystal layer 102 and one discotic liquid crystal layer 104. For example, the optical element of the present invention may have six liquid crystal layers, including a rod-shaped liquid crystal layer and a discotic liquid crystal layer that selectively reflect red light, a rod-shaped liquid crystal layer and a discotic liquid crystal layer that selectively reflect green light, and a rod-shaped liquid crystal layer and a discotic liquid crystal layer that selectively reflect blue light. Alternatively, the optical element of the present invention may have four liquid crystal layers, including a rod-shaped liquid crystal layer and a discotic liquid crystal layer that selectively reflect red light and a rod-shaped liquid crystal layer and a discotic liquid crystal layer that selectively reflect blue light. Furthermore, the optical element of the present invention may have a rod-shaped liquid crystal layer and a discotic liquid crystal layer that selectively reflect right-handed circularly polarized light and a rod-shaped liquid crystal layer and a discotic liquid crystal layer that selectively reflect left-handed circularly polarized light, which selectively reflect light of the same color. In the reflective optical element of the present invention, the combination of one rod-shaped liquid crystal layer and one discotic liquid crystal layer preferably has the same liquid crystal orientation pattern as in the above-mentioned transmissive optical element, and selectively reflects circularly polarized light of the same color and with the same rotation direction. The combination of one rod-shaped liquid crystal layer and one discotic liquid crystal layer is not limited to this, and the liquid crystal orientation pattern and the rotation direction of the circularly polarized light to be selectively reflected can be appropriately set depending on the purpose.

[0150] In the reflective optical element of the present invention, there is no limitation on the thickness of the cholesteric liquid crystal layers, that is, the rod-shaped liquid crystal layer 102 and the discotic liquid crystal layer 104. That is, the thickness of the rod-shaped liquid crystal layer 102 and the discotic liquid crystal layer 104 may be appropriately set to a thickness that can achieve a target reflectance depending on the wavelength range to be selectively reflected, the liquid crystal compound and chiral agent to be used, etc.

[0151] The optical element of the present invention can be used in various optical devices and optical systems, such as beam steering devices, structured light, hyperspectral sensing, diffractive elements for AR glasses, diffractive elements for VR goggles, and diffractive lenses, etc. In particular, the optical element of the present invention is suitably used in HMDs (head-mounted displays) such as AR glasses and VR goggles.

[0152] FIG. 15 conceptually illustrates an example of AR glasses using a reflective optical element of the present invention. The AR glasses 110 shown in FIG. 15 include a light guide plate 112, an incident portion 114, and an exit portion 116. The incident portion 114 includes an optical element 100IR of the present invention that selectively reflects red light R (red image), an optical element 100IG of the present invention that selectively reflects green light G (green image), and an optical element 100IB of the present invention that selectively reflects blue light B (blue image). The exit portion 116 includes an optical element 100OR of the present invention that selectively reflects red light R, an optical element 100OG of the present invention that selectively reflects green light G, and an optical element 100OB of the present invention that selectively reflects blue light B. The AR glasses 110 using the optical elements of the present invention are not limited thereto, and may include optical elements corresponding to only one color, or optical elements corresponding to two colors.

[0153] Optical elements 100IR, 100IG, and 100IB in incident section 114, and optical elements 100OR, 100OG, and 100OB in output section 116 are basically the same as reflective optical element 100 of the present invention shown in Figure 13, except that they selectively reflect different wavelengths of light. That is, the rod-shaped liquid crystal layer and discotic liquid crystal layer constituting these optical elements have a liquid crystal orientation pattern in which the optical axis of the liquid crystal compound changes while continuously rotating in one direction, as shown in Figures 4 to 7. Therefore, each optical element diffracts and reflects incident light by tilting it in a predetermined direction.

[0154] 1 are basically the same as known AR glasses, i.e., a display device for augmented reality images, except that the optical elements of the present invention are used as optical elements for inputting and outputting light to and from the light guide plate 112 at the entrance section 114 and the exit section 116. Therefore, the AR glasses 110 may have various optical elements (optical members) that known AR glasses have, in addition to the members shown in the figure.

[0155] In the AR glasses 110, of the images displayed (emitted) by an image display element (display) (not shown), red light R is diffracted and reflected by optical element 100IR, green light G is diffracted and reflected by optical element 100IG, and blue light B is reflected by optical element 100IB, all of which are incident on the light guide plate 112 at an angle of total reflection. Each image propagates within the light guide plate 112 by total reflection, and red light R is diffracted and reflected by optical element 100OR, green light G is diffracted and reflected by optical element 100OG, and blue light B is reflected by optical element 100OB, all of which are emitted from the light guide plate 112. The red light R, green light G, and blue light B emitted from the light guide plate 112, i.e., the augmented reality image, are observed together with the background by a user U of the AR glasses.

[0156] Here, in order to reduce the thickness and size of AR glasses, it is preferable to make the light guide plate 112 as thin as possible. To allow light to enter the thin light guide plate 112 at an angle that causes total reflection and then exit the light guide plate 112, it is necessary to diffract the light at a large diffraction angle at the entrance portion 114 and the exit portion 116. In contrast, as described above, in the optical element of the present invention, the period Λ of the liquid crystal orientation pattern of the rod-shaped liquid crystal layer and the discotic liquid crystal layer is 0.5 μm or less, allowing incident light to be reflected at a large diffraction angle. Furthermore, as described above, the optical element of the present invention is a laminate of rod-shaped and discotic liquid crystal layers, and has high diffraction efficiency. Therefore, by using the optical element of the present invention in AR glasses, it is possible to reduce the thickness and size of the AR glasses, and to efficiently utilize the image (light) displayed by the image display element to display a high-brightness augmented reality image.

