CN112204457B

CN112204457B - Optical phased array and LiDAR sensor using same

Info

Publication number: CN112204457B
Application number: CN201880092425.6A
Authority: CN
Inventors: 金成君
Original assignee: Dacheng Technology Co ltd
Current assignee: Dacheng Technology Co ltd
Priority date: 2018-04-24
Filing date: 2018-04-24
Publication date: 2024-01-19
Anticipated expiration: 2038-04-24
Also published as: JP6513884B1; JPWO2019207638A1; CN112204457A; WO2019207638A1

Abstract

The present invention proposes an Optical Phased Array (OPA) that does not require a complicated correction process for determining the amount of phase shift compensation, and can provide a function of beam steering or beam scanning with a small phase shift. The optical phased array is composed of an optical waveguide formed on a substrate, and includes: a bus waveguide for propagation of input light; a plurality of optical couplers arranged on the bus waveguide and respectively extracting a part of light propagating through the bus waveguide; a plurality of waveguide lines for propagating the light extracted from the plurality of optical couplers, respectively; and a phase shifter disposed in the bus waveguide. The plurality of waveguide lines have mutually equal optical path lengths, and the phase shifter is provided in each section sandwiched by adjacent optical couplers in the bus waveguide.

Description

Optical phased array and LiDAR sensor using same

Technical Field

The invention relates to the technical field of optical sensors, in particular to an optical phased array and a LiDAR sensor using the same.

Background

LiDAR sensors are used for remote sensing and ranging purposes, for example, in autopilot systems and the like for real-time three-dimensional mapping and detection, tracking, determination of objects, and the like.

The LiDAR sensor scans a laser beam in an observation space and irradiates an object in the space, and measures a Time of Flight (TOF) until the irradiated beam reaches the object and is reflected and returned to a receiver in the LiDAR sensor, thereby measuring a position and a distance of the object.

As such a LiDAR sensor, a sensor that scans a laser beam using a mechanical rotary member is known, but in a system that is part of an Advanced Driving Assistance System (ADAS) or an autonomous driving system, a solid-state beam scanner that can have various advantages is preferably used. Such advantages include: the sensor reliability is higher, the sensor life is longer, the sensor size is smaller, the sensor weight is lighter and the sensor cost is more reasonable, but is not limited thereto.

One such solid-state beam scanner has an optical phased array (OPA, optical Phased Array). LiDAR sensors, by applying an optical phased array, are faster and more adaptable and more useful than existing LiDARs that use mechanical beam scanning.

Conventionally, as a technique related to an optical phased array, a saw-tooth type optical waveguide having a plurality of light receivers is known to be used in a high-frequency phase shifter for a high-frequency phased array antenna (patent document 1). The high-frequency phase shifter propagates light modulated by the high-frequency signal to the sawtooth optical waveguide, and receives and detects the light at each position by a plurality of light receivers arranged at different positions along the optical waveguide, thereby extracting a plurality of high-frequency signals to which different phase shifts are applied. And, a high-frequency signal to which a desired phase shift is imparted is selectively outputted from the plurality of extracted high-frequency signals. However, this high-frequency phase shifter uses only an optical waveguide as a means for imparting delay time to a high-frequency signal, and does not impart a phase shift to light itself. Therefore, this technique cannot be applied to an optical phased array.

As a related art having other relevance, there is known an optical signal processing device including a monolithically integrated semiconductor structure constituting an optical waveguide such as an optical phase shifter (patent documents 2 and 3). In this optical signal processing apparatus, input light is branched into a plurality of beams by two branched waveguides connected in multiple stages. The individual phase shifts are imparted to the respective branched lights by phase shifters provided in output waveguides that output the branched lights, respectively. However, the optical signal processing device does not constitute an optical phased array. That is, this device is not directly applicable to LiDAR because it only branches light and controls the phase of the light, and does not include an antenna element array for outputting diffracted light (an array of light output elements that outputs phase-controlled light at predetermined intervals to generate a main maximum beam of diffracted light).

In addition, when the configuration of the optical signal processing device is to be changed to an optical phased array, it is necessary to linearly increase the phase of light output from output waveguides arranged in a row from the end in the following manner.

φ _m ＝mP(2π/λ)sinθ (1)

Where m is a number given in order from the end to the antenna elements arranged in a row when the output waveguides arranged in a row are regarded as the antenna elements arranged in a row in the optical phased array. P is an arrangement interval of the antenna elements, λ is a wavelength of the output light, and θ is a direction angle of a main maximum beam of the diffracted light with respect to a normal line of a plane formed by the light emitting ends of the antenna elements. As is clear from equation (1), the phase shifters provided to the respective channels (i.e., each of the respective antenna elements and the optical transmission paths connected to the antenna elements) must be capable of providing different phase shifts, and the accumulated value of the phase shifts must exceed 2pi.

However, in the above-described optical signal processing apparatus, since the phase of the light output from each output waveguide is determined only by the phase shifter provided to each output waveguide and the phase shifters of each output waveguide are controlled independently of each other, the process for accurately finding the value of the accumulated phase shift exceeding 2Ω becomes complicated. Therefore, the control operation for making the above-described structure function as an optical phased array becomes quite complicated.

As a prior art most relevant to the present invention, a LiDAR configured as a device based on an optical integrated circuit (PIC, photonic integrated circuit, photonic integrated circuit) is known (non-patent document 1). The device has: bus waveguide, cascade connected (series connected) thermal phase shifter (thermal phase shifters), cascade connected evanescent coupler (evanescent couplers), which are connected with a grating based antenna element. 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. I.e. the distances of the waveguides interposed between the evanescent coupler and the grating-based antenna element are mutually unequal. That is, the total optical path lengths (total OPL (Optical Path Length, optical path length)) of the respective waveguides are not equal. Therefore, the phase relationship of the output light between each adjacent antenna element is not fixed at the time of the idle operation of the phase shifter (at the time of non-energization).

