Optical scanning element

Abstract

To provide an optical scanning element that has a large scanning angle and quick response, and can be downsized.SOLUTION: An optical scanning element according to an embodiment of the present invention comprises: first optical deflection means emitting light to a first region; and second optical deflection means emitting the light emitted to the first region to a second region wider than the first region. The first optical deflection means is configured such that a refractive index is varied by varying an application voltage and such the variation in the refractive index causes the first region to be adjusted. The second optical deflection means is configured so as to adjust the second region by diffraction.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present invention relates to an optical scanning element. [Background technology]

[0002] Due to the development of multimedia and digital signage, the demand for high-definition, high-image-quality, large-screen displays and projectors is increasing, and the development of optical scanning elements that scan laser light at a wide angle is becoming more active. In recent years, optical scanning elements can be used as laser radars, laser scanners, and LiDAR (Light Detection and Ranging), and therefore their application to obstacle detection systems and distance measurement systems for automatic driving control of automobiles, or for position control of robots or drones has been considered. As an example of an optical scanning element, an optical deflector with a radiation mechanism provided in a silicon photonic crystal waveguide has been proposed (Patent Documents 1 to 4). However, such optical deflectors are configured to change the deflection angle for each wavelength or to change the deflection angle by heating the element, and the scanning angle is not sufficient when used for the above-mentioned applications. In addition, the type in which the deflection angle changes for each wavelength has the problem of requiring multiple light sources with different wavelengths, and the type that heats has the problem of slow response. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2017 / 126386 [Patent Document 2] International Publication No. 2018 / 003852 [Patent Document 3] International Publication No. 2018 / 186471 [Patent Document 4] Patent No. 4208754 Summary of the Invention [Problem to be solved by the invention]

[0004] A primary object of the present invention is to provide an optical scanning element which has a large scanning angle, a fast response, and can be made compact. [Means for solving the problem]

[0005] An optical scanning element according to an embodiment of the present invention includes a first optical deflection means for emitting light to a first region, and a second optical deflection means for emitting the light emitted to the first region to a second region larger than the first region. The first optical deflection means is configured to change a refractive index due to a change in an applied voltage, and adjust the first region by the change in refractive index; the second optical deflection means is configured to adjust the second region by diffraction. In one embodiment, the first optical deflection means is one selected from the group consisting of a combination of a photonic crystal and a diffraction grating, an optical phase array, and a variable optical metasurface. In one embodiment, the second optical deflection means is a diffraction grating. In one embodiment, the first optical deflection means comprises a photonic crystal layer formed in an electro-optic crystal substrate with periodic holes; an optical waveguide having a line defect formed in the photonic crystal layer; a diffraction grating provided in at least one portion selected from the upper portion, left side portion and right side portion of the optical waveguide; and electrodes provided on the left and right sides of the optical waveguide, and is configured to change the emission angle of light emitted from the upper surface of the optical waveguide. In one embodiment, the diffraction grating has a plurality of grating grooves extending in a direction substantially perpendicular to the waveguiding direction of the optical waveguide. In one embodiment, the second optical deflection means is a diffraction grating having grating grooves, and the direction in which the grating grooves extend in the first optical deflection means is substantially perpendicular to the direction in which the grating grooves extend in the second optical deflection means. In another embodiment, the second optical deflection means is a diffraction grating having grating grooves, and the direction in which the grating grooves extend in the first optical deflection means is substantially parallel to the direction in which the grating grooves extend in the second optical deflection means. In one embodiment, the first light deflection means is provided below the electro-optic crystal substrate and further includes a support substrate supporting the electro-optic crystal substrate; a joint portion integrating the electro-optic crystal substrate and the support substrate; and a cavity defined by the lower surface of the electro-optic crystal substrate, the upper surface of the support substrate, and the joint portion. In one embodiment, the electro-optic crystal substrate is composed of one selected from the group consisting of lithium niobate, lithium tantalate, potassium titanyl phosphate, potassium lithium niobate, potassium niobate, potassium tantalate-potassium niobate, and a solid solution of lithium niobate and lithium tantalate. Effect of the Invention

[0006] According to an embodiment of the present invention, in an optical scanning element, a first optical deflection means configured to change a refractive index by a change in an applied voltage and adjust a first region, which is a light emission region, by the change in the refractive index, and a second optical deflection means for diffracting the light emitted to the first region to a second region larger than the first region are used in combination. This makes it possible to realize an optical scanning element that has a large scanning angle, a fast response, and can be made compact. [Brief description of the drawings]

[0007] [Figure 1A] 1 is a conceptual diagram illustrating a mechanism by which the scanning range of light is expanded according to one embodiment of the present invention. [Figure 1B] 10A and 10B are conceptual diagrams illustrating a mechanism by which the scanning range of light is expanded according to another embodiment of the present invention. [Figure 2A] 1 is a schematic perspective view showing a first optical deflection means in an optical scanning element according to one embodiment of the present invention. [Figure 2B] 2B is a schematic perspective view of an optical scanning element including the first optical deflection means of FIG. 2A. [Figure 3A] FIG. 4 is a schematic perspective view showing a first optical deflection means in an optical scanning element according to another embodiment of the present invention. [Figure 3B]3B is a schematic perspective view of an optical scanning element including the first optical deflection means of FIG. 3A. [Figure 4] 2 is a schematic cross-sectional view of an example of a first optical deflection means in the optical scanning element according to the embodiment of the present invention. FIG. [Diagram 5] 5 is a schematic cross-sectional view of another example of a first optical deflection means in the optical scanning element according to the embodiment of the present invention. FIG. [Figure 6] 3 is a schematic cross-sectional view illustrating the propagation and emission (radiation) of light in a diffraction grating that can be used in a first optical deflection means of an optical scanning element according to an embodiment of the present invention. FIG. [Figure 7] 1 is a graph showing the wavelength dependency of the equivalent refractive index difference. [Figure 8] 1 is a graph showing the relationship between the equivalent refractive index difference and the applied voltage (electric field) at different wavelengths. [Figure 9] 9(a) to 9(e) are schematic cross-sectional views illustrating an example of a method for manufacturing an optical scanning element according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the embodiments of the present invention will be described, but the present invention is not limited to these embodiments. In this specification, "left side" or "right side" means the left side or right side with respect to the waveguiding direction of the optical waveguide (the traveling direction of light in the optical waveguide: also referred to as the optical waveguiding direction). "Substantially parallel" includes the angle between two directions being 0°±5°, preferably 0°±3°, and more preferably 0°±1°. "Substantially orthogonal" includes the angle between two directions being 90°±5°, preferably 90°±3°, and more preferably 90°±1°. In addition, when simply referring to "parallel" or "orthogonal", it includes "substantially parallel" or "substantially orthogonal".

[0009] A. Concept and schematic configuration of optical scanning element First, a mechanism by which the scanning range of light is expanded according to the embodiment of the present invention will be conceptually explained. FIG. 1A and FIG. 1B are each a conceptual diagram explaining such a mechanism. The optical scanning element 300 has a first optical deflection means 100 and a second optical deflection means 200. The first optical deflection means 100 emits light (light incident on the optical scanning element) to a first region A1. The first optical deflection means 100 is typically configured to change its refractive index with a change in applied voltage, and adjust the first region with the change in refractive index. More details are as follows. The light emitted from the first optical deflection means 100 is typically a so-called fan beam that is linear in plan view (linear in a direction perpendicular to the optical waveguide direction) and fan-shaped when viewed from the optical waveguide direction. The variable range α of the emission angle can be adjusted by changing the refractive index by applying a voltage to the first optical deflection means 100. As a result, the length of the first region A1 in the optical waveguide direction can be adjusted. That is, in the illustrated example, the first light deflection means 100 can emit light (fan beam) to any position in the light guide direction of the first region A1. The angle of the fan (the spread angle of the fan beam) φ can be controlled by adjusting the width of the light guide. In this way, the first light deflection means 100 can adjust the first region A1 (substantially, the shape of the first region: the length in the light guide direction and in the direction perpendicular to the light guide direction). Furthermore, by adopting a configuration in which the refractive index changes with the change in applied voltage as the first light deflection means and the light emission region is adjusted with the change in the refractive index, the following advantages can be obtained. That is, such a first light deflection means can continuously change the emission angle by continuously changing the voltage. Therefore, an optical scanning element using such a first light deflection means can irradiate a target object without causing irradiation defects. As a result, an extremely excellent resolution can be realized, and the safety and reliability can be significantly improved when the optical scanning element is used as a LiDAR.In the illustrated example, for ease of viewing, the first region A1 is defined at a position a predetermined distance away from the first optical deflection means 100, but since the first optical deflection means 100 and the second optical deflection means 200 are close to each other, the difference in the area of ​​the first region A1 due to the difference in the distance from the first optical deflection means 100 does not pose a problem. In practice, the first region A1 may be defined at the position of the second optical deflection means 200.

