JP7393066B2 - Liquid crystal panels and optical switching elements - Google Patents

Description

The present invention relates to a liquid crystal panel and an optical switching element using the liquid crystal panel.

In recent years, the development of automatic driving technology for automobiles has been progressing, and among these developments, the development of sensor technology for detecting obstacles etc. around the automobile has become important. Furthermore, the development of sensor technology is also important for detecting grasped objects and detecting obstacles in the field of robots.

As part of such sensor technology, attention is being focused on the development of LiDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging), which performs sensing using a light beam such as a laser beam. LiDAR emits a light beam to the outside, and when that light beam hits an obstacle and is reflected, it receives the reflected light and uses the time delay and phase difference between the emitted light and the reflected light. Detecting obstacles.

The inventor of the present application has proposed an optical switching element that can be used for this LiDAR (Patent Document 1). In the optical switching element disclosed in Patent Document 1, a polarizing grating is attached to the surface of a liquid crystal panel using polymer-stabilized blue-phase liquid crystal, and glass wedges, which are inclined members, are attached to both sides of the polarizing grating.

In the liquid crystal panel disclosed in Patent Document 1, thin film-like transparent electrodes are formed on the surfaces of two glass substrates, a polymer-stabilized blue phase liquid crystal is filled between the transparent electrodes, and the liquid crystal is stabilized by light irradiation. The optical switching element in Patent Document 1 achieves high-speed switching by using a polymer-stabilized blue-phase liquid crystal that can switch faster than conventional nematic liquid crystals and the like with the above configuration.

JP2020-106616

The inventors of the present application are proceeding with the development of LiDAR using the optical switching element described in Patent Document 1, and are particularly continuing research toward the practical application of LiDAR for use in vehicles. In-vehicle LiDAR uses the vehicle's battery as a power source, so if the operating voltage exceeds the battery voltage, a booster or the like is required, which is undesirable because the number of parts and weight increase.

The optical switching element described in Patent Document 1 achieves high-speed switching by employing a polymer-stabilized blue-phase liquid crystal, but requires a relatively high operating voltage. Therefore, in order to put automotive LiDAR into practical use, it is desired to lower the operating voltage and reduce power consumption.

An object of the present invention is to provide an optical switching element that can be suitably used in LiDAR, sensors for robots, etc., and can operate at a lower voltage than conventional ones, and a liquid crystal panel used in the optical switching element. shall be.

In order to achieve the above object, the liquid crystal panel of the present invention is a liquid crystal panel in which electrodes and liquid crystal are held between a pair of transparent substrates, wherein the electrodes are erected against the inner surface of the transparent substrate. A plurality of transparent spacers each having a raised surface are arranged such that the raised surfaces face each other, and a transparent electrode serving as a positive electrode and a transparent electrode serving as a negative electrode are respectively formed on the facing raised surfaces, and the transparent electrode serving as the positive electrode and A liquid crystal layer filled with the liquid crystal is provided between the transparent electrodes serving as the negative electrode, and when a refractive index ellipsoid consisting of a director in the liquid crystal generates an electric field by applying a voltage to the electrodes. It is characterized in that the long axis is along the direction of the electric field.

In the liquid crystal panel of the present invention, transparent electrodes are provided on (the side walls of) the upright surfaces of transparent spacers, and a liquid crystal layer is provided between the positive and negative transparent electrodes. Therefore, the direction of the electric field when applying voltage to the electrode can be made parallel to the transparent substrate. Therefore, a voltage can be directly applied to the liquid crystal between the positive electrode and the negative electrode, so that the liquid crystal can be operated with less electric power.

In addition, since the refractive index ellipsoid consisting of the director in the liquid crystal has the property that its long axis runs along the direction of the electric field, applying a voltage to the electrodes can cause retardation of the light incident on the transparent substrate. can be efficiently generated.

Further, in the liquid crystal panel of the present invention, the liquid crystal in the liquid crystal layer may be a polymer-stabilized blue phase liquid crystal. This configuration enables faster switching than conventional nematic liquid crystals and the like.

Further, in the liquid crystal panel of the present invention, the plurality of transparent spacers are formed in the shape of a line or rod extending in a predetermined direction in the in-plane direction of the transparent substrate, and are arranged periodically at equal intervals in the direction of the electric field. You can leave it there. When light passes through a liquid crystal panel having such a periodic structure, a plurality of light beams of 0th order, ±1st order, ±2nd order, etc. are formed.

Further, in the liquid crystal panel of the present invention, the width of the transparent spacer in the direction of the electric field and the width of the liquid crystal layer in the direction of the electric field may be the same or within a range of ±50%. With this configuration, the electrode made of the transparent spacer and the transparent electrode and the liquid crystal layer can have a periodic structure in the direction of the electric field.

In devices such as liquid crystal displays, it is necessary to generate such high-order light beams (±1st order, ±2nd order, etc.) in order to make images visible at a wide angle relative to the display. preferable. However, in liquid crystal panels used in devices such as LiDAR, when a high-order light beam is generated, the light is diffused, which is inconvenient for the application.

In the liquid crystal panel of the present invention, the above structure suppresses the generation of high-order light beams and prevents light from being diffused. In the liquid crystal panel of the present invention, the width of the transparent spacer and the transparent electrode in the direction of the electric field and the width of the liquid crystal layer in the direction of the electric field should be within 1/4 to 2 times the wavelength of the irradiated light. is preferred.

