Light detection and ranging (LIDAR) sensor system for pitch-catch extension

Abstract

A light detection and ranging (LIDAR) sensor system for a vehicle may include a transmitter, a receiver and a mixer. The transmitter may include a first grating coupler. The transmitter may transmit an optical signal. The receiver may include a pair of grating couplers configured to receive a pair of returned optical signals in response to transmitting the optical signal. The mixer may receive the pair of returned optical signals from the receiver, receive a local oscillator (LO) signal from a local oscillator, mix the pair of returned optical signals with the LO signal, and output a plurality of mixed optical signals. Two of the plurality of mixed optical signals have a relative phase difference of 90 degrees.

Description

Atty. Dkt. No.120261-0517 (A-052220-WO) LIGHT DETECTION AND RANGING (LIDAR) SENSOR SYSTEM FOR PITCH-CATCH EXTENSION CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of and priority to U.S. Patent Application No. 18 / 627,151, filed April 4, 2024, the disclosure of which is hereby incorporated herein by reference in its entirety. BACKGROUND

[0002] Optical detection of range using lasers, often referenced by a mnemonic, lidar, for light detection and ranging, is used for a variety of applications, from altimetry, to imaging, to collision avoidance. Lidar provides finer scale range resolution with smaller beam sizes than conventional microwave ranging systems, such as radio-wave detection and ranging (radar). Optical detection of range can be accomplished with several different techniques, including direct ranging based on a round trip travel time of an optical pulse to an object, chirped detection based on a frequency difference between a transmitted chirped optical signal and a returned signal scattered from an object, and phase-encoded detection based on a sequence of single frequency phase changes that are distinguishable from natural signals.

[0003] In radar or lidar, single-sideband modulation (SSB) or single-sideband suppressed-carrier modulation (SSB-SC) may be used to transmit information by radio or optical waves. SSB can avoid bandwidth increase of the original baseband signal and reduce the power wasted on a carrier, while increasing the device complexity at high cost. In-phase / quadrature (IQ) sampling (also called “complex sampling” or “quadrature sampling”) is a powerful technique commonly used in radar or lidar to retrieve full amplitude and phase information of a received signal. Optical IQ sampling often relies on having multiple detection and digitization channels and complex optical systems like optical hybrids. 1 . 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO)

[0004] When laser light illuminates a diffuse object, it may produce a random interference effect known as a speckle pattern. If there is movement in the object, the speckles fluctuate in intensity. This speckle (broadening) effect may cause a random walk in the phase / amplitude due to the random interference pattern on target, broaden Doppler (carrier) peak frequencies, and / or cause signal-to-noise ratio (SNR) reduction by greater than 8dB. In a lidar sensor system having multiple receivers, due to speckles from the target, the phase from two physically separate receivers may be random and phase correction may be impractical for low SNR targets. There is a need for a mechanism to optimize a lidar sensor system (e.g., Rx / Tx system, scanner, etc.) to resolve the speckle broadening effect. SUMMARY

[0005] Implementations of the present disclosure relate to a system and a method for a light detection and ranging (lidar) sensor system, and more particularly to a system and a method for a coherent LIDAR system for pitch-catch extension.

[0006] In some implementations of the present disclosure, a light detection and ranging (LIDAR) system may include a transmitter, a receiver and a mixer. The transmitter may include a first grating coupler. The transmitter may be configured to transmit an optical signal. The receiver may include a pair of grating couplers configured to receive a pair of returned optical signals in response to transmitting the optical signal. The mixer may be configured to receive the pair of returned optical signals from the receiver, receive a local oscillator (LO) signal from a local oscillator, mix the pair of returned optical with the LO signal, and output a plurality of mixed optical signals. Two of the plurality of mixed optical signals may have a relative phase difference of 90 degrees.

[0007] In some implementations of the present disclosure, an autonomous vehicle control system may include one or more processors and one or more computer-readable storage mediums. The mediums may store instructions which, when executed by the one or more processors, cause the one or more processors to cause a transmitter including a first grating coupler, to transmit an optical signal. The one or more processors may be configured to cause a receiver including a pair 2 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) of grating couplers, to receive a pair of returned optical signals in response to transmitting the optical signal. The one or more processors may be configured to cause a mixer to receive the pair of returned optical signals from the receiver, receive a local oscillator (LO) signal from a local oscillator, mix the pair of returned optical with the LO signal, and output a plurality of mixed optical signals. Two of the plurality of mixed optical signals may have a relative phase difference of 90 degrees. The one or more processors may be configured to control operation of a vehicle using the plurality of mixed optical signals.

[0008] In some implementations of the present disclosure, an autonomous vehicle may include at least one of a steering system or a braking system, and a vehicle controller including one or more processors. The one or more processors may be configured to cause a transmitter including a first grating coupler, to transmit an optical signal. The one or more processors may be configured to cause a receiver including a pair of grating couplers, to receive a pair of returned optical signals in response to transmitting the optical signal. The one or more processors may be configured to cause a mixer to receive the pair of returned optical signals from the receiver, receive a local oscillator (LO) signal from a local oscillator, mix the pair of returned optical with the LO signal, and output a plurality of mixed optical signals. Two of the plurality of mixed optical signals may have a relative phase difference of 90 degrees. The one or more processors may be configured to control the at least one of the steering system or the braking system using the plurality of mixed optical signals.

[0009] Those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Any of the features described herein may be used with any other features, and any subset of such features can be used in combination according to various embodiments. Other aspects, inventive features, and advantages of the devices and / or processes described herein, as defined solely by the claims, will become apparent in the detailed description set forth herein and taken in conjunction with the accompanying drawings. 3 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) BRIEF DESCRIPTION OF THE DRAWINGS

[0010] These and other aspects and features of the present implementations will become apparent to those ordinarily skilled in the art upon review of the following description of specific implementations in conjunction with the accompanying figures, wherein:

[0011] FIG.1A is a block diagram illustrating an example of a system environment for autonomous vehicles according to some implementations;

[0012] FIG.1B is a block diagram illustrating an example of a system environment for autonomous commercial trucking vehicles according to some implementations;

[0013] FIG.1C is a block diagram illustrating an example of a system environment for autonomous commercial trucking vehicles according to some implementations;

[0014] FIG.1D is a block diagram illustrating an example of a system environment for autonomous commercial trucking vehicles according to some implementations;

[0015] FIG.2A is a schematic graph that illustrates an example transmitted optical phase- encoded signal for measurement of range, according to some implementations;

[0016] FIG.2B is a schematic graph that illustrates the example transmitted signal of FIG.2A as a series of binary digits along with returned optical signals for measurement of range, according to some implementations;

[0017] FIG.2C is a schematic graph that illustrates example cross-correlations of a reference signal with two returned signals, according to some implementations;

[0018] FIG.2D is a schematic graph that illustrates an example spectrum of the reference signal and an example spectrum of a Doppler shifted return signal, according to some implementations;

[0019] FIG.2E is a schematic graph that illustrates an example cross-spectrum of phase components of a Doppler shifted return signal, according to some implementations; 4 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO)

[0020] FIG.3 is a block diagram illustrating an example of a lidar sensor system for autonomous vehicles, according to some implementations;

[0021] FIG.4A is a block diagram illustrating an example of a lidar sensor system, according to some implementations;

[0022] FIG.4B is a block diagram illustrating an example of a digital signal processing (DSP) system in a lidar sensor system, according to some implementations;

[0023] FIG.5 is a block diagram illustrating an example of a computing system according to some implementations.

[0024] FIG.6 is a block diagram illustrating an example of a lidar sensor system using a pitch- catch scanning, according to some implementations;

[0025] FIG.7A to FIG.7C are diagrams depicting example simulation results using a coherent LIDAR system;

[0026] FIG.8 is a block diagram illustrating an example of a coherent LIDAR system for pitch- catch extension, according to some implementations;

[0027] FIG.9A and FIG.9B are diagrams depicting example simulation results using a coherent LIDAR system for pitch-catch extension, according to some implementations;

[0028] FIG.10 is a block diagram illustrating an example of a coherent LIDAR system using a multi-mode transmit (Tx) / receive (Rx)-based circulator, according to some implementations;

[0029] FIG.11A to FIG.11C are diagrams depicting example simulation results using a coherent LIDAR system using a multi-mode Tx / Rx-based circulator, according to some implementations; and

[0030] FIG.12 is a flowchart illustrating an example methodology for a coherent LIDAR system for pitch-catch extension according to some implementations. 5 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) DETAILED DESCRIPTION

[0031] According to certain aspects, implementations of the present disclosure relate to a system and a method for a light detection and ranging (lidar) sensor system, and more particularly to a system and a method for a coherent LIDAR system for pitch-catch extension. Pitch-catch is a metaphorical device and refers to the arrangement of Tx and Rx optical modes such that the light is transmitted (pitched) from one location and received (caught) in a different location in an attempt to compensate for the motion of the lidar scanning system during the round-trip time from the intended targets and back. This has also been referred to as lag angle compensation in the space based and wind lidar literature.

[0032] According to certain aspects, a LIDAR system may include a transmitter, a receiver and a mixer. The transmitter may include a first grating coupler. The transmitter may transmit an optical signal. The receiver may include a pair of grating couplers configured to receive a pair of returned optical signals in response to transmitting the optical signal. The mixer may receive the pair of returned optical signals from the receiver, receive a local oscillator (LO) signal from a local oscillator, mix the pair of returned optical with the LO signal, and output a plurality of mixed optical signals. Two of the plurality of mixed optical signals may have a relative phase difference of 90 degrees. 1. System Environment for Autonomous Vehicles

[0033] FIG.1A is a block diagram illustrating an example of a system environment for autonomous vehicles according to some implementations. FIG.1A depicts an example autonomous vehicle 100 within which the various techniques disclosed herein may be implemented. The vehicle 100, for example, may include a powertrain 102 including a prime mover 104 powered by an energy source 106 and capable of providing power to a drivetrain 108, as well as a control system 110 including a direction control 112, a powertrain control 114, and a brake control 116. The vehicle 100 may be implemented as any number of different types of vehicles, including vehicles capable of transporting people and / or cargo, and capable of traveling in various environments. The aforementioned components 102 – 116 can vary widely based upon 6 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) the type of vehicle within which these components are utilized, such as a wheeled land vehicle such as a car, van, truck, or bus. The prime mover 104 may include one or more electric motors and / or an internal combustion engine (among others). The energy source may include, for example, a fuel system (e.g., providing gasoline, diesel, hydrogen, etc.), a battery system, solar panels or other renewable energy source, and / or a fuel cell system. The drivetrain 108 can include wheels and / or tires along with a transmission and / or any other mechanical drive components to convert the output of the prime mover 104 into vehicular motion, as well as one or more brakes configured to controllably stop or slow the vehicle 100 and direction or steering components suitable for controlling the trajectory of the vehicle 100 (e.g., a rack and pinion steering linkage enabling one or more wheels of the vehicle 100 to pivot about a generally vertical axis to vary an angle of the rotational planes of the wheels relative to the longitudinal axis of the vehicle). In some implementations, combinations of powertrains and energy sources may be used (e.g., in the case of electric / gas hybrid vehicles), and in some instances multiple electric motors (e.g., dedicated to individual wheels or axles) may be used as a prime mover.

[0034] The direction control 112 may include one or more actuators and / or sensors for controlling and receiving feedback from the direction or steering components to enable the vehicle 100 to follow a desired trajectory. The powertrain control 114 may be configured to control the output of the powertrain 102, e.g., to control the output power of the prime mover 104, to control a gear of a transmission in the drivetrain 108, etc., thereby controlling a speed and / or direction of the vehicle 100. The brake control 116 may be configured to control one or more brakes that slow or stop vehicle 100, e.g., disk or drum brakes coupled to the wheels of the vehicle.

[0035] Other vehicle types, including but not limited to off-road vehicles, all-terrain or tracked vehicles, construction equipment, may utilize different powertrains, drivetrains, energy sources, direction controls, powertrain controls and brake controls. Moreover, in some implementations, some of the components can be combined, e.g., where directional control of a vehicle is primarily handled by varying an output of one or more prime movers. 7 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO)

[0036] Various levels of autonomous control over the vehicle 100 can be implemented in a vehicle control system 120, which may include one or more processors 122 and one or more memories 124, with each processor 122 configured to execute program code instructions 126 stored in a memory 124. The processor(s) can include, for example, graphics processing unit(s) (“GPU(s)”)) and / or central processing unit(s) (“CPU(s)”).

[0037] Sensors 130 may include various sensors suitable for collecting information from a vehicle’s surrounding environment for use in controlling the operation of the vehicle. For example, sensors 130 can include radar sensor 134, LIDAR (Light Detection and Ranging) sensor 136, a 3D positioning sensors 138, e.g., any of an accelerometer, a gyroscope, a magnetometer, or a satellite navigation system such as GPS (Global Positioning System), GLONASS (Globalnaya Navigazionnaya Sputnikovaya Sistema, or Global Navigation Satellite System), BeiDou Navigation Satellite System (BDS), Galileo, Compass, etc. The 3D positioning sensors 138 can be used to determine the location of the vehicle on the Earth using satellite signals. The sensors 130 can include a camera 140 and / or an IMU (inertial measurement unit) 142. The camera 140 can be a monographic or stereographic camera and can record still and / or video images. The IMU 142 can include multiple gyroscopes and accelerometers capable of detecting linear and rotational motion of the vehicle in three directions. One or more encoders (not illustrated), such as wheel encoders may be used to monitor the rotation of one or more wheels of vehicle 100. Each sensor 130 can output sensor data at various data rates, which may be different than the data rates of other sensors 130.

