Lidar for installation under vehicle windshield

Abstract

A LiDAR system mountable inside a vehicle is provided. The system includes a semiconductor-based laser configured to emit laser light having a wavelength. The system further includes a scanning mechanism configured to pass the laser light through a windshield of the vehicle to a FOV. The scanning mechanism is further configured to receive return light formed based on the laser light transmitted through the windshield. The semiconductor¬ based laser is configured such that: the wavelength of the laser light is in a wavelength range that is substantially transparent to the windshield of the vehicle and insensitive to human eyes, the laser light is polarized, such that a transmission rate of the laser light is no less than a threshold at a predetermined incident angle of the laser light. The system further includes a detector configured to detect the return light received through the windshield.

Description

LIDAR FOR INSTALLATION UNDER VEHICLE WINDSHIELD CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 709,990, filed October 21, 2024, entitled “LIDAR FOR INSTALLATION UNDER VEHICLE WINDSHIELD”, 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 optical scanning and, more particularly, to a light ranging and detection (LiDAR) system mountable inside a vehicle.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 nonscanning 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 ToF technique 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 one embodiment of the present disclosure, a LiDAR system mountable inside a vehicle is provided. The system includes a semiconductor-based laser configured to emit laser light having a wavelength. The system further includes a scanning mechanism configured to pass the laser light through a windshield of the vehicle to a FOV. The scanning mechanism is further configured to receive return light formed based on the laser light transmitted through the windshield. The semiconductor-based laser is configured such that: the wavelength of the laser light is in a wavelength range that is substantially transparent to the windshield of the vehicle and insensitive to human eyes; and the laser light is polarized, such that a transmission rate of the laser light is no less than a threshold at a predetermined incident angle of the laser light. The system further includes a detector configured to detect the return light received through the windshield.

[0005] In one embodiment of the present disclosure, a vehicle including a LiDAR system mountable inside the vehicle is provided. The system includes a semiconductor-based laser configured to emit laser light having a wavelength. The system further includes a scanning mechanism configured to pass the laser light through a windshield of the vehicle to a FOV. The scanning mechanism is further configured to receive return light formed based on the laser light transmitted through the windshield. The semiconductor-based laser is configured such that: the wavelength of the laser light is in a wavelength range that is substantially transparent to the windshield of the vehicle and insensitive to human eyes; and the laser light is polarized, such that a transmission rate of the laser light is no less than a threshold at a predetermined incident angle of the laser light. The system further includes a detector configured to detect the return light received through the windshield.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] 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.

[0007] FIG. 1 illustrates one or more example LiDAR systems disposed or included in a motor vehicle.

[0008] FIG. 2 is a block diagram illustrating interactions between an example LiDAR system and multiple other systems including a vehicle perception and planning system.

[0009] FIG. 3 is a block diagram illustrating an example LiDAR system.

[0010] FIG. 4A is a block diagram illustrating an example fiber-based laser source.

[0011] FIG. 4B is a block diagram illustrating an example semiconductor-based laser source.

[0012] FIGs. 5 A-5C illustrate an example LiDAR system using pulse signals to measure distances to objects disposed in a field-of-view (FOV).

[0013] FIG. 6 is a block diagram illustrating an example apparatus used to implement systems, apparatus, and methods in various embodiments.

[0014] FIG. 7 is a diagram illustrating an example of LiDAR systems mountable at different positions of a vehicle.

[0015] FIG. 8 is a diagram illustrating an example of a LiDAR system mountable inside a vehicle in accordance with various embodiments.

[0016] FIG. 9 is a diagram illustrating an example of transmission spectrum through different types of vehicle windshield glasses with and without tinting in accordance with various embodiments.

[0017] FIGs. 10A-10B are diagrams illustrating examples of water or humidity influence on transmission, in accordance with various embodiments.

[0018] FIG. 11 A is a diagram illustrating an example of a LiDAR system emitting laser light at different incident angles with respect to the windshield glass in accordance with various embodiments.

[0019] FIG. 1 IB is a diagram illustrating an example of transmission of clear laminate windshield in accordance with various embodiments.

[0020] FIGs. 12 A and 12B are diagrams illustrating examples of photon detection efficiency (PDE) for single photon avalanche diode (SPAD) arrays in accordance with various embodiments.DETAILED DESCRIPTION

[0021] 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, thatsuch 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.

[0022] Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise:

[0023] 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.

[0024] 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.

[0025] The term “based on” is not exclusive and allows for being based on additional factors not described unless the context clearly dictates otherwise.

[0026] 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.

[0027] 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 sensor could be termed a second sensor and, similarly, a second sensor could be termed a first sensor, without departing from the scope of the various described examples. The first sensor and the second sensor can both be sensors and, in some cases, can be separate and different sensors.

[0028] In addition, throughout the specification, the meaning of “a”, “an”, and “the” includes plural references, and the meaning of “in” includes “in” and “on”.

[0029] Although some of the various embodiments presented herein constitute a single combination of inventive elements, it should be appreciated that the inventive subject matteris 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.

[0030] 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.