Further, in the liquid crystal panel of the present invention, the interval between one electrode of the transparent spacer and one electrode of the transparent spacer (next transparent spacer) adjacent to the transparent spacer is set at a period (W ₅ +W ₆ in FIG. 2). In this case, the period may be set to 1/2 or more and 4 times or less of the wavelength of the light used. In this way, by forming the transparent spacer into a periodic structure (fixed length), the liquid crystal panel can be used in a LiDAR scanner as long as the light used is near-infrared light. Further, if the light used is visible light, the liquid crystal panel can be used for goggles for VR (Virtual Reality), a head-up display for a car, or a display that projects images on a wall or screen.

Further, in the liquid crystal panel of the present invention, it is preferable that the refractive index of the transparent spacer is between the refractive index of ordinary light and the refractive index of extraordinary light when an electric field is applied to the liquid crystal. This suppresses the generation of high-order light beams, and also reduces the refractive index contrast even when the incident light entering the liquid crystal panel is oblique, significantly reducing the loss of transmitted light. I can do it.

Further, in each of the liquid crystal panels described above, it is preferable that the transparent electrode is formed of a material whose main raw material is zinc oxide. Here, the main raw material refers to a raw material that accounts for 50% or more by mass of the entire raw material. In the liquid crystal panel of the present invention, since the transparent electrode is formed on the upright surface, a portion of the light incident from the transparent substrate passes through the inside of the transparent electrode, which has a length approximately equal to the thickness of the transparent spacer. become. Therefore, in order to suppress the loss of light passing through the transparent electrode, it is preferable to use a material containing zinc oxide, which is more transparent than ITO.

Regarding the internal structure of each of the liquid crystal panels, the first aspect is that the transparent spacer and the transparent electrode are provided on the inner surfaces of both of the pair of transparent substrates, and between one transparent spacer and the other transparent spacer. A liquid crystal layer may be provided. In the liquid crystal panel of the first embodiment, a transparent spacer and a transparent electrode used in the liquid crystal panel are provided on each of a pair of transparent substrates, and processing is facilitated when forming the transparent spacer by processing such as etching. .

Regarding the internal structure of each of the liquid crystal panels, a second aspect is such that the transparent spacer and the transparent electrode are provided on the inner surface of one of the transparent substrates, and between the transparent spacer and the inner surface of the other transparent substrate. A liquid crystal layer may be provided. In the liquid crystal panel of the second embodiment, the transparent spacer and the transparent electrode are provided on one transparent substrate and not provided on the other transparent substrate, so that the structure can be simplified.

Further, in each of the liquid crystal panels described above, the thickness of the transparent spacer may be formed to be 70% or more and 95% or less of the distance between the pair of transparent substrates. According to this configuration, an electric field can be generated in the index ellipsoid made of the director in many parts of the liquid crystal sandwiched between the pair of transparent substrates. If this ratio is less than 70%, the performance when the liquid crystal panel is used as an optical switching element will be low. On the other hand, if this ratio exceeds 95%, there is a risk that the facing transparent spacers will come into contact with each other, or the transparent substrate and the transparent spacer may come into contact with each other, which is not preferable because there is a risk of scratches caused by the contact.

The optical switching element of the present invention uses each of the liquid crystal panels described above, and has a transmission type diffraction member mounted on one surface of the transparent substrate. Further, in the optical switching element of the present invention, the diffraction member is attached to the transparent substrate with the direction of the rotation axis of the director of the diffraction member facing the extending direction (within ±10°) of the transparent electrode. You may. With this configuration, even if the angle of incident light is tilted in the extending direction of each electrode, the light transmission efficiency can be maintained unchanged.

Furthermore, when the surface of the optical switching element on which the diffraction member is attached is the front surface and the other surface is the back surface, it is possible to attach the back surface of another optical switching element to the front surface of the optical switching element. It can be a switching element stack.

Further, in the optical switching element stack, the diffraction member attached to the plurality of laminated optical switching elements is arranged so that the diffraction member located on the downstream side is compared to the diffraction member located on the upstream side in the light incident direction. The deflection angle may be set large. With this configuration, it is possible to increase the emission angle of the emitted light and irradiate a wide range with the emitted light.

The method for manufacturing a substrate for a liquid crystal panel of the present invention includes a mask layer forming step of forming a mask layer on the surface of a material substrate that is a material of the substrate for a liquid crystal panel, and a pattern resist forming a predetermined pattern on the surface of the mask layer. a first etching step of etching the mask layer in the shape of the patterned resist layer, and etching the material substrate so that the shape of the pattern has a predetermined thickness to make it transparent. a second etching step of forming a transparent spacer having a raised surface that stands up on the surface of the substrate; a mask layer removing step of removing the mask layer after the second etching step; and a mask layer removing step of removing the mask layer after the second etching step; a transparent electrode forming step of forming an electrode film forming a transparent electrode on the surface of the spacer; and etching the electrode film on the flat surface of the transparent substrate and the transparent spacer, leaving the electrode film on the raised surface. The method further includes a selective sputter etching step for forming the transparent electrode.

Through these steps, a transparent spacer and a transparent substrate are formed from a material substrate, an electrode film is formed on the upright surface of the transparent spacer, and unnecessary portions of the electrode film are etched to form a transparent electrode. Note that the pattern resist layer may be removed in the second etching step, after the mask layer is etched in the first etching step, or in a mask layer removal step after the second etching step. Good too.