[0038] The outputs of sensors 130 may be provided to a set of control subsystems 150, including a localization subsystem 152, a planning subsystem 156, a perception subsystem 154, and a control subsystem 158. The localization subsystem 152 can perform functions such as precisely determining the location and orientation (also sometimes referred to as “pose”) of the vehicle 100 within its surrounding environment, and generally within some frame of reference. The location of an autonomous vehicle can be compared with the location of an additional vehicle in the same environment as part of generating labeled autonomous vehicle data. The perception subsystem 154 can perform functions such as detecting, tracking, determining, and / or identifying 8 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) objects within the environment surrounding vehicle 100. A machine learning model in accordance with some implementations can be utilized in tracking objects. The planning subsystem 156 can perform functions such as planning a trajectory for vehicle 100 over some timeframe given a desired destination as well as the static and moving objects within the environment. A machine learning model in accordance with some implementations can be utilized in planning a vehicle trajectory. The control subsystem 158 can perform functions such as generating suitable control signals for controlling the various controls in the vehicle control system 120 in order to implement the planned trajectory of the vehicle 100. A machine learning model can be utilized to generate one or more signals to control an autonomous vehicle to implement the planned trajectory.

[0039] Multiple sensors of types illustrated in FIG.1A can be used for redundancy and / or to cover different regions around a vehicle, and other types of sensors may be used. Various types and / or combinations of control subsystems may be used. Some or all of the functionality of a subsystem 152 – 158 may be implemented with program code instructions 126 resident in one or more memories 124 and executed by one or more processors 122, and these subsystems 152 – 158 may in some instances be implemented using the same processor(s) and / or memory. Subsystems may be implemented at least in part using various dedicated circuit logic, various processors, various field programmable gate arrays (“FPGA”), various application-specific integrated circuits (“ASIC”), various real time controllers, and the like, as noted above, multiple subsystems may utilize circuitry, processors, sensors, and / or other components. Further, the various components in the vehicle control system 120 may be networked in various manners.

[0040] In some implementations, the vehicle 100 may also include a secondary vehicle control system (not illustrated), which may be used as a redundant or backup control system for the vehicle 100. In some implementations, the secondary vehicle control system may be capable of fully operating the autonomous vehicle 100 in the event of an adverse event in the vehicle control system 120, while in other implementations, the secondary vehicle control system may only have limited functionality, e.g., to perform a controlled stop of the vehicle 100 in response 9 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) to an adverse event detected in the primary vehicle control system 120. In still other implementations, the secondary vehicle control system may be omitted.

[0041] Various architectures, including various combinations of software, hardware, circuit logic, sensors, and networks, may be used to implement the various components illustrated in FIG.1A. Each processor may be implemented, for example, as a microprocessor and each memory may represent the random access memory (“RAM”) devices comprising a main storage, as well as any supplemental levels of memory, e.g., cache memories, non-volatile or backup memories (e.g., programmable or flash memories), read- only memories, etc. In addition, each memory may be considered to include memory storage physically located elsewhere in the vehicle 100, e.g., any cache memory in a processor, as well as any storage capacity used as a virtual memory, e.g., as stored on a mass storage device or another computer controller. One or more processors illustrated in FIG.1A, or entirely separate processors, may be used to implement additional functionality in the vehicle 100 outside of the purposes of autonomous control, e.g., to control entertainment systems, to operate doors, lights, convenience features, etc.

[0042] In addition, for additional storage, the vehicle 100 may include one or more mass storage devices, e.g., a removable disk drive, a hard disk drive, a direct access storage device (“DASD”), an optical drive (e.g., a CD drive, a DVD drive, etc.), a solid state storage drive (“SSD”), network attached storage, a storage area network, and / or a tape drive, among others.

[0043] Furthermore, the vehicle 100 may include a user interface 164 to enable vehicle 100 to receive a number of inputs from and generate outputs for a user or operator, e.g., one or more displays, touchscreens, voice and / or gesture interfaces, buttons and other tactile controls, etc. Otherwise, user input may be received through (e.g., by way of) another computer or electronic device, e.g., through an app on a mobile device or through a web interface.

[0044] Moreover, the vehicle 110A may include one or more network interfaces, e.g., network interface 162, suitable for communicating with one or more networks 170 (e.g., a Local Area Network (“LAN”), a wide area network (“WAN”), a wireless network, and / or the Internet, among others) to permit the communication of information with other computers and electronic 10 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) device, including, for example, a central service, such as a cloud service, from which the vehicle 110A receives environmental and other data for use in autonomous control thereof. Data collected by the one or more sensors 130 can be uploaded to a computing system 172 via the network 170 for additional processing. A time stamp can be added to each instance of vehicle data prior to uploading. In some implementations, computing system 172 may have configuration similar to that of computing system 500 in FIG.5. Additional processing of autonomous vehicle data by computing system 172 in accordance with many implementations is described with respect to FIG.5.

[0045] Each processor illustrated in FIG.1A, as well as various additional controllers and subsystems disclosed herein, generally operates under the control of an operating system and executes or otherwise relies upon various computer software applications, components, programs, objects, modules, data structures, etc., as will be described in greater detail below. Moreover, various applications, components, programs, objects, modules, etc. may also execute on one or more processors in another computer coupled to vehicle 100 through network 170, e.g., in a distributed, cloud-based, or client-server computing environment, whereby the processing required to implement the functions of a computer program may be allocated to multiple computers and / or services over a network.

[0046] In general, the routines executed to implement the various implementations described herein, whether implemented as part of an operating system or a specific application, component, program, object, module or sequence of instructions, or even a subset thereof, will be referred to herein as “program code”. Program code can include one or more instructions that are resident at various times in various memory and storage devices, and that, when read and executed by one or more processors, perform the steps necessary to execute steps or elements embodying the various aspects of the present disclosure. Moreover, while implementations have and hereinafter will be described in the context of fully functioning computers and systems, it will be appreciated that the various implementations described herein are capable of being distributed as a program product in a variety of forms, and that implementations can be implemented 11 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) regardless of the particular type of computer readable media used to actually carry out the distribution.

[0047] Examples of computer readable media include tangible, non-transitory media such as volatile and non-volatile memory devices, floppy and other removable disks, solid state drives, hard disk drives, magnetic tape, and optical disks (e.g., CD-ROMs, DVDs, etc.) among others.

[0048] In addition, various program code described hereinafter may be identified based upon the application within which it is implemented in a specific implementation. Any particular program nomenclature that follows is used merely for convenience, and thus the present disclosure should not be limited to use solely in any specific application identified and / or implied by such nomenclature. Furthermore, given the typically endless number of manners in which computer programs may be organized into routines, procedures, methods, modules, objects, and the like, as well as the various manners in which program functionality may be allocated among various software layers that are resident within a typical computer (e.g., operating systems, libraries, API’s, applications, applets, etc.), the present disclosure is not limited to the specific organization and allocation of program functionality described herein. 2. LIDAR for Automotive Applications

[0049] A truck can include a LIDAR system (e.g., vehicle control system 120 in FIG.1A, LIDAR sensor system 300 in FIG.3A, among others described herein). In some implementations, the LIDAR sensor system 300 can use frequency modulation to encode an optical signal and scatter the encoded optical signal into free-space using optics. By detecting the frequency differences between the encoded optical signal and a returned signal reflected back from an object, the frequency modulated (FM) LIDAR sensor system can determine the location of the object and / or precisely measure the velocity of the object using the Doppler effect. In some implementations, an FM LIDAR sensor system may use a continuous wave (referred to as, “FMCW LIDAR”) or a quasi-continuous wave (referred to as, “FMQW LIDAR”). In some implementations, the LIDAR sensor system can use phase modulation (PM) to encode an optical signal and scatters the encoded optical signal into free-space using optics. 12 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO)

[0050] In some instances, an object (e.g., a pedestrian wearing dark clothing) may have a low reflectivity, in that it only reflects back to the sensors (e.g., sensors 130 in FIG.1A) of the FM or PM LIDAR sensor system a low amount (e.g., 10% or less) of the light that hit the object. In other instances, an object (e.g., a shiny road sign) may have a high reflectivity (e.g., above 10%), in that it reflects back to the sensors of the FM LIDAR sensor system a high amount of the light that hit the object.

[0051] Regardless of the object’s reflectivity, an FM LIDAR sensor system may be able to detect (e.g., classify, recognize, discover, etc.) the object at greater distances (e.g., 2x) than a conventional LIDAR sensor system. For example, an FM LIDAR sensor system may detect a low reflectivity object beyond 300 meters, and a high reflectivity object beyond 400 meters.

[0052] To achieve such improvements in detection capability, the FM LIDAR sensor system may use sensors (e.g., sensors 130 in FIG.1A). In some implementations, these sensors can be single photon sensitive, meaning that they can detect the smallest amount of light possible. While an FM LIDAR sensor system may, in some applications, use infrared wavelengths (e.g., 950nm, 1550nm, etc.), it is not limited to the infrared wavelength range (e.g., near infrared: 800nm – 1500nm; middle infrared: 1500nm – 5602nm; and far infrared: 5602nm – 1,000,000nm). By operating the FM or PM LIDAR sensor system in infrared wavelengths, the FM or PM LIDAR sensor system can broadcast stronger light pulses or light beams than conventional LIDAR sensor systems.

[0053] Thus, by detecting an object at greater distances, an FM LIDAR sensor system may have more time to react to unexpected obstacles. Indeed, even a few milliseconds of extra time could improve response time and comfort, especially with heavy vehicles (e.g., commercial trucking vehicles) that are driving at highway speeds.

[0054] The FM LIDAR sensor system can provide accurate velocity for each data point instantaneously. In some implementations, a velocity measurement is accomplished using the Doppler effect which shifts frequency of the light received from the object based at least one of the velocity in the radial direction (e.g., the direction vector between the object detected and the 13 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) sensor) or the frequency of the laser signal. For example, for velocities encountered in on-road situations where the velocity is less than 100 meters per second (m / s), this shift at a wavelength of 1550 nanometers (nm) amounts to the frequency shift that is less than 130 megahertz (MHz). This frequency shift is small such that it is difficult to detect directly in the optical domain. However, by using coherent detection in FMCW, PMCW, or FMQW LIDAR sensor systems, the signal can be converted to the RF domain such that the frequency shift can be calculated using various signal processing techniques. This enables the autonomous vehicle control system to process incoming data faster.

[0055] Instantaneous velocity calculation also makes it easier for the FM LIDAR sensor system to determine distant or sparse data points as objects and / or track how those objects are moving over time. For example, an FM LIDAR sensor (e.g., sensors 130 in FIG.1A) may only receive a few returns (e.g., hits) on an object that is 300m away, but if those return give a velocity value of interest (e.g., moving towards the vehicle at >70 mph), then the FM LIDAR sensor system and / or the autonomous vehicle control system may determine respective weights to probabilities associated with the objects.

[0056] Faster identification and / or tracking of the FM LIDAR sensor system gives an autonomous vehicle control system more time to maneuver a vehicle. A better understanding of how fast objects are moving also allows the autonomous vehicle control system to plan a better reaction.

[0057] The FM LIDAR sensor system can have less static compared to conventional LIDAR sensor systems. That is, the conventional LIDAR sensor systems that are designed to be more light-sensitive typically perform poorly in bright sunlight. These systems also tend to suffer from crosstalk (e.g., when sensors get confused by each other’s light pulses or light beams) and from self-interference (e.g., when a sensor gets confused by its own previous light pulse or light beam). To overcome these disadvantages, vehicles using the conventional LIDAR sensor systems often need extra hardware, complex software, and / or more computational power to manage this effect. 14 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO)

[0058] In contrast, FM LIDAR sensor systems do not suffer from these types of issues because each sensor is specially designed to respond only to its own light characteristics (e.g., light beams, light waves, light pulses). If the returning light does not match the timing, frequency, and / or wavelength of what was originally transmitted, then the FM sensor can filter (e.g., remove, ignore, etc.) out that data point. As such, FM LIDAR sensor systems produce (e.g., generates, derives, etc.) more accurate data with less hardware or software requirements, enabling smoother driving.

[0059] The FM LIDAR sensor system can be easier to scale than conventional LIDAR sensor systems. As more self-driving vehicles (e.g., cars, commercial trucks, etc.) show up on the road, those powered by an FM LIDAR sensor system likely will not have to contend with interference issues from sensor crosstalk. Furthermore, an FM LIDAR sensor system uses less optical peak power than conventional LIDAR sensors. As such, some or all of the optical components for an FM LIDAR can be produced on a single chip, which produces its own benefits, as discussed herein. 3. Commercial Trucking

[0060] FIG.1B is a block diagram illustrating an example of a system environment for autonomous commercial trucking vehicles, according to some implementations. The environment 100B includes a commercial truck 102B for hauling cargo 106B. In some implementations, the commercial truck 102B may include vehicles configured to long-haul freight transport, regional freight transport, intermodal freight transport (i.e., in which a road- based vehicle is used as one of multiple modes of transportation to move freight), and / or any other road-based freight transport applications. In some implementations, the commercial truck 102B may be a flatbed truck, a refrigerated truck (e.g., a reefer truck), a vented van (e.g., dry van), a moving truck, etc. In some implementations, the cargo 106B may be goods and / or products. In some implementations, the commercial truck 102B may include a trailer to carry the cargo 106B, such as a flatbed trailer, a lowboy trailer, a step deck trailer, an extendable flatbed trailer, a sidekit trailer, etc. 15 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO)

[0061] The environment 100B includes an object 110B (shown in FIG.1B as another vehicle) that is within a distance range that is equal to or less than 30 meters from the truck.

[0062] The commercial truck 102B may include a LIDAR sensor system 104B (e.g., an FM LIDAR sensor system, vehicle control system 120 in FIG.1A, LIDAR sensor system 300 in FIG.3A) for determining a distance to the object 110B and / or measuring the velocity of the object 110B. Although FIG.1B shows that one LIDAR sensor system 104B is mounted on the front of the commercial truck 102B, the number of LIDAR sensor systems and the mounting area of the LIDAR sensor system on the commercial truck are not limited to a particular number or a particular area. The commercial truck 102B may include any number of LIDAR sensor systems 104B (or components thereof, such as sensors, modulators, coherent signal generators, etc.) that are mounted onto any area (e.g., front, back, side, top, bottom, underneath, and / or bottom) of the commercial truck 102B to facilitate the detection of an object in any free-space relative to the commercial truck 102B.

