Retardation element, circular polarization plate and optical component

Abstract

To provide a retardation element capable of converting with high ellipticity the polarization state of light entering a retardation element at wide incident angle and incident azimuth.SOLUTION: A retardation element comprises a first retardation layer, and a second retardation layer arranged on the first retardation layer. Both optical axis directions and retardations of the second retardation layer are aligned regardless of in-plane position in top view in the first retardation layer. The retardations of the second retardation layer are aligned regardless of in-plane position in top view while the optical axis directions thereof are different from each other depending on in-plane position.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present disclosure relates to a retardation element, a circular polarizing plate, and an optical component. [Background technology]

[0002] A phase difference element is known that converts incident linearly polarized light into elliptically polarized light or converts incident elliptically polarized light into linearly polarized light.

[0003] As a retardation element, an optical film in which a plurality of optically anisotropic layers are laminated has been disclosed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-207765 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of one aspect of the present disclosure is to provide a phase difference element that can convert, with high ellipticity, the polarization state of light that is incident on the phase difference element at a wide range of angles of incidence and azimuth angles of incidence. [Means for solving the problem]

[0006] A phase difference element according to one embodiment of the present disclosure includes a first phase difference layer and a second phase difference layer disposed on the first phase difference layer, wherein the first phase difference layer has both the same optical axis direction and retardation regardless of the position in the plane when viewed from above, and the second phase difference layer has the same retardation regardless of the position in the plane when viewed from above, and the optical axis direction differs depending on the position in the plane. [Effects of the Invention]

[0007] According to one aspect of the present disclosure, it is possible to provide a phase difference element that can convert the polarization state of light incident on the phase difference element at a wide range of incident angles and incident azimuth angles with high ellipticity. [Brief explanation of the drawings]

[0008] [Figure 1A] FIG. 1 is a schematic perspective view showing an example of the configuration of a phase difference element according to a first embodiment. [Figure 1B] FIG. 2 is a schematic top view showing an example of an alignment axis of a first retardation layer included in the retardation element according to the first embodiment. [Figure 1C] FIG. 3 is a schematic top view showing an example of an alignment axis of a second retardation layer included in the retardation element according to the first embodiment. [Figure 2] FIG. 3 is a diagram showing an example of elliptically polarized light emitted from the phase difference element according to the first embodiment. [Figure 3] FIG. 2 is a schematic side view showing an example of the configuration of a first retardation layer in the retardation element according to the first embodiment. [Figure 4A] FIG. 10 is a schematic side view showing a phase difference element according to a first modified example. [Figure 4B] FIG. 10 is a schematic side view showing a phase difference element according to a second modified example. [Figure 4C] FIG. 11 is a schematic side view showing a phase difference element according to a third modified example. [Figure 4D] FIG. 10 is a schematic side view showing a phase difference element according to a fourth modified example. [Figure 5] FIG. 2 is a schematic perspective view showing an example of the orientation of liquid crystal in the retardation element of FIG. [Figure 6] FIG. 2 is a schematic perspective view illustrating an example of the configuration of an alignment layer. [Figure 7] FIG. 2 is a schematic perspective view showing an example of a method for forming an alignment layer. [Figure 8] FIG. 4 is a diagram showing an example of the relationship between a reference direction, a first point, and a second point. [Figure 9] FIG. 10 is a diagram showing a first example of the alignment axis direction in the second retardation layer. [Figure 10] FIG. 10 is a diagram showing a second example of the alignment axis direction in the second retardation layer. [Figure 11] FIG. 10 is a diagram showing a third example of the alignment axis direction in the second retardation layer. [Figure 12] FIG. 10 is a diagram showing a fourth example of the orientation axis direction in the second retardation layer. [Figure 13] FIG. 10 is a diagram showing a fifth example of the orientation axis direction in the second retardation layer. [Figure 14] FIG. 2 is a schematic perspective view showing a model M1 of the phase difference element according to the first embodiment. [Figure 15] 10 is a diagram showing the orientation axis direction of a second retardation layer of a retardation element according to Example 1. FIG. [Figure 16] FIG. 10 is a diagram showing the ellipticity of the retardation element according to Example 1 at a wavelength of 550 nm. [Figure 17] FIG. 10 is a diagram showing the ellipticity of the retardation element according to Example 2 at a wavelength of 550 nm. [Figure 18A] FIG. 2 is a schematic top view showing a model M2-1 of the phase difference element according to the first embodiment. [Figure 18B] FIG. 2 is a schematic side view showing a model M2-1 of the phase difference element according to the first embodiment. [Figure 18C] FIG. 10 is a schematic side view showing a model M2-2 of the phase difference element according to the first embodiment. [Figure 19A] 10 is a first diagram showing the orientation axis direction of a second retardation layer of a retardation element according to Example 3. FIG. [Figure 19B] 10 is a second diagram showing the orientation axis direction of the second retardation layer of the retardation element according to Example 3. FIG. [Figure 19C] FIG. 3 is a third diagram showing the orientation axis direction of the second retardation layer of the retardation element according to Example 3. [Figure 19D] FIG. 4 is a fourth diagram showing the orientation axis direction of the second retardation layer of the retardation element according to Example 3. [Figure 20A] FIG. 10 is a diagram showing the ellipticity of the retardation element according to Example 3 at a wavelength of 550 nm. [Figure 20B] FIG. 10 is a diagram showing the ellipticity of the retardation element according to Example 3′ at a wavelength of 550 nm. [Figure 21] FIG. 10 is a diagram showing the ellipticity of the retardation element according to Example 4 at a wavelength of 550 nm. [Figure 22] FIG. 10 is a schematic perspective view showing a model M3 of the phase difference element according to Examples 5 and 6. [Figure 23] 10 is a diagram showing the orientation axis direction of the second retardation layer of the retardation element according to Example 5. FIG. [Figure 24] FIG. 10 is a diagram showing the ellipticity of the retardation element according to Example 5 at a wavelength of 550 nm. [Figure 25] FIG. 10 is a diagram showing the ellipticity of the retardation element according to Example 6 at a wavelength of 550 nm. [Figure 26A] FIG. 10 is a schematic top view showing a first example of a model M4 of the phase difference element according to the first embodiment. [Figure 26B] FIG. 2 is a schematic side view showing a model M4 of the phase difference element 1 according to the first embodiment. [Figure 26C] FIG. 10 is a schematic top view showing a second example of the model M4 of the phase difference element according to the first embodiment. [Figure 27A] 10 is a diagram showing the orientation axis direction of the second retardation layer of the retardation element according to Example 7. FIG. [Figure 27B] FIG. 10 is a diagram showing the orientation axis direction of the second retardation layer of the retardation element according to Example 7′. [Figure 28A] 10 is a diagram showing the orientation axis direction of the second retardation layer of the retardation element according to Example 9. FIG. [Figure 28B] FIG. 10 is a diagram showing the orientation axis direction of the second retardation layer of the retardation element according to Example 9′. [Figure 29] 10 is a schematic diagram showing the configuration of an optical component 200 according to a second embodiment. FIG. [Figure 30A] FIG. 30 is a schematic cross-sectional view taken along the line XXX-XXX in FIG. 29. [Figure 30B] 30B is a schematic diagram showing the orientation axis direction of the retardation element in FIG. 30A in a plane. FIG. [Figure 31] FIG. 10 is a diagram showing a method for determining the orientation axis direction of the second retardation layer. [Figure 32A] FIG. 10 is a cross-sectional view showing a model M6 of the phase difference element according to the second embodiment. [Figure 32B] FIG. 10 is a top view showing a first example of a model M6 of the phase difference element according to the second embodiment. [Figure 32C] FIG. 10 is a top view showing a second example of the model M6 of the phase difference element according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the embodiments shown below are merely examples of phase difference elements for realizing the technical concept of the present embodiment, and are not limited to the following. Note that the size, positional relationship, etc. of components shown in each drawing may be exaggerated for clarity. In each drawing, the same components are denoted by the same reference numerals, and duplicated explanations will be omitted as appropriate.

[0010] In the drawings shown below, directions are represented using a Cartesian coordinate system having an X axis, a Y axis, and a Z axis. The X direction along the X axis indicates a predetermined direction in a plane along the light incidence surface of the retardation element according to the embodiment. The Y direction along the Y axis indicates a direction perpendicular to the X direction in the plane. The Z direction along the Z axis indicates a direction perpendicular to the plane. The direction in which the arrow points in the X direction is referred to as the +X direction, and the direction opposite to the +X direction is referred to as the -X direction. The direction in which the arrow points in the Y direction is referred to as the +Y direction, and the direction opposite to the +Y direction is referred to as the -Y direction. The direction in which the arrow points in the Z direction is referred to as the +Z direction, and the direction opposite to the +Z direction is referred to as the -Z direction. In the embodiments, light traveling in the +Z direction enters the retardation element, passes through the retardation element, and then exits the retardation element. In this specification, light travels in the +Z direction. In this specification, the +Z direction is referred to as "up" or "upward," and the -Z direction is referred to as "down" or "downward." A top view refers to viewing an object from the +Z direction, but these directional expressions do not limit the directions of the embodiments of the present disclosure.

[0011] In this specification and claims, "substantially parallel" means that the absolute value of the angular deviation from the parallel state is between 0.0° and 10.0°. "Substantially perpendicular" means that the absolute value of the angular deviation from the perpendicular state is between 0.0° and 10.0°. "Arranged" does not only mean direct contact, but also includes indirect arrangement, for example, via another member.

[0012] [First embodiment] <Configuration of Phase Difference Element According to First Embodiment> First, the configuration of the retardation element according to the first embodiment will be described with reference to Fig. 1A, Fig. 1B, Fig. 1C, and Fig. 2. Fig. 1A is a schematic perspective view showing an example of the configuration of the retardation element 1 according to the first embodiment. Fig. 1B is a schematic top view showing an example of the alignment axis OD1 of the first retardation layer 11 included in the retardation element 1 according to the first embodiment. Fig. 1C is a schematic top view showing an example of the alignment axis OD2 of the second retardation layer 12 included in the retardation element 1 according to the first embodiment. Fig. 2 is a diagram showing an example of elliptically polarized light emitted from the retardation element 1 according to the first embodiment.

[0013] The retardation element 1 according to the first embodiment has a first retardation layer 11 and a second retardation layer 12 disposed on the first retardation layer 11. In the first retardation layer 11, both the retardation Re and the optical axis direction are uniform regardless of the position in the plane when viewed from above. In the second retardation layer 12, the retardation Re is uniform regardless of the position in the plane when viewed from above, and the optical axis direction differs depending on the position in the plane.

[0014] 1A, 1B, and 1C, the first retardation layer 11 and the second retardation layer 12 each contain a polymerized liquid crystal. In the first retardation layer 11, both the retardation Re and the alignment axis direction pT are uniform regardless of the position in the plane when viewed from above. In the second retardation layer 12, the retardation Re is uniform regardless of the position in the plane when viewed from above, and the alignment axis direction pT varies depending on the position in the plane.

[0015] Polymerized liquid crystals are formed by coating and drying a liquid crystal composition. The liquid crystal composition includes, for example, photocurable liquid crystals containing acrylic or methacrylic groups. The liquid crystal composition may also include a component that does not form a liquid crystal layer by itself. It is sufficient that a liquid crystal layer is formed by polymerization. Examples of components that do not form a liquid crystal layer include monofunctional (meth)acrylates, bifunctional (meth)acrylates, and trifunctional or higher (meth)acrylates. The liquid crystal composition may also include a photocurable monomer. The polymerizable liquid crystal composition may also include additives. Examples of additives that can be used include polymerization initiators, surfactants, chiral agents, polymerization inhibitors, UV absorbers, antioxidants, light stabilizers, antifoaming agents, and dichroic dyes. Multiple additives may also be used in combination. Examples of methods and solvents for coating the liquid crystal composition include those described in paragraphs

[0040] and

[0041] of International Application No. PCT / JP2021 / 028750. The liquid crystal composition may have a positive or negative wavelength dispersion of the Δn value after curing. For the liquid crystal composition, for example, the polymerizable compound described in paragraphs

[0043] to

[0046] of International Application No. PCT / JP2021 / 028750 can be used.

[0016] The phase difference element 1 is an optical element that converts linearly polarized light incident on its incident surface 1a into elliptically polarized light and emits it from its exit surface 1b, or converts elliptically polarized light incident on its incident surface 1a into linearly polarized light and emits it from its exit surface 1b. This embodiment can provide a phase difference element 1 that can convert the polarization state of light L incident on the phase difference element 1 at a wide incidence angle φ and incidence azimuth angle α with high ellipticity.

[0017] A retardation layer is a layer made of a birefringent material. Retardation Re is a characteristic value expressed as (ne-no) x t, where ne is the extraordinary refractive index for light whose electric field oscillates along the slow axis, no is the ordinary refractive index for light whose electric field oscillates in a direction perpendicular to the slow axis, and t is the thickness of the retardation layer.

[0018] The optical axis direction refers to the direction of the optical axis in the retardation layer. The optical axis corresponds to either the slow axis or the fast axis of the retardation layer. The alignment axis direction pT refers to the direction of the alignment axis OD in the retardation layer containing liquid crystal. The alignment axis OD corresponds to the optical axis when the retardation layer contains liquid crystal. The alignment axis OD is an example of the optical axis. The alignment axis direction pT corresponds to the optical axis when the retardation layer contains liquid crystal. The alignment axis direction pT is an example of the optical axis direction.

[0019] The alignment axis direction pT of the first retardation layer 11 is equal to the alignment axis direction of the liquid crystal contained in the first retardation layer 11 at the interface opposite to the second retardation layer 12 side, i.e., at the interface on the incident surface 1a side. The alignment axis direction pT of the second retardation layer 12 is equal to the alignment axis direction of the liquid crystal contained in the second retardation layer 12 at the interface on the first retardation layer 11 side. Note that the retardation layer in the retardation element 1 is not limited to one containing liquid crystal, and may be made of birefringent crystal, a stretched film, an obliquely evaporated film, or the like.

[0020] The incident angle φ refers to the angle of light L incident on the phase difference element 1 with respect to the normal NL of the phase difference element 1 at the incident position. The incident azimuth angle α refers to the incident direction of light L on the phase difference element 1 when viewed from above. For ease of explanation, in FIG. 1A, the incident azimuth angle α is shown on the exit surface 1b rather than the entrance surface 1a. Furthermore, the projection L' in FIG. 1A represents the projection of light L onto the exit surface 1b of the phase difference element 1.

[0021] In FIG. 1B, multiple arrows shown inside the first retardation layer 11 in top view indicate alignment axes OD1 at the respective positions of the arrows in a plane parallel to the XY plane of the first retardation layer 11. In FIG. 1C, multiple arrows shown inside the second retardation layer 12 in top view indicate alignment axes OD2 at the respective positions of the arrows in the second retardation layer 12. The length of the arrow representing the alignment axis OD represents the magnitude of the retardation Re. The direction of the arrow representing the alignment axis OD represents the alignment axis direction pT. The meanings of the length and direction of the arrows representing the alignment axis OD, alignment axis OD1, and alignment axis OD2 are the same for the arrows representing the alignment axis OD shown below.

[0022] In the example shown in FIG. 1B, the lengths and directions of the arrows representing the alignment axis OD1 are uniform for each of the multiple arrow positions. That is, in the example shown in FIG. 1B, both the retardation Re and the light distribution axis direction pT are uniform regardless of the position in the plane. On the other hand, in the example shown in FIG. 1C, the lengths of the arrows representing the alignment axis OD2 are uniform for each of the multiple arrow positions, but the directions of the arrows representing the alignment axis OD2 are different. That is, in the example shown in FIG. 1C, the retardation Re is uniform regardless of the position in the plane, and the alignment axis direction pT differs depending on the position in the plane. Note that "aligned alignment of the alignment axis pT" does not necessarily mean perfect alignment, but also means a deviation of ±10° or less. Furthermore, "aligned retardation" does not necessarily mean perfect alignment, but also means a deviation of ±10 nm or less.

[0023] FIG. 2 shows an ellipse E1 corresponding to elliptically polarized light viewed from the direction of emission from the phase difference element 1. In FIG. 2, ellipticity refers to the ratio of the length of the major axis EL1 to the length of the minor axis ES1 of the ellipse E1. When the length of the major axis EL1 and the length of the minor axis ES1 are equal, the ellipticity is 1. The ellipticity is an index that indicates whether polarized light is close to circularly polarized light or linearly polarized light. The closer the ellipticity is to 1, the closer the polarized light is to circularly polarized light. The closer the ellipticity is to 0, the closer the polarized light is to linearly polarized light. "Converting with a high ellipticity" means converting incident linearly polarized light into elliptically polarized light with an ellipticity close to 1, or converting incident circularly polarized light into elliptically polarized light with an ellipticity close to 0.

[0024] 1 is a laminated wave plate in which a first retardation layer 11 and a second retardation layer 12 are laminated. The first retardation layer 11 and the second retardation layer 12 are arranged in this order along the traveling direction of light L. Note that the retardation element 1 is not limited to a plate-like member such as a wave plate, and may be a film-like member or the like.

[0025] The phase difference element 1 is not limited to a plate-like member or film including only a plane, but may also have a three-dimensional curved shape. Examples of three-dimensional curved shapes include spherical shapes and aspherical shapes. Examples of aspherical shapes include cylindrical shapes and parabolic shapes. When the phase difference element 1 has a three-dimensional curved shape, the optical axis direction and the orientation axis direction pT are not limited to directions in a plane parallel to the XY plane, but may include directions defined three-dimensionally according to the three-dimensional curved shape of the phase difference element 1. Methods for forming a phase difference element on a three-dimensional curved surface include, for example, the methods described in International Publication No. 2022 / 030482, International Publication No. 2022 / 030481, or Japanese Patent Application Laid-Open No. 2022-020360.

[0026] Light incident on the incident surface 1a of the retardation element 1 is given a phase difference by each of the first retardation layer 11 and the second retardation layer 12, and exits from the exit surface 1b of the retardation element 1. The first retardation layer 11 and the second retardation layer 12 are arranged so that the surface of the first retardation layer 11 facing the second retardation layer 12 and the surface of the second retardation layer 12 facing the first retardation layer 11 face each other. The first retardation layer 11 and the second retardation layer 12 may also be arranged so that the surface of the first retardation layer facing the second retardation layer 12 and the surface of the second retardation layer 12 facing the first retardation layer 11 face each other and are in contact with each other.

[0027] The first retardation layer 11 and the second retardation layer 12 are each translucent to visible light. Specifically, the first retardation layer 11 and the second retardation layer 12 are each translucent in the wavelength range of 300 nm to 1000 nm. Being translucent preferably means that the transmittance is 50% or more in the wavelength range of 300 nm to 1000 nm. The transmittance can be measured, for example, with an ultraviolet-visible spectrophotometer (product name UH-4150, Hitachi High-Tech Science Corporation).

[0028] (Configuration of the first retardation layer 11) Next, the configuration of the first retardation layer 11 will be described with reference to Fig. 3. Fig. 3 is a schematic side view showing an example of the configuration of the first retardation layer 11 in the retardation element 1 according to the first embodiment. Fig. 3 shows the first retardation layer 11 viewed from a direction perpendicular to the traveling direction of light L.

[0029] The first retardation layer 11 contains a polymerized liquid crystal. The first retardation layer 11 shown in Fig. 3 has a substrate 111, an alignment layer 112, a liquid crystal layer 113, an alignment layer 114, and a substrate 115. The liquid crystal layer 113 contains a polymerized liquid crystal.

[0030] The first interface 116 is a surface of the liquid crystal layer 113 opposite to a surface facing the second retardation layer 12. The second interface 117 is a surface of the liquid crystal layer 113 facing the second retardation layer 12. In the example shown in FIG. 3, the first interface 116 and the second interface 117 are approximately parallel. Note that the first retardation layer 11 does not necessarily include the substrate 111, the alignment layer 112, the alignment layer 114, and the substrate 115 as long as it includes the liquid crystal layer 113. When the first retardation layer 11 includes a substrate, it may include at least one of the substrate 111 and the substrate 115. When the first retardation layer 11 includes an alignment layer, it may include at least one of the alignment layer 112 and the alignment layer 114.

[0031] The substrate 111, the alignment layer 112, the liquid crystal layer 113, the alignment layer 114, and the substrate 115 are arranged in this order along the traveling direction of the light L. The alignment layer 112 is arranged on the substrate 111. The alignment layer 114 is arranged below the substrate 115. The liquid crystal layer 113 is arranged between the alignment layer 112 and the alignment layer 114. The thickness d1 is the thickness of the liquid crystal layer 113.

