JP6513884B1 - Optical phased array and LIDAR sensor using the same - Google Patents

Abstract

An optical phased array (OPA) that can provide the function of beam steering or beam scanning with relatively small phase shift without requiring complicated calibration process to determine the amount of phase shift compensation. The optical phased array is composed of an optical waveguide formed on a substrate, and includes a bus waveguide through which input light propagates and a part of light propagating through the bus waveguide disposed on the bus waveguide. A plurality of optical couplers to be extracted, a plurality of waveguide lines for respectively propagating the light extracted by the plurality of optical couplers, and a phase shifter provided in the bus waveguide. The plurality of waveguide lines have the same optical path length, and the phase shifter is provided in each section of the bus waveguide between adjacent optical couplers.

Description

  The present invention relates to a light phased array that controls the emission direction of a light beam to provide a beam steering or beam scanning function, and a LiDAR (Light Detection and Ranging) sensor using the same.

  The LiDAR sensor is used for remote sensing and ranging applications, for example, for performing real-time three-dimensional mapping and object detection, tracking, identification, etc. in an automatic driving system or the like.

  The LiDAR sensor scans the laser beam in the observation space and irradiates an object in the space, and the time of flight until the irradiated beam reaches the object and reflects it back to the receiver in the LiDAR sensor The position and distance of the object are measured by measuring (TOF, Time of Flight).

  As such a LiDAR sensor, one that scans a laser beam using mechanical rotating parts is known, but some systems such as advanced driver assistance systems (ADAS) and autonomous driving systems are known. It is desirable to use a solid state beam scanner that can have various advantages. Such benefits include higher sensor reliability, longer sensor life, smaller sensor size, lighter sensor weight, and more affordable sensor costs. It is not limited to these.

  One such solid-state beam scanner is an optical phased array (OPA). The application of optical phased arrays makes LiDAR sensors faster and more adaptive and more useful than conventional LiDAR using mechanical beam scanning.

  Conventionally, as a technique related to an optical phased array, it is known that a high frequency phase shifter for a high frequency phased array antenna uses a zigzag optical waveguide provided with a plurality of light receivers (Patent Document 1). The high frequency phase shifter causes the light modulated by the high frequency signal to propagate to the zigzag optical waveguide, and the light of each position is received and detected by a plurality of light receivers disposed at different positions along the optical waveguide. A plurality of high frequency signals given different phase shifts are extracted. Then, a high frequency signal to which a desired phase shift is given among the plurality of extracted high frequency signals is selectively output. However, this high frequency phase shifter merely uses an optical waveguide as a means for giving a delay time to a high frequency signal, and does not give a phase shift to light itself. Therefore, this technique can not be used for optical phased arrays.

  As another related prior art, an optical signal processing apparatus having a monolithic integrated semiconductor structure including an optical waveguide constituting an optical phase shifter or the like is known (Patent Document 2, Patent Document 3). In this optical signal processing device, the input light is branched into a plurality of lights by the 2-branch waveguides connected in multiple stages. Then, individual phase shifts are given to the respective branched lights by the phase shifters provided in the output waveguides that output the respective branched lights. However, this optical signal processing device does not constitute an optical phased array. That is, this device simply divides the light to individually control the phase, and an antenna element array for outputting the diffracted light (the light whose phase is controlled so that the main maximum beam of the diffracted light is generated) Can not be applied to LiDAR as it is, since it is not provided with an array of light output elements that output at predetermined intervals.

  In addition, when the configuration of the above optical signal processing apparatus is to be diverted to an optical phased array, the phase of light output from the output waveguides arranged in a line is linear as shown by the following equation in order from the end Need to increase.

  Here, m is a number sequentially assigned from the end to the arrayed antenna elements when the aligned output waveguides are regarded as the arrayed antenna elements in the optical phased array. Further, P is an arrangement interval of the antenna elements, λ is a wavelength of light to be output, and θ is a direction angle of the main maximum beam of diffracted light with respect to a normal of a plane formed by the light emitting end of the antenna element. As apparent from equation (1), the phase shifters provided for each channel (ie, each antenna element and each of the optical transmission paths leading to the antenna element) can provide different phase shifts, And the cumulative value of the phase shift must be more than 2π.

  However, in the above optical signal processing apparatus, the phase of light output from each output waveguide is determined only by the phase shifter provided in each output waveguide, and the phase shifter of each output waveguide is Because they are controlled independently of each other, the process for correctly finding the value of the accumulated phase shift exceeding 2π is complicated. Therefore, the control operation for causing the above configuration to function as an optical phased array becomes quite complicated.

  As the prior art most relevant to the present invention, LiDAR configured as a device based on a photonic integrated circuit (PIC) is known (Non-Patent Document 1). This device has bus waveguides, cascaded thermal phase shifters, and cascaded evanescent couplers, which are used as grating-based antenna elements. It is connected. In this device, the beam steering function is provided by controlling the phase increment of the bus waveguide.

  However, this device has the following drawbacks. That is, the distances of the waveguides inserted between the evanescent coupler and the grating based antenna element are not equal to each other. That is, all optical path lengths (all OPLs (Optical Path Lengths)) of the respective waveguides are not equal. Therefore, during idle operation (during non-energization) of the phase shifter, the phase relationship of the output light between the adjacent antenna elements is not constant.

  Such differences in OPL (OPL difference, optical path difference) can result in channels with unwanted phase shifts. In general, when the phase shift output from the antenna element does not follow the linear law shown in equation (1), the beam width of the main maximum beam (main beam or main lobe) of the diffracted light output from the antenna element array Spreads, resulting in poor angular resolution.

  Also, even if the phase shift in the bus waveguide maintains the linearity dependent on the refractive index and maintains the linear phase tilt as shown in Equation (1), the main beam is at a certain beam angle Because of the shifted state, a calibration process is required to provide an additional phase shift to all beam shifters to compensate for the beam angle.

  In the calibration process, it is necessary to identify the magnitude of these additional phase shifts and to include the initial bias voltage in the heater control voltage of the phase shifter in order to compensate for the additional phase shifts. This makes the operation and control of the optical phased array more complicated.

