Synchronized transmitter and receiver filtering for reducing straylight in lidar systems

Abstract

Systems and methods for reducing straylight using synchronized filtering are provided. The system comprises a light source emitting laser light having a first wavelength range and a transmitter. The transmitter is configured to provide transmission light based on the laser light having the first wavelength range. The system further comprises a receiver configured to receive return light comprising straylight and light signals formed based on the transmission light. The system further comprises a synchronized filter structure comprising one or more bandpass filters having substantially the same passband. The synchronized filter structure reduces the bandwidth of the laser light from the first wavelength range to a second wavelength range; filters out at least a portion of the straylight having wavelengths outside of the second wavelength range; and passes a substantial portion of the light signals formed based on the transmission light to the detector.

Description

SYNCHRONIZED TRANSMITTER AND RECEIVER FILTERING FOR REDUCING STRAYLIGHT IN LIDAR SYSTEMSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 541,274, filed September 28, 2023, entitled “SYNCHRONIZED TRANSMITTER AND RECEIVER FILTERING FOR REDUCING STRAYLIGHT IN LIDAR SYSTEMS,” the content of which is hereby incorporated by reference in its entirety for all purposes.FIELD OF THE TECHNOLOGY

[0002] This disclosure relates generally to light transmitting and detection and, more particularly, to a light ranging and detection (LiDAR) system for reducing straylight using synchronized filtering.BACKGROUND

[0003] Light detection and ranging (LiDAR) systems use light pulses to create an image or point cloud of the external environment. A LiDAR system may be a scanning or non-scanning system. Some typical scanning LiDAR systems include a light source, a light transmitter, a light steering system, and a light detector. The light source generates a light beam that is directed by the light steering system in particular directions when being transmitted from the LiDAR system. When a transmitted light beam is scattered or reflected by an object, a portion of the scattered or reflected light returns to the LiDAR system to form a return light pulse. The light detector detects the return light pulse. Using the difference between the time that the return light pulse is detected and the time that a corresponding light pulse in the light beam is transmitted, the LiDAR system can determine the distance to the object based on the speed of light. This technique of determining the distance is referred to as the time-of-flight (ToF) technique. The light steering system can direct light beams along different paths to allow the LiDAR system to scan the surrounding environment and produce images or point clouds. A typical non-scanning LiDAR system illuminates an entire field-of-view (FOV) rather than scanning through the FOV. An example of the non-scanning LiDAR system is a flash LiDAR, which can also use the ToFtechnique to measure the distance to an object. LiDAR systems can also use techniques other than time-of-flight and scanning to measure the surrounding environment.SUMMARY

[0004] In general, a LiDAR system has a transmitter (TX) and a receiver (RX). The transmitter transmits laser light to form transmission light. The receiver receives the return light from the field-of-view (FOV). At least a part of the return light is formed by reflected or scattered laser light from one or more target objects in the FOV. The return light may also include stray light, which can be noise and / or interference light. A LiDAR system typically works at a specified center wavelength with a bandwidth, such as 905 nm (center wavelength) + / - 5 nm (bandwidth) for semiconductor lasers. In existing LiDAR systems, a bandpass filter (BPF) is widely used in the receiver to filter out straylight from the return light received by the LiDAR system. The straylight may have wavelengths that are the same as, or different than, the transmission light wavelength.

[0005] A bandpass filter, however, is usually configured to have a wide passband to let all signal laser power to go through. With this type of wide passband BPF, the straylight with the same wavelength, or the same wavelength range, as the transmission light cannot be filtered out. One way to reduce such straylight is to narrow down the BPF’s passband (e.g., to 2 nm or even less) and only allow return light having the wavelength that is the same as the center wavelength of the transmission light to pass through. An issue of this method for reducing straylight is that a large amount of signal power of the return light may also be lost because the signal bandwidth is narrower than the passband of the BPF. To compensate the return light signal power loss caused by the BPF, the signal power of transmission light must be increased. However, increasing the signal power of the transmission laser light is limited by the eye safety requirement of the LiDAR system. Therefore, only increasing laser power to increase the signal power of the transmission light, and thus in turn increasing the return light signal power passing through the narrow passband of the BPF in the receiver, may not be possible or practical.

[0006] The present disclosure provides systems and methods for reducing straylight using synchronized filtering. In one embodiment, a light ranging and detection (LiDAR) system for reducing straylight using synchronized filtering is provided. The system comprises a light sourceemitting laser light having a first wavelength range and a transmitter comprising one or more transmitter optics disposed in a transmission light path. The transmitter is configured to provide transmission light based on the laser light having the first wavelength range. The system further comprises a receiver comprising a detector and one or more receiver optics disposed in a receiving light path. The receiver is configured to receive return light comprising straylight and light signals formed based on the transmission light beams. The system further comprises a synchronized filter structure comprising one or more bandpass filters having substantially the same passband. The synchronized filter structure is coupled to both the transmitter and the receiver. The synchronized filter structure is configured to perform: reducing the bandwidth of the laser light from a first wavelength range to a second wavelength range such that the transmission light beams have the second wavelength range; filtering out at least a portion of the straylight having wavelengths outside of the second wavelength range; passing a substantial portion of the light signals formed based on the transmission light beams to the detector.

[0007] With the synchronized filter structure, the straylight in the return light can be filtered out or reduced significantly (e.g., 60% lower) without losing much of the signal power. In addition, the increasing of the laser power to compensate the signal power loss occurs within the LiDAR system and thus the signal power of the transmission light can still satisfy the laser eye safety requirements because of the synchronized filter structure.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present application can be best understood by reference to the embodiments described below taken in conjunction with the accompanying drawing figures, in which like parts may be referred to by like numerals.

[0009] FIG. 1 illustrates one or more example LiDAR systems disposed or included in a motor vehicle.

[0010] FIG. 2 is a block diagram illustrating interactions between an example LiDAR system and multiple other systems including a vehicle perception and planning system.

[0011] FIG. 3 is a block diagram illustrating an example LiDAR system.

[0012] FIG. 4A is a block diagram illustrating an example fiber-based laser source.

[0013] FIG. 4B is a block diagram illustrating an example semiconductor-based laser source.

[0014] FIGs. 5A-5C illustrate an example LiDAR system using pulse signals to measure distances to objects disposed in a field-of-view (FOV).

[0015] FIG. 6 is a block diagram illustrating an example apparatus used to implement systems, apparatus, and methods in various embodiments.

[0016] FIG. 7 is a block diagram illustrating a prior art LiDAR device with a bandpass filter in the receiving light path.

[0017] FIGs. 8A-8B are examples of a LiDAR system for reducing straylight using synchronized filtering, in accordance with various embodiments.

[0018] FIGs. 9A-9D are examples of a transmitter of a LiDAR system for reducing straylight using synchronized filtering, in accordance with various embodiments.

[0019] FIGs. 10A-10D are examples of a receiver of a LiDAR system for reducing straylight using synchronized filtering, in accordance with various embodiments.

[0020] FIGs. 11A-11C are examples of a LiDAR system for reducing straylight using a single bandpass filter for synchronized filtering, in accordance with various embodiments.

[0021] FIG. 12 is a flowchart of an example method of reducing straylight using a synchronized filtering structure, in accordance with various embodiments.DETAILED DESCRIPTION

[0022] To provide a more thorough understanding of various embodiments of the present invention, the following description sets forth numerous specific details, such as specific configurations, parameters, examples, and the like. It should be recognized, however, that such description is not intended as a limitation on the scope of the present invention but is intended to provide a better description of the exemplary embodiments.

[0023] Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise:

[0024] The phrase “in one embodiment” as used herein does not necessarily refer to the same embodiment, though it may. Thus, as described below, various embodiments of the disclosure may be readily combined, without departing from the scope or spirit of the invention.

[0025] As used herein, the term “or” is an inclusive “or” operator and is equivalent to the term “and / or,” unless the context clearly dictates otherwise.

[0026] The term “based on” is not exclusive and allows for being based on additional factors not described unless the context clearly dictates otherwise.

[0027] As used herein, and unless the context dictates otherwise, the term “coupled to” is intended to include both direct coupling (in which two elements that are coupled to each other contact each other) and indirect coupling (in which at least one additional element is located between the two elements). Therefore, the terms “coupled to” and “coupled with” are used synonymously. Within the context of a networked environment where two or more components or devices are able to exchange data, the terms “coupled to” and “coupled with” are also used to mean “communicatively coupled with”, possibly via one or more intermediary devices. The components or devices can be optical, mechanical, and / or electrical devices.

[0028] Although the following description uses terms “first,” “second,” etc. to describe various elements, these elements should not be limited by the terms. These terms are only used to distinguish one element from another. For example, a first bandpass filter could be termed a second bandpass filter and, similarly, a second bandpass filter could be termed a first bandpass filter, without departing from the scope of the various described examples. The first bandpass filter and the second bandpass filter can both be sensors and, in some cases, can be separate and different bandpass filters.

[0029] In addition, throughout the specification, the meaning of “a”, “an”, and “the” includes plural references, and the meaning of “in” includes “in” and “on”.

[0030] Although some of the various embodiments presented herein constitute a single combination of inventive elements, it should be appreciated that the inventive subject matter is considered to include all possible combinations of the disclosed elements. As such, if one embodiment comprises elements A, B, and C, and another embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly discussed herein. Further, the transitional term “comprising” means to have as parts or members, or to be those parts or members. As used herein, the transitional term “comprising” is inclusive or open-ended and does not exclude additional, unrecited elements or method steps.

[0031] As used in the description herein and throughout the claims that follow, when a system, engine, server, device, module, or other computing element is described as being configured to perform or execute functions on data in a memory, the meaning of “configured to” or “programmed to” is defined as one or more processors or cores of the computing element being programmed by a set of software instructions stored in the memory of the computing element to execute the set of functions on target data or data objects stored in the memory.

[0032] It should be noted that any language directed to a computer should be read to include any suitable combination of computing devices or network platforms, including servers, interfaces, systems, databases, agents, peers, engines, controllers, modules, or other types of computing devices operating individually or collectively. One should appreciate the computing devices comprise a processor configured to execute software instructions stored on a tangible, non- transitory computer readable storage medium (e.g., hard drive, FPGA, PLA, solid state drive, RAM, flash, ROM, or any other volatile or non-volatile storage devices). The software instructions configure or program the computing device to provide the roles, responsibilities, or other functionality as discussed below with respect to the disclosed apparatus. Further, the disclosed technologies can be embodied as a computer program product that includes a non- transitory computer readable medium storing the software instructions that causes a processor to execute the disclosed steps associated with implementations of computer-based algorithms, processes, methods, or other instructions. In some embodiments, the various servers, systems, databases, or interfaces exchange data using standardized protocols or algorithms, possibly based on HTTP, HTTPS, AES, public-private key exchanges, web service APIs, known financial transaction protocols, or other electronic information exchanging methods. Data exchanges among devices can be conducted over a packet-switched network, the Internet, LAN, WAN, VPN, or other type of packet switched network; a circuit switched network; cell switched network; or other type of network.

[0033] In general, a LiDAR system has a transmitter (TX) and a receiver (RX). The transmitter transmits laser light to form transmission light. The receiver receives the return light from one or more target objects in the field-of-view. At least a part of the return light is formed by reflected or scattered laser light from the target objects. The return light may also include straylight, which can be noise and / or interference light. A LiDAR system typically works at a specified center wavelength with a bandwidth, such as 905 nm (center wavelength) + / - 5 nm (bandwidth)for semiconductor lasers. In existing LiDAR systems, a bandpass filter (BPF) is widely used in the receiver to filter out straylight from the return light received by the LiDAR system. The straylight may have wavelengths that are the same as, or different than, the transmission light wavelength.

[0034] A bandpass filter, however, is usually configured to have a wide passband to let all signal laser power to go through. With this type of BPF, the straylight with the same wavelength, or the same wavelength range, as the transmission light cannot be filtered out. One way to reduce such straylight is to narrow down the BPF’s passband (e.g., to 2 nm or even less) and only allow return light having the wavelength that is the same as the center wavelength of the transmission light to pass through. An issue of this method for reducing straylight is that a large amount of signal power of the return light may be lost because the signal bandwidth is narrower than the passband of the BPF. To compensate the return light signal power loss caused by the BPF, the signal power of transmission light must be increased. However, increasing the signal power of the transmission laser light is limited by the eye safety requirement of the LiDAR system. Therefore, only increasing laser power to increase the signal power of the transmission laser light, and thus in turn increasing the return light signal power passing through the narrow passband of the BPF in the receiver, may not be possible or practical.

[0035] The present disclosure provides systems and methods for reducing straylight using synchronized filtering. In one embodiment, a light ranging and detection (LiDAR) system for reducing straylight using synchronized filtering is provided. The system comprises a light source emitting laser light having a first wavelength range and a transmitter comprising one or more transmitter optics disposed in a transmission light path. The transmitter is configured to provide transmission light based on the laser light having the first wavelength range. The system further comprises a receiver comprising a detector and one or more receiver optics disposed in a receiving light path. The receiver is configured to receive return light comprising straylight and light signals formed based on the transmission light beams. The system further comprises a synchronized filter structure comprising one or more bandpass filters having substantially the same passband. The synchronized filter structure is coupled to both the transmitter and the receiver. The synchronized filter structure is configured to perform: reducing the bandwidth of the laser light from a first wavelength range to a second wavelength range such that the transmission light beams have the second wavelength range; filtering out at least a portion of thestraylight having wavelengths outside of the second wavelength range; passing a substantial portion of the light signals formed based on the transmission light beams to the detector.

