Optical elements and optical deflection devices

Abstract

To provide an optical element and optical deflection device that improve average diffraction efficiency by averaging the diffraction efficiency within the plane. [Solution] The optical element and optical polarizing device comprises a plurality of optical anisotropic layers in the thickness direction having an in-plane orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. The optical anisotropic layers have regions of different lengths until the orientation of the optical axis rotates by 180° in one direction. At least one of the plurality of optical anisotropic layers is a gradient optical anisotropic layer in which, in a cross-sectional image observed with a scanning electron microscope of a cross section cut in the thickness direction along one direction, there are a plurality of pairs of bright and dark lines derived from the orientation of the optical axis along one direction, and the pairs of bright and dark lines are inclined at different inclination angles with respect to the normal of the interface of the optical anisotropic layer.

Description

[Technical Field]

[0001] This disclosure relates to an optical element and an optical deflection device equipped with the optical element. [Background technology]

[0002] Polarization is used in many optical devices and systems, and development is underway to control the reflection, focusing, and divergence of polarized light using optical elements.

[0003] Japanese Patent Publication No. 2014-16632 (hereinafter referred to as Patent Document 1) and Japanese Patent Publication No. 2010-525394 (hereinafter referred to as Patent Document 2), etc., disclose polarizing diffraction elements formed by pattern-aligning liquid crystal compounds having optical anisotropy.

[0004] Furthermore, Japanese Patent Publication No. 2016-519327 (hereinafter referred to as Patent Document 3) discloses a polarization conversion system using a geometric phase element having optical anisotropy with a local optical axis direction that changes nonlinearly in at least one dimension along the surface. Here too, the pattern orientation of liquid crystal compounds is utilized. [Overview of the project] [Problems that the invention aims to solve]

[0005] Patent documents 1 and 2 do not describe a technique for causing light to be emitted in different directions depending on the incident position, nor do they contain any such description. Our investigations have revealed that when light is incident on a layer having optical anisotropy with a local optical axis that changes nonlinearly in one dimension, as described in Patent Document 3, the degree of diffraction differs depending on the incident position. In such an element, when light is incident and emitted at different incident angles depending on the region, the in-plane diffraction efficiency differs depending on the region, and regions with reduced diffraction efficiency sometimes occur.

[0006] In view of the above circumstances, this disclosure aims to provide an optical element and an optical deflection device that improve the average diffraction efficiency by averaging the diffraction efficiency in the plane. [Means for solving the problem]

[0007] The technology disclosed herein includes the following aspects: <1> The material comprises multiple optically anisotropic layers in the thickness direction, each having an in-plane orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. The above optical anisotropy layer has regions whose lengths differ from each other until the orientation of the optical axis rotates by 180° in one direction. An optical element in which at least one of the above-mentioned plurality of optical anisotropic layers is a gradient optical anisotropic layer in which, in a cross-sectional image obtained by observing a cross-section cut in the thickness direction along the above-mentioned direction with a scanning electron microscope, there are multiple pairs of bright and dark lines originating from the orientation of the optical axis along the above-mentioned direction, and the pairs of bright and dark lines are inclined at different inclination angles with respect to the normal to the interface of the optical anisotropic layer. <2> The above-described gradient optical anisotropy layer comprises two layers, and in the above cross-sectional image, the inclination angles of the pairs of bright and dark lines in one gradient optical anisotropy layer and the pairs of bright and dark lines in the other gradient optical anisotropy layer are different from each other in at least a portion of the opposing regions of the two gradient optical anisotropy layers. <1> Optical elements as described above. <3> The above-mentioned gradient optical anisotropy layer comprises two layers, and in the above cross-sectional image, the two gradient optical anisotropy layers are such that, in at least a portion of the opposing regions, the normal to the pair of bright and dark lines in one gradient optical anisotropy layer and the normal to the pair of bright and dark lines in the other gradient optical anisotropy layer The direction of the slope is different. <1> or <2> An optical element as described in any of the following. <4> The optical element according to any one of <1> to <3>, comprising two of the inclined optically anisotropic layers, wherein in the cross-sectional image, the inclination directions of the pairs of bright lines and dark lines in one of the two inclined optically anisotropic layers and the pairs of bright lines and dark lines in the other inclined optically anisotropic layer with respect to the normal line are the same in at least a part of the opposing regions. <5> The optical element according to any one of <1> to <4>, wherein the inclined optically anisotropic layer has a region in which the optical axis is twisted and oriented in the thickness direction. <6> The optical element according to any one of <1> to <5>, which has a function of diffracting and transmitting incident light. <7> The optical element according to any one of <1> to <5>, wherein in the inclined optically anisotropic layer, the liquid crystal compound is in a cholesteric alignment. <8> The optical element according to <7>, which has a function of diffracting and reflecting incident light. <9> The optical element according to any one of <1> to <8>, wherein the in-plane alignment pattern of the optically anisotropic layer is a pattern in which the length until the direction of the optical axis rotates 180° in the one direction gradually changes in the one direction. <10> The in-plane alignment pattern of the optically anisotropic layer is a pattern having the one direction radially from the inside to the outside. <1> to <9> The optical element according to any one of <1> to <9>. <11> The optical element according to any one of <1> to <10>, which has a region in which the length until the direction of the optical axis rotates 180° in the one direction is 10 μm or less in the in-plane alignment pattern of the optically anisotropic layer. <12> An optical deflection device including an optical deflection element that deflects and emits incident light, a driving means for driving the optical deflection element, and an optical element according to any one of <1> to <11> disposed on the light emission side of the optical deflection element.

Advantages of the Invention

[0008] According to the present disclosure, in the optical element and the optical deflection device, the diffraction efficiency in the plane can be averaged, and the average diffraction efficiency can be improved.

Brief Description of Drawings

[0009] [Figure 1] It is a plan view schematically showing the orientation pattern of the optical axis in a part of the surface of the optical element of the first embodiment. [Figure 2] It is a schematic diagram of a cross-sectional image obtained by a scanning microscope for the optical element shown in FIG. 1. [Figure 3] It is a diagram schematically showing the liquid crystal alignment patterns in the thickness direction (z direction) and the horizontal direction (x direction) of the optical element shown in FIG. 1. [Figure 4] It is a conceptual diagram showing the action of the optically anisotropic layer having a horizontal rotation alignment pattern. [Figure 5] It is a schematic diagram of a cross-sectional image obtained by a scanning microscope for the optical element of the second embodiment. [Figure 6] It is a schematic diagram of a cross-sectional image obtained by a scanning microscope for the optical element of the third embodiment. [Figure 7] It is a diagram schematically showing the cross-section of the optical element of the fourth embodiment. [Figure 8] It is a plan view schematically showing the orientation pattern of the optical axis on the surface of the optical element of the design change example. [Figure 9] It is a diagram conceptually showing an example of an exposure apparatus for exposing an alignment film to form an alignment pattern. [Figure 10] It is a diagram showing a schematic configuration of an example of an optical deflection device. [Figure 11] It is a diagram showing the layer structure of the optical element of Comparative Example 1. [Figure 12] It is a diagram showing the layer structure of the optical element of Example 1. [Figure 13] It is a diagram showing the layer structure of the optical element of Example 2. [Figure 14] It is a diagram showing the layer structure of the optical element of Example 3. [Figure 15] It is a diagram showing the layer structure of the optical element of Example 4. [Figure 16] It is a diagram showing the layer structure of the optical element of Example 5. [Figure 17]This is a conceptual diagram illustrating a method for measuring transmitted light intensity. [Figure 18] This figure shows the layer configuration of the optical element in Comparative Example 11. [Figure 19] This figure shows the layer configuration of the optical element in Example 11. [Figure 20] This is a conceptual diagram illustrating a method for measuring reflected light intensity. [Modes for carrying out the invention]

[0010] Embodiments of the optical element of the present invention will be described below with reference to the drawings. In each drawing, the scale of the components has been appropriately changed from the actual scale for ease of viewing. In this specification, numerical ranges represented by "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits, respectively. Furthermore, "orthogonal" and "parallel" in relation to angles mean a range of ±10° from the exact angle.

[0011] [Optical elements] Figure 1 is a schematic plan view showing a portion of the surface of the optical element 1 of the first embodiment, and Figure 2 is a schematic diagram of a cross-sectional image obtained by observing the cross-section of the optical element 1 with a scanning electron microscope (SEM). In the following drawings, the sheet surface of the sheet-like optical element is defined as the xy plane, and the thickness direction is defined as the z direction.

[0012] The optical element 1 comprises two optically anisotropic layers 10 and 20 stacked in the thickness direction. The optically anisotropic layers 10 and 20 consist of a cured layer of a composition containing a liquid crystal compound. The optical element 1 may also have a support and an alignment film, with the optically anisotropic layers provided on the alignment film. The optical element of this disclosure may have multiple optically anisotropic layers in the thickness direction and is not limited to a two-layer structure; it may have three or more layers.

[0013] The optically anisotropic layers 10 and 20 have an in-plane orientation pattern (in-plane liquid crystal orientation pattern) in which the orientation of the optical axis 30A derived from the liquid crystal compound changes while continuously rotating along at least one direction A in the plane. Figure 1 schematically shows the in-plane orientation pattern of the optical axis 30A derived from the liquid crystal compound on the surface of the optically anisotropic layer 20.

[0014] The optical axis 30A derived from the liquid crystal compound is the long axis direction of the rod shape (slow phase axis) in the case of a rod-shaped liquid crystal compound, and the direction perpendicular to the disc surface (advancing phase axis) in the case of a disc-shaped liquid crystal compound. In the following explanation, the optical axis 30A derived from the liquid crystal compound will also be referred to as the optical axis 30A of the liquid crystal compound, or simply as the optical axis 30A.

[0015] An in-plane orientation pattern in which the orientation of the optical axis 30A changes while continuously rotating in one direction A is a pattern in which the angle between the optical axis 30A of the liquid crystal compound, which is arranged along one direction A (hereinafter also referred to as axis A), and axis A differs depending on the position in the direction of axis A, and the angle between the optical axis 30A and axis A gradually changes from φ to φ+180° or φ-180° along axis A, and is oriented and fixed in this manner. In the following, an in-plane orientation pattern in which, as shown in Figure 1, the optical axis of the liquid crystal compound is parallel to the plane of the optical anisotropic layer and local regions (unit regions) in which the orientation of the optical axis is constant are arranged such that the orientation of the optical axis changes continuously in one direction between multiple local regions arranged in one direction. This in-plane orientation pattern is referred to as a horizontal rotation orientation pattern.

[0016] Furthermore, "the angle between the optical axis 30A and axis A gradually changes" means that the orientation of the optical axis may change by a predetermined angle within a unit region, or it may change at non-uniform angular intervals rather than constant angular intervals, or it may change continuously. This is also acceptable. However, the angular difference of the optical axes 30A between adjacent unit regions in the x-direction is preferably 45° or less, more preferably 15° or less, and even more preferably a smaller angle.