[0157] FIG. 16 conceptually illustrates an example of VR goggles using a reflective optical element of the present invention. The VR goggles 120 shown in FIG. 16 include an image display element 124, a circular polarizer 126, an optical element 128 of the present invention, and a half mirror 130. The VR goggles shown in FIG. 16 are essentially similar to known VR goggles, i.e., virtual reality image display devices, that have a folded optical system, except that the reflective optical element of the present invention is used in the folded optical system. Therefore, the VR goggles 120 may include various optical elements found in known VR goggles, such as an absorptive circular polarizer for removing unwanted circularly polarized light that initially enters and passes through the half mirror 130, as needed.

[0158] The optical element 128 is a reflective optical element of the present invention, and, like the optical element 100 of the present invention shown in FIG. 13 , is formed by laminating a rod-shaped liquid crystal layer in which rod-shaped liquid crystal compound 40c is cholesterically aligned and a discotic liquid crystal layer in which discotic liquid crystal compound 40d is cholesterically aligned. In this optical element 128, each liquid crystal layer has the concentric liquid crystal alignment pattern shown in FIG. 11 . Therefore, the optical element 128 focuses or diverges circularly polarized light in one direction and reflects it, while transmitting circularly polarized light in the other direction. In the illustrated example, the optical element 128 is formed by laminating a rod-shaped liquid crystal layer and a discotic liquid crystal layer, which are cholesteric liquid crystal layers that diffract and reflect left-handed circularly polarized light so as to selectively focus it, and acts like a concave mirror for left-handed circularly polarized light.

[0159] 16 shows only one optical element 128. However, the present invention is not limited to this, and similar to the above-described AR glasses, the VR goggles 120 may have a plurality of optical elements of the present invention, such as three optical elements 128, including an optical element that selectively reflects red light, an optical element that selectively reflects green light, and an optical element that selectively reflects blue light, as needed.

[0160] In the VR goggles 120, the image displayed by the image display element 124 is converted into right-handed circularly polarized light by the circular polarizer 126, which is composed of, for example, a linear polarizer and a λ / 4 retarder, and then enters the optical element 128. As described above, the optical element 128 is composed of a rod-shaped liquid crystal layer and a discotic liquid crystal layer, which are cholesteric liquid crystal layers that selectively reflect left-handed circularly polarized light, and therefore the right-handed circularly polarized light passes through the optical element 128. The right-handed circularly polarized light that passes through the optical element 128 then enters the half mirror 130, where half of it is reflected. This reflection converts the right-handed circularly polarized light into left-handed circularly polarized light. The left-handed circularly polarized light reflected by the half mirror 130 again enters the optical element 128. As described above, the optical element 128 diffracts and reflects the left-handed circularly polarized light so as to selectively focus it. Therefore, the left-handed circularly polarized light that enters the optical element 128 is reflected so as to be focused. Half of the left-handed circularly polarized light reflected by the optical element 128 passes through the half mirror 130 and is observed by a user U of the VR goggles as a VR image (virtual reality image).

[0161] Here, in order to reduce the thickness and size of the VR goggles 120, it is necessary to diffract reflected light significantly using the optical element 128 to focus the image so as to shorten the focal length of the optical system. In contrast, as described above, in the optical element 128 of the present invention, the period Λ of the liquid crystal orientation pattern of the rod-shaped liquid crystal layer and the discotic liquid crystal layer is 0.5 μm or less, allowing incident light to be reflected at a large diffraction angle. Furthermore, as described above, the optical element of the present invention is a laminate of rod-shaped and discotic liquid crystal layers, resulting in high diffraction efficiency. Therefore, by using the optical element of the present invention in VR goggles, the VR goggles can be reduced in thickness and size, and the image (light) displayed by the image display element 124 can be efficiently utilized to display a high-brightness AR image (augmented reality image). It is also possible to use a half mirror in the VR goggles 120 instead of the optical element 128 of the present invention. However, using a half mirror that reflects light at a large angle requires a half mirror with a large curvature, which increases the size of the VR goggles. In contrast, the optical element 128 of the present invention is sheet-shaped and does not require a large installation space, which also contributes to making the VR goggles 120 thinner and more compact.

[0162] In the above-described examples, the reflective optical element of the present invention is used in a HUD, but the transmissive optical element of the present invention can also be suitably used in a HUD. Figure 17 conceptually shows an example of VR goggles that use the transmissive optical element of the present invention. Note that the VR goggles 140 shown in Figure 17 use multiple components that are the same as those in the VR goggles 120 shown in Figure 16 described above, and therefore the same components are designated by the same reference numerals.

[0163] The VR goggles 140 shown in Figure 17 include an image display element 124, a circular polarizer 126, an optical element 142 of the present invention, a half mirror 130, a lens 144, and a reflective circular polarizer 146. The VR goggles 140 shown in Figure 17 are essentially the same as known VR goggles, i.e., virtual reality image display devices, that have a folded optical system, except that the reflective optical element of the present invention is used in the folded optical system. Therefore, the VR goggles 140 may include various optical elements that known VR goggles have, such as a circular polarizer provided downstream of the reflective circular polarizer 146 to block right-handed circularly polarized light that is unnecessarily transmitted through the reflective circular polarizer 146, as needed.

[0164] The optical element 142 is a transmissive optical element of the present invention, and, like the optical element 10 of the present invention shown in FIG. 1 , is formed by laminating a rod-shaped liquid crystal layer made of rod-shaped liquid crystal compound 40c and a discotic liquid crystal layer made of discotic liquid crystal compound 40d. In this optical element 142, each liquid crystal layer has a concentric liquid crystal orientation pattern as shown in FIG. 11 . Therefore, the optical element 142 collects and transmits circularly polarized light in one rotation direction, and diverges and transmits circularly polarized light in the other rotation direction. In the illustrated example, the optical element 142 is formed by laminating a rod-shaped liquid crystal layer and a discotic liquid crystal layer that diverge right-handed circularly polarized light, and acts like a concave lens for right-handed circularly polarized light.