[0036] With the synchronized fdter structure, the straylight in the return light can be fdtered out or reduced significantly (e.g., 60% lower) without losing much of signal power. In addition, the increasing of the laser power to compensate the signal power loss occurs within the LiDAR system and thus the signal power of the transmission light still satisfies the laser eye safety requirements because of the synchronized filter structure.

[0037] FIG. 1 illustrates one or more example LiDAR systems 110 and 120A-120I disposed or included in a motor vehicle 100. Vehicle 100 can be a car, a sport utility vehicle (SUV), a truck, a train, a wagon, a bicycle, a motorcycle, a tricycle, a bus, a mobility scooter, a tram, a ship, a boat, an underwater vehicle, an airplane, a helicopter, an unmanned aviation vehicle (UAV), a spacecraft, etc. Motor vehicle 100 can be a vehicle having any automated level. For example, motor vehicle 100 can be a partially automated vehicle, a highly automated vehicle, a fully automated vehicle, or a driverless vehicle. A partially automated vehicle can perform some driving functions without a human driver’s intervention. For example, a partially automated vehicle can perform blind-spot monitoring, lane keeping and / or lane changing operations, automated emergency braking, smart cruising and / or traffic following, or the like. Certain operations of a partially automated vehicle may be limited to specific applications or driving scenarios (e g., limited to only freeway driving). A highly automated vehicle can generally perform all operations of a partially automated vehicle but with less limitations. A highly automated vehicle can also detect its own limits in operating the vehicle and ask the driver to take over the control of the vehicle when necessary. A fully automated vehicle can perform all vehicle operations without a driver’s intervention but can also detect its own limits and ask the driver to take over when necessary. A driverless vehicle can operate on its own without any driver intervention.

[0038] In typical configurations, motor vehicle 100 comprises one or more LiDAR systems 110 and 120A-120I. Each of LiDAR systems 110 and 120A-120I can be a scanning-based LiDAR system and / or a non-scanning LiDAR system (e.g., a flash LiDAR). A scanning-based LiDAR system scans one or more light beams in one or more directions (e.g., horizontal and vertical directions) to detect objects in a field-of-view (FOV). A non-scanning based LiDAR systemtransmits laser light to illuminate an FOV without scanning. For example, a flash LiDAR is a type of non-scanning based LiDAR system. A flash LiDAR can transmit laser light to simultaneously illuminate an FOV using a single light pulse or light shot.

[0039] A LiDAR system is a frequently-used sensor of a vehicle that is at least partially automated. In one embodiment, as shown in FIG. 1, motor vehicle 100 may include a single LiDAR system 110 (e.g., without LiDAR systems 120A-120I) disposed at the highest position of the vehicle (e.g., at the vehicle roof). Disposing LiDAR system 110 at the vehicle roof facilitates a 360-degree scanning around vehicle 100. In some other embodiments, motor vehicle 100 can include multiple LiDAR systems, including two or more of systems 110 and / or 120A-120I. As shown in FIG. 1, in one embodiment, multiple LiDAR systems 110 and / or 120A-120I are attached to vehicle 100 at different locations of the vehicle. For example, LiDAR system 120A is attached to vehicle 100 at the front right comer; LiDAR system 120B is attached to vehicle 100 at the front center position; LiDAR system 120C is attached to vehicle 100 at the front left corner; LiDAR system 120D is attached to vehicle 100 at the right-side rear view mirror; LiDAR system 120E is attached to vehicle 100 at the left-side rear view mirror; LiDAR system 120F is attached to vehicle 100 at the back center position; LiDAR system 120G is attached to vehicle 100 at the back right corner; LiDAR system 120H is attached to vehicle 100 at the back left corner; and / or LiDAR system 1201 is attached to vehicle 100 at the center towards the backend (e.g., back end of the vehicle roof). It is understood that one or more LiDAR systems can be distributed and attached to a vehicle in any desired manner and FIG. 1 only illustrates one embodiment. As another example, LiDAR systems 120D and 120E may be attached to the B- pillars of vehicle 100 instead of the rear-view mirrors. As another example, LiDAR system 120B may be attached to the windshield of vehicle 100 instead of the front bumper.

[0040] In some embodiments, LiDAR systems 110 and 120A-120I are independent LiDAR systems having their own respective laser sources, control electronics, transmitters, receivers, and / or steering mechanisms. In other embodiments, some of LiDAR systems 110 and 120A- 1201 can share one or more components, thereby forming a distributed sensor system. In one example, optical fibers are used to deliver laser light from a centralized laser source to all LiDAR systems. For instance, system 110 (or another system that is centrally positioned or positioned anywhere inside the vehicle 100) includes a light source, a transmitter, and a light detector, but has no steering mechanisms. System 110 may distribute transmission light to eachof systems 120A-120I. The transmission light may be distributed via optical fibers. Optical connectors can be used to couple the optical fibers to each of system 110 and 120A-120I. In some examples, one or more of systems 120A-120I include steering mechanisms but no light sources, transmitters, or light detectors. A steering mechanism may include one or more moveable mirrors such as one or more polygon mirrors, one or more single plane mirrors, one or more multi-plane mirrors, or the like. Embodiments of the light source, transmitter, steering mechanism, and light detector are described in more detail below. Via the steering mechanisms, one or more of systems 120A-120I scan light into one or more respective FOVs and receive corresponding return light. The return light is formed by scattering or reflecting the transmission light by one or more objects in the FOVs. Systems 120A-120I may also include collection lens and / or other optics to focus and / or direct the return light into optical fibers, which deliver the received return light to system 110. System 110 includes one or more light detectors for detecting the received return light. In some examples, system 110 is disposed inside a vehicle such that it is in a temperature-controlled environment, while one or more systems 120A-120I may be at least partially exposed to the external environment.

[0041] FIG. 2 is a block diagram 200 illustrating interactions between vehicle onboard LiDAR system(s) 210 and multiple other systems including a vehicle perception and planning system 220. LiDAR system(s) 210 can be mounted on or integrated to a vehicle. LiDAR system(s) 210 include sensor(s) that scan laser light to the surrounding environment to measure the distance, angle, and / or velocity of objects. Based on the scattered light that returned to LiDAR system(s) 210, it can generate sensor data (e.g., image data or 3D point cloud data) representing the perceived external environment.

[0042] LiDAR system(s) 210 can include one or more of short-range LiDAR sensors, mediumrange LiDAR sensors, and long-range LiDAR sensors. A short-range LiDAR sensor measures objects located up to about 20-50 meters from the LiDAR sensor. Short-range LiDAR sensors can be used for, e.g., monitoring nearby moving objects (e.g., pedestrians crossing street in a school zone), parking assistance applications, or the like. A medium-range LiDAR sensor measures objects located up to about 70-200 meters from the LiDAR sensor. Medium-range LiDAR sensors can be used for, e.g., monitoring road intersections, assistance for merging onto or leaving a freeway, or the like. A long-range LiDAR sensor measures objects located up to about 200 meters and beyond. Long-range LiDAR sensors are typically used when a vehicle istravelling at a high speed (e.g., on a freeway), such that the vehicle’s control systems may only have a few seconds (e.g., 6-8 seconds) to respond to any situations detected by the LiDAR sensor. As shown in FIG. 2, in one embodiment, the LiDAR sensor data can be provided to vehicle perception and planning system 220 via a communication path 213 for further processing and controlling the vehicle operations. Communication path 213 can be any wired or wireless communication links that can transfer data.

[0043] With reference still to FIG. 2, in some embodiments, other vehicle onboard sensor(s) 230 are configured to provide additional sensor data separately or together with LiDAR system(s) 210. Other vehicle onboard sensors 230 may include, for example, one or more camera(s) 232, one or more radar(s) 234, one or more ultrasonic sensor(s) 236, and / or other sensor(s) 238. Camera(s) 232 can take images and / or videos of the external environment of a vehicle.Camera(s) 232 can take, for example, high-definition (HD) videos having millions of pixels in each frame. A camera includes image sensors that facilitate producing monochrome or color images and videos. Color information may be important in interpreting data for some situations (e.g., interpreting images of traffic lights). Color information may not be available from other sensors such as LiDAR or radar sensors. Camera(s) 232 can include one or more of narrowfocus cameras, wider-focus cameras, side-facing cameras, infrared cameras, fisheye cameras, or the like. The image and / or video data generated by camera(s) 232 can also be provided to vehicle perception and planning system 220 via communication path 233 for further processing and controlling the vehicle operations. Communication path 233 can be any wired or wireless communication links that can transfer data. Camera(s) 232 can be mounted on, or integrated to, a vehicle at any location (e.g., rear-view mirrors, pillars, front grille, and / or back bumpers, etc.).

[0044] Other vehicle onboard sensor(s) 230 can also include radar sensor(s) 234. Radar sensor(s) 234 use radio waves to determine the range, angle, and velocity of objects. Radar sensor(s) 234 produce electromagnetic waves in the radio or microwave spectrum. The electromagnetic waves reflect off an object and some of the reflected waves return to the radar sensor, thereby providing information about the object’s position and velocity. Radar sensor(s) 234 can include one or more of short-range radar(s), medium-range radar(s), and long-range radar(s). A short-range radar measures objects located at about 0.1-30 meters from the radar. A short-range radar is useful in detecting objects located near the vehicle, such as other vehicles, buildings, walls, pedestrians, bicyclists, etc. A short-range radar can be used to detect a blindspot, assist in lane changing, provide rear-end collision warning, assist in parking, provide emergency braking, or the like. A medium-range radar measures objects located at about 30-80 meters from the radar. A long-range radar measures objects located at about 80-200 meters. Medium- and / or long-range radars can be useful in, for example, traffic following, adaptive cruise control, and / or highway automatic braking. Sensor data generated by radar sensor(s) 234 can also be provided to vehicle perception and planning system 220 via communication path 233 for further processing and controlling the vehicle operations. Radar sensor(s) 234 can be mounted on, or integrated to, a vehicle at any location (e.g., rear-view mirrors, pillars, front grille, and / or back bumpers, etc.).

[0045] Other vehicle onboard sensor(s) 230 can also include ultrasonic sensor(s) 236. Ultrasonic sensor(s) 236 use acoustic waves or pulses to measure objects located external to a vehicle. The acoustic waves generated by ultrasonic sensor(s) 236 are transmitted to the surrounding environment. At least some of the transmitted waves are reflected off an object and return to the ultrasonic sensor(s) 236. Based on the return signals, a distance of the object can be calculated. Ultrasonic sensor(s) 236 can be useful in, for example, checking blind spots, identifying parking spaces, providing lane changing assistance into traffic, or the like. Sensor data generated by ultrasonic sensor(s) 236 can also be provided to vehicle perception and planning system 220 via communication path 233 for further processing and controlling the vehicle operations.Ultrasonic sensor(s) 236 can be mounted on, or integrated to, a vehicle at any location (e.g., rearview mirrors, pillars, front grille, and / or back bumpers, etc.).

[0046] In some embodiments, one or more other sensor(s) 238 may be attached in a vehicle and may also generate sensor data. Other sensor(s) 238 may include, for example, global positioning systems (GPS), inertial measurement units (IMU), or the like. Sensor data generated by other sensor(s) 238 can also be provided to vehicle perception and planning system 220 via communication path 233 for further processing and controlling the vehicle operations. It is understood that communication path 233 may include one or more communication links to transfer data between the various sensor(s) 230 and vehicle perception and planning system 220.

[0047] In some embodiments, as shown in FIG. 2, sensor data from other vehicle onboard sensor(s) 230 can be provided to vehicle onboard LiDAR system(s) 210 via communication path 231. LiDAR system(s) 210 may process the sensor data from other vehicle onboard sensor(s)230. For example, sensor data from camera(s) 232, radar sensor(s) 234, ultrasonic sensor(s) 236, and / or other sensor(s) 238 may be correlated or fused with sensor data from LiDAR system(s) 210, thereby at least partially offloading the sensor fusion process performed by vehicle perception and planning system 220. It is understood that other configurations may also be implemented for transmitting and processing sensor data from the various sensors (e.g., data can be transmitted to a cloud or edge computing service provider for processing and then the processing results can be transmitted back to the vehicle perception and planning system 220 and / or LiDAR system 210).

[0048] With reference still to FIG. 2, in some embodiments, sensors onboard other vehicle(s) 250 are used to provide additional sensor data separately or together with LiDAR system(s) 210. For example, two or more nearby vehicles may have their own respective LiDAR sensor(s), camera(s), radar sensor(s), ultrasonic sensor(s), etc. Nearby vehicles can communicate and share sensor data with one another. Communications between vehicles are also referred to as V2V (vehicle to vehicle) communications. For example, as shown in FIG. 2, sensor data generated by other vehicle(s) 250 can be communicated to vehicle perception and planning system 220 and / or vehicle onboard LiDAR system(s) 210, via communication path 253 and / or communication path 251, respectively. Communication paths 253 and 251 can be any wired or wireless communication links that can transfer data.