[0010] The first optical deflection means 100 may have any suitable configuration as long as the refractive index changes with a change in the applied voltage and the first region can be adjusted with the change in the refractive index. Examples of such configurations include a combination of a photonic crystal and a diffraction grating, an optical phase array, and a variable optical metasurface. As a representative example, a combination of a photonic crystal and a diffraction grating will be described in section B below. The optical phase array controls the phase of the input light distributed to the waveguide array by an electro-optic effect to control the deflection direction. The array may be one-dimensional (linear) or two-dimensional (matrix-like). One-dimensional arrays are preferred. This is because they have a high affinity with the second optical deflection means (typically, a diffraction grating). As the optical phase array, for example, the configuration described in JP-T-2017-521734 can be adopted. A metasurface is a technology that controls the transmittance, phase, deflection direction, wavefront, etc. of light using a structure with a size smaller than the wavelength. A variable metasurface is a metasurface that can control optical characteristics by adding, for example, a mechanical, optical, or electro-optical deformation mechanism. An example of a variable optical metasurface is a configuration in which the deflection direction is controlled by applying different voltages to each of the optical resonant antennas arranged in a one-dimensional array. As in the case of the optical phase array described above, such a one-dimensional array configuration has a high affinity with the second optical deflection means (typically, a diffraction grating). For example, a configuration described in U.S. Pat. No. 10,665,953 can be adopted as the variable optical metasurface. Note that the first optical deflection means 100 can only be a configuration in which the refractive index is directly changed by an electric field, and does not include, for example, a configuration in which the refractive index is changed by utilizing the thermo-optical effect due to Joule heat of a current generated by application of a voltage.

[0011] The second light deflection means 200 outputs the light emitted to the first region A1 to a second region A2 wider than the first region A1. The second light deflection means 200 is typically configured to adjust the second region A2 by diffraction. That is, the second light deflection means 200 can be a diffraction grating. By using diffracted light of a predetermined diffraction order of the light emitted to the first region A1, the light can be emitted to the second region A2 wider than the first region A1. The diffraction grating typically has grating grooves. By adjusting the direction in which the grating grooves extend, the second region A2 (substantially, the spread of the second region) can be adjusted. For example, by making the direction in which the grating grooves of the diffraction grating extend substantially parallel to the optical waveguide direction, a ±1st order diffraction image can be formed in a direction substantially perpendicular to the optical waveguide direction due to the diffraction effect on the first region A1, and as a result, it can be spread as the second region A2. Such a configuration may be useful when the first region A1 as shown in FIG. 1A has an elongated shape along the optical waveguide direction. In particular, the first optical deflection means, which adjusts the light output region by changing the refractive index due to a change in the applied voltage, can adjust the output range only in the optical waveguide direction, so the effect of combining the second optical deflection means is remarkable. Also, for example, by making the direction in which the grating grooves of the diffraction grating extend substantially perpendicular to the optical waveguide direction, a ±1st order diffraction image can be formed in the optical waveguide direction due to the diffraction effect on the first region A1, and as a result, it can be expanded as the second region A2. Such a configuration may be useful when the first region A1 as shown in FIG. 1B has an elongated shape along the direction substantially perpendicular to the optical waveguide direction. While it may be difficult to increase the fan beam spread angle φ and the variable range α of the output angle using only the first optical deflection means, by combining the first optical deflection means and the second optical deflection means, when the fan beam output from the first optical deflection means has a large spread angle φ, it is possible to substantially expand the variable range α of the output angle in the optical waveguide direction. Note that the illustrated example depicts a case where 0th order light and ±1st order light are used, but as the diffracted light, any appropriate diffraction order of diffracted light can be used depending on the purpose, as described above.

[0012] In this specification, the term "optical scanning element" encompasses both a wafer on which at least one optical scanning element is formed (optical scanning element wafer) and a chip obtained by cutting the optical scanning element wafer.

[0013] Hereinafter, as a representative example of an optical scanning element, a configuration in which the first optical deflection means is a combination of a photonic crystal and a diffraction grating will be described.

[0014] B. First Light Deflection Means B-1. Overall configuration of first optical deflection means FIG. 2A is a schematic perspective view showing a state in which the second optical deflection means is removed in an optical scanning element according to one embodiment of the present invention, that is, a first optical deflection means; FIG. 2B is a schematic perspective view of an optical scanning element including the first optical deflection means of FIG. 2A. FIG. 3A is a schematic perspective view showing a state in which the second optical deflection means is removed in an optical scanning element according to another embodiment of the present invention, that is, a first optical deflection means; FIG. 3B is a schematic perspective view of an optical scanning element including the first optical deflection means of FIG. 3A. As shown in FIG. 2B and FIG. 3B, an optical scanning element 300 has a first optical deflection means 100 and a second optical deflection means 200. The first optical deflection means 100 will be described with reference to FIG. 2A, FIG. 3A, FIG. 4, and FIG. 5. FIG. 4 is a schematic cross-sectional view of an example of the first optical deflection means; FIG. 5 is a schematic cross-sectional view of another example of the first optical deflection means. The first optical deflection means 100 includes a photonic crystal layer 10 in which holes 12 are periodically formed in an electro-optic crystal substrate; an optical waveguide 16 defined as a portion of the photonic crystal layer 10 in which holes 12 are not formed (i.e., a line defect formed in the photonic crystal layer); a diffraction grating 50 provided on the upper portion and / or the left side portion and / or the right side portion of the optical waveguide 16; and electrodes 40, 40 provided on the left and right sides of the optical waveguide 16. In one embodiment, as shown in the figure, the first optical deflection means 100 may further include a support substrate 30 provided on the lower portion of the electro-optic crystal substrate (photonic crystal layer) 10 and supporting the electro-optic crystal substrate (photonic crystal layer) 10; a junction 20 that integrates the electro-optic crystal substrate (photonic crystal layer) 10 and the support substrate 30; and a cavity 80 defined by the lower surface of the electro-optic crystal substrate (photonic crystal layer) 10, the upper surface of the support substrate 30, and the junction 20. The first optical deflection means 100 is configured such that the refractive index changes depending on a voltage applied between the electrodes 40, 40, and the output angle of the light output from the upper surface of the optical waveguide 16 changes due to the change in the refractive index.

[0015] The diffraction grating 50 may have any suitable configuration as long as it can emit light from the upper surface of the optical waveguide 16. For example, the diffraction grating may be a planar type, a concave-convex type, or a type that utilizes a hologram. In the planar type, the diffraction grating pattern is formed, for example, by a refractive index difference; in the concave-convex type, the diffraction grating pattern is formed, for example, by grooves or slits. Typical diffraction grating patterns include stripes, lattices, dots, and specific shapes (for example, star shapes). The direction and pitch of the stripes, the arrangement pattern of the dots, and the like can be appropriately set according to the purpose. In one embodiment, the diffraction grating 50 has a plurality of grating grooves that extend in a direction substantially perpendicular to the waveguiding direction of the optical waveguide 16. That is, in one embodiment, the diffraction grating has a stripe pattern that is substantially perpendicular to the waveguiding direction of the optical waveguide.

[0016] The diffraction grating 50 may be formed over the entire waveguiding direction of the optical waveguide 16, or may be formed in a predetermined region along the waveguiding direction of the optical waveguide 16. The predetermined region may be one or more. The ratio of the length of the diffraction grating to the length of the optical waveguide is preferably 10% to 90%, and more preferably 20% to 80%. If the ratio of the length is within such a range, the transverse mode shape of light can be stabilized in the part of the optical waveguide where the diffraction grating is not provided, and the light can be favorably output from the upper surface due to the diffraction effect in the diffraction grating region. In addition, a diffracted light pattern with favorable symmetry can be realized, and output light with a smooth intensity distribution and no ripples can be obtained. The position of the diffraction grating in the length direction of the optical waveguide can be appropriately set according to the purpose. The position of the diffraction grating can be determined, for example, according to the circuit or bonding to which the optical scanning element is connected.