Further, in the method for manufacturing a substrate for a liquid crystal panel of the present invention, in the transparent electrode forming step, the electrode film may be formed by ALD technology using Al-doped ZnO as a raw material. Here, the ALD (Atomic Layer Deposition) technology is a film forming technology that utilizes vacuum, and refers to a technology that utilizes the self-control properties of atoms to deposit atoms one layer at a time. By forming a film of Al-doped ZnO (AZO) using this ALD technique, a transparent electrode suitable for the liquid crystal panel and optical switching element of the present invention can be formed.

According to the present invention, a liquid crystal panel can be suitably used for sensors such as LiDAR or robots, VR goggles, head-up displays, or projection displays, and can operate at a lower voltage than conventional ones. , it is possible to provide a method for manufacturing an optical switching element and a substrate for a liquid crystal panel using the liquid crystal panel.

(A) is an explanatory diagram showing the appearance of the optical switching element of this embodiment, and (B) is an explanatory diagram showing the relationship between the electrode of the optical switching element and the director of the diffraction member in FIG. 1. (A) is an explanatory diagram showing a part of the cross section of the optical switching element of FIG. 1, and (B) is an explanatory diagram schematically showing the state of the electrodes of the optical switching element of FIG. 1. (A) is an explanatory diagram showing the state of an electric field in the liquid crystal panel of the first embodiment, and (B) is an explanatory diagram showing a schematic state of the refractive index ellipsoid of the liquid crystal layer. 2 is a graph showing the relationship between the refractive index of a liquid crystal and a transparent spacer, the square of the electric field, and the birefringence difference (the refractive index difference between the major axis (ne) and the minor axis (no) of a refractive index ellipsoid). FIG. 7 is an explanatory diagram showing a cross section of a liquid crystal panel according to a second embodiment. (A) is an explanatory view showing a laminate in which the optical switching elements of FIG. 1 are laminated, and (B) is an explanatory view schematically showing a cross section of the laminate in (A). (A) to (G) are explanatory diagrams showing a method for manufacturing a substrate for a liquid crystal panel according to the present invention.

Next, a liquid crystal panel and an optical switching element, which are examples of embodiments of the present invention, will be described with reference to FIGS. 1 to 6. As shown in FIGS. 1 and 2A, the optical switching element 1A of the first embodiment is attached to the liquid crystal panel 2A of the first embodiment and to the downstream side of the liquid crystal panel 2A in the light incident direction. and a diffraction member 3.

As shown in FIG. 2A, the optical switching element 1A of the first embodiment has electrodes 6A of the first embodiment in a liquid crystal panel 2A in which a liquid crystal 5 is held between a pair of transparent substrates 4. is located. The optical switching element 1A has a diffraction member 3 mounted on one surface of a liquid crystal panel 2A, and a power supply electrode 7 for supplying power to the electrode 6A.

In this embodiment, the transparent substrate 4 is made of quartz glass, and the liquid crystal 5 is a polymer-stabilized blue phase liquid crystal. This polymer-stabilized blue phase liquid crystal has a property that when a voltage is applied, the refractive index ellipsoid 5a consisting of a director has its long axis along the direction of the electric field. Here, the major axis direction of the refractive index ellipsoid 5a only needs to be approximately the same as the direction of the electric field, and only needs to be able to cause retardation in the light passing through the liquid crystal panel 2A.

The electrode 6A is provided on both inner surfaces of the pair of transparent substrates 4, and includes a transparent spacer 61 and a transparent electrode 62. The transparent spacer 61 is formed in a linear or rod shape extending in a predetermined direction in the in-plane direction of the transparent substrate 4, and has an upright surface 61a that stands up with respect to the transparent substrate 4, and has a transparent electrode on this upright surface 61a. 62 is formed.

Further, a plurality of electrodes 6A are arranged so that these transparent electrodes 62 and the upright surfaces 61a face each other, and adjacent transparent electrodes 62 each have a transparent electrode serving as a positive electrode 6P and a transparent electrode serving as a negative electrode 6M. In the liquid crystal panel 2A of this embodiment, a liquid crystal layer filled with liquid crystal 5 is provided between a transparent electrode serving as a positive electrode 6P and a transparent electrode serving as a negative electrode 6M.

In this embodiment, germanium dioxide (GeO ₂ )-doped silica glass is used for the transparent spacer 61 used in the electrode 6A. In this embodiment, the transparent electrode 62 uses a material whose main raw material is zinc oxide (ZnO), to which Al and Ga are added. In this embodiment, the content of zinc oxide is 98% by mass, the content of Al is 2% by mass, and no other additives are added. Note that ZnO added with Ga may be used instead of Al, or pure ZnO treated with hydrogen plasma may be used.

Further, the diffraction member 3 uses a polarizing grating which is a transmission type diffraction member. In this embodiment, as the diffraction member 3, for example, "Polarization Grating" manufactured by Edmund Optics Japan Co., Ltd. can be used. This "Polarization Grating" has the same phase difference as a 1/2 wavelength plate, and its optical axis rotates at a constant period. Further, as shown in FIG. 2A, an optical adhesive layer 4a having the same refractive index as the transparent substrate 4 is provided on the outer surface of the transparent substrate 4.

As shown in FIG. 2(A), the electrode 6A is composed of a positive electrode 6P and a negative electrode 6M. These positive electrodes 6P and negative electrodes 6M each have a comb-like shape when viewed from the out-of-plane direction of the transparent substrate 4 (the direction in which the surface of the transparent substrate 4 is viewed from the front), as shown in FIG. 2(B). is formed. Further, the positive electrodes 6P and the negative electrodes 6M are alternately arranged in the in-plane direction of the transparent substrate 4 (vertical direction in the figure), as shown in FIG. 2(B).