Due to such differences in OPLs (OPL differences, optical path differences) channels with undesired phase shifts may be generated. In general, when the phase shift output from the antenna element does not follow the linear rule 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 becomes wider, and as a result, the angular resolution is deteriorated.

In addition, when the phase shift in the bus waveguide is maintained in a linear manner depending on the refractive index and the phase tilt is maintained in a linear manner as shown in the equation (1), the main beam is also shifted by a certain beam angle, and therefore, correction processing is required to compensate for the beam angle by adding additional phase shift to all the beam shifters.

In the correction process, in order to determine the magnitude of these additional phase shifts and compensate for the additional phase shifts, it is necessary to include the heater control voltage of the phase shifter with an initial bias voltage. Thus, the action and control of the optical phased array becomes more complex.

Further problems arise in the case of an optical phased array operating in a wide frequency band (i.e. in a wide wavelength band). In this case, if the wavelengths are different due to the wavelength dependence of the refractive index, the phase shift is different, and thus the correction process becomes quite complicated.

Prior art literature and patent literature

Patent document 1: U.S. Pat. No. 5,222,162 Specification

Patent document 2: U.S. Pat. No. 5,770,472 Specification

Patent document 3: U.S. Pat. No. 5,930,031 Specification

Non-patent literature

Non-patent document 1: christopher V.Poulton, ami Yaacobi, david B.Cole, matthew J.Bycard, manan Raval, diedrik Vermeulen, michael R.Watts, coherent solid-state LIDAR with silicon photonic optical phased arrays, optics Letters, vol.42, no.20/October15, 2017.

Disclosure of Invention

The object of the present invention is to propose an Optical Phased Array (OPA) which does not require a complicated correction process for determining the amount of phase shift compensation and which can provide a beam steering or beam scanning function with a small phase shift.

In order to achieve the above object, the present invention provides an optical phased array including an optical waveguide formed on a substrate, the optical phased array including: a bus waveguide for propagation of input light; a plurality of optical couplers arranged on the bus waveguide and respectively extracting a part of light propagating through the bus waveguide; a plurality of waveguide lines for propagating the light extracted by the plurality of optical couplers, respectively; and a phase shifter provided to the bus waveguide, wherein the plurality of waveguide lines have optical path lengths equal to each other, and the phase shifter is provided to each section of the bus waveguide between adjacent optical couplers.

Further, the light emitting ends 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, and the plurality of optical couplers are arranged as follows: the optical coupler includes a plurality of waveguide lines each including a linear waveguide extending in the first direction at one end of the plurality of optical couplers to which the linear waveguide is connected, and a curved waveguide connected to the linear waveguide and configured to convert a propagation direction of light by 90 ° toward an output end of the waveguide line, the bus waveguide being configured by cascade connection of a plurality of meandering waveguides, a part of the plurality of meandering waveguides forming a part of the optical couplers, the plurality of waveguide lines being separated from each other by a first predetermined distance along a second direction orthogonal to the first direction and separated from each other by a second predetermined distance which is a distance obtained by adding the predetermined distance to the first predetermined distance along the first direction.

Further, the optical coupler is constituted by an evanescent coupler, the meandering waveguide constituting the bus waveguide has a straight waveguide and a curved waveguide, respectively, and a portion of the curved waveguide of the meandering waveguide constitutes a portion of the evanescent coupler.

Further, the meandering waveguide is constituted of one first curved waveguide that converts the propagation direction of light by 180 °, two second curved waveguides that converts the propagation direction of light by 90 °, and two straight waveguides that connect the first curved waveguide to the two second curved waveguides, respectively, and each of a part of the two second curved waveguides constitutes a part of the adjacent evanescent coupler.

Further, the phase shifter may be provided to one or both of the two linear waveguides connecting the first curved waveguide and the two second curved waveguides.

Further, the phase shifters are each constituted by a heater provided in a part of the bus waveguide, and the heaters are each constituted to have the same dimensions and shape including the length, width, and thickness so as to have the same temperature when the same current is supplied.

Further, each section between adjacent optical couplers along the bus waveguide is formed to have the same length, and the phase difference between the lights extracted from the adjacent optical couplers is set to a predetermined value.

Further, the prescribed value is an odd multiple of pi or an integer multiple of 2 pi.

Further, each of the waveguide lines is connected to a grating-based antenna element composed of a disturbance waveguide, and the disturbance waveguide is configured to output light from the surface of the substrate through each of the disturbance waveguides.

Further, the material of the substrate is Si ₃ N ₄ 、Si、SiON、LiNbO ₃ 、LiTaO ₃ And SiC.

The Optical Phased Array (OPA) of the present invention does not require a complicated correction process for determining the amount of phase shift compensation, and can provide a beam steering (scanning) function with a small phase shift.

The invention also provides a LiDAR sensor which is characterized by using the optical phased array.

Compared with the prior art, the invention has the advantages that: the Optical Phased Array (OPA) of the present invention does not require a complicated correction process for determining the amount of phase shift compensation, and furthermore, does not require separate control of a plurality of heaters, each heater connected through two electrode pads is all equal in temperature, and can provide a beam steering (scanning) function by a method of linearly varying the accumulated phase shift difference.

Drawings

Fig. 1 is a diagram 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 structure of an optical phased array according to an embodiment of the present invention.

