Optical element and light deflection device

Abstract

To provide an optical element and a light deflection device for increasing average diffraction efficiency by averaging diffraction efficiency in a plane.SOLUTION: An optical element 1 and a light deflection device have multiple optical anisotropic layers 10, 20 having an in-plane orientation pattern in which the direction of an optical axis originating from a liquid crystal compound 30 is changed while being rotated continuously along at least one direction in the plane, the optical anisotropic layers have areas in which length until the direction of an optical axis is rotated by 180° in one direction differs mutually, multiple pairs of bright lines and dark lines originating from the direction of an optical axis exist along one direction in a sectional image obtained by observing a section cut in a thickness direction along one direction by a scanning electron microscope in at least one layer from among multiple optical anisotropic layers, and an inclined optical anisotropic layer has an area in which the pairs of bright lines and dark lines are inclined at mutually different inclination angles relative to a normal line of an interface of the optical anisotropic layers.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to an optical element and an optical deflection device including the optical element.

Background Art

[0002] In many optical devices or systems, polarization is utilized, and the development of optical elements for controlling polarization reflection, focusing, divergence, etc. has been underway.

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

[0004] Further, Japanese Unexamined Patent Application 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 non-linearly in at least one dimension along the surface. Here too, pattern alignment of a liquid crystal compound is utilized.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Documents 1 and 2 are not technologies for emitting diffracted light of light in different directions depending on the incident position, nor is there such a description. When light is incident on a layer having optical anisotropy with a local optical axis direction that changes non-linearly in one dimension as in Patent Document 3, it has been clarified by the study of the present inventors that 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 there may be a region where the diffraction efficiency decreases.

[0006] In view of the above circumstances, an object of the present disclosure is to provide an optical element and an optical deflection device that achieve averaging of the diffraction efficiency in the plane and improve the average diffraction efficiency.

Means for Solving the Problems

[0007] The technology of the present disclosure includes the following aspects. <1> Having a plurality of optically anisotropic layers in the thickness direction, in which the orientation of the optical axis derived from the liquid crystal compound changes continuously while rotating along at least one direction in the plane, The optically anisotropic layer has regions with different lengths until the orientation of the optical axis rotates 180° in the one direction, At least one of the plurality of optically anisotropic layers is an optical element that is an inclined optically anisotropic layer having a plurality of pairs of bright lines and dark lines derived from the orientation of the optical axis along the one direction in a cross-sectional image observed with a scanning electron microscope of a cross-section cut in the thickness direction along the one direction, and having a region where the pairs of bright lines and dark lines are inclined at different inclination angles with respect to the normal of the interface of the optically anisotropic layer. <2> The optical element according to <1>, comprising two inclined optically anisotropic layers, and in the cross-sectional image, the inclination angles of the pairs of bright lines and dark lines in one inclined optically anisotropic layer and the pairs of bright lines and dark lines in the other inclined optically anisotropic layer in at least a partial opposing region of the two inclined optically anisotropic layers are different from each other. <3> The optical element according to either <1> or <2>, comprising two inclined optically anisotropic layers, and in the cross-sectional image, the inclination directions of the pairs of bright lines and dark lines in one inclined optically anisotropic layer and the pairs of bright lines and dark lines in the other inclined optically anisotropic layer in at least a partial opposing region of the two inclined optically anisotropic layers are different with respect to the normal. <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 bright and dark line pairs in one of the two inclined optically anisotropic layers and the bright and dark line pairs in the other inclined optically anisotropic layer with respect to the normal line are the same in at least a part of the facing 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>, having 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>, having 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>, having 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 deflector including an optical deflector that deflects and emits incident light, a driving means that drives the optical deflector, and an optical element according to any one of <1> to <11> disposed on the light emission side of the optical deflector.

Advantages of the Invention

[0008] According to the present disclosure, in the optical element and the optical deflector, it is possible to average the diffraction efficiency in the plane and improve the average diffraction efficiency.

Brief Description of Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the optical element of the present invention will be described with reference to the drawings. In each drawing, for easy visual recognition, the scales of the components are appropriately different from the actual ones. In this specification, the numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. Also, with respect to angles, "orthogonal" and "parallel" mean a range of strict angles of ±10°.

[0011] [Optical Element] FIG. 1 is a plan view schematically showing a part of the surface of the optical element 1 of the first embodiment, and FIG. 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 includes two layers of optically anisotropic layers 10 and 20 laminated in the thickness direction. The optically anisotropic layers 10 and 20 are formed of cured layers of a composition containing a liquid crystal compound. Note that the optical element 1 may have a configuration including a support and an alignment film, and an optically anisotropic layer may be provided on the alignment film. As the optical element of the present disclosure, it is sufficient to have a plurality of optically anisotropic layers in the thickness direction, and it is not limited to a two-layer structure, and may have three or more layers.

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

[0014] Note that the optical axis 30A derived from the liquid crystal compound is the long axis direction (slow axis) of the rod-shaped liquid crystal compound in the case of a rod-shaped liquid crystal compound, and the direction perpendicular to the disk surface (fast axis) in the case of a disk-shaped liquid crystal compound. In the following description, the optical axis 30A derived from the liquid crystal compound is also referred to as the optical axis 30A of the liquid crystal compound or simply the optical axis 30A.

[0015] The in-plane alignment pattern in which the direction of the optical axis 30A continuously rotates and changes along one direction A means that the angle formed by the optical axis 30A of the liquid crystal compound arranged along one direction A (hereinafter also referred to as axis A) and axis A is different depending on the position in the axis A direction, and along axis A, the angle formed by the optical axis 30A and axis A gradually changes from φ to φ + 180° or φ - 180° and is an alignment pattern that is oriented and fixed. Hereinafter, in the optical anisotropic layer as shown in FIG. 1, a local region (unit region) in which the optical axis of the liquid crystal compound is parallel to the plane of the optical anisotropic layer and the direction of the optical axis is constant is arranged in a row in one direction, and the in-plane alignment pattern in which the direction of the optical axis continuously rotates and changes in one direction among a plurality of arranged local regions is referred to as a horizontal rotation alignment pattern.

[0016] Note that "the angle formed by the optical axis 30A and axis A gradually changes" may mean that the direction of the optical axis changes by a predetermined angle between unit regions, or may change at non-uniform angular intervals rather than at a constant angular interval, and further may change continuously. However, the angular difference of the optical axis 30A between unit regions adjacent to each other in the x direction is preferably 45° or less, more preferably 15° or less, and even more preferably a smaller angle.

[0017] In the optical element 1, in such a horizontal alignment pattern of the 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 Λ of one period in the horizontal alignment. In other words, the length of one period in the horizontal alignment pattern is the distance from the angle φ formed between the optical axis 30A of the liquid crystal compound 30 and the axis A to φ + 180°. In the following description, this length Λ of one period is also referred to as "one-period Λ" or simply "period Λ".

[0018] The optically anisotropic layers 10 and 20 in the optical element 1 include regions where the length Λ of one period is different from each other in the direction of the axis A. In the example shown in FIG. 1, in the direction of the axis A, the lengths of one period are Λ A1 , Λ A2 , Λ A3 … (where Λ A1 < Λ A2 < Λ A3 ) and different regions A1, A2, A3... are included. In this example, it has a liquid crystal alignment pattern in which the period gradually shortens from right to left in the drawing, but as the optical element of the present disclosure, it only needs to have two or more regions where the lengths of one period are different from each other. However, when applied to the light deflection device described later, as shown in this example, a liquid crystal alignment pattern in which the length of one period gradually changes is preferable. It is preferable to include a region where the period Λ is 10 μm or less.

[0019] Note that between a plurality of optically anisotropic layers, the lengths of one period in the opposing regions may be offset, but it is preferable that they match within a range of ±10%. With such a configuration, by forming a plurality of optically anisotropic layers in the order of first forming the first optically anisotropic layer and then forming the second optically anisotropic layer by coating or the like, it becomes possible to match the periods.

[0020] As shown in FIG. 1, when observing with an optical microscope in a state where the optical element 1 having an optically anisotropic layer is sandwiched between two polarizers orthogonal to the alignment pattern of the optical axis, bright portions 42 and dark portions 44 are alternately observed. The period of light and dark (that is, the period of the bright portion or the period of the dark portion) is half of the period Λ of the horizontal alignment pattern of the optical axis.

[0021] Among the two optical anisotropic layers 10 and 20, at least one layer, in this example, the first optical anisotropic layer 10 is an inclined optical anisotropic layer. Hereinafter, the first optical anisotropic layer will also be referred to as the inclined optical anisotropic layer 10. Here, the inclined optical anisotropic layer means that in a cross-sectional image (hereinafter referred to as a cross-sectional SEM image) observed by a scanning electron microscope (SEM) of a cross-section cut in the thickness direction along one direction, there are a plurality of pairs of bright and dark lines (bright and dark lines) derived from the direction of the optical axis along one direction, and the bright and dark lines have a region inclined at different inclination angles with respect to the normal line n of the interface of the layer. The "bright and dark lines derived from the direction of the optical axis" are bright and dark lines observed according to the alignment state of the liquid crystal compound in the thickness direction of the optical anisotropic layer.