[0017] The diffraction grating 50 is preferably provided only directly above the optical waveguide (the diffraction grating may be formed on the electro-optic crystal substrate, may be formed separately from the electro-optic crystal substrate, or may be both). With such a configuration, the diffraction grating and the guided light can effectively interact with each other, resulting in very good diffraction efficiency.

[0018] The electrodes 40, 40 may be provided at any positions on the left and right sides of the optical waveguide 16 as long as they do not adversely affect the performance of the optical waveguide 16. The electrodes 40, 40 are typically provided on the upper surface of the left and right ends of the photonic crystal layer (electro-optical crystal substrate) 10.

[0019] 5 is a schematic cross-sectional view of another example of the first optical deflection means. The first optical deflection means in the illustrated example further has a cladding layer 60 provided on the upper surface of the photonic crystal layer 10. In this embodiment, the diffraction grating 50 is provided on the upper surface of the cladding layer 60 in a portion corresponding to the optical waveguide 16; the electrodes 40, 40 are provided on the upper surface of the cladding layer 60 formed on the left and right ends of the photonic crystal layer (electro-optic crystal substrate) 10. The cladding layer 60 may be formed only between the electrode 40 and the electro-optic crystal (photonic crystal layer) 10, or only directly above the optical waveguide 16.

[0020] The operation of the first light deflection means will be described below, and then the specific configuration of each component of the first light deflection means will be described later in Sections B-3 to B-8. Note that since the electrodes may have a configuration well known and commonly used in the industry, detailed description thereof will be omitted.

[0021] B-2. Operation of the first optical deflection means When the first light deflection means is in operation, light is made incident from the incident surface of the optical waveguide 16. Here, the incident light will be described. The incident light can be a laser light emitted at a single wavelength used for LiDAR. The laser light may have a multi-mode longitudinal mode or a single mode, and the transverse mode may have a multi-mode or a single mode. Preferably, both the longitudinal mode and the transverse mode of the laser light are single mode. With such a configuration, the spread of the laser light can be suppressed and the spatial resolution can be improved. While the incident light propagates through the optical waveguide 16, the diffracted light is emitted from the upper surface of the element due to the action of the diffraction grating 50. A more detailed description will be given with reference to FIG. 6. FIG. 6 is a schematic cross-sectional view illustrating the propagation and emission (radiation) of light in the diffraction grating. In one embodiment, the diffraction grating has a plurality of grating grooves extending in a direction substantially perpendicular to the waveguiding direction of the optical waveguide 16, as described above. The illustrated diffraction grating is a grating pattern in a direction perpendicular to the waveguide direction in a plan view; in a cross section along the waveguide direction, for example, convex portions with a width of Λ / 2 and slits with a width of Λ / 2 are alternately formed. In the slit portion, the optical waveguide below the diffraction grating is exposed. The width Λ of the repeating unit of the convex portions and the slits is defined as the period (pitch) of the diffraction grating. There is no particular limitation on the ratio of the width of the convex portions to the width of the slits, and it is preferable that it is in the range of 1 / 9 to 9 / 1. Light incident on the optical waveguide 16 propagates, for example, with a propagation constant βo in the waveguiding direction. In a diffraction grating with a period Λ, light with a propagation constant that satisfies the phase condition of the following formula (1) propagates. βq=βo+qK(q=0, ±1, ±2, ···) ···( 1 ) Here, βo is the propagation constant of the guided mode in the optical waveguide in the absence of a diffraction grating, and K is expressed by the following formula. K=2π / Λ When there is an order q that satisfies the following formula, light can be emitted (radiated) to both the upper and lower sides of the optical waveguide. |βq| <na·k または |βq|<ns·k Here, na and ns respectively represent the refractive indexes of the upper cladding and the lower cladding of the optical waveguide, and k represents the wave number. As described later, in the first optical deflection means, the cavity 80 functions as the lower cladding, and the upper air portion can function as the upper cladding, so that na and ns can each be 1.

[0022] The emission angles θa and θs with respect to the reference plane can be determined by the following formula (2). Note that the reference plane is a plane having the waveguiding direction of optical waveguide 16 as its normal line (this reference plane also includes the normal line of photonic crystal layer 10). na·k·sinθa=ns·k·sinθs=βq···(2) Furthermore, formula (1) can be expressed as the following formula (3). Here, the condition under which formula (3) actually holds is when q≦-1. Therefore, the first-order diffracted light can be emitted to the outside of the optical waveguide at the emission angles θa and θs calculated when q=-1.

[0023]

number

[0024] As is clear from equation (3), the emission angles θa and θs are wg and may vary depending on the wavelength λ of the incident light, where n wg corresponds to the equivalent refractive index of light propagating through an optical waveguide (line defect optical waveguide) formed by removing one row of holes in a photonic crystal. According to an embodiment of the present invention, by forming a photonic crystal (photonic crystal layer) on an electro-optic crystal substrate, the equivalent refractive index becomes very large on the long wavelength side of the photonic band, and the equivalent refractive index changes significantly when a voltage is applied. As a result, by changing the applied voltage (the electric field formed by the applied voltage), n in formula (3) can be wgcan be changed significantly, and therefore the output angle θa can be changed significantly. In other words, by changing the applied voltage, the output angle θa can be varied over a wide range and to a desired angle. As a result, the first region A1 can be adjusted over a wide range. Furthermore, the photonic crystal made of the electro-optic crystal substrate has the following advantages over the photonic crystal made of a semiconductor (for example, single crystal silicon). According to the photonic crystal made of the semiconductor, the electro-optic effect is small, so the refractive index hardly changes even when a voltage is applied. Therefore, in order to change the output angle in the first light deflection means using such a photonic crystal, it is necessary to change the wavelength of the incident light or to change the refractive index by heating. As a result, in order to change the wavelength, a plurality of light sources with different wavelengths or a multi-wavelength light source is required, which increases the cost and increases the design constraints. Furthermore, since it is difficult to change the wavelength of the light source continuously, it is also difficult to change the output angle continuously, and depending on the wavelength of the light source, the desired output angle may not be realized. In addition, when heating is used, it is difficult to make the temperature distribution in the photonic crystal portion uniform and to make the response fast, and an external circuit including a sensor is required for temperature control when the environmental temperature changes, which increases costs. Furthermore, the change in the equivalent refractive index due to temperature change is relatively small, and there have been no reports of a change in the output angle exceeding 50°. In contrast, according to the embodiment of the present invention, it is only necessary to change the voltage applied to the electrodes, and the voltage can be changed continuously, so that a first optical deflection means can be realized at low cost with few design constraints, and capable of varying the output angle over a wide range and to a desired angle.

[0025] As shown in FIG. 2A and FIG. 3A, the outgoing light beam (laser light) emitted from the first light deflection means (substantially, the optical waveguide) by the above mechanism becomes a so-called fan beam that is line-shaped in a plan view (line-shaped in a direction perpendicular to the optical waveguide direction) and fan-shaped when viewed from the optical waveguide direction. The angle of the fan (spread angle of the fan beam) φ is preferably 10° or more, more preferably 20° or more, even more preferably 30° or more, and particularly preferably 50° or more. The spread angle φ of the fan beam can be, for example, 120° or less. The spread angle φ of the fan beam can be controlled by adjusting the width of the optical waveguide. That is, similar to the relationship between the near field (near field) and the far field (far field), narrowing the width of the optical waveguide increases the spread, so the spread angle can be increased. Conversely, widening the width of the optical waveguide can narrow the spread angle. If the spread angle is in such a range, a first light deflection means having extremely excellent scanning efficiency can be realized by the synergistic effect with the effect that the output angle is variable in a wide range. That is, the first area A1 can be adjusted in a wide range. In particular, for LiDAR, a field angle of 100° or more in the horizontal direction and 25° or more in the vertical direction is required, and the spread angle (vertical direction) of the fan beam can be set as described above to satisfy this requirement. In addition, the variable range α of the output angle is preferably ±40° or more, more preferably ±60° or more. The variable range α of the output angle can be, for example, ±70° or less. As described above, according to the embodiment of the present invention, the output angle can be changed in a much wider range than in the past. As a result, the first area A1 can be adjusted in an extremely wide range. In this specification, the sign "+" of the output angle means the output side with respect to the above reference plane, and "-" means the input side with respect to the reference plane.

