JP2020194011A - Grating coupler, grating coupler array, light reception antenna, and distance measuring sensor - Google Patents

Abstract

To provide a GC, a GC array, a light reception antenna, and a distance measuring sensor which can increase the efficiency of coupling with incident light from a space.SOLUTION: Each GC 110 forming a light reception antenna 21 is made in the shape of a rhombus. A curved refraction index protrusion 111a is formed with a first corner part 113 with an acute angle as the center where one end part of a long diagonal is located, and a buried layer 112 formed of an insulating film is buried between refraction index protrusions 111a so that a diffraction grating is formed. The diffraction grating is extended in nearly all the region of the rhombus, so that the present invention can receive incident light in a wider area than a configuration in which a tapered part is formed.SELECTED DRAWING: Figure 7

Description

The present invention relates to a grating coupler (hereinafter referred to as GC), a GC array, a light receiving antenna, and a distance measuring sensor.

Conventionally, strip-shaped GC, fan-shaped GC, and square-shaped GC have been proposed as an element that couples light incident from the outside to an optical waveguide or an element that emits light from the optical waveguide to the outside. Has been done. The strip type is composed of a shape in which a rectangle and a triangle are connected, and the triangular part is a diffraction grating in which the condensing part and the rectangular part are the coupling region, and the triangular part is not in contact with the rectangle. The structure is such that a waveguide is connected to the apex. The fan shape is composed of a fan shape, and a condensing part connected to a waveguide from the center of the fan shape to a portion having a predetermined radius, and a diffraction grating having a coupling region on the radial outer side of the condensing part. The structure is such that a waveguide is connected to the tip. The square type is composed of a square shape, and is a diffraction grid in which the region inside the arc is the condensing part and the region outside the arc is the coupling region with respect to the arc passing through the two opposite sides of the square and the vicinity of the center of the square. It is said that the structure is such that the waveguide is connected to the center of the side on the center side of the arc among the four sides of the square.

However, the strip type and the fan type have a large area of the light collecting portion, and the area efficiency is poor. In addition, since a plurality of fan-shaped GCs are arranged side by side in the direction of the tip side, the gap between the GCs becomes large when the array is formed, resulting in poor area efficiency. On the other hand, in the square type, since a plurality of square GCs are arranged in a matrix, the gap between each GC when arrayed can be reduced, but the area of the condensing portion is large, so that the area efficiency is poor. Further, the diffraction grating is said to have a plurality of arcs having a constant width arranged concentrically, but since the unevenness of the diffraction grating is uniform, it is combined with incident light especially when receiving light from space. ineffective.

On the other hand, a GC having a structure that can reduce the gap between each GC when arrayed while improving the area efficiency has also been proposed. In this GC, one corner of the square is set as a specific corner, and the center side of the arc, that is, the region including the specific corner is tapered with respect to the arc passing through the two sides of the specific corner and the vicinity of the center of the square. The region outside the arc is a diffraction grating that serves as a coupling region, and a waveguide is connected to a specific angle portion.

However, this GC also has a diffraction grating in which a plurality of arcs having a constant width are arranged concentrically, and the unevenness of the diffraction grating is uniform, so that the incident light is particularly received when receiving light from space. Coupling efficiency is poor.

On the other hand, Patent Document 1 is provided with a diffraction grating which is a triangular GC in which the corners to which the waveguides are connected are designated as specific corners and concentric irregularities are arranged over the entire area of the triangle. A structure has been proposed in which the width of the convex portion of the diffraction grating is widened as the position is farther from the corner portion.

In such a structure, since almost the entire area of the GC is a diffraction grating without providing a tapered portion, area efficiency can be improved. Further, since the unevenness of the diffraction grating is not uniform and the unevenness of the diffraction grating is distributed according to the wave surface of the light, it is possible to improve the coupling efficiency with the incident light.

U.S. Pat. No. 7,245,803

However, as in Patent Document 1, the coupling efficiency can be improved by gradually widening the width of the convex portion in the unevenness of the diffraction grating as the distance from the waveguide increases, but simply increasing the width as the distance from the waveguide increases. The coupling efficiency cannot be sufficiently increased.

In particular, when the GC is used as the light receiving antenna that serves as the light receiving element of the distance measuring sensor for a vehicle, the reflected light from the object is collected by the condenser lens and input to the light receiving antenna. However, when the incoming angle of the reflected light has a certain spread, the reflected light collected by the condenser lens becomes a spot with a spread, so that a GC capable of receiving light in a wide range is required. On the other hand, the reflected light collected by the condenser lens is incident on the GC with a large viewing angle, so that a small GC is required. Therefore, an arrayed GC array is required instead of one GC. Further, since the reflected light collected by the condenser lens has substantially uniform intensity in a wide range, it is required to have high coupling efficiency in a wide range.

In view of the above points, it is an object of the present invention to provide a GC, a GC array, a light receiving antenna, and a distance measuring sensor capable of further increasing the coupling efficiency with incident light.

In order to achieve the above object, in the invention according to claim 1, the GC is an element that receives light and propagates light to the optical waveguide (12), or an element that emits light propagated from the optical waveguide. Therefore, the long diagonal line, which is a long diagonal line, and the short diagonal line, which is a short diagonal line, are orthogonal to each other, and the first corner portion (113) of a sharp angle where one end of the long diagonal line of the rhombus shape is located is an optical waveguide. With a plurality of refractive index convex portions (111a) arranged in a curved shape from the first corner portion to the second corner portion (114) where the other end of the long diagonal line is located. It has a light introduction portion (111) including an embedded layer (112) in which an insulating film (14) is embedded between the convex portions of the refractive index, and is arranged in a curved shape from the first corner portion every predetermined cycle width. The cross-sectional area of the refractive index convex portion for each cycle width is smaller or smaller as the distance from the first corner portion is increased, including the diffraction grating in which the plurality of refractive index convex portions and the embedded layer are repeatedly arranged. It is made larger, and further, it is made smaller or larger as the distance from the long diagonal line increases in the direction of the angle centered on the first corner portion.

In this way, on the long diagonal line, the cross-sectional area of the refractive index convex portion for each cycle width becomes smaller or larger as the distance from the first corner portion increases. In addition, the cross-sectional area of the refractive index convex portion for each cycle width is reduced or increased as the distance from the long diagonal line, that is, toward the end of each refractive index convex portion curve. Therefore, it is possible to increase the coupling efficiency of the incident light not only in the direction of the long diagonal line but also in the direction away from the long diagonal line. Therefore, the GC can be made capable of further increasing the coupling efficiency with the incident light.

The curved shape of the convex index portion is not a concentric circle or an arc, but is a light wave incident on the light introduction portion (111) from space and a time-reversed light wave incident on the light introduction portion (111) from the end of the optical waveguide (12). By forming the shape of the interference fringes to be formed, the waveguide light coupled by the light introduction portion (111) can be coupled to the optical waveguide (12) with high efficiency.

When the curved shape of the convex index portion is a concentric circle or an arc, the waveguide light coupled from the space by the light introduction portion (111) is collected at the end of the optical waveguide in a form different from the light wave form propagating in the optical waveguide (12). Since it shines, a coupling loss occurs due to the generated wave surface mismatch. By determining the curved shape of the convex index portion as in the previous section, loss due to wave surface mismatch can be avoided.

The reference reference numerals in parentheses attached to each component or the like indicate an example of the correspondence between the component or the like and the specific component or the like described in the embodiment described later.