Fig. 3 is a diagram showing a structure of a meandering waveguide constituting a bus waveguide of the optical phased array shown in fig. 2.

Fig. 4A is a diagram showing an example of a far-field image of light emitted when the phase shifter is in a non-operating state (in the case where the phase difference is an odd multiple of pi) in the optical phased array shown in fig. 2.

Fig. 4B is a diagram showing another example of a far-field image of light emitted when a phase shift is imparted by a phase shifter in the optical phased array shown in fig. 2 (when the phase difference is an integer multiple of 2pi).

Fig. 5A is a diagram showing an example of a disturbance waveguide that can be used as an antenna element of the optical phased array shown in fig. 2.

Fig. 5B is a diagram showing another example of a perturbation waveguide which can be used as the antenna element of the optical phased array shown in fig. 2.

100 … LiDAR sensor, 102 … light source, 104 … Optical Phased Array (OPA), 106 … light-receiving sensor, 108 … processing device, 200 … 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 … straight waveguide, 204a-2, 204b-2, 204c-2, 204d-2, 310, 312, 314 … curved waveguide, 206a-1, 206a-2, 206b-1, 206b-2, 206c-1, 206c-2, 206d-1, 206d-2 … antenna element, 208 … antenna element array, 210a, 210b, 210c, 210d … light output end, 212a, 212b, 212c, 212d … light exit end, 220a, 220b, 220c, 220d … optocouplers, 222a, 222b, 222c, 224a, 224b, 224c … phase shifters, 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.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be further described below.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments shown below are LiDAR sensors using the optical phased arrays 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 can be used for security applications such as monitoring devices, flight navigation applications such as unmanned aerial vehicles, and any applications requiring other three-dimensional information.

Fig. 1 is a diagram 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 device 108.

The light source 102 includes, for example, a semiconductor laser, and outputs modulated light based on a signal from the processing device 108. The modulation is performed, for example, by modulating the energizing current to the semiconductor laser with a signal from the processing device 108. Instead, the light source 102 is further provided with an optical modulator, which is operated by a signal from the processing device 108, and which can modulate light from the semiconductor laser and output the modulated light. The modulated light output from the light source 102 becomes input light to the OPA 104.

The OPA104 branches the input light from the light source 102 into a plurality of lights, and outputs the branched plurality of lights from the antenna element array. Thus, the OPA104 outputs a main maximum beam (main beam or main lobe) of diffracted light generated by the light outputted as described above, which are diffracted and interfere with each other. The OPA104 imparts a predetermined phase shift to each of the branched light beams, deflects the output direction of the main maximum beam, and performs beam steering or beam scanning of the main maximum beam. The specific structure of OPA104 is described later.

The light receiving sensor 106 is constituted by a light receiving element array such as a condenser lens and a CCD, for example. The light receiving sensor 106 detects light (reflected return light) returned by the main maximum light beam output from the OPA104 reaching the object and being reflected or scattered.

The processing means 108 outputs the modulated light to the light source 102. As described above, the processing device 108 applies a signal to, for example, a semiconductor laser or an optical modulator provided in the light source 102, and outputs modulated light from the light source 102. The processing device 108 calculates a Time Of Flight (Time Of Flight) Of the main maximum beam outputted from the OPA104, which is reflected or scattered by the object, and becomes reflected return light, and the reflected return light is received by the light receiving sensor 106. The processing device 108 also determines the direction of arrival of the reflected return light that reaches the light receiving sensor 106. Thus, the processing device 108 outputs spatial map information indicating the shape, position, and the like of the object in space. The processing device 108 may be constituted by a processor such as a digital signal processor (DSP, digital Signal Processor) or a computer.

Fig. 2 is a diagram showing the structure of the OPA 104. The OPA104 is a solid-state OPA using an optical waveguide formed on the substrate 200. In the present embodiment, the substrate 200 is an oxidized silicon substrate or is formed of SiO ₂ Quartz glass as main component, e.g. by embedding SiO ₂ Si of (C) ₃ N ₄ Forming an optical waveguide. However, this structure is an example, and Si may be used for the substrate 200 ₃ N ₄ 、Si、SiON、LiNbO ₃ 、LiTaO ₃ Or SiC, or the like.

OPA104 includes, as an optical waveguide formed on substrate 200: a bus waveguide 202 inputting input light from the light source 102, four waveguide lines 204a, 204b, 204c, 204d (including waveguide portions illustrating diagonally shaded portions and illustrated cross-hatched portions, respectively), and antenna elements 206a, 206b, 206c, 206d generating 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 interval p. The antenna elements 206a, 206b, 206c, 206d are constituted by linear waveguides in the present embodiment.

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

In the present embodiment, the optical couplers 220a, 220b, 220c, and 220d are evanescent couplers that couple light by evanescent waves between two optical waveguides that are close to each other with a predetermined distance therebetween. The phase shifters 222a, 222b, and 222c and the phase shifters 224a, 224b, and 224c are respectively constituted by heaters 226a, 226b, and 226c and heaters 228a, 228b, and 228c provided in a part of the bus waveguide 202.

Thus, the phase shifter 222a and the like changes the refractive index of the portion of the bus waveguide 202 directly below the heater 226a and the like by a temperature change imparted by the thermo-optical effect of the material constituting the bus waveguide 202 by the heater 226a and the like, and changes the phase of the light passing through the portion. Here, in the present embodiment, the heaters 226a, 226b, and 226c and the heaters 228a, 228b, and 228c are thin film heaters configured by forming a gold (Au) layer on titanium (Ti) as a base layer formed on the bus waveguide 202, for example.