[0026] B-3. ​​Photonic crystal layer B-3-1.Electro-optic crystal substrate The electro-optic crystal substrate 10 has an upper surface exposed to the outside and a lower surface located within the composite substrate. The electro-optic crystal substrate 10 is made of a crystal of a material having an electro-optic effect. Specifically, the refractive index of the electro-optic crystal substrate 10 can change when a voltage (electric field) is applied. This provides the following advantages over the use of a semiconductor material (e.g., single crystal silicon): When a semiconductor material is used, the effect of increasing the wavelength dependency of the equivalent refractive index due to the photonic crystal is utilized. Alternatively, the effect of increasing the temperature dependency of the equivalent refractive index is utilized. However, in the former case, problems may arise such as a need for light sources of multiple wavelengths because the wavelength dependency is increased by the photonic crystal and a fan beam is emitted at a different angle for each wavelength, and processing becomes complicated because the light receiving side individually recognizes and processes signals for multiple wavelengths. In the latter case, a certain amount of time is required to heat and cool the photonic crystal portion to set it to the desired temperature and to make the in-plane distribution uniform, making it difficult to increase the response speed. In addition, an external circuit including a sensor is also required for temperature control when the environmental temperature changes, and increased costs are also an issue. Furthermore, the change in the equivalent refractive index due to temperature change is relatively small. In contrast, when an electro-optic crystal substrate is used, the equivalent refractive index can be changed by applying a voltage (electric field) as described above. The equivalent refractive index difference of light propagating through an optical waveguide provided in a photonic crystal is shown in FIG. 7. FIG. 7 shows the calculation results when lithium niobate is used as the electro-optic crystal, the hole period is 425 nm, and the hole diameter (radius) is 144.5 nm. As shown in FIG. 7, the equivalent refractive index difference is large on the long wavelength side in the photonic band. Here, the long wavelength side means the wavelength side longer than the central wavelength of the photonic band, or the wavelength side longer than the wavelength of the photonic band confinement mode. In this region, the wavelength dependency of the equivalent refractive index difference is also large. When a voltage is applied, the equivalent refractive index difference can also increase with the change in refractive index due to the electro-optic effect. Note that the equivalent refractive index difference ΔN in FIG. 7 eff is expressed by the following formula, where N eff (0) is the equivalent refractive index when no voltage is applied, and N eff (V) is the equivalent refractive index when a voltage is applied. ΔNeff =N eff (V)-N eff (0) FIG. 8 is a graph showing the relationship between the applied electric field and the equivalent refractive index difference at a specific wavelength from the calculation results of FIG. 7. As shown in FIG. 8, in the region where the wavelength λ is short, the change in the equivalent refractive index difference due to the electric field is very small, similar to an optical waveguide type diffraction device that does not form a photonic crystal. On the other hand, in the photonic band edge region where the wavelength λ is long, the change in the equivalent refractive index difference due to the electric field can be large. As a result, a photonic crystal using an electro-optic crystal substrate can increase the equivalent refractive index difference (greatly change the equivalent refractive index) by applying a voltage, and it becomes possible to greatly change the output angle as diffracted light in response to this change.

[0027] In one embodiment, the c-axis of the electro-optic crystal substrate 10 may be parallel to the electro-optic crystal substrate 10. That is, the electro-optic crystal substrate 10 may be an X-cut substrate or a Y-cut substrate. In another embodiment, the c-axis of the electro-optic crystal substrate 10 may be perpendicular to the electro-optic crystal substrate 10. That is, the electro-optic crystal substrate 10 may be a Z-cut substrate. The thickness of the electro-optic crystal substrate 10 may be set to any appropriate thickness depending on the frequency and wavelength of the electromagnetic wave used. The thickness of the electro-optic crystal substrate 10 may be, for example, 0.1 μm to 10 μm, or, for example, 0.1 μm to 3 μm. Typically, as described above, in the first light deflection means, the electro-optic crystal substrate is integrated with the support substrate and is reinforced by the support substrate, so that the thickness of the electro-optic crystal substrate can be made thin. As a result, light of a wavelength suitable for the first light deflection means can be propagated in a single mode through the optical waveguide, and / or the coupling efficiency with the diffraction grating can be easily improved.

[0028] Any appropriate material may be used as the material for forming the electro-optic crystal substrate 10, so long as the effects of the embodiments of the present invention can be obtained. Representative examples of such materials include dielectric materials (e.g., ceramics). Specific examples include lithium niobate (LiNbO3:LN), lithium tantalate (LiTaO3:LT), potassium titanyl phosphate (KTiOPO4:KTP), potassium lithium niobate (KTiOPO4:KTP), and potassium tantalate (KTiOPO4:KTP). x Li (1-x) NbO2:KLM), potassium niobate (KNbO3:KN), potassium tantalate-niobate (KNb x Ta (1-x) O3:KTN), and solid solutions of lithium niobate and lithium tantalate. When using lithium niobate or lithium tantalate, MgO doping or stoichiometric crystals can be used to suppress optical damage.

[0029] B-3-2.Photonic crystal layer As described above, the photonic crystal layer 10 is formed by periodically forming holes 12 in an electro-optic crystal substrate. The photonic crystal constituting the photonic crystal layer is a multidimensional periodic structure in which a medium with a large refractive index and a medium with a small refractive index are arranged at a period approximately equal to the wavelength of light, and has an optical band structure similar to the band structure of electrons. Therefore, by appropriately designing the periodic structure, it is possible to realize a predetermined forbidden band (photonic band gap) of light. A photonic crystal having a forbidden band functions as an object that does not reflect or transmit light of a predetermined wavelength. When a line defect that disrupts the periodicity is introduced into a photonic crystal having a photonic band gap, a guided mode is formed within the frequency region of the band gap, and an optical waveguide that propagates light with low loss can be realized.

[0030] The photonic crystal in the illustrated example is a so-called slab-type two-dimensional photonic crystal. The slab-type two-dimensional photonic crystal is a photonic crystal in which cylindrical or polygonal low-refractive index pillars having a refractive index lower than that of the material constituting the thin slab are provided in a thin slab of a dielectric (in the embodiment of the present invention, an electro-optic crystal) at appropriate two-dimensional periodic intervals according to the intended and desired photonic band gap, and the thin slab is sandwiched between an upper clad and a lower clad having a refractive index lower than that of the thin slab. In the illustrated example, the holes 12 function as low-refractive index pillars, the portion 14 between the holes 12, 12 of the electro-optic crystal substrate 10 functions as a high-refractive index portion, the cavity 80 functions as a lower clad, and the upper air portion can function as an upper clad. The portion of the electro-optic crystal substrate 10 where the periodic pattern of the holes 12 is not formed becomes a line defect, and the line defect portion constitutes the optical waveguide 16.

[0031] The holes 12 may be formed as a periodic pattern as described above. The holes 12 are typically arranged to form a regular lattice. Any suitable lattice shape may be adopted as long as a predetermined photonic band gap can be realized. Representative examples include a triangular lattice and a square lattice. The holes 12 may be through-holes in one embodiment. Through-holes are easy to form, and as a result, the refractive index can be easily adjusted. Any suitable shape may be adopted as the shape of the holes (through-holes) in plan view. Specific examples include equilateral polygons (e.g., equilateral triangles, squares, regular pentagons, regular hexagons, and regular octagons), approximately circular, and elliptical shapes. Approximately circular shapes are preferred. The approximately circular shape has a major axis / minor axis ratio of preferably 0.90 to 1.10, and more preferably 0.95 to 1.05. The through-holes 12 may be low-refractive-index columns (columnar portions made of a low-refractive-index material) as described above. However, since through holes are easier to form and are composed of air, which has the lowest refractive index, the refractive index difference with the optical waveguide can be increased. The hole diameter may be partially different from the other hole diameters, and the hole period may be partially different from the other hole period. The relationship between the hole period P and the hole radius d / 2 is preferably d / (2P) 0.2 or more and 0.48 or less, more preferably 0.25 or more and 0.4 or less, and even more preferably 0.3 or more and 0.34 or less. Within such a range, the equivalent refractive index difference due to voltage application can be increased.