[0165] In the VR goggles 140, the image displayed by the image display element 124 is converted into right-handed circularly polarized light by the circular polarizer 126, as described above, and then enters the optical element 142. As described above, the optical element 142 is composed of a rod-shaped liquid crystal layer and a discotic liquid crystal layer that diverge right-handed circularly polarized light. Therefore, the right-handed circularly polarized light that enters the optical element 142 is diverged and emitted, as indicated by the dashed line in the figure. The VR goggles 140 shown in the figure have the optical element 142 that diverges light between the half mirror 130 and the image display element 124, thereby imparting directionality to the light (image) emitted by the image display element 124 depending on the position within the plane. As a result, the brightness of the edge portions of the displayed virtual reality image can be improved, and the brightness distribution of the virtual reality image can be made uniform.

[0166] The right-handed circularly polarized light that has passed through the optical element 142 then enters the half mirror 130, where half of it is transmitted, and then passes through the lens 144 and enters the reflective circular polarizer 146. The reflective circular polarizer 146 is a reflective circular polarizer that reflects right-handed circularly polarized light and transmits left-handed circularly polarized light. Therefore, the right-handed circularly polarized light that has entered the reflective circular polarizer 146 is reflected by the reflective circular polarizer 146. The right-handed circularly polarized light that has been reflected by the reflective circular polarizer 146 passes through the lens 144 again and enters the half mirror 130, where half of it is reflected. The right-handed circularly polarized light is converted into left-handed circularly polarized light by being reflected by the half mirror 130. The left-handed circularly polarized light that has been reflected by the half mirror 130 passes through the lens 144 again, where it is collected, and enters the reflective circular polarizer 146. As described above, the reflective circular polarizer 146 reflects right-handed circularly polarized light and transmits left-handed circularly polarized light, so the left-handed circularly polarized light passes through the reflective circular polarizer 146 and is observed by the user U of the VR goggles 140 as a virtual reality image.

[0167] Here, in order to reduce the thickness and size of the VR goggles 140, it is necessary to diffract reflected light significantly using the optical element 142 to diverge the image. In contrast, as described above, in the optical element 142 of the present invention, the period Λ of the liquid crystal orientation pattern of the rod-shaped liquid crystal layer and the discotic liquid crystal layer is 0.5 μm or less, allowing incident light to be diverged and transmitted at a large diffraction angle. Furthermore, as described above, the optical element of the present invention is a laminate of rod-shaped and discotic liquid crystal layers, and has high diffraction efficiency. Therefore, by using the optical element of the present invention in VR goggles, the VR goggles can be reduced in thickness and size, and the image (light) displayed by the image display element 124 can be efficiently utilized to display a high-brightness AR image (augmented reality image). It is also possible to use a concave lens in VR goggles instead of the optical element 142 of the present invention. However, using a concave lens that diverges light at a large angle requires a thick concave lens with a large curvature, which increases the size of the VR goggles. In contrast, the optical element 142 of the present invention is sheet-shaped and does not require a large installation space, which also allows the VR goggles 140 to be made thinner and more compact.

[0168] The optical element of the present invention has been described in detail above, but the present invention is not limited to the above examples, and various improvements and modifications may be made within the scope of the present invention.

[0169] The features of the present invention will be explained in more detail below with reference to examples. The materials, reagents, amounts used, amounts of substances, ratios, treatment details, and treatment procedures shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0170] Comparative Example 1 An alignment film was formed on a support, and an optically anisotropic layer A-1 (rod-shaped liquid crystal layer) consisting of a cured layer of liquid crystal composition D1 containing a rod-shaped liquid crystal compound was formed on the alignment film to produce an optical element of Comparative Example 1. The optically anisotropic layer A-1 had a liquid crystal alignment pattern in which the rod-shaped liquid crystal compound was horizontally rotated and aligned.

[0171] [Preparation of Optical Element of Comparative Example 1] A glass substrate was used as a support.

[0172] (Formation of Orientation Film P-1) The following coating liquid for forming the orientation film P-1 was continuously applied onto a support (glass substrate) using a wire bar #2. The support on which the coating film of the coating liquid for forming the orientation film P-1 had been formed was dried with hot air at 60°C for 60 seconds to form the orientation film P-1.

[0173] <Coating liquid for forming alignment film P-1> -------------------------------------------------- Photo alignment material below: 1.00 parts by mass Water 16.00 parts by mass Butoxyethanol 42.00 parts by mass Propylene glycol monomethyl ether 42.00 parts by mass --------------------------------------------------

[0174] -Material for photo alignment-

[0175] (Exposure of Alignment Film P-1) The alignment film was exposed using the exposure device 60 shown in Fig. 8. In the exposure device 60, a laser 52 was used that emitted laser light with a wavelength of 355 nm. The exposure amount by the interference light was 1000 mJ / cm 2 The crossing angle α of the two light beams MA and MB in the exposure device 60 was adjusted so that one period Λ of the orientation pattern formed by the interference of the two laser beams, i.e., the period in which the optical axis of the liquid crystal compound rotates by 180°, was 0.4 μm.

[0176] (Formation of Optically Anisotropic Layer A-1) First, the following liquid crystal composition D1 was prepared. <Liquid Crystal Composition D1> ----------------------------------- Rod-shaped liquid crystal compound L-1 100.00 parts by mass Polymerization initiator (Irgacure (registered trademark) 907, manufactured by BASF) 3.00 parts by mass Photosensitizer (KAYACURE DETX-S, manufactured by Nippon Kayaku) 1.00 part by mass Leveling agent T-1 0.50 parts by mass Methyl ethyl ketone 2500.00 parts by mass

[0177] -Rod-shaped liquid crystal compound L-1- -Leveling agent T-1-

[0178] The complex refractive index Δn of the cured layer of liquid crystal composition D1 was 0.15. The complex refractive index Δn was determined by measuring the retardation value and film thickness of the liquid crystal fixed layer (cured layer) obtained by applying liquid crystal composition D1 to a separately prepared support with an alignment film for retardation measurement, aligning the optical axis of the rod-shaped liquid crystal compound so that it was parallel to the substrate, and then irradiating with ultraviolet light to fix the layer. Δn can be calculated by dividing the retardation value by the film thickness. The retardation value was measured at a wavelength of 550 nm using an Axometrix Axoscan, and the film thickness was measured using a scanning electron microscope (SEM).