A part of the light propagating in the bus waveguide 202 extracted by the optical couplers 220a, 220b, 220c, 220d propagates in the waveguide lines 204a, 204b, 204c, 204d, respectively. The light output ends 210a, 210b, 210c, 210d of the waveguide lines 204a, 204b, 204c, 204d are arranged at predetermined intervals p along a line 232 parallel to the Y direction, which is the first direction of the substrate 200, and are connected to the 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 at the same predetermined interval p as the light output end 210a or the like along the edge 234 of the lower side of the substrate 200 parallel to the Y direction.

Thus, light having a predetermined phase difference is output from the antenna elements 206a, 206b, 206c, and 206d constituting the antenna element array 208, and the main maximum beam 236 of diffracted light formed by the output light is output in a direction determined by the phase difference. Then, the phase difference is changed by the phase shifter 222a or the like, whereby the deflection angle θ of the main maximum beam 236 is changed, and the beam steering operation is performed. Here, the deflection angle θ is defined as the angle formed by the main maximum light beam 236 and the normal 238 to the plane (in this embodiment, the edge 234 of the substrate 200) including the light exit ends 212a, 212b, 212c, 212 d.

In particular, in the OPA104 of the present embodiment, the waveguide lines 204a, 204b, 204c, 204d have mutually equal optical path lengths. As described above, the phase shifter 222a and the like are provided in each section of the bus waveguide 202 sandwiched between the adjacent optical couplers 220a and the like. When the phase shifter 222a or the like and the phase shifter 224a or the like are in a non-operating state (i.e., the heater 226a or the like and the heater 228a or the like are in a non-energized state), each section between adjacent optical couplers 220a or the like along the bus waveguide 202 is configured such that the phase difference between lights extracted from the adjacent optical couplers 220a or the like is an odd multiple of pi (i.e., the phases are opposite to each other).

Thus, in the OPA104, since the waveguide lines 204a and the like have the same optical path lengths, when the phase shifter 222a and the like are in the non-operating state, the phase difference of the light output from the adjacent light output end 210a and the like (and hence the adjacent light output end 212a and the like) becomes the phase difference determined by the positional relationship of the optical couplers 220a and the like along the bus waveguide 202. That is, since there is no phase shift due to the addition of the phase difference determined by the positional relationship, it is not necessary to compensate for the shift of the phase shift, and the OPA104 can be operated by simple control.

When the phase shifter 222a or the like is operated, the amount of phase shift of the light output from the optical coupler 220a or the like to the waveguide line 204a or the like is an amount of phase shift obtained by accumulating the phase shifts generated by the plurality of phase shifters 222a or the like in order from the optical coupler 220a or the like closest to the optical input terminal 230 along the bus waveguide 202. Accordingly, in the OPA104, only by imparting small phase shifts to the phase shifters 222a and the like, accumulated phase shifts exceeding 2pi can be generated linearly and with high accuracy, and the emission direction can be changed without increasing the width of the main maximum beam 236 emitted from the antenna element array 208.

When the phase shifter 222a or the like is operated to change the deflection angle θ of the main maximum beam 236, the change in the phase difference between the lights extracted from all the adjacent optical couplers 220a or the like may be partially the same between all the adjacent optical couplers 220a or the like. Accordingly, the phase shifters 222a and the like provided between the adjacent optical couplers 220a and the like may operate as follows: the phase of light extracted from the nearest optical coupler 220a or the like located upstream in the propagation direction of light along the bus waveguide 202 is imparted with only the same amount of phase shift, respectively.

Therefore, if the phase shifters 222a and 224a are configured in the same design, respectively, the same phase difference can be generated between the lights extracted from the adjacent optical couplers 220a and the like, and the deflection angle θ of the main maximum beam 236 can be changed by applying currents of substantially the same magnitude to the phase shifters 222a and 224a and the like. Specifically, the heater 226a and the heater 228a and the like constituting the phase shifters 222a and the like and the phase shifters 224a and the like may be configured to have the same dimensions and shapes including the lengths, widths, and thicknesses thereof so as to have the same temperatures when the same currents are supplied thereto. The two terminals of each heater such as heater 226a and heater 228a are connected to, for example, electrode pads (not shown) provided on substrate 200, and are electrically connected from the outside of substrate 200 through the electrode pads. This causes all of the phase shifters 222a and the like and the phase shifters 224a and the like to generate equal phase shifts, and makes it possible to operate the OPA104 more easily.

In the present embodiment, the reason why the phase difference between the lights extracted from the adjacent optical couplers 220a and the like is an odd multiple of pi (i.e., opposite phases) is that: the phase shift achieved by the phase shifter 222a or the like constituted by the heater 226a or the like can be made to be only one of increasing or decreasing with respect to the increase in the absolute value of the current to the heater 226 or the like due to the temperature dependency of the refractive index in the substrate 200. In this case, since the main maximum beam 236 is moved only in one direction with an increase in the absolute value of the current supplied to the phase shifter 222a or the like, the main maximum beam 236 needs to be arranged at the end of the operation angle range in order to continuously move the main maximum beam 236 to the end of the operation angle range when the phase shifter 222a or the like is in the non-operation state.

For this reason, liNbO is used as the substrate 200 ₃ As the phase shifter 222a, a phase shifter capable of increasing and decreasing the phase of light by reversing the direction of application of an electric field to the substrate 200 is used, and in this case, the section of the bus waveguide 202 between the adjacent optical couplers 220a and the like does not need to be configured so that the light extracted from the adjacent optical couplers 220a and the like has to be in opposite phases. In this case, when the phase shifter 222a or the like is in the non-operating state, the main maximum light flux 236 is placed at the center of the operating angle range or at the position of the predetermined deflection angle θ, and thus the section of the bus waveguide 202 between the adjacent optical couplers 220a or the like can be configured such that the phase difference between the lights extracted from the adjacent optical couplers 220a or the like is an integer multiple of 2pi or a predetermined value.