[0017] In optical element 1, in such a horizontal rotation orientation pattern of liquid crystal compound 30, the length (distance) over which the optical axis 30A of the liquid crystal compound 30 rotates by 180° is defined as the length of one period in the horizontal rotation orientation Λ. In other words, the length of one period in the horizontal rotation orientation pattern is the distance from the angle φ between the optical axis 30A of the liquid crystal compound 30 and axis A to φ+180°. In the following explanation, this length of one period Λ will also be referred to as "period Λ" or simply "period Λ".

[0018] In the optical element 1, the optical anisotropic layers 10 and 20 contain regions in the direction of axis A where the length of one period Λ is different from each other. In the example shown in Figure 1, the length of one period in the direction of axis A is Λ A1 ,Λ A2 ,Λ A3 …(Here, Λ A1 <Λ A2 <Λ A3 ) includes regions A1, A2, A3, etc. that are different from the given region. In this example, the liquid crystal alignment pattern has a period that gradually shortens from right to left on the page, but the optical element of this disclosure only needs to have two or more regions with different period lengths. However, when applied to an optical deflection device described later, a liquid crystal alignment pattern in which the period length gradually changes, as shown in this example, is preferred. It is preferable to include a region with a period Λ of 10 μm or less.

[0019] In addition, while the lengths of one period in opposing regions between multiple optically anisotropic layers may differ, it is preferable that they coincide within a range of ±10%. This configuration allows for the synchronization of periods by forming multiple optical anisotropic layers in an order in which the first optical anisotropic layer is formed first, followed by the second optical anisotropic layer through coating or other means.

[0020] As shown in Figure 1, when an optical element 1, which has an optically anisotropic layer between two polarizers orthogonal to the orientation pattern of the optical axis, is observed with an optical microscope, alternating bright areas 42 and dark areas 44 are observed. The period of light and dark (i.e., the period of the bright area or the period of the dark area) is half the period Λ of the horizontal rotation orientation pattern of the optical axis.

[0021] Of the two optically anisotropic layers 10 and 20, at least one layer, in this example the first optically anisotropic layer 10, is a gradient optically anisotropic layer. Hereinafter, the first optically anisotropic layer will also be referred to as the gradient optically anisotropic layer 10. Here, a gradient optically anisotropic layer is a layer in which, in a cross-sectional image (hereinafter referred to as a cross-sectional SEM image) obtained by observing a cross-section cut in the thickness direction along one direction with a scanning electron microscope (SEM), there are multiple pairs of bright and dark lines (bright and dark lines) along one direction, and the bright and dark lines are inclined at different angles of inclination relative to the normal n of the interface of the layer. "Bright and dark lines originating from the direction of the optical axis" are bright and dark lines observed according to the orientation state of the liquid crystal compound in the thickness direction of the optically anisotropic layer.

[0022] Figure 2 is a schematic diagram of a cross-sectional image obtained by SEM when a cross-section is cut in the thickness direction along one direction of rotation of the optical axis. As shown in Figure 2, in the cross-sectional image, there are multiple pairs of bright and dark lines that are inclined obliquely with respect to the normal n of the interface of the gradient optical anisotropy layer 10. The inclination of the interface between light and dark lines with respect to the normal n varies depending on the x-direction position, and in this example, the inclination angle gradually increases in the x-axis direction (α1 < α2 < α3…). Here, the inclination angle of the light and dark lines is defined as the acute angle less than 90° among the angles that the light and dark lines make with the normal n.

[0023] In the gradient optical anisotropy layer 10, for example, in addition to horizontal rotational orientation, twisting in the thickness direction Due to the presence of orientation, light and dark lines can be observed in the cross-sectional image described above.

[0024] Figure 3 schematically shows the liquid crystal alignment pattern in the cross-section of the optical element 1 shown in Figures 1 and 2. Here, the liquid crystal compound is a rod-shaped liquid crystal compound 30. In Figure 3, the light and dark lines observed when the cross-section is observed with an SEM are superimposed.

[0025] As shown in Figure 3, the gradient optical anisotropy layer 10 has a liquid crystal orientation pattern in which rod-shaped liquid crystal compounds 30 (hereinafter simply referred to as liquid crystal compounds 30) are horizontally rotated in the x-direction and twisted in the thickness direction.

[0026] "The optical axes are twisted in the thickness direction" means that the orientation of the optical axes, which are arranged in the thickness direction from one surface to the other of the optically anisotropic layer 10, changes relatively and becomes twisted in one direction, and is fixed in that state. There are right-hand twists and left-hand twists, and the appropriate one should be applied depending on the direction in which diffraction is to be performed. Note that the twist of the optical axes in the thickness direction is less than one rotation, i.e., the twist angle is less than 360°. For example, in the example in Figure 3, the optical axes of the liquid crystal compound 30 rotate by approximately 140° between one surface and the other surface in the thickness direction (z direction). The twist angle of the liquid crystal compound 30 in the thickness direction is preferably between 10° and 200°, and more preferably between 45° and 180°. In the case of cholesteric orientation, which will be described later, the twist angle is 360° or more, and it has selective reflectivity that reflects specific circularly polarized light in a specific wavelength range. In this specification, "torsional orientation" does not include cholesteric orientation, and selective reflectivity does not occur in optically anisotropic layers having torsional orientation.

[0027] When a cross-section of a gradient optical anisotropy layer having such a liquid crystal alignment pattern is observed using a scanning electron microscope (SEM), the light and dark lines shown in Figure 2 are observed. As shown by superimposing the light and dark lines in Figure 3, the period of these light and dark lines coincides with the period of the horizontal rotational alignment.

[0028] On the other hand, in the cross-sectional view, multiple alternating light and dark lines are also present in the second optical anisotropy layer 20, but the light and dark lines of the second optical anisotropy layer 20 are along the normal n of the interface of the optical anisotropy layer 20 and have no slope. In the second optical anisotropy layer 20, the orientation of the optical axis in the thickness direction is uniform.

[0029] Furthermore, in this optical element 1, as shown in Figure 2, the period of horizontal rotation orientation in the first optical anisotropy layer 10 is Λ A1 , Λ A2…and the period Λ of the horizontal rotational alignment in the second optically anisotropic layer 20 B1 Λ B2 …match in the opposing regions. That is, Λ A1 = Λ B1 Λ A2 = Λ B2 …and so on.

[0030] The optical element 1 diffracts and transmits the incident light. For example, when incident light L in of a predetermined circular polarization is incident, the incident light L in receives a refractive power from the optically anisotropic layer 20 and emits light in a bent direction. The refractive power varies depending on the period of the horizontal rotational alignment, and the smaller the period, the larger the diffraction angle obtained. When incident light L in of a predetermined circular polarization is incident at the same incident angle in regions where the periods of the horizontal rotational alignment in the optically anisotropic layers 10 and 20 are different, the diffraction angle of the emitted light L out1 in the region where the period is relatively small is larger than that of the emitted light L out2 in the region where the period is relatively large.

[0031] Here, the principle by which the optically anisotropic layer having a horizontal rotational alignment pattern functions as a transmissive diffraction element will be briefly described with reference to FIG. 4. When functioning as a transmissive diffraction element, the optically anisotropic layer preferably has an in-plane retardation Re(λ) (=Δn λ ×d) with respect to the wavelength λ of 0.3λ to 0.7λ. The retardation Re is preferably 0.4λ to 0.6λ, more preferably 0.45λ to 0.55λ, and particularly preferably 0.5λ. Δn λ is the Birefringence, d is the thickness of the optical anisotropy layer. For example, if we assume that 940 nm light is the incident light, the retardation Re for 940 nm light should be in the range of 282 nm to 658 nm, and 470 nm is particularly preferred. When such retardation Re is present, the optical anisotropy layer functions as a general λ / 2 plate, that is, it provides a phase difference of 180° (=π=λ / 2) between the orthogonal linearly polarized components of the incident light. Note that a retardation closer to λ / 2 is preferable as it improves diffraction efficiency, but the retardation is not limited to the above range. When the optical anisotropy layer has retardation of approximately λ / 2, it imparts a phase difference of λ / 2 to the incident light, converting the incident light, which has a predetermined circular polarization, into circularly polarized light with the opposite polarity before emission.

[0032] Figure 4 shows that for an optical anisotropy layer 11 having a horizontal rotation orientation pattern, the incident light L1 is a right-circularly polarized light P with wavelength λ. R The effect of the optical anisotropy layer 11 when used is conceptually shown. When incident light L1 of right circular polarization with wavelength λ is incident on the optical anisotropy layer 11, the incident light L1, which is right circular polarization PR, passes through the optical anisotropy layer 11 and is given a phase difference of λ / 2, becoming left circular polarization P L It is converted to this. In addition, the absolute phase of the incident light L1 changes depending on the optical axis 30A of the liquid crystal compound 30 in each unit region (local region) in the horizontal rotation orientation pattern. Here, in the optical anisotropy layer, the orientation of the optical axis 30A of the liquid crystal compound 30 changes by rotating along axis A, so the amount of change in absolute phase differs depending on the orientation of the optical axis 30A of the liquid crystal compound 30 at the position of axis A of the optical anisotropy layer 11 into which the incident light is incident. The region shown by the dashed line in Figure 4 schematically shows how the amount of change in absolute phase Q differs depending on the x coordinate.

[0033] As shown in Figure 4, the shift in absolute phase Q when passing through the optical anisotropy layer 11 forms an equiphase surface E with an absolute phase that is at an angle to the surface of the optical anisotropy layer 11. As a result, a bending force is applied to the incident light L1 that enters from the normal direction in a direction perpendicular to the equiphase surface E, and the direction of propagation of the incident light L1 changes. That is, the incident light L1, which is right-circularly polarized PR, becomes left-circularly polarized PL after passing through the optical anisotropy layer 11 and is emitted from the optical anisotropy layer 11 as emitted light L2 that travels in a direction that makes a predetermined angle with the normal direction.

[0034] Furthermore, when left-circularly polarized light is incident on the optical anisotropy layer 11, the incident light is converted to right-circularly polarized light in the optical anisotropy layer 11 and is subjected to a bending force in the opposite direction to that shown in the figure, causing a change in its direction of propagation. Also, if the rotation direction of the horizontal rotation orientation of the optical axis 30A of the liquid crystal compound 30 is reversed, the direction of refraction of light by the optical anisotropy layer will be the opposite of the above.

[0035] The shorter the period of one cycle in the in-plane orientation pattern within the optical anisotropy layer, the greater the bending force that can be imparted to the incident light, thus increasing the diffraction angle.

[0036] Furthermore, the wavelength λ of light that causes diffraction by the optical anisotropy layer 11 may range from ultraviolet to visible light, infrared, or even electromagnetic waves. For the same period, a larger wavelength of incident light results in a larger diffraction angle, while a smaller wavelength results in a smaller diffraction angle. Therefore, the period should be set according to the target wavelength and the desired diffraction angle.

[0037] The above explanation described the case where a bending force is applied to light incident from the normal direction, but the same principle applies to light incident at an oblique angle, and it is possible to obtain emitted light with an exit angle different from the angle of incidence.