[0022] FIG. 2 is a schematic diagram of a cross-sectional image when a cross-section cut in the thickness direction is observed by SEM along one direction in which the optical axis rotates. As shown in FIG. 2, in the cross-sectional image, a plurality of pairs of bright and dark lines inclined obliquely with respect to the normal line n of the interface of the inclined optical anisotropic layer 10 exist alternately. The inclination of the bright and dark lines with respect to the normal line n of the interface 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 bright and dark lines is defined as an acute angle less than 90° among the angles formed by the bright and dark lines and the normal line n.

[0023] In the inclined optical anisotropic layer 10, for example, in addition to the horizontal rotational alignment, by providing a twist alignment in the thickness direction, bright and dark lines are observed in the above cross-sectional image. By having a twist alignment in the thickness direction in addition to the horizontal rotational alignment, bright and dark lines are observed in the above cross-sectional image.

[0024] FIG. 3 schematically shows the liquid crystal alignment pattern in the cross-section of the optical element 1 shown in FIGS. 1 and 2. Here, the liquid crystal compound is a rod-shaped liquid crystal compound 30. In addition, the bright and dark lines observed when the cross-section is observed by SEM in FIG. 3 are shown superimposed.

[0025] As shown in FIG. 3, in the tilted optically anisotropic layer 10, rod-shaped liquid crystal compounds 30 (hereinafter simply referred to as liquid crystal compounds 30) are horizontally rotationally aligned in the x direction and have a liquid crystal alignment pattern that is twisted and aligned in the thickness direction.

[0026] The phrase "the optical axis is twisted and aligned in the thickness direction" means a state in which the directions of the optical axes arranged in the thickness direction from one surface to the other surface of the optically anisotropic layer 10 change relatively and are twisted and aligned in one direction and fixed. The twist property includes right-handed twist and left-handed twist, and it may be applied according to the direction in which diffraction is desired. Note that the twist of the optical axis in the thickness direction is less than one rotation, that is, the twist angle is less than 360°. For example, in the example of FIG. 3, in the thickness direction (z direction), the optical axis of the liquid crystal compound 30 rotates approximately 140° from one surface side to the other surface side. The twist angle of the liquid crystal compound 30 in the thickness direction is preferably about 10° to 200°, and more preferably about 45° to 180°. In the case of cholesteric alignment described later, the twist angle is 360° or more and has selective reflectivity for specific circularly polarized light in a specific wavelength range. The "twisted alignment" in this specification does not include cholesteric alignment, and selective reflectivity does not occur in an optically anisotropic layer having twisted alignment.

[0027] When observing a cross section of a tilted optically anisotropic layer having such a liquid crystal alignment pattern by SEM, the light and dark lines shown in FIG. 2 are observed. As shown by superimposing the light and dark lines in FIG. 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 image, there are also a plurality of light and dark lines alternately present in the second optically anisotropic layer 20, but the light and dark lines of the second optically anisotropic layer 20 are along the normal line n of the interface of the optically anisotropic layer 20 and do not have an inclination. In the second optically anisotropic layer 20, the direction of the optical axis in the thickness direction is uniform.

[0029] Also, in this optical element 1, as shown in FIG. 2, the period Λ A1 , Λ A2…and the period Λ of the horizontal rotational alignment in the second optically anisotropic layer 20 B1 、Λ B2 … coincide in the opposing regions. That is, Λ A1 = Λ B1 、Λ A2 = Λ B2 … holds.

[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 in the range of 0.3λ to 0.7λ. The retardation Re is preferably in the range of 0.4λ to 0.6λ, more preferably in the range of 0.45λ to 0.55λ, and particularly preferably 0.5λ. Δn λ is the The complex refractive index, and d is the thickness of the optically anisotropic layer. For example, when assuming light with a wavelength of 940 nm as the incident light, the retardation Re with respect to the 940 nm light may be in the range of 282 nm to 658 nm, and it is particularly preferably 470 nm. When having such a retardation Re, the optically anisotropic layer exhibits the function as a general λ / 2 plate, that is, the function of giving a phase difference of 180° (=π = λ / 2) between the linearly polarized light components orthogonal to the incident light. Note that the closer the retardation is to λ / 2, the more preferable it is because the diffraction efficiency is improved, but the retardation is not limited to the above range. When the optically anisotropic layer has a retardation of approximately λ / 2, it gives a phase difference of λ / 2 to the incident light, and converts the incident light having a predetermined circular polarization into a reverse circular polarization and emits it.

[0032] Fig. 4 conceptually shows the action of the optically anisotropic layer 11 having a horizontal rotation alignment pattern when using right circularly polarized light P with a wavelength λ as the incident light L1. R When the incident light L1 of right circularly polarized light with a wavelength λ is incident on the optically anisotropic layer 11, the incident light L1 which is right circularly polarized light PR is given a phase difference of λ / 2 by passing through the optically anisotropic layer 11 and is converted into left circularly polarized light P. L Further, the absolute phase of the incident light L1 changes due to the optical axis 30A of the liquid crystal compound 30 in each unit region (local region) in the horizontal rotation alignment pattern. Here, in the optically anisotropic layer, since the direction of the optical axis 30A of the liquid crystal compound 30 rotates and changes along the axis A, the amount of change in the absolute phase varies according to the direction of the optical axis 30A of the liquid crystal compound 30 at the position of the axis A of the optically anisotropic layer 11 where the incident light is incident. The region indicated by the broken line in Fig. 4 schematically shows how the amount of change in the absolute phase Q varies depending on the x coordinate.

[0033] As shown in FIG. 4, due to the shift of the absolute phase Q when passing through the optically anisotropic layer 11, an equiphase surface E of the absolute phase having an angle with respect to the plane of the optically anisotropic layer 11 is formed. As a result, a bending force is applied to the incident light L1 incident from the normal direction in a direction perpendicular to the equiphase surface E, and the traveling direction of the incident light L1 changes. That is, the incident light L1 which is right-circularly polarized light PR becomes left-circularly polarized light PL after passing through the optically anisotropic layer 11, and is emitted from the optically anisotropic layer 11 as the emitted light L2 traveling in a direction forming a predetermined angle with the normal direction.

[0034] In addition, when left-circularly polarized light is incident on the optically anisotropic layer 11 as incident light, the incident light is converted into right-circularly polarized light in the optically anisotropic layer 11 and receives a bending force in the direction opposite to that in the figure, and the traveling direction is changed. Further, when the rotation direction of the horizontal rotational alignment of the optical axis 30A of the liquid crystal compound 30 is reversed, the refraction direction of light by the optically anisotropic layer becomes opposite to the above.

[0035] Since the shorter the one period in the in-plane alignment pattern in the optically anisotropic layer, the greater the bending force that can be applied to the incident light, the diffraction angle can be increased.

[0036] Also, the wavelength λ of the light that causes the diffraction action by the optically anisotropic layer 11 may be from ultraviolet to visible light, infrared, or even at the electromagnetic wave level. For the same period, the larger the wavelength of the incident light, the larger the diffraction angle, and the smaller the wavelength of the incident light, the smaller the diffraction angle. Therefore, the period may be set according to the target wavelength and the desired diffraction angle.

[0037] In the above, the case where a bending force is applied to the light incident from the normal direction has been described. However, a bending force is also applied to the obliquely incident light on the same principle, and the emitted light having an emission angle at an angle different from the incident angle can be obtained.

[0038] In the optical element 1 of this configuration, since the first and second optically anisotropic layers 10 and 20 each have regions with different periods of the horizontal rotation alignment pattern in their respective planes, light with different emission angles can be emitted for the same incident angle. When not twisted and aligned in the thickness direction like the second optically anisotropic layer 20, the diffraction efficiency for light incident in the normal direction is high, but there is a problem that the diffraction efficiency for obliquely incident light is low. On the other hand, in the tilted optically anisotropic layer 10, the diffraction efficiency for obliquely incident light can be improved. When the light is obliquely incident, there is a problem that the diffraction efficiency for the obliquely incident light is low. On the other hand, in the tilted optically anisotropic layer 10, the diffraction efficiency for the obliquely incident light can be improved.

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

[0040] The optically anisotropic layer has a two-layer structure in this example, but may have three or more layers. Also, the tilted optically anisotropic layer may have one 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, FIGS. 5 and 6 show a configuration example having two tilted optically anisotropic layers. FIGS. 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 obtained by observing a cross-section cut in the thickness direction along one direction in which the horizontal rotation alignment is performed, as in the above.

[0042] As shown in FIG. 5, in the cross-sectional image, the inclination directions of the bright and dark lines in one of the two inclined optically anisotropic layers 10 with respect to the normal line n in the opposing region of the two layers may be different from the inclination directions of the bright and dark lines in the other inclined optically anisotropic layer 22 with respect to the normal line n. Different inclination directions with respect to the normal line n mean that the inclination direction of the bright and dark lines in one of the inclined optically anisotropic layers 10 with respect to the normal line n is on the negative side of the x-axis (left side of the paper surface), while the inclination direction of the bright and dark lines in the other inclined optically anisotropic layer 22 with respect to the normal line n is on the positive side of the x-axis (right side of the paper surface). The inclination angles of the two inclined optically anisotropic layers with respect to the normal line n may be the same in the opposing region (α n =β n ), or they may be different (α n ≠β n ). When two inclined optically anisotropic layers are provided, the opposing regions where the inclination directions of the bright and dark lines of each other are different may cover the entire area or may be only a part. In this specification, the opposing region of the two inclined optically anisotropic layers is a region that overlaps when viewed from the thickness direction in the same xy region.