[0032] The lattice pattern of the holes can be appropriately set according to the purpose and the desired photonic band gap. In the illustrated example, holes with a diameter d form a square lattice with a period P. Although a square lattice is formed in the illustrated example, similar operation, function, and effect can be obtained with a triangular lattice by appropriately setting the diameter and period of the holes. The square lattice pattern is formed on both sides of the photonic crystal element, and the optical waveguide 16 is formed in the center where the lattice pattern is not formed. The length of the optical waveguide 16 is preferably 5 mm or less, and more preferably 0.1 mm to 3 mm. According to the embodiment of the present invention, the length of the optical waveguide can be very short by combining a photonic crystal layer made of an electro-optic crystal with a predetermined diffraction grating. As a result, the first optical deflection means (and consequently the optical scanning element) can be miniaturized. The width of the optical waveguide 16 can be, for example, 1.01P to 3P (2P in the illustrated example) with respect to the hole period P. The number of rows of holes in the optical waveguide direction (hereinafter sometimes referred to as lattice rows) can be 3 to 10 rows (4 rows in the illustrated example) on each side of the optical waveguide. The hole period P can satisfy, for example, the following relationship. (1 / 7)×(λ / n)≦P≦1.4×(λ / n) Here, λ is the wavelength (nm) of light introduced into the optical waveguide, and n is the refractive index of the electro-optic crystal substrate. The hole period P may be specifically 0.1 μm to 1 μm. In one embodiment, the hole period P may be equal to the thickness of the photonic crystal layer (electro-optic crystal substrate). The hole diameter d may be, for example, 0.1P to 0.9P with respect to the hole period P. A desired photonic band gap can be obtained by appropriately combining and adjusting the hole diameter d, the hole period P, the number of lattice rows, the number of holes in one lattice row, the thickness of the photonic crystal layer, the constituent material of the electro-optic crystal substrate (effectively, the refractive index), the width of the line defect portion, and the width and height of the cavity described later. Furthermore, the same effect can be obtained with electromagnetic waves other than light waves. Specific examples of electromagnetic waves include millimeter waves, microwaves, and terahertz waves.

[0033] In one embodiment, an etching through hole (not shown) may be formed in the photonic crystal layer (electro-optic crystal substrate) 10. By forming the etching through hole, the etching liquid can be well spread over the entire area to be etched. As a result, the desired cavity can be formed more precisely. The number of etching through holes may be appropriately set according to the purpose. Specifically, a single etching through hole may be formed, or a plurality of etching through holes (e.g., two, three, or four) may be formed. The etching through hole may be formed, for example, at a position three or more lattice rows away from the optical waveguide. With this configuration, the etching liquid can be well spread over the entire area to be etched without adversely affecting the photonic band gap. The etching through hole may also be formed, for example, on the input section side and / or output section side (i.e., the corners of the photonic crystal layer) of the end opposite the optical waveguide of the lattice pattern. With this configuration, adverse effects on the photonic band gap can be further effectively prevented. For example, when four etching through holes are formed, they may be formed at the four corners of the photonic crystal layer. The size of the etching through hole is typically larger than the size of the hole 12. For example, the diameter of the etching through hole is preferably 5 times or more, more preferably 50 times or more, and even more preferably 100 times or more, the diameter d of the hole. On the other hand, the diameter of the etching through hole is preferably 1000 times or less, the diameter d of the hole. If the diameter of the etching through hole is too small, the etching solution may not be well distributed over the entire area to be etched. If the diameter of the etching through hole is too large, the element size may have to be larger than the desired size, and the mechanical strength may be reduced.

[0034] B-4.Joint part The bonding portion 20 is interposed between the electro-optic crystal substrate 10 and the support substrate 30, and integrates them. The bonding portion 20 integrates the electro-optic crystal substrate 10 and the support substrate 30 by directly bonding the upper layer 21 and the lower layer 22, as shown in FIG. 2A and FIG. 2B and FIG. 3A and FIG. 3B. By directly bonding the electro-optic crystal substrate 10 and the support substrate 30, peeling in the first light deflection means can be effectively suppressed, and as a result, damage (e.g., cracks) to the electro-optic crystal substrate caused by such peeling can be effectively suppressed. The bonding portion 20 is configured as a remaining portion of the etching when forming the holes 12 and the cavities 80. An amorphous layer 23 is typically formed at the bonding interface between the upper layer 21 and the lower layer 22. The amorphous layer 23 is a layer formed at the bonding interface by directly bonding the upper layer 21 and the lower layer 22. As the name suggests, the amorphous layer has an amorphous structure, and is composed of elements constituting the upper layer 21 and elements constituting the lower layer 22. In this way, by directly bonding the upper layer 21 and the lower layer 22, an amorphous layer 23 can be formed at the bonding interface between the upper layer 21 and the lower layer 22. That is, by directly bonding the upper layer 21 and the lower layer 22, it is possible to avoid direct bonding between the electro-optic crystal substrate and the support substrate, and therefore it is possible to prevent the formation of an amorphous layer in the electro-optic crystal substrate. As a result, it is possible to suppress the deterioration of the optical properties or optical loss of the electro-optic crystal substrate.

[0035] In this specification, "direct bonding" means that two layers or substrates (upper layer 21 and lower layer 22 in the illustrated example) are bonded together without the use of an adhesive. The form of direct bonding can be appropriately set depending on the configuration of the layers or substrates to be bonded together. For example, direct bonding can be achieved by the following procedure. In a high vacuum chamber (e.g., 1×10 -6A neutralizing beam is irradiated to each of the bonding surfaces of the components (layers or substrates) to be bonded at a pressure of about 100 Pa. This activates each bonding surface. Next, the activated bonding surfaces are brought into contact with each other in a vacuum atmosphere and bonded at room temperature. The load during this bonding can be, for example, 100 N to 20,000 N. In one embodiment, when performing surface activation using the neutralizing beam, an inert gas is introduced into the chamber, and a high voltage is applied from a DC power source to an electrode placed in the chamber. With this configuration, electrons are moved by an electric field generated between the electrode (positive electrode) and the chamber (negative electrode), and a beam of atoms and ions is generated by the inert gas. Of the beams that reach the grid, the ion beam is neutralized by the grid, and a beam of neutral atoms is emitted from the high-speed atom beam source. The atomic species that constitute the beam is preferably an inert gas element (for example, argon (Ar), nitrogen (N)). The voltage during activation by beam irradiation is, for example, 0.5 kV to 2.0 kV, and the current is, for example, 50 mA to 200 mA. The direct bonding method is not limited to this, and surface activation methods using FAB (Fast Atom Beam) or an ion gun, atomic diffusion methods, plasma bonding methods, etc. can also be used.

[0036] The upper layer 21 and the lower layer 22 may each have any appropriate configuration depending on the purpose, the desired configuration of the photonic crystal layer, and the manufacturing method of the first light deflection means or the optical scanning element (effectively, an etching process). Specifically, the upper layer 21 and the lower layer 22 may each be a single layer or have a laminated structure. The constituent materials of the upper layer and the lower layer (when at least one of the upper layer and the lower layer has a laminated structure, the constituent materials of each layer) may also be appropriately selected depending on the purpose, the desired configuration of the photonic crystal layer, and the etching process.

[0037] B-5.Cavity The cavity 80 is formed by removing the upper layer 21 and the lower layer 22 (and necessarily the amorphous layer) by etching as described above, and can function as a lower cladding. The width of the cavity is preferably larger than the width of the optical waveguide. For example, the cavity 80 may extend from the optical waveguide 16 to the third lattice row. In the illustrated example, the cavity 80 extends from the optical waveguide 16 to the third lattice row. Since light not only propagates through the optical waveguide, but also a part of the light energy may diffuse to the lattice row near the optical waveguide, by providing a cavity directly below such a lattice row, it is possible to suppress the propagation loss due to light leakage. From this viewpoint, the cavity may be formed over the entire area of ​​the hole formation portion. The height of the cavity is preferably 0.1 μm or more, and more preferably 1 / 5 or more of the wavelength of the propagating light. With such a height, the thin plate slab functions as a photonic crystal, and an optical waveguide with higher wavelength selectivity and lower loss can be realized. The height of the cavity can be controlled by adjusting the thickness of the upper layer 21 and the lower layer 22 .

