Liquid crystal panel, optical switching element, and liquid crystal panel electrode

Abstract

[Problem] To provide an optical switching element that is suitable for sensors in LiDAR, robots, and the like, and can be operated at a lower voltage than was needed conventionally, and to provide a liquid crystal panel and electrodes therefor. [Solution] An optical switching element 1A comprises a liquid crystal panel 2A and a diffracting member 3 that is attached on the side that is downstream in the light incidence direction. The liquid crystal panel 2A has a liquid crystal 5 and electrodes 6A between a pair of transparent substrates 4. As shown in (A), a pair of the electrodes 6A are affixed respectively to the pair of transparent substrates 4, and the liquid crystal 5 is interposed therebetween. The electrodes 6A have a positive electrode 6P and a negative electrode 6M and are formed respectively on the transparent substrates 4 in comb shapes, as shown in (A) and (C). (B) shows the electrodes 6A in a separated state. The electrodes 6A are stacked bodies obtained by stacking a plurality of transparent spacers 62 and a plurality of transparent electrodes 61. As a result of said configuration, the liquid crystal panel 2A that is suitable for a polymer-stabilized blue phase liquid crystal is formed.

Description

[Technical field]

[0001] The present invention relates to a liquid crystal panel, an optical switching element using the liquid crystal panel, and an electrode used in the liquid crystal panel. [Background technology]

[0002] In recent years, the development of autonomous driving technology for automobiles has progressed, and the development of sensor technology to detect obstacles around the automobile has become important.In addition, the development of sensor technology is also important in the field of robotics for detecting objects to be grasped and obstacles.

[0003] As part of such sensor technology, the development of LiDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging), which uses light beams such as laser light for sensing, is attracting attention. With LiDAR, a light beam is emitted to the outside, and when the light beam hits an obstacle and is reflected, the reflected light is received and the obstacle is detected by utilizing the time delay and phase difference between the emitted light and the reflected light.

[0004] The present inventors have proposed an optical switching element that can be used in LiDAR (Patent Document 1). The optical switching element in Patent Document 1 has a polarizing grating attached to the surface of a liquid crystal panel that uses polymer-stabilized blue phase liquid crystal, and glass wedges, which are inclined members, attached to both sides of the polarizing grating.

[0005] The liquid crystal panel in Patent Document 1 has thin-film transparent electrodes formed on the surfaces of two glass substrates, and polymer-stabilized blue phase liquid crystal filled between the transparent electrodes and stabilized by light irradiation. With the above configuration, the optical switching element in Patent Document 1 achieves high-speed switching by using polymer-stabilized blue phase liquid crystal that can be switched at a higher speed than conventional nematic liquid crystals. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2020-106616 Summary of the Invention [Problem to be solved by the invention]

[0007] The inventors of the present application are developing a LiDAR using the optical switching element described in Patent Document 1, and are particularly continuing their research toward practical application of an in-vehicle LiDAR. In-vehicle LiDAR is powered by the vehicle battery, so if the operating voltage exceeds the battery voltage, a booster or the like is required, which is undesirable because it increases the number of parts and the weight.

[0008] The optical switching element described in Patent Document 1 realizes high-speed switching by adopting a polymer-stabilized blue phase liquid crystal, but requires a relatively high operating voltage. Therefore, in order to put LiDAR for vehicle use, it is desirable to lower the operating voltage and reduce power consumption.

[0009] The present invention aims to provide an optical switching element that can be suitably used in sensors such as LiDAR or robots and that can operate at a lower voltage than conventional ones, a liquid crystal panel used in the optical switching element, and an electrode for the liquid crystal panel. [Means for solving the problem]

[0010] In order to achieve the above object, a liquid crystal panel according to a first aspect of the present invention is a liquid crystal panel having electrodes and liquid crystal held between a pair of transparent substrates, the liquid crystal being a polymer-stabilized blue phase liquid crystal, the electrodes being a laminate consisting of a plurality of thin-film transparent electrodes arranged parallel to the transparent substrates and thin-film transparent spacers arranged between the transparent electrodes, the laminate being arranged alternately in the in-plane direction of the transparent substrates with positive and negative electrodes, and the laminate has a surface in contact with the liquid crystal, the transparent spacers being arranged between the transparent electrodes and the transparent electrodes being arranged alternately with the transparent electrodes and ... and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the transparent spacers and the Transparent spacer that is thinner thanThe laminate is attached to both of the pair of transparent substrates, and a liquid crystal layer is provided between the laminate attached to one of the transparent substrates and the laminate attached to the other transparent substrate.