  Additional problems arise when the optical phased array operates in a wide frequency band (ie, in a wide wavelength band). In this case, due to the wavelength dependency of the refractive index, the calibration process becomes quite complicated because the phase shift becomes different at different wavelengths.

U.S. Pat. No. 5,222,162 U.S. Patent No. 5,770,472 U.S. Pat. No. 5,930,031

Christopher V. Poulton, Ami Yaacobi, David B. Cole, Matthew J. Byrd, Manan Raval, Diedrik Vermeulen, Michael R. Watts, Coherent solid-state LIDAR with silicon photonic optical phased arrays, Optics Letters, Vol. 42, No. 20 / October 15, 2017.

  The object of the present invention is to realize an optical phased array (OPA) which can provide the function of beam steering or beam scanning with relatively small phase shift without requiring complicated calibration process to determine the amount of phase shift compensation. It is.

One aspect of the present invention is an optical phased array constituted by an optical waveguide formed on a substrate, and a bus waveguide through which input light propagates, and the bus waveguide disposed on the bus waveguide. A plurality of optical couplers for respectively extracting a portion of light propagating in the waveguide, a plurality of waveguide lines for respectively propagating the light extracted by the plurality of optical couplers, and a phase shifter provided in the bus waveguide; wherein the plurality of optical couplers, the cascaded along the bus waveguide, said phase shifter, said optical coupler is provided, et al in their respective sections sandwiching the adjacent of the bus waveguide, said bus electrically The sections between the adjacent optical couplers along the waveguide are all of the same length, and the phases of the light extracted from the adjacent optical couplers in a state where no current is supplied to any of the phase shifters. All have the same predetermined value, and the plurality of waveguide lines have equal optical path lengths, and each of the plurality of waveguide lines is connected to each other from the corresponding plurality of optical couplers. The light emitting ends of the plurality of waveguide lines are arranged at predetermined intervals along a line parallel to the extending direction, and the extending direction has the portions extending in the same direction. It is configured to emit light in the direction orthogonal to the direction .
According to another aspect of the invention, the predetermined value is an odd multiple of π or an integer multiple of 2π.
According to another aspect of the present invention, the light emission end of each of the plurality of waveguide lines respectively connected to the plurality of optical couplers is determined along a line parallel to the first direction of the substrate. The plurality of optical couplers are spaced apart from each other by a first predetermined distance along a second direction orthogonal to the first direction, and along the first direction. The plurality of waveguide lines are spaced apart from each other by a second predetermined distance which is a sum of a predetermined distance and the first predetermined distance, and each of the plurality of waveguide lines is one of the plurality of optical couplers And a straight waveguide extending in the first direction whose one end is connected, and a bent waveguide connected to the straight waveguide and converting the propagation direction of light toward the output end of the waveguide line by 90 °. and waveguide, and is composed of.
According to another aspect of the present invention, the bus waveguide is configured by cascading a plurality of serpentine waveguides, a portion of which constitutes a portion of the optical coupler, and the optical coupler is configured of an evanescent coupler And each of the meandering waveguides constituting the bus waveguide has a straight waveguide and a bending waveguide, and a part of the bending waveguide of the meandering waveguide is a part of the evanescent coupler Configure
According to another aspect of the present invention, the phase shifter is provided in the straight waveguides in which the meander waveguide has.
According to another aspect of the present invention, each of the phase shifters is constituted by a heater provided on the substrate, and the heaters have the same straight line so that they have the same temperature when the same current is applied. The sizes, including the length, width and thickness along the waveguide , as well as the shape are configured to be identical to one another.
According to another aspect of the present invention, the meandering waveguide includes one first bending waveguide that converts the propagation direction of light by 180 ° and two second bending waveguides that convert the propagation direction of light by 90 °. A waveguide and two straight waveguides respectively connecting the first curved waveguide to the two second curved waveguides, a portion of each of the two second curved waveguides being And a part of the adjacent evanescent couplers.
According to another aspect of the present invention, each of the waveguide lines is connected with a grating-based antenna element composed of a perturbation waveguide whose size in the width direction or depth direction changes, Each of the waveguides is configured to output light from the surface of the substrate.
According to another aspect of the present invention, the material of the substrate is any of Si ₃ N ₄ , Si, SiON, LiNbO ₃ , LiTaO ₃ , and SiC.
Another aspect of the present invention is a LiDAR sensor using an optical phased array having any of the above-described configurations.

According to the present invention, an optical phased array (OPA) capable of providing a beam steering (scanning) function with relatively small phase shift without the need for complicated calibration processing to determine the amount of phase shift compensation. It can be realized.
According to the present invention, all of the respective heaters connected by two electrode pads are not required without requiring a complicated calibration process to determine the phase shift compensation amount and without individually controlling the plurality of heaters. Is an equal temperature, and an optical phased array (OPA) capable of providing a beam steering (scanning) function can be realized by a method of linearly changing the accumulated phase shift difference.

FIG. 1 is a view showing the configuration of a LiDAR sensor using an optical phased array according to an embodiment of the present invention. FIG. 2 is a diagram showing the configuration of an optical phased array according to an embodiment of the present invention. FIG. 3 is a view showing the configuration of one meandering waveguide constituting the bus waveguide of the optical phased array shown in FIG. FIG. 4A is a view showing an example of a far-field pattern of light emitted when the phase shifter is in the non-operating state in the optical phased array shown in FIG. 2 (case where the phase difference is an odd multiple of π). FIG. 4B is a diagram showing another example of the far-field pattern of the light emitted when the phase shift is given by the phase shifter in the optical phased array shown in FIG. 2 (when the phase difference is an integral multiple of 2π) It is. FIG. 5A is a view showing an example of a perturbation waveguide that can be used as an antenna element of the optical phased array shown in FIG. FIG. 5B is a view showing another example of a perturbation waveguide that can be used as an antenna element of the optical phased array shown in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiment shown below is a LiDAR sensor using the optical phased array of the present invention. However, the LiDAR sensor is an example, and the application field of the optical phased array of the present invention is not limited thereto. For example, the optical phased array of the present invention may be used in security applications such as surveillance devices, flight navigation applications such as drones, and any other applications requiring three-dimensional information.