[0032] The substrates 111 and 115 support the liquid crystal contained in the first retardation layer 11. Each of the substrates 111 and 115 is made of a material such as glass or resin that is translucent to visible light incident on the retardation element 1. The resin of the substrates 111 and 115 can be triacetylcellulose (TAC), polymethyl methacrylate (PMMA), cycloolefin polymer (COP), cycloolefin copolymer (COC), polyethylene terephthalate (PET), polycarbonate (PC), or the like. The glass can be, for example, synthetic quartz, BK7 by SHOTT Corporation, or D263 by SHOTT Corporation.

[0033] The retardation of the substrate 111 and the substrate 115 is, for example, 5 nm or less, and preferably 3 nm or less. From the viewpoint of reducing variations in color tone, the smaller the phase difference of the substrate, the better, and it may be zero. The retardation of the substrate 111 and the substrate 115 is measured, for example, by a rotation analyzer method.

[0034] The substrate 111 and the substrate 115 may have a single-layer structure made of a single substrate, or may have a multi-layer structure in which a film that imparts a reflecting or absorbing function is laminated on a main substrate (glass substrate or resin substrate) to transmit light in a specific wavelength band. Furthermore, the substrate 111 and the substrate 115 may be laminated with a film that imparts a function such as antifouling in addition to the reflecting or absorbing function. The substrate 111 and the substrate 115 may be a prism or a lens.

[0035] For example, the substrate 111 and the substrate 115 may further include a resin film or an inorganic film in addition to a glass substrate or a resin substrate. The resin film is, for example, a color correction filter, a base film for a silane coupling agent, or a film with an antifouling function. The resin film is formed by, for example, screen printing, vapor deposition, spray coating, or spin coating. The inorganic film is, for example, a metal oxide film that functions as an optical interference film (antireflection or wavelength selection filter). The inorganic film is formed by, for example, sputtering, vapor deposition, or CVD.

[0036] Each of the alignment layers 112 and 114 controls the alignment of liquid crystal molecules contained in the liquid crystal layer 113. Specifically, the alignment layer includes a photo-alignment layer, an organic thin film such as a rubbed polyimide film, an inorganic obliquely evaporated film, a film with a fine groove structure, etc. The photo-alignment layer refers to an alignment layer that utilizes the fact that the alignment force of liquid crystal molecules differs between the direction of linearly polarized ultraviolet light and the direction perpendicular to the direction of linear polarization when the organic thin film is irradiated with such light.

[0037] The liquid crystal layer 113 corresponds to the liquid crystal contained in the first retardation layer 11. The liquid crystal layer 113 has a so-called twisted structure in which the orientation of the liquid crystal is twisted around an axis along the traveling direction of the light L depending on the position along the traveling direction of the light L. In other words, the orientation of the liquid crystal contained in the first retardation layer 11 is twisted in the normal direction of the retardation element 1. The first interface 116 may be in contact with the alignment layer 112. The second interface 117 may be in contact with the alignment layer 114. In other words, at least one of the first interface 116 and the second interface 117 may be in contact with either the alignment layer 112 or the alignment layer 114.

[0038] The orientation axis direction of the liquid crystal contained in the liquid crystal layer 113 is preferably approximately parallel to the first interface 116 and the second interface 117. From another perspective, the inclination of the orientation axis direction of the liquid crystal contained in the liquid crystal layer 113 with respect to the first interface 116 and the second interface 117 is preferably 0° or more and 10° or less, more preferably 0° or more and 5° or less, and even more preferably 0° or more and 2° or less. It may even be 0°. When the value is within the above range, measurement of the optical performance of the retardation element can be performed using a measurement in which light is incident perpendicular to the interface, and the optical axis can be easily adjusted with a device such as an autocollimator with respect to the interface, simplifying the optical system and facilitating measurement. Furthermore, since it is sufficient to align the liquid crystal horizontally to the interface, a wide process margin can be secured for the surface energy of the alignment layer, making it easy to control alignment variations during mass production.

[0039] The second retardation layer 12 has the same configuration as the first retardation layer 11 shown in FIG. 3. That is, each of the first retardation layer 11 and the second retardation layer 12 contains a polymerized liquid crystal. In the retardation element 1, the first retardation layer 11 and the second retardation layer 12 each contain a liquid crystal, and thus have birefringence. Furthermore, in the retardation element 1, the alignment axis direction pT of each of the first retardation layer 11 and the second retardation layer 12 can be controlled by controlling the alignment of the liquid crystal in each of the first retardation layer 11 and the second retardation layer 12.

[0040] In the retardation element 1, the orientation of the liquid crystal contained in at least one of the first retardation layer 11 and the second retardation layer 12 is twisted along the normal direction of the retardation element 1. In the retardation element 1, the orientation of the liquid crystal in each of the first retardation layer 11 and the second retardation layer 12 can be controlled by controlling the amount of twist, in other words, the twist angle. The twisted structure is formed, for example, by adding a chiral agent to the liquid crystal composition. The amount of twist can be controlled by adjusting the amount of chiral agent added.

[0041] <Modification of Phase Difference Element 1> Various modified examples of the retardation element 1 will be described with reference to FIGS. 4A to 4D. The first retardation layer included in the retardation element according to each modified example includes at least a liquid crystal layer, and may include at least one of an alignment layer and a substrate in addition to the liquid crystal layer. The order in which the layers are arranged may also differ depending on the modified example. Even when the layer configuration and arrangement differ, the first retardation layer included in the retardation element according to each modified example has substantially the same function as the first retardation layer 11 described above. Therefore, the first retardation layer included in the retardation element according to each modified example will be referred to as the first retardation layer 11. Similarly, the second retardation layer included in the retardation element according to each modified example will be referred to as the second retardation layer 12. These points also apply to the following embodiments, examples, and comparative examples.

[0042] (First Modification) 4A is a schematic side view showing a retardation element 1A according to a first modified example of the first embodiment. In the retardation element 1A, a substrate 111, an alignment layer 112, a liquid crystal layer 113, an alignment layer 122, and a liquid crystal layer 123 are arranged in this order along the traveling direction of light L. The alignment layer 112 and the liquid crystal layer 113 form a first retardation layer 11. The alignment layer 122 and the liquid crystal layer 123 form a second retardation layer 12. The retardation element 1A also provides substantially the same effects as the above-mentioned retardation element 1.

[0043] (Second Modification) 4B is a schematic side view showing a retardation element 1B according to a second modified example of the first embodiment. In the retardation element 1B, a liquid crystal layer 113, an alignment layer 112, a liquid crystal layer 123, and an alignment layer 122 are arranged in this order along the traveling direction of light L. The liquid crystal layer 113 and the alignment layer 112 form a first retardation layer 11. The liquid crystal layer 123 and the alignment layer 122 form a second retardation layer 12. The retardation element 1B also provides substantially the same effects as the above-described retardation element 1.

[0044] (Third Modification) FIG. 4C is a schematic side view showing a retardation element 1C according to a third modified example of the first embodiment. In the retardation element 1C, a substrate 111, an alignment layer 112, a liquid crystal layer 113, an adhesive layer 13, a liquid crystal layer 123, and an alignment layer 122 are arranged in this order along the traveling direction of light L. The alignment layer 112 and the liquid crystal layer 113 form a first retardation layer 11. The liquid crystal layer 123 and the alignment layer 122 form a second retardation layer 12. The adhesive layer 13 bonds the first retardation layer 11 and the second retardation layer 12. An optical clear adhesive (OCA) or the like can be used for the adhesive layer 13. The retardation element 1C also provides substantially the same effects as the retardation element 1 described above.

[0045] (Fourth Modification) FIG. 4D is a schematic side view showing a retardation element 1D according to a fourth modified example of the first embodiment. The retardation element 1D shown in FIG. 4D includes an adhesive layer 13d, an alignment layer 112, a liquid crystal layer 113, an alignment layer 122, and a liquid crystal layer 123. In the retardation element 1D, the adhesive layer 13d, the alignment layer 112, the liquid crystal layer 113, the alignment layer 122, and the liquid crystal layer 123 are arranged in this order on a polarizer Pd along the traveling direction of light L. The alignment layer 112 and the liquid crystal layer 113 form the first retardation layer 11. The liquid crystal layer 123 and the alignment layer 122 form the second retardation layer 12. The polarizer Pd can extract linearly polarized light from the light L incident on the retardation element 1D. The adhesive layer 13d bonds the first retardation layer 11d and the polarizer Pd. The adhesive layer 13d is disposed between the liquid crystal layer 113 and the polarizer Pd. By providing the retardation element 1D with the adhesive layer 13d, for example, the first retardation layer 11 can be formed on an arbitrary substrate, and then peeled off from the substrate and attached to a polarizing plate Pd. Other effects of the retardation element 1D are almost the same as those of the retardation element 1 described above.

[0046] The substrates exemplified in FIGS. 4A, 4B, 4C, and 4D may have an adhesive layer on their surfaces. The adhesive strength of the adhesive layer may be 0.03 N / cm or more and 0.80 N / cm or less, preferably 0.04 N / cm or more and 0.70 N / cm or less, and more preferably 0.05 N / cm or more and 0.60 N / cm or less. An adhesive strength of 0.03 N / cm or more is sufficiently strong, so by setting the adhesive strength to 0.03 N / cm or more, sufficient durability can be obtained in a peel strength test. An adhesive strength of 0.80 N / cm or less is not too strong, so by setting the adhesive strength to 0.80 N / cm or less, handleability can be improved. Furthermore, by setting the adhesive strength to 0.80 N / cm or less, a special member as a protective member for the adhesive layer surface is not required when handling as an intermediate member, which makes it easier to select a protective member and is advantageous in terms of cost and process margin.

[0047] An example of how to measure the adhesive strength of an adhesive layer is shown below. The adhesive strength is measured as a value from a 180° peel test, as follows. A Tensilon (manufactured by A&D Corporation) is used as the testing machine, and the test specimen and measurement method follow JIS K 6854-2. The test environment is 23°C ± 2°C and 50% RH ± 10% RH. Specifically, the adhesive layer and the substrate portion on which the adhesive layer is formed are cut into a 25 mm wide and 300 mm long specimen. A PET (polyethylene terephthalate) substrate film is laminated onto the adhesive layer. 25 mm of the PET film is peeled from the edge of this specimen, and the peeled PET film is fixed to the jig of the testing machine, while the substrate with the adhesive layer is fixed to the other jig. The PET film fixed to the jig is peeled in the 180° direction at a load speed of 300 mm / min. After starting the peel measurement, ignore the measurements for the first 25 mm length, and thereafter, average the adhesive strength measurements for a length of 100 mm or more that has been peeled off from the test plate, and use this as the adhesive strength value [N / cm].

[0048] (Alignment of liquid crystal in retardation element 1) Next, the orientation of liquid crystal in the retardation element 1 will be described with reference to Fig. 5. Fig. 5 is a perspective view showing an example of the orientation of liquid crystal in the retardation element 1. The description will also refer to Fig. 1 and Fig. 3 as appropriate. Note that the retardation element 1 in Fig. 5 may be any one of retardation element 1A, retardation element 1B, retardation element 1C, and retardation element 1D.

[0049] The first retardation layer 11 and the second retardation layer 12 each contain a liquid crystal LQ. The materials of the liquid crystal LQ contained in the first retardation layer 11 and the second retardation layer 12 may be the same or different. The polarization direction of linearly polarized light L1 incident on the retardation element 1 is parallel to the X-axis.

[0050] The alignment axis direction pT1_1 represents the alignment axis direction pT of the liquid crystal LQ at the first interface 116 of the first retardation layer 11. The alignment axis direction pT of the liquid crystal LQ means the angle that the alignment axis of the liquid crystal LQ forms with the X axis in a plane along the incident surface 1a of the retardation element 1. The alignment axis direction pT1_1 substantially coincides with the angle that the alignment control direction of the alignment layer 112 forms with the X axis in a plane along the incident surface 1a. In other words, the alignment axis direction pT1_1 is substantially parallel to the direction in which the alignment layer 112 controls the alignment of the liquid crystal molecules. Hereinafter, the direction that controls the alignment of the liquid crystal molecules will be referred to as the alignment control direction.

[0051] The alignment axis direction pT1_2 represents the alignment axis direction of the liquid crystal LQ at the second interface 117 of the first retardation layer 11. The alignment axis direction pT1_2 substantially coincides with the angle that the alignment control direction of the alignment layer 114 makes with the X axis in a plane along the incident surface 1a. In other words, the alignment axis direction pT1_2 is substantially parallel to the alignment control direction of the alignment layer 114. In the first retardation layer 11, the alignment axis direction of the liquid crystal LQ is twisted from the alignment axis direction pT1_1 to the alignment axis direction pT1_2 between the first interface 116 and the second interface 117.

[0052] The alignment axis direction pT2_1 represents the alignment axis direction of the liquid crystal LQ at the first interface 116 of the second retardation layer 12. The alignment axis direction pT2_1 substantially coincides with the angle that the alignment control direction of the alignment layer 112 makes with the X-axis in the plane along the incident surface 1a. In other words, the alignment axis direction pT2_1 is substantially parallel to the alignment control direction of the alignment layer 112.

[0053] The alignment axis direction pT2_2 represents the alignment axis direction of the liquid crystal LQ at the second interface 117 of the second retardation layer 12. The alignment axis direction pT2_2 substantially coincides with the angle that the alignment control direction of the alignment layer 114 forms with respect to the X-axis in a plane along the incident surface 1a. In other words, the alignment axis direction pT2_2 is substantially parallel to the alignment control direction of the alignment layer 114. In the second retardation layer 12, the alignment axis direction of the liquid crystal LQ is twisted from the alignment axis direction pT2_1 to the alignment axis direction pT2_2 between the first interface 116 and the second interface 117. In the example shown in FIG. 5 , the liquid crystal LQ in each of the first retardation layer 11 and the second retardation layer 12 is twisted, but this is not limiting, and either the first retardation layer 11 or the second retardation layer 12 may be parallel aligned (not twisted). When the first retardation layer 11 is parallel-aligned, the alignment axis directions pT1_1 and pT1_2 are the same. When the second retardation layer 12 is parallel-aligned, the alignment axis directions pT2_1 and pT2_2 are the same.

[0054] <Configuration and Formation Method of Alignment Layer 114> Next, the structure and formation method of the alignment layer 114 will be described with reference to Fig. 6 and Fig. 7. Fig. 6 is a schematic perspective view illustrating an example of the alignment layer 114. Fig. 7 is a schematic view illustrating an example of the formation method of the alignment layer 114. The same structure and formation method can be applied to the alignment layer 112, the alignment layer 114, and the alignment layer 122. The following description will be given using the alignment layer 112 as a representative.

[0055] A surface 51 of the alignment layer 112 that contacts the liquid crystal layer 113 has, for example, a plurality of grooves 52 formed parallel to one another. The plurality of grooves 52 are formed, for example, in a stripe pattern. In top view, the longitudinal direction of the grooves 52 is the X direction, and the width direction of the grooves 52 is the Y direction. The longitudinal direction of the grooves 52 corresponds to the orientation of the alignment axis OD1.

[0056] The parallelism of the grooves 52 is, for example, 0° or more and 5° or less, and preferably 0° or more and 1° or less. The parallelism of the grooves 52 is the maximum value of the angle between two adjacent grooves 52 when viewed from above. The closer the angle between two adjacent grooves 52 is to 0°, the better the parallelism. The depth D of the grooves 52 is, for example, 3 nm or more and 500 nm or less, preferably 5 nm or more and 300 nm or less, and more preferably 10 nm or more and 150 nm or less. If the depth D is 3 nm or more, the alignment control force is strong and the liquid crystal molecules are easily aligned. On the other hand, if the depth D is 500 nm or less, the transferability of the concave-convex pattern of the mold is good. Furthermore, if the depth D is 500 nm or less, diffracted light is less likely to be generated. Thickness T1 is the thickness of the substrate 111. Thickness T2 is the thickness of the alignment layer 112.

[0057] The pitch p of the grooves 52 is, for example, 10 nm or more and 600 nm or less, preferably 50 nm or more and 300 nm or less, and more preferably 80 nm or more and 200 nm or less. If the pitch p is 600 nm or less, the alignment control force is strong and the liquid crystal molecules are easily aligned. Furthermore, if the pitch p is 300 nm or less, diffracted light is less likely to occur. On the other hand, if the pitch p is 10 nm or more, it is easy to form the concave-convex pattern of the mold.

[0058] The opening width W of the grooves 52 is, for example, 5 nm to 500 nm, preferably 20 nm to 200 nm, and more preferably 30 nm to 150 nm. The difference between the pitch p and the opening width W (pW: p>W) is the distance between the grooves 52.

[0059] 6, the cross-sectional shape of the groove 52 perpendicular to the longitudinal direction (X direction) is substantially rectangular, but it may also be substantially triangular. The shallower the depth of the groove 52 with a triangular cross section, the wider the width. In this case, it is easy to peel off the mold used in the imprint method.

[0060] The alignment layer 112 is a copolymer of an energy-curable composition. The energy-curable composition is a photocurable composition or a thermosetting composition. Photocurable compositions are particularly preferred because of their excellent processability, heat resistance, and durability. The photocurable composition is, for example, a composition containing a monomer, a photopolymerization initiator, a solvent, and optional additives (e.g., surfactant, polymerization inhibitor, antioxidant, UV absorber, light stabilizer, antifoaming agent). Examples of photocurable compositions that can be used include those described in paragraphs 0028 to 0060 of Japanese Patent No. 5978761.

[0061] As shown in FIG. 7 , the alignment layer 112 is formed, for example, by an imprinting method. In the imprinting method, an energy-curable composition 72 is sandwiched between a substrate 111 and a mold 71, the concave-convex pattern of the mold 71 is transferred to the energy-curable composition 72, and the energy-curable composition 72 is cured. Using the imprinting method allows for precise control of the dimensions and shape of the grooves 52 and reduces the risk of foreign matter contamination. The mold 71 can be made of a metal such as Ni or quartz glass. Using a transparent material such as quartz glass allows the alignment layer to be cured by UV exposure through the mold, thereby increasing the flexibility of process and material selection. The concave-convex pattern of the mold 71 can be formed by electron beam lithography, photolithography, mechanical processing, laser processing, or the like. The concave-convex pattern may be a fine parallel groove structure. To improve mold releasability, the mold surface may be subjected to a release treatment in which a release agent is applied. Examples of the release agent include Daikin's Optool-DSX.

[0062] The energy curable composition 72 may be applied onto the substrate 111, or may be applied onto the mold 71. The energy curable composition 72 may be applied by a method such as spin coating, bar coating, dip coating, casting, spray coating, bead coating, wire bar coating, blade coating, roller coating, curtain coating, slit die coating, gravure coating, slit reverse coating, microgravure coating, or comma coating.

[0063] The thickness T2 of the alignment layer 112 is, for example, 1 nm to 20 μm, preferably 50 nm to 10 μm, and more preferably 100 nm to 5 μm. The thickness T2 of the alignment layer 112 is measured in the normal direction at each point on the surface 41 of the substrate 111 on which the alignment layer 112 is formed. When the alignment layer 112 has grooves 52, the thickness T2 of the alignment layer 112 in this specification refers to the distance between the bottom of the grooves 52 and the surface 41 of the substrate 111. A thickness of 20 μm or less of the alignment layer 112 provides good processability. A thickness of 1 nm or more provides a strong alignment control force, making it easier to align the liquid crystal molecules. A thickness of 1 nm or more makes it easier to obtain a uniform film, with less unevenness during alignment layer formation.

[0064] The glass transition temperature Tg_al of the alignment layer 112 is, for example, 40°C or higher and 200°C or lower, preferably 60°C or higher and 180°C or lower, and more preferably 80°C or higher and 150°C or lower. If Tg_al is within the above range, the bending processability is good. The glass transition temperature of the alignment layer 112 is measured, for example, by TMA.

[0065] The alignment layer 112 is not limited to a so-called groove alignment, which includes a fine parallel groove structure. The alignment layer 112 may also be subjected to the following treatments. Examples of treatments that may be applied to the alignment layer 112 include rubbing of polyimide, photodecomposition of a silane coupling agent or polyimide by polarized UV irradiation, photodimerization or photoisomerization by polarized UV irradiation, flow alignment treatment by shear force, and alignment treatment by oblique deposition of inorganic materials. A combination of these treatments may also be used.