[0049] Sharing sensor data facilitates a better perception of the environment external to the vehicles. For instance, a first vehicle may not sense a pedestrian that is behind a second vehicle but is approaching the first vehicle. The second vehicle may share the sensor data related to this pedestrian with the first vehicle such that the first vehicle can have additional reaction time to avoid collision with the pedestrian. In some embodiments, similar to data generated by sensor(s) 230, data generated by sensors onboard other vehicle(s) 250 may be correlated or fused with sensor data generated by LiDAR system(s) 210 (or with other LiDAR systems located in other vehicles), thereby at least partially offloading the sensor fusion process performed by vehicle perception and planning system 220.

[0050] In some embodiments, intelligent infrastructure system(s) 240 are used to provide sensor data separately or together with LiDAR system(s) 210. Certain infrastructures may be configured to communicate with a vehicle to convey information and vice versa.Communications between a vehicle and infrastructures are generally referred to as V2I (vehicle to infrastructure) communications. For example, intelligent infrastructure system(s) 240 may include an intelligent traffic light that can convey its status to an approaching vehicle in a message such as “changing to yellow in 5 seconds.” Intelligent infrastructure system(s) 240 may also include its own LiDAR system mounted near an intersection such that it can convey traffic monitoring information to a vehicle. For example, a left-turning vehicle at an intersection may not have sufficient sensing capabilities because some of its own sensors may be blocked by traffic in the opposite direction. In such a situation, sensors of intelligent infrastructure system(s) 240 can provide useful data to the left-turning vehicle. Such data may include, for example, traffic conditions, information of objects in the direction the vehicle is turning to, traffic light status and predictions, or the like. These sensor data generated by intelligent infrastructure system(s) 240 can be provided to vehicle perception and planning system 220 and / or vehicle onboard LiDAR system(s) 210, via communication paths 243 and / or 241, respectively. Communication paths 243 and / or 241 can include any wired or wireless communication links that can transfer data. For example, sensor data from intelligent infrastructure system(s) 240 may be transmitted to LiDAR system(s) 210 and correlated or fused with sensor data generated by LiDAR system(s) 210, thereby at least partially offloading the sensor fusion process performed by vehicle perception and planning system 220. V2V and V2I communications described above are examples of vehicle-to-X (V2X) communications, where the “X” represents any other devices, systems, sensors, infrastructure, or the like that can share data with a vehicle.

[0051] With reference still to FIG. 2, via various communication paths, vehicle perception and planning system 220 receives sensor data from one or more of LiDAR system(s) 210, other vehicle onboard sensor(s) 230, other vehicle(s) 250, and / or intelligent infrastructure system(s) 240. In some embodiments, different types of sensor data are correlated and / or integrated by a sensor fusion sub-system 222. For example, sensor fusion sub-system 222 can generate a 360- degree model using multiple images or videos captured by multiple cameras disposed at different positions of the vehicle. Sensor fusion sub-system 222 obtains sensor data from different types of sensors and uses the combined data to perceive the environment more accurately. For example, a vehicle onboard camera 232 may not capture a clear image because it is facing the Sun or a light source (e.g., another vehicle’s headlight during nighttime) directly. A LiDAR system 210 may not be affected as much and therefore sensor fusion sub-system 222 cancombine sensor data provided by both camera 232 and LiDAR system 210, and use the sensor data provided by LiDAR system 210 to compensate the unclear image captured by camera 232. As another example, in a rainy or foggy weather, a radar sensor 234 may work better than a camera 232 or a LiDAR system 210. Accordingly, sensor fusion sub-system 222 may use sensor data provided by the radar sensor 234 to compensate the sensor data provided by camera 232 or LiDAR system 210.

[0052] In other examples, sensor data generated by other vehicle onboard sensor(s) 230 may have a lower resolution (e.g., radar sensor data) and thus may need to be correlated and confirmed by LiDAR system(s) 210, which usually has a higher resolution. For example, a sewage cover (also referred to as a manhole cover) may be detected by radar sensor 234 as an object towards which a vehicle is approaching. Due to the low-resolution nature of radar sensor 234, vehicle perception and planning system 220 may not be able to determine whether the object is an obstacle that the vehicle needs to avoid. High-resolution sensor data generated by LiDAR system(s) 210 thus can be used to correlated and confirm that the object is a sewage cover and causes no harm to the vehicle.

[0053] Vehicle perception and planning system 220 further comprises an object classifier 223. Using raw sensor data and / or correlated / fused data provided by sensor fusion sub-system 222, object classifier 223 can use any computer vision techniques to detect and classify the objects and estimate the positions of the objects. In some embodiments, object classifier 223 can use machine-learning based techniques to detect and classify objects. Examples of the machinelearning based techniques include utilizing algorithms such as region-based convolutional neural networks (R-CNN), Fast R-CNN, Faster R-CNN, histogram of oriented gradients (HOG), region-based fully convolutional network (R-FCN), single shot detector (SSD), spatial pyramid pooling (SPP-net), and / or You Only Look Once (Yolo).

[0054] Vehicle perception and planning system 220 further comprises a road detection subsystem 224. Road detection sub-system 224 localizes the road and identifies objects and / or markings on the road. For example, based on raw or fused sensor data provided by radar sensor(s) 234, camera(s) 232, and / or LiDAR system(s) 210, road detection sub-system 224 can build a 3D model of the road based on machine-learning techniques (e.g., pattern recognition algorithms for identifying lanes). Using the 3D model of the road, road detection sub-system224 can identify objects (e.g., obstacles or debris on the road) and / or markings on the road (e.g., lane lines, turning marks, crosswalk marks, or the like).

[0055] Vehicle perception and planning system 220 further comprises a localization and vehicle posture sub-system 225. Based on raw or fused sensor data, localization and vehicle posture sub-system 225 can determine position of the vehicle and the vehicle’s posture. For example, using sensor data from LiDAR system(s) 210, camera(s) 232, and / or GPS data, localization and vehicle posture sub-system 225 can determine an accurate position of the vehicle on the road and the vehicle’s six degrees of freedom (e.g., whether the vehicle is moving forward or backward, up or down, and left or right). In some embodiments, high-definition (HD) maps are used for vehicle localization. HD maps can provide highly detailed, three-dimensional, computerized maps that pinpoint a vehicle’s location. For instance, using the HD maps, localization and vehicle posture sub-system 225 can determine precisely the vehicle’s current position (e.g., which lane of the road the vehicle is currently in, how close it is to a curb or a sidewalk) and predict vehicle’s future positions.

[0056] Vehicle perception and planning system 220 further comprises obstacle predictor 226. Objects identified by object classifier 223 can be stationary (e.g., a light pole, a road sign) or dynamic (e.g., a moving pedestrian, bicycle, another car). For moving objects, predicting their moving path or future positions can be important to avoid collision. Obstacle predictor 226 can predict an obstacle trajectory and / or warn the driver or the vehicle planning sub-system 228 about a potential collision. For example, if there is a high likelihood that the obstacle’s trajectory intersects with the vehicle’s current moving path, obstacle predictor 226 can generate such a warning. Obstacle predictor 226 can use a variety of techniques for making such a prediction. Such techniques include, for example, constant velocity or acceleration models, constant turn rate and velocity / accel eration models, Kalman Filter and Extended Kalman Filter based models, recurrent neural network (RNN) based models, long short-term memory (LSTM) neural network based models, encoder-decoder RNN models, or the like.

[0057] With reference still to FIG. 2, in some embodiments, vehicle perception and planning system 220 further comprises vehicle planning sub-system 228. Vehicle planning sub-system 228 can include one or more planners such as a route planner, a driving behaviors planner, and a motion planner. The route planner can plan the route of a vehicle based on the vehicle’s currentlocation data, target location data, traffic information, etc. The driving behavior planner adjusts the timing and planned movement based on how other objects might move, using the obstacle prediction results provided by obstacle predictor 226. The motion planner determines the specific operations the vehicle needs to follow. The planning results are then communicated to vehicle control system 280 via vehicle interface 270. The communication can be performed through communication paths 227 and 271, which include any wired or wireless communication links that can transfer data.

[0058] Vehicle control system 280 controls the vehicle’s steering mechanism, throttle, brake, etc., to operate the vehicle according to the planned route and movement. In some examples, vehicle perception and planning system 220 may further comprise a user interface 260, which provides a user (e.g., a driver) access to vehicle control system 280 to, for example, override or take over control of the vehicle when necessary. User interface 260 may also be separate from vehicle perception and planning system 220. User interface 260 can communicate with vehicle perception and planning system 220, for example, to obtain and display raw or fused sensor data, identified objects, vehicle’s location / posture, etc. These displayed data can help a user to better operate the vehicle. User interface 260 can communicate with vehicle perception and planning system 220 and / or vehicle control system 280 via communication paths 221 and 261 respectively, which include any wired or wireless communication links that can transfer data. It is understood that the various systems, sensors, communication links, and interfaces in FIG. 2 can be configured in any desired manner and not limited to the configuration shown in FIG. 2.

[0059] FIG. 3 is a block diagram illustrating an example LiDAR system 300. LiDAR system 300 can be used to implement LiDAR systems 110, 120A-120I, and / or 210 shown in FIGs. 1 and 2. In one embodiment, LiDAR system 300 comprises a light source 310, a transmitter 320, an optical receiver and light detector 330, a steering system 340, and control circuitry 350. These components are coupled together using communications paths 312, 314, 322, 332, 342, 352, 362, and 372. These communications paths include communication links (wired or wireless, bidirectional or unidirectional) among the various LiDAR system components, but need not be physical components themselves. While the communications paths can be implemented by one or more electrical wires, buses, or optical fibers, the communication paths can also be wireless channels or free-space optical paths so that no physical communication medium is present. For example, in one embodiment of LiDAR system 300, communication path 314 between lightsource 310 and transmitter 320 may be implemented using one or more optical fibers. Communication paths 332 and 352 may represent optical paths implemented using free space optical components and / or optical fibers. And communication paths 312, 322, 342, and 362 may be implemented using one or more electrical wires that carry electrical signals. The communications paths can also include one or more of the above types of communication mediums (e.g., they can include an optical fiber and a free-space optical component, or include one or more optical fibers and one or more electrical wires).

[0060] In some embodiments, LiDAR system 300 can be a coherent LiDAR system. One example is a frequency-modulated continuous-wave (FMCW) LiDAR. Coherent LiDARs detect objects by mixing return light from the objects with light from the coherent laser transmitter. Thus, as shown in FIG. 3, if LiDAR system 300 is a coherent LiDAR, it may include a route 372 providing a portion of transmission light from transmitter 320 to optical receiver and light detector 330. Route 372 may include one or more optics (e.g., optical fibers, lens, mirrors, etc.) for providing the light from transmitter 320 to optical receiver and light detector 330. The transmission light provided by transmitter 320 may be modulated light and can be split into two portions. One portion is transmitted to the FOV, while the second portion is sent to the optical receiver and light detector 330 of the LiDAR system 300. The second portion is also referred to as the light that is kept local (LO) to the LiDAR system 300. The transmission light is scattered or reflected by various objects in the FOV and at least a portion of it forms return light. The return light is subsequently detected and interferometrically recombined with the second portion of the transmission light that was kept local. Coherent LiDAR provides a means of optically sensing an object’s range as well as its relative velocity along the line-of-sight (LOS).

[0061] LiDAR system 300 can also include other components not depicted in FIG. 3, such as power buses, power supplies, LED indicators, switches, etc. Additionally, other communication connections among components may be present, such as a direct connection between light source 310 and optical receiver and light detector 330 to provide a reference signal so that the time from when a light pulse is transmitted until a return light pulse is detected can be accurately measured.

[0062] Light source 310 outputs laser light for illuminating objects in a field of view (FOV). The laser light can be infrared light having a wavelength in the range of 700 nm to 1mm. Light source 310 can be, for example, a semiconductor-based laser (e.g., a diode laser) and / or a fiber-based laser. A semiconductor-based laser can be, for example, an edge emitting laser (EEL), a vertical cavity surface emitting laser (VCSEL), an external-cavity diode laser, a vertical- extemal-cavity surface-emitting laser, a distributed feedback (DFB) laser, a distributed Bragg reflector (DBR) laser, an interband cascade laser, a quantum cascade laser, a quantum well laser, a double heterostructure laser, or the like. A fiber-based laser is a laser in which the active gain medium is an optical fiber doped with rare-earth elements such as erbium, ytterbium, neodymium, dysprosium, praseodymium, thulium, and / or holmium. In some embodiments, a fiber laser is based on double-clad fibers, in which the gain medium forms the core of the fiber surrounded by two layers of cladding. The double-clad fiber allows the core to be pumped with a high-power beam, thereby enabling the laser source to be a high power fiber laser source.

[0063] In some embodiments, light source 310 comprises a master oscillator (also referred to as a seed laser) and power amplifier (MOP A). The power amplifier amplifies the output power of the seed laser. The power amplifier can be a fiber amplifier, a bulk amplifier, or a semiconductor optical amplifier. The seed laser can be a diode laser (e.g., a Fabry-Perot cavity laser, a distributed feedback laser), a solid-state bulk laser, or a tunable external-cavity diode laser. In some embodiments, light source 310 can be an optically pumped microchip laser. Microchip lasers are alignment-free monolithic solid-state lasers where the laser crystal is directly contacted with the end mirrors of the laser resonator. A microchip laser is typically pumped with a laser diode (directly or using a fiber) to obtain the desired output power. A microchip laser can be based on neodymium-doped yttrium aluminum garnet (Y3AI5O12) laser crystals (i.e., Nd:YAG), or neodymium-doped vanadate (i.e., ND:YVO4) laser crystals. In some examples, light source 310 may have multiple amplification stages to achieve a high power gain such that the laser output can have high power, thereby enabling the LiDAR system to have a long scanning range. In some examples, the power amplifier of light source 310 can be controlled such that the power gain can be varied to achieve any desired laser output power.

