OPTICAL DEVICE, OPTICAL TRANSCEIVER, AND LiDAR DEVICE

Abstract

Provided is a novel optical device capable of blocking return light, returning to a semiconductor laser, without using an optical isolator. The optical device has a semiconductor laser, a first λ / 4 plate, a liquid crystal lens, and an optical member for external output in this order. The liquid crystal lens has an optical anisotropic layer formed using a composition containing a liquid crystal compound. The optical anisotropic layer has, in a radial shape radiating from the inside to the outside, a liquid crystal orientation pattern in which the direction of an optical axis derived from the liquid crystal compound changes while continuously rotating in one in-plane direction. In addition, in the liquid crystal orientation pattern, when one period is defined as the length of time it takes for the direction of the optical axis derived from the liquid crystal compound to rotate 180° in the one direction that changes as the optical axis derived from the liquid crystal compound changes while continuously rotating, the length of the one period gradually decreases from the inside to the outside.

Description

Optical device, optical transceiver and LiDAR device

[0001] The present invention relates to an optical device, an optical transceiver and a LiDAR device.

[0002] In an optical device serving as an optical signal generator on the transmission side of an optical communication system, when light emitted from a semiconductor laser serving as a light source is reflected on the surface of an optical member such as an optical fiber and returns to the semiconductor laser, laser oscillation becomes unstable. Therefore, conventional optical devices use an optical isolator using a Faraday rotator that blocks such reflected return light.

[0003] For example, Patent Document 1 discloses a semiconductor laser that outputs TE-mode output laser light which is linearly polarized light, a Faraday rotator provided on the optical axis of the output laser light that rotates the polarization direction of incident light by 45°, and a polarizer provided on the optical fiber side of the Faraday rotator, the transmission axis direction of which matches the polarization direction of the output laser light after passing through the Faraday rotator, and describes a semiconductor laser module in which no selection element that selectively transmits only laser light of a specific polarization direction is provided on the semiconductor laser side of the Faraday rotator.

[0004] Japanese Unexamined Patent Application Publication No. 2013-019960

[0005] Optical isolators using Faraday rotators have problems such as large size, high cost, and reduced efficiency.

[0006] An object of the present invention is to solve such problems of the prior art, and to provide a novel optical device capable of blocking return light returning to a semiconductor laser without using an optical isolator.

[0007] The inventors of the present invention have found that the above object can be solved by the following configuration.

[0008] [1] An optical device comprising, in this order, a semiconductor laser, a first λ / 4 plate, a liquid crystal lens, and an optical element for external output, wherein the liquid crystal lens has an optically anisotropic layer formed using a composition containing a liquid crystal compound, the optically anisotropic layer has a liquid crystal alignment pattern radially from the inside outward, in which the orientation of the optical axis originating from the liquid crystal compound changes while continuously rotating in one direction within the plane, and in the liquid crystal alignment pattern, when the length of one period is defined as the length of a 180° rotation of the orientation of the optical axis originating from the liquid crystal compound in one direction in which the orientation of the optical axis originating from the liquid crystal compound changes while continuously rotating, the length of one period gradually decreases from the inside outward. [2] The optical device according to [1], wherein a second λ / 4 plate is disposed between the liquid crystal lens and the optical element, or the optical element is provided with a function to give a λ / 4 phase difference to the liquid crystal lens side. [3] The optical device according to [2], wherein the second λ / 4 plate is in contact with the optical element. [4] An optical device according to any one of [1] to [3], having a polarizing plate between a semiconductor laser and a first λ / 4 plate. [5] An optical transceiver that uses the optical device according to any one of [1] to [4] as a transmitting optical signal generator. [6] A LiDAR device that uses the optical device according to any one of [1] to [4] as a transmitting optical signal generator.

[0009] According to the present invention, a novel optical device can be provided that can shield backlight returning to a semiconductor laser without using an optical isolator.

[0010] Figure 1 is a conceptual diagram showing an example of the optical device of the present invention. Figure 2 is a diagram for explaining the operation of the optical device shown in Figure 1. Figure 3 is a conceptual diagram showing another example of the optical device of the present invention. Figure 4 is a conceptual diagram showing another example of the optical device of the present invention. Figure 5 is a diagram for explaining the operation of the optical device shown in Figure 4. Figure 6 is a conceptual plan view showing an example of a liquid crystal lens of the optical device of the present invention. Figure 7 is a cross-sectional view of the liquid crystal lens shown in Figure 6. Figure 8 is a conceptual diagram showing an example of an exposure apparatus for exposing the alignment film of the liquid crystal lens. Figure 9 is a diagram for explaining the optical anisotropy layer of the liquid crystal lens shown in Figure 6. Figure 10 is a conceptual diagram for explaining the operation of the optical anisotropy layer shown in Figure 9. Figure 11 is a conceptual diagram for explaining the operation of the optical anisotropy layer shown in Figure 9.

[0011] The optical device, optical transceiver, and LiDAR apparatus of the present invention will be described in detail below based on preferred embodiments shown in the attached drawings.

[0012] The following description of the constituent elements may be based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.

[0013] Furthermore, the following diagrams are all conceptual diagrams intended to explain the present invention. Therefore, the shape, size, thickness, and positional relationships of each component in each diagram do not necessarily correspond to those of actual objects.

[0014] In this specification, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively.

[0015] In this specification, unless otherwise specified, angles such as "45°", "parallel", "perpendicular", or "orthogonal" mean that the difference from the exact angle is within 5 degrees. Preferably, the difference from the exact angle is less than 3 degrees, and more preferably less than 1 degree.

[0016] In this specification, terms such as “same” and “equal” include a margin of error that is generally accepted in the applicable art.

[0017] [Optical Device] The optical device of the present invention comprises, in this order, a semiconductor laser, a first λ / 4 plate, a liquid crystal lens, and an optical element for external output, wherein the liquid crystal lens has an optically anisotropic layer formed using a composition containing a liquid crystal compound, and the optically anisotropic layer has a liquid crystal alignment pattern radially from the inside to the outside in which the orientation of the optical axis originating from the liquid crystal compound changes while continuously rotating in one direction within the plane, and in the liquid crystal alignment pattern, if the length of one period is defined as the length of a 180° rotation of the orientation of the optical axis originating from the liquid crystal compound in one direction in which the orientation of the optical axis originating from the liquid crystal compound changes while continuously rotating, the length of one period gradually decreases from the inside to the outside.

[0018] Figure 1 conceptually shows an example of the optical device of the present invention.

[0019] The optical device 10a shown in Figure 1 comprises, in this order, a semiconductor laser 12, a first λ / 4 plate 13, a liquid crystal lens 14, and an optical element 15 for external output. Figure 1 shows that light emitted from the semiconductor laser 12 passes through the first λ / 4 plate 13 and the liquid crystal lens 14 before being incident on the optical element 15. In Figure 1, the light emitted from the semiconductor laser 12 is shown in gray, and the polarization state of the light between each element is shown in the lower part of the figure.

[0020] In the example shown in Figure 1, the semiconductor laser 12 and the first λ / 4 plate 13 are shown spaced apart, but they may be in contact. Similarly, the first λ / 4 plate 13 and the liquid crystal lens 14 are shown spaced apart, but they may be in contact.

[0021] In the present invention, the liquid crystal lens 14 has an optically anisotropic layer formed using a composition containing a liquid crystal compound, and the optically anisotropic layer has a liquid crystal alignment pattern radially from the inside to the outside in which the orientation of the optical axis originating from the liquid crystal compound changes while continuously rotating in one direction within the plane, and in the liquid crystal alignment pattern, when the length of one period is defined as the length of a 180° rotation of the orientation of the optical axis originating from the liquid crystal compound in one direction in which the orientation of the optical axis originating from the liquid crystal compound changes while continuously rotating, the length of one period gradually decreases from the inside to the outside.