[0066] The alignment layer 112 may have any configuration and may be omitted. In that case, the base material 111 may be subjected to a treatment for aligning the liquid crystal LQ of the liquid crystal layer 113. Treatments for aligning the liquid crystal LQ include, for example, rubbing polyimide, photodecomposition of a silane coupling agent or polyimide by irradiation with polarized UV light, use of photodimerization or photoisomerization by irradiation with polarized UV light, flow alignment treatment using shear force, or alignment treatment by oblique deposition of an inorganic material.

[0067] The alignment layer 112 may be patterned into multiple regions with different alignment axis directions of the liquid crystal in the retardation layer. In the case of a fine parallel groove structure created by imprinting, the transferred alignment layer can also be patterned by patterning the groove direction of the original mold to be transferred. In the case of rubbing treatment, polarized UV irradiation, and oblique deposition of inorganic materials, patterning can be achieved, for example, by performing alignment treatment while covering the substrate with a metal mask having openings, and then shifting the openings to change the direction of alignment treatment in different regions. In the case of flow alignment treatment using shear force, patterning can be achieved, for example, by changing the movement of the shear-applying jig to change the direction of flow for each region.

[0068] <Method of Determining the Direction of the Alignment Axis in the Second Retardation Layer 12> Next, a method for determining the alignment axis direction pT2 of the second retardation layer 12 for converting the polarization state of light L incident on the retardation element 1 at a wide incidence angle and incidence azimuth angle with high ellipticity will be described. Note that the total twist amount Tw of the liquid crystal used in the following description is the difference between the alignment axis direction of the liquid crystal at one interface and the alignment axis direction of the liquid crystal at the other interface in the retardation layer, and is an amount expressed with a right-handed screw direction as positive.

[0069] (First example of a decision method) In a first example of the determination method, it is assumed that light L having a wavelength of 550 nm is perpendicularly incident on the retardation element 1 from below. In the first retardation layer 11, the retardation Re1 for light L having a wavelength of 550 nm is 90.0 nm. The total twist amount Tw of the liquid crystal LQ is 18.6°. In the second retardation layer 12, the retardation for light L having a wavelength of 550 nm is 244.7 nm. The total twist amount Tw of the liquid crystal LQ is -104.52°. In this case, in the first example of the determination method, the alignment axis direction pT of the second retardation layer 12 is determined so that the difference between the alignment axis direction pT1 of the first retardation layer 11 and the alignment axis direction pT of the second retardation layer 12 is -49.4°.

[0070] In a first example of the determination method, in the first retardation layer 11 seen from above, the reference direction Sd is the direction obtained by rotating the alignment axis direction pT1 of the first retardation layer 11 counterclockwise by 49.4°. In the second retardation layer 12 seen from above, the point at which the alignment axis direction pT2 of the second retardation layer 12 is equal to the reference direction Sd is defined as a first point U1, and when the amplitude is Am, the alignment axis direction pT2 of a second point U2 located in a direction rotated counterclockwise by a rotation angle θ around the first point U1 is expressed by the following formula (1). pT2=Am×sin(2×π×(θ+77.5) / 180) ···(1)

[0071] FIG. 8 is a diagram illustrating an example of the relationship between the reference direction Sd, the first point U1, and the second point U2. FIG. 8 shows the second retardation layer 12 in a top view. The dashed lines "0°," "90°," "180°," and "270°" represent incident angle azimuths. The reference direction Sd corresponds to the direction obtained by rotating the alignment axis direction pT1 of the first retardation layer 11 counterclockwise by 49.4°. The first point U1 is a point on the second retardation layer 12 where the alignment axis direction pT2 is equal to the reference direction Sd. The alignment axis OD2_1 is the alignment axis OD at the first point U1. The second point U2 is located in a direction obtained by rotating the first point U1 by a rotation angle θ counterclockwise. The alignment axis OD2_2 is the alignment axis OD at the second point U2. The orientation axis azimuth pT2 of the orientation axis OD2_2 is calculated by the above formula (1). The relationship between the reference direction Sd, the first point U1, and the second point U2 is the same in each example of the determination method shown below.

[0072] The retardation Re1 of the first retardation layer 11 is preferably 70.5 nm or more and 107.7 nm or less, more preferably 79.5 nm or more and 101.3 nm or less, and further preferably 87.2 nm or more and 97.5 nm or less.

[0073] The total twist amount Tw of the liquid crystal LQ in the first retardation layer 11 is preferably 6.0° or more and 27.0° or less, more preferably 10.0° or more and 24.0° or less, and even more preferably 14.0° or more and 21.0° or less.

[0074] The retardation Re2 of the second retardation layer 12 is preferably 193.7 nm or more and 265.5 nm or less, more preferably 211.6 nm or more and 256.5 nm or less, and further preferably 227.0 nm or more and 250.1 nm or less.

[0075] The magnitude of the total twist amount Tw of the liquid crystal LQ in the second retardation layer 12 is preferably -112.5° or more and -95.0° or less, more preferably -109.0° or more and -97.5° or less, and even more preferably -106.5° or more and -101.0° or less.

[0076] The value of the amplitude Am is preferably 7.5° or more and 24.0° or less, more preferably 10.0° or more and 22.0° or less, and even more preferably 13.0° or more and 19.0° or less.

[0077] The difference between the alignment axis direction pT1 of the first retardation layer 11 and the alignment axis direction pT2 of the second retardation layer 12 is preferably −60.9° or more and −38.9° or less, more preferably −58.9° or more and −40.9° or less, and even more preferably −55.9° or more and −42.9° or less.

[0078] The first point U1, which is the rotation center of the alignment axis direction pT2 of the second retardation layer 12, is preferably inclined from -11.5° to 10.5°, more preferably from -9.5° to 8.5°, and even more preferably from -6.5° to 6.5°, relative to the reference direction Sd.

[0079] By configuring the phase difference element 1 to the above values, the polarization state of incident light L can be converted with high ellipticity over a wide wavelength range from 460 nm to 630 nm, at incident angles from 0° to 50°, and at incident azimuth angles from 0° to 360°.

[0080] (Second example of determination method) In a second example of the determination method, it is assumed that light L having a wavelength of 550 nm is perpendicularly incident on the retardation element 1 from below. In the first retardation layer 11, the retardation Re1 for light L having a wavelength of 550 nm is 90.0 nm. The total twist amount Tw of the liquid crystal LQ is -18.6°. In the second retardation layer 12, the retardation for light L having a wavelength of 550 nm is 244.7 nm. The total twist amount Tw of the liquid crystal LQ is 104.52°. In this case, in the second example of the determination method, the alignment axis direction pT of the second retardation layer 12 is determined so that the difference between the alignment axis direction pT1 of the first retardation layer 11 and the alignment axis direction pT of the second retardation layer 12 is 49.4°.

[0081] In a second example of the determination method, in the first retardation layer 11 seen from above, the reference direction Sd is the direction obtained by rotating the alignment axis direction pT1 of the first retardation layer 11 counterclockwise by −49.4°. In the second retardation layer 12 seen from above, the point at which the alignment axis direction pT2 of the second retardation layer 12 is equal to the reference direction Sd is defined as a first point U1, and when the amplitude is Am, the alignment axis direction pT2 of a second point U2 located in a direction rotated counterclockwise by a rotation angle θ around the first point U1 is expressed by the following formula (2). pT2=Am×sin(2×π×(θ-77.5) / 180) ···(2)

[0082] The retardation Re1 of the first retardation layer 11 is preferably 70.5 nm or more and 107.7 nm or less, more preferably 79.5 nm or more and 101.3 nm or less, and further preferably 87.2 nm or more and 97.5 nm or less.

[0083] The total twist amount Tw of the liquid crystal LQ in the first retardation layer 11 is preferably −27.0° or more and −6.0° or less, more preferably −24.0° or more and −10.0° or less, and even more preferably −21.0° or more and −14.0° or less.

[0084] The retardation Re2 of the second retardation layer 12 is preferably 193.7 nm or more and 265.5 nm or less, more preferably 211.6 nm or more and 256.5 nm or less, and further preferably 227.0 nm or more and 250.1 nm or less.

[0085] The total twist amount Tw of the liquid crystal LQ in the second retardation layer 12 is preferably 95.0° or more and 112.5° or less, more preferably 97.5° or more and 109.0° or less, and even more preferably 101.0° or more and 106.5° or less.

[0086] The value of the amplitude Am is preferably 7.5° or more and 24.0° or less, more preferably 10.0° or more and 22.0° or less, and even more preferably 13.0° or more and 19.0° or less.

[0087] The difference between the alignment axis direction pT1 of the first retardation layer 11 and the alignment axis direction pT2 of the second retardation layer 12 is preferably 38.9° or more and 60.9° or less, more preferably 40.9° or more and 58.9° or less, and even more preferably 42.9° or more and 55.9° or less.

[0088] The first point U1, which is the rotation center of the alignment axis direction pT2 of the second retardation layer 12, is preferably inclined at an angle of -10.5° or more and 11.5° or less, more preferably -8.5° or more and 9.5° or less, and even more preferably -6.5° or more and 6.5° or less, relative to the reference direction Sd.

[0089] By configuring the phase difference element 1 to the above values, the polarization state of incident light L can be converted with high ellipticity over a wide wavelength range from 460 nm to 630 nm, at incident angles from 0° to 50°, and at incident azimuth angles from 0° to 360°.

[0090] (Third example of decision-making method) In a third example of the determination method, it is assumed that light L having a wavelength of 550 nm is perpendicularly incident on the retardation element 1 from below. In the first retardation layer 11, the retardation Re1 for light L having a wavelength of 550 nm is 103.0 nm. The total twist amount Tw of the liquid crystal LQ is 0.0°. In the second retardation layer 12, the retardation for light L having a wavelength of 550 nm is 246.2 nm. The total twist amount Tw of the liquid crystal LQ is -105.07°. In this case, in the third example of the determination method, the alignment axis direction pT of the second retardation layer 12 is determined so that the difference between the alignment axis direction pT1 of the first retardation layer 11 and the alignment axis direction pT of the second retardation layer 12 is -34.4°.

[0091] In a third example of the determination method, in the first retardation layer 11 seen from above, the reference direction Sd is the direction obtained by rotating the alignment axis direction pT1 of the first retardation layer 11 counterclockwise by 34.4°. In the second retardation layer 12 seen from above, the point at which the alignment axis direction pT2 of the second retardation layer 12 is equal to the reference direction Sd is defined as a first point U1, and when the amplitude is Am, the alignment axis direction pT2 of a second point U2 located in a direction rotated counterclockwise by a rotation angle θ around the first point U1 is expressed by the following formula (3). pT2=Am×sin(2×π×(θ+69.1) / 180) ···(3)

[0092] The retardation Re1 of the first retardation layer 11 is preferably 94.9 nm or more and 112.9 nm or less, more preferably 97.5 nm or more and 110.3 nm or less, and further preferably 100.0 nm or more and 107.7 nm or less.

[0093] The retardation Re2 of the second retardation layer 12 is preferably 220.6 nm or more and 255.2 nm or less, more preferably 228.3 nm or more and 251.4 nm or less, and further preferably 236.0 nm or more and 247.5 nm or less.

[0094] The magnitude of the total twist amount Tw of the liquid crystal LQ in the second retardation layer 12 is preferably -109.0° or more and -101.0° or less, more preferably -108.0° or more and -102.0° or less, and even more preferably -106.0° or more and -104.0° or less.

[0095] The value of the amplitude Am is preferably 1° or more and 9.5° or less, more preferably 2.5° or more and 8.5° or less, and even more preferably 3.5° or more and 7.5° or less.

[0096] The difference between the alignment axis direction pT1 of the first retardation layer 11 and the alignment axis direction pT2 of the second retardation layer 12 is preferably −38.9° or more and −29.9° or less, more preferably −37.9° or more and −30.9° or less, and even more preferably −36.9° or more and −31.9° or less.

[0097] The first point U1, which is the rotation center of the alignment axis direction pT2 of the second retardation layer 12, is preferably inclined at an angle of -4.5° or more and 4.5° or less, more preferably at an angle of -3.5° or more and 3.5° or less, and even more preferably at an angle of -2.5° or more and 2.5° or less, relative to the reference direction Sd.

[0098] By configuring the phase difference element 1 to the above values, the polarization state of incident light L can be converted with high ellipticity over a wide wavelength range from 460 nm to 630 nm, at incident angles from 0° to 30°, and at incident azimuth angles from 0° to 360°.

[0099] (Fourth example of determination method) In a fourth example of the determination method, it is assumed that light L having a wavelength of 550 nm is perpendicularly incident on the retardation element 1 from below. In the first retardation layer 11, the retardation Re1 for light L having a wavelength of 550 nm is 103.0 nm. The total twist amount Tw of the liquid crystal LQ is 0.0°. In the second retardation layer 12, the retardation for light L having a wavelength of 550 nm is 246.2 nm. The total twist amount Tw of the liquid crystal LQ is 105.07°. In this case, in the fourth example of the determination method, the alignment axis direction pT of the second retardation layer 12 is determined so that the difference between the alignment axis direction pT1 of the first retardation layer 11 and the alignment axis direction pT of the second retardation layer 12 is 34.4°.

[0100] In a fourth example of the determination method, in the first retardation layer 11 seen from above, the reference direction Sd is the direction obtained by rotating the alignment axis direction pT1 of the first retardation layer 11 counterclockwise by −34.4°. In the second retardation layer 12 seen from above, the point at which the alignment axis direction pT2 of the second retardation layer 12 is equal to the reference direction Sd is defined as a first point U1, and when the amplitude is Am, the alignment axis direction pT2 of a second point U2 located in a direction rotated counterclockwise by a rotation angle θ around the first point U1 is expressed by the following formula (4). pT2=Am×sin(2×π×(θ-69.1) / 180) ···(4)

[0101] The retardation Re1 of the first retardation layer 11 is preferably 94.9 nm or more and 112.9 nm or less, more preferably 97.5 nm or more and 110.3 nm or less, and further preferably 100.0 nm or more and 107.7 nm or less.

[0102] The retardation Re2 of the second retardation layer 12 is preferably 220.6 nm or more and 255.2 nm or less, more preferably 228.3 nm or more and 251.4 nm or less, and further preferably 236.0 nm or more and 247.5 nm or less.

[0103] The magnitude of the total twist amount Tw of the liquid crystal LQ in the second retardation layer 12 is preferably 101.0° or more and 109.0° or less, more preferably 102.0° or more and 108.0° or less, and even more preferably 104.0° or more and 106.0° or less.

[0104] The value of the amplitude Am is preferably 1.0° or more and 9.5° or less, more preferably 2.5° or more and 8.5° or less, and even more preferably 3.5° or more and 7.5° or less.

[0105] The difference between the alignment axis direction pT1 of the first retardation layer 11 and the alignment axis direction pT2 of the second retardation layer 12 is preferably 29.9° or more and 38.9° or less, more preferably 30.9° or more and 37.9° or less, and even more preferably 31.9° or more and 36.9° or less.

[0106] The first point U1, which is the rotation center of the alignment axis direction pT2 of the second retardation layer 12, is preferably inclined at an angle of -4.5° or more and 4.5° or less, more preferably at an angle of -3.5° or more and 3.5° or less, and even more preferably at an angle of -2.5° or more and 2.5° or less, relative to the reference direction Sd.

[0107] By configuring the phase difference element 1 to the above values, the polarization state of incident light L can be converted with high ellipticity over a wide wavelength range from 460 nm to 630 nm, at incident angles from 0° to 30°, and at incident azimuth angles from 0° to 360°.

[0108] (Fifth example of decision-making method) In a fifth example of the determination method, it is assumed that light L having a wavelength of 550 nm is perpendicularly incident on the retardation element 1 from below. In the first retardation layer 11, the retardation Re1 for light L having a wavelength of 550 nm is 108.6 nm. The total twist amount Tw of the liquid crystal LQ is 19.65°. In the second retardation layer 12, the retardation for light L having a wavelength of 550 nm is 243.8 nm. The total twist amount Tw of the liquid crystal LQ is −106.55°. In this case, in the fifth example of the determination method, the alignment axis direction pT of the second retardation layer 12 is determined so that the difference between the alignment axis direction pT1 of the first retardation layer 11 and the alignment axis direction pT of the second retardation layer 12 is −46.5°.

[0109] In a fifth example of the determination method, in the first retardation layer 11 seen from above, the reference direction Sd is the direction obtained by rotating the alignment axis direction pT1 of the first retardation layer 11 counterclockwise by 46.5°. In the second retardation layer 12 seen from above, the point at which the alignment axis direction pT2 of the second retardation layer 12 is equal to the reference direction Sd is the first point U1, and the alignment axis direction pT2 of the second point U2 located in a direction rotated counterclockwise by a rotation angle of −14.3° around the first point U1 is 11.7°.

[0110] The retardation Re1 of the first retardation layer 11 is preferably 79.5 nm or more and 138.5 nm or less, more preferably 84.6 nm or more and 130.8 nm or less, and further preferably 92.3 nm or more and 125.7 nm or less.

[0111] The total twist amount Tw of the liquid crystal LQ in the first retardation layer 11 is preferably 8.0° or more and 31.0° or less, more preferably 10.0° or more and 29.0° or less, and even more preferably 13.0° or more and 26.0° or less.

[0112] The retardation Re2 of the second retardation layer 12 is preferably 182.1 nm or more and 282.2 nm or less, more preferably 197.5 nm or more and 274.5 nm or less, and further preferably 209.0 nm or more and 270.6 nm or less.

[0113] The magnitude of the total twist amount Tw of the liquid crystal LQ in the second retardation layer 12 is preferably not less than -121.0° and not more than -94.0°, more preferably not less than -117.0° and not more than -97.0°, and even more preferably not less than -114.0° and not more than -100.0°.

[0114] The difference between the alignment axis direction pT1 of the first retardation layer 11 and the alignment axis direction pT2 of the second retardation layer 12 is preferably −57.7° or more and −34.7° or less, more preferably −55.7° or more and −37.7° or less, and even more preferably −53.7° or more and −39.7° or less.

[0115] The first point U1, which is the rotation center of the alignment axis direction pT2 of the second retardation layer 12, is preferably inclined at an angle of -11.3° or more and 11.7° or less, more preferably -9.3° or more and 8.7° or less, and even more preferably -7.3° or more and 6.7° or less, relative to the reference direction Sd.

[0116] The orientation axis direction pT2 of the second point U2 is preferably 2.7° or more and 19.7° or less, more preferably 4.7° or more and 17.7° or less, and even more preferably 6.7° or more and 15.7° or less.

[0117] By configuring the phase difference element 1 with the above values, the polarization state of incident light L can be converted with high ellipticity over a wide wavelength range from 460 nm to 630 nm and at incident angles from 30° to 60°.

[0118] (Sixth example of decision-making method) In a sixth example of the determination method, it is assumed that light L having a wavelength of 550 nm is perpendicularly incident on the retardation element 1 from below. In the first retardation layer 11, the retardation Re1 for light L having a wavelength of 550 nm is 108.6 nm. The total twist amount Tw of the liquid crystal LQ is -19.65°. In the second retardation layer 12, the retardation for light L having a wavelength of 550 nm is 243.8 nm. The total twist amount Tw of the liquid crystal LQ is 106.55°. In this case, in the sixth example of the determination method, the alignment axis direction pT of the second retardation layer 12 is determined so that the difference between the alignment axis direction pT1 of the first retardation layer 11 and the alignment axis direction pT of the second retardation layer 12 is 46.5°.

[0119] In a sixth example of the determination method, in the first retardation layer 11 seen from above, the reference direction Sd is the direction obtained by rotating the alignment axis direction pT1 of the first retardation layer 11 counterclockwise by −46.5°. In the second retardation layer 12 seen from above, the point at which the alignment axis direction pT2 of the second retardation layer 12 is equal to the reference direction Sd is the first point U1, and the alignment axis direction pT2 of the second point U2 located in a direction rotated counterclockwise by a rotation angle of 14.3° around the first point U1 is −11.7°.

[0120] The retardation Re1 of the first retardation layer 11 is preferably 79.5 nm or more and 138.5 nm or less, more preferably 84.6 nm or more and 130.8 nm or less, and further preferably 92.3 nm or more and 125.7 nm or less.