[0011] A liquid crystal panel according to a second aspect of the present invention is a liquid crystal panel having electrodes and liquid crystal held between a pair of transparent substrates, the liquid crystal being a polymer-stabilized blue phase liquid crystal, the electrodes being a laminate consisting of a plurality of thin-film transparent electrodes arranged parallel to the transparent substrates and thin-film transparent spacers arranged between the transparent electrodes, the laminate being arranged alternately in the in-plane direction of the transparent substrates as positive electrodes and negative electrodes, and the laminate has a surface in contact with the liquid crystal, the transparent spacers being arranged between the transparent electrodes and the thin-film transparent spacers being arranged between the transparent electrodes and the thin-film transparent spacers being arranged alternately in the in-plane direction of the transparent substrates as positive electrodes and negative electrodes, Transparent spacer that is thinner than The laminate is attached to one of the transparent substrates, and a liquid crystal layer is provided between the other transparent substrate and the laminate.

[0012] In the liquid crystal panel of the present invention, a laminate in which a plurality of transparent electrodes and a plurality of transparent spacers are laminated has electrodes arranged alternately with positive and negative electrodes in the liquid crystal, so that the direction in which a voltage is applied to the electrodes can be parallel to the transparent electrodes. Therefore, a voltage can be applied directly to the liquid crystal between the positive and negative electrodes, so that the liquid crystal can be operated with less power.

[0013] In addition, since the laminate used in the liquid crystal panel of the first embodiment is two-layered, the thickness of the laminate can be made thin, and the etching process is easy when forming the laminate by etching. On the other hand, the liquid crystal panel of the second embodiment has a laminate attached to one transparent substrate and not to the other transparent substrate, so that the configuration can be simplified.

[0014] In the liquid crystal panel of the present invention, the liquid crystal layer is preferably made of liquid crystal having a characteristic that the director has a long axis in the direction of the voltage when a voltage is applied. An example of a liquid crystal having a characteristic that the director has a long axis in the direction of the voltage when a voltage is applied is a polymer-stabilized blue phase liquid crystal, which can generate retardation in light incident on the transparent substrate.

[0015] Moreover, a light switching element can be formed by attaching a transmissive diffractive member to one surface of the liquid crystal panel of the first and second aspects described above. When the surface of this light switching element on which the diffractive member is attached is the front surface and the other surface is the back surface, a light switching element stack can be formed by attaching the back surface of another light switching element to the front surface of the light switching element.

[0016] Furthermore, in the optical switching element stack of the present invention, the diffractive elements attached to the stacked optical switching elements can be set so that the polarization angle of the diffractive element on the downstream side is larger than that of the diffractive element on the upstream side in the direction of light incidence.

[0017] When light passes through a plurality of stacked optical switching elements, the light that passes through the optical switching element on the upstream side in the incident direction is tilted by the diffractive member, so that it is obliquely incident on the surface of the next optical switching element. On the other hand, the efficiency of generating retardation is high when the angle of incidence of the light incident on the optical switching element is perpendicular to the surface. For this reason, by increasing the polarization angle of the diffractive member used in the downstream optical switching element and bringing the angle of the light incident on the liquid crystal panel closer to perpendicular to the panel, an optical switching element stack that is efficient even when multiple sheets are stacked can be obtained.