Returning to fig. 2, more specifically OPA104 is constructed as follows.

As described above, the light output ends 210a and the like of the waveguide lines 204a and the like connected to the optical couplers 220a and the like are arranged at predetermined intervals p along the line 232 parallel to the Y direction, which is the first direction of the substrate 200. Further, the optocouplers 220a, 220b, 220c, 220d are configured in the following manner: separated from each other by a first predetermined distance d in an X direction which is a second direction orthogonal to the first direction, and separated from each other by a second predetermined distance s (=d+p) which is a distance obtained by adding the predetermined distance p to the first predetermined distance d in a Y direction.

Further, the waveguide lines 204a, 204b, 204c, 204d are respectively constituted by straight waveguides 204a-1, 204b-1, 204c-1, 204d-1 (respectively diagonally shaded portions) and curved waveguides 204a-2, 204b-2, 204c-2, 204d-2 (respectively cross-shaded portions shown), the straight waveguides 204a-1, 204b-1, 204c-1, 204d-1 being connected to one ends thereof at the optical couplers 220a, 220b, 220c, 220d and extending in the Y direction, the curved waveguides 204a-2, 204b-2, 204c-2, 204d-2 being connected to the straight waveguides and transforming the propagation direction of light by 90 ° toward the light output ends 210a, 210b, 210c, 210d, respectively. Here, the curved waveguides 204a-2, 204b-2, 204c-2, 204d-2 have the same curvature r as each other.

Thus, the difference in the lengths of the linear waveguides 204b-1, 204c-1, 204d-1 with respect to the length of the linear waveguide 204a-1 is determined by the arrangement interval s in the Y direction of the optical coupler 220a or the like and the arrangement interval p of the light output ends 210a or the like, and is-s+p, -2s+2p, -3s+3p, respectively. As described above, s=d+p, and thus the above differences are-d, -2d, -3d, respectively.

Further, the lengths from the curved waveguides 204a-2, 204b-2, 204c-2, 204d-2 connected to the straight waveguides 204a-1, 204b-1, 204c-1, 204d-1 to the respective light output ends 210a, 210b, 210c, 210d arranged on the line 232 are determined by the arrangement interval d in the X direction of the optical coupler 220a or the like, and are 0, d, 2d, 3d, respectively.

Accordingly, the differences-d, -2d, -3d of the lengths of the straight waveguides 204b-1, 204c-1, 204d-1 relative to the above-mentioned straight waveguides 204a-1 are offset by the differences in lengths from the curved waveguides 204a-2, 204b-2, 204c-2, 204d-2 to the light output ends 210a, 210b, 210c, 210d, the waveguide lines 204a, 204b, 204c, 204d having the same lengths as each other, and thus having the same optical path lengths.

The bus waveguide 202 of the OPA104 is configured by cascade-connecting a plurality of meandering waveguides, a part of which constitutes a part of the optical coupler 220a and the like. More specifically, bus waveguide 202 is configured by cascade connection of meandering waveguide 202-1 connecting point A1 and point A2, meandering waveguide 202-2 connecting point A2 and point A3, and meandering waveguide 202-3 connecting point A3 and point A4 shown in fig. 2.

The meandering waveguides 202-1, 202-2, 202-3 all have the same structure, and thus the structure of the meandering waveguide 202-1 will be described in detail below as an example.

Fig. 3 is a partial detailed view showing the structure of the meandering waveguide 202-1. The meandering waveguide 202-1 has two linear waveguides 300, 302 (both hatched in the illustration) 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 curved waveguide 310 is a first curved waveguide that converts the propagation direction of light by 180 °, and the curved waveguides 312 and 314 are two second curved waveguides that convert the propagation direction of light by 90 °.

In fig. 3, the phase shifters 222a and 224a and the heaters 226a and 228a are omitted for simplicity of the drawing, but the phase shifters 222a and 224a are actually provided in the linear waveguides 300 and 302, respectively.

The linear waveguides 300 and 302 connect the curved waveguide 310 to the curved waveguides 312 and 314, respectively. Thus, the portions of the curved waveguides 312, 314, which are the second curved waveguides connected to the point A1 and the point A2, respectively, constitute portions of the optical couplers 220a, 220b adjacent to the evanescent coupler, respectively (fig. 2).

Here, as described above, the adjacent optocouplers 220a and the like are arranged to be separated from each other by the second predetermined distance s along the Y direction as the first direction, and thus the distance in the Y direction between the points A1 to A2 is s. Further, the curved waveguides 312, 314 have the same radius of curvature r, and thus the distance along the Y direction between the position where the curved waveguide 312 connects with the linear waveguide 300 and the position where the curved waveguide 314 connects with the linear waveguide 302 is also s.

Further, since the adjacent optocouplers 220a and the like are arranged to be separated by the first predetermined distance d in the X direction as the second direction, the distance in the X direction between the points A1 to A2 is d. Further, since the meandering waveguide 202-1 of the present embodiment reduces the size in the X direction, it does not include a linear waveguide extending in the X direction, and therefore the meandering waveguide 202-1 of the present embodiment does not include a linear waveguide extending in the X direction

d＝4r (2)

If the lengths of the linear waveguides 300, 302 are taken as q, b, respectively, the path length Lc of the meandering waveguide 202-1 (i.e., the path length Lc from point A1 to point A2) is

Lc＝b+q+2πr (3)

Furthermore, according to FIG. 3

The relationship of b=s+q (4) holds.