  FIG. 1 is a view showing the configuration of a LiDAR sensor using an optical phased array according to an embodiment of the present invention. The LiDAR sensor 100 includes a light source 102, an optical phased array (OPA) 104, a light receiving sensor 106, and a processing unit 108.

  The light source 102 includes, for example, a semiconductor laser, and outputs modulated modulated light based on a signal from the processing device 108. This modulation is performed, for example, by modulating the current supplied to the semiconductor laser with a signal from the processing device 108. Instead of this, the light source 102 further includes an optical modulator, operates the optical modulator according to the signal from the processing device 108, and modulates and outputs the light from the semiconductor laser by the optical modulator. It can be done. This modulated light output from the light source 102 becomes input light of the OPA 104.

  The OPA 104 splits the input light from the light source 102 into a plurality of lights, and outputs the split plurality of lights from the antenna element array. As a result, the OPA 104 outputs the main maximum beam (main beam or main lobe) of the diffracted light, which is generated when each of the output lights is diffracted and interferes with each other. In addition, the OPA 104 applies a predetermined phase shift to each of the plurality of branched lights, deflects the output direction of the main maximum beam, and performs beam steering or beam scanning of the main maximum beam. The specific configuration of the OPA 104 will be described later.

  The light receiving sensor 106 is composed of, for example, a condenser lens and a light receiving element array such as a CCD. The light receiving sensor 106 detects light (reflected return light) returned by the main maximum beam output from the OPA 104 being reflected or scattered on the object.

  The processing unit 108 causes the light source 102 to output modulated light. As described above, the processing device 108 applies a signal to, for example, the semiconductor laser or the light modulator included in the light source 102, and causes the light source 102 to output the modulated light. In addition, the processing device 108 outputs the main maximum beam from the OPA 104 and is reflected or scattered by the object, and then becomes the reflected return light and the flight time of the beam until it is received by the light receiving sensor 106 (Time Calculate Of Flight). Further, the processing device 108 specifies the arrival direction of the reflected return light arriving at the light receiving sensor 106. Thereby, the processing device 108 outputs space mapping information indicating the shape, position, and the like of the object in space. The processing device 108 may be configured by a processor such as a digital signal processor (DSP, Digital Signal Processor) or a computer.

FIG. 2 is a diagram showing the configuration of the OPA 104. As shown in FIG. The OPA 104 is configured as an OPA of a solid state type using an optical waveguide formed on the substrate 200. In the present embodiment, the substrate 200 is an oxidized silicon substrate or quartz glass containing SiO ₂ as a main component, and an optical waveguide is formed of, for example, Si ₃ N ₄ embedded in SiO ₂ . However, this configuration is an example, and the substrate 200 can be configured using a material such as Si ₃ N ₄ , Si, SiON, LiNbO ₃ , LiTaO ₃ , or SiC.

  The OPA 104 is, as an optical waveguide formed on the substrate 200, a bus waveguide 202 into which input light from the light source 102 is input, and four waveguide lines 204a, 204b, 204c, 204d A waveguide portion including cross-hatched portions), and antenna elements 206a, 206b, 206c, and 206d that generate a main maximum beam 236 of diffracted light. The antenna elements 206a, 206b, 206c, 206d constitute an antenna element array 208 arranged at a predetermined spacing p. The antenna elements 206a, 206b, 206c, and 206d are configured by linear waveguides in the present embodiment.

  The bus waveguide 202 is provided with a plurality of optical couplers 220 a, 220 b, 220 c, and 220 d that respectively extract part of the light propagating through the bus waveguide 202. Further, two phase shifters 222a and 224a, 222b and 224b, and 222c and 224c are provided between the adjacent optical couplers 220a and 220b, between 220b and 220c, and between 220c and 220d, respectively. It is done.

  The optical couplers 220a, 220b, 220c, and 220d are evanescent couplers that use coupling of light via evanescent waves between two adjacent optical waveguides separated by a predetermined distance in this embodiment. The phase shifters 222a, 222b, 222c and 224a, 224b, 224c are respectively configured by heaters 226a, 226b, 226c and 228a, 228b, 228c provided in part of the bus waveguide 202.

  Thereby, the phase shifters 222a and the like change the refractive index of the portion of the bus waveguide 202 immediately below the heater 226a and the like due to the temperature change given by the heater 226a and the like due to the thermo-optic effect of the material constituting the bus waveguide 202. To change the phase of the light passing through the part. Here, the heaters 226a, 226b, 226c and 228a, 228b, 228c are, for example, a layer of gold (Au) on titanium (Ti) which is an underlayer formed on the bus waveguide 202 in this embodiment, for example. The thin film heater is configured by forming

  Part of the light propagating through the bus waveguide 202 extracted by the optical couplers 220a, 220b, 220c, and 220d propagates through the waveguide lines 204a, 204b, 204c, and 204d, respectively. The light output ends 210a, 210b, 210c, and 210d of the waveguide lines 204a, 204b, 204c, and 204d, respectively, are at predetermined intervals p along a line 232 parallel to the Y direction, which is the first direction of the substrate 200. They are arranged and connected to antenna elements 206a, 206b, 206c, 206d which are linear waveguides, respectively. The antenna elements 206a, 206b, 206c, 206d have the same optical path length, and the light emitting ends 212a, 212b, 212c, 212d are arranged along the lower edge 234 of the substrate 200 shown in FIG. The light output end 210a and the like are arranged at the same predetermined interval p.

  As a result, light having a predetermined phase difference between each other is output from the antenna elements 206a, 206b, 206c, and 206d constituting the antenna element array 208, and the main maximum of diffracted light formed by the output light The beam 236 is output in the direction determined by the phase difference. Then, the beam steering operation is performed by changing the deflection angle θ of the main maximum beam 236 by changing the phase difference with the phase shifter 222 a or the like. Here, the deflection angle θ is defined as an angle formed by the main maximum beam 236 with respect to the normal 238 of the plane (in the present embodiment, the edge 234 of the substrate 200) including the light emitting ends 212a, 212b, 212c and 212d. Ru.