In this application, in order to make it easier to understand the structure of the electrode 6 (see FIG. 1(B)), the dimensions of each member in the thickness direction are compressed and illustrated. For example, in FIG. 2A, if the vertical scale is 1, the horizontal scale is approximately 1/6. The same applies to FIGS. 3 and 54. Furthermore, although the dimensions of the positive electrode 6P and negative electrode 6M of the electrode 6A cannot be identified with the naked eye, in FIG. It is illustrated in the figure.

As shown in FIG. 2A, in the liquid crystal panel 2A of the first embodiment, the width W ₆ of the positive electrode 6P and the negative electrode 6M and the interval W ₅ between these electrodes are formed to have the same length. In this embodiment, the thickness is set to 2 μm. Therefore, the plurality of transparent spacers 61 in this embodiment are periodically arranged at equal intervals in the in-plane direction of the transparent substrate 4 in the direction of the electric field.

Here, the distance between one transparent electrode 62 of the positive electrode 6P formed on the transparent spacer 61 and one transparent electrode 62 of the negative electrode 6M formed on the adjacent transparent spacer 61, that is, as shown in FIG. If the interval is the sum of the interval W ₅ between the liquid crystals and the width W ₆ of the transparent spacer 61 and the transparent electrode 62 in , the interval can be set to 1/2 to 4 times the wavelength of the light used.

In such a periodic structure, in addition to the 0th order (the light of the order in which the incident light propagates while preserving the same direction), the light of higher orders (±1st order, ±2nd order, etc.) Occur. In this technique, 0th order light is used, and higher order light is unnecessary light and needs to be made as small as possible.

Generally, when light is incident on a periodic structure, the output light is given by the following equation.
sinθ=sinθo+m・λ/Λ (1)
Here, θo is the incident angle defined by the angle made with the perpendicular to the transparent substrate 4 θ is the output angle defined by the angle made with the perpendicular to the transparent substrate 4 m is the order (0, ±1, ±2, etc.)
λ is the wavelength in vacuum Λ is the period of the transparent spacer (W ₅ + W ₆ )

If the period (W ₅ + W ₆ ) is smaller than 1/2 of the wavelength of the light used (for example, 1.55 μm), there is no solution to equation (1) for almost any incident angle θo (sin θ is less than 1). (larger) and higher orders (±1st order, ±2nd order, . . . ) are no longer generated, and although desired performance can be obtained, resist exposure and etching processing become extremely difficult. Further, if the interval (W ₅ +W ₆ ) exceeds four times the wavelength of the light used, unnecessary orders (±1st order, ±2nd order, . . . ) will occur, causing a disadvantage of loss.

With this configuration, when visible light (wavelength of about 0.3 to 0.7 μm) is used, the liquid crystal panel 2A can be used as goggles for VR (Virtual Reality), a head-up display for vehicles, Alternatively, it can be used in a liquid crystal panel for a display that projects images onto a wall or screen. Furthermore, when near-infrared light (wavelength of about 0.7 to 2.5 μm) is used, the liquid crystal panel 2A can be used as a scanner for LiDAR or other object detection sensors.

Further, the height (thickness) H ₆ of the upright surface 61a of the positive electrode 6P and the negative electrode 6M is set to 4 μm to 16 μm, and is set to 8 μm in this embodiment. The height H ₆ of this upright surface 61a is preferably set to 70% or more of the distance H ₅ between the pair of transparent substrates 4, and is set to 80% in this embodiment. Note that although the angle of the upright surface 61a with respect to the transparent substrate 4 is 90° in this embodiment, it may be set within the range of 70° to 90°.

As shown in FIG. 2(B), a power supply electrode 7 is connected to the root portions of the comb teeth of the positive electrode 6P and the negative electrode 6M. Due to this power supply electrode 7, the voltages of the positive electrode 6P and the negative electrode 6M become relatively positive and negative, and an electric field is generated between the positive electrode 6P and the negative electrode 6M. The positive electrode 6P and the negative electrode 6M are reversed at a certain time by an external driver (not shown) to perform a switching operation.

Here, the relationship between the liquid crystal panel 2A and the director D of the diffraction member 3 in the optical switching element 1A of this embodiment is shown in FIG. 1(B). As shown in FIG. 1(B), the diffraction member 3 has a birefringent director D rotating in one direction around a rotation axis A at a predetermined period, and generates a circularly polarized light beam. It has the function of deflecting the output light beam to the right or left in the direction of rotation of circularly polarized light.

As shown in FIG. 1(B), in the optical switching element 1A of this embodiment, the positive electrode 6P and the negative electrode 6M are formed in a comb-like shape, and the direction in which each electrode extends and the director D The liquid crystal panel 2A and the diffraction member 3 are combined so that the rotational axes A of the two are aligned (within ±10°). With this configuration, even if the angle of incident light is tilted in the X direction in the figure (the direction in which each electrode extends), the light transmission efficiency can be maintained unchanged.

On the other hand, if the angle of the incident light is tilted in the Y direction (direction of electric field) in the figure, the period consisting of the width W ₆ of the positive electrode 6P and the negative electrode 6M and the interval W ₅ between these electrodes, and The transmission efficiency changes due to the difference in refractive index between the liquid crystal 5 and the transparent spacer 61, which will be described later. In particular, as the applied voltage increases, the difference in refractive index between the liquid crystal 5 and the transparent spacer 61 increases, a high-order light beam is generated, and the transmittance of the zero-order light beam decreases greatly.