[0043] By reversing the twist property of the twist orientation in the thickness direction between one inclined optically anisotropic layer 10 and the other inclined optically anisotropic layer 22, the inclination of the bright and dark lines of each other with respect to the normal line can be reversed.

[0044] As shown in FIG. 6, in the cross-sectional image, the inclination directions of the bright and dark line interfaces in one of the two inclined optically anisotropic layers 10 in the opposing region of the two layers may be the same as the inclination directions of the bright and dark line interfaces in the other inclined optically anisotropic layer 24 with respect to the normal line n. However, here, the inclination angle α n of the bright and dark lines in one of the inclined optically anisotropic layers 10 in the opposing region n is different from the inclination angle γ of the bright and dark lines in the other inclined optically anisotropic layer 24. When two inclined optically anisotropic layers are provided, the opposing regions where the inclination directions of the bright and dark lines of each other are the same may cover the entire area or may be only a part.

[0045] By making the twist pitch of the twist orientation in the thickness direction different between one inclined optically anisotropic layer 10 and the other inclined optically anisotropic layer 22, it is possible to make the inclination of the normal lines of the bright and dark lines different from each other. Different twist pitches mean that the thickness until the optical axis is twisted to the same twist angle is different.

[0046] Note that in the two-layer inclined optically anisotropic layer provided in one optical element, it may simultaneously include an opposing region with the same inclination direction and an opposing region with different inclination directions.

[0047] In the above, an optical element that functions as a transmissive diffraction element has been described. However, the optical element shown in the present disclosure can also function as a reflective diffraction element. The optical element shown can also be made to function as a reflective diffraction element.

[0048] FIG. 7 shows a cross-sectional view of an optical element 5 of a fourth embodiment that functions as a reflective diffraction element. In FIG. 7, the bright and dark lines in the cross-sectional SEM image are schematically superimposed and shown.

[0049] The optical element 5 includes two inclined optically anisotropic layers 12 and 14. Both of the two inclined optically anisotropic layers 12 and 14 are horizontally rotationally oriented and are cholesterically oriented in the thickness direction. The two inclined optically anisotropic layers 12 and 14 have opposite directions of rotation of the optical axis in the horizontal rotational orientation and also have opposite directions of rotation in the cholesteric orientation.

[0050] Since the inclined optically anisotropic layers 12 and 14 have a cholesteric orientation, they selectively reflect only light in a specific selected wavelength range of a specific circularly polarized light. The central wavelength of the selectively reflected light is determined by the cholesteric helical pitch and the film thickness, and which circularly polarized light is reflected is determined by the direction of rotation of the helix.

[0051] Since it is a liquid crystal alignment pattern having a horizontal rotational orientation and a cholesteric orientation, in the cross-sectional image, bright and dark lines having an inclination in the normal direction and different inclination angles are observed as in the above-described embodiment (see FIG. 7).

[0052] Since the orientation pattern of the optical axis 30A in the in-plane direction of the tilted optical anisotropic layers 12 and 14 is a horizontal rotation orientation as in the previous embodiment, the same operation as that of the optical element 1 occurs. That is, it has the effect of changing the absolute phase of the incident light and bending it in a predetermined direction. Therefore, the optical element 5 has both the effect of bending the incident light in a direction different from the incident direction and the effect due to the cholesteric orientation, and reflects the light at an angle in a predetermined direction with respect to the reflection direction of specular reflection. Also, in the in-plane direction, since it has regions with different periods of horizontal rotation orientation, light can be reflected at different reflection angles for the same incident angle. In addition, when the incident angle is changed by region, the average diffraction efficiency when incident can be improved, and the intensity difference of the reflected light can be suppressed.

[0053] In each of the above embodiments, one period of the horizontal rotation orientation shows a pattern that gradually becomes longer in the x direction. As the optical element, it is also preferable that the optical anisotropic layer has an in-plane orientation pattern in which one period gradually becomes shorter from the center in the uniaxial direction toward one end and the other end in the plane.

[0054] Furthermore, as shown in FIG. 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. FIG. 8 is a plan schematic view of the optical anisotropic layer of the optical element of the design change example. In FIG. 8, the in-plane orientation pattern is indicated by the optical axis 30A of the liquid crystal compound. The optical anisotropic layer is provided with regions having the same orientation of the optical axis concentrically, and has an in-plane orientation pattern in which one direction in which the orientation of the optical axis 30A continuously changes while rotating is provided radially from the center of the optical anisotropic layer 15.

[0055] In the optical anisotropic layer 15, the orientation of the optical axis 30A changes while continuously rotating along a number of directions from the center of the optical anisotropic layer 15 toward the outside, for example, the direction indicated by arrow A1, the direction indicated by arrow A2, and the direction indicated by arrow A3. The rotation direction of the optical axis rotating along each axial direction is rotationally symmetric with respect to the center.

[0056] When an optical element 1 having an in-plane alignment pattern shown in FIG. 8 is sandwiched between two orthogonal polarizers and observed with an optical microscope, bright and dark portions are alternately observed in a concentric circle pattern. The period of light and dark on the concentric periodic alignment surface (i.e., the period of the dark portion or the bright portion) is half of the period Λ of the horizontal rotational alignment pattern. The period gradually becomes shorter toward the outside, so the difference in diameter between adjacent concentric circles becomes smaller toward the outside. Since it is getting shorter gradually toward the outside, the diameter of the concentric circles becomes smaller in the difference from the diameter of the adjacent concentric circles toward the outside.

[0057] The circularly polarized light incident on the optically anisotropic layer 15 having this in-plane alignment pattern changes its absolute phase in each local region where the direction of the optical axis of the liquid crystal compound 30 is different. At this time, the amount of change in the absolute phase of each is different depending on the direction of the optical axis of the liquid crystal compound 30 on which the circularly polarized light is incident.

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

[0059] Conversely, the period Λ in one cycle in the concentric liquid crystal alignment pattern may be gradually increased from the center of the optically anisotropic layer 15 toward the outer direction in one direction in which the optical axis continuously rotates. Furthermore, for example, when it is desired to provide a light quantity distribution in transmitted light, depending on the use of the optical element, instead of gradually changing the period Λ in one direction in which the optical axis continuously rotates, a configuration having regions where the period Λ is partially different in one direction in which the optical axis continuously rotates can also be used.

[0060] Next, the component materials and forming methods provided in the optical element of the present disclosure will be described.

[0061] <Optically Anisotropic Layer> A liquid crystal composition containing a liquid crystal compound for forming an optically anisotropic layer may contain other components such as a leveling agent, an alignment controller, a polymerization initiator, and an alignment aid in addition to the liquid crystal compound. By forming an alignment film on a support, applying the liquid crystal composition on the alignment film, and curing it, an optically anisotropic layer in which a predetermined liquid crystal alignment pattern is fixed and which is composed of a cured layer of the liquid crystal composition can be obtained.

[0062] -Rod-shaped liquid crystal compound- As the rod-shaped liquid crystal compound, azomethines, azoxyes, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, phenyl esters of cyclohexanecarboxylic acid, cyanophenylcyclohexanes, cyanine-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes, and alkenylcyclohexylbenzonitriles are preferably used. Not only low-molecular liquid crystalline molecules as described above, but also high-molecular liquid crystalline molecules can be used.

[0063] It is more preferable to fix the orientation of the rod-shaped liquid crystal compound by polymerization. As the polymerizable rod-shaped liquid crystal compound, the compounds described in Makromol. Chem., Vol. 190, p. 2255 (1989), Advanced Materials, Vol. 5, p. 107 (1993), U.S. Patent No. 4,683,327, No. 5,622,648, No. 5,770,107, International Publication No. 95 / 22586, No. 95 / 24455, No. 97 / 00600, No. 98 / 23580, No. 98 / 52905, Japanese Patent Application Laid-Open No. 1-272551, No. 6-16616, No. 7-110469, No. 11-80081, and Japanese Patent Application Laid-Open No. 2001-328973 can be used. Further, as the rod-shaped liquid crystal compound, for example, those described in Japanese Patent Application Laid-Open No. 11-513019 and Japanese Patent Application Laid-Open No. 2007-279688 can also be preferably used.

[0064] -Disc-shaped liquid crystal compound- As the disc-shaped liquid crystal compound, for example, those described in Japanese Patent Application Laid-Open No. 2007-108732 and Japanese Patent Application Laid-Open No. 2 Those described in Japanese Patent Publication No. 010-244038 can be preferably used.

[0065] -Other components- Regarding other components such as an alignment control agent, a polymerization initiator, and an alignment aid, known materials can all be used. In addition, a chiral agent is added in order to obtain an optically anisotropic layer having a twist alignment in the thickness direction or an optically anisotropic layer having a cholesteric alignment in the thickness direction.