  In particular, in the OPA 104 of this embodiment, the waveguide lines 204a, 204b, 204c, and 204d have equal optical path lengths. Further, as described above, the phase shifter 222 a and the like are provided in each section of the bus waveguide 202 which is adjacent to the adjacent optical coupler 220 a and the like. Also, when the phase shifters 222a etc., 224a etc. are in a non-operating state (ie, the heaters 226a etc., 228a etc. are non-energized), each between adjacent optical couplers 220a etc. along the bus waveguide 202 The sections are configured such that the phase difference between the lights extracted from the adjacent optical couplers 220a and the like is an odd multiple of π (that is, the phases are opposite to each other).

  As a result, in the OPA 104, the waveguide lines 204a and the like have the same optical path length, and therefore the light output end 210a and the like adjacent to each other (when the phase shifter 222a and the like are inoperative) The phase difference of the light output from the optical fiber is determined by the positional relationship of the optical coupler 220 a and the like along the bus waveguide 202. That is, since there is no additional phase shift that occurs with respect to the phase difference determined by the positional relationship, there is no need to compensate for the phase shift offset, and the OPA 104 can be operated by simple control.

  In addition, when the phase shifter 222a or the like is operated, the phase shift amount of light output from the optical coupler 220a or the like toward the waveguide line 204a or the like is the light closest to the light input end 230 along the bus waveguide 202 The phase shift amounts generated by the plurality of phase shifters 222 a and the like are sequentially accumulated, in order from the coupler 220 a and the like. For this reason, in the OPA 104, by providing relatively small phase shifts by the phase shifters 222a and the like, cumulative phase shifts exceeding 2π can be generated linearly and precisely, and the main maximum beams 236 emitted from the antenna element array 208 The emission direction can be changed without increasing the spread width of the light.

  When the phase shifter 222a or the like is operated to change the deflection angle θ of the main maximum beam 236, the light extracted from the adjacent optical couplers 220a or the like is mutually adjacent between all the adjacent optical couplers 220a or the like. It is sufficient to make the change of the phase difference be the same. Therefore, the phase shifters 222a and the like provided between the adjacent optical couplers 220a and the like are each for the phase of the light extracted from the nearest optical coupler 220a and the like located upstream along the light propagation direction of the bus waveguide 202. Each need only be operated to provide the same amount of phase shift.

  Therefore, if phase shifters 222a and so forth and 224a and so on are respectively designed to have the same design, each of phase shifters 222a and so on and 224a and so on will be adjacent to each other by applying currents of substantially the same magnitude. The deflection angle θ of the main maximum beam 236 can be changed by causing the same phase difference to occur between the lights extracted from the optical coupler 220a and the like. Specifically, the heaters 226a and so forth constituting the phase shifters 222a and so forth and 224a and so on have the length, width, and thickness so that they have the same temperature when the same current flows respectively. The included size and shape may be configured to be the same as each other. The two terminals of each heater, such as the heaters 226a and so on and 228a, are connected to, for example, an electrode pad (not shown) provided on the substrate 200, and are energized from the outside of the substrate 200 via the electrode pad. This makes it possible to make the OPA 104 operate more easily by causing all the phase shifters 222a etc., 224a etc. to have equal phase shifts.

  In the present embodiment, the heaters 226a and the like are configured such that the phase differences of light extracted from adjacent optical couplers 220a and the like are odd multiples of π (that is, opposite phases to each other). The phase shift that can be realized by the phase shifter 222a or the like is only one direction of increase or decrease relative to the increase of the current absolute value to the heater 226 or the like due to the temperature dependency of the refractive index in the substrate 200 It is for. In this case, since the main maximum beam 236 moves only in one direction along with the increase of the absolute value of current supplied to the phase shifter 222a etc., the main maximum beam 236 is continuously moved from end to end of the operating angle range. The reason is that the main maximum beam 236 needs to be disposed at the end of the operating angle range when the phase shifter 222a and the like are in the non-operating state.

Therefore, for example, a substrate having an electro-optical effect such as LiNbO ₃ is used as the substrate 200, and a phase shifter capable of increasing and decreasing the phase of light as the phase shifter 222a etc. by reversing the electric field application direction to the substrate 200 is used. In this case, the section of the bus waveguide 202 between the adjacent optical couplers 220a and the like does not necessarily have to be configured such that the light extracted from the adjacent optical couplers 220a and the like has the opposite phase. In this case, depending on whether the main maximum beam 236 is placed at the center of the operating angle range or at the position of the predetermined deflection angle θ when the phase shifter 222a or the like is not in operation, the adjacent optical coupler 220a etc. The section of the bus waveguide 202 between them may be configured such that the phase difference between the lights extracted from the adjacent optical couplers 220a etc. becomes an integral multiple of 2π or a predetermined value.

Returning to FIG. 2, the OPA 104 is more specifically configured as follows.
As described above, the light output end 210a and the like of the waveguide line 204a and the like respectively connected to the optical coupler 220a and the like are predetermined along the line 232 parallel to the Y direction which is the first direction of the substrate 200. It is distributed at intervals p. The optical couplers 220a, 220b, 220c, 220d are separated from each other by a first predetermined distance d along the X direction which is a second direction orthogonal to the first direction, and along the Y direction. It is arranged to be separated from each other by a second predetermined distance s (= d + p) which is a distance obtained by adding the predetermined interval p and the first predetermined distance d.

  The waveguide lines 204a, 204b, 204c, and 204d are connected to the optical couplers 220a, 220b, 220c, and 220d at their one ends, and extend in the Y direction into linear waveguides 204a-1, 204b-1, and 204c. -1, 204d-1 (respectively hatched portions) and a curved waveguide 204a connected to each of the straight waveguides and converting the propagation direction of light by 90 ° toward the light output ends 210a, 210b, 210c, 210d -2, 204b-2, 204c-2, and 204d-2 (each cross hatching portion shown). Here, the curved waveguides 204 a-2, 204 b-2, 204 c-2 and 204 d-2 have the same curvature r.