It is a figure which shows the whole structure of the distance measuring sensor which concerns on 1st Embodiment. It is sectional drawing of the substrate shown in FIG. It is sectional drawing of the distance measuring sensor which concerns on 1st Embodiment. It is sectional drawing of the light source shown in FIG. It is a graph which shows the change of the frequency of an optical signal. It is a perspective view which shows the appearance that the filter is laminated on the light receiving antenna. It is an enlarged top view of one of the GCs provided in a GC array. It is a top view of the GC array and the optical waveguide. It is sectional drawing of IXA-IXA of FIG. It is sectional drawing of IXB-IXB of FIG. It is a cross-sectional view of GC described by the modification of 1st Embodiment, and is the figure corresponding to the IXA-IXA cross section of FIG. It is a cross-sectional view of GC described by the modification of 1st Embodiment, and is the figure corresponding to the IXB-IXB cross section of FIG. It is a top view of the GC for explaining the structure of the GC and the curved shape of the convex part of the refractive index. It is a figure which shows the operation of the distance measurement sensor which concerns on 1st Embodiment. It is a top view of the receiver shown in FIG. It is a figure which shows the state of the incident light to a condenser lens, and the state of the light condensed by a condenser lens. It is a figure which showed the relationship between the width of a pixel and a radiation angle or a light receiving angle. It is a figure which shows the state of the incident light to a condenser lens and the light condensed by a condenser lens in the state of being attached to a distance measuring sensor. It is a figure which showed the relationship between the duty ratio and the coupling coefficient of light. It is sectional drawing of GC provided in the distance measuring sensor described in 2nd Embodiment. It is a figure which showed the relationship between the depth of a slit and the coupling coefficient of light. It is sectional drawing of GC provided in the distance measuring sensor described in 3rd Embodiment. It is a figure which showed the relationship between the height of the refractive index convex part and the coupling coefficient of light.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each of the following embodiments, parts that are the same or equal to each other will be described with the same reference numerals.

(First Embodiment)
The first embodiment will be described. In this embodiment, a distance measuring sensor in which a GC array in which GC is formed as an array is applied as a light receiving antenna will be described. The distance measuring sensor of the present embodiment is used, for example, as an in-vehicle LIDAR (Light Detection and Ranging), and irradiates a region included in a predetermined range in two directions perpendicular to each other in the space outside the vehicle to irradiate the region outside the vehicle. Detects the distance to an object. In each figure, the xyz axis is shown in order to make it easy to understand the arrangement and direction of the components of the distance measuring sensor.

As shown in FIG. 1, the distance measuring sensor of the present embodiment includes an LD (laser diode) 1, a modulator 2, an amplifier 3, a demultiplexer 4, a scanning unit 5, a receiver 6, a combiner 7, and a converter. 8. TIA (transimpedance amplifier) 9 and calculation unit 10 are provided. These components are formed on the substrate 11 by silicon photonics, and form an optical integration chip. Further, the substrate 11 is formed with an optical waveguide 12 for transmitting an optical signal and a wiring 13 for transmitting an electric signal. The optical waveguide 12 corresponds to a signal transmission optical waveguide.

As shown in FIG. 2, the substrate 11 is an SOI (Silicon on Insulator) substrate in which a support layer 11a made of Si, a sacrificial layer 11b made of SiO ₂ , and an active layer 11c made of Si are laminated in this order. For example, it is set to 10 mm □.

A part of the active layer 11c has been removed by etching, and the active layer 11c and the sacrificial layer 11b exposed by removing the active layer 11c are covered with an insulating film 14 made of SiO ₂ . The optical waveguide 12 is configured by using the active layer 11c as a core layer and the sacrificial layer 11b and the insulating film 14 as a clad layer. Further, the wiring 13 is composed of a layer such as Al formed on the surface of the insulating film 14.

In the present embodiment, the core layer of the optical waveguide 12 is made of Si and the clad layer is made of SiO ₂ , but these layers may be made of other materials. It is preferable that the core layer of the optical waveguide 12 is made of Si or at least one material selected from SiO ₂ , SiN, SiON, LN, and InP doped with impurities. Further, it is preferable to form the clad layer with at least one material selected from SiO ₂ , SiN, SiON, LN, and InGaAsP. However, the core layer and the clad layer have different material configurations. Moreover, the refractive index of the core layer is higher than that of the clad layer.

Further, as shown in FIG. 3, the distance measuring sensor is an optical device including a MEMS mirror 40, a case 16, a lid 17 having a prism 17a formed in a part thereof, a diffusion lens 18, and a condenser lens 19. It is said to be a package. The case 16 is a rectangular parallelepiped frame having an opening on one side and a space formed inside, and is made of ceramic or the like. The substrate 11 and the MEMS mirror 40 are arranged inside the case 16. The opening of the case 16 is closed by the lid 17, and the diffusion lens 18 and the condenser lens 19 are arranged outside the lid 17.

The detailed configuration of the distance measuring sensor will be described. The LD1 generates light for irradiating the outside and corresponds to a light source. In the present embodiment, the LD1 is a DFB (Distributed FeedBack) type laser diode, and is mounted on a substrate 11 with a flip chip or the like. Specifically, as shown in FIGS. 1 and 4, the LD1 has an active layer 1a composed of a group III-V semiconductor, and p-type clad layers 1b and n-type clad arranged on both sides of the active layer 1a. It includes a layer 1c. Further, the LD1 includes an n-type substrate 1d, and an n-type clad layer 1c, an active layer 1a, and a p-type clad layer 1b are formed on one surface of the n-type substrate 1d in this order. As shown in FIG. 4, in a part of the substrate 11, the insulating film 14, the active layer 11c, and a part of the sacrificial layer 11b are removed, and the LD1 is p-type in the remaining sacrificial layer 11b. The clad layers 1b are arranged so as to be laminated. That is, the p-type clad layer 1b, the active layer 1a, the n-type clad layer 1c, and the n-type substrate 1d are laminated in this order on the sacrificial layer 11b. The output of LD1 is increased because it is composed of a group III-V semiconductor.

In the present embodiment, the wavelength of the light generated by the LD1 is 0.85 μm or more and 0.95 μm or less, or 1.5 μm or more and 1.6 μm or less. As shown in FIG. 1, the LD1 is connected to the modulator 2 by an optical waveguide 12, and the optical signal generated by the LD1 is input to the modulator 2. As shown in FIG. 4, a gap is formed between the LD1 and the optical waveguide 12, and the light generated by the LD1 crosses this gap and enters the optical waveguide 12.

The modulator 2 modulates the frequency of the light generated by the LD1. As the modulator 2, for example, an SSB (Single Side Band) modulator or the like is used. Specifically, the frequency of the light generated by the LD1 is changed by the modulator 2 as shown in FIG. That is, the frequency repeatedly increases and decreases with the passage of time, and the graph showing the relationship between time and frequency becomes a triangular wave. In the graph of FIG. 5, the solid line indicates the frequency of the optical signal output by the modulator 2, and the one-point chain line indicates the frequency of the optical signal input from the receiver 6 to the combiner 7.

As shown in FIG. 1, the modulator 2 is connected to the demultiplexer 4 via the amplifier 3 by the optical waveguide 12, and the optical signal whose frequency is modulated by the modulator 2 is amplified by the amplifier 3. After that, it is input to the demultiplexer 4.

The demultiplexer 4 is composed of a coupler in which the optical waveguide 12 branches, and a part of the optical signal input to the demultiplexer 4 is input to the scanning unit 5 and the other part is input to the duplexer 7. Entered. The portion of the optical waveguide 12 that connects the demultiplexer 4 and the scanning unit 5 is referred to as an optical waveguide 12a, and the portion that connects the demultiplexer 4 and the duplexer 7 is referred to as an optical waveguide 12b.

As described above, the distance measuring sensor of the present embodiment irradiates a region included in a predetermined range in two directions perpendicular to each other in the space outside the vehicle, and detects a distance to an object outside the vehicle and the like. Specifically, the distance measuring sensor divides a predetermined area of the space outside the vehicle into a plurality of areas in the horizontal direction and the direction perpendicular to the horizontal plane, and the distance to the object included in each of the divided areas. Is calculated. Hereinafter, the horizontal direction and the direction perpendicular to the horizontal plane will be referred to as the H direction and the V direction, respectively.

A plurality of combiners 7 are arranged according to the resolution in the V direction of the distance measuring sensor, that is, the number of divisions in the V direction of the predetermined region. Then, the optical signal input to the demultiplexer 4 is divided into a plurality of duplexers 7 and input via the optical waveguide 12b.

In this embodiment, the resolution of the distance measuring sensor is 1500 in the H direction and 20 in the V direction. Correspondingly, 20 combiners 7 are arranged, and the optical waveguide 12 is branched into one optical waveguide 12a and 20 optical waveguides 12b in the demultiplexer 4.