[0063] As shown, the LIDAR sensor system 104B in environment 100B may be configured to detect an object (e.g., another vehicle, a bicycle, a tree, street signs, potholes, etc.) at short distances (e.g., 30 meters or less) from the commercial truck 102B.

[0064] FIG.1C is a block diagram illustrating an example of a system environment for autonomous commercial trucking vehicles, according to some implementations. The environment 100C includes the same components (e.g., commercial truck 102B, cargo 106B, LIDAR sensor system 104B, etc.) that are included in environment 100B.

[0065] The environment 100C includes an object 110C (shown in FIG.1C as another vehicle) that is within a distance range that is (i) more than 30 meters and (ii) equal to or less than 150 meters from the commercial truck 102B. As shown, the LIDAR sensor system 104B in environment 100C may be configured to detect an object (e.g., another vehicle, a bicycle, a tree, street signs, potholes, etc.) at a distance (e.g., 100 meters) from the commercial truck 102B. 16 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO)

[0066] FIG.1D is a block diagram illustrating an example of a system environment for autonomous commercial trucking vehicles, according to some implementations. The environment 100D includes the same components (e.g., commercial truck 102B, cargo 106B, LIDAR sensor system 104B, etc.) that are included in environment 100B.

[0067] The environment 100D includes an object 110D (shown in FIG.1D as another vehicle) that is within a distance range that is more than 150 meters from the commercial truck 102B. As shown, the LIDAR sensor system 104B in environment 100D may be configured to detect an object (e.g., another vehicle, a bicycle, a tree, street signs, potholes, etc.) at a distance (e.g., 300 meters) from the commercial truck 102B.

[0068] In commercial trucking applications, it is important to effectively detect objects at all ranges due to the increased weight and, accordingly, longer stopping distance required for such vehicles. FM LIDAR sensor systems (e.g., FMCW and / or FMQW systems) or PM LIDAR sensor systems are well-suited for commercial trucking applications due to the advantages described above. As a result, commercial trucks equipped with such systems may have an enhanced ability to move both people and goods across short or long distances. In various implementations, such FM or PM LIDAR sensor systems can be used in semi-autonomous applications, in which the commercial truck has a driver and some functions of the commercial truck are autonomously operated using the FM or PM LIDAR sensor system, or fully autonomous applications, in which the commercial truck is operated entirely by the FM or LIDAR sensor system, alone or in combination with other vehicle systems. 4. Measurement of Range Using Optical Phase-Encoded Signals

[0069] FIG.2A is a schematic graph 210 that illustrates an example transmitted optical phase- encoded signal for measurement of range, according to an embodiment. The horizontal axis 212 indicates time in arbitrary units from a start time at zero. The left vertical axis 214a indicates power in arbitrary units during a transmitted signal; and the right vertical axis 214b indicates phase of the transmitted signal in arbitrary units. To simply illustrate the technology of phase- encoded LIDAR, binary phase encoding is demonstrated. Trace 215 indicates the power relative 17 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) to the left axis 214a and is constant during the transmitted signal and falls to zero outside the transmitted signal. Dotted trace 216 indicates phase of the signal relative to a continuous wave signal.

[0070] As can be seen, the trace is in phase with a carrier (phase ൌ 0) for part of the transmitted signal and then changes by Δφ (phase ൌ Δφ) for short time intervals, switching back and forth between the two phase values repeatedly over the transmitted signal as indicated by the ellipsis 217. The shortest interval of constant phase is a parameter of the encoding called pulse duration τ and is typically the duration of several periods of the lowest frequency in the band. The reciprocal, 1 / τ, is baud rate, where each baud indicates a symbol. The number N of such constant phase pulses during the time of the transmitted signal is the number N of symbols and represents the length of the encoding. In binary encoding, there are two phase values and the phase of the shortest interval can be considered a 0 for one value and a 1 for the other, thus the symbol is one bit, and the baud rate is also called the bit rate. In multiphase encoding, there are multiple phase values. For example, 4 phase values such as Δφ* {0, 1, 2 and 3}, which, for Δφ ൌ π / 2 (90 degrees), equals {0, π / 2, π and 3π / 2}, respectively; and thus 4 phase values can represent 0, 1, 2, 3, respectively. In this example, each symbol is two bits and the bit rate is twice the baud rate.

[0071] Phase-shift keying (PSK) refers to a digital modulation scheme that conveys data by changing (modulating) the phase of a reference signal (the carrier wave) as illustrated in FIG. 2A. The modulation is impressed by varying the sine and cosine inputs at a precise time. At radio frequencies (RF), PSK is widely used for wireless local area networks (LANs), RF identification (RFID) and Bluetooth communication. Alternatively, instead of operating with respect to a constant reference wave, the transmission can operate with respect to itself. Changes in phase of a single transmitted waveform can be considered the symbol. In this system, the demodulator determines the changes in the phase of the received signal rather than the phase (relative to a reference wave) itself. Since this scheme depends on the difference between successive phases, it is termed differential phase-shift keying (DPSK). DPSK can be significantly simpler to implement than ordinary PSK, since there is no need for the demodulator to have a copy of the reference signal to determine the exact phase of the received signal (it is a non-coherent scheme). 18 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO)

[0072] For optical ranging applications, the carrier frequency is an optical frequency fcand a RF fr is modulated onto the optical carrier. The number N and duration τ of symbols are selected to achieve the desired range accuracy and resolution. The pattern of symbols is selected to be distinguishable from other sources of coded signals and noise. Thus, a strong correlation between the transmitted and returned signal is a strong indication of a reflected or backscattered signal. The transmitted signal is made up of one or more blocks of symbols, where each block is sufficiently long to provide strong correlation with a reflected or backscattered return even in the presence of noise. In the following discussion, it is assumed that the transmitted signal is made up of M blocks of N symbols per block, where M and N are non-negative integers.

[0073] FIG.2B is a schematic graph 220 that illustrates the example transmitted signal of FIG. 2A as a series of binary digits along with returned optical signals for measurement of range, according to an embodiment. The horizontal axis 222 indicates time in arbitrary units after a start time at zero. The vertical axis 224a indicates amplitude of an optical transmitted signal at frequency fc+ frin arbitrary units relative to zero. The vertical axis 224b indicates amplitude of an optical returned signal at frequency fc+ frin arbitrary units relative to zero, and is offset from axis 224a to separate traces. Trace 225 represents a transmitted signal of M*N binary symbols, with phase changes as shown in FIG.2A to produce a code starting with 00011010 and continuing as indicated by ellipsis. Trace 226 represents an idealized (noiseless) return signal that is scattered from an object that is not moving (and thus the return is not Doppler shifted). The amplitude is reduced, but the code 00011010 is recognizable. Trace 227 represents an idealized (noiseless) return signal that is scattered from an object that is moving and is therefore Doppler shifted. The return is not at the proper optical frequency fc + fr and is not well detected in the expected frequency band, so the amplitude is diminished.

[0074] The observed frequency ^^ᇱof the return differs from the correct frequency f = fc + fr of the return by the Doppler effect given by Equation 1. ^^ᇱ ൌ^^ା ௩^^^^ (Equation 1)4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO)

[0075] Where c is the speed of light in the medium. Note that the two frequencies are the same if the observer and source are moving at the same speed in the same direction on the vector between the two. The difference between the two frequencies, Δf = f’-f , is the Doppler shift, ΔfD, which causes problems for the range measurement, and is given by Equation 2. ∆^^^ ൌ ^^^ା ௩^^^^ା௩ೞ^െ 1^ ^^ (Equation 2)

[0076] Note that the magnitude of the error increases with the frequency f of the signal. Note that for a stationary LIDAR system (vo = 0), for an object moving at 10 meters a second (vo = 10), and visible light of frequency about 500 THz, then the size of the error is on the order of 16 megahertz (MHz, 1 MHz = 106hertz, Hz, 1 Hz = 1 cycle per second). In various embodiments described below, the Doppler shift error is detected and used to process the data for the calculation of range.

[0077] FIG.2C is a schematic graph 230 that illustrates example cross-correlations of the transmitted signal with two returned signals, according to an embodiment. In phase coded ranging, the arrival of the phase coded reflection is detected in the return by cross correlating the transmitted signal or other reference signal with the returned signal, implemented practically by cross correlating the code for a RF signal with an electrical signal from an optical detector using heterodyne detection and thus down-mixing back to the RF band. In some implementations, this may include correlating a sequence of phases (or phase changes) of a particular frequency in a return signal with that in the transmitted signal. The horizontal axis 232 indicates a lag time in arbitrary units applied to the coded signal before performing the cross correlation calculation with the returned signal. The vertical axis 234 indicates amplitude of the cross correlation computation. Cross correlation for any one lag is computed by convolving the two traces, i.e., multiplying corresponding values in the two traces and summing over all points in the trace, and then repeating for each time lag. Alternatively, the cross correlation can be accomplished by a multiplication of the Fourier transforms of each the two traces followed by an inverse Fourier transform. Efficient hardware and software implementations for a Fast Fourier transform (FFT) are widely available for both forward and inverse Fourier transforms. More precise mathematical 20 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) expression for performing the cross correlation are provided for some example embodiments, below. In some implementations, the Doppler peak and / or its shift (ΔfD) can be used to correct the correlation computation and determine the correct range. This may be accomplished with an autocorrelation computation, e.g., using the computational efficiencies of a FFT and inverse FFT.

[0078] In some implementations, a long code, of duration D ൌ (M*N)* τ, may be encoded onto the transmitted light, and a return signal of the same length in time can collected. Both the code and signal are broken into M shorter blocks of length N so that the correlation can be conducted several times on the same data stream and the results averaged to improve signal to noise ratio (SNR). Families of good binary spreading sequences with minimal auto-correlation sidelobes for communication systems and radar and LIDAR systems such as so-called “maximal-length sequences (m-sequences)” can provide the codes used for phase modulation of each block of the M blocks.

[0079] Note that the cross correlation computation is typically done with analog or digital electrical signals after the amplitude and phase of the return is detected at an optical detector. To move the signal at the optical detector to a RF frequency range that can be digitized easily, the optical return signal is optically mixed with the reference signal before impinging on the detector. A copy of the phase-encoded transmitted optical signal can be used as the reference signal, but it is also possible, and often preferable, to use the continuous wave carrier frequency optical signal output by the laser as the reference signal and capture both the amplitude and phase of the electrical signal output by the detector.

[0080] Trace 236 represents cross correlation with an idealized (noiseless) return signal that is reflected from an object that is not moving (and thus the return is not Doppler shifted). A peak occurs at a time Δt after the start of the transmitted signal. This indicates that the returned signal includes a version of the transmitted phase code beginning at the time Δt. The range R to the reflecting (or backscattering) object is computed from the two way travel time delay based on the speed of light c in the medium, as given by Equation 3. 21 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) ^^ ൌ ^^ ∗ ∆^^ / 2 (Equation 3)

[0081] According to various embodiments described in more detail below, the Doppler shift is determined in the electrical processing of the returned signal; and the Doppler shift is used to correct the cross correlation calculation. Thus, a peak is more readily found and range can be more readily determined. FIG.2D is a schematic graph 240 that illustrates an example spectrum of the transmitted signal and an example spectrum of a Doppler shifted return signal, according to an embodiment. The horizontal axis 242 indicates RF frequency offset from an optical carrier fc in arbitrary units. The vertical axis 244a indicates amplitude of a particular narrow frequency bin, also called spectral density, in arbitrary units relative to zero. The vertical axis 244b indicates spectral density in arbitrary units relative to zero, and is offset from axis 244a to separate traces. Trace 245 represents a transmitted signal; and a peak occurs at the proper RF f0. Trace 246 represents an idealized (noiseless) return signal that is backscatter from an object that is moving and is therefore Doppler shifted. The return does not have a peak at the proper RF f0; but, instead, is blue shifted by ΔfD to a shifted frequency fS.

[0082] In some Dopplerembodiments, rather than finding ΔfDby taking the spectrum of both transmitted and returned signals and searching for peaks in each, then subtracting the frequencies of corresponding peaks, as illustrated in FIG.2D, it is more efficient to take the cross spectrum of the in-phase and quadrature component of the down-mixed returned signal in the RF band. FIG.2E is a schematic graph 250 that illustrates an example cross- spectrum, according to an embodiment. The horizontal axis 252 indicates frequency shift in arbitrary units relative to the reference spectrum; and the vertical axis 254 indicates amplitude of the cross spectrum in arbitrary units relative to zero. Trace 255 represents a cross spectrum with an idealized (noiseless) return signal generated by one object moving toward the LIDAR system (blue shift of ΔfD1 = ΔfD in FIG.2D) and a second object moving away from the LIDAR system (red shift of ΔfD2).occurs when one of the components is blue shifted ΔfD1; and another peak occurs when one of the components is red shifted ΔfD2. Thus, the Doppler shifts are determined. These shifts can be used to determine a velocity of approach of objects in the vicinity of the LIDAR, as can be critical for collision avoidance applications. 22 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO)

[0083] As described in more detail below, the Doppler shift(s) detected in the cross spectrum are used to correct the cross correlation so that the peak 235 is apparent in the Doppler compensated Doppler shifted return at lag Δt, and range R can be determined. The information needed to determine and compensate for Doppler shifts is either not collected or not used in prior phase- encoded LIDAR systems. 5. LIDAR System for Autonomous Vehicles

[0084] FIG.3 is a block diagram illustrating an example environment of a lidar sensor system for autonomous vehicles, according to some implementations. The environment 300 includes a lidar sensor system 301 that includes a transmit (Tx) path and a receive (Rx) path. The Tx path includes one or more Tx input / output ports (not shown in FIG.3) and the Rx path includes one or more Rx input / output ports (not shown in FIG.3).