[0038] In this configuration, the optical element 1 has first and second optical anisotropy layers 10 and 20, each containing regions with different periods of horizontal rotation orientation patterns within their respective planes, so that light with different emission angles can be emitted for the same incident angle. In cases where the second optical anisotropy layer 20 is not torsionally oriented in the thickness direction, the diffraction efficiency for light incident in the normal direction is high, but for obliquely incident light... There is a problem in that the diffraction efficiency for incoming light is low. On the other hand, the gradient optical anisotropy layer 10 can improve the diffraction efficiency for light incident at an oblique angle.

[0039] The optical element 1 has a stacked structure of two or more optically anisotropic layers, of which at least one layer is a graded optically anisotropic layer. Therefore, the average diffraction efficiency can be improved when the incident angle is varied depending on the region, and the intensity difference of the emitted light can be suppressed and the emitted intensity can be averaged.

[0040] In this example, the optical anisotropy layer has a two-layer structure, but it may have three or more layers. Furthermore, the gradient optical anisotropy layer may be a single layer, but it is more preferable to have two or more layers.

[0041] As the optical elements 2 and 3 of the second and third embodiments, Figures 5 and 6 show examples of configurations comprising two gradient optical anisotropy layers. Figures 5 and 6 are schematic diagrams of cross-sectional images of the respective optical elements 2 and 3. The cross-sectional images are SEM images observed by cutting a cross section in the thickness direction along one direction of horizontal rotation orientation, as described above.

[0042] As shown in Figure 5, in a cross-sectional view of two gradient optical anisotropy layers, the inclination direction of the light and dark lines in one gradient optical anisotropy layer 10 relative to the normal n may be different from the inclination direction of the light and dark lines in the other gradient optical anisotropy layer 22 relative to the normal n in the opposing regions of the two layers. Different inclination directions relative to the normal n mean that the inclination direction of the light and dark lines in one gradient optical anisotropy layer 10 is on the negative side of the x-axis (left side of the paper), while the inclination direction of the light and dark lines in the other gradient optical anisotropy layer 22 is on the positive side of the x-axis (right side of the paper). The inclination angles of the two gradient optical anisotropy layers relative to the normal n may be the same in the opposing regions (α n =β n ) and even if they are different (α n ≠β n ) Good. In the case of two gradient optical anisotropy layers, the opposing regions where the inclination directions of the light and dark lines of each layer are different may extend over the entire region or only to a portion of it. In this specification, the opposing regions of the two gradient optical anisotropy layers are regions in the same xy region that overlap when viewed from the thickness direction.

[0043] By reversing the torsional orientation of the torsional orientation in the thickness direction of one gradient optical anisotropy layer 10 and the other gradient optical anisotropy layer 22, the inclination of the light and dark lines relative to the normal of each layer can be reversed.

[0044] As shown in Figure 6, in a cross-sectional view, the two gradient optical anisotropy layers may have the same inclination direction for the interface between light and dark lines in one gradient optical anisotropy layer 10 relative to the normal n, and the same inclination direction for the interface between light and dark lines in the other gradient optical anisotropy layer 24 relative to the normal n, in the opposing regions of the two layers. However, here, the inclination angle α of the light and dark lines in one gradient optical anisotropy layer 10 in the opposing region. n And the inclination angle γ of the light and dark lines in the other gradient optical anisotropy layer 24. n These are different from each other. Furthermore, if two gradient optical anisotropy layers are provided, the opposing regions where the inclination directions of the light and dark lines are the same may extend throughout the entire region or only partially.

[0045] By making the torsional orientation pitch in the thickness direction different in one gradient optical anisotropy layer 10 and the other gradient optical anisotropy layer 22, the inclination of the light and dark lines relative to the normal can be made different. A different torsional pitch means that the thickness required for the optical axis to twist to the same twist angle is different.

[0046] Furthermore, in a single optical element, two gradient optical anisotropy layers may simultaneously include opposing regions with the same tilt direction and opposing regions with different tilt directions.

[0047] In the above, we have described an optical element that functions as a transmission-type diffraction element, but this The optical element shown can also function as a reflective diffracting element.

[0048] Figure 7 shows a cross-sectional view of the optical element 5 of the fourth embodiment, which functions as a reflective diffraction element. Figure 7 schematically shows the light and dark lines in the cross-sectional SEM image.

[0049] The optical element 5 comprises two gradient optical anisotropy layers 12 and 14. Both of the two gradient optical anisotropy layers 12 and 14 are horizontally rotationally oriented and cholesterically oriented in the thickness direction. In the horizontal rotation orientation, the directions of rotation of the optical axes of the two gradient optical anisotropy layers 12 and 14 are opposite to each other, and the directions of rotation in the cholesteric orientation are also opposite.

[0050] The gradient optical anisotropy layers 12 and 14 have cholesteric orientation and therefore selectively reflect only light in a specific selected wavelength range of a specific circular polarization. The central wavelength of the light that is selectively reflected is determined by the cholesteric helical pitch and film thickness, and which circular polarizations are reflected is determined by the direction of rotation of the helix.

[0051] Because the liquid crystal orientation pattern has both horizontal rotational orientation and cholesteric orientation, in the cross-sectional image, light and dark lines with different angles of inclination are observed, similar to the embodiments described above, and they have an inclination in the normal direction (see Figure 7).

[0052] Since the orientation pattern of the optical axis 30A in the in-plane direction of the gradient optical anisotropy layers 12 and 14 is horizontal rotation orientation, as in the previous embodiment, it produces the same effect as the optical element 1. That is, it has the effect of changing the absolute phase of incident light and bending it in a predetermined direction. Therefore, the optical element 5 has the effect of bending incident light in a direction different from the incident direction and the effect of the cholesteric orientation described above, and reflects light at a predetermined angle with respect to the reflection direction of specular reflection. Furthermore, since there are regions with different periods of horizontal rotation orientation in the in-plane direction, it is possible to reflect light at different reflection angles for the same incident angle. Furthermore, it is possible to improve the average diffraction efficiency when the incident angle is varied depending on the region, and to suppress differences in the intensity of reflected light.

[0053] In each of the above embodiments, a pattern is shown in which one period of horizontal rotation orientation gradually lengthens in the x-direction. As an optical element, it is also preferable that the optical anisotropy layer has an in-plane orientation pattern in which one period gradually shortens from the center in one axis direction toward one end and the other end.

[0054] Furthermore, as shown in Figure 8, it is also preferable to have an in-plane orientation pattern in which one direction of horizontal rotation orientation is set radially from the inside to the outside. Figure 8 is a schematic plan view of the optical anisotropy layer of an optical element in an example of a design change. In Figure 8, the in-plane orientation pattern is indicated by the optical axis 30A of the liquid crystal compound. The optical anisotropy layer has concentric regions in which the direction of the optical axis is the same, and an in-plane orientation pattern in which one direction in which the direction of the optical axis 30A changes while continuously rotating is provided radially from the center of the optical anisotropy layer 15.

[0055] In the optical anisotropy layer 15, the orientation of the optical axis 30A changes while continuously rotating along multiple directions extending outward from the center of the optical anisotropy layer 15, such as the directions indicated by arrows A1, A2, and A3. The direction of rotation of the optical axis along each axis is rotationally symmetric with respect to the center.

[0056] When an optical element 1, which has an optically anisotropic layer with the in-plane orientation pattern shown in Figure 8, is sandwiched between two orthogonal polarizers and observed with an optical microscope, alternating bright and dark areas are observed in a concentric pattern. The period of light and dark on the concentric periodic orientation surface (i.e., the period of the dark area or the period of the bright area) is half the period Λ of the horizontal rotation orientation pattern. The period is directed outward. Because the diameters gradually shorten, the difference between the diameters of concentric circles becomes smaller as you move towards the outermost circle.

[0057] When circularly polarized light is incident on the optically anisotropic layer 15 having this in-plane orientation pattern, the absolute phase changes in each local region where the optical axis orientation of the liquid crystal compound 30 is different. In this case, the amount of change in the absolute phase differs depending on the orientation of the optical axis of the liquid crystal compound 30 to which the circularly polarized light is incident.

[0058] As mentioned above, the angle of refraction of light with respect to the incident direction increases as the period Λ in the liquid crystal alignment pattern becomes shorter. Therefore, by gradually shortening the period Λ in the in-plane alignment pattern from the center of the optical anisotropy layer 15 outward in one direction in which the optical axis rotates continuously, the focusing or diverging power of light by the optical anisotropy layer 15 can be further improved.

[0059] Conversely, the period Λ in the concentric liquid crystal alignment pattern may be gradually lengthened from the center of the optical anisotropy layer 15 outward in one direction in which the optical axis rotates continuously. Furthermore, depending on the application of the optical element, such as when it is desired to provide a light intensity distribution in transmitted light, it is also possible to use a configuration in which, instead of gradually changing the period Λ in one direction in which the optical axis rotates continuously, there are regions in which the period Λ is partially different in one direction in which the optical axis rotates continuously.

[0060] Next, the constituent materials and forming methods for the optical elements of this disclosure will be described.

[0061] <Optical anisotropy layer> A liquid crystal composition containing a liquid crystal compound for forming an optically anisotropic layer may also contain other components such as leveling agents, alignment control agents, polymerization initiators, and alignment aids in addition to the liquid crystal compound. By forming an alignment film on a support and then coating and curing the liquid crystal composition on the alignment film, an optically anisotropic layer with a predetermined liquid crystal alignment pattern fixed, consisting of a cured layer of the liquid crystal composition, can be obtained.

[0062] -Rod-shaped liquid crystal compound- Preferred rod-shaped liquid crystal compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyanosubstituted phenylpyrimidines, alkoxysubstituted phenylpyrimidines, phenyldioxanes, trans, and alkenylcyclohexylbenzonitriles. In addition to the low molecular weight liquid crystal molecules described above, high molecular weight liquid crystal molecules can also be used.

[0063] It is more preferable to fix the orientation of the rod-shaped liquid crystal compound by polymerization, and as polymerizable rod-shaped liquid crystal compounds, compounds described in Makromol. Chem., Vol. 190, p. 2255 (1989), Advanced Materials Vol. 5, p. 107 (1993), U.S. Patent No. 4683327, No. 5622648, No. 5770107, International Publication Nos. 95 / 22586, 95 / 24455, 97 / 00600, 98 / 23580, 98 / 52905, Japanese Patent Publication No. 1-272551, 6-16616, 7-110469, 11-80081, and Japanese Patent Publication No. 2001-328973 can be used. Furthermore, as rod-shaped liquid crystal compounds, those described in Japanese Patent Publication No. 11-513019 and Japanese Patent Application Publication No. 2007-279688 can also be preferably used.

[0064] -Disc-shaped liquid crystal compound- Examples of disc-shaped liquid crystal compounds include those described in Japanese Patent Publication No. 2007-108732 and Japanese Patent Publication No. 2 The materials described in Publication No. 010-244038 can be preferably used.