[0031] 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.

[0032] LiDAR is a three-dimensional (3D) sensing device that is increasingly being used in autonomous driving vehicles and vehicles with high-level advanced driver assistance system (ADAS) features. A LiDAR system is often mounted on, or integrate with, a rooftop of a vehicle. Because such a LiDAR system is mounted at a high position of the vehicle and thus has un-obstructed FOV, the LiDAR system can have a good performance. However, the protrusion of the LiDAR system represents a break of envelope or contour of the vehicle. As a result, the vehicle aerodynamic properties may be negatively impacted, which in turn impacts the performance of the vehicle. It may also increase an overall adoption cost and complexity to include a LiDAR system to the vehicle, because there needs to be a specialized design for the envelope or the contour of the vehicle to fit with the protrusion of the LiDAR system. Further, another challenge associated with mounting the LiDAR system to the rooftop of vehicle is the need for a separate clean window for the LiDAR system, because the window of the LiDAR system can be easily obstructed by fog, moisture, tree leaves, etc. Adding a cover or a case to keep the LiDAR system’s windows clean may be an option. But this option also increases the overall adoption cost. Therefore, the rooftop of vehicle may not be a desired position for placing a LiDAR system.

[0033] Placing a LiDAR system behind a windshield glass of a vehicle can alleviate or eliminate the above-described problems. However, most LiDAR systems operate in infrared wavelengths, and the transmission rate of the infrared lights through regular windshield glass is very low. As a result, special types of IR-transparent windshield glass with higher cost were used in vehicles. This in turn increases an overall adoption cost. Replacing regular windshield glass with the special types of IR-transparent windshield glass may also increase complexity in designing and manufacturing the vehicle, especially if the vehicle windshield has integrated sensors (e.g., rain sensors, light sensors, etc.). Therefore, there is a need for a LiDAR system that can be mountable inside the vehicle and can still be functional to provide laser light with good transmission rate when passing through a regular vehicle windshield.

[0034] This disclosure provides a LiDAR system mountable inside a vehicle. The system includes a semiconductor-based laser configured to emit laser light having a wavelength. The wavelength of the laser light is in a wavelength range that is substantially transparent to the windshield of the vehicle, so that there is no need to replace the windshield glass with the high-cost IR-transparent windshield glass. Further, the wavelength of the laser light is in a wavelength range that is insensitive to human eyes. The laser light is also polarized. At a predetermined incident angle of the laser light, the transmission rate of the laser light is noless than a threshold. The LiDAR system further includes a scanning mechanism configured to pass the laser light through a windshield of the vehicle to a FOV. The scanning mechanism is further configured to receive return light formed based on the laser light transmitted through the windshield. The system further includes a detector configured to detect the return light received through the windshield.

[0035] Embodiments of present invention are described below. In various embodiments of the present invention, a LiDAR system mountable inside a vehicle is provided. The system includes a semiconductor-based laser configured to emit laser light having a wavelength. The system further includes a scanning mechanism configured to pass the laser light through a windshield of the vehicle to a FOV. The scanning mechanism is further configured to receive return light formed based on the laser light transmitted through the windshield. The semiconductor-based laser is configured such that: the wavelength of the laser light is in a wavelength range that is substantially transparent to the windshield of the vehicle and insensitive to human eyes; and the laser light is polarized, such that a transmission rate of the laser light is no less than a threshold at a predetermined incident angle of the laser light. The system further includes a detector configured to detect the return light received through the windshield.

[0036] In another example, a vehicle including a LiDAR system mountable inside the vehicle is provided. The system includes a semiconductor-based laser configured to emit laser light having a wavelength. The system further includes a scanning mechanism configured to pass the laser light through a windshield of the vehicle to a FOV. The scanning mechanism is further configured to receive return light formed based on the laser light transmitted through the windshield. The semiconductor-based laser is configured such that: the wavelength of the laser light is in a wavelength range that is substantially transparent to the windshield of the vehicle and insensitive to human eyes; and the laser light is polarized, such that a transmission rate of the laser light is no less than a threshold at a predetermined incident angle of the laser light. The system further includes a detector configured to detect the return light received through the windshield.