[0064] FIG. 4A is a block diagram illustrating an example fiber-based laser source 400 having a seed laser and one or more pumps (e.g., laser diodes) for pumping desired output power. Fiberbased laser source 400 is an example of light source 310 depicted in FIG. 3. In some embodiments, fiber-based laser source 400 comprises a seed laser 402 configured to generate initial light pulses of one or more wavelengths (e.g., infrared wavelengths such as 1550 nm), which are provided to a wavelength-division multiplexor (WDM) 404 via an optical fiber 403.Fiber-based laser source 400 further comprises a pump 406 for providing laser power (e.g., of a different wavelength, such as 980 nm) to WDM 404 via an optical fiber 405. WDM 404 multiplexes the light pulses provided by seed laser 402 and the laser power provided by pump 406 onto a single optical fiber 407. The output of WDM 404 can then be provided to one or more pre-amplifier(s) 408 via optical fiber 407. Pre-amplifier(s) 408 can be optical amplifier(s) that amplify optical signals (e.g., with about 10-30 dB gain). In some embodiments, preamplifiers) 408 are low noise amplifiers. Pre-amplifier(s) 408 output to an optical combiner 410 via an optical fiber 409. Combiner 410 combines the output laser light of pre-amplifier(s) 408 with the laser power provided by pump 412 via an optical fiber 411. Combiner 410 can combine optical signals having the same wavelength or different wavelengths. One example of a combiner is a WDM. Combiner 410 provides combined optical signals to a booster amplifier 414, which produces output light pulses via optical fiber 415. The booster amplifier 414 provides further amplification of the optical signals (e.g., another 20-40 dB). The output light pulses can then be transmitted to transmitter 320 and / or steering mechanism 340 (shown in FIG. 3). It is understood that FIG. 4A illustrates one example configuration of fiber-based laser source 400. Laser source 400 can have many other configurations using different combinations of one or more components shown in FIG. 4A and / or other components not shown in FIG. 4A (e.g., other components such as power supplies, lens(es), filters, splitters, combiners, etc.).

[0065] In some variations, fiber-based laser source 400 can be controlled (e.g., by control circuitry 350) to produce pulses of different amplitudes based on the fiber gain profile of the fiber used in fiber-based laser source 400. Communication path 312 couples fiber-based laser source 400 to control circuitry 350 (shown in FIG. 3) so that components of fiber-based laser source 400 can be controlled by or otherwise communicate with control circuitry 350. Alternatively, fiber-based laser source 400 may include its own dedicated controller. Instead of control circuitry 350 communicating directly with components of fiber-based laser source 400, a dedicated controller of fiber-based laser source 400 communicates with control circuitry 350 and controls and / or communicates with the components of fiber-based laser source 400. Fiber-based laser source 400 can also include other components not shown, such as one or more power connectors, power supplies, and / or power lines.

[0066] FIG. 4B is a block diagram illustrating an example semiconductor-based laser source 440. Semiconductor-based laser source 440 is an example of light source 310 depicted in FIG. 3.In the example shown in FIG. 4B, laser source 440 is a Vertical-Cavity Surface-Emitting Laser (VCSEL), which is a type of semiconductor laser diode with a distinctive structure that allows it to emit light vertically from the surface of the chip, rather than through the edge of the chip like the edge-emitting laser (EEL) diodes. VCSELs have advantages like high-speed operation and easy integration into semiconductor devices. FIG. 4B shows a cross-sectional view of an example VCSEL 440. In this example, the VCSEL 440 includes a metal contact layer 442, an upper Bragg reflector 444, an active region 446, a lower Bragg reflector 448, a substrate 450, and another metal contact 452. In the VCSEL 440, the metal contacts 442 and 452 are for making electrical contacts so that electrical current and / or voltage can be provided to VCSEL 440 for generating laser light. The substrate layer 450 is a semiconductor substrate, which can be, for example, a gallium arsenide (GaAs) substrate. VCSEL 440 uses a laser resonator, which includes two distributed Bragg reflector (DBR) reflectors (i.e., upper Bragg reflector 444 and lower Bragg reflector 448) with an active region 446 sandwiched between the DBR reflectors. The active region 446 includes, for example, one or more quantum wells for the laser light generation. The planar DBR-r effectors can be mirrors having layers with alternating high and low refractive indices. Each layer has a thickness of a quarter of the laser wavelength in the material, yielding intensity reflectivities above e.g., 99%. High reflectivity mirrors in VCSELs can balance the short axial length of the gain region. In one example of VCSEL 440, the upper and lower DBR reflectors 444 and 448 can be doped as p-type and n-type materials, forming a diode junction. In another example, the p-type and n-type regions may be embedded between the reflectors, requiring a more complex semiconductor process to make electrical contact to the active region, but eliminating electrical power loss in the DBR structure. The active region 446 is sandwiched between the DBR reflectors 444 and 448 of the VCSEL 440. The active region is where the laser light generation occurs. The active region 446 typically has a quantum well or quantum dot structure, which contains the gain medium responsible for light amplification. When an electric current is applied to the active region 446, it generates photons by stimulated emission. The distance between the upper and lower DBR reflectors 444 and 448 defines the cavity length of the VCSEL 440. The cavity length in turn determines the wavelength of the emitted light and influences the laser's performance characteristics. When an electrical current is applied to the VCSEL 440, it generates light that bounces between the DBR reflectors 444 and 448 and exits the VCSEL 440 through, for example, the lower DBR reflector 448, producing ahighly coherent and vertically emitted laser beam 454. VCSEL 440 can provide an improved beam quality, low threshold current, and the ability to produce single-mode or multi-mode output.

[0067] In some variations, VCSEL 440 can be controlled (e.g., by control circuitry 350) to produce pulses of different amplitudes. Communication path 312 couples VCSEL 440 to control circuitry 350 (shown in FIG. 3) so that components of VCSEL 440 can be controlled by or otherwise communicate with control circuitry 350. Alternatively, VCSEL 440 may include its own dedicated controller. Instead of control circuitry 350 communicating directly with components of VCSEL 440, a dedicated controller of VCSEL 440 communicates with control circuitry 350 and controls and / or communicates with the components of VCSEL 440. VCSEL 440 can also include other components not shown, such as one or more power connectors, power supplies, and / or power lines.

[0068] VCSEL 440 can be used to generate laser pulses or continuous wave (CW) lasers. To generate laser pulses, control circuitry 350 modulates the current supplied to the VCSEL 440. By rapidly turning the supply current on and off, pulses of laser light can be generated. The duration, repetition rate, and shape of the pulses can be controlled by adjusting the modulation parameters. As another example, VCSEL 440 can also be a mode-locked VCSEL that uses a combination of current modulation and optical feedback to obtain ultra-short pulses. The mode-locked VCSEL may also be controlled to synchronize the phases of the laser modes to produce very short and high-intensity pulses. As another example, VCSEL 440 can use Q-Switching techniques, which includes an optical switch in the laser cavity, temporarily blocking the lasing action and allows energy to build up in the cavity. When the switch is opened, a high-intensity pulse is emitted. As another example, VCSEL 440 can also have external modulation performed by an external modulator (not shown), such as an electro-optic or acousto-optic modulator. The external modulation can be used in combination with the VCSEL itself to create pulsed output. The external modulator can be used to control the pulse duration and repetition rate. The type of VCSEL used as at least a part of light source 310 depends on the application and the required pulse characteristics, such as pulse duration, repetition rate, and peak power.

[0069] Referencing FIG. 3, typical operating wavelengths of light source 310 comprise, for example, about 850 nm, about 905 nm, about 940 nm, about 1064 nm, and about 1550 nm. Forlaser safety, the upper limit of maximum usable laser power is set by the U.S. FDA (U.S. Food and Drug Administration) regulations. The optical power limit at 1550 nm wavelength is much higher than those of the other aforementioned wavelengths. Further, at 1550 nm, the optical power loss in a fiber is low. There characteristics of the 1550 nm wavelength make it more beneficial for long-range LiDAR applications. The amount of optical power output from light source 310 can be characterized by its peak power, average power, pulse energy, and / or the pulse energy density. The peak power is the ratio of pulse energy to the width of the pulse (e.g., full width at half maximum or FWHM). Thus, a smaller pulse width can provide a larger peak power for a fixed amount of pulse energy. A pulse width can be in the range of nanosecond or picosecond. The average power is the product of the energy of the pulse and the pulse repetition rate (PRR). As described in more detail below, the PRR represents the frequency of the pulsed laser light. In general, the smaller the time interval between the pulses, the higher the PRR. The PRR typically corresponds to the maximum range that a LiDAR system can measure. Light source 310 can be configured to produce pulses at high PRR to meet the desired number of data points in a point cloud generated by the LiDAR system. Light source 310 can also be configured to produce pulses at medium or low PRR to meet the desired maximum detection distance. Wall plug efficiency (WPE) is another factor to evaluate the total power consumption, which may be a useful indicator in evaluating the laser efficiency. For example, as shown in FIG. 1, multiple LiDAR systems may be attached to a vehicle, which may be an electrical-powered vehicle or a vehicle otherwise having limited fuel or battery power supply. Therefore, high WPE and intelligent ways to use laser power are often among the important considerations when selecting and configuring light source 310 and / or designing laser delivery systems for vehicle-mounted LiDAR applications.

[0070] It is understood that the above descriptions provide non-limiting examples of a light source 310. Light source 310 can be configured to include many other types of light sources (e.g., laser diodes, short-cavity fiber lasers, solid-state lasers, and / or tunable external cavity diode lasers) that are configured to generate one or more light signals at various wavelengths. In some examples, light source 310 comprises amplifiers (e.g., pre-amplifiers and / or booster amplifiers), which can be a doped optical fiber amplifier, a solid-state bulk amplifier, and / or a semiconductor optical amplifier. The amplifiers are configured to receive and amplify light signals with desired gains.

[0071] With reference back to FIG. 3, LiDAR system 300 further comprises a transmitter 320. Light source 310 provides laser light (e.g., in the form of a laser beam) to transmitter 320. The laser light provided by light source 310 can be amplified laser light with a predetermined or controlled wavelength, pulse repetition rate, and / or power level. Transmitter 320 receives the laser light from light source 310 and transmits the laser light to steering mechanism 340 with low divergence. In some embodiments, transmitter 320 can include, for example, optical components (e.g., lens, fibers, mirrors, etc.) for transmitting one or more laser beams to a field-of-view (FOV) directly or via steering mechanism 340. While FIG. 3 illustrates transmitter 320 and steering mechanism 340 as separate components, they may be combined or integrated as one system in some embodiments. Steering mechanism 340 is described in more detail below.

[0072] Laser beams provided by light source 310 may diverge as they travel to transmitter 320. Therefore, transmitter 320 often comprises a collimating lens or a lens group configured to collect the diverging laser beams and produce more parallel optical beams with reduced or minimum divergence. The collimated optical beams can then be further directed through various optics such as mirrors and lens. A collimating lens may be, for example, a single plano-convex lens or a lens group. The collimating lens can be configured to achieve any desired properties such as the beam diameter, divergence, numerical aperture, focal length, or the like. A beam propagation ratio or beam quality factor (also referred to as the M2factor) is used for measurement of laser beam quality. In many LiDAR applications, it is important to have good laser beam quality in the generated transmitting laser beam. The M2factor represents a degree of variation of a beam from an ideal Gaussian beam. Thus, the M2factor reflects how well a collimated laser beam can be focused on a small spot, or how well a divergent laser beam can be collimated. Therefore, light source 310 and / or transmitter 320 can be configured to meet, for example, a scan resolution requirement while maintaining the desired M2factor.

[0073] One or more of the light beams provided by transmitter 320 are scanned by steering mechanism 340 to a FOV. Steering mechanism 340 scans light beams in multiple dimensions (e.g., in both the horizontal and vertical dimension) to facilitate LiDAR system 300 to map the environment by generating a 3D point cloud. A horizontal dimension can be a dimension that is parallel to the horizon or a surface associated with the LiDAR system or a vehicle (e.g., a road surface). A vertical dimension is perpendicular to the horizontal dimension (i.e., the vertical dimension forms a 90-degree angle with the horizontal dimension). Steering mechanism 340will be described in more detail below. The laser light scanned to an FOV may be scattered or reflected by an object in the FOV. At least a portion of the scattered or reflected light forms return light that returns to LiDAR system 300. FIG. 3 further illustrates an optical receiver and light detector 330 configured to receive the return light. Optical receiver and light detector 330 comprises an optical receiver that is configured to collect the return light from the FOV. The optical receiver can include optics (e.g., lens, fibers, mirrors, etc.) for receiving, redirecting, focusing, amplifying, and / or filtering return light from the FOV. For example, the optical receiver often includes a collection lens (e.g., a single plano-convex lens or a lens group) to collect and / or focus the collected return light onto a light detector.