Here, if the wavelength of the input light is taken as lambda ₀ The phase difference of the light output from the adjacent optical couplers 220a, 220b to the waveguide lines 204a, 204bGiven by the following formula.

As described above, in the present embodiment, since the phases of the lights outputted from the adjacent optocouplers 220a and the like are set to be mutually opposite phases (so that the phase difference is made to be an odd multiple of pi)

Therefore, from the formulas (5) and (6), the following formulas need to be established.

The expression (7) is expressed as follows using the expression (3).

Here, the radius of curvature r is given to a design value that the curved waveguide loss of the curved waveguides 310, 312, 314 does not exceed a predetermined amount. Accordingly, the first predetermined distance d of the meandering waveguide 202-1 is given as a design value of the optical characteristic. The arrangement interval p is given as a design value of an optical characteristic determined according to the wavelength of the light to be used and the requirement of the deflection angle θ of the main maximum light beam 236. That is, the second predetermined distance s (=d+p) is also given according to the design value of the optical characteristic.

Thus Lc is determined by adjusting the lengths b, q of the linear waveguides 300, 302 relative to s and d determined by the design of the optical properties. The b and q satisfy the formula (4), and d satisfies the formula (2), so that the following formulas are obtained by applying the formulas (4) and (2) to the formula (8).

As a result, the condition for making the phases of the light outputted from the optical couplers 220a and 220b adjacent to the meandering waveguide 202-1 to the waveguide lines 204a and 204b opposite to each other is expressed as follows.

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

The other meandering waveguides 202-2 and 202-3 are also designed in the same manner as the meandering waveguide 202-1, and thus the phases of the light output to the corresponding waveguide lines 204a and the like can be mutually opposite between all the adjacent optical couplers 220a and the like. If the phase shifter 222a or the like is energized to generate an equal amount of phase shift between all the adjacent optical couplers 220a or the like, the deflection angle of the main maximum beam 236 output from the antenna element array 208 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 phase shifter 222a and the like may be provided in one or both the linear waveguides 300 and 302 depending on the required phase shift amount and the power consumption condition during control. The same applies to the meandering waveguides 202-2 and 202-3.

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

Fig. 4A shows a far-field image when the phase shifter 222a or the like is in a non-operating state and the phases of the lights output from the adjacent antenna elements 206a or the like are mutually opposite phases (i.e., the phase difference is an odd multiple of pi). The two main lobes 400, 402 corresponding to the two main maxima are located at the opposite ends of the range of motion (i.e. the movable angular range of the main maxima).

Fig. 4B shows a far-field image when a phase shift of pi is introduced between adjacent antenna elements 206a and the like by a phase shifter 222a and the like, and the phases of the lights output from the adjacent antenna elements 206a and the like are the same (i.e., the phase difference is an integer multiple of 2pi). One main maximum beam moves, and one main lobe 404 corresponding to the main maximum beam is located at the center of the operation range.

In the above embodiment, the antenna element 206a and the like are normal linear waveguides, and light propagating from the light output waveguide line 204a and the like, such as the light output end 212a and the like, disposed at the edge 234 of the substrate 200, is not limited thereto. For example, the antenna element 206a or the like may be a grating-based antenna element configured by a disturbance waveguide whose width or thickness periodically varies, and light propagating through the waveguide line 204a or the like may be outputted from the surface of the substrate 200 as linear light. In this case, by operating the phase shifter 222a or the like, the deflection angle of the main maximum light beam with respect to the surface normal of the substrate 200 when viewed from the X direction can be changed.

Fig. 5A and 5B are diagrams showing examples in which the disturbance waveguide described above can be used instead of the antenna element 206a or the like. In fig. 5A and 5B, the same reference numerals are used to denote the same components as those in fig. 2.

In fig. 5A, the left side of the drawing is a plan view showing a portion of the surface of the substrate 200 where the grating-based antenna element constituted by the disturbance waveguide is formed, and the right side of the drawing is a DD cross-sectional view in the plan view of the left side of the drawing. In fig. 5A, antenna elements 206a-1, 206b-1, 206c-1, 206d-1 as disturbance waveguides whose widths periodically change as viewed from the surface of the substrate 200 are used. The antenna element 206a-1 and the like are connected to the waveguide line 204a and the like at the position of the line 232. The antenna elements 206a-1 and the like emit light distributed along the longitudinal direction thereof from the surface of the substrate 200 in the direction indicated by the arrow in the DD cross-sectional view, respectively. Thus, each of the antenna elements 206a-1 functions 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, by operating the phase shifter 222a or the like, the deflection angle of the main maximum light beam with respect to the surface normal of the substrate 200 when viewed from the X direction can be changed.

In fig. 5B, the left side of the drawing is a plan view showing a portion of the surface of the substrate 200 where the grating-based antenna element constituted by the disturbance waveguide is formed, and the right side of the drawing is an EE cross-sectional view in the plan view of the left side of the drawing. In fig. 5B, antenna elements 206a-2, 206B-2, 206c-2, 206d-2 that are perturbed waveguides whose thickness varies periodically are used as waveguides. The antenna element 206a-2, etc. is connected to the waveguide line 204a, etc. at the position of the line 232. The antenna elements 206a-2 and the like emit light distributed along the length direction thereof from the surface of the substrate 200 in the direction indicated by the arrow in the EE cross-sectional view, respectively. Thus, each of the antenna elements 206a-2 functions 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, by operating the phase shifter 222a or the like, the deflection angle of the main maximum light beam with respect to the surface normal of the substrate 200 when viewed from the X direction can be changed.