[0022] Such a liquid crystal lens 14 acts as a condensing lens (convex lens) that focuses one type of circularly polarized light, and as a diverging lens (concave lens) that diverges the other type of circularly polarized light. Whether the liquid crystal lens 14 acts as a condensing lens or a diverging lens depends on the polarization state of the incident light and the rotation direction of the optical axis in the liquid crystal alignment pattern. Furthermore, the liquid crystal lens 14 reverses the rotation direction of the circularly polarized light that has passed through the liquid crystal lens 14. The configuration of the liquid crystal lens 14 will be described later.

[0023] Furthermore, the optical component 15 for external output is, for example, an optical fiber when the optical device 10a is used as an optical signal generator for an optical transceiver in an optical communication system. In the examples in Figures 1 and 2, the optical device 10a is described as an optical signal generator for an optical transceiver in an optical communication system, and the optical component 15 is an optical fiber. The optical component 15 will be described later.

[0024] The operation of the optical device 10a of the present invention will be explained with reference to Figures 1 and 2.

[0025] The semiconductor laser 12 emits the data to be transmitted as an optical signal. The semiconductor laser 12 also emits linearly polarized light. For example, this linearly polarized light is referred to as P-polarized light. As shown in Figure 1, the light emitted from the semiconductor laser 12 has a divergence angle. The P-polarized light emitted from the semiconductor laser 12 is incident on the first λ / 4 plate 13 and converted to circularly polarized light. For example, the first λ / 4 plate 13 is described as converting P-polarized light to left-circularly polarized light, but the first λ / 4 plate 13 may also convert P-polarized light to right-circularly polarized light.

[0026] Light converted to left-circular polarization by the first λ / 4 plate 13 is incident on the liquid crystal lens 14. In the example shown in Figure 1, the liquid crystal lens 14 acts as a focusing lens (convex lens) that focuses left-circular polarization. The liquid crystal lens 14 also reverses the direction of rotation of the circularly polarized light that has passed through it. Therefore, in the illustrated example, the polarization state after passing through the liquid crystal lens 14 is right-circular polarization.

[0027] The end face of the optical fiber 15 is positioned near the focal point of the liquid crystal lens 14, and the light focused by the liquid crystal lens 14 enters the optical fiber 15. The light that enters the optical fiber 15 is transmitted through the optical fiber 15.

[0028] Next, we will explain the effect on reflected light from the surface of the optical element using Figure 2.

[0029] In the optical device 10a, the light focused by the liquid crystal lens 14 enters the optical fiber 15, but some of the light is reflected from the end face of the optical fiber 15 and becomes backlight. At that time, the direction of rotation of the circularly polarized light is converted to the opposite direction. In the example shown in Figure 2, the backlight reflected from the end face of the optical fiber 15 is converted to left-circular polarization.

[0030] The reflected light (left-circularly polarized) from the end face of the optical fiber 15 enters the liquid crystal lens 14. Here, the rotation direction of the optical axis of the liquid crystal compound in the liquid crystal alignment pattern of the optical anisotropy layer of the liquid crystal lens 14 is reversed when viewed from the semiconductor laser 12 side compared to when viewed from the optical fiber 15 side. Therefore, the liquid crystal lens 14 acts as a divergent lens for left-circularly polarized light incident from the optical fiber 15 side. Furthermore, the polarization state after passing through the liquid crystal lens 14 becomes right-circularly polarized.

[0031] The right-circularly polarized light that has passed through the liquid crystal lens 14 is incident on the first λ / 4 plate 13 and converted into linearly polarized light (S-polarized light).

[0032] A portion of the linearly polarized light that passes through the first λ / 4 plate 13 returns to the semiconductor laser 12, but since it is diverted by the liquid crystal lens 14, the reflected light returning to the semiconductor laser 12 can be greatly reduced.

[0033] As mentioned above, conventional optical devices use optical isolators employing Faraday rotators to shield against reflected light. However, optical isolators using Faraday rotators are large and expensive. Furthermore, inorganic crystals such as bismuth-substituted rare-earth iron garnet (film thickness 100-500 μm) used in Faraday rotators absorb some of the light, leading to problems such as a decrease in the ratio of light emitted from the isolator to the intensity of light incident on the optical isolator, i.e., a decrease in efficiency.

[0034] In contrast, as described above, the optical device 10a of the present invention has a liquid crystal lens 14 between the semiconductor laser 12 and the optical fiber 15, which significantly reduces the reflected light that is reflected from the end face of the optical fiber 15 and returns to the semiconductor laser 12. The liquid crystal lens 14 can be made thin and manufactured at low cost. Furthermore, the liquid crystal lens 14 has a thin film thickness (several μm) and hardly absorbs light of the communication wavelength, thus improving efficiency.

[0035] In this case, the optical device of the present invention may have a second λ / 4 plate positioned between the liquid crystal lens and the optical member, or the optical member may be provided with a function to give a λ / 4 phase difference to the liquid crystal lens side.

[0036] Figure 3 is a conceptual diagram illustrating another example of the optical device of the present invention.

[0037] The optical device 10b shown in Figure 3 comprises, in this order, a semiconductor laser 12, a first λ / 4 plate 13, a liquid crystal lens 14, a second λ / 4 plate 16, and an optical element 15 for external output. The optical device 10b shown in Figure 3 has the same configuration as the optical device 10a shown in Figure 1, except that it has a second λ / 4 plate 16.

[0038] In the example shown in Fig. 3, the second λ / 4 plate 16 is disposed in contact with the end face of an optical member (optical fiber) 15.

[0039] The operation of the optical device 10b shown in Fig. 3 will be described. A semiconductor laser 12 emits linearly polarized light (P-polarized light). The P-polarized light emitted from the semiconductor laser 12 enters the first λ / 4 plate 13 and is converted into circularly polarized light. As an example, it is assumed that the first λ / 4 plate 13 converts P-polarized light into left-handed circularly polarized light.

[0040] The light converted into left-handed circularly polarized light by the first λ / 4 plate 13 enters the liquid crystal lens 14. The liquid crystal lens 14 functions as a condensing lens (convex lens) that condenses left-handed circularly polarized light. Further, the polarization state after passing through the liquid crystal lens 14 becomes right-handed circularly polarized light.

[0041] The light condensed by the liquid crystal lens 14 enters the second λ / 4 plate 16. The second λ / 4 plate 16 converts circularly polarized light into linearly polarized light. For example, it converts right-handed circularly polarized light into P-polarized light.

[0042] The light converted into linearly polarized light (P-polarized light) by the second λ / 4 plate 16 enters the optical fiber 15 and is transmitted therethrough.

[0043] As described above, by providing the second λ / 4 plate 16, the polarization state of light incident on the optical fiber 15 can be set to linearly polarized light.

[0044] Note that, in the example shown in Fig. 3, a configuration is adopted in which the second λ / 4 plate 16 is disposed between the liquid crystal lens 14 and the optical member 15, but the present invention is not limited thereto, and the optical member 15 may be provided with a function of imparting a λ / 4 phase difference on the liquid crystal lens 14 side thereof.

[0045] For example, when the optical member 15 is an optical fiber, the end portion of the optical fiber may include a region having a function of imparting a phase difference of λ / 4. For example, an optical fiber can be wound into a coil shape to impart a phase difference by stress. Since the magnitude of the phase difference can be adjusted by the diameter of the coil and the number of turns at this time, the phase difference may be appropriately adjusted to λ / 4. An optical fiber having such a phase difference is described in, for example, "https: / / www.newport-japan.jp / pdf / technical / 1526.pdf". Commercially available fiber-type circular polarizers such as Helica In-Fiber Circular Polarizer manufactured by Chiral Photonics may also be used.