[0179] <Coating Formation of Optically Anisotropic Layer A-1> The optically anisotropic layer A-1 was formed by coating liquid crystal composition D1 in multiple layers on the alignment film P-1. Multilayer coating refers to first coating a first layer of liquid crystal composition D1 on the alignment film, heating, cooling, and then UV curing to form a liquid crystal fixed layer, and then coating second and subsequent layers on top of the liquid crystal fixed layer, heating, cooling, and UV curing in the same manner, and repeating this process. By forming the layer by multilayer coating, the alignment direction of the alignment film is reflected from the bottom surface to the top surface of the liquid crystal layer, even when the total thickness of the liquid crystal layer is large.

[0180] First, the first layer was formed by applying the following liquid crystal composition D1 to an alignment film P-1, heating the resulting coating to 110°C on a hot plate, then cooling it to 60°C, and then irradiating it with ultraviolet light of 365 nm wavelength at 300 mJ / cm using a high-pressure mercury lamp in a nitrogen atmosphere. 2 The coating film was irradiated with light at an irradiation dose of 1000 .mu.m to fix the alignment of the liquid crystal compound. The thickness of the fixed liquid crystal layer (one liquid crystal fixing layer) at this time was 0.15 .mu.m.

[0181] The second and subsequent liquid crystal fixed layers were formed by coating liquid crystal composition D1 on the previously formed liquid crystal fixed layer, followed by heating and cooling under the same conditions as above, followed by UV curing. In this manner, coating was repeated until the desired total thickness was reached, yielding optically anisotropic layer A-1. It was confirmed using a polarizing microscope that the birefringence of the liquid crystal finally reached 275 nm (= λ / 2) and that a periodic alignment surface was formed.

[0182] Comparative Example 2: An optical element was prepared that had an optically anisotropic layer A-2 (discotic liquid crystal layer) consisting of a cured layer of liquid crystal composition E1 containing a discotic liquid crystal compound instead of a rod-shaped liquid crystal compound, in contrast to Comparative Example 1. That is, the optical element of Comparative Example 2 had a liquid crystal alignment pattern in which the discotic liquid crystal compound was horizontally rotated and aligned.

[0183] (Formation of Optically Anisotropic Layer A-2) A liquid crystal composition E1 having the following composition was prepared. <Liquid Crystal Composition E1> --------------------------------------------------- Discotic liquid crystal compound L-2 80.00 parts by mass Discotic liquid crystal compound L-3 20.00 parts by mass Polymerization initiator (Irgacure (registered trademark) 907, manufactured by BASF) 5.00 parts by mass Megafac F444 (manufactured by DIC Corporation) 0.50 parts by mass Methyl ethyl ketone 2500.00 parts by mass

[0184] --Discosmic liquid crystal compound L-2-- --Discosmic liquid crystal compound L-3--

[0185] The complex refractive index Δn of the cured layer of the liquid crystal composition E1 was 0.15. The complex refractive index Δn was determined in the same manner as in the case of the liquid crystal composition D1.

[0186] <Coating Formation of Optically Anisotropic Layer A-2> First, the first layer was formed by heating the coating film obtained by coating the liquid crystal composition E1 on the alignment film P-1 to 110°C on a hot plate, and then cooling it to 60°C. After that, ultraviolet light having a wavelength of 365 nm was irradiated at 300 mJ / cm using a high-pressure mercury lamp in a nitrogen atmosphere. 2 The coating film was irradiated with light at an irradiation dose of 1000 .mu.m to fix the alignment of the liquid crystal compound. The thickness of the fixed liquid crystal layer (one liquid crystal fixing layer) at this time was 0.15 .mu.m.

[0187] The second and subsequent liquid crystal fixation layers were formed by applying liquid crystal composition E1 over the previously formed liquid crystal fixation layer, heating and cooling under the same conditions as above, and then curing with ultraviolet light. In this way, the application was repeated until the desired total thickness was reached, yielding an optically anisotropic layer A-2. It was confirmed using a polarizing microscope that the birefringence of the liquid crystal finally reached 275 nm (= λ / 2) and that a periodic alignment surface had been formed.

[0188] Example 1 First, an alignment film was formed on a support, and then an optically anisotropic layer A-1 (rod-shaped liquid crystal layer) consisting of a cured layer of liquid crystal composition D1 containing a rod-shaped liquid crystal compound was formed on the alignment film. Thereafter, an optically anisotropic layer A-2 (disk-shaped liquid crystal layer) consisting of a cured layer of liquid crystal composition E1 containing a discotic liquid crystal compound was formed, thereby producing the optical element of Example 1. Hereinafter, the optically anisotropic layer A-1 (rod-shaped liquid crystal layer) in this example will be referred to as the "first optically anisotropic layer A-1," and the optically anisotropic layer A-2 (disk-shaped liquid crystal layer) will be referred to as the "second optically anisotropic layer A-2." That is, a two-layer structure was formed, with the first layer being the first optically anisotropic layer A-1 consisting of a cured layer of liquid crystal composition D1 containing a rod-shaped liquid crystal compound, and the second layer being the second optically anisotropic layer A-2 consisting of a cured layer of liquid crystal composition E1 containing a discotic liquid crystal compound.

[0189] The optical element of Example 1 was fabricated in the same manner as in Comparative Example 1, by forming an alignment film on a support, forming a first optically anisotropic layer A-1 on the alignment film, and then forming a second optically anisotropic layer A-2 on the first optically anisotropic layer A-1 in the same manner as the optically anisotropic layer A-2 formed on the alignment film in Comparative Example 2. The coating amounts of each of the optically anisotropic layers A-1 and A-2 were adjusted so that the in-plane retardation Δnd (= Δn1d1 + Δn2d2) of the entire laminate structure was 275 nm, and the optical element was otherwise fabricated in the same manner as in Comparative Examples 1 and 2. Here, Δn1 is the birefringence of the first optically anisotropic layer, d1 is the thickness of the first optically anisotropic layer, Δn2 is the birefringence of the second optically anisotropic layer, and d2 is the thickness of the second optically anisotropic layer. Both Δn1 and Δn2 were 0.15. The complex refractive index Δn was determined in the same manner as in the case of the liquid crystal composition D1.