[0065] -Other ingredients- Furthermore, known materials can be used for other components such as orientation control agents, polymerization initiators, and orientation aids. In order to obtain an optically anisotropic layer having torsional orientation in the thickness direction or an optically anisotropic layer having cholesteric orientation in the thickness direction, a chiral agent is added.

[0066] --Chiral agents (optically active compounds)-- Chiral agents have the function of inducing a helical structure in the cholesteric liquid crystal phase. Since different chiral agents induce different helical twist directions or helical pitches, they should be selected according to the purpose. There are no particular restrictions on the chiral agent; known compounds can be used (e.g., Liquid Crystal Device Handbook, Chapter 3, Section 4-3, TN (twisted nematic), STN (Super Chiral agents for twisted nematics (described on page 199 in "Chiral agents for twisted nematics," edited by the 142nd Committee of the Japan Society for the Promotion of Science, 1989), such as isosorbide and isomannide derivatives can be used. Chiral agents generally contain an asymmetric carbon atom, but axially asymmetric compounds or planar asymmetric compounds that do not contain an asymmetric carbon atom can also be used as chiral agents. Examples of axially asymmetric compounds or planar asymmetric compounds include binaphthyl, helicene, paracyclophane, and their derivatives. Chiral agents may have polymerizable groups. If both the chiral agent and the liquid crystal compound have polymerizable groups, a polymerization reaction between the polymerizable chiral agent and the polymerizable liquid crystal compound can form a polymer having repeating units derived from the polymerizable liquid crystal compound and repeating units derived from the chiral agent. In this embodiment, it is preferable that the polymerizable group of the polymerizable chiral agent is of the same type as the polymerizable group of the polymerizable liquid crystal compound. Therefore, the polymerizable group of the chiral agent is preferably an unsaturated polymerizable group, an epoxy group, or an azilidinyl group, more preferably an unsaturated polymerizable group, and even more preferably an ethylenically unsaturated polymerizable group. Furthermore, the chiral agent may be a liquid crystal compound.

[0067] When the chiral agent has a photoisomerizing group, it is preferable because, after coating and orientation, a pattern of the desired reflection wavelength corresponding to the emission wavelength can be formed by photomask irradiation with active light or the like. Preferred photoisomerizing groups are the isomerization site of a photochromic compound, an azo group, an azoxy group, or a cinnamoyl group. Specific compounds that can be used include those described in Japanese Patent Publication No. 2002-80478, 2002-80851, 2002-179668, 2002-179669, 2002-179670, 2002-179681, 2002-179682, 2002-338575, 2002-338668, 2003-313189, and 2003-313292, etc.

[0068] -solvent- Organic solvents are preferably used as solvents for liquid crystal compositions. Examples of organic solvents include amides (e.g., N,N-dimethylformamide), sulfoxides (e.g., dimethyl sulfoxide), heterocyclic compounds (e.g., pyridine), hydrocarbons (e.g., benzene, hexane), alkyl halides (e.g., chloroform, dichloromethane), esters (e.g., methyl acetate, butyl acetate), ketones (e.g., acetone, methyl ethyl ketone, cyclohexanone), and ethers (e.g., tetrahydrofuran, 1,2-dimethoxyethane). Alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination.

[0069] <Formation of optically anisotropic layer> An optically anisotropic layer can be formed, for example, by multilayer coating of a liquid crystal composition on an alignment film. Multilayer coating refers to a process in which a liquid crystal composition is coated onto an alignment film, heated, cooled, and then cured with ultraviolet light to create the first liquid crystal immobilization layer. Subsequent layers are then applied on top of this liquid crystal immobilization layer, and the process of heating, cooling, and UV curing is repeated.

[0070] <Support> The support is used to support the optically anisotropic layer or the optically anisotropic layer and the alignment film. The support is not an essential component of the optical element. It may be used when forming the optically anisotropic layer and then peeled off.

[0071] Various sheet-like materials (films, plates) can be used as the support, as long as they can support the optically anisotropic layer. As the support, a transparent support is preferred, and examples include polyacrylic resin films such as polymethyl methacrylate, cellulose resin films such as cellulose triacetate, cycloolefin polymer films (for example, "Arton" manufactured by JSR Corporation, "Zeonor" manufactured by Nippon Zeon Corporation), polyethylene terephthalate (PET), polycarbonate, and polyvinyl chloride. The support is not limited to a flexible film, but may also be a non-flexible substrate such as a glass substrate.

[0072] There are no restrictions on the thickness of the support; the thickness should be set appropriately to accommodate the alignment film and the optical anisotropy layer, depending on the application of the optical element and the material used to form the support. The thickness of the support is preferably 1 to 1000 μm, more preferably 3 to 250 μm, and even more preferably 5 to 150 μm.

[0073] <Orientation film> The alignment film is provided to orient the liquid crystal compound into a predetermined liquid crystal alignment pattern when forming the optical anisotropic layer.

[0074] Various known alignment films can be used. Examples include rubbing-treated films made of organic compounds such as polymers, obliquely vapor-deposited films of inorganic compounds, films having microgrooves, and films formed by accumulating Langmuir-Blodgett (LB) films of organic compounds such as ω-tricosanoic acid, dioctadecylmethylammonium chloride, and methyl stearylate using the Langmuir-Blodgett method.

[0075] An oriented film formed by rubbing can be created by rubbing the surface of a polymer layer several times in a specific direction with paper or cloth. Preferred materials for use in the orientation film include polyimide, polyvinyl alcohol, polymers having polymerizable groups as described in Japanese Patent Publication No. 9-152509, materials used for forming orientation films as described in Japanese Patent Publication No. 2005-97377, Japanese Patent Publication No. 2005-99228, and Japanese Patent Publication No. 2005-128503.

[0076] In the optical elements of this disclosure, a so-called photo-alignment film is preferably used as the alignment film, which is formed by irradiating a photo-alignable material with polarized or unpolarized light. That is, in the optical elements of this disclosure, a photo-alignment film formed by coating a photo-alignment material onto a support is preferably used as the alignment film. Polarized light irradiation can be applied perpendicularly or obliquely to the photo-alignment film, while unpolarized light irradiation can be applied obliquely to the photo-alignment film.

[0077] Examples of photo-alignment materials used in photo-alignment films include those described in Japanese Patent Publication No. 2006-285197, 2007-76839, 2007-138138, 2007-94071, 2007-121721, 2007-140465, 2007-156439, and 2007-1331 Azo compounds described in Japanese Patent Publication No. 84, Japanese Patent Publication No. 2009-109831, Japanese Patent Publication No. 3883848 and Japanese Patent Publication No. 4151746, aromatic ester compounds described in Japanese Patent Publication No. 2002-229039, maleimides having photo-orienting units described in Japanese Patent Publication No. 2002-265541 and Japanese Patent Publication No. 2002-317013 and / or Examples of preferred materials include alkenyl-substituted nadiimide compounds, photocrosslinkable silane derivatives described in Japanese Patent Nos. 4205195 and 4205198, photocrosslinkable polyimides, photocrosslinkable polyamides and photocrosslinkable esters described in Japanese Patent Publication No. 2003-520878, Japanese Patent Publication No. 2004-529220 and Japanese Patent No. 4162850, and photodimerizable compounds described in Japanese Patent Publication No. 9-118717, Japanese Patent Publication No. 10-506420, Japanese Patent Publication No. 2003-505561, International Publication No. 2010 / 150748, Japanese Patent Publication No. 2013-177561 and Japanese Patent Publication No. 2014-12823, particularly cinnamate compounds, chalcone compounds and coumarin compounds. Among these, azo compounds, photocrosslinkable polyimides, photocrosslinkable polyamides, photocrosslinkable esters, cinnamate compounds, and chalcone compounds are particularly suitable for use.

[0078] There are no restrictions on the thickness of the alignment film; the appropriate thickness should be set according to the material used to form the alignment film, so as to obtain the required alignment function. The thickness of the orientation film is preferably 0.01 to 5 μm, and more preferably 0.05 to 2 μm.

[0079] There are no limitations on the method for forming the alignment film, and various known methods depending on the material used to form the alignment film can be used. As an example, one method involves coating the alignment film onto the surface of a support, drying it, and then exposing the alignment film with laser light to form an alignment pattern.

[0080] Figure 9 conceptually shows an example of an exposure apparatus for exposing an alignment film to form an alignment pattern. The exposure apparatus comprises a laser light source 81 that emits laser light, a beam expander 82 that expands the beam diameter of the laser light L emitted from the laser light source 81, a λ / 2 plate 83 positioned on the optical path of the laser light L, and a drive stage 86 on which a lens 84 and an alignment film 90 are installed. The λ / 2 plate 83 is mounted on a rotating mount (not shown) and functions as a variable polarization rotator.

[0081] The beam diameter of the laser light L emitted from the laser light source 81 is expanded by the beam expander 82, adjusted to an arbitrary polarization direction by the rotation of the λ / 2 plate 83, focused onto the photo-alignment film by the lens 84, and the drive stage 86 is driven to scan and expose the photo-alignment film for patterning. This makes it possible to form a patterned alignment film with a desired pattern.

[0082] In the optical elements of this disclosure, the alignment film is provided as a preferred embodiment and is not an essential component. For example, it is possible to form an optical anisotropic layer having a horizontal rotational orientation pattern by forming an orientation pattern on the support using methods such as rubbing the support or processing the support with laser light.

[0083] While the above descriptions of optical elements primarily assume a single-wavelength incident light configuration, configurations that produce similar effects with multi-wavelength incident light are also possible. For example, an optical element with a structure comprising stacked optically anisotropic layers having liquid crystal alignment patterns corresponding to each wavelength can be used with multi-wavelength incident light.

[0084] [Light deflection device] Figure 10 shows a schematic configuration diagram of an example of an optical deflection device according to one embodiment. The optical deflection device 130 comprises, from the upstream side in the direction of propagation of light (light beam), a focusing lens 131, a λ / 4 plate 111, an optical deflection element 132, and an optical element 120 according to one embodiment of the present invention. In the following description, upstream and downstream refer to the upstream and downstream sides in the direction of propagation of light.

[0085] The focusing lens 131 is a known focusing lens provided to slightly focus the light (light beam) from a light source (not shown) before it is incident on the light deflection element 132. The focusing lens 131 is provided as a preferred embodiment and is not an essential component. However, by providing the focusing lens 131, the light (light beam) emitted from the light deflection device 130 can be made into properly parallel light, thereby improving its straightness. Furthermore, the system is not limited to the focusing lens 131; all known focusing elements capable of focusing light (light beam) can be used.

[0086] The λ / 4 plate 111 is a known λ / 4 plate (1 / 4 phase difference plate) that converts linearly polarized light emitted from a light source to circularly polarized light. Any known λ / 4 plate 111 can be used without limitation. Therefore, the λ / 4 plate 111 may be made of polymer or liquid crystal. The λ / 4 plate 111 may be placed between the MEMS (Micro Electro Mechanical System) deflection element 132 and the optical element 120. However, it is preferable to place the λ / 4 plate 111 upstream of the MEMS optical deflection element 132, for example, to allow for miniaturization of the λ / 4 plate 111. When circularly polarized light is incident on the optical deflection device 130 using the MEMS optical deflection element 132, the λ / 4 plate 111 does not need to be provided.