[0046] Here, the optical device of the present invention may have a polarizing plate between the semiconductor laser and the first λ / 4 plate.

[0047] FIG. 4 is a diagram conceptually showing another example of the optical device of the present invention.

[0048] The optical device 10c shown in FIG. 4 includes a semiconductor laser 12, a polarizing plate 17, a first λ / 4 plate 13, a liquid crystal lens 14, a second λ / 4 plate 16, and an optical member 15 for external output in this order. The optical device 10c shown in FIG. 4 has the same configuration as the optical device 10b shown in FIG. 3 except that it includes the polarizing plate 17.

[0049] The polarizing plate 17 is a linear polarizing plate, and is arranged so as to transmit linearly polarized light (P-polarized light) emitted from the semiconductor laser 12. That is, the polarizing plate 17 is arranged such that its transmission axis is parallel to the polarization direction of the linearly polarized light emitted from the semiconductor laser 12.

[0050] The operation of the optical device 10c shown in FIG. 4 will be described. The semiconductor laser 12 emits linearly polarized light (P-polarized light). The P-polarized light emitted from the semiconductor laser 12 transmits through the polarizing plate 17 and enters the first λ / 4 plate 13. The P-polarized light incident on the first λ / 4 plate 13 is converted into left-handed circularly polarized light.

[0051] Light converted to left-circular polarization by the first λ / 4 plate 13 is incident on the liquid crystal lens 14. The liquid crystal lens 14 acts as a focusing lens (convex lens) that concentrates the left-circularly polarized light. After passing through the liquid crystal lens 14, the polarization state becomes right-circularly polarized.

[0052] The light focused by the liquid crystal lens 14 is incident on the second λ / 4 plate 16. The second λ / 4 plate 16 converts circularly polarized light into linearly polarized light. For example, it converts right-circularly polarized light into P-polarized light.

[0053] The light, converted to linearly polarized (P-polarized) light by the second λ / 4 plate 16, is incident on the optical fiber 15 and transmitted.

[0054] Next, the effect of the optical device 10c on the reflected light from the surface of the optical element will be explained using Figure 5.

[0055] In the optical device 10c, the light focused by the liquid crystal lens 14 enters the optical fiber 15 via the second λ / 4 plate 16, but some of the light is reflected back from the end face of the optical fiber 15 (second λ / 4 plate 16) and becomes back-flow light. At this time, the direction of rotation of the circularly polarized light is converted to the opposite direction. In the example shown in Figure 5, the back-flow light reflected from the end face of the second λ / 4 plate 16 is converted to left-hand circularly polarized light.

[0056] The reflected light (left-circularly polarized) from the end face of the second λ / 4 plate 16 enters the liquid crystal lens 14. Here, the rotation direction of the optical axis of the liquid crystal compound in the liquid crystal alignment pattern of the optically anisotropic layer is reversed when viewed from the semiconductor laser 12 side and when viewed from the optical fiber 15 side. Therefore, the liquid crystal lens 14 acts as a divergent lens for left-circularly polarized light incident from the optical fiber 15 side. In addition, the polarization state after passing through the liquid crystal lens 14 becomes right-circularly polarized.

[0057] The right-circularly polarized light that has passed through the liquid crystal lens 14 is incident on the first λ / 4 plate 13 and converted to S-polarized light.

[0058] This S-polarized light is incident on the polarizer 17, but since the polarizer 17 is positioned to transmit P-polarized light, the S-polarized light is blocked by the polarizer 17. Therefore, the reflected light returning to the semiconductor laser 12 can be reduced more significantly.

[0059] In the examples shown in Figures 4 and 5, a configuration with a second λ / 4 plate 16 is used, but the system is not limited to this, and may include a region that has the function of giving a λ / 4 phase difference to the end of the optical fiber 15. Alternatively, a configuration without the second λ / 4 plate 16 is also possible.

[0060] Furthermore, the optical device of the present invention may include components other than those described above. For example, the first λ / 4 plate 13, the liquid crystal lens 14, the second λ / 4 plate 16, and the polarizing plate 17 may each have an anti-reflective layer on at least one of the surfaces facing the semiconductor laser 12 and the optical fiber 15.

[0061] The components of the optical device of the present invention will be described below.

[0062] <Semiconductor Laser> There are no particular restrictions on the semiconductor laser, and it can be appropriately selected depending on the application of the optical device. When the optical device is used as an optical signal generator for an optical transceiver, the wavelength of the semiconductor laser is preferably 750 nm to 1700 nm, and more preferably 950 nm to 1650 nm. Furthermore, when the optical device is used as an optical signal generator for a LiDAR (Light Detection And Ranging) device, the wavelength of the semiconductor laser is preferably 750 nm to 1700 nm, and more preferably 950 nm to 1650 nm.

[0063] Furthermore, the semiconductor laser may emit linearly polarized light, or it may emit light with a polarization state other than linearly polarized light (for example, unpolarized light). If the semiconductor laser emits light with a polarization state other than linearly polarized light, it is preferable to have a linear polarizer on the emission side of the semiconductor laser.

[0064] <λ / 4 Plate> The first λ / 4 plate and the second λ / 4 plate convert incident linearly polarized light into circularly polarized light, and vice versa. That is, the first λ / 4 plate and the second λ / 4 plate are plates in which the in-plane retardation Re at the wavelength λnm of light emitted by the semiconductor laser is λ / 4 (or an odd multiple thereof). The in-plane retardation Re(λ) of the first λ / 4 plate and the second λ / 4 plate may have an error of about 25 nm, centered around the ideal value (λ / 4 nm). In the following explanation, the first λ / 4 plate and the second λ / 4 plate will be collectively referred to as the λ / 4 plate.

[0065] The first λ / 4 plate is positioned such that its slow axis makes an angle of approximately 45° with the polarization direction of the linearly polarized light emitted by the semiconductor laser. Furthermore, if a polarizer is present between the semiconductor laser and the first λ / 4 plate, the first λ / 4 plate is positioned such that its slow axis makes an angle of approximately 45° with the transmission axis of the polarizer.

[0066] Furthermore, the second λ / 4 plate is positioned such that the angle between its slow phase axis and the slow layer axis of the first λ / 4 plate is approximately 90°.

[0067] The λ / 4 plate used in the present invention may be a single-layer type composed of one optically anisotropic layer, or a multi-layer type composed of stacking two or more optically anisotropic layers, each having multiple different slow phase axes. Examples of multi-layer λ / 4 plates are listed in WO2013 / 137464, WO2016 / 158300, JP 2014-209219, JP 2014-209220, WO2014 / 157079, JP 2019-215416, WO2019 / 160044, and JP 2014-02 Examples include, but are not limited to, Publication No. 6266, WO2022 / 030266, WO2021 / 132624, WO2021 / 033631, WO2022 / 045185, WO2022 / 045185, WO19 / 160016, and WO2020 / 100813.

[0068] There are no restrictions on the λ / 4 plate; various known plates with λ / 4 functionality can be used. Specific examples of λ / 4 plates include those described in U.S. Patent Application Publication 2015 / 0277006.

[0069] Examples of a λ / 4 plate having a single-layer structure include a stretched polymer film and a phase difference film having an optically anisotropic layer on which a liquid crystal compound is oriented to exhibit refractive index anisotropy. Examples of a λ / 4 plate having a multi-layer structure include a broadband λ / 4 plate formed by laminating a λ / 4 plate and a λ / 2 wave plate.

[0070] There are no particular restrictions on the thickness of the λ / 4 plate, but it is preferably 1 to 500 μm, more preferably 1 to 50 μm, and even more preferably 1 to 5 μm.

[0071] The λ / 4 plate preferably has inverse wavelength dispersion. Having inverse wavelength dispersion makes the phase change in the λ / 4 plate ideal, and thus the conversion between linearly polarized and circularly polarized light becomes ideal.