[0066] --Chiral agent (optically active compound)-- The chiral agent has a function of inducing a helical structure of a cholesteric liquid crystal phase. Since the twist direction or the helical pitch of the helix induced by the compound varies depending on the compound, it may be selected according to the purpose. There is no particular limitation on the chiral agent, and known compounds (for example, described in Liquid Crystal Device Handbook, Chapter 3, Section 4-3, chiral agents for TN (twisted nematic), STN (Super Twisted Nematic), page 199, edited by the 142nd Committee of the Japan Society for the Promotion of Science, 1989), isosorbide, and isomannide derivatives, etc. can be used. The chiral agent generally contains an asymmetric carbon atom, but an axial asymmetric compound or a planar asymmetric compound that does not contain an asymmetric carbon atom can also be used as the chiral agent. Examples of the axial asymmetric compound or the planar asymmetric compound include binaphthyl, helicene, paracyclophane, and derivatives thereof. The chiral agent may have a polymerizable group. When both the chiral agent and the liquid crystal compound have a polymerizable group, a polymer having a repeating unit derived from the polymerizable liquid crystal compound and a repeating unit derived from the chiral agent can be formed by a polymerization reaction between the polymerizable chiral agent and the polymerizable liquid crystal compound. In this aspect, the polymerizable group of the polymerizable chiral agent is preferably the same kind of group as the polymerizable group of the polymerizable liquid crystal compound. Therefore, the polymerizable group of the chiral agent is also preferably an unsaturated polymerizable group, an epoxy group, or an aziridinyl group, more preferably an unsaturated polymerizable group, and even more preferably an ethylenically unsaturated polymerizable group. Also, the chiral agent may be a liquid crystal compound.

[0067] When the chiral agent has a photo-isomerizable group, it is preferable because a pattern of a desired reflection wavelength corresponding to the emission wavelength can be formed by irradiating a photomask such as actinic rays after coating and alignment. As the photo-isomerizable group, an isomerization site of a compound exhibiting photochromic properties, an azo group, an azoxy group, or a cinnamoyl group is preferable. As specific compounds, those described in JP-A-2002-80478, JP-A-2002-80851, JP-A-2002-179668, JP-A-2002-179669, JP-A-2002-179670, JP-A-2002-179681, JP-A-2002-179682, JP-A-2002-338575, JP-A-2002-338668, JP-A-2003-313189, and JP-A-2003-313292 can be used.

[0068] - Solvent - As the solvent of the liquid crystal composition, an organic solvent is preferably used. Examples of the organic solvent 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 preferable. Two or more kinds of organic solvents may be used in combination.

[0069] <Formation of the optically anisotropic layer> The optically anisotropic layer can be formed, for example, by applying a liquid crystal composition in multiple layers on an alignment film. Multiple-layer coating means applying a liquid crystal composition on an alignment film, heating it, further cooling it, and then performing ultraviolet curing to produce a first liquid crystal immobilized layer, and for the second and subsequent layers, repeating the steps of overcoating on the liquid crystal immobilized layer, heating it, cooling it, and then performing ultraviolet curing.

[0070] <Substrate> The substrate supports the optically anisotropic layer or the optically anisotropic layer and the alignment film. The substrate is not an essential component of the optical element. It is used when forming the optically anisotropic layer and may be peeled off thereafter.

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

[0072] There is no limitation on the thickness of the substrate, and the thickness capable of holding the alignment film and the optically anisotropic layer may be appropriately set according to the use of the optical element and the forming material of the substrate, etc. The thickness of the substrate is preferably 1 to 1000 μm, more preferably 3 to 250 μm, and even more preferably 5 to 150 μm.

[0073] <Alignment film> The alignment film is provided to align the liquid crystal compound in a predetermined liquid crystal alignment pattern when forming the optically anisotropic layer.

[0074] Various known alignment films can be used. For example, a rubbed film made of an organic compound such as a polymer, an obliquely evaporated film of an inorganic compound, a film having microgrooves, and a film obtained by accumulating an LB (Langmuir-Blodgett) film of an organic compound such as ω-tricosanoic acid, dioctadecylmethylammonium chloride, and methyl stearate, etc. are exemplified.

[0075] The alignment film formed by rubbing can be formed by rubbing the surface of the polymer layer several times in a certain direction with paper or cloth. Examples of materials used for the alignment film preferably include polyimide, polyvinyl alcohol, polymers having polymerizable groups described in JP-A-9-152509, alignment films described in JP-A-2005-97377, JP-A-2005-99228, and JP-A-2005-128503, and the like.

[0076] In the optical element of the present disclosure, a so-called photo-alignment film, which is obtained by irradiating a photo-alignment material with polarized light or non-polarized light to form an alignment film, is preferably used as the alignment film. That is, in the optical element of the present disclosure, a photo-alignment film formed by applying a photo-alignment material on a support is preferably used as the alignment film. The polarized light irradiation can be performed on the photo-alignment film from a vertical direction or an oblique direction, and the non-polarized light irradiation can be performed on the photo-alignment film from an oblique direction.

[0077] Examples of the photo-alignment material used for the photo-alignment film include, for example, azo compounds described in JP-A-2006-285197, JP-A-2007-76839, JP-A-2007-138138, JP-A-2007-94071, JP-A-2007-121721, JP-A-2007-140465, JP-A-2007-156439, JP-A-2007-133184, JP-A-2009-109831, Patent No. 3883848, and Patent No. 4151746; aromatic ester compounds described in JP-A-2002-229039; maleimide and / or alkenyl-substituted nadimide compounds having a photo-alignment unit described in JP-A-2002-265541 and JP-A-2002-317013; photocrosslinkable silane derivatives described in Patent Nos. 4205195 and 4205198; photocrosslinkable polyimide, photocrosslinkable polyamide, and photocrosslinkable ester described in JP-T-2003-520878, JP-T-2004-529220, and Patent No. 4162850; and photo-dimerizable compounds described in JP-A-9-118717, JP-T-10-506420, JP-T-2003-505561, WO2010 / 150748, JP-A-2013-177561, and JP-A-2014-12823, particularly cinnamate compounds, chalcone compounds, and coumarin compounds, etc. are exemplified as preferred examples. Among them, azo compounds, photocrosslinkable polyimide, photocrosslinkable polyamide, photocrosslinkable ester, cinnamate compounds, and chalcone compounds are preferably used.

[0078] There is no limitation on the thickness of the alignment film, and the thickness capable of obtaining the necessary alignment function may be appropriately set according to the material for forming the alignment film. The thickness of the alignment film is preferably 0.01 to 5 μm, more preferably 0.05 to 2 μm.

[0079] There is no limitation on the method for forming the alignment film, and various known methods according to the material for forming the alignment film can be used. As an example, a method of applying the alignment film on the surface of a support, drying it, and then exposing the alignment film with laser light to form an alignment pattern can be mentioned.

[0080] FIG. 9 conceptually shows an example of an exposure apparatus for exposing an alignment film to form an alignment pattern. The exposure apparatus includes 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 disposed on the optical path of the laser light L, a lens 84, and a drive stage 86 on which the alignment film 90 is installed. The λ / 2 plate 83 is attached to a rotary 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 rotation of the λ / 2 plate 83, condensed onto the photo-alignment film by the lens 84, and the drive stage 86 is driven to perform scan exposure of the photo-alignment film for patterning. Thereby, an alignment film with a patterned pattern of a desired pattern can be formed.

[0082] In the optical element of the present disclosure, the alignment film is provided as a preferred embodiment and is not an essential component. For example, it is also possible to form an optically anisotropic layer having a horizontal rotation alignment pattern by forming an alignment pattern on the support by a method of rubbing the support, a method of processing the support with laser light or the like.

[0083] In each of the above optical elements, the configuration assuming incident light of a single wavelength has been basically described, but a configuration that exhibits the same effect for incident light of multiple wavelengths can also be adopted. If an optical element having a structure in which optically anisotropic layers each having a liquid crystal alignment pattern corresponding to each wavelength are laminated, incident light of multiple wavelengths can be used.

[0084] [Optical Deflection Device] FIG. 10 shows a schematic configuration diagram of an example of an optical deflection device according to an embodiment. The light deflection device 130 includes, from the upstream side in the traveling direction of light (light beam), a condenser lens 131, a λ / 4 plate 111, a light deflection element 132, and an optical element 120 according to one aspect of the present invention. In the following description, upstream and downstream refer to the upstream and downstream in the traveling direction of light.

[0085] The condenser lens 131 is a known condenser lens and is provided to make the light (light beam) from a light source (not shown) incident on the light deflection element 132 in a slightly condensed state. The condenser lens 131 is provided as a preferred embodiment and is not an essential component. However, by providing the condenser lens 131, the light (light beam) emitted from the light deflection device 130 can be made into appropriate parallel light, improving the straightness. Note that the condenser lens 131 is not limited, and any known light condensing element capable of condensing light (light beam) can be used.