The scanning unit 5 scans the input optical signal in the H direction. The scanning unit 5 of this embodiment is composed of a MEMS mirror 40. Further, the optical waveguide 12a reaches the side surface of the substrate 11, and the optical signal output by the duplexer 4 is applied to the MEMS mirror 40 via the collimating lens 37 arranged on the side surface of the substrate 11.

The MEMS mirror 40 is formed by processing an SOI substrate in which a support layer made of Si, a sacrificial layer made of SiO ₂ , and an active layer made of Si are laminated in this order, and emits light. It includes a reflecting portion 41 that reflects light and a beam portion 42 that holds and supports the reflecting portion 41 on both sides.

The MEMS mirror 40 includes, for example, a drive unit (not shown) that vibrates the beam portion 42 due to deformation of the piezoelectric element, and the beam portion 42 resonates with the drive portion so that the reflection portion 41 is rotated around the axis of the beam portion 42. Swing. Then, the light emitted from the substrate 11 is reflected by the swinging reflecting portion 41 so that the traveling direction becomes substantially perpendicular to the surface of the substrate 11 and is scanned in the H direction. Such a MEMS mirror 40 can scan at high speed by utilizing resonance. Further, by forming the reflective portion 41 with an appropriate material, a high reflectance can be obtained. Further, by installing an angle sensor such as a strain gauge on the beam portion 42, the direction in which light is emitted can be grasped.

As shown in FIG. 3, the substrate 11 and the MEMS mirror 40 are arranged inside the case 16 so that the light emitted from the side surface of the substrate 11 through the collimating lens 37 irradiates the MEMS mirror 40. .. The light emitted from the substrate 11 is reflected by the MEMS mirror 40 and is applied to the lid 17. The lid 17 is made of glass or the like that transmits light emitted from the substrate 11, and the light emitted to the lid 17 passes through the lid 17 and is applied to the diffusion lens 18.

The MEMS mirror 40 adjusts the traveling direction of the light emitted from the substrate 11 so that the traveling direction of the light irradiated to the diffusion lens 18 is the z direction which is the direction perpendicular to the substrate 11. Corresponds to a direction adjustment mirror.

It should be noted that the direction perpendicular to the surface of the substrate 11 includes not only the direction completely perpendicular to the surface of the substrate 11 but also the direction substantially perpendicular to the surface of the substrate 11. Similarly, the direction parallel to the surface of the substrate 11 includes not only the direction completely parallel to the surface of the substrate 11 but also the direction substantially parallel to the surface of the substrate 11.

The diffuser lens 18 diffuses the irradiated light to form a line beam, and is composed of a cylindrical lens or the like. The diffuser lens 18 of the present embodiment is arranged on the surface of the lid 17 so as to diffuse the irradiated light in the V direction. The light diffused by the diffusing lens 18 is applied to the outside of the distance measuring sensor. Then, the light reflected by the external object is applied to the condenser lens 19.

The condenser lens 19 is arranged on the surface of the lid 17. The condenser lens 19 collects the reflected light of the light emitted from the diffusion lens 18 to the outside of the distance measuring sensor and irradiates the receiver 6.

The light emitted from the outside of the distance measuring sensor to the condenser lens 19 is emitted to the receiver 6 through the prism 17a formed on the lid 17. The prism 17a inclines the light passing through the condenser lens in the y direction. Although the detailed structure of the prism 17a is not shown in FIG. 3, it is an inclined surface that inclines light in the y direction. As shown in FIG. 1, the receiver 6 includes a plurality of light receiving antennas 21 arranged in the V direction, and the light passing through the lid 17 is emitted to each light receiving antenna 21. Twenty light receiving antennas 21 are arranged corresponding to the resolution in the V direction of the distance measuring sensor.

Each light receiving antenna 21 is composed of a GC array 100 in which a plurality of GC 110s including a diffraction grating as shown in FIGS. 6 and 7 are arranged in an array as shown in FIG. In FIG. 6, the insulating film 14 is not shown.

The diffraction grating constituting the GC 110 is composed of a light introduction portion 111 in which the active layer 11c is etched to form a plurality of refractive index convex portions 111a, and an insulating film 14 embedded between the plurality of refractive index convex portions 111a. It is composed of an embedded layer 112.

Specifically, in the shape of the upper surface of the diffraction grating, the axis parallel to the H direction is made to coincide with the diagonal line on the long side of the two diagonal lines (hereinafter referred to as the long diagonal line), and the V direction is short and orthogonal to the long diagonal line. It has a diamond shape that matches the diagonal line (hereinafter referred to as the short diagonal line). That is, the diffraction grating has a configuration having an acute-angled first corner portion 113 in which one end of the long diagonal is located and an acute-angled second corner portion 114 in which the other end of the long diagonal is located. ing. The diffraction grating is configured by forming a plurality of curved slits extending on both sides of a long diagonal line with respect to the active layer 11c and partitioning the active layer 11c into a plurality of convex indexes 111a. In the present embodiment, each of the refractive index convex portions 111a has the same height. More specifically, the refractive index convex portion extends from the first corner portion 113 on which the refractive index convex portion 111a is connected to the optical waveguide 12 to the second corner portion 114 where the other end of the long diagonal line is located. 111a has a structure in which a plurality of 111a are arranged in a curved shape. An insulating film 14 made of SiO ₂ is embedded in the slit portion, and this is used as the embedded layer 112.

As shown in FIG. 9A, the plurality of refractive index convex portions 111a are configured such that the width gradually narrows as the distance from the first corner portion 113 increases. In addition, the plurality of refractive index convex portions 111a are configured such that the width gradually narrows as the distance from the long diagonal line, that is, toward the end of each refractive index convex portion 111a, as shown in FIGS. 7 and 9B. ing.

In the case of the present embodiment, as shown in FIGS. 9A and 9B, the refractive index convex portion 111a is formed at a constant pitch. That is, the width obtained by combining the width of the refractive index convex portion 111a and the width of the recess formed as the slit is defined as a constant periodic width, and the refractive index convex portion 111a is formed at each constant periodic width. Therefore, when the width of the refractive index convex portion 111a with respect to the constant period width is expressed as the duty ratio of the refractive index convex portion 111a, the duty ratio of the refractive index convex portion 111a becomes smaller toward the right side of the paper in both FIGS. 9A and 9B. Further, as compared with FIG. 9A, the duty ratio is smaller in FIG. 9B. In this way, the duty ratio of each refractive index convex portion 111a in the direction away from the optical waveguide 12 on the long diagonal and the direction away from the optical waveguide 12 on each side of the rhombus formed by the GC 110 (hereinafter referred to as side direction). The duty ratio of each of the refractive index convex portions 111a is different. In other words, if the angle formed by the long diagonal line and the arbitrary straight line l extending around the first corner portion 113 in the rhombus is θ, the duty ratio of each refractive index convex portion 111a is different at any angle θ. I am trying to be.

In the case of the present embodiment, the width of the refractive index convex portion 111a defines the cross-sectional area of the light introduction portion 111 cut in the radial direction about the first corner portion 113 for each cycle width. .. As described above, since only the refractive index convex portion 111a is formed for each cycle width, in the case of the present embodiment, the cross-sectional area of the refractive index convex portion 111a for each cycle width is light for each cycle width. It is the cross-sectional area of the introduction portion 111.

As shown in FIG. 8, the GC array 100 has a configuration in which a plurality of GC 110s having a diamond shape are spread over. In the case of the present embodiment, the GC array 100 is configured by arranging a total of 16 GC110s so that their long diagonals are directed in the same direction and the sides of the diamond-shaped GC110s face each other. ing. Of the plurality of GC110s constituting the GC array 100, the eight on the left side in the drawing are connected to the optical waveguide 12 on the left side of each GC110, and the eight on the right side are connected to the optical waveguide 12 on the right side of each GC110. .. That is, the GC array 100 is divided into two regions in the long diagonal direction, and for the region located on the left side of the paper surface on one side of the long diagonal line, the corner portion located on the left side of the paper surface in that direction is the first corner portion. The optical waveguide 12 is connected as 113. Then, in the GC array 100, for the region located on the right side of the paper surface on the other side of the long diagonal line, the optical waveguide 12 is connected with the corner portion located on the right side in that direction as the first corner portion 113. .. As a result, the eight GC110s on the right side take out light from the right side of the GC array 100 through the optical waveguide 12, and the eight GC110s on the left side take out light from the left side of the GC array 100 through the optical waveguide 12.