[0072] <Liquid Crystal Lens> A liquid crystal lens has an optically anisotropic layer formed using a composition containing a liquid crystal compound. The optically anisotropic layer has a liquid crystal orientation pattern that is radially arranged from the inside outward, in which the orientation of the optical axis originating from the liquid crystal compound changes while continuously rotating in one direction within the plane. Furthermore, in the liquid crystal orientation pattern, when the length of a 180° rotation of the orientation of the optical axis originating from the liquid crystal compound in one direction is defined as one period, the length of one period gradually decreases from the inside outward.

[0073] Such liquid crystal lenses act as lenses that focus or diverge transmitted circularly polarized light.

[0074] Figure 6 is a conceptual plan view showing an example of an optically anisotropic layer in a liquid crystal lens. Figure 7 is a conceptual cross-sectional view showing a liquid crystal lens including an optically anisotropic layer. That is, Figure 6 is a top view of the optically anisotropic layer in Figure 7. In Figures 6 and 7, a rod-shaped liquid crystal compound is used as an example of the liquid crystal compound 30, so the direction of the optical axis coincides with the longitudinal direction of the liquid crystal compound 30. Also, although Figure 6 shows only the liquid crystal compound 30 on the surface of the alignment film, as shown in Figure 7, the optically anisotropic layer has a structure in which liquid crystal compounds 30 oriented in the same direction as the liquid crystal compound 30 on the surface of the alignment film are stacked in the thickness direction.

[0075] As shown in Figure 6, in the in-plane direction of the optical anisotropy layer 26 of the liquid crystal lens 14, the orientation of the optical axis of the liquid crystal compound 30 changes while continuously rotating along a number of directions extending outward from the center of the optical anisotropy layer 26, for example, the direction indicated by arrow A1, the direction indicated by arrow A2, the direction indicated by arrow A3, the direction indicated by arrow A4, and so on. The directions indicated by arrow A1, the direction indicated by arrow A2, the direction indicated by arrow A3, the direction indicated by arrow A4, and so on are each one direction in this invention. That is, the optical anisotropy layer 26 has a number of one directions radiating from the inside outward.

[0076] Furthermore, in the optically anisotropic layer 26, the direction of rotation of the optical axis of the liquid crystal compound 30 when viewed in the direction along each arrow is the same in all directions (unidirectional). In the illustrated example, the direction of rotation of the optical axis of the liquid crystal compound 30 is counterclockwise in all directions indicated by arrows A1, A2, A3, and A4.

[0077] In other words, if we consider arrows A1 and A4 as a single straight line, along this line, the direction of rotation of the optical axis of the liquid crystal compound 30 reverses at the center of the optical anisotropy layer 26. For example, when viewed in the direction to the right (direction of arrow A1) along the straight line formed by arrows A1 and A4, the optical axis of the liquid crystal compound 30 initially rotates clockwise from the outside of the optical anisotropy layer 26 toward the center, the direction of rotation reverses at the center of the optical anisotropy layer 26, and thereafter rotates counterclockwise from the center of the optical anisotropy layer 26 toward the outside.

[0078] In such an optically anisotropic layer 26, the lines connecting the liquid crystal compounds 30 whose optical axes are oriented in the same direction are circular, and it can be said that it has a concentric pattern in which circular line segments are arranged concentrically.

[0079] Furthermore, in the optical anisotropy layer 26 of the liquid crystal lens 14, the liquid crystal alignment pattern is such that, when the length of one period is defined as the length of a 180° rotation of the optical axis direction originating from the liquid crystal compound in one direction in which the direction of the optical axis of the liquid crystal compound 30 changes while continuously rotating, the length of one period gradually decreases from the inside to the outside.

[0080] Circularly polarized light incident on an optically anisotropic layer 26 having such a liquid crystal orientation pattern is diffracted in localized regions of the optically anisotropic layer. In this case, the direction in which the circularly polarized light is diffracted in each region is along the direction in which the orientation of the optical axis of the liquid crystal compound 30 changes as it rotates continuously. Furthermore, the diffraction direction depends on the direction of rotation of the optical axis of the liquid crystal compound 30, which rotates along this unidirectional direction. In addition, the diffraction angle becomes larger as the period becomes shorter.

[0081] Therefore, an optically anisotropic layer 26 having such a radial liquid crystal orientation pattern, that is, a liquid crystal orientation pattern having a radial direction in which the optical axis changes as it continuously rotates, can transmit incident light (light beam) by diverging or focusing it, depending on the rotation direction of the optical axis of the liquid crystal compound 30 and the rotation direction of the incident circularly polarized light.

[0082] The following provides a more detailed explanation of this liquid crystal lens 14.

[0083] Figure 7 is a conceptual diagram showing the layer structure of the liquid crystal lens 14 having the optical anisotropy layer 26 shown in Figure 6. Figure 7 can be described as a cross-sectional view along one direction in the liquid crystal alignment pattern of the optical anisotropy layer 26.

[0084] As an example, the liquid crystal lens 14 shown in Figure 7 includes a support 20, an alignment film 24, and the optical anisotropy layer 26 described above.

[0085] In this invention, the layer configuration of the liquid crystal lens is not limited thereto. That is, the liquid crystal lens may consist of an alignment film 24 and an optical anisotropy layer 26, obtained by peeling off the support 20 from the liquid crystal lens 14 shown in Figure 7. Alternatively, the liquid crystal lens may consist only of an optical anisotropy layer 26, obtained by peeling off the support 20 and alignment film 24 from the liquid crystal lens 14 shown in Figure 7. Alternatively, the liquid crystal lens may have a sheet-like material, such as another substrate, attached to the optical anisotropy layer 26.

[0086] In other words, in the present invention, any layer configuration is usable for a liquid crystal lens as long as it has an optically anisotropic layer having a liquid crystal orientation pattern radially from the inside out, in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating in one direction.

[0087] <<Support>> In the liquid crystal lens 14, the support 20 supports the alignment film 24 and the optical anisotropy layer 26.

[0088] The support 20 can be any type of sheet material (film, plate) as long as it can support the alignment film 24 and the optical anisotropy layer 26. A transparent support is preferred for the support 20, and examples include polyacrylic resin films such as polymethyl methacrylate, cellulose resin films such as cellulose triacetate, cycloolefin polymer films (e.g., "Arton" (trade name), manufactured by JSR Corporation; "Zeonor" (trade name), manufactured by Nippon Zeon Corporation), polyethylene terephthalate (PET), polycarbonate, and polyvinyl chloride. The support is not limited to a flexible film; it may also be a non-flexible substrate such as a glass substrate.

[0089] There are no restrictions on the thickness of the support 20, and the thickness that can hold the alignment film and the optical anisotropy layer may be set appropriately depending on the application of the liquid crystal lens 14 and the material used to form the support 20. The thickness of the support 20 is preferably 1 to 1000 μm, more preferably 3 to 250 μm, and even more preferably 5 to 150 μm.

[0090] <<Alignment Film>> In the liquid crystal lens 14, an alignment film 24 is formed on the surface of the support 20. The alignment film 24 is an alignment film used to orient the liquid crystal compound 30 into a predetermined liquid crystal alignment pattern when forming the optical anisotropy layer 26 of the liquid crystal lens 14.