[0018] In addition, as an electrode suitable for the liquid crystal panel of the present invention, the electrode of the present invention is disposed between a pair of transparent substrates. Polymer-stabilized blue phases The electrodes are arranged in a liquid crystal panel holding liquid crystal, and the laminate is composed of a plurality of thin-film transparent electrodes arranged parallel to the transparent substrate and thin-film transparent spacers arranged between the transparent electrodes, and the laminate is arranged alternately in the in-plane direction of the transparent substrate as positive electrodes and negative electrodes. The laminate has a transparent spacer that is thinner than the transparent spacer on a surface that contacts the liquid crystal. It is characterized by:

[0019] In the electrode of the present invention, the laminate may be formed in a comb shape when viewed from the out-of-plane direction of the transparent substrate. With this configuration, when used in a liquid crystal panel, the liquid crystal panel can be made compact. Effect of the Invention

[0020] According to the present invention, it is possible to provide an optical switching element that can be suitably used in sensors such as LiDAR or robots and that can operate at a lower voltage than conventional ones, a liquid crystal panel used in the optical switching element, and an electrode for the liquid crystal panel. [Brief description of the drawings]

[0021] [Figure 1] FIG. 2 is an explanatory diagram showing the appearance of the optical switching element according to the embodiment; [Diagram 2] 2A is an explanatory diagram showing a portion of a cross section of the optical switching element of FIG. 1, FIG. 2B is an explanatory diagram showing the state in which the electrode stack has been separated, and FIG. 2C is a schematic explanatory diagram showing the state of the electrodes of the optical switching element of FIG. 1. [Diagram 3] FIG. 4A is an explanatory diagram showing a cross section of a liquid crystal panel according to a first embodiment, and FIG. 4B is an explanatory diagram showing the state of an electric field in the liquid crystal panel according to the first embodiment. [Figure 4] 10A is an explanatory diagram showing a cross section of a liquid crystal panel according to a second embodiment, and FIG. 10B is an explanatory diagram showing the state of an electric field in the liquid crystal panel according to the second embodiment. [Diagram 5] FIG. 2A is an explanatory diagram showing a laminate in which the optical switching elements of FIG. 1 are laminated, and FIG. 2B is an explanatory diagram showing a schematic cross section of the optical switching element of FIG. [Figure 6] (A) is a graph showing the displacement of S3, and (B) is a graph showing the normalized light intensity of the zero-order light. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Next, an optical switching element, a liquid crystal panel, an electrode, and an optical switching element laminate as one embodiment of the present invention will be described with reference to Fig. 1 to Fig. 6. As shown in Fig. 1 and Fig. 2(A), an optical switching element 1A of the first embodiment includes a liquid crystal panel 2A of the first embodiment and a diffractive member 3 attached downstream of the liquid crystal panel 2A in the incident direction of light.

[0023] 2(A), the optical switching element 1A of the first embodiment has an electrode 6A of the first embodiment disposed in a liquid crystal panel 2A in which liquid crystal 5 is held between a pair of transparent substrates 4. The optical switching element 1A has a diffraction member 3 attached to one surface of the liquid crystal panel 2A, and further has a power supply electrode 7 that supplies power to the electrode 6A.

[0024] In this embodiment, the transparent substrate 4 is made of quartz glass, and the liquid crystal 5 is made of polymer-stabilized blue phase liquid crystal. This polymer-stabilized blue phase liquid crystal has a property that when a voltage is applied, the director (not shown) has a long axis in the direction of the voltage. Here, it is sufficient that the long axis direction of the director roughly coincides with the direction of the voltage, and that retardation is generated in the light passing through the liquid crystal panel 2A.

[0025] The transparent electrode 61 used for the electrode 6A is made of indium tin oxide (ITO). The diffraction member 3 is a polarizing grating that is a transmissive diffraction member. As shown in FIG. 2A, an optical adhesive layer 41 having the same refractive index as the transparent substrate 4 is provided on the outer surface of the transparent substrate 4.

[0026] 2(A) is a cross-sectional view of an optical switching element 1A of the first embodiment, in which a pair of electrodes 6A are fixed to both of a pair of transparent substrates 4, and liquid crystal 5 (liquid crystal layer) is interposed between the pair of electrodes 6A. As shown in FIGS. 2(A) and 2(C), the electrode 6A is provided with a positive electrode 6P and a negative electrode 6M.

[0027] As shown in Fig. 2(C), the positive electrodes 6P and the negative electrodes 6M are each formed to have a comb-like shape when viewed from the out-of-plane direction (the direction in which the surface of the transparent substrate 4 is viewed from the front) of the transparent substrate 4. Also, as shown in Fig. 2(C), the positive electrodes 6P and the negative electrodes 6M are alternately arranged in the in-plane direction of the transparent substrate 4 (the up-down direction in the figure).