[0074] A light detector detects the return light focused by the optical receiver and generates current and / or voltage signals proportional to the incident intensity of the return light. Based on such current and / or voltage signals, the depth information of the object in the FOV can be derived. One example method for deriving such depth information is based on the direct TOF (time of flight), which is described in more detail below. A light detector may be characterized by its detection sensitivity, quantum efficiency, detector bandwidth, linearity, signal to noise ratio (SNR), overload resistance, interference immunity, etc. Based on the applications, the light detector can be configured or customized to have any desired characteristics. For example, optical receiver and light detector 330 can be configured such that the light detector has a large dynamic range while having a good linearity. The light detector linearity indicates the detector’s capability of maintaining linear relationship between input optical signal power and the detector’s output. A detector having good linearity can maintain a linear relationship over a large dynamic input optical signal range.

[0075] To achieve desired detector characteristics, configurations or customizations can be made to the light detector’s structure and / or the detector’s material system. Various detector structures can be used for a light detector. For example, a light detector structure can be a PIN based structure, which has an undoped intrinsic semiconductor region (i.e., an “i” region) between a p- type semiconductor and an n-type semiconductor region. Other light detector structures comprise, for example, an APD (avalanche photodiode) based structure, a PMT (photomultiplier tube) based structure, a SiPM (Silicon photomultiplier) based structure, a SPAD (single-photon avalanche diode) based structure, and / or quantum wires. For material systems used in a lightdetector, Si, InGaAs, and / or Si / Ge based materials can be used. It is understood that many other detector structures and / or material systems can be used in optical receiver and light detector 330.

[0076] A light detector (e.g., an APD based detector) may have an internal gain such that the input signal is amplified when generating an output signal. However, noise may also be amplified due to the light detector’s internal gain. Common types of noise include signal shot noise, dark current shot noise, thermal noise, and amplifier noise. In some embodiments, optical receiver and light detector 330 may include a pre-amplifier that is a low noise amplifier (LNA). In some embodiments, the pre-amplifier may also include a transimpedance amplifier (TIA), which converts a current signal to a voltage signal. For a linear detector system, input equivalent noise or noise equivalent power (NEP) measures how sensitive the light detector is to weak signals. Therefore, they can be used as indicators of the overall system performance. For example, the NEP of a light detector specifies the power of the weakest signal that can be detected and therefore it in turn specifies the maximum range of a LiDAR system. It is understood that various light detector optimization techniques can be used to meet the requirement of LiDAR system 300. Such optimization techniques may include selecting different detector structures, materials, and / or implementing signal processing techniques (e.g., filtering, noise reduction, amplification, or the like). For example, in addition to, or instead of, using direct detection of return signals (e.g., by using ToF), coherent detection can also be used for a light detector. Coherent detection allows for detecting amplitude and phase information of the received light by interfering the received light with a local oscillator. Coherent detection can improve detection sensitivity and noise immunity.

[0077] FIG. 3 further illustrates that LiDAR system 300 comprises steering mechanism 340. As described above, steering mechanism 340 directs light beams from transmitter 320 to scan an FOV in multiple dimensions. A steering mechanism is also referred to as a raster mechanism, a scanning mechanism, or simply a light scanner. Scanning light beams in multiple directions (e.g., in both the horizontal and vertical directions) facilitates a LiDAR system to map the environment by generating an image or a 3D point cloud. A steering mechanism can be based on mechanical scanning and / or solid-state scanning. Mechanical scanning uses rotating mirrors to steer the laser beam or physically rotate the LiDAR transmitter and receiver (collectively referred to as transceiver) to scan the laser beam. Solid-state scanning directs the laser beam to various positions through the FOV without mechanically moving any macroscopic componentssuch as the transceiver. Solid-state scanning mechanisms include, for example, optical phased arrays based steering and flash LiDAR based steering. In some embodiments, because solid- state scanning mechanisms do not physically move macroscopic components, the steering performed by a solid-state scanning mechanism may be referred to as effective steering. A LiDAR system using solid-state scanning may also be referred to as a non-mechanical scanning or simply non-scanning LiDAR system (a flash LiDAR system is an example non-scanning LiDAR system).

[0078] Steering mechanism 340 can be used with a transceiver (e.g., transmitter 320 and optical receiver and light detector 330) to scan the FOV for generating an image or a 3D point cloud. As an example, to implement steering mechanism 340, a two-dimensional mechanical scanner can be used with a single-point or several single-point transceivers. A single-point transceiver transmits a single light beam or a small number of light beams (e.g., 2-8 beams) to the steering mechanism. A two-dimensional mechanical steering mechanism comprises, for example, polygon mirror(s), oscillating mirror(s), rotating prism(s), rotating tilt mirror surface(s), singleplane or multi-plane mirror(s), or a combination thereof. In some embodiments, steering mechanism 340 may include non-mechanical steering mechanism(s) such as solid-state steering mechanism(s). For example, steering mechanism 340 can be based on tuning wavelength of the laser light combined with refraction effect, and / or based on reconfigurable grating / phase array. In some embodiments, steering mechanism 340 can use a single scanning device to achieve two- dimensional scanning or multiple scanning devices combined to realize two-dimensional scanning.

[0079] As another example, to implement steering mechanism 340, a one-dimensional mechanical scanner can be used with an array or a large number of single-point transceivers. Specifically, the transceiver array can be mounted on a rotating platform to achieve 360-degree horizontal field of view. Alternatively, a static transceiver array can be combined with the onedimensional mechanical scanner. A one-dimensional mechanical scanner comprises polygon mirror(s), oscillating mirror(s), rotating prism(s), rotating tilt mirror surface(s), or a combination thereof, for obtaining a forward-looking horizontal field of view. Steering mechanisms using mechanical scanners can provide robustness and reliability in high volume production for automotive applications.

[0080] As another example, to implement steering mechanism 340, a two-dimensional transceiver can be used to generate a scan image or a 3D point cloud directly. In some embodiments, a stitching or micro shift method can be used to improve the resolution of the scan image or the field of view being scanned. For example, using a two-dimensional transceiver, signals generated at one direction (e.g., the horizontal direction) and signals generated at the other direction (e.g., the vertical direction) may be integrated, interleaved, and / or matched to generate a higher or full resolution image or 3D point cloud representing the scanned FOV.

[0081] Some implementations of steering mechanism 340 comprise one or more optical redirection elements (e.g., mirrors or lenses) that steer return light signals (e.g., by rotating, vibrating, or directing) along a receive path to direct the return light signals to optical receiver and light detector 330. The optical redirection elements that direct light signals along the transmitting and receiving paths may be the same components (e.g., shared), separate components (e.g., dedicated), and / or a combination of shared and separate components. This means that in some cases the transmitting and receiving paths are different although they may partially overlap (or in some cases, substantially overlap or completely overlap).

[0082] With reference still to FIG. 3, LiDAR system 300 further comprises control circuitry 350. Control circuitry 350 can be configured and / or programmed to control various parts of the LiDAR system 300 and / or to perform signal processing. In a typical system, control circuitry 350 can be configured and / or programmed to perform one or more control operations including, for example, controlling light source 310 to obtain the desired laser pulse timing, the pulse repetition rate, and power; controlling steering mechanism 340 (e.g., controlling the speed, direction, and / or other parameters) to scan the FOV and maintain pixel registration and / or alignment; controlling optical receiver and light detector 330 (e.g., controlling the sensitivity, noise reduction, filtering, and / or other parameters) such that it is an optimal state; and monitoring overall system health / status for functional safety (e.g., monitoring the laser output power and / or the steering mechanism operating status for safety).

[0083] Control circuitry 350 can also be configured and / or programmed to perform signal processing to the raw data generated by optical receiver and light detector 330 to derive distance and reflectance information, and perform data packaging and communication to vehicle perception and planning system 220 (shown in FIG. 2). For example, control circuitry 350determines the time it takes from transmitting a light pulse until a corresponding return light pulse is received; determines when a return light pulse is not received for a transmitted light pulse; determines the direction (e.g., horizontal and / or vertical information) for a transmitted / retum light pulse; determines the estimated range in a particular direction; derives the reflectivity of an object in the FOV, and / or determines any other type of data relevant to LiDAR system 300.

[0084] LiDAR system 300 can be disposed in a vehicle, which may operate in many different environments including hot or cold weather, rough road conditions that may cause intense vibration, high or low humidities, dusty areas, etc. Therefore, in some embodiments, optical and / or electronic components of LiDAR system 300 (e g., optics in transmitter 320, optical receiver and light detector 330, and steering mechanism 340) are disposed and / or configured in such a manner to maintain long term mechanical and optical stability. For example, components in LiDAR system 300 may be secured and sealed such that they can operate under all conditions a vehicle may encounter. As an example, an anti-moisture coating and / or hermetic sealing may be applied to optical components of transmitter 320, optical receiver and light detector 330, and steering mechanism 340 (and other components that are susceptible to moisture). As another example, housing(s), enclosure(s), fairing(s), and / or window can be used in LiDAR system 300 for providing desired characteristics such as hardness, ingress protection (IP) rating, selfcleaning capability, resistance to chemical and resistance to impact, or the like. In addition, efficient and economical methodologies for assembling LiDAR system 300 may be used to meet the LiDAR operating requirements while keeping the cost low.

[0085] It is understood by a person of ordinary skill in the art that FIG. 3 and the above descriptions are for illustrative purposes only, and a LiDAR system can include other functional units, blocks, or segments, and can include variations or combinations of these above functional units, blocks, or segments. For example, LiDAR system 300 can also include other components not depicted in FIG. 3, such as power buses, power supplies, LED indicators, switches, etc. Additionally, other connections among components may be present, such as a direct connection between light source 310 and optical receiver and light detector 330 so that light detector 330 can accurately measure the time from when light source 310 transmits a light pulse until light detector 330 detects a return light pulse.

[0086] These components shown in FIG. 3 are coupled together using communications paths 312, 314, 322, 332, 342, 352, 362, and 372. These communications paths represent communication paths (bidirectional or unidirectional) among the various LiDAR system components but need not be physical components themselves. While the communications paths can be implemented by one or more electrical wires, buses, or optical fibers, the communication paths can also be wireless channels or open-air optical paths so that no physical communication medium is present. For example, in one example LiDAR system, communication path 314 includes one or more optical fibers; communication path 352 represents an optical path; and communication paths 312, 322, 342, and 362 are all electrical wires that carry electrical signals. The communication paths can also include more than one of the above types of communication mediums (e.g., they can include an optical fiber and an optical path, or one or more optical fibers and one or more electrical wires).

[0087] As described above, some LiDAR systems use the time-of-flight (ToF) of light signals (e g., light pulses) to determine the distance to objects in a light path. For example, with reference to FIG. 5A, an example LiDAR system 500 includes a laser light source (e.g., a fiber laser), a steering mechanism (e.g., a system of one or more moving mirrors), and a light detector (e g., a photodetector with one or more optics). LiDAR system 500 can be implemented using, for example, LiDAR system 300 described above. LiDAR system 500 transmits a light pulse 502 along light path 504 as determined by the steering mechanism of LiDAR system 500. In the depicted example, light pulse 502, which is generated by the laser light source, is a short pulse of laser light. Further, the signal steering mechanism of the LiDAR system 500 is a pulsed-signal steering mechanism. However, it should be appreciated that LiDAR systems can operate by generating, transmitting, and detecting light signals that are not pulsed and derive ranges to an object in the surrounding environment using techniques other than time-of-flight. For example, some LiDAR systems use frequency modulated continuous waves (i.e., “FMCW”). It should be further appreciated that any of the techniques described herein with respect to time-of-flight based systems that use pulsed signals also may be applicable to LiDAR systems that do not use one or both of these techniques.

[0088] Referring back to FIG. 5A (e.g., illustrating a time-of-flight LiDAR system that uses light pulses), when light pulse 502 reaches object 506, light pulse 502 scatters or reflects to form a return light pulse 508. Return light pulse 508 may return to system 500 along light path 510.The time from when transmitted light pulse 502 leaves LiDAR system 500 to when return light pulse 508 arrives back at LiDAR system 500 can be measured (e.g., by a processor or other electronics, such as control circuitry 350, within the LiDAR system). This time-of-flight combined with the knowledge of the speed of light can be used to determine the range / di stance from LiDAR system 500 to the portion of object 506 where light pulse 502 scattered or reflected.

[0089] By directing many light pulses, as depicted in FIG. 5B, LiDAR system 500 scans the external environment (e.g., by directing light pulses 502, 522, 526, 530 along light paths 504, 524, 528, 532, respectively). As depicted in FIG. 5C, LiDAR system 500 receives return light pulses 508, 542, 548 (which correspond to transmitted light pulses 502, 522, 530, respectively). Return light pulses 508, 542, and 548 are formed by scattering or reflecting the transmitted light pulses by one of objects 506 and 514. Return light pulses 508, 542, and 548 may return to LiDAR system 500 along light paths 510, 544, and 546, respectively. Based on the direction of the transmitted light pulses (as determined by LiDAR system 500) as well as the calculated range from LiDAR system 500 to the portion of objects that scatter or reflect the light pulses (e.g., the portions of objects 506 and 514), the external environment within the detectable range (e.g., the field of view between path 504 and 532, inclusively) can be precisely mapped or plotted (e.g., by generating a 3D point cloud or images).