[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 scanningbased 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 system transmits 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 corner; 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 comer; LiDAR system 120D is attached to vehicle100 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 comer; 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 each of 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-1201. 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-controlledenvironment, 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, medium-range 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 mediumrange 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 is travelling 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 interpretingdata 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 narrow-focus 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., rearview 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 blind spot, 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, checkingblind 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., rear-view 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 communicationpath 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 can combine 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 subsystem 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 machine-learning 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 LiD AR 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-system 224 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 LiD AR 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 subsystem 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 formaking such a prediction. Such techniques include, for example, constant velocity or acceleration models, constant turn rate and velocity / acceleration 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 current location 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 transmitter320, 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 light source 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:YVC>4) 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 enablingthe 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. Fiber-based 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, pre-amplifier(s) 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-reflectors 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 orquantum 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 a highly 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 beused 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. For laser 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 system300 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 340 will 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 light detector, 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 LiDARtransmitter and receiver (collectively referred to as transceiver) to scan the laser beam. Solidstate scanning directs the laser beam to various positions through the FOV without mechanically moving any macroscopic components such as the transceiver. Solid-state scanning mechanisms include, for example, optical phased arrays based steering and flash LiD AR 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 LiD AR system using solid-state scanning may also be referred to as a non-mechanical scanning or simply non-scanning LiD AR system (a flash LiD AR system is an example non-scanning LiD AR 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), single-plane 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 one-dimensional 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 350 determines 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 atransmitted 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, self-cleaning 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 communicationspaths 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. 5 A (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 determinethe 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 other dimension(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 orimage 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 (w+1) dimensional data. This is because the LiDAR system can measure the depth of an object or the rang e / 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 densityof 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, magneto-optical 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 the FIGS. 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 600comprises 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 magneticdisk 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 that FIG. 6 is a high-level representation of some of the components of such a computer for illustrative purposes.

[0103] FIG. 7 is a diagram illustrating an example of LiDAR systems mounted at different positions of a vehicle 706. LiDAR systems rely on line-of-sight to function, and therefore LiDAR systems often need to have un-obstructed FOV. As shown in FIG. 7, a LiDAR system 701 is mounted on, or integrate with, a rooftop of vehicle 706. Because LiDAR system 701 is mounted at a high position of vehicle 706 and has un-obstructed FOV, the LiDAR system 701 can have a good performance. However, the protrusion of LiDAR system 701 represents a break of envelope or contour of the vehicle 706. As a result, the vehicle 706 aerodynamic properties may be negatively impacted, and in turn impacts the performance of the vehicle 706. It may also increase an overall adoption cost and complexity to include a LiDAR system 701 to the vehicle 706, because there needs to be a specialized design for the envelope or the contour of the vehicle 706 to fit with the protrusion of the LiDAR system 701. Further, another challenge associated with mounting the LiDAR system 701 to the rooftop of vehicle 706 is the need for a separate clean window for LiDAR system701, because the window of LiDAR system 701 may easily become obstructed by fog, moisture, tree leaves, etc. Adding a cover or a case to keep the LiDAR system 701’s window clean is an option, but this option may also increase the overall adoption cost. Therefore, the rooftop of vehicle 706 is not a desired position for placing LiDAR systems.

[0104] As shown in FIG. 7, another position for mounting a LiDAR system 703 is at a front end of the vehicle 706, e.g., either inside a front grille or integrated with a headlamp.However, this position limits the height of the LiDAR system 703, thus greatly reduces the 3D coverage of the environment, and in turn degrades the performance of the LiDAR system 703. Further, being mounted at the front end of vehicle 706, the LiDAR system 703 is much more susceptible to stone chips and contaminants by dust and dirt during driving, because it is at a low and front place. As described above, using a separate clean window for LiDAR system 703 is another challenge. Therefore, the front end of vehicle 706 may also not be a desired position for placing LiDAR systems.

[0105] As shown in FIG. 7, another LiDAR system 702 may be positioned behind a windshield glass of the vehicle 706. This position eliminates the above-described problems, and thus it can be a desired place for placing LiDAR systems. However, most LiDAR systems operate in infrared wavelengths, and the transmission rate of the infrared lights through a regular windshield glass can be very low. As a result, special types of IR-transparent windshield glass need to be used if a LiDAR system 702 is placed inside vehicle 706 behind its windshield glass. Using special types of IR-transparent glass in turn increases an overall adoption cost. Replacing regular windshield glass with the special types of IR-transparent windshield glass may also increase complexity associated with designing and manufacturing the vehicle 706. Therefore, there is a need for a LiDAR system that can be mountable inside a vehicle behind a regular windshield glass but can still be functional to provide laser light with good transmission rate.

[0106] FIG. 8 is a block diagram illustrating an example of a LiDAR system 800 mountable inside a vehicle in accordance with various embodiments. As described above, the LiDAR system 800 can be mounted to a position that enables good FOV coverage for near and far objects. Further, the LiDAR system 800, mounted inside a vehicle, is shielded from contamination and external objects during driving, and there is no need for a separate clean LiDAR system window or maintenance.

[0107] The LiDAR system 800 can be the same or similar to system LiDAR system 300. For example, the LiDAR system 800 also includes a transmitter 802, a receiver 812, a scanning mechanism 806, and semiconductor-based laser 804. They are similar to transmitter 320,optical receiver and light detector 330, steering mechanism 340, and light source 310, respectively, in LiDAR system 300. For simplicity, the LiDAR system 800 in FIG. 8 may not include certain components like control circuitry. As shown in FIG. 8, the LiDAR system 800 includes a semiconductor-based laser 804 in a transmitter 802, a scanning mechanism 806, and a detector 814 in a receiver 812. The semiconductor-based laser 804 is configured to emit laser light 832 having a wavelength denoted as . The scanning mechanism 806 is configured to pass the laser light 832 through a windshield 808 of the vehicle to a FOV. The laser light 832 may be reflected or scattered by one or more objects (e.g., object 810) in the FOV to form return light 834. The scanning mechanism 806 is further configured to receive the return light 834 formed based on the laser light 832 transmitted through the windshield 808. The detector 814 is configured to detect the return light 834 received through the windshield 808.