The light transmission efficiency when the light angle is tilted in the Y direction is less degraded as the period determined by the dimensions of W ₆ and W ₅ is smaller, but resist exposure and etching processing become difficult. According to verification by the inventors of the present application, the dimensions of the width W ₆ of the positive electrode 6P and the negative electrode 6M and the interval W ₅ between these electrodes are preferably within 1/4 to 2 times the wavelength of the incident light. . Further, it is desirable that the difference in refractive index between the liquid crystal refractive index (ni) and the transparent spacer 61 when no electric field is applied be within 0.05. Furthermore, it is preferable to set the refractive index difference between the transparent spacer 61 and the refractive index between ordinary light (no) and extraordinary light (ne) of the refractive index ellipsoid of the liquid crystal when an electric field is applied.

As described above, it is better that the width W ₆ of the positive electrode 6P and the negative electrode 6M and the interval W ₅ between these electrodes are smaller, but at present, due to limitations in manufacturing technology, the widths W ₆ and W ₅ is in the range of 0.2 μm to 6 μm. Further, the height H ₆ of the upright surface 61a is preferably higher because the higher the voltage, the lower the voltage. However, also for reasons of manufacturing technology, the height H ₆ is in the range of 2 μm to 25 μm. Further, the height H ₆ of this upright surface 61a is preferably 70% or more of the distance H ₅ between the pair of transparent substrates 4, and in this embodiment is set to 84%.

Next, with reference to FIG. 3, the state of the electric field in the liquid crystal panel 2A of the first embodiment will be described. FIG. 3 is an explanatory diagram showing contour lines and directions of an electric field when a voltage is applied to the electrodes of the liquid crystal panel 2A.

As shown in FIG. 3, when a voltage is applied to the positive electrode 6P and negative electrode 6M of the electrode 6A, an electric field is generated between the positive electrode 6P and the negative electrode 6M in the direction from the positive electrode 6P to the negative electrode 6M, as shown by the arrow in the figure. arise. The direction of this electric field is parallel to the transparent substrate 4 between the positive electrode 6P and the negative electrode 6M, and coincides with the in-plane direction of the transparent substrate 4. In addition, although the liquid crystal 5 is interposed between the electrode 6A located on the left side and the electrode 6A located on the right side in the figure, an electric field parallel to the transparent substrate 4 is also generated in the liquid crystal 5 between the electrodes 6A. There is.

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 as the liquid crystal 5, and as shown in FIG. 3(B), by applying an electric field, the refractive index ellipsoid 5a in the liquid crystal 5 is can be arranged in parallel. When the liquid crystal panel 2A is irradiated with light in this state, the action of the liquid crystal 5 can efficiently cause retardation in the light passing through the liquid crystal panel 2A.

On the other hand, when no electric field is applied between the positive electrode 6P and the negative electrode 6M, the refractive index ellipsoid 5a in the liquid crystal becomes a spherical refractive index ellipsoid (not shown) in side view, and is optically isotropic (isotropic). Even if the liquid crystal panel 2A is irradiated with light, no retardation occurs in the light passing through the liquid crystal panel 2A.

In this way, the high-speed polymer-stabilized blue phase liquid crystal can be switched by turning on and off the electric field between the positive electrode 6P and the negative electrode 6M. Therefore, the liquid crystal panel 2A using the electrode 6A of this embodiment can form an optical switching element 1A capable of high-speed switching. Here, for convenience, the electrode 6A is designated as a positive electrode 6P and a negative electrode 6M, but in reality, the positive and negative electrodes are controlled by an alternating voltage that is reversed in time, so the positive electrode 6P and the negative electrode 6M are alternately switched.

Furthermore, in the liquid crystal panel 2A of the first embodiment, germanium dioxide-doped quartz glass is used for the transparent spacer 61, and its refractive index is adjusted to fall within a predetermined range of the refractive index of the liquid crystal layer. As a result, even when the incident light is oblique, the refractive index contrast is reduced, so the loss of the transmitted zero-order light is reduced without being coupled to higher-order light such as ±1st and ±2nd orders. be able to.

Specifically, the refractive index of the transparent spacer 61 is adjusted to a value between n _o (E) and n _e (E) below, which is the refractive index of liquid crystal. Here, n _o (E) is the refractive index of ordinary light when an electric field is applied, and n _e (E) is the refractive index of extraordinary light when an electric field is applied, and is expressed by the following formula.
n _o (E) = n _i -Δn _ind (E)/3 (2A)
n _e (E) = n _i +2Δn _ind (E)/3 (2B)

However, n _i is the refractive index when no electric field is applied, and Δn _ind (E) is the difference between the two refractive indexes taking into account the influence of the extended Kerr effect, which is expressed by the following formula. Ru.
Δn _ind (E)=Δn _S (1-exp[-(E/E _s ) ² ]) (3)
Here, Δn _S is the saturation refractive index change and E _s represents the saturation electric field.

FIG. 4(A) is a graph showing changes in the refractive index of the liquid crystal 5 when no electric field is applied, and changes in n _o (E) and n _e (E) when an electric field is applied. In the graph of FIG. 4(B), the vertical axis is the refractive index difference Δn between _no (E) and _ne (E), and the horizontal axis is the value of the square of the applied voltage. Generally, when an electric field (E) is applied to a blue-phase liquid crystal, the refractive index difference Δn is dominated by the Kerr effect in which the refractive index difference changes in proportion to the square of E in a small voltage region.