[0028] Fig. 2(B) is an explanatory diagram showing the electrode 6A in a separated state. The electrode 6A is a laminated body in which a plurality of thin-film-like transparent spacers 62 and a plurality of transparent electrodes 61 are laminated. As shown in Fig. 2(B), the electrode 6A is formed by alternately laminating five transparent spacers 62 and four transparent electrodes 61 symmetrically in the figure.

[0029] Of the transparent spacers 62 constituting each of the electrodes 6P and 6M, only the pair of transparent spacers 62 located in the center are thinner than the other transparent spacers 62, and the other four transparent spacers 62 on each of the left and right sides have the same thickness.

[0030] As an example, in this embodiment, the thickness of the pair of transparent spacers 62 in the center is 1 μm, the thickness of the four transparent spacers 62 on the left and right is 2 μm, and the thickness of the transparent electrode 61 is 15 nm. Also, the vertical distance between the electrodes 6P, 6M in FIG. 2(A) is set to 2 μm in this embodiment. Note that these numerical values ​​are merely examples and can be changed as appropriate depending on the wavelength of the light used, etc.

[0031] In the present application, the thickness dimension of each member is compressed in order to make it easier to understand the structure of electrode 6. For example, in Fig. 2(A), if the vertical scale is 1, the horizontal scale is approximately 1 / 6. The same is true for Figs. 3 and 4. Furthermore, although the shapes of electrodes 6P and 6M of electrode 6A cannot be discerned with the naked eye due to their dimensions, in Fig. 2(C) the portions of electrodes 6P and 6M are enlarged so that their shapes can be discerned.

[0032] 2(C), a power supply electrode 7 is connected to the base of the comb teeth of the positive electrode 6P and the negative electrode 6M. The power supply electrode 7 makes the voltages of the positive electrode 6P and the negative electrode 6M relatively positive and negative, generating an electric field between the electrodes 6P and 6M.

[0033] Next, the state of the electric field in the liquid crystal panel 2A of the first embodiment will be described with reference to Fig. 3. Fig. 3(A) is an explanatory diagram showing a cross section of the liquid crystal panel 2A equipped with the electrode 6A of the first embodiment, and Fig. 3(B) is an explanatory diagram showing the contour lines and direction of the electric field when a voltage is applied to the electrode of the liquid crystal panel 2A.

[0034] 3(B), when a voltage is applied to the positive electrode 6P and the negative electrode 6M of the electrode 6A, an electric field is generated between the electrodes 6P and 6M in the direction from the positive pole to the negative pole, as indicated by the arrow in the figure. The direction of this electric field is parallel to the transparent substrate 4 between the electrodes 6P and 6M, and coincides with the in-plane direction of the transparent substrate 4. In addition, liquid crystal 5 is interposed between the electrode 6A located above and the electrode 6A located below in the figure, and an electric field parallel to the transparent substrate 4 is also generated in the liquid crystal 5 between the electrodes 6A.

[0035] In this way, an electric field acts on the liquid crystal 5 in a direction parallel to the transparent substrate 4. In this embodiment, a polymer-stabilized blue phase liquid crystal is used for the liquid crystal 5, and by applying an electric field, the directors in the liquid crystal 5 can be aligned parallel to the transparent substrate 4. When light is irradiated onto the liquid crystal panel 2A in this state, the liquid crystal 5 acts to generate retardation in the light passing through the liquid crystal panel 2A.

[0036] On the other hand, when no electric field is applied between electrodes 6P, 6M, the director in the liquid crystal becomes a spherical refractive index ellipsoid in side view, and the liquid crystal becomes an optically isotropic medium, so that even when light is irradiated onto liquid crystal panel 2A, no retardation occurs in the light passing through liquid crystal panel 2A.

[0037] In this way, the polymer stabilized blue phase liquid crystal, which operates at high speed, can be switched by turning on and off the electric field between the electrodes 6P and 6M. Therefore, the electrode 6A of this embodiment and the liquid crystal panel 2A using this electrode 6A can form an optical switching element 1A capable of switching at high speed.