[0108] In some embodiments, the semiconductor-based laser 804, the scanning mechanism 806, and the detector 814 are arranged horizontally. As shown in FIG. 8, the horizontal direction is parallel to the plane of the paper, while the vertical direction is the direction perpendicular to the plane of the paper. The semiconductor-based laser 804, the scanning mechanism 806, and the detector 814 are arranged horizontally with respect to each other in a direction that is parallel or substantially parallel to the plane of the paper. At the vertical direction, the semiconductor-based laser 804, the scanning mechanism 806, and the detector 814 may or may not be exactly positioned on a same plane (e.g., the plane of the paper) and may have vertical positioning differences. The vertical positioning differences, if any, do not affect, or at least do not significantly affect, the desired operations of the LiDAR system 800. For example, any vertical positioning differences (the direction perpendicular to the plane of the paper) should not affect the scanning mechanism 806 to receive the laser light 832 from transmitter 802 or receive the redirect the return light 834 to the receiver 812. Other orientations or positions of the components shown in FIG. 8 can also be implemented, as long as they do not affect, or at least do not significantly affect, the desired operations of the LiDAR system 800.

[0109] As shown in FIG. 8, similar to the light source 310 shown in FIG.3, semiconductorbased laser 804 can be, for example, an edge emitting laser (EEL), a vertical cavity surface emitting laser (VCSEL), an external-cavity diode laser, a vertical -external-cavity surfaceemitting 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. The laser light 832 has a wavelength denoted as . Thesemiconductor-based laser 804 is configured such that: the wavelength is in a wavelength range that is substantially transparent to the windshield 808 of the vehicle. For example, the wavelength can be no more than 900 nm. This will be described below in more detail.

[0110] Furthermore, the laser light 832 can be polarized, such that a transmission rate of the laser light 832 is no less than a threshold at a predetermined incident angle of the laser light 832. The predetermined incident angle of the laser light 832 is an angle determined with respect to the windshield 808 of the vehicle. With the proper configurations of the wavelength and the polarization, the laser light 832 can have a good transmission rate when passing through the windshield 808 of the vehicle to detect the objects (e.g., object 810) in the FOV. Therefore, by using the LiDAR system 800 in the vehicle, there is no need to replace the regular windshield glass with costly IR-transparent windshield glass, thereby reducing the overall cost. Further, the wavelength is in a wavelength range that is insensitive to human eyes, so that it does not disturb, or cause damage to, people when the LiDAR system 800 is operating. Further details of the configurations of the wavelength and the incident angle are described below using FIGs. 9-12.

[0111] Continuing with FIG. 8, the scanning mechanism 806 includes one or more polygon mirrors, one or more oscillation mirrors, or a combination thereof. In some embodiments, a polygon mirror can have three, four, or five reflective facets. As shown in FIG. 8, the scanning mechanism 806 includes a polygon mirror having three reflective facets 842, 844 and 846. As shown in FIG. 8, the reflective facets 842, 844 and 846 are substantially parallel to a rotational axis 818 of the polygon mirror 806. Thus, facets of the polygon mirror 806 are not tilted with respect to the rotational axis 818. Reflective facets of a polygon mirror can direct light to a desired direction, as shown in the example in FIG. 8. In other examples, scanning mechanism 806 can include oscillation mirrors (not shown) like a planar mirror controlled to oscillate between two end positions. A combination of a polygon mirror and an oscillation mirror may also be used for scanning mechanism 806. Scanning mechanism 806 may also be referred to as an optical scanner, a scanning engine, or just a scanner.

[0112] As shown in FIG. 8, the scanning mechanism 806 includes an actuator 816 to rotate or oscillate the scanning mechanism 806. In some embodiments, the actuator 816 includes at least one of a motor, a galvanometer mirror, or a voice coil actuator. The galvanometer mirror refers to a movable mirror, in which electric current is provided by a motor and used to move a mirror to deflect light beams. The voice coil actuator refers to an actuator utilizing a magnetic field generated by permanent magnets in connection with a coil of wires to produce an electric driving force for high-precision position control. In some embodiments,the scanning mechanism 806 is a polygon mirror and configured to rotate at a speed in the range of 150-600 RPM (rounds per minute). And therefore, the LiDAR system 800 can have a 10-30 Hz frame rate. The frame rate refers to how many times the LiDAR repeats the processing of an entire FOV within a second. In some embodiments as shown in FIG.8, the scanning mechanism 806 is a polygon mirror and configured to perform scanning with no scanline stitching required. In some examples, when the polygon mirror 806 rotates one reflective facet about the rotational axis 818, the laser light 832 directed by the reflective facet of the polygon mirror 806 can scan the entire horizontal FOV. The LiDAR system 800 (e.g., via the control circuitry) processes all the data obtained from the one reflective facet to produce one frame of scanline pattern. In other embodiments, scanline stitching is required, when data obtained from the one facet of the polygon mirror 806 covers a portion of the frame, but not the entire frame. In this scenario, laser light 832 scans the entire horizontal FOV by using multiple facets (e.g., all reflective facets 842, 844 and 846) of the polygon mirror 806. The LiDAR system 800 (e.g., via control circuitry) stitches the scanlines generated from the multiple facets to produce one frame of scanline pattern. In the example shown in FIG. 8, the vertical scanning can be realized by using the array of semiconductorbased light emitting elements and corresponding an array of photon detecting elements in the detector 814. In other examples, vertical stitching can be enabled by using multiple facets to cover different vertical portions of the FOV.