[0090] If a corresponding light pulse is not received for a particular transmitted light pulse, then LiDAR system 500 may determine that there are no objects within a detectable range of LiDAR system 500 (e.g., an object is beyond the maximum scanning distance of LiDAR system 500). For example, in FIG. 5B, light pulse 526 may not have a corresponding return light pulse (as illustrated in FIG. 5C) because light pulse 526 may not produce a scattering event along its transmission path 528 within the predetermined detection range. LiDAR system 500, or an external system in communication with LiDAR system 500 (e.g., a cloud system or service), can interpret the lack of return light pulse as no object being disposed along light path 528 within the detectable range of LiDAR system 500.

[0091] In FIG. 5B, light pulses 502, 522, 526, and 530 can be transmitted in any order, serially, in parallel, or based on other timings with respect to each other. Additionally, while FIG. 5B depicts transmitted light pulses as being directed in one dimension or one plane (e.g., the plane of the paper), LiDAR system 500 can also direct transmitted light pulses along otherdimension(s) or plane(s). For example, LiDAR system 500 can also direct transmitted light pulses in a dimension or plane that is perpendicular to the dimension or plane shown in FIG. 5B, thereby forming a 2-dimensional transmission of the light pulses. This 2-dimensional transmission of the light pulses can be point-by-point, line-by-line, all at once, or in some other manner. That is, LiDAR system 500 can be configured to perform a point scan, a line scan, a one-shot without scanning, or a combination thereof. A point cloud or image from a 1-dimensional transmission of light pulses (e.g., a single horizontal line) can generate 2- dimensional data (e.g., (1) data from the horizontal transmission direction and (2) the range or distance to objects). Similarly, a point cloud or image from a 2-dimensional transmission of light pulses can generate 3-dimensional data (e.g., (1) data from the horizontal transmission direction, (2) data from the vertical transmission direction, and (3) the range or distance to objects). In general, a LiDAR system performing an / / -dimensional transmission of light pulses generates ( / / + ! ) dimensional data. This is because the LiDAR system can measure the depth of an object or the range / di stance to the object, which provides the extra dimension of data. Therefore, a 2D scanning by a LiDAR system can generate a 3D point cloud for mapping the external environment of the LiDAR system.

[0092] The density of a point cloud refers to the number of measurements (data points) per area performed by the LiDAR system. A point cloud density relates to the LiDAR scanning resolution. Typically, a larger point cloud density, and therefore a higher resolution, is desired at least for the region of interest (ROI). The density of points in a point cloud or image generated by a LiDAR system is equal to the number of pulses divided by the field of view. In some embodiments, the field of view can be fixed. Therefore, to increase the density of points generated by one set of transmission-receiving optics (or transceiver optics), the LiDAR system may need to generate a pulse more frequently. In other words, a light source in the LiDAR system may have a higher pulse repetition rate (PRR). On the other hand, by generating and transmitting pulses more frequently, the farthest distance that the LiDAR system can detect may be limited. For example, if a return signal from a distant object is received after the system transmits the next pulse, the return signals may be detected in a different order than the order in which the corresponding signals are transmitted, thereby causing ambiguity if the system cannot correctly correlate the return signals with the transmitted signals.

[0093] To illustrate, consider an example LiDAR system that can transmit laser pulses with a pulse repetition rate between 500 kHz and 1 MHz. Based on the time it takes for a pulse to return to the LiDAR system and to avoid mix-up of return pulses from consecutive pulses in a typical LiDAR design, the farthest distance the LiDAR system can detect may be 300 meters and 150 meters for 500 kHz and 1 MHz, respectively. The density of points of a LiDAR system with 500 kHz repetition rate is half of that with 1 MHz. Thus, this example demonstrates that, if the system cannot correctly correlate return signals that arrive out of order, increasing the repetition rate from 500 kHz to 1 MHz (and thus improving the density of points of the system) may reduce the detection range of the system. Various techniques are used to mitigate the tradeoff between higher PRR and limited detection range. For example, multiple wavelengths can be used for detecting objects in different ranges. Optical and / or signal processing techniques (e.g., pulse encoding techniques) are also used to correlate between transmitted and return light signals.

[0094] Various systems, apparatus, and methods described herein may be implemented using digital circuitry, or using one or more computers using well-known computer processors, memory units, storage devices, computer software, and other components. Typically, a computer includes a processor for executing instructions and one or more memories for storing instructions and data. A computer may also include, or be coupled to, one or more mass storage devices, such as one or more magnetic disks, internal hard disks and removable disks, magnetooptical disks, optical disks, etc.

[0095] Various systems, apparatus, and methods described herein may be implemented using computers operating in a client-server relationship. Typically, in such a system, the client computers are located remotely from the server computers and interact via a network. The client-server relationship may be defined and controlled by computer programs running on the respective client and server computers. Examples of client computers can include desktop computers, workstations, portable computers, cellular smartphones, tablets, or other types of computing devices.

[0096] Various systems, apparatus, and methods described herein may be implemented using a computer program product tangibly embodied in an information carrier, e.g., in a non-transitory machine-readable storage device, for execution by a programmable processor; and the method processes and steps described herein, including one or more of the steps of at least some of theFIGS. 1-12, may be implemented using one or more computer programs that are executable by such a processor. A computer program is a set of computer program instructions that can be used, directly or indirectly, in a computer to perform a certain activity or bring about a certain result. A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.

[0097] A high-level block diagram of an example apparatus that may be used to implement systems, apparatus and methods described herein is illustrated in FIG. 6. Apparatus 600 comprises a processor 610 operatively coupled to a persistent storage device 620 and a main memory device 630. Processor 610 controls the overall operation of apparatus 600 by executing computer program instructions that define such operations. The computer program instructions may be stored in persistent storage device 620, or other computer-readable medium, and loaded into main memory device 630 when execution of the computer program instructions is desired. For example, processor 610 may be used to implement one or more components and systems described herein, such as control circuitry 350 (shown in FIG. 3), vehicle perception and planning system 220 (shown in FIG. 2), and vehicle control system 280 (shown in FIG. 2).Thus, the method steps of at least some of FIGS. 1-12 can be defined by the computer program instructions stored in main memory device 630 and / or persistent storage device 620 and controlled by processor 610 executing the computer program instructions. For example, the computer program instructions can be implemented as computer executable code programmed by one skilled in the art to perform an algorithm defined by the method steps discussed herein in connection with at least some of FIGS. 1-12. Accordingly, by executing the computer program instructions, the processor 610 executes an algorithm defined by the method steps of these aforementioned figures. Apparatus 600 also includes one or more network interfaces 680 for communicating with other devices via a network. Apparatus 600 may also include one or more input / output devices 690 that enable user interaction with apparatus 600 (e.g., display, keyboard, mouse, speakers, buttons, etc.).

[0098] Processor 610 may include both general and special purpose microprocessors and may be the sole processor or one of multiple processors of apparatus 600. Processor 610 may comprise one or more central processing units (CPUs), and one or more graphics processing units (GPUs),which, for example, may work separately from and / or multi-task with one or more CPUs to accelerate processing, e.g., for various image processing applications described herein. Processor 610, persistent storage device 620, and / or main memory device 630 may include, be supplemented by, or incorporated in, one or more application-specific integrated circuits (ASICs) and / or one or more field programmable gate arrays (FPGAs).

[0099] Persistent storage device 620 and main memory device 630 each comprise a tangible non-transitory computer readable storage medium. Persistent storage device 620, and main memory device 630, may each include high-speed random access memory, such as dynamic random access memory (DRAM), static random access memory (SRAM), double data rate synchronous dynamic random access memory (DDR RAM), or other random access solid state memory devices, and may include non-volatile memory, such as one or more magnetic disk storage devices such as internal hard disks and removable disks, magneto-optical disk storage devices, optical disk storage devices, flash memory devices, semiconductor memory devices, such as erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM), digital versatile disc read-only memory (DVD-ROM) disks, or other non-volatile solid state storage devices.

[0100] Input / output devices 690 may include peripherals, such as a printer, scanner, display screen, etc. For example, input / output devices 690 may include a display device such as a cathode ray tube (CRT), plasma or liquid crystal display (LCD) monitor for displaying information to a user, a keyboard, and a pointing device such as a mouse or a trackball by which the user can provide input to apparatus 600.

[0101] Any or all of the functions of the systems and apparatuses discussed herein may be performed by processor 610, and / or incorporated in, an apparatus or a system such as LiDAR system 300. Further, LiDAR system 300 and / or apparatus 600 may utilize one or more neural networks or other deep-learning techniques performed by processor 610 or other systems or apparatuses discussed herein.

[0102] One skilled in the art will recognize that an implementation of an actual computer or computer system may have other structures and may contain other components as well, and thatFIG. 6 is a high-level representation of some of the components of such a computer for illustrative purposes.

[0103] FIG. 7 is a block diagram illustrating a prior art LiDAR device 700 with a bandpass filter in the receiving light path. As shown in FIG. 7, LiDAR device 700 includes a light source 702 (e.g., a laser light source), which sends out laser light 703 with a wide bandwidth. For example, laser light 703 may have a center wavelength of 905 nm and a bandwidth of + / - 5 nm (i.e., total of 10 nm) if light source 702 is a semiconductor laser. LiDAR device 700 may also include a transmitter lens (or lens group) 704 that transmits the laser light 703 to downstream components of the LiDAR system or the FOV. In either case, the transmission laser light 705 provided by the LiDAR device 700 has a wide bandwidth (e g., same as the wide bandwidth of laser light 703 emitted by light source 702).

[0104] The transmission laser light 705 may illuminate one or more target objects in an FOV of the LiDAR device 700. The target objects reflect and / or scatter the transmission laser light 705 to form a part of return light. As shown in FIG. 7, the return light may often also include not only desired return light signals 707 formed based on the transmission laser light 705, but also straylight 709. Light signals 707 generally has a wide bandwidth similar to that of the transmission laser light 705 because it is formed from the reflecting / scattering of transmission laser light 705. For instance, if transmission laser light 705 has a center wavelength of 905 nm and bandwidth of + / - 5 nm, the light signal 707 in the return light may also have a wide bandwidth of about 10 nm. Straylight 709 may include any type of noise and / or interference light such as Sunlight, streetlight, laser light from other LiDAR devices, moonlight, headlight, taillight, etc. Therefore, straylight 709 may have a very wide bandwidth.

[0105] In LiDAR device 700, to reduce the impact of the straylight 709, a bandpass filter 706 is used in the receiving light path. The bandpass filter 706 may filter out the portion of straylight 709 that has wavelengths outside of the passband of the filler 706. To preserve as much signal power as possible for the desired light signals 707, which are formed based on the transmission laser light 705 (i.e., the desired return light), filter 706 is usually configured to have a wide passband corresponding to the bandwidth of the transmission laser light 705, such that all or a substantial portion of light signals 707 can pass through filter 706. For example, the bandpassfilter 706 may filter out any light outside of a passband of 10 nm with a center wavelength at 905 nm.

[0106] This bandpass filter 706, however, cannot filter out the portion of straylight 709 having the wavelengths that fall inside the same wavelength range as the transmission laser light 705, because such portion of straylight 709 would fall inside the passband of the filter 706. Thus, as shown in FIG. 7, the receiver lens (or lens group) 710 of device 700 provides filtered return light including signals 713 and straylight 711. All or a substantial portion of desired light signals 707, which are formed based on the target objects, pass through filter 706 and are received by receiver lens 710. Receiver lens 710 redirects the received signals to form light signals 713, which have a same wide bandwidth as the transmission laser light 705. For the straylight 709, the portion of it that falls outside of the passband of filter 706 is filtered out. The remaining of straylight 709, which has wavelength inside the passband of filter 706, passes through filter 706 and is received by receiver lens 710. Receiver lens 710 redirects the remaining straylight to form straylight 711. Straylight 711 may have the same or substantially the same wide wavelength range as that of the transmission laser light 705 (and light signals 707). Therefore, there are still quite some straylight remaining after filter 706. The remaining straylight 711 is noise and thus may cause erroneous detections by light detector 714, may interfere with desired light signals 713, and / or may cause downstream processing errors (e.g., mis-identification of an object).

[0107] One way to reduce such remaining straylight 711 is to narrow down filter 706’ s bandwidth to, e.g., 2 nm or even less and only allow light signals having essentially the center wavelength to pass through. The issue with this solution is that a large amount of signal power in desired signals 707 may also be lost because the bandwidth of the filtered signals is narrower than that of the bandpass filter 706. For instance, if the bandpass filter’s passband is only 2 nm, the bandwidth of the filtered signals may be only 1 nm or less, depending on the filter characteristics. As such, significant signal power may be lost due to filtering. When the filtered signals are received by the detector 714, they may or may not be detected due to the low signal power, thereby reducing the detectability of the detector 714. To compensate signal power loss, the power of the laser light source 702 must be increased. However, this means that the power of transmission laser light 705 is also increased. The transmission laser light power cannot be increased without limit because laser emitting devices have eye safety requirements. Increasing the transmission laser light power too much imposes eye safety risks. Therefore, only increasinglaser power to improve the signal power for signals passing through the narrow passband of the filter 706 in device 700 may not be possible or practical.

[0108] FIGs. 8A-8B are examples of a novel LiDAR system 800 for reducing straylight using synchronized filtering, in accordance with various embodiments. LiDAR system 800 includes a light source 802, transmitter optics 804, receiver optics 810 and detector 814. These components of system 800 can be the same or substantially the same as light source 310, optics in transmitter 320, and optics and the light detector in optical receiver and light detector 330, respectively. For example, transmitter optics 804 may include one or more of: a collimation lens, an optical filter, a beam-shifting device, an optical fiber array, a moveable or fixed mirror, a lens group, a prism, or a combination thereof. The receiver optics 810 may include one or more of: a collection lens, an optical filter, an optical fiber array, a beam-homogenizer, a moveable or fixed mirror, a lens group, a prism, or a combination thereof.