[0038] Next, an optical switching element 1B, a liquid crystal panel 2B, and an electrode 6B according to a second embodiment of the present invention will be described with reference to Fig. 4. The liquid crystal panel 2B of the second embodiment differs from the electrode 6A of the first embodiment in that the electrode 6B is fixed to only one side of the transparent substrate 4.

[0039] The electrode 6B of the second embodiment is formed by stacking eight transparent electrodes 61 and nine transparent spacers 62. In Fig. 4(A), the topmost transparent spacer 62 in the figure is formed thinner than the other transparent spacers 62.

[0040] 4(B) is an explanatory diagram showing the contour lines and direction of the electric field when a voltage is applied to the electrode 6B of the liquid crystal panel 2B. As shown in the figure, in the electrode 6B of the second embodiment, the direction of the electric field between the electrodes 6P and 6M is parallel to the transparent substrate 4 and coincides with the in-plane direction of the transparent substrate 4, almost similar to the first embodiment.

[0041] Next, the optical switching element stack 10 will be described with reference to Fig. 5. The optical switching element stack 10 is formed by stacking a plurality of optical switching elements 1A shown in Fig. 1. In this embodiment, eight optical switching elements 1A are stacked, but the number of stacked elements is appropriately selected depending on the angle resolution (minimum deflection angle for switching) and maximum deflection angle, etc.

[0042] Fig. 5(B) is a schematic cross-sectional view of the liquid crystal panel 2A of the optical switching element laminate 10 of Fig. 5(A). As shown in Fig. 5(B), the optical switching element 1A has a transmissive diffractive member 3 attached to one surface of the liquid crystal panel 2A.

[0043] The optical switching element stack 10 of this embodiment is formed by positioning the surface on which the diffractive member 3 is attached as the front surface and the other surface as the back surface, downstream in the direction of light incidence, and attaching the back surface of another optical switching element 1A to this front surface.

[0044] In this embodiment, the polarization angle of the diffraction member 3 provided on the downstream side is set to be larger than the polarization angle of the diffraction member 3 provided on the upstream side of the incident direction of light. For example, the polarization angle of the diffraction member 3 on the upstream side of the incident direction of light is set to 0.1°, and the polarization angle of the second diffraction member 3 is set to 0.2°, so that the polarization angle increases by two times on the downstream side.

[0045] By changing the polarization angle of the diffractive element 3 from the upstream side to the downstream side of the incident light direction in this manner, the angle of the light incident on the liquid crystal panel 2A can be made closer to perpendicular to the liquid crystal panel 2A, thereby making it possible to obtain an optical switching element stack 10 that is efficient even when multiple sheets are stacked.

[0046] Next, the displacement of S3 and the normalized light intensity of the zeroth-order light of the optical switching element 1A of the first embodiment and the optical switching element 1B of the second embodiment will be described with reference to Fig. 6. Fig. 6(A) is a graph showing the displacement of S3, and Fig. 6(B) is a graph showing the normalized light intensity of the zeroth-order light. The values ​​of each graph were measured with the temperature of the blue phase liquid crystal in the optical switching element stack 10 and the liquid crystal panel 2A set to 50°C, the frequency of the applied voltage set to 1 kHz to 50 kHz, and the light wavelength set to 1550 nm.

[0047] Here, S3 is the Stokes parameter, with 1 representing right-handed circular polarization and -1 representing left-handed circular polarization. Therefore, when S3 changes from 1 to -1, the light is deflected by the deflection grating placed after it. In addition, the normalized light intensity of the zeroth-order light indicates the ratio of the zeroth-order light to the transmitted light from the liquid crystal panel, which also includes higher-order diffracted light, and a high value indicates high switching efficiency.

[0048] 6A, in the optical switching element 1A of the first embodiment, when the displacement of S3 is -1, the voltage is 40 V. On the other hand, in the optical switching element 1B of the second embodiment, when the displacement is -1, the voltage is 36 V. Note that with light of a shorter wavelength (for example, in the visible light band), it operates at a lower voltage of about 10 V.

[0049] In this way, both the optical switching element 1A and the optical switching element 1B of this embodiment can be operated at a voltage of about 40 V or less. This means that in hybrid cars and electric cars, they can be operated without using a booster or the like, making them suitable optical switching elements for in-vehicle LiDAR.