[0113] The movement of the scanning mechanism 806 described in this disclosure can also be controlled using control circuitry 350 shown in FIG. 3. The control circuitry 350 can be used to control, for example, one or more of the rotational speed, an oscillation speed or trajectory, an angular position, a tilt angle, etc., associated with the scanning mechanism 806. In another example, the oscillation speed or the rotational speed of the scanning mechanism 806 can be configured to correspond to the pulse repetition rate, pulse emitting time, etc. of the laser light 832, such that the scanning mechanism 806 is not rotating / oscillating too fast or too slow. If the scanning mechanism 806 is moving too fast or too slow, the scanning mechanism 806 may not produce the correct horizontal angular resolution as desired. The various characteristics of the laser light 832 (e.g., the pulse repetition rate, the pulse emitting time, the average or peak power of the pulses, etc.) are referred to as the pulse emitting pattern. If scanning mechanism 806 does not move in synchronization with the pulse emitting pattern, the scanning mechanism 806 may not correctly direct the laser light 832 to the desired locations in FOV (e.g., the laser light 832 may hit the reflective facet 846 at a comer or another non-desired location).

[0114] As shown in FIG. 8, the LiDAR system 800 further includes one or more transmitter optics (e.g., lens or lens group 820 and combiner mirror 824). Lens or lens group 820 are shown to be included in transmitter 802 and combiner mirror 824 is shown to be placed outside of transmitter 802. In other examples, combiner mirror 824 may be also a part of transmitter 802. In one example, the lens or lens group 820 can be a collimation lens or lens group. The collimation lens or lens group can receive the laser light 832 from the semiconductor-based laser 804 and collimate it to form collimated laser light 832. As shown in FIG. 8, the one or more transmitter optics further include a combiner mirror 824. In some embodiments, the combiner mirror 824 has high reflective coatings in one portion and anti-reflective coatings in another portion. As shown in FIG. 8, the combiner mirror 824 has high reflective coatings at a central portion of the combiner mirror 824 to redirect the laser light 832 to the scanning mechanism 806. The combiner mirror 824 also has anti-reflective coatings on a surrounding area of the combiner mirror 824 for enabling the return light 834 to pass through toward the folding mirror 826.

[0115] As shown in FIG. 8, the LiDAR system 800 further includes one or more receiver optics (e.g., lens or lens group 822 and folding mirror 826). For example, the lens or lens group 822 can be a collection lens or lens group (e.g., a single plano-convex lens or a lens group) to collect and / or focus the collected return light 834 onto the detector 814. As shown in FIG. 8, the one or more receiver optics further include a folding mirror 826. The folding mirror 826 is configured to redirect the return light 834 from the FOV and passing through the windshield 808 to a direction of the lens or lens group 822 and the detector 814.

[0116] As described above, the wavelength of the laser light 832 needs to be configured such that the regular windshield 808 is transparent, or has a good transparency, to the laser light 832. FIG. 9 is diagram illustrating an example of transmission spectrum through different types of vehicle windshield glasses with and without tinting, in accordance with various embodiments. As shown in FIG. 9, for a regular un-tinted windshield glass (e.g., curve 901), the transmission rate is no less than 35% within the wavelength range of 350 nm to 800 nm. FIG. 9 also shows that the transmission rates for different types of vehicle windshield glasses (curves 901-904) are all less than 35% at a wavelength above 800 nm. Therefore, for a typical LiDAR operating with a laser light having a wavelength in the infrared range (e.g., about 905 / 940 nm or about 1550 nm), the transmission rate through the windshield glass is rather low.

[0117] With reference back to FIG. 8, in some embodiments, the semiconductor-based laser 804 includes a VCSEL array. VCSEL laser technology can provide a pulsed laser light witha wavelength, for example, in the range of 600-650 nm or higher. As described above, the wavelength 1 of the laser light 832 should be configured in a wavelength range that is substantially transparent to the windshield of the vehicle. Therefore, to obtain a good transmission rate, the wavelength 1 of the laser light 832 can be configured to no more than 900 nm.

[0118] Further, a front vehicle windshield, where the LiDAR system 800 is placed behind, is normally a regular un-tinted windshield glass. As shown in FIG. 9, within the wavelength range of 350 nm to 800 nm, the transmission rate of the regular un-tinted windshield glass (e.g., curve 901) is no less than 35%. Therefore, the transmission rate of the laser light 832, if unpolarized, is no less than 35% for a regular un-tinted vehicle windshield.