[0091] As described above, in the liquid crystal lens 14, the optical anisotropic layer 26 has a liquid crystal alignment pattern that radiates from the inside outward, in which the orientation of the optical axis 30A (see Figure 8), derived from the liquid crystal compound 30, changes while continuously rotating along one direction in the plane (such as the direction of arrows A1 to A4 mentioned above). Furthermore, in the present invention, in the liquid crystal alignment pattern of the optical anisotropic layer 26, when the length of one period (rotation period of the optical axis) is defined as the length of a 180° rotation of the optical axis 30A in one direction in which the orientation of the optical axis 30A changes while continuously rotating, the length of one period gradually decreases from the inside outward. That is, the length of one period of the liquid crystal alignment pattern of the optical anisotropic layer 26 gradually decreases from the center outward. Accordingly, the alignment film of the liquid crystal lens 14 is formed such that the optical anisotropic layer 26 can form this liquid crystal alignment pattern.

[0092] In the following explanation, "the direction of the optical axis 30A rotates" will also be referred to simply as "the optical axis 30A rotates."

[0093] Various known orientation films are available. Examples include rubbing films made of organic compounds such as polymers, obliquely deposited films of inorganic compounds, films having microgrooves, and films formed by accumulating Langmuir-Blodgett (LB) films of organic compounds such as ω-tricosanoic acid, dioctadecylmethylammonium chloride, and methyl stearylate using the Langmuir-Blodgett method.

[0094] An oriented film formed by rubbing can be created by rubbing the surface of a polymer layer several times in a specific direction with paper or cloth.

[0095] Examples of materials used for the orientation film include polyimide, polyvinyl alcohol, polymers having polymerizable groups as described in Japanese Patent Publication No. 9-152509, materials used for forming orientation films as described in Japanese Patent Publication No. 2005-097377, Japanese Patent Publication No. 2005-099228, and Japanese Patent Publication No. 2005-128503.

[0096] Furthermore, as the alignment film, a so-called photo-alignment film is preferably used, which is formed by irradiating a photo-alignable material with polarized or unpolarized light to create an alignment film. In other words, in the liquid crystal lens 14, a photo-alignment film formed by coating a photo-alignment material onto a support 20 is preferably used as the alignment film 24.

[0097] Polarized light irradiation can be applied perpendicularly or obliquely to the photo-alignment film, while unpolarized light irradiation can be applied obliquely to the photo-alignment film.

[0098] Examples of photo-alignment materials used in the photo-alignment film applicable to the present invention include those described in Japanese Patent Publication No. 2006-285197, Japanese Patent Publication No. 2007-076839, Japanese Patent Publication No. 2007-138138, Japanese Patent Publication No. 2007-094071, Japanese Patent Publication No. 2007-121721, Japanese Patent Publication No. 2007-140465, Japanese Patent Publication No. 2007-156439, and Japanese Patent Publication No. 2 Azo compounds described in Japanese Patent Publication No. 007-133184, Japanese Patent Publication No. 2009-109831, Japanese Patent No. 3883848 and Japanese Patent No. 4151746, aromatic ester compounds described in Japanese Patent Publication No. 2002-229039, maleimides having photo-orienting units described in Japanese Patent Publication No. 2002-265541 and Japanese Patent Publication No. 2002-317013 Examples of preferred examples include alkenyl-substituted nadiimide compounds, photocrosslinkable silane derivatives described in Japanese Patent No. 4205195 and Japanese Patent No. 4205198, photocrosslinkable polyimides, photocrosslinkable polyamides and photocrosslinkable esters described in Japanese Patent Publication No. 2003-520878, Japanese Patent Publication No. 2004-529220 and Japanese Patent No. 4162850, and photodimerizable compounds described in Japanese Patent Publication No. 9-118717, Japanese Patent Publication No. 10-506420, Japanese Patent Publication No. 2003-505561, International Publication No. 2010 / 150748, Japanese Patent Publication No. 2013-177561 and Japanese Patent Publication No. 2014-012823, particularly cinnamate compounds, chalcone compounds and coumarin compounds. Among these, azo compounds, photocrosslinkable polyimides, photocrosslinkable polyamides, photocrosslinkable esters, cinnamate compounds, and chalcone compounds are particularly suitable for use.

[0099] There are no restrictions on the thickness of the orientation film; the thickness should be set appropriately to obtain the required orientation function depending on the material used to form the orientation film. The thickness of the orientation film is preferably 0.01 to 5 μm, and more preferably 0.05 to 2 μm.

[0100] There are no limitations on the method for forming the alignment film, and various known methods depending on the material used to form the alignment film can be used. As an example, one method involves coating the alignment film onto the surface of the support 20, drying it, and then exposing the alignment film with laser light to form an alignment pattern.

[0101] Figure 8 conceptually shows an example of an exposure apparatus that exposes an alignment film to form an alignment film 24 having this alignment pattern.

[0102] The exposure apparatus 80 shown in Figure 8 includes a light source 84 equipped with a laser 82, a polarizing beam splitter 86 that splits the laser light M from the laser 82 into S-polarized MS and P-polarized MP, a mirror 90A arranged in the optical path of the P-polarized MP and a mirror 90B arranged in the optical path of the S-polarized MS, a lens 92 arranged in the optical path of the S-polarized MS, the polarizing beam splitter 94, and a λ / 4 plate 96.

[0103] The P-polarized beam MP, split by the polarizing beam splitter 86, is reflected by the mirror 90A and incident on the polarizing beam splitter 94. On the other hand, the S-polarized beam MS, split by the polarizing beam splitter 86, is reflected by the mirror 90B, focused by the lens 92, and incident on the polarizing beam splitter 94.

[0104] The P-polarized MP and S-polarized MS beams are combined by the polarizing beam splitter 94 and converted into right-circularly polarized and left-circularly polarized beams according to their polarization direction by the λ / 4 plate 96, and then incident on the alignment film 24 on the support 20.

[0105] Here, the interference between right-circularly polarized and left-circularly polarized light causes the polarization state of the light irradiated onto the alignment film 24 to change periodically in an interference fringe pattern. As you move from the inside to the outside of the concentric circles, the intersection angle between the left-circularly polarized and right-circularly polarized light changes, resulting in an exposure pattern in which the pitch changes from the inside to the outside. As a result, a radial alignment pattern in which the alignment state changes periodically is obtained in the alignment film 24.

[0106] In this exposure apparatus 80, one cycle of the liquid crystal alignment pattern, in which the optical axis of the liquid crystal compound 30 rotates continuously by 180° along one direction, can be controlled by changing the refractive power of the lens 92 (F-number of the lens 92), the focal length of the lens 92, and the distance between the lens 92 and the alignment film 24. Furthermore, by adjusting the refractive power of the lens 92 (F-number of the lens 92), the length of one cycle of the liquid crystal alignment pattern in the direction in which the optical axis rotates continuously can be changed.

[0107] Specifically, by interfering with parallel light and changing the angle of light spread by lens 92, the length of one period of the liquid crystal alignment pattern can be changed in one direction in which the optical axis rotates continuously. More specifically, if the refractive power of lens 92 is weakened, the light approaches parallel light, so the length of one period Λ of the liquid crystal alignment pattern gradually shortens from the inside to the outside, and the F number increases. Conversely, if the refractive power of lens 92 is strengthened, the length of one period Λ of the liquid crystal alignment pattern shortens abruptly from the inside to the outside, and the F number decreases.

[0108] As mentioned above, in the liquid crystal lens 14, the alignment film 24 is provided as a preferred embodiment and is not an essential component. For example, by forming an alignment pattern on the support 20 by a rubbing method or a method of processing the support 20 with laser light, the optical anisotropy layer 26 can be configured to have a liquid crystal alignment pattern in which the orientation of the optical axis 30A originating from the liquid crystal compound 30 changes while continuously rotating radially along one direction.

[0109] <<Optical Anisotropy Layer>> In the liquid crystal lens 14 shown in Figure 7, an optical anisotropy layer 26 is formed on the surface of the alignment film 24.

[0110] As described above, in the liquid crystal lens 14, the optical anisotropy layer 26 is formed using a composition containing a liquid crystal compound.