[0050] In the above embodiment, a polymer-stabilized blue phase liquid crystal is used as the liquid crystal 5, but this is not limited thereto. Liquid crystals made of other materials may also be used as long as they have the property that when a voltage is applied, the director has the long axis in the direction of the voltage. [Explanation of symbols]

[0051] 1A, 1B...Optical switching element 2A, 2B...LCD panel 3... Diffractive material 4...Transparent substrate 5. Liquid crystal 6A,6B…electrode 6M…Positive electrode 6P…negative electrode 61...Transparent electrode 62...Transparent spacer 7...Power supply electrode 10... Optical switching element laminate

Claims

1. A liquid crystal panel having electrodes and liquid crystal held between a pair of transparent substrates, the liquid crystal is a polymer-stabilized blue phase liquid crystal, the electrodes are laminated bodies each including a plurality of thin-film transparent electrodes arranged parallel to the transparent substrate and thin-film transparent spacers arranged between the transparent electrodes, the laminated bodies being arranged alternately in the in-plane direction of the transparent substrate as positive electrodes and negative electrodes; the laminate has a transparent spacer on a surface in contact with the liquid crystal, the transparent spacer being thinner than the transparent spacer; A liquid crystal panel characterized in that the laminate is attached to both of a pair of the transparent substrates, and a liquid crystal layer is provided between the laminate attached to one of the transparent substrates and the laminate attached to the other transparent substrate.

2. A liquid crystal panel having electrodes and liquid crystal held between a pair of transparent substrates, the liquid crystal is a polymer-stabilized blue phase liquid crystal, the electrodes are laminated bodies each including a plurality of thin-film transparent electrodes arranged parallel to the transparent substrate and thin-film transparent spacers arranged between the transparent electrodes, the laminated bodies being arranged alternately in the in-plane direction of the transparent substrate as positive electrodes and negative electrodes; the laminate has a transparent spacer on a surface in contact with the liquid crystal, the transparent spacer being thinner than the transparent spacer; A liquid crystal panel comprising the laminate attached to one of the transparent substrates, and a liquid crystal layer provided between the other transparent substrate and the laminate.

3. 3. The liquid crystal panel according to claim 1, wherein the liquid crystal layer is made of liquid crystal having a property that, when a voltage is applied, the director has a long axis in the direction of the voltage.

4. 2. An optical switching element comprising: a liquid crystal panel according to claim 1, and a transmission type diffractive member attached to one surface of the liquid crystal panel.

5. 3. An optical switching element comprising: a liquid crystal panel according to claim 2, and a transmission type diffractive member attached to one surface of the liquid crystal panel.

6. When the surface of the optical switching element according to claim 4 on which the diffractive member is attached is defined as a front surface and the other surface is defined as a back surface, 2. An optical switching element stack comprising: an optical switching element having a rear surface attached to a front surface of the optical switching element;

7. When the surface of the optical switching element according to claim 5 on which the diffractive member is attached is defined as a front surface and the other surface is defined as a back surface, 2. An optical switching element stack comprising: an optical switching element having a rear surface attached to a front surface of the optical switching element;

8. 8. The optical switching element laminate according to claim 6, The diffractive member attached to the plurality of stacked optical switching elements includes:

1. An optical switching element stack, comprising: a diffractive element disposed downstream in a direction of incidence of light, the diffractive element having a polarization angle set to be larger than that of the diffractive element disposed upstream in a direction of incidence of light.

9. An electrode disposed in a liquid crystal panel having a polymer-stabilized blue phase liquid crystal held between a pair of transparent substrates, a laminate including a plurality of thin-film transparent electrodes arranged parallel to the transparent substrate and thin-film transparent spacers arranged between the transparent electrodes, the laminate being arranged alternately in the in-plane direction of the transparent substrate as positive electrodes and negative electrodes; The laminate has a transparent spacer, the transparent spacer being thinner than the transparent spacer, on a surface of the laminate that contacts the liquid crystal.

10. 10. The electrode of claim 9, The laminate is formed in a comb-like shape when viewed from an out-of-plane direction of the transparent substrate.

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