[0119] As described above, the semiconductor-based laser 804 is also configured such that: the wavelength 1 of the laser light 832 is insensitive to human eyes. It is known that human eye is insensitive to infrared light (e.g., a wavelength above 700 nm). Also, human eye is less sensitive to red light (e.g., 620-750 nm), compared to green or blue light (e.g., 380-570 nm) in the visible light range. As shown in FIG. 9, for light having a wavelength in the 600-800 nm region, the transmission rate is good (e.g., no less than 35%) for passing through the windshield glass. Therefore, the semiconductor-based laser 804 in LiDAR system 800 can be configured such that: the wavelength 1 of the laser light 832 is in a visible light wavelength range (e.g., 600-700 nm) or in a near-infrared wavelength range (e.g., 700-800 nm) for vehicles equipped with regular laminated windshields. In some embodiments, the wavelength range that is substantially transparent to the windshield 808 of the vehicle and insensitive to human eyes is from 650 nm to 800 nm.

[0120] In some embodiments, the semiconductor-based laser 804 is configured such that the wavelength 1 of the laser light 832 is fixed. In other embodiments, the semiconductor-based laser 804 is configured such that the wavelength 1 of the laser light 832 is tunable based on environmental conditions. FIGs. 10A and 10B are diagrams illustrating examples of water or humidity influence on transmission, in accordance with various embodiments. The selection of the wavelength 1 of the laser light 832 should also consider natural absorption in the atmosphere. For example, water vapor absorption lines in the visible and near-infrared wavelength range should be avoided.

[0121] FIG. 10A shows absorption efficient of liquid water at different wavelengths. As shown in FIG. 10A, there is an absorption peak 1010 at aboutl450 nm, and an absorption peak 1012 at about 940 nm for liquid water. In comparison, as shown in FIG. 10A, the absorption efficient of liquid water is approximate to zero at a wavelength below 940 nm.Therefore, the specific wavelength 1 of the laser light 832 can be tunable to avoid absorption peaks of water at about 940 nm and 1450 nm.

[0122] FIG. 10B shows transmission spectrum of 100% humidity environment at 30 °C, 1000 m. As shown in FIG. 10B, the transmission rate (also referred to as the transmittance) is approximately 100% for a laser light having a wavelength of 400-680 nm. In comparison, there are several absorption peaks at a wavelength range of 680-900 nm. For example, an absorption peak 1020 has a very low transmission rate of 0.35 at about 770 nm. Therefore, the specific wavelength 1 of the laser light 832 can be tunable to avoid the absorption peaks and achieve a good transmission rate in humid environments. In some examples, to avoid an absorption peak, the wavelength of laser light 832 can be tuned to change just a few nanometers. The particular value of the wavelength of laser light 832 can therefore be adjusted to accommodate the environmental conditions. As LiDAR systems are often mounted to a vehicle, which can be operated under vastly different environmental conditions, the ability of adjusting the wavelength of laser light 832 can be desirable to maintain a good transmission rate under all operating conditions, and in turn provide good LiDAR operational performance.

[0123] Another factor that may affect the transmission rate of the laser light through a windshield is the incident angle, especially for windshield glasses without anti-reflective (AR) coatings. FIG. 11 A is an example of a LiDAR system 1104 (e.g., LiDAR system 800 shown in FIG. 8) emitting laser light at different incident angles with respect to different windshield glasses 1108, 1110, and 1112 in accordance with various embodiments. As shown in FIG. 11 A, the windshield glasses 1108, 1110, 1112 have different rake angles of 70 degrees, 60 degrees, and 50 degrees, respectively. The rake angles for these windshield glasses 1108, 1110, and 1112 is an angle between the plane of the windshield glass and a plane perpendicular to the ground on which the vehicle 1102 operates. As shown in FIG. 11 A, behind these windshield glasses 1108, 1110, and 1112, there is also a keep-out zone 1106 for the LiDAR system 1104. No objects should be located within the keep-out zone 1106 to prevent interfering with the operation of the LiDAR system 1104. Windshield glasses on different types of vehicles have different rake angles. For example, a windshield glass on a truck has a smaller rake angle than that on a sedan. As shown in FIG. 11 A, the LiDAR system 1104 mounted inside a vehicle 1102 is positioned behind a windshield glass 1108, 1110, or 1112. In turn, the LiDAR system 1104 emits laser light at different incident angles with respect to the different windshield glasses 1108, 1110, and 1112. The incident angle is the angle between the direction of the light incident to the surface of the windshield glass andthe local normal direction of the windshield glass (e.g., the direction perpendicular to the surface of the windshield glass at the point of incidence). Therefore, if the laser light source orientation is fixed and therefore the direction of the laser light is the same for the different windshield glasses 1108, 1110, and 1112, the incident angle for the windshield glass 1108 tends to be bigger than incident angle for the windshield glass 1110. Similarly, incident angle for the windshield glass 1110 tends to be bigger than the incident angle for the windshield glass 1112. Unlike the rake angle, which does not change when the windshield is assembled to a vehicle, the incident angle (also referred to as the angle of incidence) may change based on the direction of the laser beam during horizontal and vertical scanning. The angle of incidence has an impact of the transmission rate of the laser light through the windshield and the relation is described in detail below with reference to FIG. 1 IB.