[0109] As shown in FIG. 8A, light source 802 emits laser light 803 having a first wavelength range. The first wavelength range may be a wide wavelength range such as 10 nm (e.g., + / - 5 nm with a center wavelength in the range of 700 nm - 20,000 nm). One example of the center wavelength is at 905 nm. The transmitter optics 804 are disposed in the transmission light path and receives the laser light 803. The transmission light path is the optical path from the light source 802 to the FOV of the LiDAR system 800 for transmitting laser light to illuminate one or more target objects in the FOV. The transmitter optics 804 thus are configured to provide transmission light 805 based on the laser light 803 having the first wavelength range. The transmission light 805, however, has a second wavelength range because of the synchronized filter structure 806. Typically, the second wavelength range is narrower than the first wavelength range. For instance, the second wavelength range has a center wavelength in the range of 700 nm - 20000 nm (e.g., at 905 nm) and a bandwidth of + / - 2 nm. Thus, using the synchronized filter structure 806, if the first wavelength range is centered at 905 nm with a bandwidth of 10 nm; the second wavelength range may also be centered at 905 nm with a narrower bandwidth of 4 nm. Synchronized filter structure 806 is described in greater detail below.

[0110] With continued reference to FIG. 8A, on the receiver side, a receiver may include receiver optics 810 and detector 814, which can be the same or similar as those described abovein optical receiver and light detector 330 of LiDAR system 300. The receiver optics 810 and detector 814 are disposed in the receiving light path to receive return light. The return light can include light signals 807 formed based on the transmission light 805 and straylight 809. The light signals 807 are formed based on the transmission light 805 so that it includes light scattered and / or reflected from one or more objects in the FOV. Therefore, these light signals 807 have the same wavelength as the transmission light 805. As described above, transmission light 805 has the second wavelength range, which has a narrower bandwidth than the first wavelength range (e.g., 4 nm bandwidth compared to 10 nm bandwidth). Therefore, the light signals 807 also have a narrower bandwidth (e.g., centered in the range of 700 nm - 20000 nm (e.g., at 905 nm) having a bandwidth of + / - 2 nm).[OUl] The straylight 809 can be noise and / or interference light such as sunlight, moonlight, streetlight, other vehicle’s LiDAR transmission light, vehicle’s headlight, taillight, reflected / scattered light from internal components of the present LiDAR system, etc. Straylight 809 usually has a wide bandwidth and thus needs to be filtered. In the configuration shown in FIG. 8A, at least a substantial portion of the return light, which includes the desired light signals 807 and undesired stray light 809, passes through the synchronized filter structure 806. The filtered light signals are received by the receiver optics 810 and passed to light detector 814. The filtered light signals received by the light detector 814 can include filtered light signals 813 and filtered straylight 811. Light signals 813 are filtered signals from light signals 807. Because light signals 807 already have a narrow bandwidth (e.g., the second wavelength range), there is no or little loss of the signal power when light signals 807 pass through synchronized filter structure 806. In other words, the synchronized filter structure 806 passes a substantial portion of the desired light signals 807 formed based on the transmission light 805 to detector 814.Thus, light signals 813 can have a good signal strength with a narrow bandwidth, thereby improving the detectability of detector 814. As described above, usually, when the transmission light 805 is filtered to reduce its bandwidth, the signal power will also be reduced and thus, to compensate for the signal power loss, the light source power needs to be increased. This may cause eye safety concerns. In this example, by using the synchronized filter structure 806, the bandwidth of the transmission light 805 is reduced (e.g., from 10 nm to 4 nm). As a result, even if the light source power is increased, the eye safety requirements can still be satisfied because the power increase occurs within the LiDAR system prior to the synchronized filter structure806. The transmission light 805 is filtered light with narrow bandwidth and therefore the power increase does not impose an eye safety issue same as the prior art LiDAR system 700 described above.

[0112] For straylight 809, the synchronized filter structure 806 can also filter out at least a portion of the straylight having wavelengths outside of the second wavelength range. For example, if the transmission light 805 has the second wavelength range (e.g., the center wavelength in the range of 700 nm - 20000 nm (e.g., at 905 nm) and a bandwidth of + / - 2 nm), the synchronized filter structure 806 can be configured to remove a substantial portion of straylight 809 that falls out of this second wavelength range. For instance, if straylight 809 has a 10 nm bandwidth, after passing through the synchronized filter structure 806, its bandwidth reduces to 4 nm bandwidth.

[0113] With reference still to FIG. 8A, in some embodiments, a synchronized filter structure includes one or more bandpass filters having substantially the same passband; and the synchronized filter structure 806 is coupled to both the transmitter and the receiver. For example, as shown in FIG. 8A, in this example, synchronized filter structure 806 includes a first bandpass filter 806A and a second bandpass filter 806B. The first bandpass filter 806A is disposed in the transmission light path and the second bandpass filter is disposed in the receiving light path. In some examples, the first bandpass filter 806A and the second bandpass filter 806B have substantially the same passband. For example, they may both allow light having a center wavelength at 905 nm with a bandwidth of + / - 2nm to pass through, but filter out any light signals fall outside of this wavelength range.

[0114] FIG. 8A shows an example of synchronized filter structure 806 where two individual bandpass filters 806A and 806B are used, one for the transmission light path and one for the receiving light path. By using two bandpass filters, the synchronized filter structure 806 provides flexibilities as to the locations the two bandpass filters can be placed, the size of each filter, the type of filters, and other aspects. For instance, while FIG. 8A illustrates that filter 806A is placed downstream of the transmitter optics 804 in the transmission light path, it can be placed in other places in the transmission light path, as described below. Similarly, filter 806B does not need to be placed upstream of receiver optics 810 and can be placed elsewhere in the receiving light path. The sizes of the filters 806A and 806B can be the same or different, depending onfactors like the optical aperture requirements for the transmission and receiving light paths, the types of the filters used, and other things. In one example, the LiDAR system 800 may have large dimensions; the transmission light path and the receiving light path may be relatively further away from each other, and / or the optical components in the transmission light path and in the receiving light path may be arranged at particular angles / orientations (e.g., not in parallel as shown in FIG. 8A). In these configurations, using two bandpass filters can provide the flexibility for independently incorporating them into the transmission light path and the receiving light path at their respective desired positions.

[0115] FIG. 8B illustrates another embodiment where the synchronized filter structure 806 includes a single bandpass filter shared between the transmission light path and the receiving light path. FIG. 8B is the same as FIG. 8A, except that the synchronized filter structure 806 is formed by a single bandpass filter. The single bandpass filter is placed both in the transmission light path and the receiving light path. The benefit of using the single bandpass filter is that there is no filter passband mismatch compared to if two filters are used. If two bandpass filters are used (as shown in FIG. 8A), the two bandpass filters should ideally have their passbands and other optical characteristics matched exactly with each other. Sometimes, mismatch between the two filters may occur, but should be minimized, or may be tolerable. Using a single passband filter can remove the need for matching the characteristics of the two bandpass filters. In some examples, the single bandpass filter in structure 806 can be used if the LiDAR system 800 has a small and compact dimension, or a co-axial configuration, such that the transmission light path and the receiver light path are near each other or at least partially overlap.

[0116] FIGs. 9A-9D are various examples of a transmitter of a LiDAR system for reducing straylight using synchronized filtering, in accordance with various embodiments. As described above, if a synchronized filter structure 806 includes two individual bandpass filters, one can be placed in various places in the transmission light path and the other one can be placed in various places in the receiving light path. FIG. 9A illustrates one example, where a first bandpass filter 8O6A1 of a synchronized filter structure is disposed downstream of the light source 802 at a position between the light source 802 and transmitter optics 804. FIG. 9B illustrates another example, where a first bandpass filter 806 A2 of the synchronized filter structure is disposed downstream of the light source 802 at a position between any two transmitter optics 804A and 804B. The transmitter optics 804 may include, for example, lens, lens groups, mirrors, prisms,optical fibers, etc., for redirecting the light 803 from the light source 802. Thus, the first bandpass filter 8O6A2 can be placed anywhere inside the transmitter optics 804 between two optical components (e.g., between optical fibers and a collimation lens).

[0117] FIG. 9C illustrates another example, where a first bandpass filter 8O6A3 of the synchronized filter structure is disposed downstream of the light source 802 at a position between the one or more transmitter optics 804 and a steering mechanism 840. The steering mechanism 840 receives the transmission light 805 from the first bandpass filter 8O6A3 and scans the transmission light 805 in one or more directions to a field-of-view (FOV). The steering mechanism 840 can be substantially the same or similar to steering mechanism 340 described above. For example, steering mechanism 840 can include one or more polygon mirrors, one or more galvanometer mirrors, one or more folding mirrors, lens, prisms, etc., for scanning the transmission light 805 in two dimensions (e.g., the horizontal and vertical dimensions).

[0118] FIG. 9D illustrates another example, where a first bandpass filter 8O6A4 of the synchronized filter structure is disposed downstream of the light source 802 at a position downstream of the steering mechanism 840 in the transmission light path. In one example, the first bandpass filter 8O6A4 may have an optical aperture that is large enough to encompass all areas of scanning as the steering mechanism 840 moves. In another example, the first bandpass filter 8O6A4 and the steering mechanism 840 may be mounted to a same movable platform such that the first bandpass filter 806 A4 moves together with the steering mechanism 840.

[0119] FIGs. 10A-10D are examples of a receiver of a LiDAR system for reducing straylight using synchronized filtering, in accordance with various embodiments. Similar to the filter disposed in the transmission light path, the filter disposed in the receiving light path can be at various positions too. FIG. 10A illustrates an example where the second bandpass filter 8O6B1 is disposed upstream of the detector 814 in the receiving light path at a position upstream of a steering mechanism 840 in the receiving light path. In this example, the steering mechanism 840 is substantially the same or similar to steering mechanism 340 in LiDAR system 300. The steering mechanism 840 receives the filtered return light and directs the filtered return light to the one or more receiver optics 810. As described above, the return light includes desired light signals 807 and undesired straylight 809. The light signals 807 have the second wavelength range, which is the same as the wavelength range of the transmission light 805. Therefore, lightsignals 807, or a substantial portion thereof, can pass through filter 8O6B1, which has a narrow passband corresponding to the second wavelength range. The straylight 809, after passing through the filter 8O6B1, can be filtered out except the portion in the narrow passband corresponding to the second wavelength range. In one example, the second bandpass filter 8O6B1 may have an optical aperture that is large enough to encompass all areas of scanning as the steering mechanism 840 moves, such that it can filter return light coming from all angles of the scanning. In another example, the second bandpass filter 8O6B1 and the steering mechanism 840 may be mounted to a same movable platform such that the second bandpass filter 8O6B1 moves together with the steering mechanism 840.

[0120] FIG. 10B illustrates an example where the second bandpass filter 8O6B2 is disposed upstream of the detector 814 in the receiving light path at a position between the steering mechanism 840 and the receiver optics 810. In this example, the steering mechanism 840 directs unfiltered return light to second bandpass filter 8O6B2. Second passband filter 8O6B2 filters the return light including the desired light signals 807 and the undesired straylight 809 as described above, and direct the filtered return light to the receiver optics 810, which in turn passes the filtered return light to detector 814.

[0121] FIG. 10C illustrates another example, where a second bandpass filter 8O6B3 of the synchronized filter structure is disposed upstream of the detector 814 in the receiving light path at a position between any two receiver optics 810A and 810B. The receiver optics 810 may include, for example, lens, lens groups, mirrors, prisms, optical fibers, etc., for redirecting return light from a steering mechanism to light detector 814. Thus, the second bandpass filter 8IOB3 can be placed anywhere inside the receiver optics 810 between two optical components (e.g., between a collection lens and a folding mirror).

[0122] FIG. 10D illustrates another example, where a second bandpass filter 8O6B4 of the synchronized filter structure is disposed upstream of the detector 814 in the receiving light path at a position between the receiver optics 810 and detector 814. In this example, the return light is filtered after it passes the steering mechanism (not shown in FIG. 10D) and receiver optics 810, but before the detector 814. The filter 8O6B4 can therefore be placed close to the detector 814 and in some examples, integrated with detector 814.

[0123] It is understood that FIGs. 9A-9D and 10A-10D provide examples of the positions of the first bandpass filter and the second bandpass filter, respectively. The filters can be also placed elsewhere not limited to the examples described above.