  Thereby, the difference between the lengths of the linear waveguides 204b-1, 204c-1 and 204d-1 with respect to the length of the linear waveguide 204a-1 is the arrangement interval s in the Y direction of the optical coupler 220a etc. The value is determined by the arrangement interval p of 210 a and the like, and becomes −s + p, −2s + 2p, and −3s + 3p. As described above, since s = d + p, the differences are −d, −2d, and −3d, respectively.

  In addition, the curved waveguides 204a-2, 204b-2, 204c-2, and 204d-2 connected to the linear waveguides 204a-1, 204b-1, 204c-1, and 204d-1 are arranged in the line 232. The lengths to the respective light output ends 210a, 210b, 210c and 210d are determined by the arrangement interval d in the X direction of the optical coupler 220a etc., and become 0, d, 2d and 3d, respectively.

  Therefore, the difference in length -d, -2d, -3d of the straight waveguides 204b-1, 204c-1, 204d-1 with respect to the straight waveguide 204a-1 is a curved waveguide 204a-2, 204b-2, The waveguide lines 204a, 204b, 204c, 204d have the same length, and thus the same optical path length, offset by the difference in length from 204c-2, 204d-2 to the light output end 210a, 210b, 210c, 210d. It becomes what you have.

  Further, the bus waveguide 202 of the OPA 104 is configured by cascading a plurality of serpentine waveguides, a part of which constitutes a part of the optical coupler 220a or the like. More specifically, the bus waveguide 202 includes a meandering waveguide 202-1 connecting the points A1 and A2 shown in FIG. 2, and a meandering waveguide 202-2 connecting the points A2 and A3. The meandering waveguide 202-3 connecting the point A3 and the point A4 is connected in cascade.

  The serpentine waveguides 202-1, 202-2, and 202-3 all have the same configuration, and therefore, the configuration of the serpentine waveguide 202-1 will be described by way of example.

  FIG. 3 is a partial detailed view showing the configuration of the meandering waveguide 202-1. The meandering waveguide 202-1 has two straight waveguides 300, 302 (both shown hatched) and three curved waveguides 310, 312, 314. The curved waveguides 310, 312, 314 are, for example, arc-shaped waveguides having the same radius of curvature r. The bending waveguide 310 is a first bending waveguide that converts the light propagation direction by 180 °, and the bending waveguides 312 and 314 are two second bending waveguides that convert the light propagation direction by 90 °. is there.

  Although the phase shifters 222a and 224a and the heaters 226a and 228a are omitted in FIG. 3 in order to simplify the drawing and facilitate understanding, in practice, the linear waveguides 300 and 302 are not shown. Phase shifters 222a and 224a are provided, respectively.

  The straight waveguides 300 and 302 connect the curved waveguides 310 to the curved waveguides 312 and 314, respectively. Therefore, a part of the bent waveguides 312 and 314 which are the second bent waveguides respectively connected to the point A1 and the point A2 constitutes a part of the adjacent optical couplers 220a and 220b which are evanescent couplers ( Figure 2).

  Here, as described above, the adjacent optical couplers 220a and so on are arranged to be separated from each other by the second predetermined distance s along the Y direction which is the first direction. The distance in the direction is s. In addition, since the bending waveguides 312 and 314 have the same radius of curvature r, the Y direction between the position where the bending waveguide 312 connects to the linear waveguide 300 and the position where the bending waveguide 314 connects to the linear waveguide 302 The distance along is also s.

Further, since the adjacent optical couplers 220a and the like are arranged to be separated by the first predetermined distance d along the X direction which is the second direction, the distance between the points A1 and A2 in the X direction is d. is there. Further, since the meandering waveguide 202-1 and the like of the present embodiment do not include a straight waveguide extending in the X direction in order to reduce the size in the X direction,
d = 4r (2)
It is.

Assuming that the lengths of the linear waveguides 300 and 302 are q and b, respectively, the path length Lc of the serpentine waveguide 202-1 (that is, the path length Lc from point A1 to A2) is
Lc = b + q + 2πr (3)
It becomes. Also, from FIG.
b = s + q (4)
The relationship of

Here, assuming that the wavelength of the input light is λ ₀ , the phase difference φ _{0 of the} light output from the adjacent optical couplers 220 a and 220 b to the waveguide lines 204 a and 204 b is given by the following equation.

As described above, in this embodiment, the phases of light output from the adjacent optical couplers 220a and the like are opposite to each other (therefore, the phase difference is an odd multiple of π).
φ ₀ = π (2i + 1) (i = 0, 1, 2,...) (6)
It is. Therefore, it can be understood from the equations (5) and (6) that the following equation needs to hold.

Moreover, Formula (7) becomes following Formula using Formula (3).

  Here, the radius of curvature r is given as a design value in which the bending waveguide loss of the bending waveguides 310, 312, 314 does not exceed a predetermined amount. Therefore, the first predetermined distance d of the meandering waveguide 202-1 is given as a design value of the optical characteristic. Further, the arrangement interval p is given as a design value of optical characteristics determined from the wavelength of light used and the requirement for the deflection angle θ of the main maximum beam 236. That is, the second predetermined distance s (= d + p) is also given from the design value of the optical characteristic.

  Therefore, Lc is determined by adjusting the lengths b and q of the linear waveguides 300 and 302 with respect to s and d determined from the optical property design. Since b and q satisfy equation (4) and d satisfy equation (2), equations (4) and (2) are applied to equation (8) to obtain the following equation.

  As a conclusion, it can be seen that the condition for making the phases of light output from the adjacent optical couplers 220a and 220b to the waveguide lines 204a and 204b by the meandering waveguide 202-1 opposite to each other is as follows.

  In other words, by setting the distances q and b of the linear waveguides 300 and 302 so as to have the lengths q and b satisfying the equations (10) and (4), the adjacent optical couplers 220a and 220b The phases of light output to the waveguide lines 204a and 204b can be opposite to each other.