However, in a large voltage region, the refractive index difference Δn also tends to be saturated, as shown in FIG. 4(B), due to saturation of the refractive index of ordinary light ( _no ) and extraordinary light ( _ne ). Therefore, in this embodiment, formula (3) is used to accurately derive the refractive index of n _o (E) and n _e (E) at a large voltage, and the refractive index of the transparent spacer 61 is The substance doped into the quartz glass and the amount of doping are adjusted so that the value of n _o and n _e of 4(A) is obtained. Here, quartz glass is doped with germanium dioxide.

Note that the electrode 6A in the first embodiment is made by, for example, forming a layer doped with germanium dioxide on one surface of quartz glass, etching it into the shape of the electrode, adhering zinc oxide to the surface, and etching it. It can be formed by removing unnecessary zinc oxide through processing. Alternatively, the electrode 6A may be made of quartz glass doped with germanium dioxide from the beginning.

Next, referring to FIG. 5, 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. The liquid crystal panel 2B of the second embodiment is different from the electrode 6A of the first embodiment in that the electrode 6B is fixed to only one side of the transparent substrate 4. Note that the same configurations as those in the first embodiment are given the same reference numerals and detailed explanations will be omitted.

As shown in FIG. 5, in the electrode 6B of the second embodiment, a transparent spacer 61 and a transparent electrode 62 are provided on the inner surface of the transparent substrate 4 on the right side of the figure, and a transparent spacer 61 and a transparent electrode 62 are provided on the inner surface of the transparent substrate 4 on the left side of the figure. The electrode 6B is not provided. Liquid crystal 5 is filled between the inner surface of transparent substrate 4 and transparent spacer 61 on the left side of the figure.

The electrode 6B of the second embodiment, like the electrode 6A of the first embodiment, is provided with a positive electrode 6P and a negative electrode 6M, and a liquid crystal layer is formed between them, and these structures are shown in FIG. 2(B). It is similar to Further, the height (thickness) H ₆ of the upright surface 61a of the positive electrode 6P and the negative electrode 6M is set to 4 μm to 16 μm, and is set to 16 μm in this embodiment. The height H ₆ of this upright surface 61a is preferably set to 70% or more of the distance H ₅ between the pair of transparent substrates 4, and is set to 80% in this embodiment.

Also in the electrode 6B of the second embodiment, the direction of the electric field between the positive electrode 6P and the negative electrode 6M is parallel to the transparent substrate 4, and coincides with the in-plane direction of the transparent substrate 4, as in the first embodiment. It is possible to generate an electric field that

Next, with reference to FIG. 6, the optical switching element stack 10 will be described. The optical switching element laminate 10 is made by laminating 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 optical switching elements is appropriately selected depending on the angular resolution (minimum deflection angle for switching), maximum deflection angle, etc.

FIG. 6(B) is a diagram schematically showing a cross section of the liquid crystal panel 2A of the optical switching element stack 10 of FIG. 6(A). As shown in FIG. 6(B), the optical switching element 1A has a transmission type diffraction member 3 attached to one surface of a liquid crystal panel 2A.

In the optical switching element laminate 10 of this embodiment, the surface on which the diffraction member 3 is mounted is the front surface, and the other side is the back surface, and the front surface is disposed on the downstream side in the direction of light incidence, and other surfaces are placed on this surface. It is formed by attaching the back side of the optical switching element 1A.

In this embodiment, the deflection angle of the diffraction member 3 provided on the downstream side is set larger than the polarization angle of the diffraction member 3 provided on the upstream side in the light incident direction. For example, if the polarization angle of the diffraction member 3 on the upstream side of the light incident direction is 0.1°, and the polarization angle of the second diffraction member 3 is 0.2°, the polarization angle increases by twice on the downstream side. The structure is as follows.

By changing the polarization angle of the diffraction member 3 from the upstream side to the downstream side in the direction of light incidence, it is possible to increase the output angle of the emitted light and irradiate a wide range of the emitted light. . Although this structure is a one-dimensional optical switching element, a two-dimensional optical switching element can be realized by using two sets and arranging them rotated by 90 degrees.

Both the optical switching element 1A and the optical switching element 1B of this embodiment can operate at a voltage of about 10V or less. This optical switching element is suitable for on-vehicle LiDAR because it can be operated without using a booster or the like in hybrid vehicles, electric vehicles, and ordinary vehicles with internal combustion engines.

In the above embodiment, a polymer-stabilized blue-phase liquid crystal is used as the liquid crystal 5, but the present invention is not limited to this, and when a voltage is applied, the refractive index ellipsoid 5a has a long axis along the direction of the electric field. Liquid crystals made of other materials may be used as long as they have the characteristics.

Further, in the above embodiment, germanium dioxide (GeO ₂ )-doped quartz glass is used for the transparent spacer 61, but the material is not limited to this, and diphosphorus pentoxide (P ₂ O ₅ ), titanium dioxide (TiO ₂ ), etc. A dopant that increases the refractive index of quartz glass may also be used. Further, in the above embodiment, the transparent electrode 62 is made of aluminum-added zinc oxide (ZnO), but zinc oxide may contain other additives such as Ga. Alternatively, in the wavelength range of visible light, ITO (Indium Tin Oxide) may be used instead of ZnO.