[0124] FIGs. 11A-11C are various examples of a LiDAR system for reducing straylight using a single bandpass filter for synchronized filtering, in accordance with various embodiments. As described above, the synchronized filter structure 806 can include a single bandpass filter (instead of two) for both the transmission light path and the receiving light path. FIG. 11 A illustrates one example where the single bandpass filter 806i is disposed downstream of the light source 802 in the transmission light path and upstream of the detector 814 in the receiving light path at a position between the one or more transmitter optics 804 and a steering mechanism 840 and between the steering mechanism 840 and the one or more receiver optics 810. Thus, the steering mechanism 840 (e.g., substantially the same as or similar to steering mechanism 340) scans the transmission light 805, which has been filtered to have the second wavelength range (e g., a narrow bandwidth of 4 nm). The steering mechanism 840 receives the desired return light signal 807 and straylight 809, and forwards them to the same filter 806i for filtering. As such, the receiving optics 810 can receive filtered return light, which includes the signals 813 having the second wavelength range (e.g., substantially the same as the transmission light 805 and the return light signals 807) and filtered straylight 811. The filtered straylight 811 has significantly less noise and interference because return light outside the second wavelength range has been filtered out. In one example, the bandpass filter 806i may have an optical aperture that is large enough to encompass all areas of scanning as the steering mechanism 840 moves, such that it can filter return light coming from all angles of the scanning. In another example, the bandpass filter 806i and the steering mechanism 840 may be mounted to a same moving platform such that the bandpass filter 806i moves together with the steering mechanism 840.

[0125] FIG. 1 IB illustrates one example where the single bandpass filter 806i is disposed downstream of the light source 802 in the transmission light path and upstream of the detector 814 in the receiving light path at a position upstream of the steering mechanism 840 in the transmission light path. For instance, in the example shown in FIG. 1 IB, the single bandpass filter 8O62 can be placed both between the light source 802 and transmitter optics 804 and between the receiver optics 810 and light detectors 814. Thus, light 803 from the light source 802 are filtered to generate the transmission light 805 having the second wavelength range (e.g., thenarrow bandwidth of 4 nm). In the meantime, the return light (including desired return light signals 807 and straylight 809) is filtered before it reaches the light detector 814, eliminating the noise and interferences as much as possible. The light detector 814 still receives filtered light signals 813 with the second wavelength range and the filtered straylight 811 (which is a small portion of noise or interference fall inside the passband of filter 8O62).

[0126] FIG. 11C illustrates one example where the single bandpass filter 8O63 is disposed downstream of the light source 802 in the transmission light path and upstream of the detector 814 in the receiving light path at a position upstream of a steering mechanism 840 in the receiving light path. In this example, the single bandpass filter 8O63 is disposed downstream of steering mechanism 840 in the transmission light path but upstream of steering mechanism 840 in the receiving light path. Thus, light 803 from the light source 802 and scanned by steering mechanism 840 is filtered to generate the transmission light 805 having the second wavelength range (e.g., the narrow bandwidth of 4 nm). In the meantime, the return light (including desired return light signals 807 and straylight 809) is filtered before it reaches the steering mechanism 840, eliminating the noise and interferences as much as possible. The light detector 814 still receives filtered light signals 813 with the second wavelength range and the filtered straylight 811 (which is a small portion of noise or interference fall inside the passband of filter 8O62). In this example, the bandpass filter 8O63 may have an optical aperture that is large enough to encompass all areas of scanning as the steering mechanism 840 moves, such that it can filter return light coming from all angles of the scanning. In another example, the bandpass filter 8O63 and the steering mechanism 840 may be mounted to a same moving platform such that the bandpass filter 8O63 moves together with the steering mechanism 840.

[0127] FIGs. 11 A-l 1C are examples and do not limit the positions of the single bandpass filter. So long as the single passband filter is placed to provide a narrowband transmission light for scanning the FOV and provide a narrowband return light for detecting, it can be placed anywhere in the LiDAR system. In the description herein, “upstream” and “downstream” refer to the relative positions between optical components in a light path. For instance, for any particular light path, if light flows from component A to component B, component A is positioned upstream of component B, and component B is positioned downstream of component A.

[0128] In the above examples, the steering mechanism (e.g., 840) can include one or more of: a rotatable polygon mirror, an oscillation mirror, an oscillation prism, or a combination thereof. The steering mechanism can be controlled to perform two-dimensional scanning (e.g., a horizontal direction and a vertical direction). The controller can be control circuitry 350 as shown in FIG. 3 and described above.

[0129] In some embodiments, the controller can further be configured to set a power level of the laser light emitted by the light source to compensate the power loss of the transmission light caused by the synchronized filter structure. As described above, a synchronized filter structure can reduce the bandwidth of the transmission light (e.g., from a bandwidth of 10 nm to a bandwidth of 4 nm). During the filtering, a part of the signal power may be lost. Therefore, the transmission light 805 may have less power compared to the light 803 emitted by the light source 802 (as shown in FIGs. 8A and 9A). Because the transmission light 805 may have less power, the detection range of the LiDAR system may be compromised. For instance, it may be reduced from 250 m to only 100 m. To compensate for such a signal power loss, the controller can increase the power level of the laser light emitted by the light source such that it is set at an increased level compared to the power level of the laser light emitted by the light source if no synchronized filter structure is used. In one example, the amount of power level increased by the controller is inversely proportional to the power loss caused by the synchronized filter structure. Thus, the more signal loss caused by the synchronized filter structure, the greater amount of power level increases the controller needs to set. However, the controller can still set the power level of the transmission light compensated for the power loss such that it is within an eye-safe laser power threshold. In other words, the controller cannot increase the power level of laser light 803 emitted by the light source 802 too much such that the transmission light 805 (which is filtered light by the synchronized filter structure 806) is no longer safe according to the laser eye safety standard. In some examples, the laser eye safety standard is set by taking into account the scanning speed of the LiDAR system and the exposure time and power of the transmission light with respect to eyes of live beings.

[0130] FIG. 12 is a flowchart of an example method 1200 of reducing straylight using a synchronized filtering structure, in accordance with various embodiments. In block 1202, a light source (e.g., 802) emits laser light having a first wavelength range. In block 1204, a transmitter, which includes one or more transmitter optics (e.g., 804) disposed in a transmission light path,provides transmission light (e.g., 805) based on the laser light having the first wavelength range. In block 1206 a receiver, which includes a detector (e.g., 814) and one or more receiver optics (e.g., 810) disposed in a receiving light path, receives return light comprising straylight (e.g., 809) and light signals (e.g., 807) formed based on the transmission light.

[0131] In some examples, blocks 1206-1210 are performed by a synchronized filter structure (e g., 806) comprising one or more bandpass filters having substantially the same passband. The synchronized filter structure is coupled to both the transmitter and the receiver. In block 1206, the synchronized filter structure reduces the bandwidth of the laser light from a first wavelength range to a second wavelength range such that the transmission light has the second wavelength range. In block 1208, the synchronized filter structure filters out at least a portion of the straylight having wavelengths outside of the second wavelength range. In block 1210, the synchronized filter structure passes a substantial portion of the light signals formed based on the transmission light to the detector.

[0132] The foregoing specification is to be understood as being in every respect illustrative and exemplary, but not restrictive, and the scope of the invention disclosed herein is not to be determined from the specification, but rather from the claims as interpreted according to the full breadth permitted by the patent laws. It is to be understood that the embodiments shown and described herein are only illustrative of the principles of the present invention and that various modifications may be implemented by those skilled in the art without departing from the scope and spirit of the invention. Those skilled in the art could implement various other feature combinations without departing from the scope and spirit of the invention.

Claims

CLAIMSWHAT IS CLAIMED IS:

1. A light ranging and detection (LiDAR) system for reducing straylight using synchronized filtering, the system comprising: a light source emitting laser light having a first wavelength range; a transmitter comprising one or more transmitter optics disposed in a transmission light path, the transmitter being configured to provide transmission light based on the laser light having the first wavelength range; a receiver comprising a detector and one or more receiver optics disposed in a receiving light path, the receiver being configured to receive return light comprising straylight and light signals formed based on the transmission light; and a synchronized filter structure comprising one or more bandpass filters having substantially the same passband, wherein the synchronized filter structure is coupled to both the transmitter and the receiver, the synchronized filter structure being configured to perform: reducing a bandwidth of the laser light from the first wavelength range to a second wavelength range such that the transmission light has the second wavelength range, filtering out at least a portion of the straylight having wavelengths outside of the second wavelength range, and passing a substantial portion of the light signals formed based on the transmission light to the detector.

2. The system of claim 1, wherein the first wavelength range has a center wavelength in a range of 700 nm - 20000 nm and a bandwidth of at least + / - 5nm.

3. The system of any of claims 1-2, wherein the second wavelength range has a center wavelength in a range of 700 nm - 20000 nm and a bandwidth of + / - 2nm.

4. The system of any of claims 1-2, wherein the one or more bandpass filters of the synchronized filter structure comprise:a first bandpass filter disposed in the transmission light path; and a second bandpass filter disposed in the receiving light path, wherein the first bandpass filter and the second bandpass filter have substantially the same passband.

5. The system of claim 4, wherein the first bandpass filter is disposed downstream of the light source in the transmission light path at a position: between the light source and the one or more transmitter optics; between any two transmitter optics; between the one or more transmitter optics and a steering mechanism, wherein the steering mechanism receives the transmission light from the first bandpass filter and scans the transmission light in one or more directions to a field-of-view (FOV); or downstream of the steering mechanism in the transmission light path.

6. The system of claim 4, wherein the second bandpass filter is disposed upstream of the detector in the receiving light path at a position: upstream of a steering mechanism in the receiving light path, wherein the steering mechanism receives filtered return light and directing the filtered return light to the one or more receiver optics; between the steering mechanism and the one or more receiver optics; between any two receiver optics; or between the one or more receiver optics and the detector.

7. The system of claims 1-2, wherein the one or more bandpass filters of the synchronized filter structure comprise a single bandpass filter shared between the transmission light path and the receiving light path.

8. The system of claim 7, wherein the single bandpass filter is disposed downstream of the light source in the transmission light path and upstream of the detector in the receiving light path at a position: between the one or more transmitter optics and a steering mechanism and between the steering mechanism and the one or more receiver optics;upstream of the steering mechanism in the transmission light path; or upstream of the steering mechanism in the receiving light path.

9. The system of any of claims 1-2, wherein the transmitter optics comprises one or more of: a collimation lens, an optical filter, a beam-shifting device, an optical fiber array, a moveable or fixed mirror, a lens group, a prism, or a combination thereof.

10. The system of any of claims 1-2, wherein the receiver optics comprise one or more of: a collection lens, an optical filter, an optical fiber array, a beam-homogenizer, a moveable or fixed mirror, a lens group, a prism, or a combination thereof.

11. The system of any of claims 1-2, further comprising a steering mechanism comprising one or more of: a rotatable polygon mirror, an oscillation mirror, an oscillation prism, or a combination thereof.

12. The system of any of claims 1-2, further comprising control circuitry configured to: set a power level of the laser light emitted by the light source to compensate a power loss of the transmission light caused by the synchronized filter structure.

13. The system of claim 12, wherein the power level of the laser light emitted by the light source is set at an increased level compared to the power level of the laser light emitted by the light source if no synchronized filter structure is used.

14. The system of claim 13, wherein an amount of power level increased is inversely proportional to the power loss caused by the synchronized filter structure.

15. The system of claim 12, wherein the power level of the transmission light compensated for the power loss is within an eye-safe laser power threshold.

16. A vehicle comprising a LiDAR system for reducing straylight using synchronized filtering, the system comprising: a light source emitting laser light having a first wavelength range;a transmitter comprising one or more transmitter optics disposed in a transmission light path, the transmitter being configured to provide transmission light based on the laser light having the first wavelength range; a receiver comprising a detector and one or more receiver optics disposed in a receiving light path, the receiver being configured to receive return light comprising straylight and light signals formed based on the transmission light; and a synchronized filter structure comprising one or more bandpass filters having substantially the same passband, wherein the synchronized filter structure is coupled to both the transmitter and the receiver, the synchronized filter structure being configured to perform: reducing a bandwidth of the laser light from the first wavelength range to a second wavelength range such that the transmission light has the second wavelength range, filtering out at least a portion of the straylight having wavelengths outside of the second wavelength range, and passing a substantial portion of the light signals formed based on the transmission light to the detector.

17. A method for reducing straylight using synchronized filtering, the method comprising: emitting, by a light source, laser light having a first wavelength range; providing, by a transmitter comprising one or more transmitter optics disposed in a transmission light path, transmission light based on the laser light having the first wavelength range; receiving, by a receiver comprising a detector and one or more receiver optics disposed in a receiving light path, return light comprising straylight and light signals formed based on the transmission light; and performing, by a synchronized filter structure comprising one or more bandpass filters having substantially the same passband, wherein the synchronized filter structure is coupled to both the transmitter and the receiver: reducing a bandwidth of the laser light from the first wavelength range to a second wavelength range such that the transmission light has the second wavelength range,filtering out at least a portion of the straylight having wavelengths outside of the second wavelength range, and passing a substantial portion of the light signals formed based on the transmission light to the detector.

18. The method of claim 17, wherein the first wavelength range has a center wavelength in a range of 700 nm - 20000 nm and a bandwidth of at least + / - 5nm.

19. The method of any of claims 17-18, wherein the second wavelength range has a center wavelength in a range of 700 nm - 20000 nm and a bandwidth of + / - 2nm.

20. The method of any of claims 17-18, further comprising: setting a power level of the laser light emitted by the light source to compensate a power loss of the transmission light caused by the synchronized filter structure.

21. The method of claim 20, wherein the power level of the laser light emitted by the light source is set at an increased level compared to the power level of the laser light emitted by the light source if no synchronized filter structure is used.

22. The method of claim 21, wherein an amount of power level increased is inversely proportional to the power loss caused by the synchronized filter structure.

23. The method of claim 20, wherein the power level of the transmission light compensated for the power loss is within an eye-safe laser power threshold.

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