As described above, the OPA104 of the present invention is a solid-state optical phased array including an optical waveguide formed on the substrate 200. The OPA104 includes: a bus waveguide 202 for propagation of input light; and a plurality of optical couplers 220a and the like, each of which extracts a part of light propagating through the bus waveguide 202, the light being disposed on the bus waveguide 202. Further, the OPA104 includes: a plurality of waveguide lines 204a and the like for propagating light extracted by the plurality of optical couplers 220a and the like, respectively; and a phase shifter 222a provided in the bus waveguide 202. The plurality of waveguide lines 204a and the like have optical path lengths equal to each other, and the phase shifter 222a and the like are provided in each section sandwiched by adjacent optical couplers 220a and the like in the bus waveguide 202.

According to this configuration, since the waveguide lines 204a and the like have the same optical path length, the phase difference of the light outputted from the adjacent light output end 210a and the like (and hence the adjacent light output end 212a and the like) when the phase shifter 222a and the like are in the non-operation state is mainly determined by the positional relationship of the plurality of optical couplers 220a and the like along the bus waveguide 202. That is, since there is no phase shift that is added to the phase difference determined by the positional relationship, it is not necessary to compensate for the shift in the phase shift, and the OPA104 can be operated by simple control.

In addition, when the phase shifter 222a or the like is operated, since the phase shift amounts of the light output from the optical coupler 220a or the like to the waveguide line 204a or the like are the phase shift amounts of the phase shifts generated by the plurality of phase shifters 222a or the like are sequentially accumulated in order from the closest to the optical input end 230 along the bus waveguide 202, the accumulated phase shift exceeding 2pi can be generated with high accuracy only by imparting small phase shifts to the phase shifters 222a or the like, and the emission direction of the main maximum beam 236 emitted from the antenna element array 208 can be changed.

The OPA104 further includes light output ends 210a and the like of the respective lights of the plurality of waveguide lines 204a and the like connected to the plurality of optical couplers 220a and the like, respectively, along a line 232 parallel to the Y direction, which is the first direction of the substrate 200, at a predetermined interval p. Further, the plurality of optocouplers 220a and the like are configured in the following manner: separated from each other by a first prescribed distance d in the X direction, which is a second direction orthogonal to the Y direction, and separated from each other by a second prescribed distance s (=d+p) in the Y direction. The plurality of waveguide lines 204a and the like are each composed of a linear waveguide 204a-1 and the like, one end of which is connected to one of the plurality of optical couplers 220a and the like and extends in the X direction, and a curved waveguide 204a-2 and the like, which is connected to the linear waveguide 204a-1 and converts the propagation direction of light by 90 ° toward the light output end 210a and the like of the waveguide line 204a and the like. The bus waveguide 202 is configured by cascade-connecting a plurality of meandering waveguides 202-1, a part of which constitutes a part of the optical coupler 220a, and the like.

According to this structure, the waveguide lines 204a and the like having the same optical path length can be simply configured. In order to provide a larger number of channels, the meandering waveguide 202-1 and the corresponding waveguide line 204a and the like connected in cascade need to be additionally arranged at predetermined intervals, and therefore, OPA with high design expandability can be realized.

In the OPA104, the optical coupler 220a and the like are constituted by an evanescent coupler that uses optical coupling via an evanescent wave between two optical waveguides that are close to each other with a predetermined distance therebetween. The meandering waveguide 202-1 and the like constituting the bus waveguide 202 have the linear waveguides 300 and 302 and the curved waveguides 310, 312 and 314, and a part of the curved waveguides 312 and 314 of the meandering waveguide 202-1 and the like constitutes a part of the evanescent coupler which is the optical coupler 220a and the like.

According to this configuration, light propagating through the bus waveguide 202 can be distributed to the waveguide line 204a and the like without increasing the propagation loss of the bus waveguide 202.

In the OPA104, the curved waveguide constituting the meandering waveguide 202-1 is constituted by one first curved waveguide 310 for converting the propagation direction of light by 180 °, two second curved waveguides 312 and 314 for converting the propagation direction of light by 90 °, and two linear waveguides 300 and 302 for connecting the first curved waveguide 310 to the two second curved waveguides 312 and 314, respectively. And, each of the two second curved waveguides 312, 314 constitutes a part of the optical coupler 220a, 220b as an adjacent evanescent coupler.

According to this configuration, the phase difference between the lights emitted from the adjacent optical couplers 220a and the like to the waveguide line 204a and the like can be fixed by a simple configuration in which the adjacent optical couplers 220a and the like arranged at a predetermined distance interval are connected by the meandering waveguides 202-1 and the like having the same predetermined optical path length.

In the OPA104, the phase shifter 222a and the like are provided on one or both of the two linear waveguides 300 and 302 connecting the first curved waveguide 310 and the two second curved waveguides 312 and 314. According to this configuration, the total length of the phase shifters 222a, 224a along the meandering waveguide 202-1 can be freely selected within the range of the length obtained by adding the lengths of the linear waveguides 300, 302, and thus the degree of freedom in designing the operating voltages of the phase shifters 222a, 224a is improved.

In the OPA104, the phase shifter 222a and the like are constituted by a heater 226a and the like provided in a part of the bus waveguide 202, a heater 228a and the like. The heater 226a and the like and the heater 228a and the like are configured to have the same dimensions and shapes including the length, width, and thickness so as to have the same temperature when the same current is supplied. According to this structure, a phase shift can be imparted to light propagating through the bus waveguide 202 by a simple structure in which only a metal thin film or the like is provided on the bus waveguide 202. Further, by simply passing the same current through the heater 226a or the like and the heater 228a or the like, the same phase shift can be generated between the lights emitted from the adjacent optocouplers 220a or the like to the waveguide 204a or the like.