[0085] In some implementations, a semiconductor substrate and / or semiconductor package may include the Tx path and the Rx. In some implementations, the semiconductor substrate and / or semiconductor package may include at least one of silicon photonics circuitry, photonic lightwave circuit (PLC), or III-V semiconductor circuitry.

[0086] In some implementations, a first semiconductor substrate and / or a first semiconductor package may include the Tx path and a second semiconductor substrate and / or a second semiconductor package may include the Rx path. In some arrangements, the Rx input / output ports and / or the Tx input / output ports may occur (or be formed / disposed / located / placed) along one or more edges of one or more semiconductor substrates and / or semiconductor packages.

[0087] The environment 300 includes one or more transmitters 316 and one or more receivers 318.

[0088] The environment 300 includes one or more optics 310 (e.g., an oscillatory scanner, a unidirectional scanner, a Risley prism, a circulator optic, and / or a beam collimator, etc.) that are coupled to the lidar system 301. In some implementations, the one or more optics 310 may be coupled to the Tx path through the one or more Tx input / output ports. In some implementations, 23 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) the one or more optics 310 may be coupled to the Rx path through the one or more Rx input / output ports.

[0089] The environment 300 includes a vehicle control system 120 (e.g., vehicle control system 120 in FIG.1) that is coupled to the lidar system 301. In some implementations, the vehicle control system 120 may be coupled to the Rx path through the one or more Rx input / output ports.

[0090] The Tx path may include a laser source 302, a modulator 304A, a modulator 304B, an amplifier 306, and one or more transmitters 316. The Rx path may include one or more receivers 318, a mixer 308, a detector 312, a transimpedance amplifier (TIA) 314, and one or more analog- to-digital converters (ADCs). Although FIG.3 shows only a select number of components and only one input / output channel; the environment 300 may include any number of components and / or input / output channels (in any combination) that are interconnected in any arrangement to facilitate combining multiple functions of a lidar system, to support the operation of a vehicle.

[0091] The laser source 302 may be configured to generate a light signal (or beam) that is derived from (or associated with) a local oscillator (LO) signal. In some implementations, the light signal may have an operating wavelength that is equal to or substantially equal to 1550 nanometers. In some implementations, the light signal may have an operating wavelength that is between 1400 nanometers and 1400 nanometers.

[0092] The laser source 302 may be configured to provide the light signal to the modulator 304A, which is configured to modulate a phase and / or a frequency of the light signal based on a first radio frequency (RF) signal (shown in FIG.3 as, “RF1”) and using Continuous Wave (CW) modulation or quasi-CW modulation to generate a modulated light signal. The modulator 304A may be configured to send the modulated light signal to the amplifier 306. The amplifier 306 may be configured to amplify the modulated light signal to generate an amplified light signal to the optics 310 through the one or more transmitters 316. The one or more transmitters 316 may include one or more optical waveguides or antennas. 24 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO)

[0093] The optics 310 may be configured to steer the amplified light signal that it receives from the Tx path into an environment within a given field of view toward an object 318, may receive a returned signal reflected back from the object 318, and provide the returned signal to the mixer 308 of the Rx path through the one or more receivers 318. The one or more receivers 318 may include one or more optical waveguides or antennas. In some arrangements, the transmitters 316 and the receivers 318 may constitute one or more transceivers (not shown in FIG.3). In some arrangements, the one or more transceivers may include a monostatic transceiver or a bistatic transceiver.

[0094] The laser source 302 may be configured to provide the LO signal to the modulator 304B, which is configured to modulate a phase and / or a frequency of the LO signal based on a second RF signal (shown in FIG.3 as, “RF2”) and using Continuous Wave (CW) modulation or quasi- CW modulation to generate a modulated LO signal and send the modulated LO signal to the mixer 308 of the Rx path.

[0095] The mixer 308 may be configured to mix (e.g., combine, multiply, etc.) the modulated LO signal with the returned signal to generate a down-converted signal and send the down- converted signal to the detector 312. In some arrangements, the mixer 308 may be configured to send the modulated LO signal to the detector 312.

[0096] The detector 312 may be configured to generate an electrical signal based on the down- converted signal and send the electrical signal to the TIA 314. In some arrangements, the detector 312 may be configured to generate an electrical signal based on the down-converted signal and the modulated signal.

[0097] The TIA 314 may be configured to amplify the electrical signal and send the amplified electrical signal to the vehicle control system 120 through the one or more ADCs 320.

[0098] In some implementations, the TIA 314 may have a peak noise-equivalent power (NEP) that is less than 5 picoWatts per square root Hertz (i.e., 5x10-12 Watts per square root Hertz). In some implementations, the TIA 314 may have a gain between 4 kiloohms and 25 kiloohms. 25 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO)

[0099] In some implementations, detector 312 and / or TIA 314 may have a 3 decibel bandwidth between 80 kilohertz (kHz) and 450 megahertz (MHz).

[0100] A vehicle control system (e.g., the control subsystem 150) may be configured to determine a distance to the object 318 and / or measures the velocity of the object 318 based on the one or more electrical signals that it receives from the TIA through the one or more ADCs 324.

[0101] In some implementations, modulator 304A and / or modulator 304B may have a bandwidth between 400 megahertz (MHz) and 1000 (MHz).

[0102] In some implementations, the modulator 304A may be configured to send a first modulated light (optical) signal and a second modulated light (optical) signal to the amplifier 306. The amplifier 306 may be configured to amplify the first and second modulated light signals to generate amplified light signals to the optics 310 through the transmitters 316. The optics 310 may be configured to steer the first and second modulated light signals that it receives from the Tx path into an environment within a given field of view toward an object 318, may receive corresponding first and second returned signals reflected back from the object 318, and provide the first and second returned signals to the mixer 308 of the Rx path through the receivers 318. The modulator 304B may be configured to generate (1) a first modulated LO signal associated with the first modulated light signal and (2) a second modulated LO signal associated with the second modulated light signal, and send the first and second modulated LO signals to the mixer 308 of the Rx path. The mixer 308 may be configured to pair (e.g., associate, link, identify, etc.) the first returned light signal and the first modulated LO signal, and mix (e.g., combine, multiply, etc.) the first returned light signal and the first modulated LO signal to generate a first down-converted signal and send the first down-converted signal to the detector 312. Similarly, the mixer 308 may be configured to pair the second returned light signal and the second modulated LO signal, and mix the second returned light signal and the second modulated LO signal to generate a second down-converted signal and send the second down-converted signal to the detector 312. The detector 312 may be configured to generate first and second 26 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) electrical signals based on the first and second down-converted signal, respectively. The vehicle control system 120 may be configured to determine a distance to the object 318 and / or measures the velocity of the object 318 based on the first and second electrical signals, received through TIA 314 and ADCs 320. 6. A lidar System Using a Digital Signal Processing (DSP)

[0103] FIG.4A is a block diagram illustrating an example of a lidar sensor system 400, according to some implementations. The lidar sensor system 400 may include a laser source 402, a local oscillator 412, a modulator 404 (e.g., optical modulator), circulator optics 406, a scanner 408, an optical mixer 414, one or more detectors 416 (e.g., a pair of detectors), and a DSP system 418. FIG.4B is a block diagram illustrating an example of the DSP system 418 in a lidar sensor system, according to some implementations. The DSP system 418 may include a digital sampling system 450 and other DSP components 460. The digital sampling system 450 may include a digitizer 452 (e.g., ADC), a digital mixer 454 (e.g., a direct digital synthesizer (DDS), digital multipliers), a low pass filter 456, and a down-sampler 458. In some implementations, DSP system 418 may include circuits or one or more processors (e.g., processor 510 in FIG.5) configured to perform demodulation, decoding, and related tasks. These circuits may be generally based on application-specific ICs (ASICs), field-programmable gate arrays (FPGAs) and programmable DSP devices.

[0104] Referring to FIG.4A, the laser 402 may generate a beam which is oscillated by the local oscillator 412 to output an optical LO signal. In some implementations, the modulator 404 may determine a frequency offset (fo) between a transmit (Tx) optical signal and the optical LO signal, generate an optical signal with its frequency shifted from the LO frequency by the frequency offset (fo), and perform modulation (e.g., IQ modulation) of the frequency-shifted optical signal (hereinafter referred to as “^^^–shifted waveform”) based on a data signal (e.g., I / Q data signal) to generate a transmit (Tx) optical waveform 405. In some implementations, the modulator 404 may generate a ^^^–shifted waveform using a plurality of methods. The methods may include (1) optical single-sideband generation using a nested Mach-Zehnder electro-optic 27 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) modulator, (2) serrodyne shifting with an electro-optic modulator, (3) optical phase-lock loop with two separate lasers, (4) optical injection locking with two separate lasers, or (5) using acousto-optic modulators.

[0105] The circulator optics 406 may receive the Tx optical waveform 405, which is input to the scanner 408 as a Tx signal. The Tx signal may be transmitted through the scanner 408 to illuminate an object 410 (or an area of interest). The scanner 408 may receive a return optical signal reflected by the object 410 as a receive (Rx) optical signal. In some implementations, the optical mixer 414 may mix the Rx optical signal with an optical LO signal 413 to produce an optical signal, which may be then detected by the detector 416 and further delivered to the digital sampling system 450 of the DSP system 418 as analog data input 449 (see FIG.4B).

[0106] Referring to FIG.4B, the digitizer 452 of the digital sampling system 450 may digitize the analog data input to output a digital signal of interest. In some implementations, the digital signal of interest may include strictly positive frequency content because the Rx optical signal may have a frequency range that has been shifted by the frequency offset (fo) from the LO frequency. The digital mixer 454 of the digital sampling system 450 (e.g., digital down converter (DDC)) may extract a full complex signal (e.g., I / Q components) from the digital signal by digitally mixing the digital signal to produce I data and Q data and recombine the I / Q data into a complex signal (not shown). In some implementations, the lidar sensor system (e.g., lidar sensor system 400) may mix the Rx optical signal with an LO signal using the optical mixer 414 to produce an optical signal, which may be then detected by one or more detectors 416 (e.g., a pair of balanced detectors) and digitized by a digitizer 452 (e.g., ADC), producing a digital signal of interest. The resulting digital signal of interest may include strictly positive frequency content because the Rx optical signal may have a frequency range that has been shifted by the frequency offset (fo) from the LO frequency.

[0107] Referring to FIG.4B, the digital sampling system 450 of the lidar sensor system 400 may extract a full complex signal (e.g., I / Q components) from the digital signal. The digital 28 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) sampling system 450 may digitally mix the digital signal to produce I data and Q data and recombine the I / Q data into a complex signal. If ^^^^^^ and ^^′^^^^ denote the original digital signal and the complex signal, respectively, and ^^^^^^ and ^^^^^^ denote the I data and Q data, respectively, the digital sampling system 450 may perform the step of generating the complex signal ^^′^^^^ according to the following equations:

[0108] ^^^^^^ ൌ ^^^^^^^^^^^^2^^^^^^^^ ൈ ^^^^^^^ ^^^^^ (Equation 4)

[0109] ^^^^^^ ൌ െ1 ൈ ^^^^^^^^^^^ ^^^^^^ ^2^^^^^^^^ ൈ ^^^^^^^ ^^^^^ (Equation 5)

[0110] ^^′^^^^ ൌ ^^^^^^ ^ 1^^ ^^^^^^ ^^^^^ (Equation 6)where 1^^ is the imaginary unit, ^^^is the frequency offset of the Tx optical waveform, LP[] is a low pass filtering (LPF) operation (e.g., LPF operation performed by the low pass filter 456). After performing this step, the lidar sensor system may deliver the ^^′^^^^ signal to another DSP system (e.g., DSP component 460). The DSP system may bandpass filtered (e.g., by a bandpass filter) and / or down-sample or decimate (e.g., by down-sampler 458) the ^^′^^^^ signal as dictated by signal processing needs.

[0111] Referring to FIG.4B, if ^^^^^^ and ^^′^^^^ denote the original digital signal and the complex signal, respectively, and ^^^^^^ and ^^^^^^ denote the I data and Q data, respectively, the digital sampling system 450 may perform the step of generating the complex signal ^^′^^^^ according to Equation 4 to Equation 6. For example, the digital mixer 454 may digitally mix the digital signal ^^^^^^ based on the frequency offset ^^^to generate I data and Q data according to Equation 4 and Equation 5. The low pass filter 456 may further process the I data and Q data to eliminate a high-frequency component. The down-sampler (or decimator) 458 may down-sample (or decimate) the output of the low pass filter 456 to reduce the sample rate of the I data and Q data. After performing LPF and / or down-sampling, The DDC system 450 may recombine the I / Q data into the complex signal ^^′^^^^ and further deliver the ^^′^^^^ signal 459 to the another DSP system 460. The DSP system 460 may perform further processing (e.g., bandpass filtering and / or down-sampling) on the ^^′^^^^ signal as dictated by signal processing needs. 29 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO)

[0112] FIG.5 is a block diagram illustrating an example of a computing system according to some implementations. Referring to FIG.5, the illustrated example computing system 500 includes one or more processors 510 in communication, via a communication system 540 (e.g., bus), with memory 560, at least one network interface controller 530 with network interface port for connection to a network (not shown), and other components, e.g., an input / output (“I / O”) components interface 550 connecting to a display (not illustrated) and an input device (not illustrated). Generally, the processor(s) 510 will execute instructions (or computer programs) received from memory. The processor(s) 510 illustrated incorporate, or are directly connected to, cache memory 520. In some instances, instructions are read from memory 560 into the cache memory 520 and executed by the processor(s) 510 from the cache memory 520.