[0121] The magnitude of the total twist amount Tw of the liquid crystal LQ in the first retardation layer 11 is preferably not less than -31.0° and not more than -8.0°, more preferably not less than -29.0° and not more than -10.0°, and even more preferably not less than -26.0° and not more than -13.0°.

[0122] The retardation Re2 of the second retardation layer 12 is preferably 182.1 nm or more and 282.2 nm or less, more preferably 197.5 nm or more and 274.5 nm or less, and further preferably 209.0 nm or more and 270.6 nm or less.

[0123] The total twist amount Tw of the liquid crystal LQ in the second retardation layer 12 is preferably 94.0° or more and 121.0° or less, more preferably 97.0° or more and 117.0° or less, and even more preferably 100.0° or more and 114.0° or less.

[0124] The difference between the alignment axis direction pT1 of the first retardation layer 11 and the alignment axis direction pT2 of the second retardation layer 12 is preferably 34.7° or more and 57.7° or less, more preferably 37.7° or more and 55.7° or less, and even more preferably 39.7° or more and 53.7° or less.

[0125] The first point U1, which is the rotation center of the alignment axis direction pT2 of the second retardation layer 12, is preferably inclined from -11.7° to 11.3°, more preferably from -8.7° to 9.3°, and even more preferably from -6.7° to 7.3°, relative to the reference direction Sd.

[0126] The orientation axis direction pT2 of the second point U2 is preferably −19.7° or more and −2.7° or less, more preferably −17.7° or more and −4.7° or less, and even more preferably −15.7° or more and −6.7° or less.

[0127] By configuring the phase difference element 1 with the above values, the polarization state of incident light L can be converted with high ellipticity over a wide wavelength range from 460 nm to 630 nm and at incident angles from 30° to 60°.

[0128] In the first, second, fifth, and sixth examples, "preferably" means that the ellipticity ε is 0.7 or more, "more preferably" means that the ellipticity ε is 0.75 or more, and "even more preferably" means that the ellipticity ε is 0.8 or more. In the third and fourth examples, "preferably" means that the ellipticity ε is 0.85 or more, "more preferably" means that the ellipticity ε is 0.875 or more, and "even more preferably" means that the ellipticity ε is 0.9 or more.

[0129] <Example of orientation axis pT2> Next, various examples of the alignment axis direction pT2 that varies depending on the position in the plane in top view, which can be applied to the second retardation layer 12, will be described with reference to FIGS. 9 to 11, 12A and 12B.

[0130] (First example of orientation axis pT2) Fig. 9 is a diagram showing a first example of the alignment axis direction pT2 of the second retardation layer 12. Fig. 9 shows the second retardation layer 12 in a top view. Multiple arrows shown inside the second retardation layer 12 indicate alignment axes OD2 at the positions of the multiple arrows in the second retardation layer 12.

[0131] In the first example shown in FIG. 9, the alignment axis direction pT2 of the second retardation layer 12 changes monotonically in top view according to the change in position in the predetermined direction. On the other hand, in the direction perpendicular to the predetermined direction, the alignment axis direction pT2 of the second retardation layer 12 is consistent regardless of the position. In the first example shown in FIG. 9, the predetermined direction is the X direction, and the direction perpendicular to the predetermined direction is the Y direction. However, the predetermined direction is not limited to the X direction and may be any direction in the XY plane. The meanings of the predetermined direction and the direction perpendicular to the predetermined direction, as well as the fact that the predetermined direction and the direction perpendicular to the predetermined direction may be any direction in the XY plane, are the same in other examples of the alignment axis direction pT2 described below.

[0132] By arranging the orientation axis pT2 as in the first example shown in Figure 9, for example, in the case of oblique incidence from a linear light source as shown in Figure 14 described later, the polarization state of the incident light L can be converted with high ellipticity over the entire plane over a wide wavelength range from 460 nm to 630 nm.

[0133] (Second example of orientation axis pT2) Fig. 10 is a diagram showing a second example of the alignment axis direction pT2 of the second retardation layer 12. In the second example, an axis extending along the alignment axis OD2 at which the ellipticity becomes maximum when light is perpendicularly incident on the second retardation layer 12 is called a symmetry axis OD20. In the second example shown in Fig. 10, the alignment axis direction pT2 of the second retardation layer 12 monotonically changes symmetrically about a point OP on the symmetry axis OD20 in a predetermined direction as the position changes, when viewed from above, and is aligned regardless of the position in a direction perpendicular to the predetermined direction.

[0134] 10, the orientation axis OD21 located on the -X side of the point OP and the orientation axis OD22 located on the +X side correspond to orientation axes located symmetrically with respect to the point OP. The orientation of the orientation axis OD21 and the orientation of the orientation axis OD22 are aligned. Furthermore, the orientation of the orientation axis OD, which changes monotonically as it moves in the -X direction with respect to the point OP as the center, is aligned with the orientation of the orientation axis OD, which changes monotonically as it moves in the +X direction.

[0135] By arranging the orientation axis direction pT2 as in the second example shown in Figure 10, for example, when incident from directly below a linear light source as shown in Figure 22 described below, the polarization state of incident light L can be converted with high ellipticity over the entire plane over a wide wavelength range from 460 nm to 630 nm.

[0136] (Third example of orientation axis pT2) Fig. 11 is a diagram showing a third example of the alignment axis direction pT2 of the second retardation layer 12. In the third example shown in Fig. 11, the alignment axis directions pT2 of the second retardation layer 12 are aligned at positions that are point-symmetric about a point OP on the symmetry axis OD20 in top view.

[0137] 11 , an alignment axis OD21 positioned in the −X direction and the +Y direction with respect to a point OP and an alignment axis OD22 positioned in the +X direction and the −Y direction with respect to the point OP correspond to alignment axes positioned point-symmetrically with respect to the point OP. The orientations of the alignment axes OD21 and OD22 are the same. From another perspective, the alignment axis direction pT2 of the second retardation layer 12 changes continuously in the circumferential direction of a circle CR centered on the point OP on the symmetry axis OD20 in top view.

[0138] By arranging the orientation axis direction pT2 as in the third example shown in Figure 10, for example, when incident from directly below a point light source as shown in Figures 18A and 18B described below, the polarization state of incident light L can be converted with high ellipticity over the entire plane over a wide wavelength range from 460 nm to 630 nm.

[0139] (Fourth and fifth examples of orientation axis direction pT2) 12 is a diagram showing a fourth example of the alignment axis direction pT2 of the second retardation layer 12. FIG.

[0140] In the fourth and fifth examples, the second retardation layer 12 includes a plurality of regions Ar having different alignment axis directions pT2 in top view. The plurality of regions Ar are arranged in a mosaic pattern in top view. In the fourth example shown in FIG. 12 and the fifth example shown in FIG. 13, the alignment axis directions pT2 of the alignment axes OD are aligned inside each of the plurality of regions Ar in top view, regardless of the position in the plane. The alignment axis directions pT2 of each of the plurality of regions Ar differ depending on the position of each of the plurality of regions Ar in the plane in top view.

[0141] In a fourth example shown in FIG. 12 , each of the multiple regions Ar has a substantially rectangular outer edge shape in a top view. The multiple regions Ar are arranged in a matrix in a top view. In a top view, the orientation axis direction pT2 of the orientation axis OD is uniform inside a region Ar11 among the multiple regions Ar, regardless of the position in the plane. Similarly, in a top view, the orientation axis direction pT2 of the orientation axis OD is uniform inside a region Ar12 among the multiple regions Ar, regardless of the position in the plane. On the other hand, in a top view, the orientation axis direction pT2 of the orientation axis OD21 in the region Ar11 and the orientation axis direction pT2 of the orientation axis OD22 in the region Ar12 are different from each other.

[0142] By arranging the orientation axis direction pT2 as in the fourth example shown in Figure 12, for example, when incident from directly below a point light source as shown in Figures 18A and 18B described below, the polarization state of incident light L can be converted with high ellipticity over the entire plane over a wide wavelength range from 460 nm to 630 nm.

[0143] In the fourth example, the alignment axis directions pT2 of the regions Ar may vary monotonically among the regions Ar in accordance with the change in the position of the regions Ar in the predetermined direction in a top view, whereas the alignment axis directions pT2 of the regions Ar may be uniform in a direction perpendicular to the predetermined direction regardless of the position.

[0144] In addition, in the top view, the orientation axis directions pT2 of the multiple regions Ar according to the fourth example may change monotonically between the multiple regions Ar in a predetermined direction so as to be symmetrical about the point OP on the symmetry axis OD20 in response to changes in the positions of the regions Ar, whereas in a direction perpendicular to the predetermined direction, the orientation axis directions pT2 of the multiple regions Ar may be the same regardless of position.

[0145] Furthermore, the orientation axis directions pT2 of the regions Ar according to the fourth example may be the same among the regions Ar that are positioned point-symmetrically about the point OP on the symmetry axis OD20 in top view. From another perspective, the orientation axis directions pT2 of the regions Ar according to the fourth example may change continuously in the circumferential direction of a circle CR centered on the point OP on the symmetry axis OD20 in top view.

[0146] 13, the multiple regions Ar are arranged concentrically in a top view. Of the multiple regions Ar, region Ar21 is arranged in the center in a top view. Of the multiple regions Ar, regions Ar22 and Ar23 are arranged outside region Ar21 in a top view.

[0147] In the regions Ar21, Ar22, and Ar23, the orientation axis direction pT2 of the orientation axis OD is consistent regardless of the position in the plane when viewed from above. On the other hand, the orientation axis direction pT of the orientation axis OD21 in the region Ar21, the orientation axis direction pT2 of the orientation axis OD22 in the region Ar22, and the orientation axis direction pT2 of the orientation axis OD23 in the region Ar22 are different from one another.

[0148] Furthermore, the orientation axis directions pT2 of the regions Ar according to the fifth example may be the same among the regions Ar that are positioned point-symmetrically about the point OP on the symmetry axis OD20 in top view. From another perspective, the orientation axis directions pT2 of the regions Ar according to the fifth example may be continuously changed in the circumferential direction of a circle CR centered on the point OP on the symmetry axis OD20 in top view.

[0149] The arrangement of the multiple regions Ar in top view is not limited to a matrix or concentric circles, and may be, for example, a triangular lattice or a honeycomb lattice.

[0150] [Examples and Comparative Examples According to the First Embodiment] Examples and comparative examples will be described below, but the present invention is not limited to these examples.

[0151] <Simulation method> The extraordinary refractive index ne and ordinary refractive index no used in the simulation were obtained by applying the materials used for each of the first retardation layer 11 and the second retardation layer 12 to a quartz substrate and measuring each of them using a prism coupler.

[0152] In the simulation, the extended Jones matrix method was used to calculate the Stokes parameters (S0, S1, S2, S3) of polarized light transmitted through the polarizer Pd fixed to the first retardation layer 11, the first retardation layer 11, and the second retardation layer 12. Based on the Stokes parameters (S0, S1, S2, S3), the ellipticity ε was calculated using the following formula.

[0153]

number

[0154] <Example 1, Example 1-2, and Example 2 to Example 1-1-11> (Model M1) 14 is a schematic perspective view showing an example of a model M1 of the phase difference element 1 according to Examples 1, 1-2, and 2 to 1-1-11. Examples 1 and 1-2 are working examples, and Examples 2 to 1-1-11 are comparative examples.

[0155] In model M1, a linear light source SL was placed, and the retardation elements 1 according to Examples 1, 1-2, and 2 were placed diagonally above the linear light source SL. In the retardation elements 1 according to Examples 1, 1-2, and 2, a polarizing plate Pd was placed on the side where light L is incident from the linear light source SL, so that the X direction in which the linear light source SL extends and the transmission axis Dr of the polarizing plate Pd were parallel to each other. The outer edge shape of the retardation elements 1 according to Examples 1, 1-2, and 2 in top view was approximately rectangular.

[0156] The light L emitted from the linear light source SL is assumed to spread mainly in the Y direction. In FIG. 14, light L11 represents linear light extending in the X direction, emitted in a direction forming an angle K1 with respect to the Z axis, and incident on the +Y side end of the polarizer Pd. Light L12 represents linear light extending in the X direction, emitted in a direction forming an angle K2 with respect to the Z axis, and incident on the center of the polarizer Pd in ​​the Y direction. Light L13 represents linear light extending in the X direction, emitted in a direction forming an angle K3 with respect to the Z axis, and incident on the -Y side end of the polarizer Pd. In the simulation, the angle K1 was set to 60.0°, the angle K2 was set to 45.0°, and the angle K3 was set to 30.0°. In other words, in the model M1, the light L emitted from the linear light source SL is incident on the retardation element 1 at an incident angle of 30.0° or more and 60.0° or less. The orientation axis direction pT was defined as the angle with respect to the transmission axis Dr of the polarizing plate Pd.

[0157] In model M1, light L emitted from a linear light source SL passes through a polarizing plate Pd and then enters the first retardation layer 11 through a first interface 116 of the first retardation layer 11. The light L that has passed through the first retardation layer 11 passes through a second interface 117 of the first retardation layer 11 and enters the second retardation layer 12 through a third interface 126 of the second retardation layer 12. The light L that has passed through the first retardation layer 11 passes through a fourth interface 127 of the second retardation layer 12 and exits the second retardation layer 12. In the simulation, the Stokes parameters of light L that exits the second retardation layer 12 were calculated.

[0158] In Examples 1, 1-2, and 2 to 1-1-11, the configurations of the polarizing plate Pd, the first retardation layer 11, and the second retardation layer 12 were modeled as shown in Table 1 below.

[0159] [Table 1]

[0160] As shown in Table 1, the retardation elements 1 according to Examples 1 and 1-2 were configured such that a polarizing plate Pd, a first retardation layer 11, and a second retardation layer 12 were laminated in this order from the linear light source SL side. The alignment axis direction pT2 of the second retardation layer 12 according to Examples 1 and 2 was determined using the fifth and sixth examples of the method for determining the alignment axis direction pT2.

[0161] In the first retardation layer 11 in Examples 1 and 1-2, the retardation Re1 was made uniform for each wavelength. In addition, in the first retardation layer 11 in Example 1, the alignment axis direction pT1 was made uniform regardless of the position in the plane when viewed from above, and a twist of a total twist amount Tw1 was imparted to the liquid crystal in the thickness direction (Z direction) of the first retardation layer 11.

[0162] In the second retardation layer 12 in Examples 1 and 1-2, the retardation Re2 was made uniform for each wavelength. Furthermore, in the second retardation layer 12 of the retardation element 1 in Examples 1 and 1-2, the alignment axis direction pT2 was made different depending on the position in the plane when viewed from above. Corresponding to the first to fifth positions of the retardation element 1 described below with reference to FIG. 15, the alignment axis direction pT2 at each position was set to alignment axis direction pT21 to alignment axis direction pT25. Examples 1-1-2 to 1-1-11 were modeled in the same way as Example 1, and included one or more values ​​outside the ranges of the fifth and sixth examples of the method for determining the alignment axis direction pT2.

[0163] The retardation element 1 according to Example 2 was configured to include only a first retardation layer 11. In the first retardation layer 11 of the retardation element 1 in Example 2, the retardation Re1 was made uniform for each wavelength. Furthermore, in the first retardation layer 11 in Example 2, the alignment axis direction pT1 was made uniform regardless of the position in the plane when viewed from above.

[0164] Fig. 15 is a diagram showing the alignment axis direction pT2 of the second retardation layer 12 in the retardation element 1 according to Example 1. In Fig. 15, the distribution of the alignment axis direction pT2 at each position in the plane of the second retardation layer 12 is expressed by differences in the density of dot hatching when viewed from above. In Fig. 15, arrows displayed near the color scale are displayed to indicate the correspondence between the density of dot hatching on the color scale and the alignment axis direction pT2.

[0165] 15, point P1 represents the first position, point P2 represents the second position, point P3 represents the third position, point P4 represents the fourth position, and point P5 represents the fifth position. As shown in Fig. 15, the alignment axis direction pT2 of the retardation element 1 according to Example 1 changes monotonically in the Y direction.

[0166] (Simulation results) Fig. 16 is a diagram showing the ellipticity ε at a wavelength of 550 nm of the retardation element 1 according to Example 1. Fig. 17 is a diagram showing the ellipticity ε at a wavelength of 550 nm of the retardation element 1 according to Example 2. In each diagram, the distribution of the ellipticity ε of the retardation element 1 in top view is expressed by differences in the density of dot hatching.

[0167] Tables 2A and 2B show the ellipticity ε for each wavelength at the first position to the fifth position of the phase difference element 1 according to Example 1 and Example 1-2, the ellipticity ε for each wavelength at the first position to the fifth position of the phase difference element 1 according to Example 2, and the ellipticity ε for each wavelength at each of two positions of the phase difference element 1 according to Examples 1-1-2 to 1-1-11. The first position to the fifth position of the phase difference element 1 according to Examples 1, 1-2, and 2 to 1-1-11 correspond to points P1 to P5 shown in FIG.

[0168] [Table 2A]

[0169] [Table 2B]

[0170] In the retardation element 1 of Example 1, a high ellipticity ε of 0.890 or more was obtained at any position in the plane when viewed from above. Also, in the retardation element 1 of Example 1, a high ellipticity ε of 0.890 or more was obtained at any wavelength. In other words, it can be seen that a high ellipticity can be obtained over a wide wavelength range in the visible range. Example 1-2 provides the same results as Example 1.

[0171] On the other hand, in the phase difference element 1 according to Example 2, the difference in ellipticity ε increased depending on the position in the plane in the Y direction when viewed from above. The range of ellipticity ε was 0.744 or more and 0.953 or less. Furthermore, in the phase difference element 1 according to Example 2, the difference in ellipticity ε for each wavelength increased. In the phase difference elements 1 according to Examples 1-1-2 to 1-1-11, the ellipticity ε changed depending on the position in the plane in the Y direction when viewed from above, and the minimum in-plane ellipticity ε was less than 0.7.

[0172] From the above, it was found that in the phase difference elements 1 according to Examples 1 and 1-2, in model M1 in which light L emitted from a linear light source SL is incident on the phase difference element 1 at an incident angle of 30.0° or more and 60.0° or less, the ellipticity of the elliptically polarized light emitted from the phase difference element 1 can be made to have a high ellipticity ε over the entire wavelength range of visible light.

[0173] <Example 3 to Example 2-1-11, Example 3' to Example 2-1-11'> (Model M2-1) A model M2-1 of the phase difference element 1 according to Examples 3 to 2-1-11 and Examples 3' to 2-1-11' will be described with reference to Figs. 18A and 18B. Examples 3 and 3' are working examples, and Examples 4 to 2-1-11 and Examples 4' to 2-1-11' are comparative examples. Fig. 18A is a schematic top view showing the model M2-1 of the phase difference element 1. Fig. 18B is a first schematic side view showing the model M2-1 of the phase difference element 1.

[0174] In model M2-1, a point light source SP was placed, and a retardation element 1 according to Example 3 to Example 2-1-11' was placed directly above the point light source SP. Each of the retardation elements 1 according to Examples 3 to 2-1-11' had a substantially circular outer edge shape when viewed from above. In the retardation elements 1 according to Examples 3 to 2-1-11', a polarizing plate Pd was placed on the side where light L from the point light source SP is incident, so that the X direction and the transmission axis Dr of the polarizing plate Pd were parallel. The radius Rd of the retardation element 1 when viewed from above was 50.0 mm.

[0175] The light L emitted from the point light source SP was assumed to spread spherically around the point light source SP. The model also assumed that the light L emitted from the point light source was incident on a retardation element 1 integrated with a polarizing plate Pd at an incident angle of 0.0° or more and 50.0° or less. The orientation axis direction was the angle relative to the transmission axis Dr of the polarizing plate Pd.

[0176] In model M2-1, light L emitted from a point light source SP passes through a polarizing plate Pd and then enters the first retardation layer 11 through a first interface 116 of the first retardation layer 11. The light L that has passed through the first retardation layer 11 passes through a second interface 117 of the first retardation layer 11 and enters the second retardation layer 12 through a third interface 126 of the second retardation layer 12. The light L that has passed through the first retardation layer 11 passes through a fourth interface 127 of the second retardation layer 12 and exits the second retardation layer 12. In the simulation, the Stokes parameters of the light L that exits the second retardation layer 12 were calculated.

[0177] In Examples 3 and 4 to 2-1-11, the configurations of the polarizing plate Pd, the first retardation layer 11, and the second retardation layer 12 were modeled as shown in Table 3A below. In Examples 3' to 2-1-11', the configurations of the polarizing plate Pd, the first retardation layer 11, and the second retardation layer 12 were modeled as shown in Table 3B below.