[0124] FIG. 1 IB is an example of a relation between transmission rate of clear laminate windshield and angle of incidence for different polarizations in accordance with various embodiments. As shown in FIG. 1 IB, the transmission rate through windshield glass is also polarization dependent. As the incident angle to the windshield glass increases, the difference of optical transmission between the two orthogonal polarizations also increases. As shown in FIG. 1 IB, a p-polarized laser light (e.g., curve 1116) has a higher transmission rate than that of s-polarized laser light (e.g., curve 1114). Here, the p-polarization (also called parallel polarization) refers to the orientation of light waves where the electric field vector oscillates parallel to the plane of incidence. The s-polarization (also called perpendicular polarization) refers to the orientation of light waves where the electric field vector oscillates perpendicular to the plane of incidence. As shown in FIG. 1 IB, the transmission rate for a p-polarized laser light (e.g., curve 1116) is no less than 80% when the predetermined incident angle is in the range of 40 degrees to 70 degrees. While at 75 degrees to 80 degrees, the transmission rate for a p-polarized laser light is no less than 60% (see curve 1116).

[0125] With reference back to FIG. 8, as described above, the semiconductor-based laser 804 includes a VCSEL array. A VCSEL array can be produced with high polarization extinction ratio. Such VCSEL technologies are described in greater detail in “ANNUAL REPORT 2003,” By Optoelectronics Department of University of Ulm, available at https: / / www.uniulm.de / fileadmin / website_uni_ulm / iui.inst.140 / Jahresbericht / 2003 / ar2003.pd f, last visited October 2, 2025, which is incorporated by reference in its entirety for all purposes. In some embodiments, the semiconductor-based laser 804 can further include optics (not shown) configured to produce the polarized laser light 832. In someembodiments, the optics configured to produce the polarized laser light 832 includes one or more of: a polarizing filter, a polarizer, a reflector, an optics having double refraction, a dichroic polarizer, a light-scattering optics, or a grating.

[0126] As described above, a p-polarized laser light (e.g., curve 1116 shown in FIG. 1 IB) has a higher transmission rate than that of s-polarized laser light (e.g., curve 1114 shown in FIG. 1 IB) for large angles of incidence (e.g., for angles of incidence above 40 degrees). Therefore, to further improve the detection performance through regular windshield glass, the laser light 832 produced by the semiconductor-based laser 804 can be configured to provide predominantly p-polarized while going through the windshield 808 of the vehicle. For the example shown in FIG. 1 IB, the transmission rate for a p-polarized laser light (e.g., curve 1116) is no less than 80% when the incident angle is in the range of 40 degrees to 70 degrees. Also, for the example shown in FIG. 1 IB, at 75 degrees to 80 degrees, the transmission rate for a p-polarized laser light is no less than 60% (see curve 1116). As described above, although the incident angle may change based on the direction of the laser beam during horizontal and vertical scanning, the semiconductor-based laser 804 is configured to produce predominantly p-polarized laser light 832, the transmission rate through regular windshield glass is still good (e.g., no less than 60%) for a large incident angle range from 0 degree to 80 degrees.

[0127] Other than enhancing the transmission rate of the laser light transmitted through the windshield glass and the configuration of the light source, the detector efficiency can also be enhanced. With reference back to FIG. 8, in some embodiments, the detector 814 includes a Single-Photon Avalanche Diode (SPAD) detector array or a SiPM array. In some embodiments, the detector 814 has a peak photon detection efficiency (PDE) of no less than 50% at the wavelength 1 of the laser light 832, with or without light trapping.

[0128] FIGs. 12A and 12B are diagrams illustrating examples of PDE for SPAD arrays, in accordance with various embodiments. FIG. 12A shows measurement results of PDE at 25 °C. As shown in FIG. 12 A, curves 1201-1203 show that a SPAD array has a high PDE of no less than 50 % at 400-600 nm. FIG. 12B shows measured PDE as a function of wavelength for a SPAD array. As shown in FIG. 12B, for wavelengths at 400-600 nm, both curves 1204 and 1205 have a high PDE of no less than 50 % for a SPAD array with or without light trapping. The SPAD array with light trapping (e.g., curve 1205) can have a higher PDE than that of the SPAD array without light trapping (e.g., curve 1204) in a near-infrared wavelength range. Therefore, in some embodiments, the detector 814 can be configured to have light trapping capability. In turn, the detector 814 can have higher photon detection efficiency(PDE). For instance, a SPAD array with light trapping integrates SPAD detectors in a grid with nanostructures to enhance sensitivity and photon detection efficiency by reflecting and guiding more photons into the active detection area. This light trapping technology allows SPAD arrays to achieve higher PDE and thus higher performance, especially in low-light conditions for time-of-flight systems. Light-trapping structures, such as etched nano-textures on the SPAD's surface, effectively increase the number of detected photons compared to conventional flat SPADs, which are limited to detecting photons only within their high-field sensitivity regions.