  Further, by designing the other meandering waveguides 202-2 and 202-3 in the same manner as the meandering waveguide 202-1, it is possible to connect to the corresponding waveguide line 204a etc. between all the adjacent optical couplers 220a etc. The phases of light to be output can be made opposite to each other. Then, if an equal amount of phase shift is generated between all the adjacent optical couplers 220a and the like by energizing the phase shifter 222a and the like, the deflection angle of the main maximum beam 236 output from the antenna element array 208 is It can be changed.

  In the present embodiment, the phase shifters 222a and 224a are provided in both the linear waveguides 300 and 302 of the meandering waveguide 202-1, but the required phase shift amount and the power consumption condition for control are provided. Thus, the phase shifter 222a or the like can be provided in one or both of the linear waveguides 300 and 302. The same applies to the meandering waveguides 202-2 and 202-3.

  FIGS. 4A and 4B are diagrams showing far-field patterns of light output from the antenna element array 208. FIG. In both FIGS. 4A and 4B, the horizontal axis is the value of sin θ with respect to the deflection angle θ measured from the normal 238 of the edge 234 of the substrate 200, and the vertical axis is the light intensity.

  FIG. 4A is a far-field image when the phase shifters 222a and the like are in a non-operating state and the phases of light output from adjacent antenna elements 206a and the like are opposite to each other (that is, the phase difference is an odd multiple of π). Is shown. Two main lobes 400 and 402 corresponding to the two main maximum beams are respectively located at both ends of the operating range (ie, the movable angle range of the main maximum beam).

  In FIG. 4B, a phase shift of size π is introduced between adjacent antenna elements 206a and the like by phase shifter 222a and the like, and the phases of light output from the adjacent antenna elements 206a and the like are the same (ie, the phase difference is A far-field pattern is shown when it becomes an integer multiple of 2π. One main maximal beam moves, and one main lobe 404 corresponding to the main maximal beam is located at the center of the operating range.

  In the embodiment described above, the antenna elements 206a and the like are normal linear waveguides and output the light propagated by the waveguide lines 204a and the like from the light emitting end 212a and the like arranged at the edge 234 of the substrate 200. However, it is not limited to this. For example, the antenna elements 206a and the like are grating-based antenna elements configured by a perturbation waveguide whose width or thickness changes periodically, and light propagated by the waveguide lines 204a and the like is linearly formed from the surface of the substrate 200. It can be output as light of In this case, by operating the phase shifter 222a or the like, the deflection angle of the main maximum beam with respect to the surface normal of the substrate 200 when viewed from the X direction can be changed.

  FIGS. 5A and 5B show examples of the above-described perturbation waveguides that can be used instead of the antenna element 206a and the like. In FIGS. 5A and 5B, the same elements as the elements in FIG. 2 are indicated by the same reference numerals.

  In FIG. 5A, the left in the figure is a plan view showing a portion of the surface of the substrate 200 on which the grating based antenna element composed of the perturbation waveguide is formed, and the figure right is a DD cross section in the plan view in the left . In FIG. 5A, antenna elements 206 a-1, 206 b-1, 206 c-1, and 206 d-1, which are perturbation waveguides in which the width of the waveguide viewed from the surface of the substrate 200 changes periodically, are used. The antenna elements 206 a-1 and the like are connected to the waveguide lines 204 a and the like at the position of the line 232. Each of the antenna elements 206a-1 and the like emits light distributed along the length direction from the surface of the substrate 200 in the direction indicated by the arrow in the DD sectional view. Thus, each of the antenna elements 206a-1 and so on acts as a linear light source extending in the X direction on the surface of the substrate 200, and generates a main maximum beam directed upward from the surface of the substrate 200. In this configuration, it is possible to change the deflection angle of the main maximum beam with respect to the surface normal of the substrate 200 when viewed from the X direction by operating the phase shifter 222a and the like.

  In FIG. 5B, the left in the figure is a plan view showing a portion of the surface of the substrate 200 on which the grating based antenna element composed of the perturbation waveguide is formed, and the figure right is an EE cross section in the plan view in the left . In FIG. 5B, antenna elements 206 a-2, 206 b-2, 206 c-2 and 206 d-2 which are perturbation waveguides in which the thickness of the waveguide periodically changes are used. The antenna elements 206 a-2 and the like are connected to the waveguide lines 204 a and the like at the position of the line 232. Each of the antenna elements 206a-2 and the like emits light distributed along the length direction from the surface of the substrate 200 in the direction indicated by the arrow in the EE cross-sectional view. Thus, each of the antenna elements 206a-2 and the like acts as a linear light source extending in the X direction on the surface of the substrate 200, and generates a main maximum beam directed upward from the surface of the substrate 200. In this configuration, as in FIG. 5A, it is possible to change the deflection angle of the main maximum beam with respect to the surface normal of the substrate 200 when viewed from the X direction by operating the phase shifter 222a etc. .

  As described above, the OPA 104 of the present invention is a solid-state type optical phased array composed of optical waveguides formed on the substrate 200. The OPA 104 includes a bus waveguide 202 through which input light propagates, and a plurality of optical couplers 220 a and the like disposed on the bus waveguide 202 for extracting a part of the light propagating through the bus waveguide 202. . Further, the OPA 104 includes a plurality of waveguide lines 204 a and the like that respectively propagate the light extracted by the plurality of optical couplers 220 a and the like, and a phase shifter 222 a and the like provided in the bus waveguide 202. Further, the plurality of waveguide lines 204 a and the like have equal optical path lengths, and the phase shifter 222 a and the like are provided in each section of the bus waveguide 202 sandwiched by the adjacent optical couplers 220 a and the like.

  According to this configuration, since the waveguide lines 204a and the like have the same optical path length, when the phase shifter 222a and the like are in the non-operating state, the light output end 210a and the like adjacent to each other The phase difference of the light output from the light source is determined mainly by the positional relationship between the plurality of optical couplers 220 a and the like along the bus waveguide 202. That is, since there is no additional phase shift that occurs with respect to the phase difference determined by the positional relationship, there is no need to compensate for the phase shift offset, and the OPA 104 can be operated by simple control.