[0178] [Table 3A]

[0179] [Table 3B]

[0180] As shown in Table 3A, the retardation element 1 according to Example 3 had a configuration in which a polarizing plate Pd, a first retardation layer 11, and a second retardation layer 12 were laminated in this order from the point light source SP side. The alignment axis direction pT2 of the second retardation layer 12 was determined using the first example of the method for determining the alignment axis direction pT2.

[0181] As shown in Table 3B, the retardation element 1 according to Example 3' had a configuration in which a polarizing plate Pd, a first retardation layer 11, and a second retardation layer 12 were laminated in this order from the point light source SP side. The second example of the method for determining the alignment axis direction pT2 was used to determine the alignment axis direction pT2 of the second retardation layer 12.

[0182] In the first retardation layer 11 in Examples 3 and 3', the retardation Re1 was made uniform for each wavelength. In addition, in the first retardation layer 11 in Examples 3 and 3', the alignment axis direction pT1 was made uniform regardless of the position in the plane when viewed from above, and a twist of a total twist amount Tw1 was imparted to the liquid crystal in the thickness direction (Z direction) of the first retardation layer 11.

[0183] In the second retardation layer 12 in Examples 3 and 3′, the retardation Re2 was made uniform for each wavelength. In addition, in the second retardation layer 12 of the retardation element 1 in Examples 3 and 3′, the alignment axis direction pT2 was made different depending on the position in the plane when viewed from above.

[0184] In the modeling of Table 3A, the alignment axis direction pT2 at each position is set to the alignment axis direction pT21 to the alignment axis direction pT26, corresponding to the first to sixth positions of the retardation element 1, which will be described later with reference to FIG. 19A. In the modeling of Table 3B, the alignment axis direction pT2 at each position is set to the alignment axis direction pT21 to the alignment axis direction pT26, corresponding to the first to sixth positions of the retardation element 1, which will be described later with reference to FIG. 19B. Examples 2-1-2 to 2-1-11 are modeled similarly to Example 3, but include one or more values ​​outside the range of the first example of the method for determining the alignment axis direction pT2. Examples 2-1-2' to 2-1-11' are modeled similarly to Example 3', but include one or more values ​​outside the range of the second example of the method for determining the alignment axis direction pT2.

[0185] The retardation elements 1 according to Examples 4 and 4' were configured to include only a first retardation layer 11. In the first retardation layer 11 of the retardation elements 1 in Examples 4 and 4', the retardation Re1 for each wavelength was made uniform. Furthermore, in the first retardation layer 11 in Examples 4 and 4', the alignment axis direction pT1 was made uniform regardless of the position in the plane when viewed from above.

[0186] FIG. 19A is a diagram showing the alignment axis direction pT2 of the second retardation layer 12 in the retardation element 1 according to Example 3. In FIG. 19A, the distribution of the alignment axis direction pT2 at each position in the plane of the second retardation layer 12 is expressed by the difference in the density of dot hatching when viewed from above. In FIG. 19A, arrows displayed near the color scale are displayed to indicate the correspondence between the density of dot hatching on the color scale and the alignment axis direction pT2. Point P1 represents the first position, point P2 represents the second position, point P3 represents the third position, point P4 represents the fourth position, point P5 represents the fifth position, and point P6 represents the sixth position. FIG. 19B and Example 3' have similar relationships.

[0187] 19A, the numerical values ​​between 0° and 330° shown around the phase difference element 1 represent the incident azimuth angles. At incident azimuth angles of 60° and 240°, the orientation axis direction pT2 gradually increases from the center of the phase difference element 1 toward the periphery. On the other hand, at incident azimuth angles of 0° and 150°, the orientation axis direction pT2 gradually decreases from the center of the phase difference element 1 toward the periphery.

[0188] 19B, the numerical values ​​between 0° and 330° shown around the phase difference element 1 represent the incident azimuth angles. At incident azimuth angles of 30° and 180°, the alignment axis direction pT2 gradually increases from the center of the phase difference element 1 toward the periphery. On the other hand, at incident azimuth angles of 120° and 300°, the alignment axis direction pT2 gradually decreases from the center of the phase difference element 1 toward the periphery.

[0189] (Simulation results) Fig. 20A is a graph showing the ellipticity ε of the phase difference element 1 according to Example 3 at a wavelength of 550 nm. Fig. 20B is a graph showing the ellipticity ε of the phase difference element 1 according to Example 3' at a wavelength of 550 nm. Fig. 21 is a graph showing the ellipticity ε of the phase difference element 1 according to Example 4 at a wavelength of 550 nm. In each graph, the distribution of the ellipticity ε of the phase difference element 1 in top view is expressed by differences in the density of dot hatching.

[0190] Tables 4A and 4B show the ellipticity ε for each wavelength at the first to fifth positions of the phase difference element 1 according to Example 3, the ellipticity ε for each wavelength at the first to fifth positions of the phase difference element 1 according to Example 4, and the ellipticity ε for each wavelength at each of two positions of the phase difference elements 1 according to Examples 2-1-2 to 2-1-11. The first to sixth positions of the phase difference elements 1 according to Examples 3 and 4 to 2-1-11 correspond to points P1 to P6 shown in FIG. 19A.

[0191] Tables 4C and 4D show the ellipticity ε for each wavelength at the first to fifth positions of the phase difference element 1 according to Example 3', the ellipticity ε for each wavelength at the first to fifth positions of the phase difference element 1 according to Example 4', and the ellipticity ε for each wavelength at each of two positions of the phase difference element 1 according to Examples 2-1-2' to 2-1-11'. The first to sixth positions of the phase difference elements 1 according to Examples 3' and 4' to 2-1-11' correspond to points P1 to P6 shown in FIG. 19B.

[0192] [Table 4A]

[0193] [Table 4B]

[0194] [Table 4C]

[0195] [Table 4D]

[0196] In the retardation elements 1 according to Examples 3 and 3', a high ellipticity ε of 0.840 or more was obtained at any position in the plane when viewed from above. Furthermore, in the retardation elements 1 according to Examples 3 and 3', a high ellipticity ε of 0.840 or more was obtained at any wavelength. In other words, it can be seen that a high ellipticity can be obtained over a wide wavelength range in the visible range.

[0197] On the other hand, in the phase difference elements 1 of Examples 4 and 4', the difference in ellipticity ε increased depending on the position in the plane in the Y direction when viewed from above. The range of ellipticity ε was 0.503 or more and 0.991 or less. Furthermore, in the phase difference elements 1 of Examples 4 and 4', the difference in ellipticity ε for each wavelength increased. In the phase difference elements 1 of Examples 2-1-2 to 2-1-11 and Examples 2-1-2' to 2-1-11', the ellipticity ε changed depending on the position in the plane when viewed from above, and the minimum in-plane ellipticity ε was less than 0.7.

[0198] From the above, it was found that in the phase difference elements 1 of Examples 3 and 3', in model M2-1 in which light L emitted from a point light source SP is incident on the phase difference element 1 at an incident angle of 0.0° or more and 50.0° or less, the ellipticity of the elliptically polarized light emitted from the phase difference element 1 can be made to have a high ellipticity ε over the entire wavelength range of visible light.

[0199] <Example 2-2 to Example 2-1-9, and Example 2-2' to Example 2-1-9'> (Model M2-2) Model M2-2 of the phase difference element 1 according to Examples 2-2 to 2-1-9 and Examples 2-2' to 2-1-9' will be described with reference to FIGS. 18A and 18C. Examples 2-2 and 2-2' are working examples, and Examples 2-2-1 to 2-1-9 and Examples 2-2-1' to 2-1-9' are comparative examples. A schematic top view of model M2-2 of the phase difference element 1 is the same as the schematic top view of model M21-2 of the phase difference element 1. FIG. 18C is a schematic side view showing model M2-2 of the phase difference element 1.

[0200] In model M2-2, a point light source SP was placed, and a retardation element 1 according to Examples 2-2 to 2-1-9' was placed directly above the point light source SP. Each of the retardation elements 1 according to Examples 2-2 to 2-1-9' had a substantially circular outer edge shape when viewed from above. In the retardation elements 1 according to Examples 2-2 to 2-1-9', a polarizing plate Pd was placed on the side where light L from the point light source SP is incident, so that the X direction and the transmission axis Dr of the polarizing plate Pd were parallel. The radius Rd of the retardation element 1 when viewed from above was 30.0 mm.

[0201] The light L emitted from the point light source SP was assumed to spread spherically around the point light source SP. The model also assumed that the light L emitted from the point light source was incident on a retardation element 1 integrated with a polarizing plate Pd at an incident angle of 0.0° or more and 30.0° or less. The orientation axis direction was the angle relative to the transmission axis Dr of the polarizing plate Pd.

[0202] In model M2-2, light L emitted from the point light source SP passes through the polarizing plate Pd and then enters the first retardation layer 11 through the first interface 116 of the first retardation layer 11. The light L that has passed through the first retardation layer 11 passes through the second interface 117 of the first retardation layer 11 and enters the second retardation layer 12 through the third interface 126 of the second retardation layer 12. The light L that has passed through the first retardation layer 11 passes through the fourth interface 127 of the second retardation layer 12 and exits the second retardation layer 12. In the simulation, the Stokes parameters of the light L that exits the second retardation layer 12 were calculated.

[0203] In Examples 2-2 to 2-2-9, the polarizer Pd, the first retardation layer 11, and the second retardation layer 12 were modeled as shown in Table 4E below. In Examples 2-2' to 2-2-9', the polarizer Pd, the first retardation layer 11, and the second retardation layer 12 were modeled as shown in Table 4F below.

[0204] [Table 4E]

[0205] [Table 4F]

[0206] As shown in Table 4E, the retardation element 1 according to Example 2-2 had a configuration in which a polarizing plate Pd, a first retardation layer 11, and a second retardation layer 12 were laminated in this order from the point light source SP side. The alignment axis direction pT2 of the second retardation layer 12 was determined using the third example of the method for determining the alignment axis direction pT2. As shown in Table 4F, the retardation element 1 according to Example 2-2' had a configuration in which a polarizing plate Pd, a first retardation layer 11, and a second retardation layer 12 were laminated in this order from the point light source SP side. The alignment axis direction pT2 of the second retardation layer 12 was determined using the fourth example of the method for determining the alignment axis direction pT2.

[0207] In the first retardation layer 11 in Examples 2-2 and 2-2', the retardation Re1 was made uniform for each wavelength. In addition, in the first retardation layer 11 in Examples 2-2 and 2-2', the alignment axis direction pT1 was made uniform regardless of the position in the plane when viewed from above, and a twist of a total twist amount Tw1 was given to the liquid crystal in the thickness direction (Z direction) of the first retardation layer 11.

[0208] In Examples 2-2 and 2-2', the second retardation layer 12 had the same retardation Re2 for each wavelength. In addition, in Examples 2-2 and 2-2', the second retardation layer 12 of the retardation element 1 had different alignment axis directions pT2 depending on the in-plane position when viewed from above. In the modeling of Table 4E, the alignment axis directions pT2 at each position were set to alignment axis directions pT21 to pT25, corresponding to the first to fifth positions of the retardation element 1 described later with reference to FIG. 19C. In the modeling of Table 4F, the alignment axis directions pT2 at each position were set to alignment axis directions pT21 to pT25, corresponding to the first to fifth positions of the retardation element 1 described later with reference to FIG. 19D. Examples 2-2-2 to 2-1-9 were modeled similarly to Example 2-2, but included one or more values ​​outside the range of the third example of the method for determining the alignment axis direction pT2. Example 2-2-2' to Example 2-1-9' are modeling similar to Example 2-2', and include one or more values ​​outside the range of the fourth example of the method for determining the orientation axis direction pT2.

[0209] The retardation elements 1 according to Examples 2-2-1 and 2-2-1' were configured to include only a first retardation layer 11. In the first retardation layers 11 of the retardation elements 1 in Examples 2-2-1 and 2-2-1', the retardation Re1 for each wavelength was made uniform. Furthermore, in the first retardation layers 11 in Examples 2-2-1 and 2-2-1', the alignment axis direction pT1 was made uniform regardless of the position in the plane when viewed from above.

[0210] FIG. 19C is a diagram showing the alignment axis direction pT2 of the second retardation layer 12 in the retardation element 1 according to Example 2-2. In FIG. 19C, the distribution of the alignment axis direction pT2 at each position in the plane of the second retardation layer 12 is expressed by the difference in the density of dot hatching when viewed from above. In FIG. 19*, the arrows displayed near the color scale are displayed to indicate the correspondence between the density of dot hatching on the color scale and the alignment axis direction pT2. Point P1 represents the first position, point P2 represents the second position, point P3 represents the third position, point P4 represents the fourth position, and point P5 represents the fifth position. FIG. 19D and Example 2-2′ have the same relationship.

[0211] 19C, the numerical values ​​between 0° and 330° shown around the phase difference element 1 represent the incident azimuth angles. At incident azimuth angles of 60° and 240°, the alignment axis direction pT2 gradually increases from the center of the phase difference element 1 toward the outside. On the other hand, at incident azimuth angles of 0° and 150°, the alignment axis direction pT2 gradually decreases from the center of the phase difference element 1 toward the outside.

[0212] 19D, the numerical values ​​between 0° and 330° shown around the phase difference element 1 represent the incident azimuth angles. At incident azimuth angles of 0° and 30°, the alignment axis direction pT2 gradually increases from the center of the phase difference element 1 toward the outside. On the other hand, at incident azimuth angles of 120° and 300°, the alignment axis direction pT2 gradually decreases from the center of the phase difference element 1 toward the outside.

[0213] Tables 4G and 4J show the ellipticity ε for each wavelength at the first to fifth positions of the phase difference element 1 according to Example 2-2, the ellipticity ε for each wavelength at the first to fifth positions of the phase difference element 1 according to Comparative Example 2-2-1, and the ellipticity ε for each wavelength at each of two positions of the phase difference elements 1 according to Examples 2-2-2 to 2-2-9. The first to fifth positions of the phase difference elements 1 according to Examples 2-2 to 2-2-9 correspond to points P1 to P5 shown in FIG. 19C.

[0214] Tables 4K and 4L show the ellipticity ε for each wavelength at the first to fifth positions of the phase difference element 1 according to Example 2-2', the ellipticity ε for each wavelength at the first to fifth positions of the phase difference element 1 according to Comparative Example 2-2-1', and the ellipticity ε for each wavelength at each of two positions of the phase difference element 1 according to Examples 2-2-2' to 2-2-9'. The first to fifth positions of the phase difference element 1 according to Examples 2-2' to 2-2-9' correspond to points P1 to P5 shown in FIG. 19D.

[0215] [Table 4G]

[0216] [Table 4J]

[0217] [Table 4K]

[0218] [Table 4L]

[0219] In the retardation elements 1 according to Examples 2-2 and 2-2', a high ellipticity ε of 0.920 or more was obtained at any position in the plane when viewed from above. Also, in the retardation elements 1 according to Examples 2-2 and 2-2', a high ellipticity ε of 0.920 or more was obtained at any wavelength. That is, it can be seen that a high ellipticity can be obtained over a wide wavelength range in the visible range.

[0220] On the other hand, in the phase difference elements 1 according to Comparative Example 2-2-1 and Example 2-2-1', the difference in ellipticity ε increased depending on the position in the plane in the Y direction when viewed from above. The range of ellipticity ε was 0.725 or more and 0.991 or less. Furthermore, in the phase difference elements 1 according to Examples 2-2-1 and 2-2-1', the difference in ellipticity ε for each wavelength increased. In the phase difference elements 1 according to Examples 2-2-2 to 2-2-9 and Examples 2-2-2' to 2-2-9', the ellipticity ε changed depending on the position in the plane when viewed from above, and the minimum in-plane ellipticity ε was less than 0.81.

[0221] From the above, it was found that in the phase difference elements 1 of Examples 2-2 and 2-2', in model M2-2 in which light L emitted from a point light source SP is incident on the phase difference element 1 at an incident angle of 0.0° or more and 30.0° or less, the ellipticity of the elliptically polarized light emitted from the phase difference element 1 can be made to have a high ellipticity ε over the entire wavelength range of visible light.

[0222] <Example 5, Example 5-2, and Example 6 to Example 3-1-8> (Model M3) 22 is a schematic perspective view showing a model M3 of the phase difference element 1 according to Examples 5, 5-2, and 6 to 3-1-8. Note that Example 5 is an example, and Examples 6 to 3-1-8 are comparative examples.

[0223] In model M3, a linear light source SL was placed, and the retardation elements 1 according to Examples 5, 5-2, and 6 to 3-1-8 were placed directly above the linear light source SL. In the retardation elements 1 according to Examples 5, 5-2, and 6 to 3-1-8, a polarizer Pd was placed on the side where light L is incident from the linear light source SL so that the X direction in which the linear light source SL extends and the transmission axis Dr of the polarizer Pd were perpendicular to each other. The outer edge shape of the retardation elements 1 according to Examples 5, 5-2, and 6 to 3-1-8 in top view was approximately rectangular.

[0224] The light L emitted from the linear light source SL was assumed to spread mainly in the Y direction. In model M3, the light L emitted from the linear light source SL was assumed to be incident on the retardation element 1 at an incident angle of 50.0° or less. The orientation axis direction was set at an angle relative to the transmission axis Dr of the polarizing plate Pd.

[0225] In model M3, light L emitted from a linear light source SL passes through a polarizing plate Pd and then enters the first retardation layer 11 through a first interface 116 of the first retardation layer 11. The light L transmitted through the first retardation layer 11 passes through a second interface 117 of the first retardation layer 11 and enters the second retardation layer 12 through a third interface 126 of the second retardation layer 12. The light L transmitted through the first retardation layer 11 passes through a fourth interface 127 of the second retardation layer 12 and exits the second retardation layer 12. In the simulation, the Stokes parameters of light L exiting the second retardation layer 12 were calculated.

[0226] In Examples 5, 5-2, and 6 to 3-1-8, the configurations of the polarizing plate Pd, the first retardation layer 11, and the second retardation layer 12 were modeled as shown in Table 5 below.

[0227] [Table 5]

[0228] As shown in Table 5, the retardation elements 1 according to Examples 5 and 5-2 were configured such that a polarizing plate Pd, a first retardation layer 11, and a second retardation layer 12 were laminated in this order from the linear light source SL side. The alignment axis direction pT2 of the second retardation layer 12 was determined using the first and second examples of the method for determining the alignment axis direction pT2.

[0229] In the first retardation layer 11 in Examples 5 and 5-2, the retardation Re1 was made uniform for each wavelength. In addition, in the first retardation layer 11 in Examples 5 and 5-2, the alignment axis direction pT1 was made uniform regardless of the position in the plane when viewed from above, and a twist of a total twist amount Tw1 was imparted to the liquid crystal in the thickness direction (Z direction) of the first retardation layer 11.

[0230] In the second retardation layer 12 in Example 5 and Example 5-2, the retardation Re2 was made uniform for each wavelength. Furthermore, in the second retardation layer 12 of the retardation element 1 in Example 5, the alignment axis direction pT2 was made different depending on the position in the plane when viewed from above. The alignment axis directions pT2 at each position were set to alignment axis directions pT21 to pT25, corresponding to the first to fifth positions of the retardation element 1 described below with reference to FIG. 23. Examples 3-1-2 to 3-1-8 are modeled in the same way as Example 5, and include one or more values ​​outside the ranges of the first and second examples of the method for determining the alignment axis direction pT2.

[0231] The retardation element 1 according to Example 6 was configured to include only a first retardation layer 11. In the first retardation layer 11 of the retardation element 1 according to Example 6, the retardation Re1 was uniform for each wavelength. Furthermore, in the first retardation layer 11 according to Example 6, the alignment axis direction pT1 was uniform regardless of the position in the plane when viewed from above.

[0232] Fig. 23 is a diagram showing the alignment axis direction pT2 of the second retardation layer 12 in the retardation element 1 according to Example 5. In Fig. 23, the distribution of the alignment axis direction pT2 at each position in the plane of the second retardation layer 12 is expressed by differences in the density of dot hatching when viewed from above. In Fig. 23, arrows displayed near the color scale are displayed to indicate the correspondence between the density of dot hatching on the color scale and the alignment axis direction pT2.

[0233] 23, point P1 represents the first position, point P2 represents the second position, point P3 represents the third position, point P4 represents the fourth position, and point P5 represents the fifth position. As shown in Fig. 23, the alignment axis direction pT2 of the retardation element 1 according to Example 5 changes monotonically in the X direction.