[0113] In more detail, the processor(s) 510 may be any logic circuitry that processes instructions, e.g., instructions fetched from the memory 560 or cache 520. In some implementations, the processor(s) 510 are microprocessor units or special purpose processors. The computing device 500 may be based on any processor, or set of processors, capable of operating as described herein. The processor(s) 510 may be single core or multi-core processor(s). The processor(s) 510 may be multiple distinct processors.

[0114] The memory 560 may be any device suitable for storing computer readable data. The memory 560 may be a device with fixed storage or a device for reading removable storage media. Examples include all forms of non-volatile memory, media and memory devices, semiconductor memory devices (e.g., EPROM, EEPROM, SDRAM, and flash memory devices), magnetic disks, magneto optical disks, and optical discs (e.g., CD ROM, DVD-ROM, or Blu- Ray® discs). A computing system 500 may have any number of memory devices as the memory 560.

[0115] The cache memory 520 is generally a form of computer memory placed in close proximity to the processor(s) 510 for fast read times. In some implementations, the cache 30 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) memory 520 is part of, or on the same chip as, the processor(s) 510. In some implementations, there are multiple levels of cache 520, e.g., L2 and L3 cache layers.

[0116] The network interface controller 530 manages data exchanges via the network interface (sometimes referred to as network interface ports). The network interface controller 530 handles the physical and data link layers of the OSI model for network communication. In some implementations, some of the network interface controller’s tasks are handled by one or more of the processor(s) 510. In some implementations, the network interface controller 530 is part of a processor 510. In some implementations, a computing system 500 has multiple network interfaces controlled by a single controller 530. In some implementations, a computing system 500 has multiple network interface controllers 530. In some implementations, each network interface is a connection point for a physical network link (e.g., a cat-5 Ethernet link). In some implementations, the network interface controller 530 supports wireless network connections and an interface port is a wireless (e.g., radio) receiver / transmitter (e.g., for any of the IEEE 802.11 protocols, near field communication “NFC”, Bluetooth, ANT, or any other wireless protocol). In some implementations, the network interface controller 530 implements one or more network protocols such as Ethernet. Generally, a computing device 500 exchanges data with other computing devices via physical or wireless links through a network interface. The network interface may link directly to another device or to another device via an intermediary device, e.g., a network device such as a hub, a bridge, a switch, or a router, connecting the computing device 500 to a data network such as the Internet.

[0117] The computing system 500 may include, or provide interfaces for, one or more input or output (“I / O”) devices. Input devices include, without limitation, keyboards, microphones, touch screens, foot pedals, sensors, MIDI devices, and pointing devices such as a mouse or trackball. Output devices include, without limitation, video displays, speakers, refreshable Braille terminal, lights, MIDI devices, and 2-D or 3-D printers.

[0118] Other components may include an I / O interface, external serial device ports, and any additional co-processors. For example, a computing system 500 may include an interface 31 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) (e.g., a universal serial bus (USB) interface) for connecting input devices, output devices, or additional memory devices (e.g., portable flash drive or external media drive). In some implementations, a computing device 500 includes an additional device such as a co-processor, e.g., a math co-processor can assist the processor 510 with high precision or complex calculations. 7. A LIDAR Sensor System Using Pitch-Catch Scanning

[0119] FIG.6 depicts a block diagram of an example of a LIDAR sensor system 600. The LIDAR sensor system 600 can facilitate pitch-catch compensation, i.e. accounting for time delays or other offsets resulting from the round-trip path of the transmit beam outputted from the LIDAR sensor system 600, reflected or otherwise scattered by object(s), and then returned as the return beam to the LIDAR sensor system 600 for detection and processing, which might otherwise affect characteristics of the LIDAR sensor system 600 such as signal-to-noise ratio.

[0120] The LIDAR sensor system 600 can include a chip 605 on which various components of the LIDAR sensor system 600, including transmitter 610 and receiver 612, can be provided. For example, the chip 605 can be a photonic integrated chip, such that various components of the LIDAR sensor system 600 for generating, modulating, and processing optical signals and performing photonic operations are implemented by the chip 605. The chip 605 can be a semiconductor circuit chip. The chip 605 can be made from at least one III-V semiconductor material. For example, the chip 605 can be made from a silicon material or pure silicon. The chip 605 can be made from silicon nitride. The chip 605 can be made from aluminum nitride. The chip 605 can be made from silicon nitride and pure silicon.

[0121] The LIDAR sensor system 600 includes at least one transmitter 610. The transmitter 610 can receive a beam and output transmit beam 635 with particular characteristics such as direction, polarization, or various combinations thereof. The transmitter 610 can include at least one grating coupler 615 (e.g., a first grating coupler). The grating coupler 615 can be a structure having a plurality of spaced apart channels, such as parallel channels, which may have various shapes of the same or differing sizes. The grating coupler 615 can be a structure formed 32 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) by etching on the chip 605. The grating coupler 615 can be a structure formed by deposition of material on the chip 605. The grating coupler 615 can be configured to couple light off of the chip 605, such as into free space away from the chip 605. For example, the grating coupler 615 can couple light off of the chip 605 in a two-dimensional pattern, such as a two-dimensional polarization. As such, the grating coupler 615 can output a transmit beam 635, such as based on a beam outputted by laser source. The grating coupler 615 can output the transmit beam 635 to have a transmit polarization 695. For example, various components upstream or downstream of the grating coupler 615 (e.g., optic module 624) can be used to control the polarization of the transmit beam 635.

[0122] The LIDAR sensor system 600 can include at least one scanner 640, e.g., a steering mirror. For example, the scanner 640 can be coupled with a motor, so that the scanner 640 can be rotated relative to the direction along which the transmit beam 635 is directed towards the scanner 640. The scanner 640 can scan bi-directionally. For example, the scanner 640 can scan in a first direction 660 and a second direction 665. The scanner 640 can receive the transmit beam 635 from the transmitter 610 and direct the transmit beam 635 towards the environment around the LIDAR sensor system 600. As depicted in FIG.6, an object 602 can be present in the environment. The scanner 640 can receive a return beam 655 from reflection or scattering of the transmit beam 635 by the object 602. In the time it takes for the transmit beam 635 to reach the object 602 and the return beam 655 to return from the object 602 to the scanner 640, the scanner 640 may have rotated by a particular angle. The scanner 640 can provide the return beam 655 to the receiver 612.

[0123] The receiver 612 can include a plurality of grating couplers. For example, the receiver 612 can include a grating coupler 625 and a grating coupler 630. The grating couplers 625, 630 can be provided or formed in a manner similar to or identical to the grating coupler 615. The grating couplers 615, 625, 630 can be arranged in an array on the chip 605 (e.g., at least two parallel spaced-apart lines can extend through each of the grating couplers 615, 625, 630). The grating couplers 615, 625, 630 can be arranged in a focal plane of at least one of the scanner 640 33 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) or one or more optical components between the grating couplers 615, 625, 630 and the scanner 640.

[0124] The grating couplers 625, 630 can be spaced from the grating coupler 615. For example, the grating coupler 625 can be spaced from the grating coupler 615 by a first spacing. The first spacing can be associated with a first target range from the scanner 640 for detecting the object 602. For example, the first target range can be within a range of distances from the scanner 640 for which an expected signal to noise ratio of determining at least one of range to or velocity of the object 602 is greater than a threshold signal to noise ratio. The first spacing can be proportional to a mode field diameter of the grating coupler 615 and / or the grating couplers 625, 630, such as to be between about 1 time and 3 times the mode field diameter. The first spacing can be between about 8 micrometers (μm) and 24 μm. The first spacing can be between about 12 micrometers (μm) and about 16 μm. For example, the grating coupler 625 can be spaced from the grating coupler 615 by about 14 μm. The grating coupler 630 can be spaced from the grating coupler 615 by a second spacing. The second spacing can be associated with a second target range from the scanner 640. The second target range can be greater than the first target range. The second spacing can be between about 10 μm and about 20 μm. For example, the grating coupler 630 can be spaced from the grating coupler 615 by about 12 micrometers.

[0125] The grating couplers 625, 630 can receive the return beam 655 provided by the scanner 640. The grating couplers 625, 630 can couple light, e.g., the return beam 655, from free space onto the chip 605. As previously mentioned, the scanner 640 can rotate in the time it takes for the transmit beam 635 to travel to the object 602 and be returned as the return beam 655 to the receiver 612, which can result in an angular displacement of the return beam 655 in the direction the scanner 640 is scanning. The angular displacement can manifest as a translation in the focal plane when the return beam 655 is provided to the receiver 612. The translation can be referred to as focal plane drift. Since the grating couplers 625, 630 can couple light on the chip 605 and are distinct and spatially separated, the grating couplers 625, 630 can be provided for two directions of focal plane drift. Additionally, the translational distance can be optimized for a target time for the transmit beam 635 to travel to the object 602 and the return beam 655 to 34 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) return from the object 602 to the receiver 612, and thus a specific range to the object 602 (because the scan velocity of the transmit beam 635 and the return beam 655 is known).

[0126] The return beam 655 can have components associated with various polarizations, such as based on how the transmit beam 635 is outputted and / or passed through devices such as optic module 624. As such, the scanner 640 can provide a first component 670 of the return beam 655, which can be associated with a first polarization 680, and the grating coupler 625 can receive the first component 670 of the return beam 655. The scanner 640 can provide a second component 675 of the return beam 655 associated with a second polarization 685, and the grating coupler 630 can receive the second component 675. The first polarization 680 can be different than the second polarization 685. The transmit polarization 695 can be the same as the first polarization 680. For example, the grating coupler 615 can output the transmit beam 635 at the first polarization 680. The grating couplers 625, 630 can receive the return beam 655 at the first polarization 680 or at the second polarization 685. The second polarization 685 can be orthogonal to the first polarization 680. The grating couplers 625, 630 can be configured to only receive a single polarization of a beam, e.g., light. The grating couplers 625, 630 can receive light of different polarizations. For example, the grating coupler 625 can receive light of the same polarization as that of the transmit beam 635 and the grating coupler 630 can receive light of a polarization orthogonal to the polarization of the transmit beam 635. The grating couplers 625, 630 can be configured to receive the same polarization of light as each other. For example, the grating couplers 625, 630 can receive light (only) of a polarization orthogonal to the polarization of the transmit beam 635, as depicted in FIG.6, or that is the same as the polarization of the transmit beam 635. The receiver 612 can output at least one signal based on the first component 670 of the return beam 655 received by the grating coupler 625 and based on the second component 675 of the return beam 655 received by the grating coupler 630. The at least one signal outputted by the receiver 612 can be used by various systems described herein, such as the vehicle control system 120, to determine at least one of a range to or a velocity of the object 602, such as to control operation of an autonomous vehicle responsive to the at least one of the range or the velocity. 35 4871-5753-4389.1Atty. Dkt. No. 120261-0517 (A-052220-WO) 8. A lidar System For Pitch-Catch Extension

[0127] In one aspect, it would be generally difficult for a rapidly scanning coherent LIDAR system (e.g., LIDAR sensor system 600 in FIG. 6) to achieve high Tx-Rx beam coupling efficiency over all ranges (e.g., ranges to target objects) simultaneously. An Rx spot imaged at a spot,divergence needed by a coherent lidar to achieve low free space coupling. As expressed in the following Equation (1), in an angle space, the angle shift θpc (e.g., an angle between the transmit beam 635 and the first component 670 of the return beam 655 in FIG. 6) corresponds to a Time of Flight (TOF) round-trip time 2R / c to the target object multiplied by an angular rate Ω of scanning. Similarly, a focal plane drift Δxpc corresponding to the angle shift θpc (e.g., displacement in the focal plane corresponding to the angle between the transmit beam 635 and the first component 670 of the return beam 655 in FIG.6) equals the angle shift θpcmultiplied by f.

[0128] Equation (2) expresses a normalized coherent overlap of two Gaussian optical modes with matched wavefronts and identical 1 / e2widths (^^). In Equation (2), E00refers to the TEM00 spatial mode (i.e. zeroth order Hermite-Gaussian) of the Tx or Rx beam in the focal plane of the lidar system (E00* is the complex conjugate), x refers to the spatial dimension in the focal plane along the scanning direction, y is the direction perpendicular to the scanning direction, and w0is the 1 / e2width at the minimum beam size (a.k.a. the waist). The normalized coherent overlap has a full width half maximum at ∆^^0= ^^0^^^^^^2^. Supposing numbers corresponding an automotive lidar of an angular scan speed of 7200 deg / sec, a 10.5 µm mode4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) field diameter of the Rx waveguides, and a 70mm collimating lens are used, in the far-field (i.e., ^^ ≫ ^^R) where ^^Ris a Rayleigh distance, the 3 dB full width of the coupling around a tuned pitch catch condition is approximately 150 m.

[0129] FIG.7A to FIG.7C are diagrams depicting example simulation results (e.g., SNR and expected shot noise limited probability of detection (PoD) effects) using a coherent LIDAR system. FIG.7A shows SNRs over ranges to the target object when a single pitch-catch tuning (e.g., with a single RX grating coupler) is used. For example, line 701, line 702, line 703, line 704, line 705 show simulation results when using configurations of (1) no scanning, (2) a nominally designed beam size and pitch-catch size (e.g., 3.1 shift normalized to the beam radius), (3) tuning near distance performance, (4) tuning far distance performance, and (5) combining the near distance tuned configuration and the far distance tuned configuration, respectively. As shown in FIG.7A, using only a single pitch-catch tuning sacrifices performance (e.g., SNR) from 50 - 125 m.

[0130] FIG.7B and FIG.7C show example simulation results when two RX grating couplers are used for tuning, showing how the two RX grating couplers can be utilized to improve the performance of the scanning lidar system. FIG.7B shows SNRs over ranges to the target object. For example, line 751, line 752, line 753, line 754, line 755 show simulation results when using configurations of (1) no scanning, (2) a nominally designed beam size and pitch- catch size (e.g., 3.1 shift normalized to the beam radius), (3) tuning near distance performance, (4) tuning far distance performance, and (5) combining the near distance tuned configuration and the far distance tuned configuration, respectively. As shown in FIG.7B. the pitch catch tuning of placing a second grating coupler at 0 relative shift between the Tx and Rx modes (i.e., no purposeful shift) can significantly increase the performance at these shorter ranges (50 - 125 m).