[0087] The optical deflection element 132 is a MEMS optical deflection element that performs two-dimensional scanning of light. There are no particular restrictions on the MEMS optical deflection element, and any known MEMS optical deflection element (MEMS (optical) scanner, MEMS optical deflector, MEMS mirror, or DMD (Digital Micromirror Device)) that deflects (blinds and scans) light by oscillating a mirror using a piezoelectric actuator, etc., can be used as appropriate. This includes MEMS optical deflection elements described in Japanese Patent Application Publication No. 2012-208352, MEMS optical deflection elements described in Japanese Patent Application Publication No. 2014-134642, and MEMS optical deflection elements described in Japanese Patent Application Publication No. 2015-22064.

[0088] A drive device 134 for rotating the mirror is connected to the optical deflection element 132. The drive device 134 can be any known device, depending on the configuration of the MEMS optical deflection element 132.

[0089] The optical element 120 comprises two optical anisotropic layers, as shown in Figure 8, which have an in-plane liquid crystal alignment pattern in which the optical axes are horizontally rotated along axes radiating from the center, and the period decreases towards the outside. As shown in Figure 10, the period decreases towards the outside (Λ1>Λ2>Λ3>Λ4…) compared to the period Λ1 in the central region of the optical element 120. Here, one optical anisotropic layer 121 is a gradient optical anisotropic layer, and the other optical anisotropic layer 122 is an optical anisotropic layer that does not have torsion in the thickness direction and has a uniform pattern in the thickness direction. The optical element 120 is positioned so that its center coincides with the center of deflection of the optical deflection element 132. In the cross-sectional SEM image of the optical element 120, the inclination of the light and dark lines with respect to the normal is larger towards the center and smaller towards the outside.

[0090] The optical deflection device 130 partially focuses the P-polarized light emitted from a light source (not shown) with respect to the emission surface 120b of the optical element 120 by the focusing lens 131, and then λ / 4 The plate 111 converts the light to, for example, right-circular polarization.

[0091] Light converted to circular polarization by the λ / 4 plate 111 is deflected by the MEMS optical deflection element 132 and incident on the incident surface 120a of the optical element 120. The light incident on the optical element 120 is diffracted and emitted from the exit surface 120b of the optical element 120, i.e., from the optical deflection device 130.

[0092] Since the center of the optical element 120 is positioned to coincide with the center of deflection of the optical deflection element 132, the light scanned by the optical deflection element 132 is incident on one surface of the optical element 120 at an angle of incidence that increases as it moves away from the center of that surface. The period of horizontal rotation orientation is configured to become shorter as it moves away from the center, and the bending force is stronger towards the outside. Therefore, the optical element 120 generates almost no bending force for light incident perpendicularly, allowing it to pass through directly, and then bends it more significantly towards the outside of the optical element 120 before it is emitted. By injecting polarization that is given a bending force from the center outward due to the horizontal rotation orientation of the optical anisotropy layers 121 and 122 into the optical element 120, a scan angle θmaxout larger than the scan angle θmax of the optical deflection element 132 can be obtained.

[0093] Here, if we let θ1 be the angle of incidence of light incident on the incident surface 120a of the optical element 120, n1 be the refractive index of the incident medium, θ2 be the angle of emission of light emitted from the exit surface 120b of the optical element 120, n2 be the refractive index of the exit medium, λ be the wavelength of light, Λ be the periodic structure pitch of the liquid crystal diffraction element, and m be the order of diffraction, then these values ​​are related by the following equation (1). n1·sinθ1-n2·sinθ2=m·λ / Λ (1)

[0094] As previously described, the angle of the light emitted from the optical element 120 can be changed by changing the period Λ of the horizontal rotational orientation pattern in the optical anisotropy layer of the optical element 120. Considering Snell's law, the angle at which the light is finally emitted into the air can be up to approximately 80° in absolute value, making it possible to expand the emission angle to a very large angle. Furthermore, by continuously changing the period of the horizontal rotational orientation pattern in the optical anisotropy layer of the optical element 120 within the plane, light can be continuously emitted in any direction.

[0095] As is clear from the above explanation, the optical deflection device of this disclosure enables optical scanning at a wider scan angle (field of view) than that of the optical deflection element. In Figure 10, the scan angle is shown to widen in the x-direction, but since the horizontal rotation orientation pattern is arranged radially, the scan angle can also be widened in the y-direction using the same principle. Therefore, by diffracting the deflected light (scanning light) from the optical deflection element 132 with the optical element 120 and scanning it, it is possible to widen the scan range significantly beyond the scan range that can be scanned in two dimensions by the optical deflection element 132.

[0096] Even if the optical element 120 applied to such an optical deflection device 130 does not have a gradient optical anisotropy layer 121, the effect of expanding the scan angle can be obtained. However, when an optical element is applied that does not have a gradient optical anisotropy layer 121 and only has an optical anisotropy layer 122, there is a problem that a large difference in diffraction efficiency occurs between the central region where the incident angle is small and the outer region where the incident angle is large and the diffraction angle is large, resulting in a low overall diffraction efficiency (average diffraction efficiency). By providing a gradient optical anisotropy layer 121, the diffraction efficiency of the outer region of the element where the incident angle is large can be improved, the difference in diffraction efficiency due to the incident position and incident angle can be suppressed, and the variation in the amount of light emitted can be suppressed. In addition, by providing two or more optical anisotropy layers, the average diffraction efficiency can also be improved.

[0097] Furthermore, in the optical deflection device, not limited to the optical element 120 described above, for example, a horizontal rotation orientation pattern in which the period in the x-axis direction gradually decreases from one side to the other, as shown in Figure 1, may be used. An optical element having an optically anisotropic layer may be used. Alternatively, an optical element having an optically anisotropic layer having a horizontal rotation orientation pattern in which the period gradually decreases from the center of the element outward in the x-axis direction, and in which the rotation direction of the optical axes of the horizontal rotation orientation patterns on both sides of the center is opposite. [Examples]

[0098] The features of the present invention will be further described in detail below with reference to examples. The materials, reagents, amounts used, amounts of substance, ratios, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following specific examples. In the following examples and comparative examples, the liquid crystal alignment pattern was designed assuming infrared light with a target wavelength of 940 nm as the incident light.

[0099] [Comparative Example 1] As Comparative Example 1, an optical element was fabricated that included a non-gradient optical anisotropy layer 211 as the first optical anisotropy layer, in which the light and dark lines were not gradual in the cross-sectional SEM image (see Figure 11).

[0100] <Fabrication of optical elements> (Formation of orientation film) The alignment film-forming coating solution described below was applied to a glass substrate by spin coating. The support coated with this alignment film-forming coating solution was dried on a 60°C hot plate for 60 seconds to form an alignment film.

[0101] Coating solution for forming alignment films -------------------------------------------------- Photoalignment material A 1.00 parts by mass Water 16.00 parts by mass Butoxyethanol 42.00 parts by mass Propylene glycol monomethyl ether 42.00 parts by mass --------------------------------------------------

[0102] -Photo alignment material A- [ka]

[0103] (Exposure of alignment layer) As shown in Figure 9, an alignment film P-1 with an alignment pattern was formed by exposing the alignment film using an exposure apparatus that scans and patterns the photo-alignment film while arbitrarily changing the polarization direction of the focused laser beam. In the exposure apparatus, a laser beam with a wavelength of 325 nm was used. The alignment pattern was concentric, and the period of the alignment pattern gradually shortened from the center outwards.

[0104] (Formation of the first optically anisotropic layer) Composition A-1 was prepared as a liquid crystal composition for forming an optically anisotropic layer.

[0105] Composition A-1 ------------------------------------------------------------------ Liquid crystal compound L-1 100.00 parts by mass Polymerization initiator (BASF, Irgacure® 907) 3.00 parts by mass Photosensitizer (manufactured by Nippon Kayaku, KAYACURE DETX-S) 1.00 parts by mass Leveling agent T-1: 0.08 parts by mass Methyl ethyl ketone 2840.00 parts by mass ------------------------------------------------------------------

[0106] Liquid crystal compound L-1 [ka]

[0107] Leveling agent T-1 [ka]

[0108] The first optically anisotropic layer was formed by multilayer coating of composition A-1 on the alignment film P-1. First, the first layer of composition A-1 was coated onto the alignment film, heated, cooled, and then cured with ultraviolet light to create a liquid crystal immobilization layer. Subsequent layers were then applied on top of this liquid crystal immobilization layer, and the process of heating, cooling, and UV curing was repeated.

[0109] First, for the first layer, composition A-1 is applied to the alignment film P-1, the coating is heated to 70°C on a hot plate, then cooled to 25°C, and then exposed to ultraviolet light at a wavelength of 365 nm at 300 mJ / cm² using a high-pressure mercury lamp under a nitrogen atmosphere. 2 The orientation of the liquid crystal compound was fixed by irradiating the coating film with this irradiation dose. The thickness of the first liquid crystal layer at this time was 0.2 μm.

[0110] For the second and subsequent layers, the liquid crystal layer was layered on top of this liquid crystal layer, heated and cooled under the same conditions as above, and then cured with ultraviolet light to create a liquid crystal immobilization layer. In this way, the layering was repeated until the desired total thickness was achieved, forming the first optical anisotropic layer.

[0111] The optical element of Comparative Example 1 was fabricated using the above process.

[0112] The complex refractive index Δn of the cured layer of liquid crystal composition A1 was determined by applying liquid crystal composition A1 to a support with an alignment film prepared separately for retardation measurement, aligning the liquid crystal compound director horizontally to the substrate, and then fixing it by ultraviolet irradiation. The retardation Re(λ) and film thickness of the resulting liquid crystal immobilized layer (cured layer) were then measured. Δn was obtained by dividing the retardation Re(λ) by the film thickness. λ The retardation Re(λ) is measured at the desired wavelength using a Woollam spectroscopic ellipsometer, and the film thickness is measured using a SEM. In the notation Re(λ), λ is the wavelength of the incident light. Below, the wavelength of the incident light, λ, is assumed to be 940 nm.

[0113] The first optical anisotropy layer ultimately forms the Δn of the liquid crystal. 940 The thickness (×thickness = Re(940)) was 470 nm, and it was confirmed by polarizing microscope that the surface had a concentric, periodic orientation as shown in Figure 8. A concentric, periodic orientation means that the axes of horizontal rotation orientation are arranged radially from the center in an in-plane orientation pattern. In this horizontal rotation orientation pattern of the first optical anisotropy layer, the period was very large at the center (the reciprocal of the period can be considered as 0), 9.0 μm at a distance of 1.0 mm from the center, 4.5 μm at a distance of 2.5 mm from the center, and 3.0 μm at a distance of 4.0 mm from the center, with the period decreasing towards the outside. The twist angle in the thickness direction of the first optical anisotropy layer was 0°. Unless otherwise specified, Δn 940 Measurements such as 'thickness' were performed in the same manner. In addition, in the cross-sectional image obtained by SEM, light and dark lines extending perpendicular to the lower interface of the optically anisotropic layer (interface with the glass substrate), i.e., along the normal, were observed. In the repeating pattern of light and dark lines, it was observed that the period shortened from the center outwards.