[0234] (Simulation results) Fig. 24 is a diagram showing the ellipticity ε of the retardation element 1 according to Example 5 at a wavelength of 550 nm. Fig. 25 is a diagram showing the ellipticity ε of the retardation element 1 according to Example 6 at a wavelength of 550 nm. In each diagram, the distribution of the ellipticity ε of the retardation element 1 in top view is expressed by differences in the density of dot hatching.

[0235] Tables 6A and 6B show the ellipticity ε for each wavelength at the first position to the fifth position of the phase difference element 1 according to Example 5 and Example 5-2, the ellipticity ε for each wavelength at the first position to the fifth position of the phase difference element 1 according to Example 6, and the ellipticity ε for each wavelength at each of two positions of the phase difference element 1 according to Examples 3-1-2 to 2-1-8. Note that the first position to the fifth position of the phase difference element 1 according to Example 5, Example 5-2, and Examples 6 to 3-1-8 correspond to points P1 to P5 shown in FIG.

[0236] [Table 6A]

[0237] [Table 6B]

[0238] In the retardation element 1 of Example 5, a high ellipticity ε of 0.880 or more was obtained at any position in the plane when viewed from above. Also, in the retardation element 1 of Example 5, a high ellipticity ε of 0.880 or more was obtained at any wavelength. In other words, it can be seen that a high ellipticity can be obtained over a wide wavelength range in the visible range. Example 5-2 provides the same results as Example 5.

[0239] On the other hand, in the phase difference element 1 according to Example 6, the difference in ellipticity ε increased depending on the position in the plane in the Y direction when viewed from above. The range of ellipticity ε was 0.749 or more and 0.991 or less. Furthermore, in the phase difference element 1 according to Example 6, the difference in ellipticity ε for each wavelength increased. In the phase difference elements 1 according to Examples 3-1-2 to 3-1-8, the ellipticity ε changed depending on the position in the plane in the Y direction when viewed from above, and the minimum in-plane ellipticity ε was less than 0.7.

[0240] From the above, it was found that in the phase difference element 1 of Example 5, in model M3 in which light L emitted from a linear light source SL is incident on the phase difference element 1 at an incident angle of 0.0° or more and 50.0° or less, the ellipticity of the elliptically polarized light emitted from the phase difference element 1 can be made to have a high ellipticity ε over the entire wavelength range of visible light.

[0241] <Example 7, Example 8 to Example 4-1-7, Example 7' and Example 8' to Example 4-1-7'> (Model M4) 26A, 26B, and 26C, a model M4 of the phase difference element 1 according to Example 7, Example 8 to Example 4-1-7, Example 7', and Example 8' to Example 4-1-7' will be described. FIG. 26A is a schematic top view showing a first example of the model M4 of the phase difference element 1 according to Example 7 to Example 4-1-7. FIG. 26B is a schematic side view showing the model M4 of the phase difference element 1 according to Example 7 to Example 4-1-7. Note that Example 7 is an example, and Examples 8 to 4-1-7 are comparative examples. FIG. 26C is a schematic top view showing a second example of the model M4 of the phase difference element 1 according to Example 7' to Example 4-1-7'. The schematic side views showing the model M4 of the phase difference element 1 according to Example 7' to Example 4-1-7' are similar to FIG. 26B. Note that Example 7' is an example, and Examples 8' to 4-1-7' are comparative examples.

[0242] In model M4, a point light source SP was placed, and a retardation element 1 according to Examples 7 to 4-1-7' was placed directly above the point light source SP. Each of the retardation elements 1 according to Examples 7 to 4-1-7' had a substantially circular outer edge shape when viewed from above. In the retardation elements 1 according to Examples 7 to 4-1-7', a polarizing plate Pd was placed on the side where light L from the point light source SP is incident, so that the X direction and the transmission axis Dr of the polarizing plate Pd were parallel. The radius Rd of the retardation element 1 when viewed from above was 50.0 mm.

[0243] As shown in FIG. 26A, in the retardation element 1 according to Example 7, the second retardation layer 12 includes, in top view, a plurality of regions Ar having different alignment axis directions pT2. The plurality of regions Ar are arranged in a mosaic pattern or a concentric pattern in top view. Inside each of the plurality of regions Ar in top view, the alignment axis directions pT2 are uniform regardless of the position in the plane. The alignment axis directions pT2 of each of the plurality of regions Ar differ depending on the position in the plane of each of the plurality of regions Ar in top view. Of the plurality of regions Ar, region Ar21 is arranged in the center in top view. Of the plurality of regions Ar, region Ar22 is arranged outside region Ar21 in top view. The relationship between FIG. 26C and Example 7′ is the same as the relationship between FIG. 26A and Example 7.

[0244] The light L emitted from the point light source SP was assumed to spread spherically around the point light source SP. The model also assumed that the light L emitted from the point light source was incident on a retardation element 1 integrated with a polarizing plate Pd at an incident angle of 0.0° or more and 50.0° or less. The orientation axis direction was the angle relative to the transmission axis Dr of the polarizing plate Pd.

[0245] In model M4, light L emitted from the point light source SP passes through the polarizing plate Pd and then enters the first retardation layer 11 through the first interface 116 of the first retardation layer 11. The light L that has passed through the first retardation layer 11 passes through the second interface 117 of the first retardation layer 11 and enters the second retardation layer 12 through the third interface 126 of the second retardation layer 12. The light L that has passed through the first retardation layer 11 passes through the fourth interface 127 of the second retardation layer 12 and exits the second retardation layer 12. In the simulation, the Stokes parameters of the light L that exits the second retardation layer 12 were calculated.

[0246] In Examples 7 and 8 to 4-1-7, the configurations of the polarizer Pd, the first retardation layer 11, and the second retardation layer 12 were modeled as shown in Table 7A below. In Examples 7' and 8' to 4-1-7', the configurations of the polarizer Pd, the first retardation layer 11, and the second retardation layer 12 were modeled as shown in Table 7B below.

[0247] [Table 7A]

[0248] [Table 7B]

[0249] As shown in Table 7A, the retardation element 1 according to Example 7 had a configuration in which a polarizing plate Pd, a first retardation layer 11, and a second retardation layer 12 were laminated in this order from the point light source SP side. The alignment axis direction pT2 of the second retardation layer 12 was determined using the first example of the method for determining the alignment axis direction pT2. As shown in Table 7B, the retardation element 1 according to Example 7' had a configuration in which a polarizing plate Pd, a first retardation layer 11, and a second retardation layer 12 were laminated in this order from the point light source SP side. The alignment axis direction pT2 of the second retardation layer 12 was determined using the second example of the method for determining the alignment axis direction pT2.

[0250] In the first retardation layer 11 in Examples 7 and 7', the retardation Re1 was made uniform for each wavelength. In addition, in the first retardation layer 11 in Examples 7 and 7', the alignment axis direction pT1 was made uniform regardless of the position in the plane when viewed from above, and a twist of a total twist amount Tw1 was imparted to the liquid crystal in the thickness direction (Z direction) of the first retardation layer 11.

[0251] In the second retardation layer 12 in Examples 7 and 7', the retardation Re2 was uniform for each wavelength. Furthermore, in the second retardation layer 12 of the retardation element 1 in Examples 7 and 7', the alignment axis direction pT2 was varied depending on the position in the plane when viewed from above. In the modeling of Table 7A, the alignment axis direction pT2 at each position was set to the alignment axis direction pT21 to the alignment axis direction pT25, corresponding to the first to fifth positions of the retardation element 1 described later with reference to FIG. 27A. In the modeling of Table 7B, the alignment axis direction pT2 at each position was set to the alignment axis direction pT21 to the alignment axis direction pT25, corresponding to the first to fifth positions of the retardation element 1 described later with reference to FIG. 27B.

[0252] Examples 4-1-2 to 4-1-7 are modeled similarly to Example 7, but include one or more values ​​outside the range of the first example of the method for determining the orientation axis direction pT2. Examples 4-1-2' to 4-1-7' are modeled similarly to Example 7', but include one or more values ​​outside the range of the second example of the method for determining the orientation axis direction pT2.

[0253] The retardation elements 1 according to Examples 8 and 8' were configured to include only a first retardation layer 11. In the first retardation layers 11 of the retardation elements 1 in Examples 8 and 8', the retardation Re1 was uniform for each wavelength. Furthermore, in the first retardation layers 11 in Examples 8 and 8', the alignment axis direction pT1 was uniform regardless of the position in the plane when viewed from above.

[0254] FIG. 27A is a diagram showing the alignment axis direction pT2 of the second retardation layer 12 in the retardation element 1 according to Example 7. FIG. 27B is a diagram showing the alignment axis direction pT2 of the second retardation layer 12 in the retardation element 1 according to Example 7′. In each of FIGS. 27A and 27B, the distribution of the alignment axis direction pT2 at each position in the plane of the second retardation layer 12 is expressed by the density of dot hatching when viewed from above. In FIGS. 27A and 27B, arrows are displayed near the color scale to indicate the correspondence between the density of dot hatching on the color scale and the alignment axis direction pT2. Point P1 represents the first position, point P2 the second position, point P3 the third position, point P4 the fourth position, point P5 the fifth position, and point P6 the sixth position. The relationship between FIG. 27B and Example 7′ is similar to the relationship between FIG. 27A and Example 7.

[0255] 27, the numerical values ​​from 0° to 330° shown around the phase difference element 1 represent the incident azimuth angles. In top view, the alignment axis directions pT2 are uniform inside each of the multiple regions Ar shown in FIG. 26A. On the other hand, in top view, the alignment axis directions pT2 of each of the multiple regions Ar differ depending on the position of each of the multiple regions Ar.

[0256] In Fig. 27', the numerical values ​​between 0° and 330° shown around the phase difference element 1 represent the incident azimuth angles. In top view, the alignment axis directions pT2 are uniform inside each of the multiple regions Ar shown in Fig. 26C. On the other hand, in top view, the alignment axis directions pT2 of each of the multiple regions Ar differ depending on the position of each of the multiple regions Ar.

[0257] (Simulation results) Tables 8A and 8B show the ellipticity ε for each wavelength at the first to fifth positions of the phase difference element 1 according to Example 7, the ellipticity ε for each wavelength at the first to fifth positions of the phase difference element 1 according to Example 8, and the ellipticity ε for each wavelength at each of two positions of the phase difference elements 1 according to Examples 4-1-2 to 4-1-7. The first to fifth positions of the phase difference elements 1 according to Examples 7 and 8 to 4-1-7 correspond to points P1 to P5 shown in FIG.

[0258] [Table 8A]

[0259] [Table 8B]

[0260] Tables 8C and 8D show the ellipticity ε for each wavelength at the first to fifth positions of the phase difference element 1 according to Example 7', the ellipticity ε for each wavelength at the first to fifth positions of the phase difference element 1 according to Example 8', and the ellipticity ε for each wavelength at each of two positions of the phase difference element 1 according to Examples 4-1-2' to 4-1-7'. The first to sixth positions of the phase difference element 1 according to Example 7' and Examples 8' to 4-1-7' correspond to points P1 to P6 shown in FIG.

[0261] [Table 8C]

[0262] [Table 8D]

[0263] In the retardation elements 1 of Examples 7 and 7', a high ellipticity ε of 0.710 or more was obtained at any position in the plane when viewed from above. Furthermore, in the retardation elements 1 of Examples 7 and 7', a high ellipticity ε of 0.710 or more was obtained at any wavelength. That is, it can be seen that high ellipticity can be obtained over a wide wavelength range in the visible range. On the other hand, in the retardation elements 1 of Examples 8 and 8', the difference in ellipticity ε increased depending on the position in the plane in the Y direction when viewed from above. The range of ellipticity ε was 0.591 or more and 0.991 or less. Furthermore, in the retardation elements 1 of Examples 8 and 8', the difference in ellipticity ε for each wavelength increased. In the retardation elements 1 of Examples 4-1-2 to 4-1-7 and Examples 4-1-2' to 4-1-7', the ellipticity ε changed depending on the position in the plane when viewed from above, and the minimum in-plane ellipticity ε was less than 0.7.

[0264] From the above, it was found that in the phase difference elements 1 of Examples 7 and 7', in model M4 in which light L emitted from a point light source SP is incident on the phase difference element 1 at an incident angle of 0.0° or more and 50.0° or less, the ellipticity of the elliptically polarized light emitted from the phase difference element 1 can be made to have a high ellipticity ε over the entire wavelength range of visible light.

[0265] <Examples 9 and 10 to 4-2-5, Example 9' and 10' to 4-2-5'> (Model M5) The schematic top view of model M5 of the phase difference element 1 is the same as Fig. 18B. The schematic side view of model M5 of the phase difference element 1 is the same as Fig. 18C. Example 9' is an embodiment, and Examples 10' to 4-1-5' are comparative examples.

[0266] In model M5, a point light source SP was placed, and the retardation element 1 according to Examples 9 to 4-2-5' was placed directly above the point light source SP. Each of the retardation elements 1 according to Examples 9 to 4-2-5' had a substantially circular outer edge shape when viewed from above. In the retardation elements 1 according to Examples 9 to 4-2-5', a polarizing plate Pd was placed on the side where light L from the point light source SP is incident, so that the X direction and the transmission axis Dr of the polarizing plate Pd were parallel. The radius Rd of the retardation element 1 when viewed from above was 30.0 mm.

[0267] As shown in FIG. 26A, in the retardation element 1 according to Example 9, the second retardation layer 12 includes, in top view, a plurality of regions Ar having different alignment axis directions pT2. The plurality of regions Ar are arranged in a mosaic pattern or a concentric pattern in top view. Inside each of the plurality of regions Ar in top view, the alignment axis directions pT2 are uniform regardless of the position in the plane. The alignment axis directions pT2 of each of the plurality of regions Ar differ depending on the position in the plane of each of the plurality of regions Ar in top view. Of the plurality of regions Ar, region Ar21 is arranged in the center in top view. Of the plurality of regions Ar, region Ar22 is arranged outside region Ar21 in top view. FIG. 26C and Example 9′ have the same relationship as FIG. 26A and Example 9.

[0268] The light L emitted from the point light source SP was assumed to spread spherically around the point light source SP. The model also assumed that the light L emitted from the point light source was incident on a retardation element 1 integrated with a polarizing plate Pd at an incident angle of 0.0° or more and 30.0° or less. The orientation axis direction was the angle relative to the transmission axis Dr of the polarizing plate Pd.

[0269] In model M5, light L emitted from the point light source SP passes through the polarizing plate Pd and then enters the first retardation layer 11 through the first interface 116 of the first retardation layer 11. The light L that has passed through the first retardation layer 11 passes through the second interface 117 of the first retardation layer 11 and enters the second retardation layer 12 through the third interface 126 of the second retardation layer 12. The light L that has passed through the first retardation layer 11 passes through the fourth interface 127 of the second retardation layer 12 and exits the second retardation layer 12. In the simulation, the Stokes parameters of light L that exits the second retardation layer 12 were calculated.

[0270] In Examples 9 and 10 to 4-2-5, the configurations of the polarizer Pd, the first retardation layer 11, and the second retardation layer 12 were modeled as shown in Table 9A below. In Examples 9' and 10' to 4-2-5', the configurations of the polarizer Pd, the first retardation layer 11, and the second retardation layer 12 were modeled as shown in Table 9B below.

[0271] [Table 9A]

[0272] [Table 9B]

[0273] As shown in Table 9A, the retardation element 1 according to Example 9 had a configuration in which a polarizing plate Pd, a first retardation layer 11, and a second retardation layer 12 were laminated in this order from the point light source SP side. The alignment axis direction pT2 of the second retardation layer 12 was determined using the third example of the method for determining the alignment axis direction pT2. As shown in Table 9B, the retardation element 1 according to Example 9' had a configuration in which a polarizing plate Pd, a first retardation layer 11, and a second retardation layer 12 were laminated in this order from the point light source SP side. The alignment axis direction pT2 of the second retardation layer 12 was determined using the fourth example of the method for determining the alignment axis direction pT2.

[0274] In the first retardation layer 11 in Examples 9 and 9', the retardation Re1 was made uniform for each wavelength. In addition, in the first retardation layer 11 in Examples 9 and 9', the alignment axis direction pT1 was made uniform regardless of the position in the plane when viewed from above, and a twist of a total twist amount Tw1 was imparted to the liquid crystal in the thickness direction (Z direction) of the first retardation layer 11.

[0275] In the second retardation layer 12 in Examples 9 and 9', the retardation Re2 was made uniform for each wavelength. In addition, in the second retardation layer 12 of the retardation element 1 in Examples 9 and 9', the alignment axis direction pT2 was made different depending on the position in the plane when viewed from above.

[0276] In the modeling of Table 9A, the alignment axis direction pT2 at each position was set to the alignment axis direction pT21 to the alignment axis direction pT25, corresponding to the first to fifth positions of the retardation element 1, which will be described later with reference to Fig. 28A. In the modeling of Table 9B, the alignment axis direction pT2 at each position was set to the alignment axis direction pT21 to the alignment axis direction pT25, corresponding to the first to fifth positions of the retardation element 1, which will be described later with reference to Fig. 28B.

[0277] Examples 4-2-2 to 4-2-5 are modeled similarly to Example 9, and include one or more values ​​outside the range of the third example of the method for determining the orientation axis direction pT2. Examples 4-2-2' to 4-2-5' are modeled similarly to Example 9', and include one or more values ​​outside the range of the fourth example of the method for determining the orientation axis direction pT2.

[0278] The retardation elements 1 according to Examples 10 and 10' were configured to include only a first retardation layer 11. In the first retardation layers 11 of the retardation elements 1 in Examples 10 and 10', the retardation Re1 was uniform for each wavelength. Furthermore, in the first retardation layers 11 in Examples 10 and 10', the alignment axis direction pT1 was uniform regardless of the position in the plane when viewed from above.

[0279] FIG. 28A is a diagram showing the alignment axis direction pT2 of the second retardation layer 12 in the retardation element 1 according to Example 9. FIG. 28B is a diagram showing the alignment axis direction pT2 of the second retardation layer 12 in the retardation element 1 according to Example 9′. In each of FIGS. 28A and 28B, the distribution of the alignment axis direction pT2 at each position in the plane of the second retardation layer 12 is expressed by the density of dot hatching when viewed from above. In FIGS. 28A and 28B, arrows are displayed near the color scale to indicate the correspondence between the density of dot hatching on the color scale and the alignment axis direction pT2. Point P1 represents the first position, point P2 the second position, point P3 the third position, point P4 the fourth position, and point P5 the fifth position. The relationship between FIG. 28B and Example 9′ is similar to the relationship between FIG. 28A and Example 9.

[0280] 28A, the numerical values ​​between 0° and 330° shown around the phase difference element 1 represent the incident azimuth angles. In top view, the alignment axis directions pT2 are uniform inside each of the multiple regions Ar shown in FIG. 26A. On the other hand, in top view, the alignment axis directions pT2 of each of the multiple regions Ar differ depending on the position of each of the multiple regions Ar.

[0281] In Fig. 28B, the numerical values ​​between 0° and 330° shown around the phase difference element 1 represent the incident azimuth angles. In top view, the alignment axis directions pT2 are uniform inside each of the multiple regions Ar shown in Fig. 26C. On the other hand, in top view, the alignment axis directions pT2 of each of the multiple regions Ar differ depending on the position of each of the multiple regions Ar.

[0282] (Simulation results) Tables 10A and 10B show the ellipticity ε for each wavelength at the first to fifth positions of the phase difference element 1 according to Example 9, the ellipticity ε for each wavelength at the first to fifth positions of the phase difference element 1 according to Example 10, and the ellipticity ε for each wavelength at each of two positions of the phase difference elements 1 according to Examples 4-2-2 to 4-2-5. The first to fifth positions of the phase difference elements 1 according to Examples 9 and 10 to 4-2-5 correspond to points P1 to P5 shown in FIG. 28A.

[0283] [Table 10A]

[0284] [Table 10B]

[0285] Tables 10C and 10D show the ellipticity ε for each wavelength at the first to fifth positions of the phase difference element 1 according to Example 9', the ellipticity ε for each wavelength at the first to fifth positions of the phase difference element 1 according to Example 10', and the ellipticity ε for each wavelength at each of two positions of the phase difference element 1 according to Examples 4-2-2' to 4-2-5'. The first to fifth positions of the phase difference element 1 according to Example 9' and Examples 10' to 4-2-5' correspond to points P1 to P5 shown in FIG. 28B.