[0190] Cross-sectional SEM of the optical element of Example 1 confirmed that two liquid crystal alignment patterns having horizontal rotation alignment were overlapped. Furthermore, measurement using an Axometrix Axoscan confirmed that the first optically anisotropic layer (the first layer) was composed of aligned rod-shaped liquid crystal compounds, and the second optically anisotropic layer (the second layer) was composed of aligned discotic liquid crystal compounds. The optical element thus fabricated had a two-layer structure, and the first optically anisotropic layer had an in-plane retardation Δn1d1 = 138 nm and a twist angle of 0 degrees, while the second optically anisotropic layer had an in-plane retardation Δn2d2 = 137 nm and a twist angle of 0 degrees.

[0191] "Example 2"

[0192] First, the following liquid crystal composition D2 was prepared. <Liquid Crystal Composition D2> ----------------------------------- Rod-shaped liquid crystal compound L-1 100.00 parts by mass Polymerization initiator (Irgacure (registered trademark) 907, manufactured by BASF) 3.00 parts by mass Photosensitizer (KAYACURE DETX-S, manufactured by Nippon Kayaku) 1.00 part by mass Leveling agent T-1 0.50 parts by mass Chiral agent Ch-2 0.12 parts by mass Methyl ethyl ketone 2500.00 parts by mass

[0193] -Chiral Agent Ch-2-

[0194] A liquid crystal composition E2 having the following composition was prepared. <Liquid Crystal Composition E2> ------------------------------------------------------------------ Discotic liquid crystal compound L-2 80.00 parts by mass Discotic liquid crystal compound L-3 20.00 parts by mass Polymerization initiator (Irgacure (registered trademark) 907, manufactured by BASF) 5.00 parts by mass Megafac F444 (manufactured by DIC Corporation) 0.50 parts by mass Chiral agent Ch-2 0.14 parts by mass Methyl ethyl ketone 2500.00 parts by mass

[0195] First, an alignment film was formed on a support, and then an optically anisotropic layer A2-1 (rod-shaped liquid crystal layer) consisting of a cured layer of liquid crystal composition D2 containing a rod-shaped liquid crystal compound was formed on the alignment film. Then, an optically anisotropic layer A2-2 (discotic liquid crystal layer) consisting of a cured layer of liquid crystal composition E2 containing a discotic liquid crystal compound was formed to produce the optical element of Example 2. Hereinafter, the optically anisotropic layer A2-1 (rod-shaped liquid crystal layer) in this example will be referred to as the "first optically anisotropic layer A2-1," and the optically anisotropic layer A2-2 (discotic liquid crystal layer) will be referred to as the "second optically anisotropic layer A2-2." That is, a two-layer structure was formed, with the first layer being the first optically anisotropic layer A2-1 consisting of a cured layer of liquid crystal composition D2 containing a rod-shaped liquid crystal compound, and the second layer being the second optically anisotropic layer A2-2 consisting of a cured layer of liquid crystal composition E2 containing a discotic liquid crystal compound.

[0196] The optical element of Example 2 was prepared in the same manner as in Example 1, by forming an alignment film on a support, forming a first optically anisotropic layer A2-1 on the alignment film, and then forming a second optically anisotropic layer A2-2 on the first optically anisotropic layer A2-1 in the same manner as in Example 1. The coating amounts of each of the optically anisotropic layers A2-1 and A2-2 were adjusted so that the in-plane retardation Δnd (= Δn1d1 + Δn2d2) of the entire laminate structure was 275 nm, except that the optically anisotropic layer was prepared in the same manner as in Example 1. Here, Δn1 is the birefringence of the first optically anisotropic layer, d1 is the thickness of the first optically anisotropic layer, Δn2 is the birefringence of the second optically anisotropic layer, and d2 is the thickness of the second optically anisotropic layer. Both Δn1 and Δn2 were 0.15. The complex refractive index Δn was determined in the same manner as in the case of liquid crystal composition D1.

[0197] Cross-sectional SEM of the optical element of Example 2 confirmed that two liquid crystal alignment patterns having horizontal rotation alignment were overlapped. Furthermore, measurement using an Axometrix Axoscan confirmed that the first optically anisotropic layer (the first layer) was composed of aligned rod-shaped liquid crystal compounds, and the second optically anisotropic layer (the second layer) was composed of aligned discotic liquid crystal compounds. The optical element fabricated had a two-layer structure, and the first optically anisotropic layer had an in-plane retardation Δn1d1 = 138 nm and a twist angle of 37 degrees, and the second optically anisotropic layer had an in-plane retardation Δn2d2 = 137 nm and a twist angle of 37 degrees.

[0198] [Evaluation] The diffraction efficiency of each optical element was measured by measuring the light intensity of the diffracted light diffracted by the optical element fabricated in each example using the following method. As shown in FIG. 18 , the fabricated optical element 400 was placed on the surface (top surface in the figure) of a Dove prism 410. The Dove prism 410 was made of glass and had a refractive index of 1.5. The support (glass substrate) of the optical element 400 was peeled off, and the optical element 400 was adhered to the Dove prism 410 using a heat-sensitive adhesive. As shown in FIG. 18 , a laser light source (not shown) was placed opposite the optical element 400 placed on the top surface of the Dove prism 410. Furthermore, a linear polarizer 412 and a λ / 4 plate 414 were placed between the laser light source and the Dove prism 410.

[0199] Laser light Li emitted from the laser light source passes through linear polarizer 412 and λ / 4 plate 414, and is then incident as circularly polarized light on optical element 400 disposed on the upper surface of Dove prism 410. Laser light Li incident on optical element 400 (optically anisotropic layer) is diffracted by optical element 400 as described above, propagates through Dove prism 410, and is emitted from Dove prism 410.