Next, a method for manufacturing a substrate for a liquid crystal panel according to the present invention will be explained with reference to FIG. The method for manufacturing a substrate for a liquid crystal panel according to the present embodiment is a method for manufacturing a substrate 40 (see FIG. 7(G)) that can be used for a liquid crystal panel having the same configuration as the liquid crystal panel 2A or the liquid crystal panel 2B. . The substrate 40 in this embodiment is formed by integrally forming the transparent substrate and transparent spacer in the above embodiments.

The manufacturing method of this embodiment includes a mask layer forming step of forming a mask layer 42 on the surface of a material substrate 41 that is a material of a transparent substrate and transparent spacers, and a pattern resist that becomes a predetermined pattern of transparent spacers on the surface of the mask layer. A patterned resist layer forming step for forming the layer 43, a first etching step for etching the mask layer 42 in the shape of the patterned resist layer 43, and a transparent etching step for etching the material substrate 41 so that the pattern shape has a predetermined thickness. a second etching step of forming a transparent spacer 61 having an upright surface 61a standing up on the surface of the substrate 4; a mask layer removal step of removing the mask layer 42 after the second etching step; and a transparent spacer 61 including the transparent substrate 4 and the upright surface 61a. A transparent electrode forming step of forming an electrode film 44 forming a transparent electrode on the surface of the spacer 61, and etching the electrode film 44 on the flat parts of the transparent substrate 4 and the transparent spacer 61, leaving the electrode film 44 on the upright surface 61a. A selective sputter etching step is provided to form a transparent electrode 62.

First, in a mask layer forming step, a mask layer 42 is formed on the surface of a material substrate 41, as shown in FIG. 7(A). In this embodiment, quartz glass is used as the material for the material substrate 41. Further, chromium (Cr) is used as the material of the mask layer 42. The mask layer 42 is formed on the surface of the material substrate 41 using a commonly used sputtering method. Alternatively, the mask layer 42 can also be formed by known electron beam evaporation. In addition to chromium (Cr), other metals such as tungsten silicide (WSix) can also be used as the material for the mask layer 42 .

Next, in a patterned resist layer forming step, a patterned resist layer 43 that becomes a pattern of transparent spacers 61 is formed on the surface of the mask layer 42, as shown in FIG. 7(B). The patterned resist layer 43 can be formed by a method such as photoresist using a known photosensitive film. In this embodiment, a novolac resin is used as the material for the patterned resist layer 43, but a commercially available photoresist can be used.

Next, a first etching step shown in FIG. 7(C) is performed. In this first etching step, a mask layer 42 is formed in the shape of the patterned resist layer 43 using a technique called RIE (Reactive Ion Etching). In the etching process, for example, chlorine-based gas is turned into a plasma state by discharging under reduced pressure, and active species such as generated ions and neutral radicals react with the mask layer 42 to be etched, thereby shaping the mask layer 42 into a desired shape. This is an etching process. This etching treatment may be a treatment using an etching solution capable of removing the chromium film.

Next, a second etching step shown in FIG. 7(D) is performed. In this second etching step, an etching process is performed to remove the patterned resist layer 43 and to etch the material substrate 41 to a thickness necessary for the transparent spacers 61. In this embodiment, a known method called reactive ion etching (RIE) is used in the second etching step. In the second etching step, by using RIE using fluorine-based gas, the material substrate 41 can be efficiently processed.

Next, as shown in FIG. 7E, the mask layer 42 is removed by a mask layer removal step, thereby forming the transparent substrate 4 and transparent spacers 61 from the material substrate 41. The mask layer 42 is removed by an etching process that can remove the chromium film.

Next, a transparent electrode forming step shown in FIG. 7(F) is performed. In this embodiment, in this transparent electrode forming step, an AZO (Al-doped ZnO) film is formed using ALD technology on the surfaces of the transparent substrate 4 and the transparent spacers 61 from which the mask layer 42 has been removed in the mask layer removing step. An electrode film 44 is formed. In this embodiment, the electrode film 44 is formed to have a thickness of 30 to 40 nm so that it can be used as the transparent electrode 62.

Next, a selective sputter etching step shown in FIG. 7(G) is performed. In this embodiment, the electrode film 44 on the flat parts of the transparent substrate 4 and the transparent spacer 61 is etched, leaving the electrode film 44 on the upright surface 61a to form the transparent electrode 62. In the selective sputter etching step in this embodiment, active species are irradiated from the normal direction of the surfaces of the transparent substrate 4 and the transparent spacer 61 in dry etching, so that the active species does not come into contact with the upright surface 61a of the transparent spacer 61. Etching is being done.

By this process, only the electrode film 44 on the surfaces of the transparent substrate 4 and the transparent spacer 61 is removed, and the electrode film 44 on the raised surface of the transparent spacer 61 remains, and this electrode film 44 becomes the transparent electrode 62. In this way, in the manufacturing method of this embodiment, the transparent electrode 62 can be efficiently formed on the transparent spacer 61 by the selective sputter etching step.

Note that in the above embodiment, the patterned resist layer 43 is removed in the second etching step, but is not limited to this, and may be removed in the first etching step or mask layer removal step.