[0114] [Example 1] As Example 1, an optical element was fabricated comprising two optically anisotropic layers, wherein the first optically anisotropic layer is a gradient optically anisotropic layer 212 in which the light and dark lines in the cross-sectional SEM image are tilted toward the normal to the interface, and the second optically anisotropic layer is a non-gradient optically anisotropic layer 211 (see Figure 12).

[0115] (Formation of the first optically anisotropic layer) Composition A-2 was prepared as a liquid crystal composition for forming an optically anisotropic layer.

[0116] Composition A-2 -------------------------------------------------- Liquid crystal compound L-1 100.00 parts by mass Chiral agent A: 0.21 parts by mass Polymerization initiator (BASF, Irgacure® 907) 3.00 parts by mass Photosensitizer (manufactured by Nippon Kayaku, KAYACURE DETX-S) 1.00 parts by mass Leveling agent T-1: 0.08 parts by mass Methyl ethyl ketone 2840.00 parts by mass --------------------------------------------------

[0117] Chiral agent A [ka]

[0118] A first optical anisotropic layer was formed on the alignment film P-1 in the same manner as in Comparative Example 1, except that composition A-2 was used.

[0119] (Formation of the second optically anisotropic layer) The second optical anisotropy layer in Example 1 was the same as the first optical anisotropy layer in Comparative Example 1. Using composition A-1, the second optical anisotropy layer was formed on the first optical anisotropy layer in the same manner as the first optical anisotropy layer in Comparative Example 1, and the optical element of Example 1 was fabricated.

[0120] The first optical anisotropy layer and the second optical anisotropy layer ultimately form the Δn of the liquid crystal. 940The thickness (×thickness = Re(940)) was 470 nm, and it was confirmed using a polarizing microscope that the surface had a concentric, periodic orientation as shown in Figure 8. In the horizontal rotation orientation pattern of this first optical anisotropic layer, one period was very large at the center (the reciprocal of the period can be considered as 0), 9.0 μm at a distance of 1.0 mm from the center, 4.5 μm at a distance of 2.5 mm from the center, and 3.0 μm at a distance of 4.0 mm from the center, with the period decreasing towards the outside. The second optical anisotropic layer is formed by coating on the first optical anisotropic layer, so its period is the same as that of the first optical anisotropic layer. In the following sections, other layers formed by coating on the first optical anisotropic layer also have the same period. The twist angle in the thickness direction of the first optical anisotropic layer was 140° right-handed twist. The twist angle in the thickness direction of the second optical anisotropic layer was 0°. Furthermore, in cross-sectional images obtained by SEM, diagonally inclined light and dark lines were observed in the first optical anisotropy layer relative to the normal of the interface beneath the optical anisotropy layer (interface with the glass substrate), while light and dark lines extending in the direction of the normal were observed in the second optical anisotropy layer. In the first optical anisotropy layer, the angle of inclination of the light and dark lines relative to the normal decreased from the center outward. In both the first and second optical anisotropy layers, the pattern of light and dark lines showed a decrease in period from the center outward.

[0121] [Example 2] As Example 2, an optical element was fabricated having two optical anisotropy layers, where the first optical anisotropy layer is a non-graded optical anisotropy layer 211 and the second optical anisotropy layer is a graded optical anisotropy layer 212 (see Figure 13). In other words, Example 2 has a configuration in which the first optical anisotropy layer and the second optical anisotropy layer of Example 1 are configured in reverse.

[0122] An optical element of Example 2 was fabricated in the same manner as in Example 1, except that a first optical anisotropy layer was formed using composition A-1 and a second optical anisotropy layer was formed using composition A-2.

[0123] The first optical anisotropy layer and the second optical anisotropy layer ultimately form the Δn of the liquid crystal. 940The thickness (Re(940)) was 470 nm, and it was confirmed using a polarizing microscope that the surface had a concentric, periodic orientation as shown in Figure 8. In the horizontal rotation orientation pattern of this first optical anisotropy layer, one period was very large at the center (the reciprocal of the period could be considered to be 0), 9.0 μm at a distance of 1.0 mm from the center, 4.5 μm at a distance of 2.5 mm from the center, and 3.0 μm at a distance of 4.0 mm from the center, with the period decreasing towards the outside. The twist angle in the thickness direction of the first optical anisotropy layer was 0°. The twist angle in the thickness direction of the second optical anisotropy layer was 140° right-handed twist. Furthermore, in the cross-sectional image obtained by SEM, light and dark lines extending in the direction normal to the optical anisotropy layer interface (interface with the glass substrate) were observed in the first optical anisotropy layer, and light and dark lines sloping obliquely to the normal were observed in the second optical anisotropy layer. In the second optical anisotropy layer, the angle of inclination of the light and dark lines relative to the normal decreased from the center outward. In both the first and second optical anisotropy layers, the pattern of light and dark lines showed a decrease in period from the center outward.

[0124] [Comparative Example 2] As Comparative Example 2, an optical element was fabricated that included a first optical anisotropy layer, 212, in which the light and dark lines in the cross-sectional SEM image were tilted with respect to the normal of the interface.

[0125] (Formation of the first optically anisotropic layer) The first optical anisotropy layer of Comparative Example 2 is the same as the first optical anisotropy layer of Example 1. Using composition A-2, the first optical anisotropy layer was formed on the alignment film P-1 in the same manner as the first optical anisotropy layer of Example 1, and the optical element of Comparative Example 2 was fabricated. In other words, the optical element of Comparative Example 2 has a configuration that includes only one gradient optical anisotropy layer as the optical anisotropy layer.

[0126] The first optical anisotropy layer ultimately forms the Δn of the liquid crystal. 940The thickness (×thickness = Re(940)) was 470 nm, and it was confirmed by polarizing microscope that the surface had a concentric, periodic orientation as shown in Figure 8. In the horizontal rotation orientation pattern of this first optical anisotropy layer, one period was very large at the center (the reciprocal of the period can be considered as 0), 9.0 μm at a distance of 1.0 mm from the center, 4.5 μm at a distance of 2.5 mm from the center, and 3.0 μm at a distance of 4.0 mm from the center, with the period decreasing towards the outside. The twist angle in the thickness direction of the first optical anisotropy layer was 140° to the right. Furthermore, in the cross-sectional image obtained by SEM, diagonally inclined light and dark lines were observed in the first optical anisotropy layer with respect to the normal to the interface beneath the optical anisotropy layer (interface with the glass substrate). In the first optical anisotropy layer, the angle of inclination of the light and dark lines with respect to the normal decreased from the center outward. The pattern of light and dark lines showed a decrease in period from the center outwards.

[0127] [Example 3] As Example 3, an optical element was fabricated comprising two optically anisotropic layers, where the first and second optically anisotropic layers are gradient optically anisotropic layers 213 and 214, in which the light and dark lines in the cross-sectional SEM image are inclined toward the normal to the interface (see Figure 14). The direction of the inclination of the light and dark lines in the cross-sectional SEM image was the same for the first and second optically anisotropic layers, but the inclination angles were different.

[0128] (Formation of the first optically anisotropic layer) Composition A-3 was prepared as a liquid crystal composition for forming the first optical anisotropy layer.

[0129] Composition A-3 -------------------------------------------------- Liquid crystal compound L-1 100.00 parts by mass Chiral agent A: 0.24 parts by mass Polymerization initiator (BASF, Irgacure® 907) 3.00 parts by mass Photosensitizer (manufactured by Nippon Kayaku, KAYACURE DETX-S) 1.00 parts by mass Leveling agent T-1: 0.08 parts by mass Methyl ethyl ketone 2840.00 parts by mass --------------------------------------------------

[0130] A first optical anisotropic layer was formed on the alignment film P-1 in the same manner as in Example 1, except that composition A-3 was used.

[0131] (Formation of the second optically anisotropic layer) Composition A-4 was prepared as a liquid crystal composition for forming an optically anisotropic layer.

[0132] Composition A-4 -------------------------------------------------- Liquid crystal compound L-1 100.00 parts by mass Chiral agent A: 0.03 parts by mass Polymerization initiator (BASF, Irgacure® 907) 3.00 parts by mass Photosensitizer (manufactured by Nippon Kayaku, KAYACURE DETX-S) 1.00 parts by mass Leveling agent T-1: 0.08 parts by mass Methyl ethyl ketone 2840.00 parts by mass --------------------------------------------------

[0133] An optical element of Example 3 was fabricated in the same manner as in Example 1, except that composition A-4 was used, by forming a second optical anisotropic layer on the first optical anisotropic layer.

[0134] The first optical anisotropy layer and the second optical anisotropy layer ultimately form the Δn of the liquid crystal. 940The thickness (×thickness = Re(940)) was 470 nm, and it was confirmed using a polarizing microscope that the surface had a concentric, periodic orientation as shown in Figure 8. In the horizontal rotation orientation pattern of this first optical anisotropy layer, one period was very large at the center (the reciprocal of the period can be considered as 0), 9.0 μm at a distance of 1.0 mm from the center, 4.5 μm at a distance of 2.5 mm from the center, and 3.0 μm at a distance of 4.0 mm from the center, with the period decreasing towards the outside. The twist angle in the thickness direction of the first optical anisotropy layer was 160° right-handed twist. The twist angle in the thickness direction of the second optical anisotropy layer was 20° right-handed twist. The twist direction of the first and second optical anisotropy layers was the same. Furthermore, in cross-sectional images obtained by SEM, diagonally inclined light and dark lines were observed in both the first and second optical anisotropic layers, relative to the normal of the interface beneath the optical anisotropy layer. Moreover, the inclination angle of the light and dark lines relative to the normal decreased from the center outward, and the direction of inclination of the light and dark lines from the normal was the same for both the first and second optical anisotropic layers. In both the first and second optical anisotropic layers, the pattern of the light and dark lines showed a decrease in period from the center outward.

[0135] [Example 4] As Example 4, an optical element was fabricated comprising two optically anisotropic layers, where the first and second optically anisotropic layers are gradient optically anisotropic layers 215 and 216, in which the light and dark lines in the cross-sectional SEM image are inclined toward the normal to the interface (see Figure 15). The direction of the inclination of the light and dark lines in the cross-sectional SEM image was made different for the first and second optically anisotropic layers.

[0136] (Formation of the first optically anisotropic layer) Composition A-5 was prepared as a liquid crystal composition for forming an optically anisotropic layer.