[0111] The optical anisotropy layer 26 functions as a general λ / 2 plate (half-wave plate) when the in-plane retardation value is set to λ / 2. That is, the optical anisotropy layer 26, with its in-plane retardation value set to λ / 2, has the function of giving a half-wavelength, or 180°, phase difference to two mutually orthogonal linearly polarized components contained in the incident light.

[0112] As described above, the optically anisotropic layer 26 has a liquid crystal alignment pattern that radiates from the inside outward, in which the orientation of the optical axes originating from the liquid crystal compound changes while continuously rotating in one direction (such as the directions of arrows A1 to A4 in Figure 6) within the plane of the optically anisotropic layer.

[0113] The optical axis 30A derived from the liquid crystal compound 30 is the axis in the liquid crystal compound 30 where the refractive index is highest, also known as the slow axis. For example, if the liquid crystal compound 30 is a rod-shaped liquid crystal compound, the optical axis 30A is aligned with the long axis of the rod shape.

[0114] In the following explanation, the optical axis 30A derived from the liquid crystal compound 30 will also be referred to as "the optical axis 30A of the liquid crystal compound 30" or "the optical axis 30A".

[0115] The optical anisotropy layer 26 will be described below with reference to the optical anisotropy layer 26A shown in Figure 9. Figure 9 is a conceptual plan view showing the optical anisotropy layer 26A having a liquid crystal alignment pattern that changes as the optical axis 30A rotates continuously in one direction indicated by arrow A.

[0116] In the liquid crystal alignment pattern shown in Figure 6, which has a radial pattern from the inside outward with one direction in which the optical axis changes while continuously rotating, the same optical effects as those of the liquid crystal alignment pattern shown in Figure 9 are exhibited with respect to the direction in which the optical axis changes while continuously rotating (such as the directions of arrows A1 to A4). That is, in the optically anisotropic layer 26 shown in Figure 6, the directions of arrows A1 to A4 in the radial liquid crystal alignment pattern correspond to the direction of arrow A in Figure 9.

[0117] In the optically anisotropic layer 26A, the liquid crystal compound 30 is arranged two-dimensionally in a plane parallel to the direction indicated by arrow A and the Y direction which is perpendicular to the direction of arrow A. In Figures 10 and 11, which will be described later, the Y direction is perpendicular to the plane of the paper.

[0118] In the following explanation, "the one direction indicated by arrow A" will also simply be referred to as "the direction of arrow A."

[0119] In the optical anisotropy layer 26 shown in Figure 6, the circumferential direction in the radial liquid crystal alignment pattern corresponds to the Y direction in Figure 9.

[0120] The plan view is a view of the optically anisotropic layer 26A from the thickness direction (i.e., the stacking direction of each layer (film)). In other words, it is a view of the optically anisotropic layer 26 from a direction perpendicular to the main surface. The main surface is the largest surface in a sheet-like material (plate-like material, film, layer).

[0121] Furthermore, in Figure 9, in order to clearly show the structure of the optically anisotropic layer 26A, similar to Figure 6, only the liquid crystal compound 30 on the surface of the alignment film 24 is shown. However, this optically anisotropic layer 26A also has a structure in the thickness direction in which the liquid crystal compound 30 is stacked from the liquid crystal compound 30 on the surface of the alignment film, as shown in Figure 7.

[0122] The optically anisotropic layer 26A has a liquid crystal orientation pattern in which the orientation of the optical axis 30A originating from the liquid crystal compound 30 changes while continuously rotating along the direction of arrow A within the plane of the optically anisotropic layer 26A.

[0123] Specifically, the statement that the orientation of the optical axis 30A of the liquid crystal compound 30 changes while continuously rotating in the direction of arrow A (a predetermined one direction) means that the angle between the optical axis 30A of the liquid crystal compound 30 arranged along the direction of arrow A and the direction of arrow A differs depending on the position in the direction of arrow A, and that the angle between the optical axis 30A and the direction of arrow A changes sequentially from θ to θ+180° or θ-180° along the direction of arrow A.

[0124] Furthermore, the difference in angle between the optical axes 30A of adjacent liquid crystal compounds 30 in the direction of arrow A is preferably 45° or less, more preferably 15° or less, and even more preferably a smaller angle.

[0125] On the other hand, in the liquid crystal compound 30 that forms the optical anisotropy layer 26A, in the Y direction perpendicular to the direction of arrow A, that is, in the Y direction perpendicular to the direction in which the optical axis 30A rotates continuously, the liquid crystal compound 30 with the same orientation of the optical axis 30A is arranged at equal intervals.

[0126] In other words, in the liquid crystal compound 30 that forms the optical anisotropy layer 26, the angle between the direction of the optical axis 30A and the direction of arrow A is equal for liquid crystal compounds 30 arranged in the Y direction.

[0127] In the optical anisotropy layer 26 shown in Figure 6, regions are formed in a ring shape with the same center, where the orientation of the optical axis 30A is the same.

[0128] In a liquid crystal alignment pattern where the optical axis 30A rotates continuously in one direction, the length (distance) required for the optical axis 30A of the liquid crystal compound 30 to rotate 180° is defined as the length Λ of one period in the liquid crystal alignment pattern. That is, in the case of the optically anisotropic layer 26A shown in Figure 9, the length (distance) required for the optical axis 30A of the liquid crystal compound 30 to rotate 180° in the direction of arrow A, where the orientation of the optical axis 30A changes continuously within the plane, is defined as the length Λ of one period in the liquid crystal alignment pattern. In other words, the length of one period in the liquid crystal alignment pattern is defined by the distance from θ to θ + 180° in the angle between the optical axis 30A of the liquid crystal compound 30 and the direction of arrow A.

[0129] In other words, the length of one period Λ is defined as the distance between the centers in the direction of arrow A of two liquid crystal compounds 30 whose angles with respect to arrow A are equal. Specifically, as shown in Figure 9, the length of one period Λ is defined as the distance between the centers in the direction of arrow A of two liquid crystal compounds 30 whose directions of arrow A coincide with the direction of the optical axis 30A. In the following explanation, this length of one period Λ will also be referred to as "period Λ".

[0130] In the optically anisotropic layer 26A (optically anisotropic layer 26), the liquid crystal alignment pattern of the optically anisotropic layer repeats this one period Λ in one direction, i.e., in which the direction of arrow A, i.e., the direction of the optical axis 30A, continuously rotates and changes.

[0131] In the optically anisotropic layer 26, which has a radial liquid crystal alignment pattern in which the optical axis 30A rotates continuously, the period Λ gradually shortens from the inside (center) outwards.

[0132] As described above, in the optically anisotropic layer 26A, the liquid crystal compounds arranged in the Y direction have an equal angle between the optical axis 30A and the direction of arrow A (one direction in which the orientation of the optical axis of the liquid crystal compound 30 rotates). The region in which the liquid crystal compounds 30 having an equal angle between the optical axis 30A and the direction of arrow A are arranged in the Y direction is defined as region R.

[0133] In this case, the in-plane retardation (Re) value in each region R is preferably half a wavelength, i.e., λ / 2. These in-plane retardations are calculated by the product of the refractive index difference Δn due to the refractive index anisotropy of region R and the thickness of the optical anisotropy layer. Here, the refractive index difference due to the refractive index anisotropy of region R in the optical anisotropy layer is defined as the refractive index difference between the refractive index in the direction of the slow axis in the plane of region R and the refractive index in the direction perpendicular to the direction of the slow axis. That is, the refractive index difference Δn due to the refractive index anisotropy of region R is equal to the difference between the refractive index of the liquid crystal compound 30 in the direction of the optical axis 30A and the refractive index of the liquid crystal compound 30 in the direction perpendicular to the optical axis 30A in the plane of region R. In other words, the above refractive index difference Δn is equal to the refractive index difference of the liquid crystal compound.