1A, 1B... Optical switching elements 2A, 2B... Liquid crystal panel 3... Diffraction member 4... Transparent substrate 4a... Optical adhesive layer 40... Substrate 41... Material substrate 42... Mask layer 43... Patterned resist layer 44... Electrode film 5... Liquid crystal (liquid crystal layer)
5a... Refractive index ellipsoid 6A, 6B... Electrode 6P... Positive electrode 6M... Negative electrode 61... Transparent spacer 61a... Upright surface 62... Transparent electrode 7... Power supply electrode 10... Optical switching element laminate

Claims (10)

A liquid crystal panel in which electrodes and liquid crystal are held between a pair of transparent substrates,
A plurality of transparent spacers each having an upright surface where the electrode stands up against the inner surface of the transparent substrate are arranged such that the upright surfaces face each other, and a transparent electrode serving as a positive electrode and a negative electrode are respectively provided on the facing upright surfaces. Form a transparent electrode that becomes
A liquid crystal layer filled with the liquid crystal is provided between the transparent electrode serving as the positive electrode and the transparent electrode serving as the negative electrode,
the liquid crystal in the liquid crystal layer is a polymer stabilized blue phase liquid crystal;
A refractive index ellipsoid made of a director in the liquid crystal has a property that when a voltage is applied to the electrode to generate an electric field, the long axis is along the direction of the electric field,
The plurality of transparent spacers are formed in a line or rod shape extending in a predetermined direction in the in-plane direction of the transparent substrate, and are arranged periodically at equal intervals in the direction of the electric field,
A liquid crystal panel characterized in that a width of the transparent spacer in the direction of the electric field and a width of the liquid crystal layer in the direction of the electric field are the same or within a range of ±50%. A liquid crystal panel in which electrodes and liquid crystal are held between a pair of transparent substrates,
A plurality of transparent spacers each having an upright surface where the electrode stands up against the inner surface of the transparent substrate are arranged such that the upright surfaces face each other, and a transparent electrode serving as a positive electrode and a negative electrode are respectively provided on the facing upright surfaces. Form a transparent electrode that becomes
A liquid crystal layer filled with the liquid crystal is provided between the transparent electrode serving as the positive electrode and the transparent electrode serving as the negative electrode,
the liquid crystal in the liquid crystal layer is a polymer stabilized blue phase liquid crystal;
A refractive index ellipsoid made of a director in the liquid crystal has a property that when a voltage is applied to the electrode to generate an electric field, the long axis is along the direction of the electric field,
The plurality of transparent spacers are formed in a line or rod shape extending in a predetermined direction in the in-plane direction of the transparent substrate, and are arranged periodically at equal intervals in the direction of the electric field,
When the interval between one electrode of the transparent spacer and one electrode of the transparent spacer adjacent to the transparent spacer is defined as a period, the period is set to 1/2 or more and 4 times or less of the wavelength of the light used. A liquid crystal panel characterized by: The liquid crystal panel according to claim 1 or 2,
A liquid crystal panel characterized in that the refractive index of the transparent spacer is set to a value between the refractive index of ordinary light and the refractive index of extraordinary light when an electric field is applied to the liquid crystal. The liquid crystal panel according to claim 1 or 2,
A liquid crystal panel characterized in that the transparent electrode is formed of a material whose main raw material is zinc oxide. The liquid crystal panel according to claim 1 or 2,
A liquid crystal characterized in that the transparent spacer and the transparent electrode are provided on the inner surfaces of both of the pair of transparent substrates, and the liquid crystal layer is provided between one of the transparent spacers and the other transparent spacer. panel. The liquid crystal panel according to claim 1 or 2,
A liquid crystal panel characterized in that the transparent spacer and the transparent electrode are provided on the inner surface of one of the transparent substrates, and the liquid crystal layer is provided between the transparent spacer and the inner surface of the other transparent substrate. The liquid crystal panel according to claim 1 or 2,
A liquid crystal panel characterized in that a thickness of the transparent spacer in an out-of-plane direction of the transparent substrates is formed to be 70% or more and 95% or less of the distance between the pair of transparent substrates. An optical switching element using a liquid crystal panel in which electrodes and liquid crystal are held between a pair of transparent substrates,
The liquid crystal panel includes a plurality of transparent spacers in which the electrodes have raised surfaces that stand up against the inner surface of the transparent substrate, and a plurality of transparent spacers are arranged so that the raised surfaces face each other, and a positive electrode and a positive electrode are respectively arranged on the facing raised surfaces. A transparent electrode that will become a negative electrode and a transparent electrode that will become a negative electrode are formed.
A liquid crystal layer filled with the liquid crystal is provided between the transparent electrode serving as the positive electrode and the transparent electrode serving as the negative electrode,
the liquid crystal in the liquid crystal layer is a polymer stabilized blue phase liquid crystal;
A refractive index ellipsoid consisting of a director in the liquid crystal has a property that when a voltage is applied to the electrode to generate an electric field, the long axis is along the direction of the electric field,
The plurality of transparent spacers are formed in a line or rod shape extending in a predetermined direction in the in-plane direction of the transparent substrate, and are arranged periodically at equal intervals in the direction of the electric field,
A transmission type diffraction member is attached to one surface of the transparent substrate,
The diffraction member has a director having birefringence that rotates in one direction around a rotation axis at a predetermined period,
An optical switching element characterized in that the diffraction member is mounted on the transparent substrate with the direction of the rotation axis of the director of the diffraction member facing the extending direction of the transparent electrode. An optical switching element laminate in which the optical switching elements according to claim 8 are laminated,
When the surface of the optical switching element on which the diffraction member is attached is the front surface, and the other surface is the back surface,
An optical switching element laminate, characterized in that the back surface of another optical switching element is attached to the front surface of the optical switching element. The optical switching element laminate according to claim 9,
The diffraction member attached to the plurality of stacked optical switching elements is
An optical switching element laminate, characterized in that the deflection angle of the diffraction member located on the downstream side is set larger than that of the diffraction member located on the upstream side in the direction of light incidence.

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