[0131] FIG.7C shows PoDs over ranges to the target object. For example, line 771, line 772 show simulation results when using configurations of (1) a nominally designed beam size and pitch-catch size (e.g., 1.7 shift normalized to the beam radius, reflectivity equal to 0.01), (2) combining a near distance tuned configuration and a far distance tuned configuration (e.g., 3.7 37 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) shift normalized to the beam radius, reflectivity equal to 0.01), respectively. As shown in FIG. 7C, if the pitch-catch separation between the two grating couplers can be made to be only 2 w0, the link budget (e.g., a calculation of all of the power gains and losses that a communication signal experiences from a transmitter through a communication medium to a receiver) nearly can match with the link budget for no scanning, thereby creating significant gains in PoD for low reflectivity targets (see FIG.7C).

[0132] In some implementations, a coherent LIDAR sensor system can include a multiport 90 degree hybrid for pitch-catch extension. For example, the multiport 90 degree hybrid may be a 4 port (4x4) multi-mode interference structure (MMI) IQ for multiplexed coherent detection. The use of a 4 MMI can enable the collection of a second Rx channel without any additional detectors or ADCs compared to the conventional IQ detection. One drawback of using a multiport 90 degree hybrid is an ambiguity as to which input port an Rx signal has been collected on. To address the ambiguity, a method of disambiguation like quasi-CW (QCW) and or principal component (PC) analysis can be used to identify short-range and long-range returns. For example, a CW LIDAR sensor system can spread a total transmit (TX) energy per shot over a longer period (e.g., 13.3 µs) than a period (e.g., 0.83 µs) in a QCW LIDAR sensor system.

[0133] In some implementations, a coherent lidar configuration in which received light from two waveguides or grating coupled apertures are combined optically in a multiport input port 90 degree hybrid to provide an extended pitch-catch coverage (e.g., extended coverage of Tx / Rx beam lag due to scanning) to improve the performance of a coherent lidar over range. This pitch-catch extension may enable larger beams and better performance for all target reflectivities over range. In some implementations, the received light can be combined from two closely spaced Rx channels simultaneously in a 90 degree optical hybrid with a local oscillator (LO) signal in a fashion where each Rx signal combines with the LO signal to generate output signals whose phases are equivalent to 0, 90, 180, and 270 degrees, respectively. For example, the two Rx channels can be separated from each other by less than 4w0 or 2 beam widths. A 90 degree hybrid based on an MMI coupler may have 4 input ports, among which two ports are connected to a pair of Rx receivers (e.g., waveguides, grating couplers) and one port is connected 38 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) to the LO signal. By optically and / or directly combining the hybrid in an integrated circuit, no additional losses or shot noise sources can be incurred, providing up to a 3 dB boost in SNR (see the simulation result shown in FIG.7B around 100m or 350m). If the spacing of the two Rx receivers is positioned appropriately for different pitch-catch spacings, a much greater than 3dB improvement can be achieved across different range bands.

[0134] In some implementations, a 90 degree hybrid may have 4 input ports that come in pairs, so there are multiple combinations of inputs that yield a 90 degree hybrid operation. For example, if a pair of signals received from two grating couplers are connected to different ports of the same 90 degree hybrid, one of the pair of signals (e.g., signals received from both grating couplers) can be detected without additional penalty of LO shot noise as if the other of the pair of signals would be non-existent and the configuration is identical to what one would use for a single Rx channel. Similarly, the other of the pair of signals can be detected without additional penalty of LO shot noise as if the one of the pair of signals would be non-existent and the configuration is identical to what one would use for a single Rx channel. This configuration using the 90 degree hybrid can perform better than a configuration of mixing and detecting two received signals (e.g., mixing first and second received signals with first and second LO signals, respectively) with two separate coherent receivers (and either summing currents or digitizing and processing the currents), because there is no additional shot noise from the second LO signal that does not contribute to thefirst received signal. If a relative phase between the received signals is known, then separately coherent mixing, detecting, and summing currents can be performed without penalty. However, due to speckles from the target object, the relative phase from the two physically separate receivers may be random, and phase correction may be impractical for low SNR targets, for example. Therefore, separately detecting and processing the signals using two separate coherent receivers may lead to at most a boost in detectability due to multiple speckle realizations but at the cost of performance. In contrast, the configuration using the 90 degree hybrid according to some implementations can perform phase correction for low SNR targets better than the configuration of separately detecting and processing the signals. The 90 degree hybrid configuration is subject to the same speckle effect because the two Rx receivers are 39 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) spatially distinct; however, because the signals are combined optically before coherent detection, the 90 degree hybrid configuration do not suffer an additional shot noise penalty by summing the electrical currents, thereby achieving larger SNR and thus better phase correction.

[0135] In some implementations, a coherent LIDAR system for pitch-catch extension may include a first amplifier, a second amplifier, a first pair of detectors (e.g., photodetectors), a second pair of detectors, an optical mixer, a transmitter, a first receiver, and a second receiver. The transmitter may be a waveguide or a grating coupler. Each of the first receiver and the second receiver may be a waveguide or a grating coupler. Each of the first amplifier and the second amplifier may be a transimpedance amplifier (TIA). The first pair of detectors may be a pair of balanced detectors (e.g., balanced photodetectors). The second pair of detectors may be a pair of balanced detectors. The optical mixer may include four input ports (In1, In2, In3, In4) and four output ports (Out1, Out2, Out3, Out4). In some implementations, the optical mixer may be a 90° optical hybrid including 4 input ports and 4 output ports. In some implementations, the optical mixer may be a 4x4 MMI.

[0136] In some implementations, the transmitter may transmit a transmit (Tx) optical signal to illuminate an object (or an area of interest). In response to transmitting the Tx optical signal, the optical mixer may receive a pair of returned / received (Rx1, Rx2) optical signals at two of the four input ports (e.g., In2, In4) through the first receiver and the second receiver, and receive an optical LO signal at one of the four input ports (e.g., In1). In some implementations, the first receiver may be spatially separated (e.g., spaced) from the transmitter by a separation, which may a focal plane drift corresponding to an angle between the Tx optical signal after being transmitted by the transmitter and one of the pair of returned signals Rx1. Similarly, the second receiver may be spatially separated (e.g., spaced) from the transmitter by a separation, which may a focal plane drift corresponding to an angle between the Tx optical signal after being transmitted and the other of the pair of returned signals Rx2. In some implementations, the coherent LIDAR system may include a displacer (e.g., birefringent displacer) that can displace the pair of returned signals Rx1, Rx2 by a predetermined amount. The first receiver and the 40 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) second receiver may be located such that the two receivers can receive the pair of returned signals displaced by the displacer.

[0137] In some implementations, the optical mixer may mix the pair of returned optical signals with four quadratural states associated with the optical LO signal in a complex-field space to generate four optical signals at the four output ports. The optical mixer may then deliver (e.g., output, provide, send) the four optical signals to the two pairs of detectors. For example, the optical mixer may deliver two optical signals from two of the four outputs (e.g., Out 2 and Out3) to the first pair of detectors, and deliver the other two optical signals from the other two of the four outputs (e.g., Out4, Out1) to the second pair of detectors. In response to receiving the optical signals, the two pairs of detectors may generate an electrical signal, and transmit (e.g., output, provide, send, deliver) the electrical signal to ADCs via the first amplifier and the second amplifier. In this manner, the pair of returned optical signals can be received (e.g., collected) in different Rx channels (e.g., Rx1, Rx2) by the first receiver and the second receiver, which are placed in close proximity to each other, and can be mixed and / or detected simultaneously via the optical mixer and the two pairs of detectors for both channels. In some implementations, the first pair of detectors may transmit an in-phase (I) component of the electrical signal to the first amplifier, and the second pair of detectors may transmit a quadrature (Q) component of the electrical signal to the second amplifier.

[0138] In some implementations, the optical mixer (e.g., a 4x4 MMI, 8 ports 90 degree optical hybrid) may use a scattering matrix M1 to generate output optical signals as follows. 41 4871-5753-4389.1Atty. Dkt. No. 120261-0517 (A-052220-WO) … (Equation 3)the output ports Out2 and Out3 to the first pair of detectors, and deliver the other two optical signals from the output ports Out4, Out1 to the second pair of detectors, an in-phase (Is) component of an electrical signal s output from the two pairs of detectors and a quadrature (Qs) component of the electrical signal s output from the two pairs of detectors may be given as follows.

[0140] Is = Out1-Out3 … (Equation 4).

[0141] Qs= Out2-Out4 … (Equation 5).

[0142] Noting the coefficients of this scattering matrix M1, either input port 1 (In1) or input port 3 (In3) can be used as the LO optical signal, and then input port 2 (In2) and input port 4 (In4) can be used as returned optical signals, resulting in the Iscomponent and Qscomponent of the electrical signal s as follows.

[0143] Is = Out1-Out3=2(In2+In4) … (Equation 6).

[0144] Qs= Out2-Out4=2(In2-In4)i … (Equation 7).

[0145] That is, there is a relative complex conjugate (e.g., ± 2|In2-In4|i) between the signals from In2 and In4 so that any Doppler shifts can appear as opposite signs (except at DC where the circulator is). As shown in FIG. 7C, the result of running a full time domain Monte Carlo simulation with shot noise and the link budgets shows that a significant POD increase is 42 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) achieved for a 1% reflectivity target, when the difference in the sign of the Doppler shift is ignored and the data is processed as normal. However, for improved phase correction, it may be needed to disambiguate between different signs of the Doppler shift. In some implementations, this Doppler ambiguity can be resolved based on the range by determining from which Rx channel the range would likely have come. This disambiguation method can well perform for long ranges but in the nearfield where both grating couplers can have significant collection efficiency this method may not perform well. Because the relative strength of the signal in the two receivers is a function of range, at ranges greater than 60 m the link budgets for the Rx channel with large displacement and Rx channel with small displacement are very different. For example, see the difference between curve 753 and curve 754 in Fig.7B at like 300 m or alternatively at like 120 m. At these ranges, it is likely that the signal only came from one of the two Rx’s (and which one is determined by the range). However, at 250 m or at less than 50 m the link budget efficiency for the two curves is quite similar so it may be close or equally likely that the signal was captured by both Rx’s to make equal contributions, thus making it hard to decide whether it was a positive Doppler signal detected simultaneously in each Rx or a negative Doppler signal detected simultaneously in each Rx.

[0146] In some implementations, the correlation between the range and the Doppler phase can be used to resolve the sign of the Doppler shift. In some implementations, a digital down converter (DDC; e.g., digital sampling system 450 in FIG.4B) can be used to resolve the sign of the Doppler because all the signal information is known to be on one side of the frequency spectrum, and therefore the + / - frequencies can resolve the signals from the two gratings separately.

[0147] In some implementations, other phases than 90 degrees can be designed into a 4x4 hybrid, e.g., either 180 degrees or 0 degrees. For example, an optical mixer (e.g., a 4x4 hybrid) may use a scattering matrix M2 to generate output optical signals that have a relative phase difference of 180 degrees, as follows. 43 4871-5753-4389.1Atty. Dkt. No. 120261-0517 (A-052220-WO) … (Equation 8)

[0148] , signals I1= Out1- Out2 and I2 = Out3-Out4 are used, the output signals I1 and I2 can be given as follows:

[0149] I1 = Out1-Out2=2(In2+In3) … (Equation 9).

[0150] I2= Out3-Out4=-2(In2-In3) … (Equation 10).

[0151] As shown in Equation 9 and Equation 10, the signals in input port 2 and input port 3 (e.g., In2 and In3) add constructively, but the signal in input port 4 (e.g., In4) adds destructively. Then, at the next level of summing signals I1+I2 (=4*In3) results in the signal in input port 3 (e.g., In3) adding constructively, but the signal in input port 2 (e.g., In2) adding destructively. Therefore, it is impossible to get the two signals (e.g., In2 and In3) to both add constructively in a coherent fashion.

[0152] In another aspect, in a LIDAR sensor system, pitch-catch separation (e.g., separation by an angle shift θpc or a focal plane drift Δxpc) to separate the outgoing Tx illumination and the incoming Rx signal may affect the performance of the LIDAR sensor system (e.g., estimation of velocity, etc.). With the conventional physical pitch-catch approach, the minimum amount of pitch-catch separation is limited by the ability to place individual grating antennas close to each other. There is a need for a mechanism to perform pitch-catch separation regardless of the ability to place individual grating antennas close to each other. 44 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO)

[0153] To solve this problem, in some implementations, a LIDAR sensor system can include a multi-mode Tx / Rx based circulator. The LIDAR sensor system can use interference of different TEM modes (transverse modes) to implement a circulation method of transmitting in the (TEM00+TEM10) mode where TEM00 is a fundamental Gaussian beam and TEM10 is a beam shaped as having a twobumps along x and one bump along y in electromagnetic field, and receiving in the (TEM00-TEM10) mode. This circulation method can be easily implemented by use of integrated photonics and / or a couple mode fiber.

[0154] In some implementations, a coherent LIDAR system can use one or more multi- mode waveguide devices (e.g., multi-mode waveguide or multi-mode optical fiber) to implement a circulation function. The circulation function can use coherent interference of two low order TEM00 Gaussian modes and an angle lag / shift that results from continuous scanning to implement efficient lidar circulation to separate the outgoing Tx illumination and the incoming Rx signal. If a laser mode (e.g., beam) is formed at the focal plane of a collimating lens that is equal power (TEM00 + TEM10) mode, the beam formed after the lens (~3m in Fig 11B) begins as a roughly elliptical mode with two weak but noticeable peaks in the x-direction, but in the far- field (~300m in Fig 11A) the beam becomes mostly compact nearly circular mode that is shifted relative to the central ray of the beam. If this shift is in same direction as the pitch-catch shift the compact nearly circular mode can couple more efficiently to the (TEM00 - TEM10) mode which has a far-field pattern reflected about the y-axis relative to the (TEM00 + TEM10) mode, and will interfere constructively in the opposite incoming port of the multi-mode circulator implementation, effecting an efficient circulation action for the far-field. The (TEM00-TEM10) beam may be emitted from the same multi-mode emitter (e.g., a port of the circulator, or a multi- mode waveguide or a multi-mode optical fiber coupled to an emitter) as that from which the (TEM00+TEM10) beam has been emitted.