Further, each GC 110 is configured to have a similar shape having the same acute angle and obtuse angle, but the dimensions are reduced toward the left and right ends of the GC array 100. Therefore, the width of the gap between each GC 110 becomes wider toward the left and right ends of the GC array 100, and the gap is connected to the GC 110 arranged on the center side of the GC array 100. The optical waveguide 12 is arranged. In this way, considering the arrangement space of the optical waveguide 12, the dimensions of each GC 110 are reduced toward the left and right ends of the GC array 100. However, the optical waveguides 12 are arranged in the same direction for all GC 110s so that the light can be taken out from both the left and right sides instead of taking out the light in the same direction. Therefore, although the dimensions of each GC 110 become smaller toward the left and right ends of the GC array 100, the dimensions can be made as large as possible. Therefore, the gap between each GC 110, which is the placement space of the optical waveguide 12, can be minimized, the size of each GC 110 can be made as large as possible, the integration density can be increased, and the area efficiency can be maximized. It is possible.

Hereinafter, among the GC110, the one arranged in the center which is the position divided into two regions of the GC array 100 is the central GC110a, the one arranged at the left and right ends is the end GC110b, and the central GC110a and the end GC110b. The one arranged between them is called an intermediate GC110c.

Each GC110 has a diamond shape, but for the intermediate GC110c, the chamfered portions 115a and 116a in which the vertices of the third corner portion 115 and the fourth corner portion 116, which are obtuse angles where both ends of the short diagonal line are located, are cut out. Is provided. For the GC110 other than the central GC110a or the end GC110b, and in the case of the present embodiment, the intermediate GC110c, the optical waveguide 12 of the central GC110a located inside the central GC110a is arranged next to it. Therefore, the bending of the optical waveguide 12 can be made gentle, and the waveguide damage such as light leakage caused by the sudden bending can be suppressed, and the light propagation efficiency can be improved.

Further, as shown in FIG. 6, a BPF (bandpass filter) 22 and a polarizing filter 23 are laminated on the light receiving antenna 21. The BPF 22 allows light in a predetermined frequency band to pass through and blocks light in other frequency bands. BPF22 is a high refractive index TiO2 film 24, a low refractive index SiO ₂ film 25 is formed by laminating alternately, are both the lowermost layer and the uppermost layer of TiO2 film 24.

The polarizing filter 23 allows light polarized in a predetermined direction to pass through and blocks light polarized in another direction. Here, s-polarized light is passed through the polarizing filter 23. The polarizing filter 23 is composed of a SiO ₂ film 26 laminated on the BPF 22 and an Al wire grid 27 laminated on the SiO ₂ film 26.

The BPF 22 and the polarizing filter 23 remove unnecessary noise component light, and the light receiving antenna 21 is irradiated with light in a predetermined frequency band polarized in a predetermined direction. The light receiving antenna 21 is connected to the combiner 7 by an optical waveguide 12, and the optical signal output by the light receiving antenna 21 is input to the combiner 7.

The light receiving antenna 21 of the present embodiment has a width in the H direction larger than a width in the V direction. As a result, the reflected light can be received in a wide range in the H direction, so that the SNR of the distance measuring sensor is improved.

The combiner 7 generates a waveform by combining the optical signal input from the demultiplexer 4 and the optical signal input from the light receiving antenna 21, and corresponds to the resolution in the V direction of the ranging sensor. There are multiple locations.

Optical signals from the demultiplexer 4 and each light receiving antenna 21 are input to each combiner 7. Then, each combiner 7 outputs an optical signal formed by the combined wave of the two input optical signals. The combiner 7 is connected to the converter 8 by an optical waveguide 12, and the optical signal formed by the combiner 7 is input to the converter 8.

The converter 8 converts the input optical signal into an electric signal. The converter 8 of the present embodiment is composed of a PIN photodiode, and outputs a current signal according to an input optical signal. The converter 8 may be composed of an avalanche photodiode.

When the wavelength of the light generated by the LD1 is 0.85 μm or more and 0.95 μm or less as in the present embodiment, the distance measuring sensor is formed by using the converter 8 as a photodiode composed of a Si semiconductor. SNR can be improved. When the wavelength of the light generated by the LD1 is 1.5 μm or more and 1.6 μm or less, the SNR of the distance measuring sensor is improved by using the transducer 8 as a photodiode composed of a Ge semiconductor. Can be done.

As shown in FIG. 1, a plurality of converters 8 are arranged corresponding to the resolution in the V direction of the distance measuring sensor like the combiner 7, and each converter 8 is connected to each of the combiner 7 and the like. An optical signal is input. The converter 8 is connected to the TIA 9 by the wiring 13. A plurality of TIA 9s are arranged on the substrate 11 like the converter 8, and the current signal output by each converter 8 is input to each TIA 9.

The TIA 9 converts the current signal input from the converter 8 into a voltage signal and outputs it. The TIA 9 is connected to the calculation unit 10 by the wiring 13, and the voltage signal output by the TIA 9 is input to the calculation unit 10.

A plurality of such light receiving antennas 21, combiners 7, converters 8, and TIA 9 can be formed on the substrate 11 by using a batch process of semiconductor technology.

The calculation unit 10 processes the input electric signal and calculates the distance to the object by heterodyne detection, and includes an ADC (AD converter) 28, an FFT (fast Fourier transform) circuit 29, and an imaging processing circuit 30. It has. The converter 8, TIA 9, and calculation unit 10 correspond to processing units.

The ADC 28 converts the electric signal output by the TIA 9 into a digital signal and outputs the signal. The FFT circuit 29 detects a frequency component included in the digital signal output by the ADC 28.

The imaging processing circuit 30 calculates the distance to the object and the speed of the object based on the frequency component detected by the FFT circuit 29, and forms two-dimensional data. The data formed by the imaging processing circuit 30 is transmitted to an ECU (not shown) mounted on the vehicle and used for automatic braking or the like for avoiding a collision with an object.

The above is the configuration of the distance measuring sensor of this embodiment. The LD1, the modulator 2, the converter 8, the TIA 9, and the calculation unit 10 are connected to an external control circuit by wiring (not shown), and operate in response to an electric signal input from the control circuit.

The operation of the distance measuring sensor of this embodiment will be described. The ranging sensor of the present embodiment detects the distance to the object and the speed of the object by the FMCW method utilizing the coherence of the laser beam.

First, when the LD1 generates light, an optical signal is input from the LD1 to the modulator 2. The modulator 2 periodically increases or decreases the frequency of the input optical signal to form a triangular wave as shown by the solid line in FIG. Here, the modulator 2 forms a triangular wave having a period T that repeatedly increases and decreases the frequency between f0−Δf / 2 and f0 + Δf / 2 with f0 as the center. The optical signal formed by the modulator 2 is amplified by the amplifier 3 and then input to the collimating lens 37 and the combiner 7 via the demultiplexer 4.

Further, the optical signal is output to the MEMS mirror 40 as irradiation light via the collimating lens 37. Then, a drive unit (not shown) vibrates the beam portion 42, so that the reflection portion 41 of the MEMS mirror 40 is oscillated around the axis of the beam portion 42, and the light is scanned in the H direction. The light emitted from the side surface of the substrate 11 to the outside of the substrate 11 is reflected by the MEMS mirror 40, and the traveling direction is set to be perpendicular to the surface of the substrate 11 and is applied to the lid 17 and the diffuser lens 18.

The light emitted to the diffuser lens 18 is diffused in the V direction and is irradiated to the outside of the vehicle. At this time, since the light is diffused in the V direction, it is possible to irradiate a wide range in the V direction at once as shown in FIG.

That is, when the region to be irradiated with light is divided into m in the H direction and n is divided in the V direction, the i-th region in the H direction and the j-th region in the V direction are the regions Ri and j. As shown, the regions R1,1 to R1, n can be irradiated with light at once. Then, by scanning the light in the H direction by the scanning unit 5, the regions Ri, 1 to Ri, n can be irradiated with the light at once. When the resolution in the V direction of the distance measuring sensor is 20 as in the present embodiment, the regions Ri, 1 to Ri, 20 can be irradiated with light. Therefore, the scanning control becomes easier as compared with the case where the light is scanned in both the H direction and the V direction.