[0200] The wavelength of the laser light Li was 532 nm. The angle of the laser light source was set so that the laser light Li was incident at 0° with respect to the normal direction of the principal surface of the optical element 400. That is, the laser light Li was incident on the optical element 400 from the normal direction of the principal surface of the optical element 400. The laser light Li was incident on the optical element 400, and the optical element 400 diffracted the laser light Li in a desired direction oblique to the normal line of the principal surface of the optical element 400 (the direction of the slope of the Dove prism 410), and the light intensity of the output light Lo output from the Dove prism 410 was measured.

[0201] The diffraction efficiency Deff of the fabricated optical element 400 is calculated by multiplying the light intensity of the laser light Li incident on the Dove prism 410 by I ｉｎ The light intensity of the diffracted light (first-order light) diffracted by the optical element 400 and emitted from the Dove prism 410 in the desired direction, i.e., the emitted light Lo, is expressed as I ｏｕｔ When the diffraction efficiency is 1 / 100, the diffraction efficiency is calculated by the following formula: ｏｕｔ / I ｉｎ The calculation of the diffraction efficiency was performed excluding the loss of transmittance at the interface when the light was incident on the Dove prism 410 and when it was emitted from the Dove prism 410 .

[0202] As a result, higher diffraction efficiency was obtained at a wavelength of 532 nm for the optical elements fabricated in Examples 1 and 2 than for Comparative Examples 1 and 2. Furthermore, higher diffraction efficiency was obtained at a wavelength of 532 nm for the optical element fabricated in Example 2 than for Example 1.

[0203] Comparative Example 11 An alignment film was formed on a support in the same manner as in Comparative Example 1. An optically anisotropic layer C-1 (rod-shaped liquid crystal layer) consisting of a cured layer of a liquid crystal composition DC1 containing a rod-shaped liquid crystal compound was formed on the alignment film, thereby producing an optical element of Comparative Example 11. The optically anisotropic layer C-1 had a liquid crystal alignment pattern in which the rod-shaped liquid crystal compound was horizontally rotated and had a cholesteric phase in the thickness direction.

[0204] [Preparation of Optical Element of Comparative Example 11] An optical element of Comparative Example 11 was prepared in the same manner as in Comparative Example 1, except that an optically anisotropic layer having a liquid crystal alignment pattern with a cholesteric phase was formed using liquid crystal composition DC1 instead of liquid crystal composition D1. A cross-sectional SEM of the optical element confirmed that the liquid crystal alignment pattern had a cholesteric phase.

[0205] (Formation of Optically Anisotropic Layer C-1) A liquid crystal composition DC1 having the following composition was prepared. <Liquid Crystal Composition DC1> ----------------------------------- Rod-shaped liquid crystal compound L-1 100.00 parts by mass Polymerization initiator (Irgacure (registered trademark) 907, manufactured by BASF) 3.00 parts by mass Photosensitizer (KAYACURE DETX-S, manufactured by Nippon Kayaku) 1.00 parts by mass Leveling agent T-1 0.08 parts by mass Chiral agent Ch-1 5.45 parts by mass Methyl ethyl ketone 300.00 parts by mass

[0206] -Chiral Agent Ch-1-

[0207] <Formation of Optically Anisotropic Layer C-1 by Coating> The optically anisotropic layer C-1 was formed by coating the liquid crystal composition DC1 on the alignment film P-1 in multiple layers.

[0208] The liquid crystal composition DC1 was applied to the alignment film P-1, and the resulting coating was heated to 110°C on a hot plate. After that, the coating was cooled to 60°C, and then irradiated with ultraviolet light having a wavelength of 365 nm at 300 mJ / cm using a high-pressure mercury lamp in a nitrogen atmosphere.2 The coating film was irradiated with light at an irradiation dose of 1000 .mu.m to fix the alignment of the liquid crystal compound. The thickness of the fixed liquid crystal layer (one liquid crystal fixing layer) at this time was 2.3 .mu.m.

[0209] The second and subsequent liquid crystal fixation layers were formed by applying liquid crystal composition DC1 over the previously formed liquid crystal fixation layer, heating and cooling under the same conditions as above, and then curing with ultraviolet light. In this way, the layer was repeatedly applied until the desired total thickness (here, 4.6 μm) was reached, thereby obtaining an optically anisotropic layer C-1. Furthermore, the formation of a periodic alignment surface was confirmed using a polarizing microscope and an SEM.

[0210] Comparative Example 12 An alignment film was formed on a support in the same manner as in Comparative Example 1. An optically anisotropic layer C-2 (disctic liquid crystal layer) consisting of a cured layer of liquid crystal composition EC1 containing a discotic liquid crystal compound was formed on the alignment film, thereby producing an optical element of Comparative Example 12. The optically anisotropic layer C-2 had a liquid crystal alignment pattern in which the discotic liquid crystal compound was horizontally rotated and had a cholesteric phase in the thickness direction.

[0211] [Preparation of Optical Element of Comparative Example 12] An optical element of Comparative Example 12 was prepared in the same manner as in Comparative Example 2, except that an optically anisotropic layer having a liquid crystal alignment pattern with a cholesteric phase was formed using liquid crystal composition EC1 instead of liquid crystal composition E1. A cross-sectional SEM of the optical element confirmed that the liquid crystal alignment pattern had a cholesteric phase.

[0212] (Formation of Optically Anisotropic Layer C-2) A liquid crystal composition EC1 having the following composition was prepared. <Liquid Crystal Composition EC1> ------------------------------------------------------------------ Discotic liquid crystal compound L-2 80.00 parts by mass Discotic liquid crystal compound L-3 20.00 parts by mass Polymerization initiator (Irgacure (registered trademark) 907, manufactured by BASF) 5.00 parts by mass Chiral agent Ch-2 3.79 parts by mass Megafac F444 (manufactured by DIC Corporation) 0.50 parts by mass Methyl ethyl ketone 300.00 parts by mass

[0213] -Chiral Agent Ch-2-

[0214] <Formation of Optically Anisotropic Layer C-2 by Coating> The optically anisotropic layer was formed by coating the liquid crystal composition EC1 on the alignment film P-1 in multiple layers instead of using the liquid crystal composition DC1 in Comparative Example 11.