In the OPA104, each section between adjacent optical couplers 220a and the like along the bus waveguide 202 is formed to have the same length, and the phase differences between the lights extracted from the adjacent optical couplers 220a and the like are all the same predetermined value.

With this configuration, 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 can be set to an arbitrary predetermined direction. Thus, for example, when the present optical phased array is used in a LiDAR sensor, the initial direction of the main maximum beam 236 can be set in advance to the direction to be searched for at the start of operation, and thus spatial information in a desired direction can be obtained quickly.

In the OPA104, each section between adjacent optical couplers 220a and the like along the bus waveguide 202 is formed to have the same length, and the phase difference between the lights extracted from the adjacent optical couplers 220a and the like is formed to be an odd multiple of pi or an integer multiple of 2 pi.

According to this configuration, the emission direction of the main maximum beam 236 when the phase shifter 222a or the like is in the non-operating state can be set to the end or the center of the operating range, and the main maximum beam 236 can be moved from the end to scan the entire operating range or can be moved from the center of the operating range to a desired direction to scan the operating range at the start of the operation.

In addition, in the OPA104, as the antenna element 206a and the like connected to the waveguide 204a and the like, a grating-based antenna element including a disturbance waveguide whose dimension in the width direction or the depth direction is changed is used, and light can be output from the surface of the substrate 200 through the disturbance waveguide. According to this configuration, since the linear main maximum light beam can be emitted from the surface of the substrate 200 along the length of the disturbance waveguide, for example, a LiDAR sensor that performs three-dimensional space mapping can be easily configured.

Furthermore, the present invention is a LiDAR sensor 100 that uses OPA 104. According to this configuration, a highly reliable and easily controllable LiDAR sensor can be realized by using the solid-state OPA104 that operates with a small phase shift without requiring complicated control.

The present invention is not limited to the configuration of the above-described embodiment, and may be implemented in various modes within a range not departing from the gist thereof.

For example, in the above embodiment, the antenna element 206a and the like are also formed on one substrate 200 similar to the bus waveguide 202, but the present invention is not limited thereto. For example, the antenna element 206a and the like may be formed on a substrate different from the substrate 200, and the waveguide line 204a and the like and the antenna element 206a and the like may be optically connected via a linear waveguide or an optical fiber formed on the substrate 200.

The foregoing is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any person skilled in the art will make any equivalent substitution or modification to the technical solution and technical content disclosed in the invention without departing from the scope of the technical solution of the invention, and the technical solution of the invention is not departing from the scope of the invention.

Claims

1. An optical phased array comprising an optical waveguide formed on a substrate, comprising a bus waveguide for propagation of input light; a plurality of optical couplers disposed on the bus waveguide and provided in each of the bus waveguide and each of which is a part of light propagating through the bus waveguide; a plurality of waveguide lines for propagating the light extracted by the plurality of optical couplers, respectively; and a phase shifter disposed in the bus waveguide;

the waveguide lines have mutually equal optical path lengths, and the phase shifters are arranged between the adjacent optical couplers in the bus waveguide;

the light emitting ends of the light emitting lines connected to the optical couplers are arranged at predetermined intervals along lines parallel to the first direction of the substrate;

The plurality of optocouplers are arranged in the following manner: separated from each other by a first predetermined distance along a second direction orthogonal to the first direction, and separated from each other by a second predetermined distance along the first direction that is a distance obtained by adding the predetermined interval to the first predetermined distance;

the plurality of waveguide lines are respectively composed of a straight line waveguide and a curved waveguide, the straight line waveguide is connected with one end of the plurality of optical couplers, the straight line waveguide extends in the first direction, the curved waveguide is connected with the straight line waveguide, and the propagation direction of light is converted by 90 degrees towards the output end of the waveguide line;

the bus waveguide is formed by cascade connection of a plurality of meandering waveguides, and a part of the meandering waveguides forms a part of the optical coupler;

the optical coupler is composed of an evanescent coupler, the meandering waveguide constituting the bus waveguide has a straight waveguide and a curved waveguide, respectively, and a part of the curved waveguide of the meandering waveguide constitutes a part of the evanescent coupler;

the meandering waveguide is composed of one first curved waveguide that changes the propagation direction of light by 180 °, two second curved waveguides that changes the propagation direction of light by 90 °, and two linear waveguides that connect the first curved waveguide to the two second curved waveguides, respectively, each of the two second curved waveguides being a part of the adjacent evanescent coupler;

The phase shifter is provided on one or both of two linear waveguides connecting the first curved waveguide and the two second curved waveguides;

the phase shifters are respectively composed of heaters arranged on a part of the bus waveguide, and the sizes and shapes of the length, the width and the thickness of a part of the heaters are mutually the same so as to form the same temperature when the same current is electrified;

the lengths of the sections between adjacent optical couplers along the bus waveguide are the same, and the phase differences between the lights extracted from the adjacent optical couplers are all the same predetermined value.

2. The optical phased array of claim 1, where the prescribed value is an odd multiple of pi or an integer multiple of 2 pi.

3. The optical phased array according to claim 2, wherein each of the waveguide lines is connected to a grating-based antenna element formed of a disturbance waveguide, and wherein a change in a dimension in a width direction or a depth direction of the disturbance waveguide is configured to output light from a surface of the substrate through each of the disturbance waveguides.

4. An optical phased array as claimed in claim 3, characterised in that the material of the substrate is Si ₃ N ₄ 、Si、SiON、LiNbO ₃ 、LiTaO ₃ And SiC.

5. A LiDAR sensor characterized by using the optical phased array of any of claims 1 to 4.