[0086] The λ / 4 plate 111 is a known λ / 4 plate (quarter-wave plate) that converts linearly polarized light emitted from an external light source into circularly polarized light. Any known λ / 4 plate 111 can be used without limitation. Therefore, the λ / 4 plate 111 may be derived from a polymer or from liquid crystal. The λ / 4 plate 111 may be disposed between the MEMS (Micro Electro Mechanical System) deflection element 132 and the optical element 120. However, in terms of miniaturization of the λ / 4 plate 111, etc., it is preferably provided upstream of the MEMS light deflection element 132. When circularly polarized light is incident on the light deflection device 130 using the MEMS light deflection element 132, the λ / 4 plate 111 may not be provided.

[0087] The light deflection element 132 is a MEMS light deflection element that two-dimensionally scans light. There is no particular limitation on the MEMS light deflection element, and known MEMS light deflection elements such as those described in Japanese Unexamined Patent Application Publication No. 2012-208352, those described in Japanese Unexamined Patent Application Publication No. 2014-134642, and those described in Japanese Unexamined Patent Application Publication No. 2015-22064, etc., can be appropriately used, which deflect (deflection scan) light by swinging a mirror (mirror) using a piezoelectric actuator or the like (MEMS (optical) scanner, MEMS light deflector, MEMS mirror, or DMD (Digital Micromirror Device)).

[0088] A drive device 134 for rotationally driving the mirror is connected to the light deflection element 132. As the drive device 134, a known one may be used according to the configuration of the MEMS light deflection element 132 or the like.

[0089] The optical element 120 includes two layers of optically anisotropic layers having an in-plane liquid crystal alignment pattern in which the optical axis is horizontally rotationally oriented along an axis radially provided from the center as shown in FIG. 8, and the period becomes smaller toward the outside. As shown in FIG. 10, the period becomes smaller toward the outside compared to the period Λ1 in the central region of the optical element 120 (Λ1>Λ2>Λ3>Λ4...). Here, one of the optically anisotropic layers 121 is an inclined optically anisotropic layer, and the other optically anisotropic layer 122 is an optically anisotropic layer having no twist property in the thickness direction and having a uniform pattern in the thickness direction. The optical element 120 is arranged such that the center coincides with the center of deflection of the light deflection element 132. The inclination of the normal to the bright and dark lines in the cross-sectional SEM image of the optical element 120 is larger at the center and smaller toward the outside.

[0090] For the light deflection device 130, the P-polarized light emitted from a light source (not shown) to the emission surface 120b of the optical element 120 is slightly condensed by the condenser lens 131, and then, for example, is converted into right circularly polarized light by the λ / 4 plate 111.

[0091] The light converted into circular polarization by the λ / 4 plate 111 is deflected by the MEMS optical deflector 132 and is incident on the incident surface 120a of the optical element 120. The light incident on the optical element 120 is diffracted and exits from the exit surface 120b of the optical element 120, that is, exits from the optical deflector 130.

[0092] Since the center of the optical element 120 is arranged to coincide with the center of deflection of the optical deflector 132, the light scanned by the optical deflector 132 is incident on one surface of the optical element 120 at a larger incident angle as it moves away from the center of that surface. The period of the 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 on the vertically incident light and transmits it as it is, and bends and emits it more greatly towards the outside of the optical element 120. By making the polarized light, which is given a bending force from the center towards the outside due to the horizontal rotation orientation of the optically anisotropic layers 121 and 122, incident on the optical element 120 as the incident light, a scan angle θmaxout larger than the scan angle θmax of the optical deflector 132 can be obtained.

[0093] Here, assuming that the incident angle of the light incident on the incident surface 120a of the optical element 120 is θ1, the refractive index of the incident-side medium is n1, the exit angle of the light exiting from the exit surface 120b of the optical element 120 is θ2, the refractive index of the exit-side medium is n2, the wavelength of the light is λ, the period structure pitch of the liquid crystal diffraction element is Λ, and the diffraction order is m, these values are related by the following formula (1). n1·sinθ1 - n2·sinθ2 = m·λ / Λ (1)

[0094] As described above, by changing the period Λ of the horizontal rotation orientation pattern in the optically anisotropic layer of the optical element 120, the angle of the light exiting from the optical element 120 can be changed. Considering Snell's law, the angle when finally emitted into the air can be up to about 80° in absolute value, so it is possible to expand the emission angle to a very large angle. Further, by continuously changing the period of the horizontal rotation alignment pattern in the optically anisotropic layer of the optical element 120 within the plane, light can be emitted continuously in an arbitrary direction.

[0095] As is clear from the above description, the light deflection device of the present disclosure enables light scanning at a scanning angle wider than the scanning angle (field angle) of the light deflection element. In FIG. 10, although the state where the scanning angle in the x direction expands is shown, since the horizontal rotation alignment pattern is provided radially, the scanning angle can be expanded by the same principle also in the y direction. Therefore, by diffracting and scanning the deflected light (scanning light) from the light deflection element 132 with the optical element 120, it becomes possible to significantly expand the scanning range compared to the scanning range that can be two-dimensionally scanned by the light deflection element 132.

[0096] Even when the optical element 120 applied to such a light deflection device 130 does not include the inclined optically anisotropic layer 121, the effect of expanding the scanning angle can be obtained. However, when an optical element having only the optically anisotropic layer 122 and not having the inclined optically anisotropic layer 121 is applied, there is a problem that there is a large difference in diffraction efficiency between the vicinity of the center where the incident angle is small and the outer peripheral region where the incident angle is large and the diffraction angle is large, and the overall diffraction efficiency (average diffraction efficiency) is low. By providing the inclined optically anisotropic layer 121, the diffraction efficiency of the outer peripheral portion of the element where the incident angle becomes large can be improved, the difference in diffraction efficiency due to the incident position and the incident angle can be suppressed, and the variation in the light amount of the emitted light can be suppressed. Further, by providing two or more optically anisotropic layers, the average diffraction efficiency can also be improved.

[0097] In the light deflection device, not limited to the above optical element 120, for example, a horizontal rotation alignment pattern in which the period gradually decreases from one side to the other side in the x-axis direction as shown in FIG. 1 An optical element having an optically anisotropic layer may be used. Also, in the x-axis direction, an optical element having a horizontal rotation alignment pattern in which the period gradually decreases from the center of the element toward the outside, and the rotation directions of the optical axes of the horizontal rotation alignment patterns on both sides sandwiching the center are opposite may be used.

Example

[0098] The features of the present invention will be described more specifically with reference to the following examples. The materials, reagents, amounts used, amounts of substances, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below. In the following examples and comparative examples, a liquid crystal alignment pattern was designed assuming infrared light with a target wavelength of 940 nm as incident light.

[0099] [Comparative Example 1] An optical element having a non-inclined optically anisotropic layer 211 in which the bright and dark lines are not inclined in the cross-sectional SEM image was produced as Comparative Example 1 (see FIG. 11).

[0100] <Fabrication of Optical Element> (Formation of Alignment Film) The following coating liquid for forming an alignment film was spin-coated on a glass substrate. The support on which the coating film of the coating liquid for forming an alignment film was formed was dried on a hot plate at 60 °C for 60 seconds to form an alignment film.

[0101] Coating Liquid for Forming Alignment Film ―――――――――――――――――――――――――――――――― Photoalignment Material A 1.00 part by mass Water 16.00 parts by mass Butoxyethanol 42.00 parts by mass Propylene Glycol Monomethyl Ether 42.00 parts by mass ――――――――――――――――――――――――――――――――

[0102] -Material A for Photoalignment- [Chemical formula]

[0103] (Exposure of the Alignment Film) Using the exposure apparatus shown in Fig. 9, while arbitrarily changing the polarization direction of the condensed laser light, the alignment film was scanned and exposed to pattern it, and an alignment film P-1 having an alignment pattern was formed. In the exposure apparatus, one that emits laser light with a wavelength of 325 nm was used as the laser. Note that a concentric alignment pattern was used, and one cycle of the alignment pattern was made to gradually shorten from the center outward.

[0104] (Formation of the First Optical Anisotropic Layer) As the liquid crystal composition for forming the optical anisotropic layer, the following Composition A-1 was prepared.

[0105] Composition A-1 ――――――――――――――――――――――――――――――――― 100.00 parts by mass of liquid crystal compound L-1 Photoinitiator (manufactured by BASF, Irgacure (registered trademark) 907) 3.00 parts by mass Photosensitizer (manufactured by Nippon Kayaku Co., Ltd., KAYACURE DETX-S) 1.00 part by mass 0.08 part by mass of leveling agent T-1 2840.00 parts by mass of methyl ethyl ketone ―――――――――――――――――――――――――――――――――

[0106] Liquid crystal compound L-1 [Chemical formula]

[0107] Leveling agent T-1 [Chemical formula]

[0108] The first optical anisotropic layer was formed by applying the composition A-1 onto the alignment film P-1 in multiple layers. First, the first layer of the composition A-1 was applied onto the alignment film, heated, cooled, and then ultraviolet cured to produce a liquid crystal immobilization layer. After that, for the second layer and subsequent layers, overcoating was performed on the liquid crystal immobilization layer, and heating, cooling, and then ultraviolet curing were repeated in the same manner.