[0215] First, the first layer was formed by applying the following liquid crystal composition EC1 to an alignment film P-1, heating the resulting coating to 95°C on a hot plate, then cooling it to 25°C, and irradiating it with ultraviolet light of 365 nm wavelength at 300 mJ / cm using a high-pressure mercury lamp in a nitrogen atmosphere. 2 The coating film was irradiated with light at an irradiation dose of 1000 .mu.m to fix the alignment of the liquid crystal compound. The thickness of the fixed liquid crystal layer (one liquid crystal fixing layer) at this time was 2.3 .mu.m.

[0216] The second and subsequent liquid crystal fixation layers were formed by applying liquid crystal composition EC1 to the previously formed liquid crystal fixation layer, heating and cooling under the same conditions as above, and then curing with ultraviolet light. In this way, the layer was repeatedly applied until the desired total thickness (here, 4.6 μm) was reached, thereby obtaining an optically anisotropic layer C-2. Furthermore, the formation of a periodic alignment surface was confirmed using a polarizing microscope and an SEM.

[0217] Example 11 An alignment film was formed on a support, and an optically anisotropic layer C-3 (rod-shaped liquid crystal layer) consisting of a cured layer of liquid crystal composition DC1 containing a rod-shaped liquid crystal compound was formed on the alignment film. Then, an optically anisotropic layer C-4 (disk-shaped liquid crystal layer) consisting of a cured layer of liquid phase composition EC1 containing a discotic liquid crystal compound was formed to produce the optical element of Example 11. Hereinafter, the optically anisotropic layer C-3 (rod-shaped liquid crystal layer) in this example will be referred to as the "first optically anisotropic layer C-3," and the optically anisotropic layer C-4 (disk-shaped liquid crystal layer) will be referred to as the "second optically anisotropic layer C-4." That is, a two-layer structure was produced, with the first layer being the first optically anisotropic layer C-3 consisting of a cured layer of a liquid crystal composition containing a rod-shaped liquid crystal compound, and the second layer being the second optically anisotropic layer C-4 consisting of a cured layer of a liquid crystal composition containing a discotic liquid crystal compound.

[0218] The optical element of Example 11 was prepared in the same manner as in Comparative Example 11, by forming an alignment film on a support, forming a first optically anisotropic layer C-3 on the alignment film, and then forming a second optically anisotropic layer C-4 on the first optically anisotropic layer C-3 in the same manner as the optically anisotropic layer C-2 formed on the alignment film in Comparative Example 12. In this case, the thicknesses of the optically anisotropic layers C-3 and C-4 were each 2.3 μm, and the coating amounts were adjusted so that the total thickness of the two layers was 4.6 μm, so that the total thickness was the same as the thickness of the optically anisotropic layer of Comparative Example 12. The optical element of Example 11 was prepared in the same manner as in Comparative Examples 11 and 12. The optical element of Example 11 had a continuous cholesteric alignment formed in the thickness direction by the two layers, the first optically anisotropic layer C-3 and the second optically anisotropic layer C-4. Furthermore, it was confirmed using a polarizing microscope and an SEM that the surface had a periodic alignment.

[0219] [Evaluation] The diffraction efficiency of each optical element was measured by measuring the light intensity of the diffracted light diffracted by the optical element fabricated in each example using the following method. As shown in FIG. 19 , the fabricated optical element 401 was placed on the surface (top surface in the figure) of a Dove prism 410. The Dove prism 410 was a glass Dove prism with a refractive index of 1.5. The support (glass substrate) of the optical element 401 was peeled off, and the optical element 401 was adhered to the Dove prism 410 using a heat-sensitive adhesive. As shown in FIG. 19 , a laser light source (not shown) was placed opposite the lower surface of the Dove prism 410, which faces the surface on which the optical element 401 was placed. Furthermore, a linear polarizer 412 and a λ / 4 plate 414 were placed between the laser light source and the Dove prism 410.

[0220] Laser light Li emitted from the laser light source passes through linear polarizer 412 and λ / 4 plate 414 and enters Dove prism 410 as circularly polarized light. The laser light Li incident on Dove prism 410 propagates through Dove prism 410 and enters optical element 401, which is positioned opposite the incident surface (lower surface). As described above, optical element 401 has a cholesterically oriented optically anisotropic layer (cholesteric liquid crystal layer). The laser light Li incident on optical element 401 is reflected and diffracted by optical element 401 (cholesteric liquid crystal layer) as described above, propagates through Dove prism 410, and is emitted from Dove prism 410.

[0221] The wavelength of the laser light Li was set to 532 nm. The angle of the laser light source was adjusted so that the laser light Li was incident at 0° with respect to the normal direction of the principal surface of the optical element 401. That is, the laser light Li was incident on the optical element 401 from the normal direction of the principal surface of the optical element 401. The laser light Li was incident on the optical element 401, and the optical element 401 reflected and diffracted the laser light Li in a desired direction oblique to the normal line of the principal surface of the optical element 401 (the direction of the slope of the Dove prism 410), and the light intensity of the output light Lo output from the Dove prism 410 was measured.

[0222] The diffraction efficiency Deff of the fabricated optical element 401 is calculated by multiplying the light intensity of the laser light Li incident on the Dove prism 410 by I ｉｎThe light intensity of the diffracted light (first-order light) diffracted by the optical element 401 and emitted from the Dove prism 410 in the desired direction, i.e., the emitted light Lo, is expressed as I ｏｕｔ When the diffraction efficiency is 1 / 100, the diffraction efficiency is calculated by the following formula: ｏｕｔ / I ｉｎ The diffraction efficiency was calculated excluding the loss of transmittance at the interface when light is incident on the Dove prism 410 and when light is emitted from the Dove prism 410 .