[0137] Composition A-5 -------------------------------------------------- Liquid crystal compound L-1 100.00 parts by mass Chiral agent A: 0.13 parts by mass Polymerization initiator (BASF, Irgacure® 907) 3.00 parts by mass Photosensitizer (manufactured by Nippon Kayaku, KAYACURE DETX-S) 1.00 parts by mass Leveling agent T-1: 0.08 parts by mass Methyl ethyl ketone 2840.00 parts by mass --------------------------------------------------

[0138] A first optical anisotropic layer was formed on the alignment film P-1 in the same manner as in Example 1, except that composition A-5 was used.

[0139] (Formation of the second optically anisotropic layer) Composition A-6 was prepared as a liquid crystal composition for forming an optically anisotropic layer.

[0140] Composition A-6 -------------------------------------------------- Liquid crystal compound L-1 100.00 parts by mass Chiral agent B 0.22 parts by mass Polymerization initiator (BASF, Irgacure® 907) 3.00 parts by mass Photosensitizer (manufactured by Nippon Kayaku, KAYACURE DETX-S) 1.00 parts by mass Leveling agent T-1: 0.08 parts by mass Methyl ethyl ketone 2840.00 parts by mass --------------------------------------------------

[0141] Chiral agent B [ka]

[0142] An optical element of Example 4 was fabricated in the same manner as in Example 1, except that composition A-6 was used, by forming a second optical anisotropic layer on the first optical anisotropic layer.

[0143] The first optical anisotropy layer and the second optical anisotropy layer ultimately form the Δn of the liquid crystal. 940 The thickness × Re(940) was 470 nm, and it was confirmed using a polarizing microscope that the surface had a concentric, periodic orientation as shown in Figure 8. In the horizontal rotation orientation pattern of this first optical anisotropy layer, one period was very large at the center (the reciprocal of the period can be considered as 0), 9.0 μm at a distance of 1.0 mm from the center, 4.5 μm at a distance of 2.5 mm from the center, and 3.0 μm at a distance of 4.0 mm from the center, with the period decreasing towards the outside. The twist angle in the thickness direction of the first optical anisotropy layer was 80° to the right. The twist angle in the thickness direction of the second optical anisotropy layer was 80° to the left. The twist directions of the first and second optical anisotropy layers were opposite. Furthermore, in cross-sectional images obtained by SEM, both the first and second optical anisotropic layers showed that the light and dark lines were obliquely inclined with respect to the normal of the interface beneath the optical anisotropy layer. Moreover, the angle of inclination of the light and dark lines relative to the normal decreased from the center outward, and the direction of inclination of the light and dark lines from the normal was opposite for the first and second optical anisotropic layers. In both the first and second optical anisotropic layers, the pattern of the light and dark lines showed that the period became shorter from the center outward.

[0144] [Example 5] As Example 5, an optical element was fabricated comprising three optically anisotropic layers, wherein the first and third optically anisotropic layers are gradient optically anisotropic layers 217 and 218 in which the light and dark lines in the cross-sectional SEM image are inclined toward the normal to the interface, and the second optically anisotropic layer 219, positioned between the first and third optically anisotropic layers, is a non-gradient optically anisotropic layer (see Figure 16). The direction of the inclination of the light and dark lines in the cross-sectional SEM image was made different for the first optically anisotropic layer and the third optically anisotropic layer.

[0145] (Formation of the first optically anisotropic layer) Composition A-7 was prepared as a liquid crystal composition for forming an optically anisotropic layer.

[0146] Composition A-7 -------------------------------------------------- Liquid crystal compound L-1 100.00 parts by mass Chiral agent A: 0.19 parts by mass Polymerization initiator (BASF, Irgacure® 907) 3.00 parts by mass Photosensitizer (manufactured by Nippon Kayaku, KAYACURE DETX-S) 1.00 parts by mass Leveling agent T-1: 0.08 parts by mass Methyl ethyl ketone 2840.00 parts by mass --------------------------------------------------

[0147] A first optical anisotropic layer was formed on the alignment film P-1 in the same manner as in Example 1, except that composition A-7 was used.

[0148] (Formation of the second optically anisotropic layer) A second optical anisotropic layer was formed on the first optical anisotropic layer in the same manner as the first optical anisotropic layer in Comparative Example 1, except that composition A-1 was used and the film thickness was changed.

[0149] (Formation of the third optically anisotropic layer) Composition A-8 was prepared as a liquid crystal composition for forming an optically anisotropic layer.

[0150] Composition A-8 -------------------------------------------------- Liquid crystal compound L-1 100.00 parts by mass Chiral agent B: 0.32 parts by mass Polymerization initiator (BASF, Irgacure® 907) 3.00 parts by mass Photosensitizer (manufactured by Nippon Kayaku, KAYACURE DETX-S) 1.00 parts by mass Leveling agent T-1: 0.08 parts by mass Methyl ethyl ketone 2840.00 parts by mass --------------------------------------------------

[0151] An optical element of Example 5 was fabricated in the same manner as in Example 1, except that composition A-8 was used, by forming a third optical anisotropic layer on the second optical anisotropic layer.

[0152] The first optical anisotropy layer and the third optical anisotropy layer ultimately form the Δn of the liquid crystal. 940 ×Thickness = Re(940) is 470 nm, and the second optical anisotropy layer is Δn 940 The thickness (Re(940)) was 564 nm. Furthermore, a concentric, periodic orientation surface was confirmed using a polarizing microscope, as shown in Figure 8. In the horizontal rotation orientation pattern of this first optical anisotropy layer, one period was very large at the center (the reciprocal of the period can be considered as 0), 9.0 μm at a distance of 1.0 mm from the center, 4.5 μm at a distance of 2.5 mm from the center, and 3.0 μm at a distance of 4.0 mm from the center, with the period decreasing towards the outside. The twist angle in the thickness direction of the first optical anisotropy layer was 130° to the right. The twist angle in the thickness direction of the second optical anisotropy layer was 0°, and the twist angle in the thickness direction of the third optical anisotropy layer was 130° to the left. The twist directions of the first and third optical anisotropy layers were opposite. Furthermore, in cross-sectional images obtained by SEM, obliquely inclined light and dark lines were observed in the first and third optical anisotropic layers, relative to the normal of the interface beneath the optical anisotropy layer, while light and dark lines extending along the normal were observed in the second optical anisotropic layer. In the first and third optical anisotropic layers, the inclination angle of the light and dark lines relative to the normal decreased from the center outward, and the direction of the inclination of the light and dark lines relative to the normal was opposite between the first and third optical anisotropic layers. In the light and dark line patterns of the first, second, and third optical anisotropic layers, a decrease in period was observed from the center outward.

[0153] [evaluation] The optical elements of Comparative Example 1 and Examples 1-5 function as transmissive diffracting elements. For each optical element, the angle of the transmitted diffracted light relative to the normal direction of the optical element was measured when light was incident on it, and the rate of increase in light intensity compared to the element of Comparative Example 1 was evaluated. The specific measurement method is as follows.

[0154] First, laser light was incident on a predetermined position on the surface of an optical element at a predetermined angle of incidence. The transmitted light was projected onto a screen placed 30 cm away from the optical element in the normal direction, and the angle of the transmitted diffracted light was calculated from the image captured by an infrared camera. A laser diode with a wavelength of 940 nm was used as the light source.

[0155] Next, as shown in Figure 17, laser light with a wavelength of 940 nm emitted from the laser light source 251 was transmitted through the linear polarizer 252 and the λ / 4 plate 254 to obtain right-circularly polarized light Li. This light Li was incident on a predetermined position on the surface of the optical element S at a predetermined incident angle. The light intensity of the transmitted diffracted light Ld diffracted by the optical element S was measured with the photodetector 256. The ratio of the light intensity of the diffracted light Ld to the light intensity of light Li was taken to determine the relative light intensity value of the diffracted light Ld with respect to the incident light. The relative light intensity value was similarly determined by changing the incident angle. The increase in light intensity of the example compared to Comparative Example 1 was evaluated using the average value of the relative light intensity values ​​for different incident angles according to the following criteria.

[0156] A: Light intensity increase rate of 20% or more B: Light intensity increase rate is 10% or more, but less than 20%. C: Light intensity increase rate is 5% or more, but less than 10%. D: Light intensity increase rate is less than 5%

[0157] In the comparison between Comparative Examples 1 and 2 and Examples 1-3, the incident angle at a distance of 1.0 mm from the center (1 period of 9.0 μm) was set to 10°, the incident angle at a distance of 2.5 mm from the center (1 period of 4.5 μm) was set to 20°, and the incident angle at a distance of 4.0 mm from the center (1 period of 3.0 μm) was set to 30° for evaluation. Furthermore, in the comparison between Comparative Examples 1 and 2 and Examples 4 and 5, the incident angle at a distance of 1.0 mm from the center (1 period of 9.0 μm) was set to ±10°, the incident angle at a distance of 2.5 mm from the center (1 period of 4.5 μm) was set to ±20°, and the incident angle at a distance of 4.0 mm from the center (1 period of 3.0 μm) was set to ±30° for evaluation.

[0158] The results are shown in Table 1. [Table 1]

[0159] Examples 1-3 showed higher average diffraction efficiencies than Comparative Example 1 in the incident angle range of 10-30°, and Examples 4 and 5 showed higher average diffraction efficiencies than Comparative Example 1 in the incident angle range of -30-+30°. By combining gradient optical anisotropy layers with opposite gradients of light and dark lines in the cross-sectional SEM image, it was possible to increase the diffraction efficiency over a wider range of incident angles. Note that comparative examples equipped with only one gradient optical anisotropy layer The optical element in Comparative Example 2 did not show any effect in improving the average diffraction efficiency.

[0160] [Comparative Example 11] As Comparative Example 11, an optical element was fabricated that had a first optical anisotropic layer 221 having a horizontal rotation orientation pattern with a gradually changing period and cholesterically oriented in the thickness direction (see Figure 18). In Figure 18, a portion of the cholesteric orientation in the thickness direction is schematically shown.

[0161] (Formation of the first optically anisotropic layer) Composition C-1 was prepared as a liquid crystal composition for forming an optically anisotropic layer. Composition C-1 is a liquid crystal composition that forms a cholesteric liquid crystal layer that reflects right-circularly polarized light with a selective reflection center wavelength of 940 nm.

[0162] Composition C-1 -------------------------------------------------- Liquid crystal compound L-1 100.00 parts by mass Chiral agent A: 3.11 parts by mass Polymerization initiator (BASF, Irgacure® 907) 3.00 parts by mass Photosensitizer (manufactured by Nippon Kayaku, KAYACURE DETX-S) 1.00 parts by mass Leveling agent T-1: 0.08 parts by mass Methyl ethyl ketone 2840.00 parts by mass --------------------------------------------------

[0163] A first optical anisotropic layer was formed on the alignment film P-1 using composition C-1, in the same manner as in Example 1 except that the film thickness was changed, and an optical element of Comparative Example 11 was fabricated.