[0109] First, for the first layer, the following composition A-1 was applied onto the alignment film P-1, the coating film was heated to 70 °C on a hot plate, then cooled to 25 °C, and then irradiated with ultraviolet light having a wavelength of 365 nm using a high-pressure mercury lamp at an irradiation dose of 300 mJ / cm 2 onto the coating film in a nitrogen atmosphere to fix the alignment of the liquid crystal compound. The film thickness of the first liquid crystal layer at this time was 0.2 μm.

[0110] For the second layer and subsequent layers, overcoating was performed on this liquid crystal layer, and after heating and cooling under the same conditions as above, ultraviolet curing was performed to produce a liquid crystal immobilization layer. In this way, overcoating was repeated until the total thickness reached the desired film thickness to form the first optical anisotropic layer.

[0111] The optical element of Comparative Example 1 was fabricated through the above steps.

[0112] Note that the complex refractive index Δn of the cured layer of the liquid crystal composition A1 was obtained by applying the liquid crystal composition A1 onto a support with an alignment film for retardation measurement prepared separately, aligning the director of the liquid crystal compound to be horizontal with respect to the substrate, and then irradiating with ultraviolet light for fixation, and measuring the retardation Re(λ) and film thickness of the obtained liquid crystal immobilization layer (cured layer). Δn can be calculated by dividing Re(λ) by the film thickness. Re(λ) was measured at the target wavelength using a spectroscopic ellipsometer manufactured by Woollam Co., Ltd., and the film thickness was measured using SEM. λ In the notation of Re(λ), λ is the wavelength of the incident light. In the following, the wavelength λ of the incident light was set to 940 nm.

[0113] ​The first optically anisotropic layer finally has a Δn of liquid crystal 940 × thickness = Re(940) of 470 nm, and it was confirmed by a polarizing microscope that the surface had a concentric periodic alignment as shown in Fig. 8. The concentric periodic alignment surface means an in-plane alignment pattern in which the axes of horizontal rotational alignment are radially arranged from the center. In the horizontal rotational alignment pattern of this first optically anisotropic layer, one period is very large at the center (the reciprocal of the period can be regarded 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, and the period becomes shorter toward the outer direction. Also, the twist angle in the thickness direction of the first optically anisotropic layer was 0°. Hereinafter, unless otherwise specified, measurements such as 'Δn 940 × thickness' were performed in the same manner. Also, in the cross-sectional image by SEM, bright and dark lines extending along the vertical direction, that is, the normal line, were observed with respect to the lower interface of the optically anisotropic layer (the interface with the glass substrate). In the repeating pattern of the bright and dark lines, it was observed that the period became shorter from the center toward the outside.

[0114] [Example 1] An optical element having two optically anisotropic layers, in which the first optically anisotropic layer is an inclined optically anisotropic layer 212 with bright and dark lines inclined with respect to the normal line of the interface in the cross-sectional SEM image, and the second optically anisotropic layer is a non-inclined optically anisotropic layer 211, was fabricated as Example 1 (see Fig. 12).

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

[0116] Composition A-2 ―――――――――――――――――――――――――――――――― Liquid crystal compound L-1 100.00 parts by mass Chiral agent A 0.21 parts by mass Polymerization initiator (manufactured by BASF, Irgacure (registered trademark) 907) 3.00 parts by mass Photo sensitizer (manufactured by Nippon Kayaku Co., Ltd., KAYACURE DETX-S) 1.00 part by mass Leveling agent T-1 0.08 part by mass Methyl ethyl ketone 2840.00 parts by mass ――――――――――――――――――――――――――――――――

[0117] Chiral agent A [Chemical formula]

[0118] A first optically 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 optically anisotropic layer of Example 1 was the same as the first optically anisotropic layer of Comparative Example 1. Using Composition A-1, a second optically anisotropic layer was formed on the first optically anisotropic layer in the same manner as the first optically anisotropic layer of Comparative Example 1, and the optical element of Example 1 was fabricated.

[0120] The first optically anisotropic layer and the second optically anisotropic layer finally have a Δn of the liquid crystal 940The thickness × = Re(940) was 470 nm, and it was confirmed by a polarization microscope that the surface had a concentric periodic alignment as shown in Fig. 8. In the horizontal rotation alignment pattern of this first optically anisotropic layer, one period was very large at the center (the reciprocal of the period can be regarded 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, and the period became shorter toward the outer direction. Since the second optically anisotropic layer was formed by coating on the first optically anisotropic layer, its period was the same as that of the first optically anisotropic layer. Also, in the following, other layers formed by coating on the first optically anisotropic layer have the same period. Further, the twist angle in the thickness direction of the first optically anisotropic layer was 140° right twist. The twist angle in the thickness direction of the second optically anisotropic layer was 0°. Also, in the cross-sectional image by SEM, in the first optically anisotropic layer, light and dark lines inclined obliquely with respect to the normal of the lower interface of the optically anisotropic layer (interface with the glass substrate) were observed, and in the second optically anisotropic layer, light and dark lines extending in the normal direction were observed. In the first optically anisotropic layer, the inclination angle of the light and dark lines with respect to the normal became smaller from the center toward the outside. It was observed that the period of the light and dark line pattern became shorter from the center toward the outside in both the first optically anisotropic layer and the second optically anisotropic layer.

[0121] [Example 2] An optical element having two optically anisotropic layers, where the first optically anisotropic layer is the non-inclined optically anisotropic layer 211 and the second optically anisotropic layer is the inclined optically anisotropic layer 212, was fabricated as Example 2 (see Fig. 13). That is, Example 2 has a configuration in which the first optically anisotropic layer and the second optically anisotropic 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 the first optically anisotropic layer was formed using Composition A-1 and the second optically anisotropic layer was formed using Composition A-2.

[0123] The first optically anisotropic layer and the second optically anisotropic layer finally have a Δn of the liquid crystal 940The thickness (Re(940)) was 470 nm, and it was confirmed by a polarization microscope that the surface had a concentric periodic alignment as shown in Fig. 8. In the horizontal rotation alignment pattern of this first optically anisotropic layer, one period was very large at the center (the reciprocal of the period can be regarded 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, and the period became shorter toward the outer direction. Also, the twist angle in the thickness direction of the first optically anisotropic layer was 0°. The twist angle in the thickness direction of the second optically anisotropic layer was 140° clockwise. Further, in the cross-sectional image by SEM, in the first optically anisotropic layer, bright and dark lines extending in the normal direction of the lower interface of the optically anisotropic layer (the interface with the glass substrate) were observed, and in the second optically anisotropic layer, bright and dark lines inclined obliquely with respect to the normal were observed. In the second optically anisotropic layer, the inclination angle of the bright and dark lines with respect to the normal became smaller from the center toward the outside. A state where the period of the bright and dark line pattern became shorter from the center toward the outside was observed in both the first optically anisotropic layer and the second optically anisotropic layer.

[0124] [Comparative Example 2] An optical element having an inclined optically anisotropic layer 212 in which bright and dark lines were inclined with respect to the normal of the interface in the cross-sectional SEM image was prepared as Comparative Example 2 as the first optically anisotropic layer.

[0125] (Formation of the first optically anisotropic layer) The first optically anisotropic layer of Comparative Example 2 was the same as the first optically anisotropic layer of Example 1. Using Composition A-2, in the same manner as the first optically anisotropic layer of Example 1, the first optically anisotropic layer was formed on the alignment film P-1 to fabricate the optical element of Comparative Example 2. That is, the optical element of Comparative Example 2 has a configuration including only one inclined optically anisotropic layer as the optically anisotropic layer.

[0126] The first optically anisotropic layer finally has a Δn of the liquid crystal 940The thickness × = Re(940) was 470 nm, and it was confirmed by a polarization microscope that the surface had a concentric periodic orientation as shown in Fig. 8. In the horizontal rotation orientation pattern of this first optically anisotropic layer, one period was very large at the center (the reciprocal of the period can be regarded 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, and the period became shorter toward the outer direction. Also, the twist angle in the thickness direction of the first optically anisotropic layer was 140° clockwise. Further, in the cross-sectional image by SEM, in the first optically anisotropic layer, light and dark lines inclined obliquely with respect to the normal of the lower interface of the optically anisotropic layer (interface with the glass substrate) were observed. In the first optically anisotropic layer, the inclination angle with respect to the normal of the light and dark lines became smaller from the center toward the outside. The pattern of the light and dark lines was observed to have a shorter period from the center toward the outside.

[0127] [Example 3] An optical element having two optically anisotropic layers, where the first optically anisotropic layer and the second optically anisotropic layer are inclined optically anisotropic layers 213 and 214 in which light and dark lines are inclined with respect to the normal of the interface in the cross-sectional SEM image, was fabricated as Example 3 (see Fig. 14). For the first optically anisotropic layer and the second optically anisotropic layer, the direction of the inclination of the light and dark lines in the cross-sectional SEM image was the same, and the inclination angles were made different.

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

[0129] Composition A-3 ―――――――――――――――――――――――――――――――― Liquid crystal compound L-1 100.00 parts by mass Chiral agent A 0.24 parts by mass Polymerization initiator (manufactured by BASF, Irgacure (registered trademark) 907) 3.00 parts by mass Photosensitizer (manufactured by Nippon Kayaku Co., Ltd., 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 optically 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) As a liquid crystal composition for forming the optically anisotropic layer, the following Composition A-4 was prepared.