[0223] In comparison with Comparative Examples 11 and 12, the optical element fabricated in Example 11 exhibited high diffraction efficiency at a wavelength of 532 nm.

[0224] From the above results, the effects of the present invention are clear.

[0225] The present invention can be suitably used in various optical devices and optical systems, such as HMDs such as AR glasses and VR goggles.

[0226] 10, 10b, 10c, 100, 100IR, 100IG, 100IB, 100OR, 100OG, 100OB, 128, 142 Optical element 30 Support 32 Alignment film 37b First laminate 37c Second laminate 40c Rod-shaped liquid crystal compound 40d Discotic liquid crystal compound 40A Optical axis 42, 42b, 46, 102 Rod-shaped liquid crystal layer 44, 44b, 104 Discotic liquid crystal layer 60 Exposure device 62 Laser 64 Light source 65 λ / 2 plate 68, 86, 94 Polarizing beam splitter 70A, 70B, 90A, 90B Mirror 72A, 72B, 96 λ / 4 plate 92 Lens 110 AR glass 112 Light guide plate 114 Incident section 116 Exit section 120, 140 VR goggles 124 Image display element 126 Circular polarizer 130 Half mirror 144 Lens 146 Reflective circular polarizer 400, 401 Optical element 410 Dove prism 412 Linear polarizer 414 λ / 4 plate Li Laser light Lo Exit light D Array axis R Region Λ One period M Laser light MA, MB Light ray P O Linear polarized light P R , right circularly polarized light P LLeft circularly polarized light α Angle L1, L4 Incident light L2, L5 Emitted light

Claims

1. It comprises a first optically anisotropic layer which is a cured layer of a liquid crystal composition containing a rod-shaped liquid crystal compound, and a second optically anisotropic layer which is a cured layer of a liquid crystal composition containing a disc-shaped liquid crystal compound. The first optically anisotropic layer is a liquid crystal alignment pattern in which the rod-shaped liquid crystal compounds are arranged along at least one direction in the plane, and has a first liquid crystal alignment pattern in which the orientation of the optical axis originating from the rod-shaped liquid crystal compounds changes while continuously rotating, and has a region in the first liquid crystal alignment pattern in which the orientation of the optical axis of the rod-shaped liquid crystal compounds rotates by 180° with a period shorter than 0.5 μm. The optical element is characterized in that the second optical anisotropy layer is a liquid crystal alignment pattern in which the disc-shaped liquid crystal compounds are arranged along at least one direction in a plane, and the orientation of the optical axis originating from the disc-shaped liquid crystal compounds changes while continuously rotating in the second liquid crystal alignment pattern, and the second liquid crystal alignment pattern has a region in which the orientation of the optical axis of the disc-shaped liquid crystal compounds rotates by 180° with a period shorter than 0.5 μm.

2. The optical element according to claim 1, wherein in the first optical anisotropy layer, the rod-shaped liquid crystal compound is torsionally oriented in the thickness direction of the first optical anisotropy layer according to a first torsion.

3. The optical element according to claim 1, wherein in the second optical anisotropy layer, the disc-shaped liquid crystal compound is torsionally oriented in the thickness direction of the second optical anisotropy layer according to the second torsion.

4. The optical element according to claim 2, wherein in the second optical anisotropy layer, the disc-shaped liquid crystal compound is torsionally oriented in the thickness direction of the second optical anisotropy layer according to a second torsion, the first torsion and the second torsion are in the same direction, and in the first optical anisotropy layer and the second optical anisotropy layer, the torsion orientation of the optical axis of the rod-shaped liquid crystal compound and the torsion orientation of the optical axis of the disc-shaped liquid crystal compound are continuous torsion orientations.

5. The optical element according to claim 2, wherein in the second optical anisotropy layer, the disc-shaped liquid crystal compound is torsionally oriented in the thickness direction of the second optical anisotropy layer according to a second torsion, and the first torsion and the second torsion are in opposite directions.

6. In the first optically anisotropic layer, the rod-shaped liquid crystal compound is cholesterically oriented in the thickness direction. The optical element according to claim 1, wherein in the second optical anisotropy layer, the disc-shaped liquid crystal compound is cholesterically oriented in the thickness direction.

7. The optical element according to claim 6, wherein the rod-shaped liquid crystal compound in the first optical anisotropic layer and the disc-shaped liquid crystal compound in the second optical anisotropic layer are continuously cholesterically oriented in the thickness direction.

8. The optical element according to claim 1, wherein the first optical anisotropy layer has a region in which the rod-shaped liquid crystal compound is tilted in the plane of the optical anisotropy layer in the thickness direction of the first optical anisotropy layer.

9. The optical element according to claim 1, wherein the second optical anisotropy layer has a region in which the disc-shaped liquid crystal compound is tilted in the plane of the optical anisotropy layer in the thickness direction of the second optical anisotropy layer.

10. The optical element according to claim 1, having a configuration in which an optically anisotropic layer which is a cured layer of a liquid crystal composition containing the rod-shaped liquid crystal compound and an optically anisotropic layer which is a cured layer of a liquid crystal composition containing the disc-shaped liquid crystal compound are alternately laminated.

11. The optical element is a transmissive optical element, A combination of the first optical anisotropy layer and the second optical anisotropy layer, which are twisted and oriented clockwise in the thickness direction of the optical element, A combination of the first optical anisotropy layer and the second optical anisotropy layer, which are twisted and oriented counterclockwise in the thickness direction of the optical element, The optical element according to claim 1, having the following characteristics.

12. The optical element is a reflective optical element, The optical element according to claim 1, comprising a combination of a first optical anisotropy layer and a second optical anisotropy layer that selectively reflects right-circularly polarized light, and a combination of a first optical anisotropy layer and a second optical anisotropy layer that selectively reflects left-circularly polarized light, wherein the combination that selectively reflects right-circularly polarized light and the combination that selectively reflects left-circularly polarized light selectively reflect light of the same color.

13. A head-mounted display having an optical element according to any one of claims 1 to 12.