[0134] In the optical anisotropic layer 26, which has a radial pattern of continuous rotation of the optical axis 30A in one direction (such as the directions of arrows A1 to A4), the region where the optical axis 30A is oriented in the same direction, and which is formed in a ring shape with a coincident center, corresponds to region R in Figure 9.

[0135] When circularly polarized light is incident on such an optically anisotropic layer 26A, the light is refracted and the direction of the circular polarization is changed. This effect will be explained using Figures 10 and 11. The optically anisotropic layer 26A is assumed to have a product value of λ / 2 between the refractive index difference of the liquid crystal compound and the thickness of the optically anisotropic layer.

[0136] Furthermore, as described above, this effect is exactly the same even in the optically anisotropic layer 26, which has a radial direction in which the optical axis 30A rotates continuously.

[0137] As shown in Figure 10, when the product of the refractive index difference of the liquid crystal compound in the optical anisotropy layer 26A and the thickness of the optical anisotropy layer is λ / 2, when left-circularly polarized incident light L1 is incident on the optical anisotropy layer 26A, the incident light L1 passes through the optical anisotropy layer 26A, giving it a phase difference of 180°, and the transmitted light L2 is converted to right-circularly polarized light.

[0138] Furthermore, since the liquid crystal alignment pattern formed in the optical anisotropy layer 26A is a periodic pattern in the direction of arrow A, the transmitted light L2 travels in a direction tilted by a certain angle in the direction of arrow A with respect to the direction of propagation of the incident light L1. In this way, the left-circularly polarized incident light L1 is converted into right-circularly polarized transmitted light L2, which is tilted by a certain angle in the direction of arrow A with respect to the direction of incidence.

[0139] On the other hand, as conceptually shown in Figure 11, when the product of the refractive index difference of the liquid crystal compound in the optical anisotropy layer 26A and the thickness of the optical anisotropy layer is λ / 2, when right-circularly polarized incident light L4 is incident on the optical anisotropy layer 26A, the incident light L4 passes through the optical anisotropy layer 26A, is given a phase difference of 180°, and is converted into left-circularly polarized transmitted light L5.

[0140] Furthermore, since the liquid crystal alignment pattern formed in the optically anisotropic layer 26A is a periodic pattern in the direction of arrow A, the transmitted light L5 travels in a direction tilted by a certain angle in the direction of arrow A with respect to the direction of propagation of the incident light L4. At this time, the transmitted light L5 travels in a different direction from the transmitted light L2, that is, in a direction opposite to the direction of arrow A with respect to the direction of incidence. In this way, the incident light L4 is converted into transmitted light L5 which is left-circularly polarized and tilted by a certain angle in the direction of arrow A with respect to the direction of incidence.

[0141] In the optically anisotropic layer 26A (optically anisotropic layer 26), the in-plane retardation values ​​of multiple regions R are preferably half a wavelength, but the in-plane retardation Re(550) = Δn of multiple regions R in the optically anisotropic layer 26A for incident light with a wavelength of 550 nm is 550 It is preferable that ×d is within the range defined in the following formula (1). Here, Δn 550 Δn is the refractive index difference due to refractive index anisotropy in region R when the wavelength of incident light is 550 nm, and d is the thickness of the optical anisotropy layer 26A (optical anisotropy layer 26). 200 nm ≤ Δn 550 ×d ≤ 350 nm ... (1)

[0142] That is, the in-plane retardation Re(550) = Δn of multiple regions R in the optical anisotropy layer 26A 550If ×d satisfies equation (1), a sufficient amount of circularly polarized light incident on the optical anisotropic layer 26A can be converted into circularly polarized light traveling in a direction tilted forward or backward with respect to the direction of arrow A.

[0143] Note that while the above equation (1) is for incident light with a wavelength of 550 nm, the in-plane retardation Re(λ) = Δn for multiple regions R of the optical anisotropy layer 26A for incident light with a wavelength of λ nm. λ ×d is preferably within the range defined by the following formula (1-2), and can be set as appropriate: 0.7 × (λ / 2) nm ≤ Δn λ ×d≦1.3×(λ / 2)nm...(1-2)

[0144] The optically anisotropic layer 26A (optically anisotropic layer 26) functions as a so-called λ / 2 plate. However, in the present invention, when a support 20 and an alignment film 24 are present, the laminate comprising these integrally functions as a λ / 2 plate.

[0145] Here, the optically anisotropic layer 26A can adjust the refraction angles of transmitted light L2 and L5 by changing the period Λ of the formed liquid crystal alignment pattern. Specifically, the shorter the period Λ of the liquid crystal alignment pattern, the stronger the interference between light passing through adjacent liquid crystal compounds 30, thereby allowing for greater refraction of transmitted light L2 and L5.

[0146] Furthermore, the angle of refraction of transmitted light L2 and L5 relative to incident light L1 and L4 differs depending on the wavelength of the incident light L1 and L4 (and transmitted light L2 and L5). Specifically, the longer the wavelength of the incident light, the greater the refraction of the transmitted light. That is, when the incident light is red, green, and blue light, the red light is refracted the most, and the blue light is refracted the least.

[0147] Furthermore, by reversing the rotation direction of the optical axis 30A of the liquid crystal compound 30, which rotates along the direction of arrow A, the direction of refraction of transmitted light can be reversed.

[0148] As described above, in the present invention, in the optical anisotropy layer 26 of the liquid crystal lens 14, the period Λ of the liquid crystal alignment pattern gradually shortens from the inside (center) to the outside in one direction of rotation of the optical axis 30A. Therefore, depending on the wavelength and polarization state of the incident light, the degree to which light is focused toward the center (optical axis) of the liquid crystal lens 14 can be adjusted by setting the rotation direction of the optical axis 30A from the inside to the outside so that the light is refracted toward the center of the liquid crystal lens 14, and by appropriately adjusting the degree of gradual reduction in the length of the period Λ of the liquid crystal alignment pattern. In other words, by greatly gradually reducing the length of the period Λ of the liquid crystal alignment pattern, the liquid crystal lens 14 can be made to act as a focusing lens (convex lens).

[0149] The optically anisotropic layer 26 is formed using a liquid crystal composition containing a rod-shaped liquid crystal compound or a disc-shaped liquid crystal compound, and has a liquid crystal alignment pattern in which the optical axis of the rod-shaped liquid crystal compound or the optical axis of the disc-shaped liquid crystal compound is oriented as described above.

[0150] An alignment film 24 having an alignment pattern corresponding to the above-described liquid crystal alignment pattern is formed on the support 20, and a liquid crystal composition is applied to the alignment film 24 and cured to obtain an optical anisotropy layer consisting of a cured layer of the liquid crystal composition.

[0151] The liquid crystal composition for forming the optically anisotropic layer 26 may contain a rod-shaped liquid crystal compound or a disc-shaped liquid crystal compound, and may also contain other components such as a leveling agent, an orientation control agent, a polymerization initiator, and an orientation aid.

[0152] Furthermore, it is desirable that the optical anisotropy layer 26 has a broad bandwidth with respect to the wavelength of the incident light, and is preferably composed of a liquid crystal material with inversely dispersed birefringence. It is also preferable to make the optical anisotropy layer substantially broadband with respect to the wavelength of the incident light by imparting a torsional component to the liquid crystal composition or by stacking different optical anisotropy layers. For example, a method for realizing a broadband patterned optical anisotropy layer by stacking two optical anisotropy layers with different torsional directions is shown in Japanese Patent Application Publication No. 2014-089476, and can be preferably used in the present invention.