[0155] In some implementations, a LIDAR system may include a laser source, an optical circulator, an optical mixer, and / or a scanner. The optical circulator may include a plurality of ports (e.g., three or more ports) and one or more multi-mode waveguides or multi-mode optical fibers. In some implementations, each port may be an emitter coupled to a multi-mode 45 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) waveguide or a multi-mode optical fiber. In some implementations, the laser source may generate a Tx beam in (TEM00+TEM10) mode. The optical circulator may receive the Tx beam at a first port and transmit the Tx beam at a third port to the scanner. The Tx beam may be transmitted through the scanner to illuminate an object (or an area of interest). The scanner may receive a return optical signal reflected by the object as a receive (Rx) beam. The optical circulator may receive the Rx beam at the third port and transmit the Rx beam at a second port to the optical mixer.

[0156] All optical circulators may be fundamentally considered as 4 port devices. A multi-mode circulator device in some implementations may have two single mode waveguide ports that represent a first input port (e.g., port 1) from a laser and a second single mode output port (e.g., port 2) to an optical mixer. The device may have third and fourth ports (e.g., port 3, port 4) that are coupled into a two mode waveguide and / or directly into free-space, where the third port may be defined as the Tx port (TEM00+TEM10) mode and the fourth as the Rx port (TEM00-TEM10) mode. The circulation action of the device may be designed or performed such that more than 99% of the power input to port 1 can be directed to port 3 the (TEM00+TEM10) mode and 99% of the light entering port 4 the (TEM00-TEM10) mode can be directed to port 2 (e.g., a single mode waveguide attached to the optical mixer). The local oscillator for the optical mixer may be sourced from the laser through a completely separate path.

[0157] Various implementations in the present disclosure have one or more of the following advantages and benefits.

[0158] First, implementations in the present disclosure can provide useful techniques for extending a pitch-catch coverage by combining received light from two waveguides or grating coupled apertures optically in a multiport input port 90 degree hybrid to improve the performance of a coherent lidar system over range. This may enable larger beams and better performance for all target reflectivities over range. By combining optically in an integrated circuit directly in the hybrid, no additional losses or shot noise sources are incurred, achieving up to a 3 dB boost in SNR, and if the spacing of the two Rx receivers is positioned appropriately for 46 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) different pitch-catch spacings, a much greater than 3dB improvement can be achieved across different range bands.

[0159] Second, implementations in the present disclosure can provide useful techniques for transmitting a beam in the (TEM00+TEM10) mode and receiving a beam in the (TEM00- TEM10) mode. With this circulation method, pitch-catch separation can be performed regardless of the ability to place individual grating antennas close to each other.

[0160] FIG.8 is a block diagram illustrating an example of a coherent LIDAR system 800 for pitch-catch extension, according to some implementations. FIG.8 shows that a single local oscillator (LO) signal (e.g., LO signal 842) and a Tx signal (e.g., Tx signal 844) are input to a coherent pixel where two Rx grating couplers (e.g., receivers 851, 852) placed in close proximity collect light in respective channels (e.g., Rx1, Rx2), and lights can be detected via the LO and an optical mixer 830 (e.g., single 4x4 MMI) used as 90 degree hybrid for both channels (e.g., Rx1, Rx2) simultaneously.

[0161] Referring to FIG.8, the coherent LIDAR system 800 for pitch-catch extension may include a first amplifier 810, a second amplifier 812, a first pair of detectors 822, 824 (e.g., photodetectors), a second pair of detectors 826, 828, an optical mixer 830, a transmitter 861, a first receiver 851, and a second receiver 852. The transmitter 861 may be a waveguide or a grating coupler. Each of the first receiver 851 and the second receiver 852 may be a waveguide or a grating coupler. Each of the first amplifier 810 and the second amplifier 820 may be a transimpedance amplifier (TIA). Each of the first pair of detectors and the second pair of detectors may be a balanced detector (e.g., balanced photodetectors). The optical mixer 830 may include four input ports (In1, In2, In3, In4) and four output ports (Out1, Out2, Out3, Out4). In some implementations, the optical mixer 830 may be a 90° optical hybrid including 4 input ports and 4 output ports. In some implementations, the optical mixer 830 may be a 4x4 MMI.

[0162] Referring to FIG.8, the transmitter 861 may transmit a Tx optical signal 844 to illuminate an object (not shown). In response to transmitting the Tx optical signal 844, the optical mixer 830 may receive a pair of returned / received (Rx1, Rx2) optical signals at two of 47 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) the four input ports (e.g., In2, In4) through the first receiver 851 and the second receiver 852, and receive an optical LO signal 842 at one of the four input ports (e.g., In1). The first receiver 851 may be spatially separated (e.g., spaced) from the transmitter 861 by a separation, which may a focal plane drift corresponding to an angle between the Tx optical signal after being transmitted by the transmitter 861 and one of the pair of returned signals Rx1. Similarly, the second receiver may be spatially separated (e.g., spaced) from the transmitter by a separation, which may a focal plane drift corresponding to the angle between the Tx optical signal after being transmitted by the transmitter 861 and the other of the pair of returned signals Rx2. The coherent LIDAR system 800 may include a displacer 870 (e.g., birefringent displacer) that can displace the pair of returned signals Rx1, Rx2 by a predetermined amount 807. The first receiver 851 and the second receiver 852 may be located such that the two receivers can receive the pair of returned signals displaced by the displacer.

[0163] Referring to FIG.8, the optical mixer may 830 mix the pair of returned optical signals with four quadratural states associated with the optical LO signal 842 in a complex-field space to generate four optical signals at the four output ports (e.g., Out1, Out2, Out3, Out4). The optical mixer 830 may then deliver (e.g., output, provide, send) the four optical signals to the two pairs of detectors 822, 824, 826, 828. For example, the optical mixer 830 may deliver two optical signals from two of the four outputs (e.g., Out 2 and Out3) to the first pair of detectors 822, 824, and deliver the other two optical signals from the other two of the four outputs (e.g., Out4, Out1) to the second pair of detectors 826, 828. In response to receiving the optical signals, the two pairs of detectors may generate an electrical signal, and transmit (e.g., output, provide, send, deliver) the electrical signal to ADCs (not shown) via the first amplifier 810 and the second amplifier 812. In this manner, the pair of returned optical signals can be received (e.g., collected) in different Rx channels (e.g., Rx1, Rx2) by the first receiver 851 and the second receiver 852, which are placed in close proximity to each other, and can be mixed and / or detected simultaneously via the optical mixer 830 and the two pairs of detectors for both channels Rx1, Rx2. In some implementations, the first pair of detectors 822, 824 may transmit an in-phase (I) component of the electrical signal to the first amplifier 810, and the second pair of detectors 826, 48 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) 828 may transmit a quadrature (Q) component of the electrical signal to the second amplifier 812.

[0164] Referring to FIG.8, the optical mixer 830 (e.g., a 4x4 MMI, 8 ports 90 degree optical hybrid) may use a scattering matrix M1 (according to Equation 3) to generate output optical signals. If the optical mixer 830 may deliver two optical signals from the output ports Out2 and Out3 to the first pair of detectors, and deliver the other two optical signals from the output ports Out4, Out1 to the second pair of detectors, an in-phase (Is) component of an electrical signal s output from the two pairs of detectors and a quadrature (Qs) component of the electrical signal s output from the two pairs of detectors may be calculated using Equations 4-7.

[0165] The coherent lidar system 800 in which received light from two waveguides or grating coupled apertures (e.g., receivers 851, 852) are combined optically in a multiport input port 90 degree hybrid (e.g., optical mixer 830) to provide an extended pitch-catch coverage (e.g., extended coverage of Tx / Rx beam lag due to scanning) to improve the performance of a coherent lidar over range. This pitch-catch extension may enable larger beams and better performance for all target reflectivities over range. The received light can be combined from two closely spaced Rx channels simultaneously in the 90 degree optical hybrid 830 with the LO signal 842 in a fashion where each Rx signal combines with the LO signal to generate output signals whose phases are equivalent to 0, 90, 180, and 270 degrees, respectively. By optically and / or directly combining the hybrid 830 in an integrated circuit, no additional losses or shot noise sources can be incurred, providing up to a 3 dB boost in SNR. If the spacing of the two Rx receivers 851, 852 is positioned appropriately for different pitch-catch spacings, a much greater than 3dB improvement can be achieved across different range bands.

[0166] FIG.9A and FIG.9B show diagrams 900, 950 depicting example simulation results using a coherent LIDAR system for pitch-catch extension, according to some implementations. FIG.9A shows that using two couplers has higher POD than using one coupler. FIG.9B shows a coherent average range of the Rx spot (from top to bottom, 10 m, 20 m, 40 m, 80 m, 120 m, 160 m, 200 m, 250 m, 300 m, 400 m, 500 m) in the focal plane of a 49 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) collimating lens over many speckle realizations. In FIG.9B, the y-axis shows coherent average ranges, and the x-axis shows positions in the focal plane of the system. For each speckle realization, the phase can be compensated at a specific pixel. The spots for different ranges are stacked in the vertical direction. As shown in FIG.9B, the pitch-catch extension causes the center position of the spot to increase quadratically as a function of range (10 → 500 meters).

[0167] FIG.10 is a block diagram illustrating an example of a coherent LIDAR system 1000 using a multi-mode transmit (Tx) / receive (Rx)-based circulator 1020, according to some implementations. The LIDAR system 1000 may include a laser source 1010, an optical circulator 1020, an optical mixer 1040, and / or a scanner 1030. The optical circulator 1020 may include a plurality of ports (e.g., three or more ports 1021, 1022, 1023) and one or more multi- mode waveguides or multi-mode optical fibers (not shown). Each port may be an emitter (not shown) coupled to a multi-mode waveguide or a multi-mode optical fiber. The laser source 1010 may generate a Tx beam in (TEM00+TEM10) mode 1011. The optical circulator 1020 may receive the Tx beam 1011 at a first port 1021 and transmit the Tx beam1011 at a third port 1023 to the scanner 1030. Next, the Tx beam may be transmitted through the scanner 1030 to illuminate an object 1050 (or an area of interest). The scanner 1030 may receive a return optical signal reflected by the object as a receive (Rx) beam. The optical circulator 1020 may receive the Rx beam (TEM00-TEM10) mode 1012 (referred to as “(TEM00-TEM10) mode beam”) at the third port 1023 and transmit the Rx beam at a second port 1022 to the optical mixer 1040.

[0168] As shown in FIG.10, the LIDAR sensor system 1000 can include a multi-mode Tx / Rx based circulator 1020. The LIDAR sensor system 1000 can use interference of different TEM modes (transverse modes) to implement a circulation method of transmitting in the (TEM00+TEM10) mode 1011 where TEM00 is a fundamental Gaussian beam and TEM10 is a beam shaped as having a single bump along x and two bumps along y in electromagnetic field, and receiving in the (TEM00-TEM10) mode. This circulation method can be easily implemented by use of integrated photonics and / or a couple mode fiber. In some implementations, a coherent LIDAR system can use one or more multi-mode waveguide devices (not shown; e.g., multi-mode waveguide or multi-mode optical fiber) to implement a circulation function. The circulation 50 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) function can use coherent interference of two low order TEM00 Gaussian modes and an angle lag / shift that results from continuous scanning to implement efficient lidar circulation to separate the outgoing Tx illumination and the incoming Rx signal. If a laser mode (e.g., Tx beam 1011) is formed at the focal plane of a collimating lens that is equal power (TEM00 + TEM10) mode, the beam formed after the lens begins as an elliptical mode, but in the far-field the beam becomes a compact nearly circular mode that is shifted relative to the central ray of the beam. If this shift is in an appropriate direction for the angle lag, the compact nearly circular mode can couple more efficiently to the (TEM00 - TEM10) mode (e.g., the (TEM00-TEM10) mode beam 1012) which can interfere constructively in the opposite incoming port (e.g., the third port 1023), effecting an efficient circulation action for the far-field. The (TEM00-TEM10) mode beam 1012 may be emitted from the same multi-mode emitter (e.g., a multi-mode waveguide or a multi-mode optical fiber coupled to an emitter at the first port 1021) as that from which the (TEM00+TEM10) mode beam 1011 has been emitted.

[0169] In some embodiments, a light detection and ranging (LIDAR) sensor system for a vehicle may include a multi-mode circulator (e.g., multi-mode circulator 1020). The multi-mode circulator may include at least one of one or more multi-mode grating couplers, one or more multi-mode waveguides, one or more multi-mode optical fibers, or a plurality of ports (e.g., ports 1021, 1022, 1023). The multi-mode circulator may be configured to transmit a first beam in a combination of spatial modes (e.g., a beam in (TEM00+TEM10) mode generated by the laser source 1010 and transmitted at the third port 1023). The multi-mode circulator may be configured to receive, in response to transmitting the first beam, a second beam in an orthogonal combination of spatial modes. The first beam in the combination of spatial modes comprises a beam in (TEM00+TEM10) mode. The second beam in the orthogonal combination of spatial modes comprises a combination of a returned beam reflected from an object (e.g., Rx beam incoming from the third port 1023) and a beam in (TEM00-TEM10) mode (e.g., a beam in (TEM00-TEM10) mode generated by the laser source 1010).