[0132] Composition A-4 ―――――――――――――――――――――――――――――――― Liquid crystal compound L-1: 100.00 parts by mass Chiral agent A: 0.03 parts by mass Polymerization initiator (manufactured by BASF, Irgacure (registered trademark) 907) 3.00 parts by mass Photosensitizer (manufactured by Nippon Kayaku Co., Ltd., 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] A second optically anisotropic layer was formed on the first optically anisotropic layer in the same manner as in Example 1 except that Composition A-4 was used, and the optical element of Example 3 was fabricated.

[0134] The first optically anisotropic layer and the second optically anisotropic layer finally had a Δn of the liquid crystal 940The thickness × = Re(940) was 470 nm, and it was confirmed by a polarization microscope that the surface had a concentric periodic alignment as shown in Fig. 8. In the horizontal rotation alignment pattern of this first optically anisotropic layer, one period was very large at the center (the reciprocal of the period can be regarded 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, and the period became shorter toward the outer direction. Also, the twist angle in the thickness direction of the first optically anisotropic layer was 160° right-handed twist. The twist angle in the thickness direction of the second optically anisotropic layer was 20° right-handed twist. The directions of twist of the first optically anisotropic layer and the second optically anisotropic layer were the same. Also, in the cross-sectional image by SEM, in both the first optically anisotropic layer and the second optically anisotropic layer, light and dark lines inclined obliquely with respect to the normal of the lower interface of the optically anisotropic layer were observed. Furthermore, the inclination angle with respect to the normal of the light and dark lines became smaller from the center toward the outside, and the inclination directions from the normal of the light and dark lines of the first optically anisotropic layer and the second optically anisotropic layer were the same. It was observed that the pattern of the light and dark lines became shorter in period from the center toward the outside in both the first optically anisotropic layer and the second optically anisotropic layer.

[0135] [Example 4] An optical element having two optically anisotropic layers, wherein the first optically anisotropic layer and the second optically anisotropic layer are inclined optically anisotropic layers 215 and 216 in which light and dark lines are inclined with respect to the normal of the interface in the cross-sectional SEM image, was fabricated as Example 4 (see Fig. 15). For the first optically anisotropic layer and the second optically anisotropic layer, the inclination directions of the light and dark lines in the cross-sectional SEM image were made different.

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

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

[0138] A first optically 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) As a liquid crystal composition for forming an optically anisotropic layer, the following Composition A-6 was prepared.

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

[0141] Chiral agent B

Chemical formula

[0142] A second optically anisotropic layer was formed on the first optically anisotropic layer in the same manner as in Example 1 except that Composition A-6 was used, and the optical element of Example 4 was produced.

[0143] The first optical anisotropic layer and the second optical anisotropic layer finally achieve Δn of liquid crystal 940 × thickness = Re(940) of 470 nm, and it was confirmed by a polarization microscope that the surface had a concentric periodic alignment as shown in FIG. 8. In the horizontal rotation alignment pattern of this first optical anisotropic layer, one period is very large at the center (the reciprocal of the period can be regarded 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, and the period becomes shorter toward the outer direction. Also, the twist angle in the thickness direction of the first optical anisotropic layer was 80° right twist. The twist angle in the thickness direction of the second optical anisotropic layer was 80° left twist. The directions of twist of the first optical anisotropic layer and the second optical anisotropic layer were opposite. Also, in the cross-sectional image by SEM, in both the first optical anisotropic layer and the second optical anisotropic layer, it was observed that the bright and dark lines were inclined obliquely with respect to the normal of the lower interface of the optical anisotropic layer. Furthermore, the inclination angle of the bright and dark lines with respect to the normal became smaller from the center toward the outside, and the inclination directions of the bright and dark lines from the normal of the first optical anisotropic layer and the second optical anisotropic layer were opposite. It was observed that the pattern of the bright and dark lines became shorter in period from the center toward the outside in both the first optical anisotropic layer and the second optical anisotropic layer.

[0144] [Example 5] An optical element having three optical anisotropic layers, where the first optical anisotropic layer and the third optical anisotropic layer are inclined optical anisotropic layers 217 and 218 in which the bright and dark lines are inclined with respect to the normal of the interface in the cross-sectional SEM image, and the second optical anisotropic layer 219 disposed between the first and third optical anisotropic layers is a non-inclined optical anisotropic layer, was fabricated as Example 5 (see FIG. 16). The directions of inclination of the bright and dark lines in the cross-sectional SEM image were made different between the first optical anisotropic layer and the third optical anisotropic layer.

[0145] (Formation of the first optical anisotropic layer) As a liquid crystal composition for forming the optical anisotropic layer, the following Composition A-7 was prepared.

[0146] Composition A-7 ────────────────────────────────────── 100.00 parts by mass of liquid crystal compound L-1 0.19 parts by mass of chiral agent A Polymerization initiator (manufactured by BASF, Irgacure® 907) 3.00 parts by mass Photosensitizer (manufactured by Nippon Kayaku Co., Ltd., KAYACURE DETX-S) 1.00 parts by mass 0.08 parts by mass of leveling agent T-1 2840.00 parts by mass of methyl ethyl ketone ──────────────────────────────────────

[0147] Except for using Composition A-7, a first optically anisotropic layer was formed on the alignment film P-1 in the same manner as in Example 1.

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

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

[0150] Composition A-8 ────────────────────────────────────── 100.00 parts by mass of liquid crystal compound L-1 0.32 parts by mass of chiral agent B Polymerization initiator (manufactured by BASF, Irgacure® 907) 3.00 parts by mass Photosensitizer (manufactured by Nippon Kayaku Co., Ltd., KAYACURE DETX-S) 1.00 parts by mass 0.08 parts by mass of leveling agent T-1 2840.00 parts by mass of methyl ethyl ketone ──────────────────────────────

[0151] Except for using Composition A-8, in the same manner as in Example 1, a third optically anisotropic layer was formed on the second optically anisotropic layer to fabricate the optical element of Example 5.

[0152] The first optically anisotropic layer and the third optically anisotropic layer finally had a Δn of liquid crystal 940 × thickness = Re(940) of 470 nm, and the second optically anisotropic layer had a Δn 940 × thickness (Re(940)) of 564 nm. Also, it was confirmed by a polarizing microscope that the surface had a concentric periodic alignment as shown in Fig. 8. In the horizontal rotation alignment pattern of this first optically anisotropic layer, one period was very large at the center (the reciprocal of the period can be regarded 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, and the period became shorter toward the outer direction. Also, the twist angle in the thickness direction of the first optically anisotropic layer was 130° right-handed twist. The twist angle in the thickness direction of the second optically anisotropic layer was 0°, and the twist angle in the thickness direction of the third optically anisotropic layer was 130° left-handed twist. The directions of twist of the first optically anisotropic layer and the third optically anisotropic layer were opposite. Also, in the cross-sectional image by SEM, in the first optically anisotropic layer and the third optically anisotropic layer, light and dark lines inclined obliquely with respect to the normal of the lower interface of the optically anisotropic layer were observed, and in the second optically anisotropic layer, light and dark lines extending along the normal were observed. In the first and third optically anisotropic layers, the inclination angle of the light and dark lines with respect to the normal became smaller from the center toward the outside, and the inclination directions of the light and dark lines with respect to the normal of the first optically anisotropic layer and the third optically anisotropic layer were opposite. A state where the period of the light and dark line pattern became shorter from the center toward the outside was observed in all of the first optically anisotropic layer, the second optically anisotropic layer, and the third optically anisotropic layer.

[0153] [Evaluation] The optical elements of Comparative Example 1 and Examples 1 to 5 function as transmissive diffraction elements. For each optical element, when light was incident, the angle of the transmitted diffracted light with respect to the normal direction of the optical element was measured, and the light intensity increase rate with respect 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 the optical element at a predetermined incident angle, and the transmitted light was projected onto a screen arranged at a distance of 30 cm in the normal direction of the optical element, 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 FIG. 17, the 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 by the photodetector 256. Then, the ratio of the light intensity of the diffracted light Ld to the light intensity of the light Li was taken to obtain the relative light intensity value of the diffracted light Ld with respect to the incident light. Also, the relative light intensity value was obtained in the same manner by changing the incident angle. The light intensity increase rate of the examples with respect to Comparative Example 1 was evaluated according to the following criteria based on the average value of the relative light intensity values for different incident angles.

[0156] A: The light intensity increase rate is 20% or more B: The light intensity increase rate is 10% or more and less than 20% C: The light intensity increase rate is 5% or more and less than 10% D: The light intensity increase rate is less than 5%

[0157] In the comparison between Comparative Example 1 and Comparative Example 2 and Examples 1 to 3, the evaluation was performed with the incident angle at a distance of 1.0 mm (one period of 9.0 μm) from the center being 10°, the incident angle at a distance of 2.5 mm (one period of 4.5 μm) from the center being 20°, and the incident angle at a distance of 4.0 mm (one period of 3.0 μm) from the center being 30°. In addition, in the comparison between Comparative Example 1 and Comparative Example 2 and Examples 4 and 5, the evaluation was carried out with the incident angle at a distance of 1.0 mm from the center (9.0 μm per cycle) being ±10°, the incident angle at a distance of 2.5 mm from the center (4.5 μm per cycle) being ±20°, and the incident angle at a distance of 4.0 mm from the center (3.0 μm per cycle) being ±30°.