[0286] [Table 10C]

[0287] [Table 10D]

[0288] In the retardation elements 1 of Examples 9 and 9, a high ellipticity ε of 0.880 or more was obtained at any position in the plane when viewed from above. Furthermore, in the retardation elements 1 of Examples 9 and 9', a high ellipticity ε of 0.880 or more was obtained at any wavelength. This means that high ellipticity can be obtained over a wide wavelength range in the visible range. On the other hand, in the retardation elements 1 of Examples 10 and 10', the difference in ellipticity ε increased depending on the position in the plane in the Y direction when viewed from above. The range of ellipticity ε was 0.753 or more and 0.991 or less. Furthermore, in the retardation elements 1 of Examples 10 and 10', the difference in ellipticity ε for each wavelength increased. In the retardation elements 1 of Examples 4-2-2 to 4-2-5 and Examples 4-2-2' to 4-2-5', the ellipticity ε varied depending on the position in the plane when viewed from above, and the minimum in-plane ellipticity ε was less than 0.7.

[0289] From the above, it was found that in the phase difference elements 1 of Examples 9 and 9', in model M4 in which light L emitted from a point light source SP is incident on the phase difference element 1 at an incident angle of 0.0° or more and 30.0° or less, the ellipticity of the elliptically polarized light emitted from the phase difference element 1 can be made to have a high ellipticity ε over the entire wavelength range of visible light.

[0290] [Second embodiment] Next, an optical component according to a second embodiment will be described.

[0291] <Configuration of Optical Component According to Second Embodiment> The configuration of an optical component 200 according to the second embodiment will be described with reference to FIGS. 29, 30A, 30B, and 31. FIG. 29 is a schematic diagram illustrating the configuration of an optical component 200 according to the second embodiment. FIG. 30A is a schematic cross-sectional view taken along the line XXX-XXX in FIG. 29. FIG. 30B is a schematic planar view illustrating the alignment axis direction of retardation element 1aa in FIG. 30A. FIG. 31 is a diagram illustrating a method for determining alignment axis direction pT2 of second retardation layer 12. FIG. 29 shows a top view of optical component 200 and a side view of optical component 200 associated with the top view. Optical component 200-1 represents optical component 200 as viewed from the +X direction, and optical component 200-2 represents optical component 200 as viewed from the -Y direction. FIG. 30A shows a planar light source SS that emits light L incident on optical component 200, along with a cross-sectional view of optical component 200. In FIG. 29, the polarizer Pd and the phase difference element 1aa are omitted.

[0292] The optical component 200 includes a polarizing plate Pd and a retardation element 1aa. In the example shown in FIGS. 30A and 30B, the optical component 200 includes a substrate 111aa having a three-dimensional curved surface. The polarizing plate Pd and the retardation element 1aa are formed in layers along the surface of the substrate 111aa, which also has a three-dimensional curved surface. Since the retardation element 1aa is formed along the three-dimensional curved surface of the substrate 111aa, the optical axis direction when viewed perpendicular to the surface varies depending on the inclination direction and inclination angle of the surface of the three-dimensional curved surface. The retardation element 1aa is formed to follow the surface of the substrate 111aa and is a member that is much thinner than the substrate 111aa. The retardation element 1aa itself does not have a three-dimensional curved surface.

[0293] The base material 111aa is a member having a transmittance of 80% or more for light L emitted by the surface light source SS. The polarizing plate Pd is disposed on the +Z side surface of the base material 111aa. In other words, the retardation element 1aa is disposed on the +Z side surface of the base material 111aa, and the polarizing plate Pd is disposed on the +Z side surface of the retardation element 1aa. For example, as shown in FIG. 4D , the retardation element 1aa is composed of a first retardation layer 11 and a second retardation layer 12. The retardation element 1aa is integrated with the polarizing plate Pd via an adhesive layer 13d, and the polarizing plate Pd, first retardation layer 11, and second retardation layer 12 may be stacked in this order with respect to the incident light L.

[0294] In FIG. 30A, the surface light source SS emits light L, which is a plane wave. The light L is neither diverging nor converging, but is incident on the optical component 200 as parallel light traveling in the normal direction of the light-emitting surface SS0 of the surface light source SS. The cross-sectional shape of the optical component 200 shown in FIG. 30A is defined for each point on a slope on the +Z side surface of the optical component 200 (hereinafter simply referred to as the slope of the optical component 200), and is a plane spanned by two vectors: the normal to each point and the direction of the incident light. In FIGS. 29, 30A, and 30B, a point on the slope of the optical component 200 is conveniently referred to as point P. Point O in FIGS. 29, 30A, and 30B is the point at which light from the surface light source SS is perpendicularly incident, as will be described later.

[0295] In FIG. 29, the direction of the arrow 120 indicates the alignment axis direction pT2 of the second retardation layer 12 formed at point O. The azimuth angle φ is the angle between a line along the alignment axis direction pT2 of the second retardation layer 12 at point O and the XXX-XXX line. The azimuth angle φ represents the azimuth angle at point P on the inclined surface of the optical component 200. Note that in FIG. 29, the contour line T indicated by the dashed circle indicates a portion where the heights on the +Z side surface of the optical component 200 (i.e., the length of the optical component 200 in the Z direction) are equal in top view. In FIG. 29, the height indicated by the contour line T and the respective heights of the optical components 200-1 and 200-2 shown in side view are associated with each other using dashed straight lines.

[0296] FIG. 30B is a cross-sectional view defining a plane that shares a normal with point O. Point P on the inclined surface of optical component 200 shown in FIG. 30A corresponds to point P' on the plane of FIG. 30B. The inclined surface of optical component 200 shown in FIG. 30A is divided into regions with different angles θ, such as region AR in FIG. 26A to which point P belongs. As shown in FIG. 29, the inclined surface of optical component 200 can also be divided into regions with different azimuth angles φ. That is, the curved surface on which retardation element 1aa is formed can be divided into multiple regions with different azimuth angles φ and θ. By configuring the retardation element 1aa to have different orientations for each region with different azimuth angles θ and φ, the ellipticity of light L transmitted through polarizer Pd and retardation element 1aa can be increased throughout the entire retardation element 1aa.

[0297] In the retardation element 1aa, the retardation Re1 of the first retardation layer 11 and the total twist amount Tw1 of the liquid crystal, the retardation Re2 of the second retardation layer 12 and the total twist amount Tw2 of the liquid crystal, and the difference pTw12 in the alignment axis direction at point O between the first retardation layer 11 and the second retardation layer 12 are common when viewed from the normal direction of each region. The alignment axis direction pT2 of the second retardation layer 12 faces in different directions for the different regions with different azimuth angles φ and θ, and the retardation element 1aa has a different orientation for each region.

[0298] 30A and 30B, a method for adjusting the alignment axis direction pT2 of the second retardation layer 12 will be described. As shown in FIG. 30A, consider point O at which light L is perpendicularly incident and point P on the slope of the optical component 200. With respect to point P, a line XXX-XXX determined by the azimuth angle φ of the slope of the optical component 200 and an angle θ of the slope with respect to the incident light L are defined. Also, FIG. 30B is a diagram of a plane sharing a normal vector with point O, viewed along the line XXX-XXX determined by the azimuth angle φ in FIG. 30A.

[0299] Point P' is a point on a plane, and is located at the same position as point P when the inclined surface of optical component 200 shown in Fig. 30A and the plane shown in Fig. 30B are viewed from above. Hereinafter, point P on the inclined surface of optical component 200 and point P' on the plane will be described in correspondence with each other.

[0300] As shown in FIG. 30A, light L incident on point P on the inclined surface at angle θ has an incident angle of angle θ. Increasing the ellipticity of this light L after it passes through polarizer Pd and retardation element 1aa formed at point P on the inclined surface can be considered the same as increasing the ellipticity of light L passing through polarizer Pd and retardation element 1aa for virtual light L0 obliquely incident on point P' on the plane at angle θ, as shown in FIG. 30B. Furthermore, since the XXX-XXX line in FIGS. 30A and 30B is the same, it can be seen that virtual light L0 obliquely incident on point P' at angle θ is obliquely incident at an azimuth angle φ when viewed from above. In this way, a plane wave incident on each point P on the three-dimensional curved surface can be associated with virtual light L0 incident on point P' on the plane at an azimuth angle φ and an oblique incidence angle θ.

[0301] The above-described <Method for determining the alignment axis direction in the second retardation layer 12> can be applied to a method for increasing the ellipticity when virtual light L0 incident on a point P' on a plane at an azimuth angle φ and an incident angle θ is transmitted through the polarizer Pd and the retardation element 1aa. For example, when both virtual light L0 with θ=0° (i.e., perpendicular incidence) and θ=50° are included, the retardation Re1, retardation Re2, total twist amount Tw1, total twist amount Tw2, and alignment axis direction pT2 of the retardation element 1aa are given as follows, similar to Example 3 shown in Table 3. Re1=90.0nm Re2=244.7nm Tw1=18.6° Tw2=-104.5°

[0302] The alignment axis direction pT2 of the second retardation layer 12 at each point represented by the azimuth angle φ and the angle θ is determined by Equation (1). The alignment axis direction of the retardation element 1aa at point P' on the plane thus determined can be determined. Specifically, as shown in FIG. 31 , the alignment axis direction pT2 of the second retardation layer 12 when viewed perpendicular to the plane at point P is determined to be the same as the alignment axis direction pT2 of the second retardation layer 12 when viewed perpendicular to the plane at point P'. In addition, the retardation Re1 and total twist amount Tw1 of the first retardation layer 11, the retardation Re2 and total twist amount Tw2 of the second retardation layer 12, and the difference pTw12 between the alignment axis directions of the first retardation layer 11 and the second retardation layer 12 at point O are determined to be the same between point P and point P' when viewed perpendicular to the plane.

[0303] The above has described a method for adjusting the retardation element 1aa, which is formed together with a polarizing plate Pd on a three-dimensional curved surface including a point where a plane wave is perpendicularly incident and an inclined surface P where the plane wave is incident at θ = 50°, so that the ellipticity of the transmitted light is high. Similarly, in a model of a plane wave incident on a three-dimensional curved surface on which the retardation element 1aa and the polarizing plate Pd are formed, in the case of a three-dimensional curved surface including a point where the incident angle is perpendicular and a point where the incident angle is 30°, a high ellipticity can be obtained by using the configuration shown in Example 2-2 of Table 4E above.

[0304] The substrate 111aa may be a convex lens, a concave lens, a curved mirror, a curved display, etc. The retardation element 1aa has a three-dimensional curved shape that conforms to the three-dimensional curved shape of the substrate 111aa, and can be formed on the surface of the substrate 111aa.

[0305] The substrate 111aa can also be a cylindrical lens. In this case, the polarizing plate Pd and the phase difference element 1aa are formed along the three-dimensional cylindrical curved surface of the cylindrical lens. When a plane wave is incident on the polarizing plate Pd and the phase difference element 1aa formed on the substrate 111aa, which is a cylindrical lens, a high ellipticity can be obtained by using the configuration of the phase difference element 1aa shown in Example 5 of Table 5 above.

[0306] In the optical component 200, the configuration of the phase difference element 1aa can be determined in a similar manner not only when the light L that is a plane wave (parallel light) is incident, but also when the light L that is a convergent light or a divergent light is incident, based on the point of perpendicular incidence. The three-dimensional curved surface is not limited to a convex shape, but may also be a concave shape or a shape in which convex and concave shapes are mixed.

[0307] [Examples and Comparative Examples According to the Second Embodiment] <Example 11, Example 12, Example 5-1-2 to Example 11, Example 13, Example 14, and Example 5-2-2 to Example 11,> (Model M6) Referring to FIGS. 32A and 32B, a model M6 of the retardation element 1aa according to Example 11, Example 12, Examples 5-1-2 to 11, Examples 13 and 14, and Examples 5-1-2 to 11 will be described. Note that the polarizer Pd and the retardation element 1aa are omitted in FIGS. 32A and 32B, but they are disposed in the same arrangement as in FIG. 30A. FIG. 32A is a cross-sectional view showing an example of the model M6 of the retardation element 1aa according to Examples 11, 12, Examples 5-1-2 to 11, Examples 13 and 14, and Examples 5-1-2 to 11. FIG. 32B is a top view of the model M6. Note that Examples 11 and 13 are working examples, and Examples 12, 14, Examples 5-1-2 to 11, and Examples 5-2-2 to 11 are comparative examples.

[0308] In model M6, a planar light source SS was disposed, and the phase difference element 1aa according to Examples 11 to 14, Examples 5-1-2 to 11, and Examples 5-2 to 2 to 11 was disposed along a three-dimensional curved surface disposed opposite the planar light source SS. FIG. 32A is a cross-sectional view perpendicular to FIG. 32B, passing through angles below 0° and below 180° in FIG. 32B. For simplicity, the three-dimensional curved surface is symmetrical with respect to a line passing through point P1 in FIG. 32B, and the cross-sectional shape of FIG. 32A was formed by rotating 360° around the axis of symmetry passing through point P1. Therefore, the angles of the slopes on the three-dimensional curved surface shape are point-symmetrical with respect to point P1 in FIG. 32B, and the azimuth angles of the slopes are radial directions of a circle centered on point P1 in FIG. 32B. Therefore, slopes in the same radial direction of a circle centered on point P1 share a normal to the slope within the cross-section, and the azimuth angles φ of the slopes described using FIG. 29 can be considered to be the same.

[0309] On the retardation elements 1aa according to Examples 11 to 14, 5-1-2 to 11, and 5-2-2 to 11, a polarizing plate Pd was arranged along a three-dimensional curved surface on the side where light L is incident from the planar light source SS so that the transmission axis Dr of the polarizing plate Pd was parallel to the direction of 0° or more and 180° or less in FIG. 32B. The outer edge shape of the retardation elements 1aa according to Examples 11 to 14, 5-1-2 to 11, and 5-2-2 to 11 in top view was approximately circular.

[0310] Light L emitted from the surface light source SS is assumed to be a plane wave, a parallel light traveling perpendicular to the light-emitting surface SS0 of the surface light source SS. In Figure 32A, light L1 is emitted parallel to the Z axis and enters a retardation element 1aa integrated with a polarizing plate Pd. Because the retardation element 1aa is inclined according to the inclination of the slope on the three-dimensional curved surface, the incident light is obliquely incident depending on the angle of inclination, and the magnitude of the angle of incidence is the same as the magnitude of the inclination. In the simulation, as shown in Figure 32A, the inclination angles were set to 0°, 20.0°, 50.0°, and 30.0°, starting from the position closest to the surface light source SS. In other words, in model M6, light L emitted from the surface light source SS is assumed to enter the retardation element 1aa at an incident angle of 0.0° or more and 50.0° or less. The orientation axis direction pT is the angle relative to the transmission axis Dr of the polarizing plate Pd.

[0311] In model M6, light L emitted from the surface light source SS passes through the polarizing plate Pd and then enters the first retardation layer 11 through the first interface 116 of the first retardation layer 11. The light L that has passed through the first retardation layer 11 passes through the second interface 117 of the first retardation layer 11 and enters the second retardation layer 12 through the third interface 126 of the second retardation layer 12. The light L that has passed through the first retardation layer 11 passes through the fourth interface 127 of the second retardation layer 12 and exits the second retardation layer 12. In the simulation, the Stokes parameters of light L that exits the second retardation layer 12 were calculated.

[0312] In Examples 11, 12, and 5-1-2 to 11, the configurations of the polarizing plate Pd, the first retardation layer 11, and the second retardation layer 12 were modeled as shown in Table 11 below. In Examples 13, 14, and 5-2-2 to 11, the configurations of the polarizing plate Pd, the first retardation layer 11, and the second retardation layer 12 were modeled as shown in Table 12 below.

[0313] [Table 11]

[0314] [Table 12]

[0315] As shown in Table 11, the retardation element 1aa according to Example 11 had a configuration in which a polarizing plate Pd, a first retardation layer 11, and a second retardation layer 12 were laminated in this order from the surface light source SS side. The method for determining the alignment axis direction pT2 in the second retardation layer 12 according to Examples 1 and 2 was the first example of the method for determining the alignment axis direction pT2.

[0316] As shown in Table 12, the retardation element 1aa according to Example 13 had a configuration in which a polarizing plate Pd, a first retardation layer 11, and a second retardation layer 12 were laminated in this order from the surface light source SS side. The second example of the method for determining the alignment axis direction pT2 was used to determine the alignment axis direction pT2 in the second retardation layer 12 according to Examples 1 and 2.

[0317] In the first retardation layer 11 in Examples 11 and 13, the retardation Re1 was made uniform for each wavelength. In addition, in the first retardation layer 11 in Examples 11 and 13, the alignment axis direction pT1 was made uniform regardless of the position in the plane when viewed from above, and a twist of a total twist amount Tw1 was imparted to the liquid crystal in the thickness direction (Z direction) of the first retardation layer 11.

[0318] In the second retardation layer 12 in Examples 11 and 13, the retardation Re2 was uniform for each wavelength. In addition, in the second retardation layer 12 of the retardation element 1aa in Examples 11 and 13, the alignment axis direction pT2 was varied depending on the in-plane position when viewed from above. In the modeling of Table 13, the alignment axis direction pT2 at each position was set to the alignment axis direction pT21 to the alignment axis direction pT26, corresponding to the first to sixth positions of the retardation element 1aa in FIG. 32B. In the modeling of Table 14, the alignment axis direction pT2 at each position was set to the alignment axis direction pT21 to the alignment axis direction pT26, corresponding to the first to sixth positions of the retardation element 1aa in FIG. 32C. Examples 5-1-2 to 11 were modeled similarly to Example 11, but included one or more values ​​outside the range of the first example of the method for determining the alignment axis direction pT2. Examples 5-2-2 to 11 are modeled similarly to Example 13, and include one or more values ​​outside the range of the second example of the method for determining the orientation axis direction pT2.

[0319] The retardation elements 1aa according to Examples 12 and 14 were configured to include only a first retardation layer 11. In the first retardation layer 11 of the retardation elements 1aa in Examples 12 and 14, the retardation Re1 for each wavelength was made uniform. In addition, in the first retardation layer 11 in Examples 12 and 14, the alignment axis direction pT1 was made uniform regardless of the position in the plane when viewed from above.

[0320] Fig. 32B is a diagram showing the alignment axis direction pT2 of the second retardation layer 12 in the retardation element 1aa according to Example 11. Fig. 32B shows the distribution of the alignment axis direction pT2 at each position in the plane of the second retardation layer 12 in a top view, expressed by differences in the density of dot hatching. In Fig. 32B, arrows displayed near the color scale are displayed to indicate the correspondence between the density of dot hatching on the color scale and the alignment axis direction pT2. Point P1 represents the first position, point P2 the second position, point P3 the third position, point P4 the fourth position, point P5 the fifth position, and point P6 the sixth position.

[0321] Fig. 32C is a diagram showing the alignment axis direction pT2 of the second retardation layer 12 in the retardation element 1aa according to Example 13. Fig. 32C shows the distribution of the alignment axis direction pT2 at each position in the plane of the second retardation layer 12 in a top view, expressed by differences in the density of dot hatching. In Fig. 32C, arrows displayed near the color scale are displayed to indicate the correspondence between the density of dot hatching on the color scale and the alignment axis direction pT2. Point P1 represents the first position, point P2 the second position, point P3 the third position, point P4 the fourth position, point P5 the fifth position, and point P6 the sixth position.

[0322] In FIG. 32B, the numerical values ​​between 0° and 330° shown around the phase difference element 1aa represent the incident azimuth angle. The orientation axis direction is determined by the incident azimuth angle and the incident angle. At an incident azimuth angle of 60° and an incident azimuth angle of 240°, the orientation axis direction pT2 gradually increases as the incident angle of the oblique surface increases relative to the center of the phase difference element 1aa, where the incident angle is 0°. On the other hand, at an incident azimuth angle of 0° and an incident azimuth angle of 150°, the orientation axis direction pT2 gradually decreases as the incident angle of the oblique surface increases relative to the center of the phase difference element 1aa, where the incident angle is 0°.