The light emitted to the outside of the vehicle is reflected by an object outside the vehicle and is applied to the condenser lens 19, passing through the condenser lens 19, lid 17, prism 17a, polarizing filter 23, and BPF 22 to receive the light receiving antenna 21. Is irradiated to. As shown in FIG. 12, since the plurality of light receiving antennas 21 are arranged in the V direction, the light reflected by the objects included in the plurality of regions arranged in the V direction can be received at one time. For example, the reflected light from the object included in the regions R1,1 to R1, n irradiates the region R1 in FIG. 12, and the reflected light from the object included in the regions Rm, 1 to Rm, n irradiates the region R2. Will be done. Then, the plurality of light receiving antennas 21 are irradiated with the reflected light from the objects included in the regions Ri, 1 to Ri, n, respectively.

The light emitted to the light receiving antenna 21 is input to the combiner 7, and is combined with the optical signal input from the duplexer 4 to the combiner 7. The optical signal formed by the combiner 7 combining the two optical signals is converted into a current signal by the converter 8, further converted into a voltage signal by the TIA 9, and input to the calculation unit 10.

The combiner 7, the converter 8, and the TIA 9 simultaneously process an optical signal for each light receiving antenna 21. That is, the plurality of combiners 7 simultaneously combine the reflected light from the regions Ri, 1 to Ri, n with the optical signal input from the demultiplexer 4 for each region. Then, the plurality of converters 8 and the plurality of TIA 9s simultaneously convert the optical signal formed by the combiner 7 into an electric signal for each region.

The signal input to the calculation unit 10 is converted into a digital signal by the ADC 28 and input to the FFT circuit 29. The FFT circuit 29 detects the frequency component of the input signal, and the imaging processing circuit 30 calculates the distance to the object and the speed of the object based on the detected frequency component.

The phase and frequency difference between the light input from the light receiving antenna 21 to the combiner 7 and the light input from the demultiplexer 4 depends on the distance to the object and the speed of the object, as shown in FIG. Occurs.

Then, in the optical signal formed by the combiner 7, two beat frequencies appear due to the difference in phase and frequency between the two optical signals before they are combined. One beat frequency fB1 is the difference in frequency when the frequencies of the two lights are both increasing, and the other beat frequency fB2 is the difference in frequency when the frequencies of the two lights are both decreasing. is there.

Since these two beat frequencies depend on the distance to the object and the speed of the object, they can be calculated from the two beat frequencies. Specifically, if the distance to the object is l, the relative velocity of the object to the distance measuring sensor is v, and the speed of light is c, then l = cT (fB1 + fB2) / 8Δf, v = c (fB2-fB1) / 4f0. ..

The distance to the object and the speed of the object are calculated each time the scanning unit 5 scans the light in the H direction. That is, when the regions Ri, 1 to Ri, n are irradiated with light and the distance to the object included in the regions Ri, 1 to Ri, n is calculated, the scanning unit 5 changes the traveling direction of the light. As a result, the region irradiated with light changes as shown by the arrow A1 in FIG. Then, the regions Ri + 1,1 to Ri + 1, n are irradiated with light, and the distance to the object included in the regions Ri + 1,1 to Ri + 1, n is calculated. By performing such an operation in order for i = 1 to m, the distance to the object included in the regions R1, 1 to Rm, n and the like are calculated. However, when the calculation of the distance to the object is completed when i = m, the distance measuring sensor sets i = m-1 and turns back to repeat the operation.

The imaging processing circuit 30 forms two-dimensional data based on the calculated distance and speed each time the calculation of the distance to the object when i = m is completed, and transmits the two-dimensional data to an ECU or the like (not shown). .. As a result, when there is an object near the vehicle, an automatic brake or the like for avoiding a collision with the object is activated.

The effect of this embodiment will be described. In the distance measuring sensor of the present embodiment, each GC 110 constituting the light receiving antenna 21 has a diamond shape. Then, a curved refractive index convex portion 111a is formed, and an insulating film 14 is embedded between the respective refractive index convex portions 111a to form a diffraction grating. Further, since the diffraction grating spreads over almost the entire area of the diamond shape, it is possible to receive the incident light in a wider range as compared with the configuration in which the tapered portion is provided.

Further, for each GC 110, the duty ratio of the convex portions is set so that the width of the plurality of refractive index convex portions 111a becomes narrower as the distance from the first corner portion 113 increases on the long diagonal line. In addition, the width of the refractive index convex portion 111a is gradually narrowed as the distance from the long diagonal line, that is, toward the end of each refractive index convex portion 111a. Therefore, it is possible to increase the coupling efficiency of the incident light not only in the direction of the long diagonal line but also in the direction away from the long diagonal line.

Specifically, regarding the coupling efficiency of the incident light in the GC110, it is preferable that the incident light is 100% coupled not only in the long diagonal direction but also in each direction. Then, if the total amount of light can be received from the first corner portion 113 to the second corner portion 114 on the opposite side in the long diagonal direction, the coupling efficiency becomes 100% in that direction. The duty ratio of the width of each refractive index convex portion 111a is set on the long diagonal line so as to approach such a high coupling efficiency.

However, this is a duty ratio set according to the length of the long diagonal as shown in FIG. 9A, and if the same duty ratio is set for the side direction of the diamond shape, the total amount of light cannot be received in the side direction. .. Therefore, as shown in FIG. 9B, in the side direction, the width of each refractive index convex portion 111a is wider than that on the long diagonal line so that the total amount of light can be received corresponding to the length of the side of the diamond shape. Is narrowed as the distance from the optical waveguide 12 increases, so that the duty ratio becomes smaller. This makes it possible to increase the coupling efficiency of the incident light in any direction of the GC 110.

With such a configuration, the GC110 can be made capable of increasing the coupling efficiency in a wider range. Therefore, by arranging such GC 110s in an array to form a GC array 100, and further applying such a GC array 100 to a light receiving antenna 21, it is possible to improve the coupling efficiency in a wide range. Can be done.

Further, each GC110 having a diamond shape has a short diagonal line along the V direction and a long diagonal line along the H direction. Therefore, on the long diagonal line, the tangential direction of each refractive index convex portion 111a is the V direction, and the direction of the long diagonal line, which is the vertical direction thereof, is the H direction. On the other hand, the reflected light returning from an object outside the distance measuring sensor is incident on the light receiving antenna 21 as incident light, and the s-polarized light of the reflected light is in the V direction and the p-polarized light is in the H direction.

In the distance measuring sensor of the present embodiment, distance measurement is performed based on the s polarization of the incident light. Therefore, it is important to be able to efficiently receive the incident light of s-polarized light. In order to efficiently receive the incident light of s-polarized light, it is preferable that the direction of the unevenness of the diffraction grating is the same as that of s-polarized light, and the closer the direction of the unevenness is to perpendicular to the s-polarized light, the more efficiently the light is received. Can't be done. Even if the GC 110 has a diamond shape, if the corner portion connected to the optical waveguide 12 is an obtuse angle portion, the inclination angle of the curve formed by the refractive index convex portion 111a is also obtuse. In this case, the tangential direction of the end of the convex index 111a approaches perpendicular to the s-polarized light. Therefore, the light receiving efficiency with respect to the incident light deteriorates. However, in the present embodiment, the corner portion connected to the optical waveguide 12 is an acute-angled corner portion. Therefore, the inclination angle of the curve formed by the refractive index convex portion 111a can be made acute, and the tangential direction of the end portion of the refractive index convex portion 111a can be prevented from approaching perpendicular to s-polarized light. Therefore, it is possible to increase the light receiving efficiency with respect to the incident light in the entire area of the GC 110.

Further, in the light receiving antenna 21 of the ranging sensor as in the present embodiment, since the incident light enters the condenser lens 19 from various directions, the focal position on the light receiving antenna 21 according to each incident angle. It shifts. Therefore, it is necessary to use the light receiving antenna 21 which can obtain high coupling efficiency in a wider range. This will be described with reference to FIG.