[0038] B-6.Support board The support substrate 30 has an upper surface located inside the composite substrate and a lower surface exposed to the outside. The support substrate 30 is provided to increase the strength of the composite substrate, and thus the thickness of the electro-optic crystal substrate can be reduced. Any suitable configuration can be adopted for the support substrate 30. Specific examples of materials constituting the support substrate 30 include silicon (Si), glass, sialon (Si3N4-Al2O3), mullite (3Al2O3·2SiO2, 2Al2O3·3SiO2), aluminum nitride (AlN), silicon nitride (Si3N4), magnesium oxide (MgO), sapphire, quartz, crystal, gallium nitride (GaN), silicon carbide (SiC), and gallium oxide (Ga2O3). The linear expansion coefficient of the material constituting the support substrate 30 is preferably as close as possible to the linear expansion coefficient of the material constituting the electro-optic crystal substrate 10. With such a configuration, thermal deformation (typically, warpage) of the composite substrate can be suppressed. Preferably, the linear expansion coefficient of the material constituting the support substrate 30 is within a range of 50% to 150% of the linear expansion coefficient of the material constituting the electro-optic crystal substrate 10. From this perspective, the support substrate may be made of the same material as the electro-optic crystal substrate 10.

[0039] B-7. Diffraction Grating As described above, the illustrated diffraction grating 50 is a grating pattern in a direction perpendicular to the optical waveguide direction in a plan view; in a cross section along the optical waveguide direction, convex portions with a width of Λ / 2 and slits with a width of Λ / 2 are alternately formed. The period of the convex portions and the slits is preferably 40 nm to 1000 nm, more preferably 100 nm to 800 nm, and even more preferably 150 nm to 650 nm. If the period of the convex portions and the slits (hence, the width that is 1 / 2 times the width of these) is in such a range, it is easy to realize a desired output angle. Note that the width of the convex portions and the slits does not have to be 1 / 2 the period. The thickness of the convex portions or the depth of the slits can be, for example, 10 nm to 300 nm. If it is in such a range, there is an advantage that the light propagating through the optical waveguide is periodically reflected due to the effective refractive index difference caused by the unevenness of the diffraction grating, and a diffraction effect can be expressed.

[0040] The diffraction grating (substantially the convex portion) may be made of any suitable material as long as the desired emitted light can be obtained. Typical materials for making the diffraction grating include metal oxides. Specific examples include tantalum oxide, silicon oxide, aluminum oxide, titanium oxide, niobium oxide, magnesium oxide, tungsten oxide, and hafnium oxide. The diffraction grating may also be formed directly on the electro-optic crystal substrate.

[0041] B-8. Cladding layer The cladding layer 60 is an optional layer provided for the purpose of suppressing absorption of the guided light by the electrodes and / or improving coupling of the guided light with the diffraction grating. The cladding layer may be made of any appropriate material. Specific examples include silicon oxide, tantalum oxide, aluminum oxide, titanium oxide, niobium oxide, magnesium oxide, tungsten oxide, and hafnium oxide. The cladding layer may be made of the same material as the diffraction grating. The thickness of the cladding layer may be, for example, 0.1 μm to 1 μm.

[0042] B-9.Other Although the configuration in which a photonic crystal and a diffraction grating are combined has been described as a representative example of the first optical deflection means, as described in Section A, any appropriate configuration can be adopted as the first optical deflection means as long as the refractive index changes with a change in the applied voltage and the first region can be adjusted by the change in the refractive index. For example, the first optical deflection means may be an optical phase array or a variable optical metasurface, as described in Section A above. Since either of these can emit a fan beam in the same way as the configuration in which a photonic crystal and a diffraction grating are combined, it is obvious to those skilled in the art that the same effect can be obtained by the same mechanism as the configuration in which a photonic crystal and a diffraction grating are combined.

[0043] C. Second Light Deflection Means The second light deflection means may typically be a diffraction grating as described above. Any appropriate configuration may be adopted as the diffraction grating as long as the effects of the embodiments of the present invention can be obtained. The basic configuration of the diffraction grating is the configuration described in Sections B-2 and B-7 regarding the diffraction grating in the first light deflection means. The following describes the characteristic parts of the second light deflection means.

[0044] In addition to the materials described in Section B-7, glass may be used as the material for the diffraction grating. For example, grating grooves may be formed on a glass plate by etching.

[0045] The direction in which the grating grooves of the diffraction grating extend may be substantially parallel to the optical waveguide direction or substantially perpendicular to the optical waveguide direction. When the first region A1 as shown in FIG. 2A has an elongated shape along the optical waveguide direction (for example, when the fan beam spread angle φ is 30° and the variable range α of the fan beam output angle is 120°=±60°), as shown in FIG. 2B, the second region A2 can be expanded in a direction substantially perpendicular to the optical waveguide direction compared to the first region A1 by making the direction in which the grating grooves of the diffraction grating extend substantially parallel to the optical waveguide direction. For example, in the example shown in FIG. 2B, the fan beam spread angle φ is substantially expanded about three times in the direction perpendicular to the optical waveguide direction. In this case, the direction in which the grating grooves of the diffraction grating in the first optical deflection means extend and the direction in which the grating grooves of the diffraction grating in the second optical deflection means extend are substantially perpendicular to each other. In the case where the first region A1 as shown in FIG. 3A has an elongated shape along a direction substantially perpendicular to the optical waveguide direction (for example, when the fan beam spread angle φ is 60° and the variable range α of the fan beam output angle is 40°=±20°), as shown in FIG. 3B, the direction in which the grating grooves of the diffraction grating extend is substantially perpendicular to the optical waveguide direction, so that the second region A2 can be expanded in the optical waveguide direction compared to the first region A1. For example, in the example shown in FIG. 3B, the variable range α of the output angle of the fan beam is substantially expanded about three times in the optical waveguide direction. In this case, the direction in which the grating grooves of the diffraction grating in the first optical deflection means extend and the direction in which the grating grooves of the diffraction grating as the second optical deflection means extend are substantially parallel. In this way, the direction in which the grating grooves of the diffraction grating extend can be appropriately set to adjust the spread direction of the second region A2 relative to the first region A1. Furthermore, by adjusting the pitch, diffraction order and diffraction angle of the diffraction grating, and the wavelength of the incident light in combination, it is possible to control the extent to which the second region A2 extends relative to the first region A1.

[0046] D. Manufacturing method of optical scanning element An example of a method for manufacturing an optical scanning element will be briefly described with reference to Figures 9(a) to 9(e). In the illustrated example, the upper layer 21 is an optical loss suppression layer, and the lower layer 22 is a cavity processed layer. The optical loss suppression layer 21 can be provided to prevent an amorphous layer from being formed in the electro-optic crystal substrate during direct bonding, thereby suppressing the optical loss of the electro-optic crystal substrate. The cavity processed layer 22 is provided to form a cavity in the optical scanning element and to stop etching (typically, dry etching) at an appropriate level.

[0047] First, as shown in FIG. 9(a), a composite substrate is fabricated. The composite substrate is fabricated as follows. An optical loss suppression layer 21 is formed on an electro-optic crystal substrate 10 by, for example, sputtering. Meanwhile, a cavity processed layer 22 is formed on a support substrate 30 by, for example, sputtering. A laminate of an electro-optic crystal substrate 10 / optical loss suppression layer 21 and a laminate of a support substrate 30 / cavity processed layer 22 are directly bonded to each other with the optical loss suppression layer 1 and the cavity processed layer 22 as bonding surfaces. By direct bonding, an amorphous layer 23 can be formed at the bonding interface between the optical loss suppression layer 21 and the cavity processed layer 22. In this way, a composite substrate in which the electro-optic crystal substrate 10 and the support substrate 30 are integrated can be obtained. Next, electrodes 40, 40 are formed on the left and right ends of the electro-optic crystal substrate 10, and a diffraction grating 50 is formed at the position where the optical waveguide is to be formed. The electrodes 40, 40 can be typically formed by lift-off. The diffraction grating 50 can be formed by dry etching (e.g., reactive ion etching) using a mask with a predetermined pattern (typically, a stripe pattern extending in a direction substantially perpendicular to the waveguiding direction of the optical waveguide). The electrodes 40, 40 may be formed before or after the diffraction grating 50 is formed.