[0129] As shown in FIG. 12B, with light trapping (curve 1205), the wavelength for the laser light can be selected more toward red visible light or infrared light area (e.g., about 600-800 nm) with the PDE being still no less than 40%. In contrast, without light trapping, the PDE decreases faster in red visible light or infrared light area. Therefore, for the laser light 832 having wavelength 1 in visible light or near-infrared wavelength range, the detector 814 can be configured to have light trapping capability to achieve a better detection performance.

[0130] 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 mountable inside a vehicle, the system comprising:a semiconductor-based laser configured to emit laser light having a wavelength; a scanning mechanism configured to pass the laser light through a windshield of the vehicle to a field-of-view and receive return light formed based on the laser light transmitted through the windshield, wherein the semiconductor-based laser is configured such that:the wavelength of the laser light is in a wavelength range that is substantially transparent to the windshield of the vehicle and insensitive to human eyes,the laser light is polarized such that a transmission rate of the laser light is no less than a threshold at a predetermined incident angle of the laser light; and a detector configured to detect the return light received through the windshield.

2. The system of claim 1, wherein the semiconductor-based laser comprises a vertical cavity surface emitting laser (VCSEL) array.

3. The system of claim 1, wherein the semiconductor-based laser is configured such that the wavelength of the laser light is in a visible light wavelength range or in a near-infrared wavelength range for vehicles equipped with regular laminated windshield.

4. The system of claim 1, wherein the wavelength of the laser light is no more than 900 nm.

5. The system of claim 1, wherein the wavelength range that is substantially transparent to the windshield of the vehicle and insensitive to human eyes is from 650 nm to 800 nm.

6. The system of claim 1, wherein the transmission rate of the laser light, if unpolarized, is no less than 35% for a regular un-tinted vehicle windshield.

7. The system of claim 1, wherein the semiconductor-based laser is configured such that the wavelength of the laser light is tunable based on environmental conditions.

8. The system of claim 1, wherein the semiconductor-based laser is configured such that the wavelength of the laser light is fixed.

9. The system of claim 1, wherein the laser light produced by the semiconductor-based laser is predominantly p-polarized while going through the windshield of the vehicle.

10. The system of claim 9, wherein the transmission rate of the laser light through the windshield of the vehicle is no less than 80% when the predetermined incident angle is in a range of 40 degrees to 70 degrees.

11. The system of claim 9, wherein the transmission rate of the laser light is no less than 60% at the predetermined incident angle of 75 degrees to 80 degrees.

12. The system of claim 1, wherein the semiconductor-based laser comprises optics configured to produce the polarized laser light.

13. The system of claim 12, wherein the optics configured to produce the polarized laser light comprise one or more of: a polarizing filter, a polarizer, a reflector, an optics having double refraction, a dichroic polarizer, a light-scattering optics, or a grating.

14. The system of claim 1, wherein the scanning mechanism comprises one or more polygon mirrors, one or more oscillation mirrors, or a combination thereof.

15. The system of claim 14, wherein the one or more polygon mirrors have 3, 4, or 5 reflective facets.

16. The system of claim 15, wherein the reflective facets are substantially parallel to a rotational axis of the one or more polygon mirrors.

17. The system of claim 1, wherein the scanning mechanism is configured to perform scanning with no stitching.

18. The system of claim 1, wherein the scanning mechanism is configured to rotate at a speed in the range of 150-600 RPM, and the LiDAR system has a 10-30 Hz frame rate.

19. The system of claim 1, wherein the detector comprises a single-photon avalanche diode (SPAD) detector array or a Silicon photomultiplier (SiPM) array.

20. The system of claim 1, wherein the detector is configured to have light trapping capability.

21. The system of claim 1, wherein the detector has a peak photon detection efficiency (PDE) of no less than 50% at the wavelength of the laser light, with or without light trapping.

22. The system of claim 1, wherein the semiconductor-based laser, the scanning mechanism, and the detector are arranged horizontally.

23. The system of claim 1, further comprising one or more transmitter optics and one or more receiver optics.

24. The system of claim 23, wherein the one or more transmitter optics comprise a combiner mirror having high reflective coatings in one portion and anti -reflective coatings in another portion.

25. A vehicle comprising a light ranging and detection (LiDAR) system mountable inside the vehicle, the system comprising:a semiconductor-based laser configured to emit laser light having a wavelength; a scanning mechanism configured to pass the laser light through a windshield of the vehicle to a field-of-view and receive return light formed based on the laser light transmitted through the windshield, wherein the semiconductor-based laser is configured such that:the wavelength of the laser light is in a wavelength range that is substantially transparent to the windshield of the vehicle and insensitive to human eyes,the laser light is polarized such that a transmission rate of the laser light is no less than a threshold at a predetermined incident angle of the laser light; and a detector configured to detect the return light received through the windshield.

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