As shown in FIG. 13, for example, the incident light is parallel light having a light receiving diameter of about 3 mm, but light inclined to the left or right in the figure with the center line of the condenser lens 19 as the center also enters. In the present embodiment, the range extends to 0.25 °, and it is necessary to be able to detect the incident light satisfactorily even if it is inclined in that range. That is, a detection angle β of 0.25 ° is required.

Further, the light transmitted through the condenser lens 19 is condensed by refraction by the condenser lens 19 and enters the light receiving antenna 21 at a position where the focal length Ls = 12 mm. The light receiving angle ξ is 14.25 °, and the limit spot diameter φL is 17 μm. At this time, if the incident light is not inclined and is incident only from a certain direction, it is sufficient that the light receiving antenna 21 can receive light within the range of 17 μm, which is the limit spot diameter φL. However, since inclined light also enters the condenser lens 19, the focusing area size RL is expected to be about 69 μm when the deviation is taken into consideration. Therefore, it is necessary to have a light receiving antenna 21 that can obtain a high coupling efficiency in a wide range corresponding to such a wide focusing area size RL.

However, assuming that one GC110 is one pixel, the relationship between the width of one pixel and the radiation angle or the light receiving angle is estimated as shown in FIG. 14, and the larger the width of one pixel, the smaller the light receiving angle. Then, in order to satisfactorily receive light having a light receiving angle of 14.25 °, it is necessary to suppress the width of the GC110 of one pixel to, for example, about 10 μm, and when the width is 69 μm, it is 14.25 °. Cannot adapt to the light receiving angle.

On the other hand, the light receiving antenna 21 of the present embodiment makes it possible to obtain a high coupling efficiency in a wide range by forming the GC array 100 in which a plurality of narrow GC 110s are spread as described above. Specifically, as shown in FIG. 8, the width Wz of the GC array 100 is the width w of the optical waveguide 12, the distance s between the optical waveguides 12, the length La of one side of the central GC110a, and the rhombus formed by the GC110. It is expressed by Equation 1 using the acute angle angle 2θ _G of. The central GC110a has the largest dimension among the GC110s, and the length of one side of the intermediate GC110c and the end GC110b is shorter than that.

ここで、ＧＣアレイ１００の幅Ｗｚについて、６９μｍ以上となる７０μｍとし、間隔ｓ＝０．５μｍ、角度θ_Ｇ＝３０°とすると、長さＬａは１１μｍとなる。つまり、中央ＧＣ１１０ａの一辺の長さａを１１μｍという１０μｍ程度の値にでき、中間ＧＣ１１０ｃや端部ＧＣ１１０ｂについては、一辺の長さをそれよりも短くできる。したがって、上記した１４．２５°の受光角に適応することができ、集光レンズ１９への入射光が様々な方向からの光を含んでいても、受光アンテナ２１によって効率よく受光することが可能となり、長距離の測距が可能となる。

Here, if the width Wz of the GC array 100 is 70 μm, which is 69 μm or more, the interval s = 0.5 μm, and the angle θ _G = 30 °, the length La is 11 μm. That is, the length a of one side of the central GC110a can be set to a value of about 10 μm of 11 μm, and the length of one side of the intermediate GC110c and the end GC110b can be made shorter than that. Therefore, it can be adapted to the above-mentioned light receiving angle of 14.25 °, and even if the light incident on the condenser lens 19 includes light from various directions, it can be efficiently received by the light receiving antenna 21. Therefore, long-distance distance measurement becomes possible.

Further, the light receiving area ratio η _A of the GC array 100, that is, the area ratio of the GC array 100 to the occupied area is expressed by Equation 2.

そして、ＧＣアレイ１００の幅Ｗｚについて、６９μｍ以上となる７０μｍとし、間隔ｓ＝０．５μｍ、角度θ_Ｇ＝３０°、一辺の長さＬａ＝１１μｍ、幅ｗ＝０．４μｍとすると、受光面積率η_Ａは、０．８５となる。このように、高い受光面積率η_Ａを得ることができ、高い結合効率が得られることが判る。ここで説明した寸法においては、受光アンテナ２１を構成するＧＣアレイ１００の面積が集光レンズ１９で集光された入射光のスポットの面積よりも大きくなる。また、ＧＣアレイ１００を構成する個々のＧＣ１１０の面積が集光レンズ１９で集光された入射光のスポットの面積と略同じ大きさとなる。そして、ＧＣアレイ１１０の面積が、集光レンズ１９に入射する光の入射角により広がる集光エリアサイズＲＬと略同じ大きさになる。

Then, when the width Wz of the GC array 100 is 70 μm, which is 69 μm or more, the interval s = 0.5 μm, the angle θ _G = 30 °, the length of one side La = 11 μm, and the width w = 0.4 μm, the light receiving area The rate η _A is 0.85. As described above, it can be seen that a high light-receiving area ratio η _A can be obtained and a high coupling efficiency can be obtained. In the dimensions described here, the area of the GC array 100 constituting the light receiving antenna 21 is larger than the area of the spot of the incident light collected by the condenser lens 19. Further, the area of each GC 110 constituting the GC array 100 is substantially the same as the area of the spot of the incident light collected by the condenser lens 19. Then, the area of the GC array 110 becomes substantially the same as the condensing area size RL which is widened by the incident angle of the light incident on the condensing lens 19.

Although the central axis of the condenser lens 19 is shown in FIGS. 3 and 13 so as to coincide with the normal direction of the light receiving antenna 21, it is actually inclined in the y-axis direction as shown in FIG. It is said that the state has been completed. Although the light receiving antenna 21 is composed of the GC 110, in order to improve the light receiving efficiency in the GC 110, it is preferable that the light receiving antenna 21 is incident on the GC 110 not from the normal direction with respect to the surface of the GC 110 but from an inclined direction. Therefore, as shown in FIG. 15, the central axis of the condenser lens 19 is tilted from the normal direction of the light receiving antenna 21, so that high light receiving efficiency can be obtained.

Here, as described above, with respect to the refractive index convex portion 111a, the width of the plurality of refractive index convex portions 111a becomes narrower as the distance from the first corner portion 113 connected to the optical waveguide 12 increases on the long diagonal line. The duty ratio of the convex part is set. In addition, the width of the refractive index convex portion 111a is gradually narrowed as the distance from the long diagonal line increases. With such a configuration, it is possible to increase the coupling efficiency in a wide range, but with the following settings, it is possible to further enhance the coupling efficiency.

Specifically, each of the refractive index convex portions 111a is formed by etching the active layer 11c, and has an end face on the side far from the optical waveguide 12 (hereinafter referred to as the first edge) and an end face on the near side (hereinafter referred to as the first edge). It has a structure with (called 2 edges).

Here, as shown in FIG. 10, when the GC 110 is viewed from above, the center of the boundary end connected to the optical waveguide 12 among the rhombuses constituting the GC 110 is set as the origin (0,0) of the xy coordinate, and the length is set. It is assumed that the diagonal line is the y-axis and the short diagonal line is a line segment parallel to the x-axis. In that case, Equation 3 holds for the center line of the refractive index convex portion 111a, that is, a curve (hereinafter, referred to as a central curve) that draws the center positions of the first edge and the second edge. Then, based on this formula 3, the curve drawn by the first edge (hereinafter referred to as the positive curve) is represented by the formula 4, and the curve drawn by the second edge (hereinafter referred to as the negative curve) is represented by the formula 5. Curve. For convenience, the y of the curve drawn by the first edge is described as "y ₊ ", and the y of the curve drawn by the second edge is described as "y ₋ ". From these equations, the curved shape of the refractive index convex portion 111a of the GC 110 is different depending on the incident angle of the incident light from the condenser lens 19 to the GC 110.