[0048] Next, as shown in FIG. 9(b), holes 12 are formed in the electro-optic crystal substrate 10, the optical loss suppression layer 21, and the amorphous layer 23 by dry etching (e.g., reactive ion etching) through a predetermined mask. Then, as shown in FIG. 9(c), predetermined portions of the cavity processed layer 22 are removed by wet etching (e.g., immersion in an etching solution). Then, as shown in FIG. 9(d), the remaining optical loss suppression layer 21 and the amorphous layer 23 are removed by wet etching (e.g., immersion in an etching solution). As a result, a cavity 80 is formed, and a first optical deflection means 100 is obtained.

[0049] Finally, as shown in FIG. 9(e), the second light deflection means 200 is provided on the diffraction grating 50 of the obtained first light deflection means 100, thereby obtaining an optical scanning element 300. The second light deflection means 200 can be provided by any appropriate method. For example, the second light deflection means 200 can be produced by forming a grating groove in a glass plate by dry etching (e.g., reactive ion etching) through a predetermined mask (e.g., a metal mask such as Al). The obtained second light deflection means 200 is disposed on the diffraction grating 50 of the first light deflection means 100, thereby obtaining an optical scanning element 300. The method of disposing the second light deflection means 200 includes, for example, placing, bonding with an adhesive that does not adversely affect optically, and mechanical fixing. The second light deflection means may be disposed on a wafer-shaped first light deflection means, or on a chip-shaped first light deflection means.

[0050] In this manner, the optical scanning element 300 can be manufactured. EXAMPLES

[0051] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0052] <Example 1> An optical scanning element as shown in Figures 2A and 2B was produced by the following specific procedures.

[0053] 1. Preparation of the first optical deflection means 1-1. Preparation of composite substrate An X-cut lithium niobate substrate with a diameter of 4 inches was prepared as the electro-optic crystal substrate, and a silicon substrate with a diameter of 4 inches was prepared as the support substrate. First, amorphous silicon (a-Si) was sputtered onto the electro-optic crystal substrate to form an optical loss suppression layer with a thickness of 20 nm. Meanwhile, silicon oxide was sputtered onto the support substrate to form a cavity processing layer with a thickness of 0.5 μm, and a-Si was sputtered onto the cavity processing layer to form a bonding layer with a thickness of 20 nm. Next, the surfaces of the optical loss suppression layer and the bonding layer were polished by CMP, respectively, so that the arithmetic mean roughness Ra of the surfaces of the optical loss suppression layer and the bonding layer was 0.3 nm or less. Next, the surfaces of the optical loss suppression layer and the bonding layer were cleaned, and then the optical loss suppression layer and the bonding layer were directly bonded to integrate the electro-optic crystal substrate and the support substrate. The direct bonding was performed as follows. 10 -6 In a vacuum of the Pa range, the bonding surfaces (surfaces of the optical loss suppression layer and bonding layer) of the electro-optic crystal substrate and the support substrate were irradiated with a high-speed Ar neutral atomic beam (accelerating voltage 1 kV, Ar flow rate 60 sccm) for 70 seconds. After irradiation, the electro-optic crystal substrate and the support substrate were left to cool for 10 minutes, and then the bonding surfaces of the electro-optic crystal substrate and the support substrate were brought into contact and pressed at 4.90 kN for 2 minutes to bond the electro-optic crystal substrate and the support substrate. After bonding, the electro-optic crystal substrate was polished until the thickness was 0.4 μm, and a composite substrate was obtained. No defects such as peeling were observed at the bonding interface in the obtained composite substrate.

[0054] 1-2. Formation of diffraction grating A diffraction grating was formed on the surface of the electro-optic crystal substrate of the composite substrate obtained in 1-1 above. Specifically, the process was as follows. First, aluminum (Al) was formed as a metal mask on the surface of the electro-optic crystal substrate, and a resin pattern was formed on the metal mask by nanoimprinting. The resin pattern was formed in a stripe shape with a period of 567 nm (line / space: 283.5 nm / 283.5 nm) extending in a direction perpendicular to the waveguiding direction of the optical waveguide, on the upper part of the part that will become the optical waveguide of the electro-optic crystal substrate, and with a length of 1000 μm in the waveguiding direction of the optical waveguide. Next, a metal mask in the shape of a diffraction grating pattern was formed by chlorine-based reactive ion etching using this resin pattern as a mask. Next, a diffraction grating groove with a depth of 0.05 μm was formed by fluorine-based reactive ion etching through a metal mask in the shape of a diffraction grating pattern. Finally, the metal mask was removed with an Al etching solution. In this way, a diffraction grating was formed on the part that will become the optical waveguide of the electro-optic crystal substrate.

[0055] 1-3. Formation of electrodes A pair of electrodes was formed on the surface of the electro-optic crystal substrate of the composite substrate on which the diffraction grating obtained in 1-2 above was formed. Specifically, resist was applied to the left and right ends of the electro-optic crystal substrate, and a resist pattern for the electrodes was formed by a photolithography process. Next, a Ti film with a thickness of 20 nm, a Pt film with a thickness of 100 nm, and an Au film with a thickness of 300 nm were successively formed by sputtering, and after the films were formed, they were lifted off to form the electrodes. The gap between the formed electrodes was 5 μm.

[0056] 1-4. Fabrication of the first optical deflection means A first optical deflection means was produced from the composite substrate on which the diffraction grating and electrodes obtained in 1-3 above were formed. Specifically, the first optical deflection means was produced by the following procedure. First, a molybdenum (Mo) film was formed as a metal mask on the electro-optic crystal substrate. Next, a resin pattern having holes in a predetermined arrangement was formed on the metal mask by nanoimprinting. Specifically, as a hole pattern corresponding to the holes of the photonic crystal, 10 lattice rows having holes with a diameter of 289 nm and a period (pitch) of 425 nm in the optical waveguide direction and in the direction perpendicular to the optical waveguide direction were formed on the left and right sides. A line defect optical waveguide was formed by not forming holes in the center. The distance between adjacent holes sandwiching the line defect was set to 950 nm. Furthermore, four holes (patterns of through holes for etching) with a diameter of 100 μm were formed in the corners (the input and output sides of the ends opposite to the portions that become the optical waveguides of the left and right lattice row portions). Next, holes corresponding to the above pattern were formed in the Mo mask by etching with a Mo etching solution (a mixed solution of nitric acid: acetic acid: phosphoric acid in a mixing ratio of 10:15:1). Next, a hole pattern and an etching through hole were formed in the electro-optic crystal substrate, the optical loss suppression layer, and the bonding layer by fluorine-based reactive ion etching through the patterned Mo mask. Next, the composite substrate was immersed in a BHF (buffered hydrofluoric acid) etching solution to remove the cavity processing layer and form a cavity. Furthermore, the remainder of the Mo mask was removed with the Mo etching solution. Finally, the composite substrate was immersed in tetramethylammonium hydroxide (TMAH) diluted to about 10% to etch the optical loss suppression layer and the bonding layer, and a wafer of the first optical deflection means was produced. The obtained wafer was cut into chips by dicing to obtain the first optical deflection means. The length of the optical waveguide of the first optical deflection means was set to 5 mm. After cutting into chips, the input side end face and the output side end face of the optical waveguide were subjected to end face polishing.

[0057] 1-5. Measurement of optical insertion loss of first optical deflection means The optical insertion loss of the obtained first optical deflection means (chip) was measured. Specifically, a laser beam with a wavelength of 1.025 μm was introduced into the chip (effectively, the optical waveguide of the photonic crystal layer) through the input-side bulb-tipped fiber coupled to the optical fiber, and the amount of light output through the output-side bulb-tipped fiber was measured with a photodetector to calculate the propagation loss. The propagation loss of the optical waveguide was 0.5 dB / cm. Furthermore, the voltage applied between the electrodes was switched between ±100V, and the pattern and output angle of the laser light output from the optical waveguide were observed. The pattern and output angle of the laser light were measured using an Otsuka Electronics high-speed light distribution measurement system (RH50) to measure the output angle dependence characteristics of the fan angle and applied voltage. As a result, the output laser light was a so-called fan beam, which was line-shaped when viewed in a plan view and fan-shaped when viewed from the optical waveguide direction, with a fan angle (fan spread angle) of 30°. It was also confirmed that the output angle could be varied from -60° to +60° with respect to the reference plane (plane normal to the optical waveguide direction) by changing the applied voltage. Additionally, to experimentally verify the responsiveness, observations were made as to whether light could be scanned at a voltage of ±15V and 50MHz. As a result, it was confirmed that scanning was possible without any problems. In principle, the first light deflection means depends on the responsiveness of the electro-optic effect, so it can be assumed that it can operate on the order of GHz. Note that the operation of the first light deflection means may be affected by the electrode structure.