  In addition, when the phase shifter 222a or the like is operated, the phase shift amount of light output from the optical coupler 220a or the like toward the waveguide line 204a or the like is closest to the light input end 230 along the bus waveguide 202. Since the phase shifts generated by the plurality of phase shifters 222a and so on become sequentially accumulated phase shifts, cumulative phase shifts exceeding 2π can be accurately obtained only by providing relatively small phase shifts by each of the phase shifters 222a and the like. As a result, the emission direction of the main maximum beam 236 emitted from the antenna element array 208 can be changed.

  The OPA 104 is also a line in which light output ends 210 a and the like of light of the plurality of waveguide lines 204 a and the like respectively connected to the plurality of optical couplers 220 a and the like are parallel to the first direction of the substrate 200. It is disposed at a predetermined interval p along 232. The plurality of optical couplers 220a and so on are separated from each other by a first predetermined distance d along the X direction which is the second direction orthogonal to the Y direction, and a second predetermined distance s (along the Y direction). They are spaced apart from each other with = d + p). A plurality of waveguide lines 204a etc. are respectively connected with one end of one of the plurality of optical couplers 220a etc. and extend in the X direction, and a straight waveguide 204a-1 etc. And a bent waveguide 204 a-2 or the like that is connected to 1 and converts the propagation direction of light by 90 ° toward the light output end 210 a of the waveguide line 204 a or the like. Further, the bus waveguide 202 is configured by cascading a plurality of serpentine waveguides 202-1 and the like, a part of which constitutes a part of the optical coupler 220a and the like.

  According to this configuration, the waveguide lines 204 a and the like having the same optical path length can be simply configured. Also, in order to provide more channels, it is only necessary to additionally arrange the cascaded meandering waveguides 202-1 and the like and the corresponding waveguide lines 204a and the like at predetermined intervals, so that an OPA with high design extensibility is realized. be able to.

  Further, in the OPA 104, the optical coupler 220a and the like are configured as evanescent couplers that use coupling of light via evanescent waves between two optical waveguides that are separated by a predetermined distance. The meandering waveguides 202-1 and the like constituting the bus waveguide 202 have straight waveguides 300 and 302 and bending waveguides 310, 312 and 314, and the bending waveguides such as the meandering waveguide 202-1 and the like A part of 312 and 314 constitutes a part of an evanescent coupler which is the optical coupler 220a or the like.

  According to this configuration, it is possible to distribute the light propagating through the bus waveguide 202 to the waveguide line 204 a or the like without increasing the propagation loss of the bus waveguide 202.

  Further, in the OPA 104, the bending waveguides constituting the meandering waveguide 202-1 are one first bending waveguide 310 for converting the propagation direction of light by 180 °, and two for converting the propagation direction of light by 90 °. It comprises a second curved waveguide 312, 314 and two linear waveguides 300, 302 connecting the first curved waveguide 310 to the two second curved waveguides 312 and 314 respectively. Then, a part of each of the two second curved waveguides 312 and 314 constitutes a part of the optical couplers 220a and 220b which are adjacent evanescent couplers.

  According to this configuration, the adjacent optical coupler 220a is connected by a simple configuration in which adjacent optical couplers 220a and the like arranged at predetermined distance intervals are connected by meandering waveguide 202-1 and the like having the same predetermined optical path length. It is possible to make the phase difference between each light emitted from the light source to the waveguide line 204 a etc. constant.

  Further, in the OPA 104, the phase shifters 222a and the like are provided in one or both of the two linear waveguides 300, 302 connecting the first curved waveguide 310 to the two second curved waveguides 312, 314. . According to this configuration, the total length of the phase shifters 222a and 224a along the meandering waveguide 202-1 can be freely selected to a range of lengths obtained by adding the lengths of the linear waveguides 300 and 302. Since this can be done, the design freedom of the operating voltage of the phase shifters 222a and 224a is improved.

  Further, in the OPA 104, the phase shifter 222a and the like are configured by the heaters 226a and the like 228a and the like provided in a part of the bus waveguide 202. The heaters 226a and the like 228a and the like are configured to have the same size, shape, and length, including the length, width, and thickness, to have the same temperature when passing the same current. There is. According to this configuration, it is possible to give a phase shift to the light propagating through the bus waveguide 202 with a simple configuration in which only a metal thin film or the like is provided on the bus waveguide 202. Further, the same phase shift can be generated between the respective lights emitted from the adjacent optical couplers 220a and the like to the waveguide lines 204a and the like only by supplying the same current to the heaters 226a and the like 228a and the like.

  Further, in the OPA 104, the sections between adjacent optical couplers 220a and the like along the bus waveguide 202 are all configured to have the same length, and the phase difference between the lights extracted from the adjacent optical couplers 220a and the like Are all configured to have the same predetermined value.

  According to this configuration, it is possible to set the emission direction (initial direction) of the main maximum beam 236 when the phase shifter 222a or the like is in the non-operating state, to any predetermined direction. Thereby, for example, when the present optical phased array is used for a LiDAR sensor, the initial direction of the main maximum beam 236 can be set in advance in the direction to be searched first at the start of operation. Spatial information can be acquired quickly.

  Further, in the OPA 104, the sections between adjacent optical couplers 220a and the like along the bus waveguide 202 are all configured to have the same length, and the phase difference between the lights extracted from the adjacent optical couplers 220a and the like Are all configured to be an odd multiple of π or an integer multiple of 2π.

  According to this configuration, the emission direction of the main maximum beam 236 when the phase shifter 222a or the like is not operating is set at the end or center of the operating range, and the main maximum beam 236 is moved from end to end at the start of operation. It is possible to scan the entire operating range or to move it from the center of the operating range in a desired direction for scanning.