In the above formulas 3 to 5, m is a number from the optical waveguide 12 of the plurality of refractive index convex portions 111a, and the one closest to the optical waveguide 12 is set to "1" and numbered in order from there. is there. λ is the wavelength of the incident light on the diffraction grating constituting the GC 110, θ _IN is the incident angle of the incident light on the diffraction grating, N ₀ is the effective refractive index of the diffraction grating, and w ₀ is the waveguide light in the optical waveguide 12. It is 1 / e ² half width of the intensity x direction distribution. The effective refractive index is the total refractive index of the refractive index convex portion 111a constituting the diffraction lattice and the embedded layer 112 embedded in the slit between them, and in the case of the present embodiment, the refractive index convex portion 111a is formed. It is the total refractive index of Si and SiO ₂ constituting the insulating film 14. f _G is the unevenness ratio of the diffraction grating. The unevenness ratio of the diffraction grating means the ratio of the width of the refractive index convex portion 111a and the width of the slit portion within a fixed period width including the refractive index convex portion 111a and the slit portion adjacent to it, that is, the portion in which the insulating film 14 is embedded. doing.

なお、ｆ_Ｇについては、数式６で表される。この式において、Ｌ_ＧＣは、角度θの方向の導波光の伝搬長であり、数式７で表され、α_ＭＡＸは、放射損失係数の最大値、ηRは放射効率である。角度θについては、ＧＣ１１０が構成する菱形の鋭角の角度を２θ_Ｇとすると、長対角線を挟んだ両側において０°〜θ_Ｇの範囲で変化する。

Note that f _G is expressed by Equation 6. In this formula, L _GC is the propagation length in the direction of guided light angle theta, expressed in Equation 7, alpha _MAX is the maximum value of the radiation loss coefficient, .eta.r is radiation efficiency. As for the angle θ, assuming that the acute angle of the rhombus formed by the GC 110 is 2 θ _G , it changes in the range of 0 ° to θ _{G on} both sides of the long diagonal line.

例えば、上記各式において、実効屈折率Ｎ_０は、２．０８５、長対角線における放射損失係数αは、０．３３３μｍ^−１、波長λは、１．５５μｍ、入射角θ_ＩＮは、１０°として設計される。

For example, in each of the above equations, the effective refractive index N ₀ is 2.085, the radiation loss coefficient α on the long diagonal is 0.333 μm ^-1 , the wavelength λ is 1.55 μm, and the incident angle θ _IN is 10 °. Designed.

In this way, if the first edge draws the positive curve shown in Equation 4 and the second edge draws the negative curve shown in Equation 5, the coupling efficiency can be further improved.

(Modified example of the first embodiment)
In the first embodiment, as shown in FIGS. 9A and 9B, a case where the convex index 111a gradually becomes narrower as it is separated from the first corner 113 has been described. On the other hand, the form may be such that the width gradually increases as the distance from the first corner portion 113 increases.

For example, the relationship between the duty ratio of the refractive index convex portion 111a and the light coupling coefficient is the relationship shown in FIG. That is, when the duty ratio is 0.5 or less, the coupling coefficient gradually increases as the duty ratio increases, and when the duty ratio is 0.5 or more, the coupling coefficient gradually decreases as the duty ratio increases.

In the case where the relationship between the duty ratio and the light coupling coefficient is the relationship shown in FIG. 16, when the refractive index convex portion 111a is gradually narrowed as it is separated from the first corner portion 113 as in the first embodiment. , The duty ratio should approach 0.5 from a value greater than 0.5. As a result, the coupling coefficient can be gradually increased.

On the contrary, when the shape gradually widens as the distance from the first corner portion 113 increases, the duty ratio is set to approach 0.5 from a value smaller than 0.5. In this case as well, the coupling coefficient can be gradually increased.

Further, in the first embodiment, the refractive index convex portion 111a is formed so as to penetrate the active layer 11c, and the embedded layer 112 is provided between the refractive index convex portions 111a. On the other hand, as shown in FIGS. 9C and 9D, the refractive index convex portion 111a may be formed by etching halfway without penetrating the active layer 11c.

(Second Embodiment)
The second embodiment will be described. Since this embodiment is the same as the first embodiment in that the structure of the diffraction grating is changed from that of the first embodiment, only the parts different from the first embodiment will be described.

As shown in FIG. 17, also in this embodiment, the active layer 11c is etched to form the diffraction grating of GC110 by using the SOI substrate in which the sacrificial layer 11b and the active layer 11c are formed on the support layer 11a. However, the etching depth is different from that of the first embodiment. The relationship between the depth of the slit and the coupling coefficient of light is shown as shown in FIG. 18 when the width of the convex index 111a is constant. The deeper the slit, the more refraction from the bottom of the slit. The higher the height of the rate convex portion 111a, the larger the coupling coefficient. Based on this, the depth of the slit is set in this embodiment. Specifically, as shown in FIG. 17, each convex index 111a in the diffraction grating is formed by gradually deeply etching the active layer 11c as the distance from the optical waveguide 12 increases. That is, although each of the refractive index convex portions 111a has the same height and the same plane at the highest position, the height from the bottom surface of the slit is different due to the change in the depth of the slit. ing. For example, each of the refractive index convex portions 111a has a low slit depth on the optical waveguide 12 side, so that the height from the bottom surface of the slit is low, and the etching groove depth is deepened as the distance from the optical waveguide 12 increases. As a result, the height from the bottom of the slit is increased. Such slits can be formed using so-called grayscale exposure techniques.

In the case of the present embodiment, there is a slit bottom 111b in which the active layer 11c is not removed between the refractive index convex portions 111a, and the slit bottom 111b also constitutes a part of the light introduction portion 111. The cross-sectional area of the light introduction portion 111 formed for each cycle width is the total cross-sectional area of the refractive index convex portion 111a and the slit bottom portion 111b. Then, the embedded layer 112 in which the insulating film 14 is embedded is arranged in the groove-shaped slit between the convex indexes 111a. As a result, a diffraction grating is formed by the light introduction portion including the convex index portion 111a and the embedded layer 112 embedded in the slit between them.

For example, the thickness of the support layer 11a is 625 μm, the thickness of the sacrificial layer 11b is 2.20 μm, the thickness of the active layer 11c is 0.22 μm, and the thickness of the insulating film 14 is 2.65 μm. The depth of the groove-shaped slit formed between the convex portions 111a of the refractive index is determined from the apex of the rhombus formed by the GC 110 on the opposite side of the apex of the acute angle connected to the optical waveguide 12 or the apex. The thickness of the active layer 11c is set to be zero at the apex of the obtuse angle. In FIG. 17, the depth of the groove-shaped slit formed between the convex indexes 111a is deep corresponding to the distance from the apex of the acute angle connected to the optical waveguide 12 in the rhombus formed by the GC 110. Has been done.

Further, since the effective refractive index changes depending on the cross-sectional area of the light introducing portion 111 for each cycle width, the cross-sectional area of the light introducing portion 111 for each cycle width becomes smaller as the distance from the long diagonal line increases in the direction of the angle θ. In addition, the depth of the slit is gradually increased.

In this way, the etching depth when forming the refractive index convex portion 111a may be adjusted, and the etching depth may be gradually increased from the apex connected to the optical waveguide 12. Even in this way, the same effect as that of the first embodiment can be obtained.

(Third Embodiment)
The third embodiment will be described. This embodiment is also a modification of the structure of the diffraction grating with respect to the first embodiment, and the other parts are the same as those of the first embodiment. Therefore, only the parts different from the first embodiment will be described.

As shown in FIG. 19, also in this embodiment, the active layer 11c is etched to form the diffraction grating of GC110 by using the SOI substrate in which the sacrificial layer 11b and the active layer 11c are formed on the support layer 11a. However, the height of the convex index 111a is different from that of the first embodiment. The relationship between the height of the refractive index convex portion 111a and the light coupling coefficient is shown as shown in FIG. 20 when the width of the refractive index convex portion 111a is constant, and the higher the height of the refractive index convex portion 111a, the higher the coupling coefficient. Becomes larger. Based on this, the height of the refractive index convex portion 111a is set in the present embodiment. Specifically, as shown in FIG. 19, the refractive index convex portion 111a in the diffraction grating is configured to gradually increase in height as the distance from the optical waveguide 12 increases. Such a configuration is formed by etching so that the height of the active layer 11c becomes higher as the height of the active layer 11c increases away from the first corner portion 113. The convex index 111a having different heights can also be formed by using the so-called gray scale exposure technique.