[0058] 2. Fabrication of Optical Scanning Element 2-1. Fabrication of second optical deflection means The second optical deflection means was fabricated by the following procedure. A film of aluminum (Al) was formed as a metal mask on one surface of a glass plate having a thickness of 0.5 mm and a length of 3 cm x 3 cm, and a resin pattern was formed on the surface of the metal mask by a nanoimprint method. The resin pattern was formed in a stripe shape with a period of 2 μm in an area of ​​2 cm x 2 cm on the surface of the glass plate. Next, a metal mask in the shape of a diffraction grating pattern was formed by chlorine-based reactive ion etching using this resin pattern as a mask. Next, a grating groove was formed on the glass plate by fluorine-based reactive ion etching through this metal mask. Finally, the metal mask was removed with an Al etching solution. In this way, a second optical deflection means having a stripe pattern of grating grooves with a period of 2 μm on the glass plate was fabricated.

[0059] 2-2. Fabrication of optical scanning element The second optical deflection means obtained in 2-1 above was placed on top of the diffraction grating of the first optical deflection means obtained in 1 above. More specifically, the second optical deflection means was attached so that the direction in which the grating grooves of the second optical deflection means (diffraction grating) extend was substantially parallel to the optical waveguide direction, and therefore substantially perpendicular to the direction in which the grating grooves of the diffraction grating in the first optical deflection means extend. The distance between the first optical deflection means (the diffraction grating) and the second optical deflection means was 5 mm. In this way, an optical scanning element was produced.

[0060] 2-3.Evaluation of output light characteristics of optical scanning element A laser beam was input to the obtained optical scanning element in the same manner as in 1-5 above, and the pattern of the emitted light was observed. As a result, before the voltage was applied, the 0th-order and ±1st-order diffracted light were observed as a fan beam as the emitted light. The diffracted light (fan beam) was linear in plan view (linear in a direction perpendicular to the optical waveguide direction) and fan-shaped when viewed from the optical waveguide direction, and the spread angle φ of the diffracted light as a whole was 120° or more. That is, the emitted light from the optical scanning element (effectively the second optical deflection means) was observed to spread four times or more in the direction perpendicular to the optical waveguide direction compared to the emitted light from the first optical deflection means (spread angle φ=30°). Next, when a voltage in the range of ±100V was applied to the optical scanning element, it was confirmed that the 0th-order light and ±1st-order light could be varied from -60° to +60° relative to the reference plane (plane normal to the optical waveguide direction) in conjunction with each other. That is, the light emitted from the optical scanning element (effectively, the second optical deflection means) maintained the same variable range α of the emission angle as the light emitted from the first optical deflection means. In this way, it was confirmed that the obtained optical scanning element can scan an extremely wide range with a spread angle φ of 120° and a variable range α of the emission angle of 120°.

[0061] <Example 2> An optical scanning element as shown in Figures 3A and 3B was produced by the following specific procedures.

[0062] 1. Preparation of the first optical deflection means A first optical deflection means was fabricated in the same manner as in Example 1, except that the distance between adjacent holes sandwiching the line defect was changed from 950 nm to 760 nm when forming the line defect optical waveguide. The obtained first optical deflection means was subjected to the same evaluation as in Example 1. As a result, the propagation loss of the optical waveguide was 0.5 dB / cm. In addition, the output laser light was a so-called fan beam shape that was line-shaped in a plan view and fan-shaped when viewed from the optical waveguide direction, and the angle of the fan (the spread angle of the fan) was 60°. Furthermore, when the voltage applied between the electrodes was switched between ±50V, it was confirmed that the output angle could be changed from -20° to +20° with respect to the reference plane (the plane normal to the optical waveguide direction). Finally, in order to experimentally verify the responsiveness, it was observed whether light could be scanned at a voltage of ±15V and 50MHz, and it was confirmed that scanning could be performed without any problems.

[0063] 2. Fabrication of Optical Scanning Element A second light deflection means (diffraction grating) having a stripe pattern grating groove on a glass plate was produced in the same manner as in Example 1, except that the period was set to 1.6 μm. An optical scanning element was produced in the same manner as in Example 1, except that this second light deflection means was used, and the direction in which the grating groove of the second light deflection means extends was substantially perpendicular to the optical waveguide direction, and therefore the second light deflection means was attached so as to be substantially parallel to the direction in which the grating groove of the diffraction grating in the first light deflection means extends. A laser beam was input to the obtained optical scanning element in the same manner as in Example 1, and the pattern of the emitted light was observed. As a result, before the voltage was applied, 0th order and ±1st order diffracted light were observed as a fan beam as the emitted light. It was confirmed that the fan beam has -1st order diffracted light, 0th order diffracted light, and +1st order diffracted light aligned along the optical waveguide direction, the spread angle φ of each fan beam is 60°, and the variable range α of the output angle of each fan beam can be varied from -20° to +20° with respect to the reference plane. In this way, it was confirmed that the obtained optical scanning element can scan an extremely wide range with a spread angle φ of 60° and a variable range α of the output angle of 120°. [Industrial Applicability]

[0064] The optical scanning element according to the embodiment of the present invention can be widely used as a so-called scanner. The optical scanning element can be used as, for example, a laser radar, a laser scanner, or a LiDAR, and can be applied to an obstacle detection system and a distance measurement system for automatic driving control of an automobile or for position control of a robot or a drone. [Explanation of symbols]

[0065] 10 Electro-optic crystal substrate 12 Vacancies 14 Thin plate slab 16 Optical waveguide 20 Joint 30 Support substrate 40 electrodes 50 Diffraction Grating 60 Cladding Layer 80 hollow 100 First light deflection means 200 Second optical deflection means 300 Optical scanning element

Claims

1. A first optical deflection means for emitting light to a first region; a second light deflection means for directing the light emitted to the first region to a second region larger than the first region; having The first optical deflection means is configured to change a refractive index in response to a change in an applied voltage, and adjust the first region by the change in the refractive index; the second light deflection means being configured to condition the second region by diffraction; Optical scanning element.

2. 2. The optical scanning element according to claim 1, wherein the first optical deflection means is one selected from the group consisting of a combination of a photonic crystal and a diffraction grating, an optical phase array, and a variable optical metasurface.

3. 3. The optical scanning element according to claim 2, wherein the second optical deflection means is a diffraction grating.

4. The first optical deflection means a photonic crystal layer formed by periodically forming holes in an electro-optic crystal substrate; an optical waveguide having a line defect formed in the photonic crystal layer; a diffraction grating provided on at least one portion selected from an upper portion, a left side portion, and a right side portion of the optical waveguide; Electrodes provided on the left and right sides of the optical waveguide; having The output angle of the light emitted from the upper surface of the optical waveguide is changed.

2. The optical scanning element according to claim 1.

5. 5. The optical scanning element according to claim 4, wherein the diffraction grating has a plurality of grating grooves extending in a direction substantially perpendicular to a waveguiding direction of the optical waveguide.

6. the second optical deflection means is a diffraction grating having grating grooves, 6. The optical scanning element according to claim 5, wherein a direction in which the grating grooves extend in the first optical deflection means and a direction in which the grating grooves extend in the second optical deflection means are substantially perpendicular to each other.

7. the second optical deflection means is a diffraction grating having grating grooves, 6. The optical scanning element according to claim 5, wherein a direction in which the grating grooves extend in the first optical deflection means and a direction in which the grating grooves extend in the second optical deflection means are substantially parallel to each other.

8. The first optical deflection means a support substrate provided under the electro-optic crystal substrate and supporting the electro-optic crystal substrate; a joint portion that integrates the electro-optic crystal substrate and the support substrate; a cavity defined by a lower surface of the electro-optic crystal substrate, an upper surface of the support substrate, and the joint; The optical scanning element according to claim 4 , further comprising:

9. The optical scanning element according to any one of claims 4 to 8, wherein the electro-optic crystal substrate is made of one selected from the group consisting of lithium niobate, lithium tantalate, potassium titanyl phosphate, potassium lithium niobate, potassium niobate, potassium tantalate-potassium niobate, and a solid solution of lithium niobate and lithium tantalate.

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