[0158] The results are shown in Table 1.

Table 1

[0159] In Examples 1 to 3, in the range of incident angles of 10 to 30°, and in Examples 4 and 5, in the range of incident angles of -30 to +30°, higher average diffraction efficiencies were obtained than in Comparative Example 1. By combining the tilt optical anisotropic layers with opposite bright and dark line inclinations in the cross-sectional SEM image, the diffraction efficiency could be increased over a wider range of incident angles. Note that in the optical element of Comparative Example 2 having only one tilt optical anisotropic layer, the effect of increasing the average diffraction efficiency was not obtained. In the optical element of Comparative Example 2 having only one tilt optical anisotropic layer, the effect of increasing the average diffraction efficiency was not obtained.

[0160] [Comparative Example 11] An optical element having a horizontally rotating alignment pattern with a gradually changing period and having a first optically anisotropic layer 221 cholesterically aligned in the thickness direction was fabricated as Comparative Example 11 (see Fig. 18). In Fig. 18, a part of the cholesteric alignment in the thickness direction is schematically shown.

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

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

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

[0164] When the cross-section of the coating layer of the first optically anisotropic layer was confirmed by a scanning electron microscope, it was confirmed by a polarizing microscope that the cholesteric liquid crystal phase had 8 pitches and had a concentric periodic alignment surface as shown in FIG. 8. In the horizontal rotation alignment pattern of this first optically anisotropic layer, one period was very large at the center (the reciprocal of the period can be regarded 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, and the period became shorter toward the outer direction. Also, in the cross-sectional image by SEM, in the first optically anisotropic layer, the bright and dark lines were inclined obliquely with respect to the normal of the lower interface of the optically anisotropic layer. In the first optically anisotropic layer, the inclination angle of the bright and dark lines increased from the center to the outside. It was observed that the pattern of the bright and dark lines of the first optically anisotropic layer became shorter in period from the center to the outside.

[0165] [Example 11] An optical element having a first optically anisotropic layer 222 and a second optically anisotropic layer 223 having a horizontal rotation alignment pattern in which the period gradually changes and having a cholesteric alignment in the thickness direction was fabricated as Example 11 (see FIG. 19). In FIG. 19, a part of the cholesteric alignment 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 alignment film P-1 in the same manner as in Comparative Example 11.

[0167] When the cross-section of the coating layer of the first optically anisotropic layer was observed with a scanning electron microscope, it was confirmed that the cholesteric liquid crystal phase had a pitch of 8, and the polarizing microscope confirmed that the surface had a concentric (radial) periodic alignment as shown in Fig. 8. In the horizontal rotation alignment pattern of this first optically anisotropic layer, one period was very large at the center (the reciprocal of the period can be regarded 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, and the period became shorter toward the outer direction.

[0168] (Formation of the second optically anisotropic layer) As the liquid crystal composition for forming the second optically anisotropic layer, the following Composition C-2 was prepared. This Composition C-2 is a liquid crystal composition that forms a cholesteric liquid crystal layer having a selective reflection center wavelength of 940 nm and reflecting left-circularly polarized light.

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

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

[0171] ​When the cross-section of the coating layer was observed with a scanning electron microscope, it was confirmed that the cholesteric liquid crystal phase had a pitch of 8, and the concentric periodic alignment surface as shown in Fig. 8 was confirmed with a polarizing microscope. In the horizontal rotation alignment pattern of the first optically anisotropic layer, one period was very large at the center (the reciprocal of the period can be regarded 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, and the period became shorter toward the outer direction.

[0172] The first optically anisotropic layer and the second optically anisotropic layer were bonded together to fabricate the optical element of Example 11. When laminating the first optically anisotropic layer and the second optically anisotropic layer, they were bonded so that the continuous rotation directions of the optical axis directions in the liquid crystal alignment pattern were different from each other.

[0173] In the cross-sectional image by SEM, it was observed that both the first optically anisotropic layer and the second optically anisotropic layer had a state where the bright and dark lines were inclined obliquely with respect to the normal line of the lower interface of the optically anisotropic layer. Further, the inclination angle of the bright and dark lines became smaller from the center toward the outside, and the inclination directions of the bright and dark lines with respect to the normal lines of the first optically anisotropic layer and the second optically anisotropic layer were the same. It was observed that the period of the bright and dark line pattern became shorter from the center toward the outside in both the first optically anisotropic layer and the second optically anisotropic layer.

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

[0175] Laser light was incident on a predetermined position on the surface of the optical element at a predetermined incident angle, and the reflected light was projected onto a screen arranged at a distance of 30 cm in the normal direction of the optical element and photographed with an 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 FIG. 20, the 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 by the photodetector 256. Then, the ratio of the light intensity of the diffracted light Ldr to the light intensity of the light Lir was taken to obtain the relative light intensity value of the diffracted light Ldr with respect to the incident light. Further, the relative light intensity value was obtained in the same manner by changing the incident angle. Regarding the average value of the relative light intensity values for different incident angles, the light intensity increase rate of the example with respect to the comparative example was evaluated according to the following criteria.

[0177] A: The light intensity increase rate is 20% or more B: The light intensity increase rate is 10% or more and less than 20% C: The light intensity increase rate is 5% or more and less than 10% D: The light intensity increase rate is less than 5%

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

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

[0180] In Example 11, a higher average diffraction efficiency was obtained than in Comparative Example 11 in the range of incident angles from 10° to 30°.

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

Claims

1. a plurality of optically anisotropic layers in a thickness direction, each having an in-plane orientation pattern in which the direction of an optical axis derived from a liquid crystal compound changes while continuously rotating along at least one direction in the plane; The optically anisotropic layers have a region in which the length of one period until the orientation of the optical axis in the one direction rotates by 180° coincides within a range of ±10%, each of the optically anisotropic layers has a plurality of pairs of bright and dark lines along the one direction, the pairs being derived from the orientation of the optical axis, in a cross-sectional image obtained by observing a cross-section cut in the thickness direction along the one direction with a scanning electron microscope; a first optically anisotropic layer which is one of the plurality of optically anisotropic layers is an inclined optically anisotropic layer having an area in which the pair of bright and dark lines in the cross-sectional image are inclined at different angles to a normal to an interface of the optically anisotropic layer; the plurality of optically anisotropic layers includes a second optically anisotropic layer disposed adjacent to the first optically anisotropic layer, the plurality of optically anisotropic layers include a third optically anisotropic layer different from the first optically anisotropic layer and the second optically anisotropic layer, the third optically anisotropic layer is an inclined optically anisotropic layer having a region in which the pair of bright and dark lines are inclined at different angles to a normal to an interface of the optically anisotropic layer in the cross-sectional image, the third optically anisotropic layer is adjacent to the second optically anisotropic layer, and in the cross-sectional image, the bright lines and the dark lines of the second optically anisotropic layer and the third optically anisotropic layer are connected at the interface therebetween, In the cross-sectional images of the first optically anisotropic layer and the third optically anisotropic layer, the pair of bright and dark lines of the first optically anisotropic layer and the pair of bright and dark lines of the third optically anisotropic layer have different inclination directions with respect to the normal line. Optical elements.

2. In the cross-sectional images of the second optically anisotropic layer and the third optically anisotropic layer, the pair of bright and dark lines of the second optically anisotropic layer and the pair of bright and dark lines of the third optically anisotropic layer have different inclination directions with respect to the normal line. The optical element according to claim 1 .

3. the first optically anisotropic layer and the third optically anisotropic layer are such that, in the cross-sectional images, the pair of bright and dark lines of the first optically anisotropic layer and the pair of bright and dark lines of the third optically anisotropic layer have mutually different inclination angles; The optical element according to claim 1 .

4. the second optically anisotropic layer and the third optically anisotropic layer are such that, in the cross-sectional images, the pair of bright and dark lines of the second optically anisotropic layer and the pair of bright and dark lines of the third optically anisotropic layer have mutually different inclination angles; The optical element according to claim 1 .

5. 5. The optical element according to claim 1, wherein the tilted optically anisotropic layer has a region in which the optical axis is twisted in a thickness direction.

6. 6. The optical element according to claim 1, having a function of diffracting and transmitting incident light.

7. 5. The optical element according to claim 1, wherein the liquid crystal compound is cholesterically aligned in the tilted optically anisotropic layer.

8. 8. The optical element according to claim 7, having a function of diffracting and reflecting incident light.

9. 9. An optical element according to claim 1, wherein the in-plane orientation pattern of each of the plurality of optically anisotropic layers is a pattern in which the length until the orientation of the optical axis rotates 180° in the one direction gradually changes in the one direction.

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

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

12. an optical deflection element that deflects and emits incident light; A driving means for driving the optical deflection element; An optical deflection device comprising: the optical element according to claim 1 , which is disposed on a light exit side of the optical deflection element.

Images