  Further, in the OPA 104, as the antenna element 206a connected to each of the waveguide lines 204a etc., a grating based antenna element formed of a perturbation waveguide whose size in the width direction or the depth direction changes is used. Each of the waveguides can be configured to output light from the surface of the substrate 200. According to this configuration, since the linear main maximum beam can be emitted from the surface of the substrate 200 along the length of the perturbation waveguide, it is easy to configure, for example, a LiDAR sensor that performs three-dimensional space mapping. Can.

  Further, the present invention is a LiDAR sensor 100 using the OPA 104. According to this configuration, it is possible to realize a highly reliable and easy-to-control LiDAR sensor using solid-state OPA 104 that does not require complicated control and operates with relatively few phase shifts.

  The present invention is not limited to the configuration of the above-described embodiment, and can be implemented in various modes without departing from the scope of the invention.

  For example, in the above embodiment, the antenna elements 206a and the like are also formed on the same substrate 200 as the bus waveguide 202 and the like, but the present invention is not limited thereto. For example, when the antenna elements 206a and the like are formed on a substrate different from the substrate 200, the waveguide lines 204a and the antenna elements 206a and the like are formed on the substrate 200 via a linear waveguide or an optical fiber. Can be connected.

  DESCRIPTION OF SYMBOLS 100 ... LiDAR sensor, 102 ... light source, 104 ... optical phased array (OPA) 106 ... light reception sensor, 108 ... processing apparatus, 200 ... board | substrate, 202 ... bus waveguide, 202-1, 202-2, 202-3 ... Meandering waveguide, 204a, 204b, 204c, 204d ... waveguide line, 204a-1, 204b-1, 204c-1, 204d-1, 300, 302 ... linear waveguide, 204a-2, 204b-2, 204c- 2, 204d-2, 310, 312, 314 ... curved waveguides 206a, 206a-1, 206a-2, 206b, 206b-1, 206b-2, 206c-1, 206c-1, 206c-2, 206d, 206d- 1, 206d-2 ... antenna element, 208 ... antenna element array, 210a, 210b, 210c, 2 0d ... light output end 212a, 212b, 212c, 212d ... light emission end 220a, 220b, 220c, 220d ... optical coupler, 222a, 222b, 222c, 224a, 224b, 224c ... phase shifter, 226a, 226b, 226c, 228a, 228b, 228c ... heater, 230 ... light input end, 232 ... line, 234 ... edge, 236 ... main maximum beam, 238 ... normal, 400, 402, 404 ... main lobe.

Claims (10)

An optical phased array comprising an optical waveguide formed on a substrate, the optical phased array comprising:
A bus waveguide through which input light propagates,
A plurality of optical couplers disposed on the bus waveguide for respectively extracting a part of light propagating in the bus waveguide;
A plurality of waveguide lines respectively propagating the light extracted by the plurality of optical couplers;
A phase shifter provided in the bus waveguide;
Equipped with
The plurality of optical couplers are cascaded along the bus waveguide,
The phase shifters are provided in respective sections sandwiching the adjacent optical couplers in the bus waveguide,
The sections between the adjacent optical couplers along the bus waveguide are all configured to have the same length, and the light extracted from the adjacent optical couplers in a state in which none of the phase shifters is energized All the phase differences are configured to have the same predetermined value,
The plurality of waveguide lines are
Have equal optical path lengths,
Wherein each of the plurality of waveguide line, from a corresponding plurality of optical couplers, have a portion extending in the same direction,
Light emitting end of said plurality of waveguide lines, before being arranged in the direction Kinobe standing along one line parallel at a predetermined interval, for emitting light in a direction perpendicular to the forward direction of Kinobe standing ,
Is configured as
Optical phased array. The predetermined value is an odd multiple of π or an integer multiple of 2π.
The optical phased array according to claim 1. The light emission ends of the light of the plurality of waveguide lines connected to the plurality of optical couplers are arranged at predetermined intervals along a line parallel to the first direction of the substrate,
The plurality of optical couplers are spaced apart from each other by a first predetermined distance along a second direction orthogonal to the first direction, and the first and second optical couplers are separated from each other along the first direction. It is arranged to be separated from each other by a second predetermined distance which is a distance obtained by adding the predetermined distance and
The plurality of waveguide lines are respectively connected to the linear waveguide extending in the first direction, one end of which is connected to one of the plurality of optical couplers, and the linear waveguide; A curved waveguide that converts the light propagation direction by 90 ° toward the output end of the line;
The optical phased array according to claim 1 or 2. The bus waveguide is configured by cascading a plurality of serpentine waveguides, a part of which constitutes a part of the optical coupler,
The optical coupler is composed of an evanescent coupler,
Each of the meandering waveguides constituting the bus waveguide has a linear waveguide and a curved waveguide,
A portion of the curved waveguide of the serpentine waveguide constitutes a portion of the evanescent coupler,
The optical phased array according to any one of claims 1 to 3. The phase shifter is provided to the linear waveguide included in the meandering waveguide.
The optical phased array according to claim 4. Each of the phase shifters is constituted by a heater provided on the substrate,
The heaters are configured to be the same in size, as well as in shape, including the length, width, and thickness along the linear waveguide, such that the same current flows when the same current is applied. ing,
The optical phased array according to claim 5. The meandering waveguide includes one first bending waveguide that converts the propagation direction of light by 180 °, two second bending waveguides that convert the propagation direction of light by 90 °, and the first bending waveguide. Consisting of two straight waveguides connecting the waveguide to the two second curved waveguides,
A portion of each of the two second bending waveguides constitutes a portion of the adjacent evanescent coupler,
The optical phased array according to any one of claims 4 to 6. Each of the waveguide lines is connected to a grating-based antenna element composed of a perturbation waveguide whose size in the width direction or depth direction changes, and the surface of the substrate is connected by the perturbation waveguides. Is configured to output light from
The optical phased array according to any one of claims 1 to 7. The material of the substrate is any of Si ₃ N ₄ , Si, SiON, LiNbO ₃ , LiTaO ₃ , and SiC.
The optical phased array according to any one of claims 1 to 8.   A LiDAR sensor using the optical phased array according to any one of claims 1 to 9.

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