[0323] In FIG. 32C, the numerical values ​​between 0° and 330° shown around the phase difference element 1aa represent the incident azimuth angle. The orientation axis direction is determined by the incident azimuth angle and the incident angle. At an incident azimuth angle of 30° and an incident azimuth angle of 180°, the orientation axis direction pT2 gradually increases as the incident angle of the oblique surface increases relative to the center of the phase difference element 1aa, where the incident angle is 0°. On the other hand, at an incident azimuth angle of 120° and an incident azimuth angle of 300°, the orientation axis direction pT2 gradually decreases as the incident angle of the oblique surface increases relative to the center of the phase difference element 1aa, where the incident angle is 0°.

[0324] (Simulation results) Tables 13A and 13B show the ellipticity ε for each wavelength at the first position to the fifth position of the phase difference element 1aa according to Example 11, the ellipticity ε for each wavelength at the first position to the fifth position of the phase difference element 1aa according to Example 12, and the ellipticity ε for each wavelength at each of two positions of the phase difference elements 1aa according to Examples 5-1-2 to 11. The first position to the sixth position of the phase difference elements 1aa according to Examples 11, 12, and 5-1-2 to 11 correspond to points P1 to P6 shown in FIG.

[0325] [Table 13A]

[0326] [Table 13B]

[0327] Tables 14A and 14B show the ellipticity ε for each wavelength at the first position to the fifth position of the phase difference element 1aa according to Example 13, the ellipticity ε for each wavelength at the first position to the fifth position of the phase difference element 1aa according to Example 14, and the ellipticity ε for each wavelength at each of two positions of the phase difference elements 1aa according to Examples 5-2-2 to 11. The first position to the sixth position of the phase difference elements 1aa according to Examples 13, 14, and 5-2-2 to 11 correspond to points P1 to P6 shown in FIG.

[0328] [Table 14A]

[0329] [Table 14B]

[0330] In the retardation elements 1aa according to Examples 11 and 13, a high ellipticity ε of 0.840 or more was obtained at any position in the plane when viewed from above. Furthermore, in the retardation elements 1aa according to Examples 11 and 13, a high ellipticity ε of 0.840 or more was obtained at any wavelength. In other words, it can be seen that a high ellipticity can be obtained over a wide wavelength range in the visible range.

[0331] On the other hand, in the phase difference elements 1aa according to Examples 12 and 14, the difference in ellipticity ε increased depending on the position in the plane when viewed from above. The range of ellipticity ε was 0.503 or more and 0.991 or less. Furthermore, in the phase difference elements 1aa according to Examples 12 and 14, the difference in ellipticity ε for each wavelength increased. In the phase difference elements 1aa according to Examples 5-1-2 to 11 and 5-2-2 to 11, the ellipticity ε changed depending on the position in the plane when viewed from above, and the minimum in-plane ellipticity ε was less than 0.7.

[0332] From the above, it was found that in the phase difference elements 1aa according to Examples 11 and 13, in model M6 in which light L emitted from the planar light source E is incident on the phase difference element 1aa at an incident angle of 0° or more and 50.0° or less, the ellipticity of the elliptically polarized light emitted from the phase difference element 1 can be made to have a high ellipticity ε over the entire wavelength range of visible light.

[0333] [Other Preferred Embodiments] The phase difference element 1 and the phase difference element 1aa may each receive circularly polarized light or linearly polarized light.

[0334] The retardation element 1 and the retardation element 1aa may be integrated with a linear polarization element and used as a circular polarizer. From another perspective, a circular polarizer may be configured by integrating either the retardation element 1 or the retardation element 1aa with a linear polarization element. For example, in FIG. 30A , the circular polarizer is configured by the polarizer Pd and the retardation element 1aa, with the polarizer Pd being the linear polarization element. The circular polarizer according to the embodiment can convert the polarization state of light incident on the circular polarizer at a wide incidence angle and incidence azimuth angle with high ellipticity. Furthermore, in FIG. 30A , when the circular polarizer is configured by the polarizer Pd and the retardation element 1aa, the optical component 200 corresponds to an optical component including a circular polarizer.

[0335] The circularly polarizing plate according to the embodiment can have, for example, any one of the following distributions (1) to (3). (1) It is flat, and receives circularly polarized or linearly polarized light, with the angle of the incident light having a distribution of 0° to 30° or 0° to 50°. (2) It is formed along a three-dimensional curved surface, and circularly polarized or linearly polarized light is incident, with the angle of the incident light having a distribution of 0° to 30° or 0° to 50°. (3) Circularly polarized or linearly polarized light is incident, and the angle of the incident light has a distribution of 0° to 50° or a distribution of 30° to 60°. With this configuration, the circular polarizer according to the embodiment can convert the polarization state of light incident on the circular polarizer at a wide range of incident angles and incident azimuth angles with high ellipticity.

[0336] Divergent or convergent light may be incident on or emitted from a circular polarizer. Divergent or convergent light includes light that is off the optical axis, but off-axis light enters or exits a circular polarizer installed on the optical path with a distribution of angles. For this reason, a circular polarizer using a typical quarter-wave plate will have a distribution in the phase difference modulated according to the distribution of incident angles, resulting in a distribution of phase difference between on-axis light and off-axis light in the transmitted light. This can cause uneven brightness and color after passing through an analyzer such as a crossed Nicol arrangement, resulting in reduced image quality.

[0337] As a circular polarizer, for example, the retardation element 1 shown in the above-mentioned (third example of the determination method) and (fourth example of the determination method) can be used together with a linear polarizer. Because this retardation element 1 functions as a good retardation element 1 for light with an incident angle of ±30°, it also functions well as a circular polarizer for light incident off the optical axis. Furthermore, the retardation elements 1 shown in the above-mentioned (first example of the determination method) and (second example of the determination method) function well as a retardation element 1 for light with an incident angle of ±50°, and therefore function even better as a circular polarizer for light incident off the optical axis. The retardation elements 1 shown in the above-mentioned (first example of the determination method) and (second example of the determination method) can be used for light with a wider incident angle than the retardation elements 1 shown in the above-mentioned (third example of the determination method) and (fourth example of the determination method). Since the phase difference element 1 shown in (third example of determination method) and (fourth example of determination method) has a phase difference layer without twist, it has a simpler structure and is easier to manufacture than the phase difference element 1 shown in (first example of determination method) and (second example of determination method). Note that although the phase difference element 1 has been described as an example here, the phase difference element 1 may also be a phase difference element 1aa. This also applies to the examples of the embodiments shown below.

[0338] (Example of an embodiment using a phase difference element 1 with an incident light angle of 0° to 30° or 0° to 50°) Diverging or converging light may be incident on or emitted from the phase difference element 1. The diverging or converging light is incident on or emitted from the optical element on the optical path with an angular distribution. For example, in head-mounted display devices used for AR (Augmented Reality) or VR (Virtual Reality), a wider viewing angle is required than the horizontal angle of view of a typical HDTV (High-Definition Television), which is approximately 33 degrees, to create a sense of realism, as shown in, for example, JP 2022-180368 A or WO 2016 / 002657 A. Furthermore, to achieve a sufficient sense of realism, it is necessary to provide light with a viewing angle of 90 degrees or more. For this reason, the device is optically designed to accommodate a viewing angle of 33 degrees or more, and up to 90 degrees or more. Furthermore, as shown in JP 2020-519964 A, a folded optical system is used to miniaturize the device, but a flat phase difference element is used here. The retardation element 1 shown in the (third example of the determination method) and (fourth example of the determination method) described above functions as a retardation element up to an incident angle of ±30°, i.e., a viewing angle of 60°, and therefore, when used in a head-mounted display device, improvement in image quality such as color unevenness and brightness unevenness can be expected. Furthermore, the retardation element 1 shown in the (first example of the determination method) and (second example of the determination method) functions as a retardation element up to an incident angle of ±50°, i.e., a viewing angle of 100°, and therefore, improvement in image quality such as color unevenness and brightness unevenness can be expected. The retardation element 1 shown in the (first example of the determination method) and (second example of the determination method) can be used for light with a wider incident angle than the retardation element 1 shown in the (third example of the determination method) and (fourth example of the determination method). Furthermore, because the retardation element 1 has a twist-free retardation layer, the retardation element 1 shown in the (third example of the determination method) and (fourth example of the determination method) has a simpler structure and is easier to manufacture than the retardation element 1 shown in the (first example of the determination method) and (second example of the determination method).

[0339] (Example of an embodiment using a phase difference element 1 with an incident light angle of 30° or more and 60° or less) Diverging or converging light may be incident on or emitted from the phase difference element 1. The diverging or converging light enters or exits the optical elements along the optical path with a distribution of angles. For example, Japanese Patent Application Laid-Open No. 7-21580 discloses an example in which a quarter-wave plate is formed on the surface of a rising mirror that reflects obliquely incident light. Japanese Patent Application Laid-Open No. 7-21580 discloses that polarized light emitted from a semiconductor laser and linearly polarized light determined by an opposing polarizing beam splitter enter the phase difference element. However, due to the distribution of incident angles, the polarized light transmitted through the phase difference element cannot be properly modulated, generating noise and potentially degrading signal quality. By using the phase difference elements 1 described above in the (fifth example of the determination method) and (sixth example of the determination method), phase difference control corresponding to each incident angle can be performed, reducing the distribution of the polarization state transmitted through the phase difference element and potentially improving signal quality.

[0340] Although the preferred embodiments have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

[0341] For example, by using a soft material for forming the retardation element 1, it is possible to provide a bendable, flexible retardation element 1. The flexible retardation element 1 can be suitably attached to a three-dimensional structure, particularly a three-dimensional structure having a three-dimensional curved surface, and can impart to the three-dimensional structure the function of converting linearly polarized light into circularly polarized light or the function of converting circularly polarized light into linearly polarized light. Examples of three-dimensional structures include curved display devices such as liquid crystal displays and organic EL (Electro Luminescence) displays, curved cover glasses, optical lenses, and curved mirrors. Lenses include concave lenses with a concave surface and convex lenses with a convex surface.

[0342] The retardation element according to the embodiment can be applied to a variety of fields that use optical techniques, such as display devices such as liquid crystal displays or organic EL displays, optical measurement devices such as polarization measurement devices, or optical heads. Depending on the purpose, incident light can be converted into circularly polarized light, linearly polarized light, or the like to improve display quality, observe the properties of materials, remove background noise, or the like. For example, in display devices such as liquid crystal displays or organic EL displays, the retardation element according to the embodiment is used for viewing angle compensation or anti-reflection. [Explanation of symbols]

[0343] 1, 1aa, 1A, 1B, 1C, 1D phase difference element 1a Incidence plane 1b Output surface 11 First retardation layer 111, 111aa, 115, 121 base material 112, 114, 122 Alignment layer 113, 123 Liquid crystal layer 116 First Interface 117 Second Interface 12 Second retardation layer 126 The Third Interface 127 The Fourth Interface 13, 13d adhesive layer 41 Surface 51 Surface 52 Groove 71 Mold 72 Energy-curable composition 200 Optical Components Ar, Ar11, Ar12, Ar21, Ar22, Ar23 area d1 Thickness D Depth Dr transmission axis E1 Elliptical polarization ES1 short axis EL1 long axis K1, K2, K3 angle L, L11, L12, L13 light L0 Virtual Light L' projection L1 Linearly polarized LQ LCD NL normal OD, OD1, OD2 orientation axes OD20 symmetrical axis OP points P1, P2, P3, P4, P5 points Pd polarizer pT, pT1, pT2 Light distribution axis direction p pitch Rd radius Sd Reference direction SL Linear light source SP point light source SS surface light source SS0 Light-emitting surface T1, T2 U1 First point U2 Second point W Opening width α Incident azimuth φ incident angle

Claims

1. a first retardation layer; a second retardation layer disposed on the first retardation layer; In the first retardation layer, both the retardation and the optical axis direction are uniform regardless of the position in the plane when viewed from above, A phase difference element, wherein the second phase difference layer has a uniform retardation regardless of the position in the plane when viewed from above, and the optical axis direction differs depending on the position in the plane.

2. Including three-dimensional curved shapes, 2. The phase difference element according to claim 1, wherein the direction of the optical axis when viewed perpendicularly to the surface varies depending on the tilt direction and tilt angle of the surface of the three-dimensional curved shape.

3. each of the first retardation layer and the second retardation layer contains a polymerized liquid crystal; In the first retardation layer, both the retardation and the orientation axis direction are uniform regardless of the position in the plane when viewed from above, 2. The retardation element according to claim 1, wherein the second retardation layer has a uniform retardation regardless of the position in the plane when viewed from above, and an alignment axis direction differs depending on the position in the plane.

4. The retardation element according to claim 3 , wherein the liquid crystal contained in at least one of the first retardation layer and the second retardation layer is twisted in a normal direction of the retardation element.

5. the second retardation layer includes a plurality of regions having different alignment axis directions in a top view, the plurality of regions are arranged in a mosaic pattern when viewed from above, Within each of the plurality of regions in a top view, the orientation axis directions are aligned regardless of the position within the plane, The phase difference element according to claim 4 , wherein the orientation axis directions of the plurality of regions differ depending on the positions of the plurality of regions in the plane when viewed from above.

6. When light having a wavelength of 550 nm is incident perpendicularly on the phase difference element from below, the first retardation layer has a retardation of 70.5 nm or more and 107.7 nm or less for the light, and a total twist amount of the liquid crystal is 6.0° or more and 27.0° or less; In the second retardation layer, when the retardation for the light is 193.7 nm or more and 265.5 nm or less, and the total twist amount of the liquid crystal is −112.5° or more and −95.0° or less, 5. The retardation element according to claim 4, wherein a difference between the alignment axis direction of the first retardation layer and the alignment axis direction of the second retardation layer is −60.9° or more and −38.9° or less.

7. In the first retardation layer as viewed from above, a direction obtained by rotating the orientation axis direction of the first retardation layer counterclockwise by 49.4° is defined as a reference direction, In the second retardation layer as viewed from above, when a point where the alignment axis direction of the second retardation layer is −11.5° or more and 10.5° or less from the reference direction is defined as a first point and an amplitude is defined as Am, an alignment axis direction pT2 of a second point located in a direction rotated counterclockwise by a rotation angle θ around the first point as a rotation center is expressed by the following formula: pT2=Am×sin(2×π×(θ+77.5) / 180) The phase difference element according to claim 6 .

8. When light having a wavelength of 550 nm is incident perpendicularly on the phase difference element from below, the first retardation layer has a retardation of 70.5 nm or more and 107.7 nm or less for the light, and a total twist amount of the liquid crystal is −27.0° or more and −6.0° or less; In the second retardation layer, when the retardation to the light is 193.7 nm or more and 265.5 nm or less, and the total twist amount of the liquid crystal is 95.0° or more and 112.5° or less, 5. The retardation element according to claim 4, wherein a difference between the alignment axis direction of the first retardation layer and the alignment axis direction of the second retardation layer is 38.9° or more and 60.9° or less.

9. In the first retardation layer as viewed from above, a direction obtained by rotating the orientation axis direction of the first retardation layer counterclockwise by −49.4° is defined as a reference direction, In the second retardation layer as viewed from above, a point where the orientation axis direction of the second retardation layer is −10.5° or more and 11.5° or less from the reference direction is defined as a first point, and an amplitude is defined as Am. Then, an orientation axis direction pT2 of a second point located in a direction rotated counterclockwise by a rotation angle θ around the first point as a rotation center is expressed by the following formula: pT2=Am×sin(2×π×(θ-77.5) / 180) The phase difference element according to claim 8 .

10. When light having a wavelength of 550 nm is incident perpendicularly on the phase difference element from below, the first retardation layer has a retardation of 94.9 nm or more and 112.9 nm or less for the light, and a total twist amount of the liquid crystal is 0°; In the second retardation layer, when the retardation to the light is 220.6 nm or more and 255.2 nm or less, and the total twist amount of the liquid crystal is −109.0° or more and −101.0° or less, 5. The retardation element according to claim 4, wherein a difference between the alignment axis direction of the first retardation layer and the alignment axis direction of the second retardation layer is −4.5° or more and 4.5° or less.

11. In the first retardation layer as viewed from above, a direction obtained by rotating the orientation axis direction of the first retardation layer counterclockwise by 34.4° is defined as a reference direction, In the second retardation layer as viewed from above, when a point where the alignment axis direction of the second retardation layer is −4.5° or more and 4.5° or less from the reference direction is defined as a first point and an amplitude is defined as Am, an alignment axis direction pT2 of a second point located in a direction rotated counterclockwise by a rotation angle θ around the first point as a rotation center is expressed by the following formula: pT2=Am×sin(2×π×(θ+69.1) / 180) The phase difference element according to claim 10.

12. When light having a wavelength of 550 nm is incident perpendicularly on the phase difference element from below, the first retardation layer has a retardation of 94.9 nm or more and 112.9 nm or less for the light, and a total twist amount of the liquid crystal is 0°; In the second retardation layer, when the retardation to the light is 220.6 nm or more and 255.2 nm or less, and the total twist amount of the liquid crystal is 101.0° or more and 109.0° or less, 5. The retardation element according to claim 4, wherein a difference between the alignment axis direction of the first retardation layer and the alignment axis direction of the second retardation layer is 29.9 degrees or more and 38.9 degrees or less.

13. In the first retardation layer when viewed from above, a direction obtained by rotating the orientation axis direction of the first retardation layer counterclockwise by −34.4° is defined as a reference direction, In the second retardation layer as viewed from above, when a point where the alignment axis direction of the second retardation layer is −4.5° or more and 4.5° or less from the reference direction is defined as a first point and an amplitude is defined as Am, an alignment axis direction pT2 of a second point located in a direction rotated counterclockwise by a rotation angle θ around the first point as a rotation center is expressed by the following formula: pT2=Am×sin(2×π×(θ-69.1) / 180) The phase difference element according to claim 12.

14. When light having a wavelength of 550 nm is incident perpendicularly on the phase difference element from below, the first retardation layer has a retardation of 79.5 nm or more and 138.5 nm or less for the light, and a total twist amount of the liquid crystal is 8.0° or more and 31.0° or less; In the second retardation layer, when the retardation to the light is 182.1 nm or more and 282.2 nm or less, and the total twist amount of the liquid crystal is −121.0° or more and −94.0° or less, 5. The retardation element according to claim 4, wherein a difference between the alignment axis direction of the first retardation layer and the alignment axis direction of the second retardation layer is −57.7° or more and −34.7° or less.

15. In the first retardation layer as viewed from above, a direction obtained by rotating an alignment axis direction of the first retardation layer by 46.5° counterclockwise is defined as a reference direction, In the second retardation layer when viewed from above, when a point where the orientation axis direction of the second retardation layer is -11.3° or more and 11.7° or less from the reference direction is defined as a first point, the orientation axis direction of a second point located in a direction rotated counterclockwise by -14.3° around the first point as a rotation center is 2.7° or more and 19.7° or less. The phase difference element according to claim 14.

16. When light having a wavelength of 550 nm is incident perpendicularly on the phase difference element from below, the first retardation layer has a retardation of 79.5 nm or more and 138.5 nm or less for the light, and a total twist amount of the liquid crystal is −31.0° or more and −8.0° or less; In the second retardation layer, when the retardation to the light is 182.1 nm or more and 282.2 nm or less, and the total twist amount of the liquid crystal is 94.0° or more and 121.0° or less, 5. The retardation element according to claim 4, wherein a difference between the alignment axis direction of the first retardation layer and the alignment axis direction of the second retardation layer is 34.7° or more and 57.7° or less.

17. In the first retardation layer as viewed from above, a direction obtained by rotating the orientation axis direction of the first retardation layer counterclockwise by −46.5° is defined as a reference direction, In the second retardation layer when viewed from above, when a point where the orientation axis direction of the second retardation layer is -11.7° or more and 11.3° or less from the reference direction is defined as a first point, the orientation axis direction of a second point located in a direction rotated 14.3° counterclockwise around the first point as a rotation center is -19.7° or more and -2.7° or less. The phase difference element according to claim 16.

18. A circularly polarizing plate comprising the retardation element according to claim 1 and a linear polarization element integrated together.

19. The circularly polarizing plate according to claim 18 , having any one of the following distributions (1) to (3): (1) It is flat, and circularly polarized or linearly polarized light is incident, and the angle of the incident light has a distribution of 0° to 30°, or 0° to 50°. (2) Formed along a three-dimensional curved surface, circularly polarized light or linearly polarized light is incident, and the angle of the incident light has a distribution of 0° to 30° or 0° to 50°. (3) Circularly polarized or linearly polarized light is incident, and the angle of the incident light has a distribution of 0° to 50° or a distribution of 30° to 60°.

20. An optical component comprising the circular polarizer according to claim 18.

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