For example, the thickness of the support layer 11a is 625 μm, the thickness of the sacrificial layer 11b is 2.20 μm, the thickness of the active layer 11c is 0.22 μm, and the thickness of the insulating film 14 is 2.65 μm. The height of each of the refractive index convex portions 111a is increased as the distance from the first corner portion 113 connected to the optical waveguide 12 among the rhombuses formed by the GC 110 increases, and the second corner portion 114 or the third corner portion 115 or It is set to be the highest at the fourth corner 116. In FIG. 19, the height of each of the refractive index convex portions 111a is increased corresponding to the distance from the apex of the first corner portion 113 connected to the optical waveguide 12 in the rhombus formed by the GC 110.

Further, the height of the refractive index convex portion 111a is gradually increased so that the cross-sectional area of the light introduction portion 111 for each cycle width increases as the distance from the long diagonal line increases in the direction of the angle θ.

As described above, in the etching when the refractive index convex portion 111a is formed, the height of the refractive index convex portion 111a may gradually increase from the apex connected to the optical waveguide 12. Even in this way, the same effect as that of the first embodiment can be obtained.

(Other embodiments)
The present invention is not limited to the above-described embodiment, and can be appropriately modified within the scope described in the scope of patent claims. For example, in the above embodiment, it goes without saying that the elements constituting the embodiment are not necessarily essential except when it is clearly stated that they are essential and when they are clearly considered to be essential in principle. Further, in the above embodiment, when numerical values such as the number, numerical value, amount, and range of the constituent elements of the embodiment are mentioned, when it is clearly stated that they are particularly essential, and in principle, the number is clearly limited to a specific number. It is not limited to the specific number except when In addition, in each of the above embodiments, when referring to the shape, positional relationship, etc. of a component or the like, the shape, unless otherwise specified or limited in principle to a specific shape, positional relationship, etc. It is not limited to the positional relationship.

For example, in each of the above embodiments, the case where the GC110 is applied as an element for receiving light and propagating the light to the optical waveguide 12 has been described as an example, but the light emitted from the optical waveguide 12 is emitted. It can also be applied as an element for performing the above.

Further, the configuration may be a combination of the second embodiment or the third embodiment and the first embodiment. That is, when the second embodiment and the first embodiment are combined, the slit is deepened as the distance from the first corner portion 113 on the long diagonal line as in the second embodiment. Then, as in the first embodiment, in the direction of the angle θ, the width of the refractive index convex portion 111a is narrowed as the distance from the long diagonal line increases. Further, when the third embodiment and the first embodiment are combined, as in the third embodiment, the refractive index convex portion 111a is set to increase as the distance from the first corner portion 113 increases on the long diagonal line. Then, as in the first embodiment, in the direction of the angle θ, the width of the refractive index convex portion 111a is narrowed as the distance from the long diagonal line increases.

That is, the cross-sectional area of the light introduction portion 111 for each cycle width becomes larger as the distance from the first corner portion 113 increases on the long diagonal line, and increases as the distance from the long diagonal line increases in the direction of the angle θ. I just need to be there.

21 Light receiving antenna 100 GC array 111 Light introduction part 111a Refractive index convex part 111b Slit bottom 112 Embedded layer 113 to 116 First to fourth corners 115a, 116a Chamfered part

Claims (14)

A grating coupler that receives light and propagates light to the optical waveguide (12), or an element that emits light propagated from the optical waveguide.
The long diagonal line, which is a long diagonal line, and the short diagonal line, which is a short diagonal line, are orthogonal to each other in a rhombic shape, and the sharp first corner portion (113) where one end of the long diagonal line of the rhombic shape is located is used as the optical waveguide. With a plurality of refractive index convex portions (111a) that are connected and arranged in a curved shape from the first corner portion to the second corner portion (114) where the other end of the long diagonal line is located. It has a light introduction portion (111) including an embedded layer (112) in which an insulating film (14) is embedded between the plurality of convex indexes having a refractive index, and every predetermined cycle width from the first corner portion. Includes a diffraction grating in which the convex index portion and the embedded layer are repeatedly arranged.
The refractive index convex portion for each cycle width is made smaller or larger as the distance from the first corner portion is increased on the long diagonal line, and further, in the direction of an angle centered on the first corner portion. A grating coupler that is made smaller or larger as it goes away from the long diagonal. The plurality of refractive index protrusions are partitioned by slits formed in the active layer (11c) formed on the sacrificial layer (11b) formed on the support layer (11a), and the plurality of convex portions have a refractive index. Each of the refractive index convex portions is configured to have the same height, and the width is narrowed or widened as the distance from the first corner portion is increased on the long diagonal line, and the width is further narrowed or widened as the distance from the first corner portion is increased. The grating coupler according to claim 1, wherein the width is narrowed or widened. The plurality of refractive index protrusions are partitioned by slits formed in a part of the active layer (11c) formed on the sacrificial layer (11b) formed on the support layer (11a). Each of the plurality of refractive index convex portions is configured to have the same height, and the width is narrowed or widened as the distance from the first corner portion is increased on the long diagonal line, and further, the long diagonal line is formed in the direction of the angle. The grating coupler according to claim 1, wherein the width is narrowed or widened as the distance from the ground increases. The plurality of refractive index convex portions are partitioned by slits formed in the active layer in a laminated structure of the support layer (11a), the sacrificial layer (11b), and the active layer (11c), and the first corner portion. The grating coupler according to claim 1, wherein the depth of the slit becomes deeper as the distance from the angle increases, and the depth of the slit becomes deeper as the distance from the long diagonal line increases. The plurality of refractive index convex portions are partitioned by slits formed in the active layer in a laminated structure of the support layer (11a), the sacrificial layer (11b), and the active layer (11c), and the first corner portion. The grating coupler according to claim 1, wherein the height of the active layer is increased as the distance from the grating coupler is increased, and the height of the grating coupler is increased as the distance from the angle is increased. In each of the plurality of refractive index convex portions, the end face on the side far from the first corner portion of the refractive index convex portions is set as the first edge, and the end face on the near side is set as the second edge.
The curve drawn by the first edge

Meet and
The curve drawn by the second edge

The grating coupler according to any one of claims 1 to 5, which satisfies the above. A plurality of grating couplers according to any one of claims 1 to 6 are arranged.
A grating coupler array in which long diagonal lines of each of the plurality of grating couplers are directed in the same direction, and the rhombic sides of each of the grating couplers are arranged so as to face each other. The plurality of grating couplers are divided into two regions in the long diagonal direction, and for a region located on one side of the long diagonal, the diamond-shaped corner portion located in the direction is the first corner portion. The optical waveguide is connected as described above, and the optical waveguide is connected with the diamond-shaped corner portion located in the direction as the first corner portion for the region located on the other side of the long diagonal line. Item 7. The grating coupler array according to item 7. Among the plurality of the grating couplers, the one arranged in the center which is the position divided into the two regions is referred to as the central grating coupler (110a), and the one arranged on one side and the other side of the long diagonal line most. Is the end grating coupler (110b), and the one arranged between the central grating coupler and the end grating coupler is the intermediate grating coupler (110c).
In the intermediate grating coupler, among the obtuse-angled corners where the ends of the short diagonal lines are located, the vertices of the corners are cut out at the corners (115, 116) where the optical waveguide is arranged next to each other. The grating coupler array according to claim 7 or 8, which is a chamfered portion (115a, 116a). The grating according to any one of claims 7 to 9, wherein the curved shape of the convex index portion of the grating coupler is different depending on the incident angle of the incident light from the condenser lens to the grating coupler. Coupler array The grating coupler array according to any one of claims 7 to 10, wherein the area of the grating coupler array is larger than the area of the spot of the incident light collected by the condenser lens. The area of each grating coupler constituting the grating coupler array is approximately the same as the area of the spot of the incident light collected by the condenser lens, and the area of the grating coupler array is the light incident on the condenser lens. The grating coupler array according to any one of claims 7 to 11, wherein the grating area has substantially the same size as the light-collecting area that expands depending on the incident angle of A light receiving antenna having the grating coupler array according to any one of claims 7 to 12 and receiving light by the grating coupler array. A ranging sensor that irradiates an object with light, receives the reflected light from the object, and measures the distance to the object based on the irradiation light to the object and the reflected light from the object. ,
A distance measuring sensor that receives the reflected light with the light receiving antenna according to claim 13.

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