[0164] When the cross-section of the coated layer of the first optical anisotropic layer was examined with a transcatheter electron microscope, it was confirmed that the cholesteric liquid crystal phase had 8 pitches and that the surface had a concentric, periodic orientation as shown in Figure 8, as confirmed with a polarizing microscope. In the horizontal rotation orientation pattern of this first optical anisotropic layer, one period was very large at the center (the reciprocal of the period can be considered as 0), 9.0 μm at a distance of 1.0 mm from the center, 4.5 μm at a distance of 2.5 mm from the center, and 3.0 μm at a distance of 4.0 mm from the center, with the period decreasing towards the outside. Furthermore, in the cross-sectional image obtained by SEM, the light and dark lines in the first optical anisotropic layer were inclined obliquely with respect to the normal to the interface beneath the optical anisotropic layer. The inclination angle of the light and dark lines in the first optical anisotropic layer increased from the center outward. The pattern of light and dark lines in the first optical anisotropic layer showed that the period decreased from the center outward.

[0165] [Example 11] As Example 11, an optical element was fabricated comprising a first optical anisotropy layer 222 and a second optical anisotropy layer 223 having a horizontal rotation orientation pattern with a gradually changing period and cholesterically oriented in the thickness direction (see Figure 19). In Figure 19, a portion of the cholesteric orientation in the thickness direction is schematically shown.

[0166] (Formation of the first optically anisotropic layer) Using composition C-1, a first optically anisotropic layer was formed on the orientation film P-1 in the same manner as in Comparative Example 11.

[0167] The first optically anisotropic layer was observed using a type electron microscope to examine the cross-section of the coated layer. The liquid crystal phase has an 8-pitch configuration, and its concentric (radial) periodic orientation surface was confirmed using a polarizing microscope as shown in Figure 8. In the horizontal rotation orientation pattern of this first optical anisotropic layer, one period was very large at the center (the reciprocal of the period could be considered to be 0), 9.0 μm at a distance of 1.0 mm from the center, 4.5 μm at a distance of 2.5 mm from the center, and 3.0 μm at a distance of 4.0 mm from the center, with the period decreasing towards the outside.

[0168] (Formation of the second optically anisotropic layer) Composition C-2 was prepared as a liquid crystal composition for forming the second optical anisotropy layer. Composition C-2 is a liquid crystal composition that forms a cholesteric liquid crystal layer that reflects left-circularly polarized light with a selective reflection center wavelength of 940 nm.

[0169] <Composition C-2> -------------------------------------------------- Liquid crystal compound L-1 100.00 parts by mass Chiral agent B: 4.42 parts by mass Polymerization initiator (BASF, Irgacure® 907) 3.00 parts by mass Photosensitizer (manufactured by Nippon Kayaku, KAYACURE DETX-S) 1.00 parts by mass Leveling agent T-1: 0.08 parts by mass Methyl ethyl ketone 2840.00 parts by mass --------------------------------------------------

[0170] A second optically anisotropic layer was formed on the alignment film P-1 in the same manner as in Comparative Example 11.

[0171] When the cross-section of the coated layer of the first optical anisotropic layer was examined with a lithographic electron microscope, it was confirmed that the cholesteric liquid crystal phase had 8 pitches and that the surface had a concentric, periodic orientation as shown in Figure 8, as confirmed with a polarizing microscope. Furthermore, in the horizontal rotation orientation pattern of this first optical anisotropic layer, one period was very large at the center (the reciprocal of the period can be considered to be 0), 9.0 μm at a distance of 1.0 mm from the center, 4.5 μm at a distance of 2.5 mm from the center, and 3.0 μm at a distance of 4.0 mm from the center, with the period decreasing towards the outside.

[0172] The optical element of Example 11 was fabricated by laminating the first optical anisotropy layer and the second optical anisotropy layer. When laminating the first optical anisotropy layer and the second optical anisotropy layer, they were laminated in such a way that the continuous rotational directions of the optical axes in the liquid crystal alignment pattern were different from those of the other layer.

[0173] In cross-sectional images obtained by SEM, both the first and second optical anisotropic layers showed that the light and dark lines were obliquely inclined with respect to the normal to the interface beneath the optical anisotropy layer. Furthermore, the inclination angle of the light and dark lines decreased from the center outward, and the direction of the inclination of the light and dark lines with respect to the normal of both the first and second optical anisotropic layers was the same. In both the first and second optical anisotropic layers, the period of the light and dark line patterns was observed to decrease from the center outward.

[0174] [evaluation] The optical elements of Comparative Example 11 and Example 11 function as reflective diffracting elements. For each element, the angle of the reflected diffracted light with respect to the normal direction of the optical element when light is incident was measured, and the rate of increase in light intensity was evaluated. The specific measurement method is as follows.

[0175] Laser light is incident at a predetermined position on the surface of an optical element at a predetermined angle of incidence, and the reflected light is projected onto a screen placed at a distance of 30 cm in the normal direction of the optical element. From the image captured by the infrared camera... The angle of the reflected diffracted light was calculated. A laser diode with a wavelength of 940 nm was used as the light source.

[0176] Next, as shown in Figure 20, laser light with a wavelength of 940 nm emitted from the laser light source 251 was transmitted through the linear polarizer 252 to obtain linearly polarized light Lir. This light Lir was incident on a predetermined position on the surface of the optical element S at a predetermined incident angle. The light intensity of the reflected diffracted light Ldr diffracted by the optical element S was measured with a photodetector 256. The ratio of the light intensity of the diffracted light Ldr to the light intensity of the light Lir was taken to determine the relative light intensity value of the diffracted light Ldr with respect to the incident light. The relative light intensity value was similarly determined by changing the incident angle. The average value of the relative light intensity for different incident angles was used to evaluate the increase in light intensity of the example compared to the comparative example according to the following criteria.

[0177] A: Light intensity increase rate of 20% or more B: Light intensity increase rate is 10% or more, but less than 20%. C: Light intensity increase rate is 5% or more, but less than 10%. D: Light intensity increase rate is less than 5%

[0178] In the comparison between Comparative Example 11 and Example 11, the incident angle was set to 10° at a distance of 1.0 mm from the center (1 period of 9.0 μm), 20° at a distance of 2.5 mm from the center (1 period of 4.5 μm), and 30° at a distance of 4.0 mm from the center (1 period of 3.0 μm) for evaluation.

[0179] The results are shown in Table 2. [Table 2]

[0180] Example 11 achieved a higher average diffraction efficiency than Comparative Example 11 in the incident angle range of 10 to 30°.

[0181] The disclosure of Japanese Patent Application No. 2018-185584, filed on 28 September 2018, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. The material comprises multiple optically anisotropic layers in the thickness direction, each having an in-plane orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. Between the plurality of optically anisotropic layers, there is a region in which the length of one period until the orientation of the optical axis in one direction rotates by 180° coincides within a range of ±10%. Each of the aforementioned plurality of optical anisotropic layers, in a cross-sectional image obtained by observing a cross-section cut in the thickness direction along the aforementioned one direction using a scanning electron microscope, has a plurality of pairs of bright and dark lines along the aforementioned one direction, originating from the orientation of the optical axis. The first optical anisotropic layer, which is one of the plurality of optical anisotropic layers, is a gradient optical anisotropic layer having regions in which pairs of bright and dark lines are inclined at different angles of inclination with respect to the normal of the interface of the optical anisotropic layer in the cross-sectional image. The plurality of optical anisotropic layers include a second optical anisotropic layer arranged adjacent to the first optical anisotropic layer. There is no alignment film between the first optical anisotropy layer and the second optical anisotropy layer. The second optical anisotropy layer is a non-gradient optical anisotropy layer in which, in the cross-sectional image, each pair of bright and dark lines extends along the normal. Optical element.

2. The optical element according to claim 1, wherein the first optical anisotropic layer and the second optical anisotropic layer are stacked so that the lengths of the regions where the direction of the optical axis rotates by 180° coincide, and in the cross-sectional image, the bright lines and dark lines of the first optical anisotropic layer and the second optical anisotropic layer are connected at their interface.

3. The material comprises multiple optically anisotropic layers in the thickness direction, each having an in-plane orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. Between the plurality of optically anisotropic layers, there is a region in which the length of one period until the orientation of the optical axis in one direction rotates by 180° coincides within a range of ±10%. Each of the aforementioned plurality of optical anisotropic layers, in a cross-sectional image obtained by observing a cross-section cut in the thickness direction along the aforementioned one direction using a scanning electron microscope, has a plurality of pairs of bright and dark lines along the aforementioned one direction, originating from the orientation of the optical axis. The first optical anisotropic layer, which is one of the plurality of optical anisotropic layers, is a gradient optical anisotropic layer having regions in which pairs of bright and dark lines are inclined at different angles of inclination with respect to the normal of the interface of the optical anisotropic layer in the cross-sectional image. The plurality of optical anisotropic layers include a second optical anisotropic layer arranged adjacent to the first optical anisotropic layer. There is no alignment film between the first optical anisotropy layer and the second optical anisotropy layer. The second optical anisotropy layer is a gradient optical anisotropy layer having regions in which pairs of bright and dark lines are inclined at different angles of inclination with respect to the normal in the cross-sectional image. In the cross-sectional image, in at least a portion of the opposing regions of the first optical anisotropy layer and the second optical anisotropy layer, the inclination direction with respect to the normal is different for the pair of bright and dark lines in the first optical anisotropy layer and the pair of bright and dark lines in the second optical anisotropy layer. Optical element.

4. The optical element according to claim 3, wherein in the cross-sectional image, the inclination angles of the pairs of bright and dark lines in the first optical anisotropy layer and the pairs of bright and dark lines in the second optical anisotropy layer are different from each other in at least a portion of the opposing regions of the first optical anisotropy layer and the second optical anisotropy layer.

5. The optical element according to any one of claims 1 to 4, wherein the gradient optical anisotropy layer has a region in which the optical axis is twisted in the thickness direction.

6. An optical element according to any one of claims 1 to 5, having the function of diffracting and transmitting incident light.

7. The optical element according to any one of claims 1 to 4, wherein the liquid crystal compound in the gradient optical anisotropy layer is cholesterically oriented.

8. The optical element according to claim 7, which has the function of diffracting and reflecting incident light.

9. The optical element according to any one of claims 1 to 8, wherein the in-plane orientation pattern of each of the plurality of optical anisotropic layers is a pattern in which the length until the orientation of the optical axis in that direction is rotated by 180° changes gradually in that direction.

10. The optical element according to any one of claims 1 to 8, wherein the in-plane orientation pattern of each of the plurality of optical anisotropic layers is a pattern having one direction radially from the inside to the outside.

11. The optical element according to any one of claims 1 to 10, wherein in the in-plane orientation pattern of each of the plurality of optical anisotropic layers, there is a region in which the length until the orientation of the optical axis rotates by 180° in one direction is 10 μm or less.

12. An optical deflection element that deflects incident light and emits it, A driving means for driving the optical deflection element, A light deflection device comprising an optical element according to any one of claims 1 to 11, disposed on the light-emitting side of the light deflection element.

Images