[0170] FIG.11A to FIG.11C are diagrams 1100, 1120, 1150 depicting example simulation results using a coherent LIDAR system using a multi-mode Tx / Rx-based circulator, 51 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) according to some implementations. FIG.11A shows a simulation result of a multi-mode superposition spot at 300 m (e.g., far-field) where most of the power is contained in one side of the spot pattern. FIG.11B shows a simulation result of a multi-mode superposition spot at 3m from a collimating lens (e.g., near-field) where the intensity pattern is elliptical and two lobed.

[0171] FIG.11C shows a pitch-catch angle (e.g., angle shift θpc) over various shifts and sizes of the beam in the x-direction. The x-axis is range in meters and the y-axis is the pitch- catch displacement (shift) normalized to the initial mode field radius w0. For example, line 1151 shows a simulation result of the normalized effective Tx / Rx pitch-catch shift vs. range when using the single mode TEM00. Line 1152 shows a simulation result of the normalized effective Tx / Rx pitch-catch shift vs. range when using a multimode combination beam of TEM00+TEM10 for the Tx beam and TEM00-TEM10 for the Rx beam. Line 1153 shows a simulation result of the normalized size of the Tx beam vs range when using TEM00 (i.e. zeroth order Gaussian) for the Tx beam and an identical unshifted beam for the Rx. Line 1154 shows a simulation result of the normalized size of the Tx beam vs range when using a multimode combination beam of TEM00+TEM10 for the Tx beam and TEM00-TEM10 for the Rx beam. As the graph shows, the single mode TEM00 approach results in an effective Tx / Rx pitch-catch shift that does not shift with range (see line 1151) and an effective normalized beam size on target that expands following the standard Gaussian divergence (see line 1153). The multi-mode combination beam shows an effective pitch-catch shift that increases linearly with range that can partially compensate the quadratic pitch-catch shift that results from the lidar scanning mechanism (see line 1152). A slight drawback of the multimode beam is that the effective beam size and far-field beam divergence (see line 1154) are larger than for the single TEM00 mode beam (see line 1153), which slightly reduces the overall collection efficiency without scanning. Using a multi-mode circulator according to some embodiments, the pitch-catch angle can be twice what is shown in FIG.11C.

[0172] FIG.12 is a flowchart illustrating an example methodology for a coherent LIDAR system (e.g., LIDAR sensor system 300, LIDAR sensor system 400, LIDAR sensor system 600, LIDAR sensor system 800) for pitch-catch extension according to some implementations. The 52 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) LIDAR system may include a transmitter (e.g., transmitter 861), a pair of receivers or a pair of grating couplers (e.g., receivers 851, 852), and an optical mixer (e.g., optical mixer 830). In this example methodology, a process 1200 begins at step 1210 by transmitting, by the transmitter 861 including a first grating coupler, an optical signal (e.g., Tx optical signal 844).

[0173] At step 1220, in some implementations, the receiver including a pair of grating couplers (e.g., first and second receivers 851, 852) may receive a pair of returned optical signals in response to transmitting the optical signal. In some implementations, the LIDAR sensor system may include a displacer (e.g., birefringent displacer 870) configured to displace the pair of returned optical signals by a predetermined amount (e.g., displace amount 807). The pair of grating couplers (e.g., first and second receivers 851, 852) may be located such that the pair of grating couplers receive the pair of returned optical signal displaced by the displacer, respectively

[0174] At step 1230, in some implementations, the mixer may receive the pair of returned optical signals from the receiver and receive a local oscillator (LO) signal (e.g., LO optical signal 842) from a local oscillator. In some implementations, the mixer may include a plurality of input ports (e.g., In1, In2, In3, In4 in FIG.8). The mixer may receive the pair of returned optical signals and the LO signal at different ones of the plurality of input ports. For example, the optical mixer 830 may receive the pair of returned optical signals at In2 and In4, and receive the LO signal 842 at In1. In some implementations, the mixer may be a 90 degree optical hybrid having 4 input ports and 4 output ports (e.g., Out1, Out2, Out3, Out4 in FIG.8). In some implementations, the mixer may be a 4x4 multi-mode interference (MMI) structure.

[0175] At step 1240, in some implementations, the mixer may mix the pair of returned optical with the LO signal.

[0176] At step 1250, in some implementations, the mixer may output a plurality of mixed optical signals. Two of the plurality of mixed optical signals may have a relative phase difference of 90 degrees. In some implementations, the mixer may simultaneously (1) mix the one of the pair of returned optical with the LO signal and (2) mix the other of the pair of returned optical 53 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) with the LO signal. In some implementations, the mixer may include a plurality of output ports (e.g., Out1, Out2, Out3, Out4 in FIG.8). The mixer may be configured to output the plurality of mixed optical signals at different ones of the plurality of output ports. In some implementations, the LIDAR system may include an optical detector (e.g., detectors 822, 824, 826, 828) configured to detect the plurality of mixed optical signals to produce an in-phase (I) component and a quadrature (Q) component of an electrical signal.

[0177] In some implementations, the LIDAR system may include one or more processors configured to generate a digital signal (e.g., digital signals generated by digitizer 452 in FIG.4) based on the plurality of mixed optical signals (e.g., data input 449 in FIG.4). The one or more processors may be configured to determine a Doppler frequency shift of the pair of returned optical signals based, at least in part, on the digital signal. The one or more processors may be configured to operate the vehicle based on the Doppler frequency shift.

[0178] The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean "one and only one" unless specifically so stated, but rather "one or more.” Unless specifically stated otherwise, the term "some" refers to one or more. All structural and functional equivalents to the elements of the various aspects described throughout the previous description that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed as a means plus function unless the element is expressly recited using the phrase "means for." 54 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO)

[0179] It is understood that the specific order or hierarchy of blocks in the processes disclosed is an example of illustrative approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes may be rearranged while remaining within the scope of the previous description. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

[0180] The previous description of the disclosed implementations is provided to enable any person skilled in the art to make or use the disclosed subject matter. Various modifications to these implementations will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of the previous description. Thus, the previous description is not intended to be limited to the implementations shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0181] The various examples illustrated and described are provided merely as examples to illustrate various features of the claims. However, features shown and described with respect to any given example are not necessarily limited to the associated example and may be used or combined with other examples that are shown and described. Further, the claims are not intended to be limited by any one example.

[0182] The foregoing method descriptions and the process flow diagrams are provided merely as illustrative examples and are not intended to require or imply that the blocks of various examples must be performed in the order presented. As will be appreciated by one of skill in the art the order of blocks in the foregoing examples may be performed in any order. Words such as “thereafter,” “then,” “next,” etc. are not intended to limit the order of the blocks; these words are simply used to guide the reader through the description of the methods. Further, any reference to claim elements in the singular, for example, using the articles “a,” “an” or “the” is not to be construed as limiting the element to the singular. 55 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO)

[0183] The various illustrative logical blocks, modules, circuits, and algorithm blocks described in connection with the examples disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and blocks have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

[0184] The hardware used to implement the various illustrative logics, logical blocks, modules, and circuits described in connection with the examples disclosed herein may be implemented or performed with a general purpose processor, a DSP, an ASIC, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but, in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Alternatively, some blocks or methods may be performed by circuitry that is specific to a given function.

[0185] In some exemplary examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or code on a non-transitory computer- readable storage medium or non-transitory processor-readable storage medium. The blocks of a method or algorithm disclosed herein may be embodied in a processor-executable software module which may reside on a non-transitory computer-readable or processor-readable storage medium. Non-transitory computer-readable or processor-readable storage media may be any 56 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) storage media that may be accessed by a computer or a processor. By way of example but not limitation, such non-transitory computer-readable or processor-readable storage media may include RAM, ROM, EEPROM, FLASH memory, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that may be used to store desired program code in the form of instructions or data structures and that may be accessed by a computer. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of non-transitory computer-readable and processor- readable media. Additionally, the operations of a method or algorithm may reside as one or any combination or set of codes and / or instructions on a non-transitory processor-readable storage medium and / or computer-readable storage medium, which may be incorporated into a computer program product.

[0186] The preceding description of the disclosed examples is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these examples will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to some examples without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the examples shown herein but is to be accorded the widest scope consistent with the following claims and the principles and novel features disclosed herein. 57 4871-5753-4389.1

Claims

Atty. Dkt. No.120261-0517 (A-052220-WO) WHAT IS CLAIMED IS:

1. A light detection and ranging (LIDAR) sensor system for a vehicle, comprising: a transmitter comprising a first grating coupler, the transmitter configured to transmit an optical signal; a receiver comprising a pair of grating couplers configured to receive a pair of returned optical signals in response to transmitting the optical signal; and a mixer configured to receive the pair of returned optical signals from the receiver, receive a local oscillator (LO) signal from a local oscillator, mix the pair of returned optical signals with the LO signal, and output a plurality of mixed optical signals, wherein two of the plurality of mixed optical signals have a relative phase difference of 90 degrees.

2. The LIDAR system according to claim 1, wherein the mixer is configured to simultaneously (1) mix the one of the pair of returned optical with the LO signal and (2) mix the other of the pair of returned optical with the LO signal.

3. The LIDAR system according to claim 1, wherein the mixer comprises a plurality of input ports, and the mixer is configured to receive the pair of returned optical signals and the LO signal at different ones of the plurality of input ports.

4. The LIDAR system according to claim 1, wherein the mixer comprises a plurality of output ports, and the mixer is configured to output the plurality of mixed optical signals at different ones of the plurality of output ports.

5. The LIDAR system according to claim 1, further comprising an optical detector configured to: 58 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) detect the plurality of mixed optical signals to produce an in-phase (I) component and a quadrature (Q) component of an electrical signal.

6. The LIDAR system according to claim 1, further comprising: a displacer configured to displace the pair of returned optical signals by a predetermined amount, wherein the pair of grating couplers are located such that the pair of grating couplers receive the pair of returned optical signal displaced by the displacer, respectively.

7. The LIDAR system according to claim 1, wherein the mixer is a 90 degree optical hybrid having 4 input ports and 4 output ports.

8. The LIDAR system according to claim 1, wherein the mixer is a 4x4 multi-mode interference (MMI) structure.

9. The LIDAR system according to claim 1, further comprising one or more processors configured to: generate a digital signal based on the plurality of mixed optical signals; determine a Doppler frequency shift of the pair of returned optical signals based, at least in part, on the digital signal; and operate the vehicle based on the Doppler frequency shift.

10. An autonomous vehicle control system comprising: one or more processors; and one or more computer-readable storage mediums storing instructions which, when executed by the one or more processors, cause the one or more processors to: cause a transmitter comprising a first grating coupler, to transmit an optical signal; cause a receiver comprising a pair of grating couplers, to receive a pair of returned optical signals in response to transmitting the optical signal; 59 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) cause a mixer to receive the pair of returned optical signals from the receiver, receive a local oscillator (LO) signal from a local oscillator, mix the pair of returned optical signals with the LO signal, and output a plurality of mixed optical signals, wherein two of the plurality of mixed optical signals have a relative phase difference of 90 degrees; and control operation of a vehicle using the plurality of mixed optical signals.

11. The autonomous vehicle control system as recited in claim 10, wherein the one or more processors are configured to cause the mixer to: simultaneously (1) mix the one of the pair of returned optical with the LO signal and (2) mix the other of the pair of returned optical with the LO signal.

12. The autonomous vehicle control system according to claim 10, wherein the mixer comprises a plurality of input ports, and the one or more processors are configured to cause the mixer to receive the pair of returned optical signals and the LO signal at different ones of the plurality of input ports.

13. The autonomous vehicle control system according to claim 10, wherein the mixer comprises a plurality of output ports, and the one or more processors are configured to cause the mixer to output the plurality of mixed optical signals at different ones of the plurality of output ports.

14. An autonomous vehicle comprising: at least one of a steering system or a braking system; and a vehicle controller comprising one or more processors configured to: cause a transmitter comprising a first grating coupler, to transmit an optical signal; 60 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) cause a receiver comprising a pair of grating couplers, to receive a pair of returned optical signals in response to transmitting the optical signal; cause a mixer to receive the pair of returned optical signals from the receiver, receive a local oscillator (LO) signal from a local oscillator, mix the pair of returned optical signals with the LO signal, and output a plurality of mixed optical signals, wherein two of the plurality of mixed optical signals have a relative phase difference of 90 degrees; and control the at least one of the steering system or the braking system using the plurality of mixed optical signals.

15. The autonomous vehicle according to claim 14, wherein the one or more processors are configured to cause the mixer to: simultaneously (1) mix the one of the pair of returned optical with the LO signal and (2) mix the other of the pair of returned optical with the LO signal.

16. The autonomous vehicle according to claim 14, wherein the mixer comprises a plurality of input ports, and the one or more processors are configured to cause the mixer to receive the pair of returned optical signals and the LO signal at different ones of the plurality of input ports.

17. The autonomous vehicle according to claim 14, wherein the mixer comprises a plurality of output ports, and the one or more processors are configured to cause the mixer to output the plurality of mixed optical signals at different ones of the plurality of output ports.

18. A light detection and ranging (LIDAR) sensor system for a vehicle, comprising: a multi-mode circulator configured to: 61 4871-5753-4389.1Atty. Dkt. No.120261-0517 (A-052220-WO) transmit a first beam in a combination of spatial modes; and receive, in response to transmitting the first beam, a second beam in an orthogonal combination of spatial modes.

19. The LIDAR system according to claim 18, wherein the multi-mode circulator comprises at least one of one or more multi-mode grating couplers, one or more multi-mode waveguides, one or more multi-mode optical fibers, or a plurality of ports.

20. The LIDAR system according to claim 18, wherein the first beam in the combination of spatial modes comprises a beam in (TEM00+TEM10) mode, and the second beam in the orthogonal combination of spatial modes comprises a combination of a returned beam reflected from an object and a beam in (TEM00-TEM10) mode. 62 4871-5753-4389.1

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