[0153] ―Rod-shaped liquid crystal compounds― Preferably used rod-shaped liquid crystal compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyanosubstituted phenylpyrimidines, alkoxysubstituted phenylpyrimidines, phenyldioxanes, trans, and alkenylcyclohexylbenzonitriles. In addition to the low molecular weight liquid crystalline molecules mentioned above, high molecular weight liquid crystalline molecules can also be used as rod-shaped liquid crystal compounds.

[0154] In the optically anisotropic layer 26, it is more preferable to fix the orientation of the rod-shaped liquid crystal compound by polymerization. Examples of polymerizable rod-shaped liquid crystal compounds include those described in Makromol. Chem., Vol. 190, p. 2255 (1989), Advanced Materials. Compounds described in Volume 5, page 107 (1993), U.S. Patent No. 4683327, No. 5622648, No. 5770107, International Publication Nos. 95 / 022586, 95 / 024455, 97 / 000600, 98 / 023580, 98 / 052905, Japanese Patent Publication No. 1-272551, 6-016616, 7-110469, 11-080081, and Japanese Patent Application No. 2001-064627 can be used. Furthermore, as rod-shaped liquid crystal compounds, those described in, for example, Japanese Patent Publication No. 11-513019 and Japanese Patent Application No. 2007-279688 can also be preferably used.

[0155] —Disk-shaped liquid crystal compounds—As disc-shaped liquid crystal compounds, for example, those described in Japanese Patent Publication No. 2007-108732 and Japanese Patent Publication No. 2010-244038 can be preferably used.

[0156] Furthermore, when a disc-shaped liquid crystal compound is used in the optically anisotropic layer, the liquid crystal compound 30 rises in the thickness direction within the optically anisotropic layer, and the optical axis 30A derived from the liquid crystal compound is defined as an axis perpendicular to the disc surface, a so-called phase-advancing axis.

[0157] The liquid crystal lens 14 having such an optically anisotropic layer 26 has a flat, sheet-like surface with no irregularities. Furthermore, the liquid crystal lens 14 is thin, with a thickness of 1 to 100 μm. Therefore, by using the liquid crystal lens 14, the optical device of the present invention can be miniaturized.

[0158] <Optical Components> Optical components are components in optical devices that output light emitted by a semiconductor laser to the outside.

[0159] The type of optical component should be selected appropriately depending on the application of the optical device. Examples of optical components include optical fibers, lenses, flat glass substrates, and prisms. Specifically, when the optical device is used as an optical signal generator for an optical transceiver in an optical communication system, the optical component is an optical fiber. Also, when the optical device is used as an optical signal generator for a LiDAR (Light Detection and Ranging) device, the optical component is a lens.

[0160] <Polarizer> The polarizer is not particularly limited as long as it is a linear polarizer that has the function of transmitting linearly polarized light in one polarization direction and blocking linearly polarized light in the other polarization direction, and conventionally known linear polarizers can be used. The linear polarizer may be an absorption type linear polarizer or a reflection type linear polarizer.

[0161] Absorbing linear polarizers include iodine-based polarizers, dye-based polarizers utilizing dichroic dyes, and polyene-based polarizers. Iodine-based and dye-based polarizers include coated polarizers and stretched polarizers, both of which are applicable. Among these, polarizers made by adsorbing iodine or a dichroic dye onto polyvinyl alcohol and then stretching it are preferred.

[0162] Furthermore, as a method for obtaining a polarizer by stretching and dyeing a laminated film in which a polyvinyl alcohol layer is formed on a substrate, examples include those described in Japanese Patent Publication No. 5048120, Japanese Patent Publication No. 5143918, Japanese Patent Publication No. 4691205, Japanese Patent Publication No. 4751481, and Japanese Patent Publication No. 4751486, and these known technologies related to polarizers can also be preferably utilized.

[0163] As an absorbing polarizer, a light-absorbing anisotropic layer in which a dichroic dye is oriented using the orientation properties of liquid crystal without stretching is particularly preferred. Polarizers have many advantages, such as being able to be made into a very thin layer with a thickness of about 0.1 μm to 5 μm, being resistant to cracking when bent and having small thermal deformation as described in Japanese Patent Publication No. 2019-194685, having excellent durability even with polarizers with high transmittance exceeding 50% as described in Japanese Patent Publication No. 6483486, and having excellent heat-moldability.

[0164] As reflective linear polarizers, films made by stretching layers containing two types of polymers, as described in Japanese Patent Application Publication No. 2011-053705, and wire grid polarizers can be used. From the viewpoint of brightness, films made by stretching layers containing polymers are preferred. Commercially available products such as reflective polarizers (product name APF) manufactured by 3M and wire grid polarizers (product name WGF) manufactured by Asahi Kasei Corporation can be suitably used. Alternatively, a reflective linear polarizer combining a cholesteric liquid crystal film and a λ / 4 plate may be used.

[0165] [Optical Transceiver] The optical transceiver of the present invention uses the above-described optical device as an optical signal generator on the transmitting side.

[0166] The optical transceiver has the same configuration as conventionally known optical transceivers, except that it has the optical device of the present invention as an optical signal generator. For example, in addition to the optical device, the optical transceiver may also have an optical receiving unit, an optical signal modulation mechanism, a temperature control mechanism, a laser output control mechanism, a digital signal processing unit, and the like.

[0167] [LiDAR device] The LiDAR device of the present invention uses the above-mentioned optical device as an optical signal generator on the transmitting side.

[0168] The LiDAR device has the same configuration as conventionally known LiDAR devices, except that it has the optical device of the present invention as an optical signal generator. For example, the LiDAR device may have, in addition to the optical device, an optical receiving unit, a temperature control mechanism, a laser output control mechanism, a digital signal processing unit, an optical scanning mechanism, and the like.

[0169] Although the optical device, optical transceiver, and LiDAR apparatus of the present invention have been described in detail above, the present invention is not limited to the examples described above, and various improvements and modifications may be made without departing from the spirit of the present invention.

[0170] 10a-10c Optical device 12 Semiconductor laser 13 First λ / 4 plate 14 Liquid crystal lens 15 Optical component 16 Second λ / 4 plate 17 Polarizer 20 Support 24 Alignment film 26, 26A Optical anisotropy layer 30 Liquid crystal compound 30A Optical axis 80 Exposure apparatus 82 Laser 84 Light source 86, 94 Polarizing beam splitter 90A, 90B Mirror 92 Lens 96 λ / 4 plate A, A1-A4 Arrow R Region Λ 1 period M Laser light MP P polarization MS S polarization L1, L4 Incident light L2, L5 Transmitted light

Claims

1. An optical device comprising, in this order, a semiconductor laser, a first λ / 4 plate, a liquid crystal lens, and an optical element for external output, wherein the liquid crystal lens has an optically anisotropic layer formed using a composition containing a liquid crystal compound, the optically anisotropic layer has a liquid crystal alignment pattern radially from the inside to the outside in which the orientation of the optical axis originating from the liquid crystal compound changes while continuously rotating in one direction within the plane, and in the liquid crystal alignment pattern, when the length of one period is defined as the length of a 180° rotation of the orientation of the optical axis originating from the liquid crystal compound in the one direction in which the orientation of the optical axis originating from the liquid crystal compound changes while continuously rotating, the length of the one period gradually decreases from the inside to the outside.

2. The optical device according to claim 1, wherein a second λ / 4 plate is disposed between the liquid crystal lens and the optical member, or the optical member is provided with a function to give a λ / 4 phase difference to the liquid crystal lens side.

3. The optical device according to claim 2, wherein the second λ / 4 plate is in contact with the optical member.

4. The optical device according to claim 1, further comprising a polarizing plate between the semiconductor laser and the first λ / 4 plate.

5. An optical transceiver that uses the optical device described in any one of claims 1 to 4 as a transmitting optical signal generator.

6. A LiDAR apparatus that uses the optical device described in any one of claims 1 to 4 as the transmitting optical signal generator.

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