Patent Publication Number: US-2023152428-A1

Title: Wobble adjustment capability for polygon mirrors

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 63/279,676, filed Nov. 15, 2021, entitled “WOBBLE ADJUSTMENT CAPABILITY FOR POLYGON MIRRORS,” the content of which is hereby incorporated by reference in its entirety for all purposes. 
    
    
     FIELD 
     This disclosure relates generally to optical scanning and, more particularly, to a motorized optical scanner of a Light Detection and Ranging (LiDAR) system used in a motor vehicle. 
     BACKGROUND 
     Light detection and ranging (LiDAR) systems use light pulses to create an image or point cloud of the external environment. Some typical 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 by an object, a portion of the scattered light returns to the LiDAR system as 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 using the speed of light. 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. LiDAR systems can also use techniques other than time-of-flight and scanning to measure the surrounding environment. 
     SUMMARY 
     A LiDAR system is often an essential component of a motor vehicle. A LiDAR system may include a motorized optical scanner. A motorized optical scanner may include an optical reflector and a motor rotor body for rotating the optical reflector. An optical reflector may be a polygon mirror having a plurality of reflective surfaces (also referred to as facets). The polygon mirror is usually made from glass with multiple reflective facets to reflect light pulses. Due to various factors of manufacturing process, center of a polygon mirror may have a small angular deviation from its center of rotation. When center of a polygon mirror is not perfectly in-line with its center of rotation, tilt angles of the polygon facets may change in the process of angular rotation, and the polygon mirror may wobble. This may affect the overall performance of the LiDAR system. Thus, there is a need to eliminate or reduce the impact caused by these conditions. 
     Embodiments of the present disclosure use an adjustment ring configured to adjust the tilt angles of one or more reflective surfaces of the polygon mirror with respect to the rotor and rotational axis, thereby reducing wobble and improving long-term stability of the motorized optical scanner. Embodiments of the present disclosure further use fastening mechanisms configured to apply proper adjustment forces to the adjustment ring. The fastening mechanisms may be fine-tuned to apply desired adjustment forces to different portions of the adjustment ring to tilt the polygon mirror. As a result, wobbling of the polygon mirror can be substantially reduced by such fine tuning of the adjustment forces. Various embodiments of the present disclosure are described in more detail below. 
     In one embodiment, a motorized optical scanner device of a Light Detection and Ranging (LiDAR) scanning system used in a motor vehicle is provided. The motorized optical scanner device comprises a glass-based optical reflector including a plurality of reflective surfaces and a flange. The rotatable optical reflector device further comprises an adjustment ring and a metal-based motor rotor body at least partially disposed in an inner opening of the glass-based optical reflector. The flange extends from an inner sidewall of the glass-based optical reflector towards the metal-based motor rotor body. The flange includes a first mounting surface that is in contact with the adjustment ring. The motorized optical scanner device further comprises a plurality of fastening mechanisms. The plurality of fastening mechanisms facilitates applying adjustment forces to the adjustment ring to reduce wobble associated with rotation of the glass-based optical reflector. 
     In one embodiment, a Light Detection and Ranging (LiDAR) system used in a motor vechile is provided. The LiDAR system comprises a motorized optical scanner device. The motorized optical scanner device comprises a glass-based optical reflector including a plurality of reflective surfaces and a flange. The rotatable optical reflector device further comprises an adjustment ring and a metal-based motor rotor body at least partially disposed in an inner opening of the glass-based optical reflector. The flange extends from an inner sidewall of the glass-based optical reflector towards the metal-based motor rotor body. The flange includes a first mounting surface that is in contact with the adjustment ring. The motorized optical scanner device further comprises a plurality of fastening mechanisms. The plurality of fastening mechanisms facilitates applying adjustment forces to the adjustment ring to reduce wobble associated with rotation of the glass-based optical reflector. 
     In one embodiment, a motor vehicle is provided. The motor vehicle comprises a Light Detection and Ranging (LiDAR) system that comprises a motorized optical scanner device. The motorized optical scanner device comprises a glass-based optical reflector including a plurality of reflective surfaces and a flange. The rotatable optical reflector device further comprises an adjustment ring and a metal-based motor rotor body at least partially disposed in an inner opening of the glass-based optical reflector. The flange extends from an inner sidewall of the glass-based optical reflector towards the metal-based motor rotor body. The flange includes a first mounting surface that is in contact with the adjustment ring. The motorized optical scanner device further comprises a plurality of fastening mechanisms. The plurality of fastening mechanisms facilitates applying adjustment forces to the adjustment ring to reduce wobble associated with rotation of the glass-based optical reflector. 
     In one embodiment, a method for adjusting a motorized optical scanner device of a Light Detection and Ranging (LiDAR) system for reducing wobble is provided. The method comprises assembling a motorized optical scanner device. The motorized optical scanner device comprises a glass-based optical reflector including a plurality of reflective surfaces, an adjustment ring, and a metal-based motor rotor body at least partially disposed in an inner opening of the glass-based optical reflector. The method also comprises measuring wobble of the motorized optical scanner device. The method further comprises selecting at least two positions with respect to the adjustment ring based on the measured wobble. The method further comprises installing a plurality of fastening mechanisms to apply adjustment forces to the adjustment ring at the at least two selected positions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present application can be best understood by reference to the figures described below taken in conjunction with the accompanying drawing figures, in which like parts may be referred to by like numerals. 
         FIG.  1    illustrates one or more exemplary LiDAR systems disposed or included in a motor vehicle. 
         FIG.  2    is a block diagram illustrating interactions between an exemplary LiDAR system and multiple other systems including a vehicle perception and planning system. 
         FIG.  3    is a block diagram illustrating an exemplary LiDAR system. 
         FIG.  4    is a block diagram illustrating an exemplary fiber-based laser source. 
         FIGS.  5 A- 5 C  illustrate an exemplary LiDAR system using pulse signals to measure distances to objects disposed in a field-of-view (FOV). 
         FIG.  6    is a block diagram illustrating an exemplary apparatus used to implement systems, apparatus, and methods in various embodiments. 
         FIG.  7    is a top view of an exemplary motorized optical scanner device according to some embodiments. 
         FIG.  8    is a bottom view of the exemplary motorized optical scanner device according to some embodiments. 
         FIG.  9    is a cross-sectional view of the exemplary motorized optical scanner device according to some embodiments. 
         FIG.  10    is a perspective view of the exemplary motorized optical scanner device according to some embodiments. 
         FIG.  11    is a perspective view of the exemplary motorized optical scanner device according to some embodiments. 
         FIG.  12    is a cut-off view of the exemplary motorized optical scanner device according to some embodiments. 
         FIG.  13    is an exploded view of the exemplary motorized optical scanner device according to some embodiments. 
         FIG.  14    is a flow chart of exemplary method for adjusting a motorized optical scanner device disposed or included in a motor vehicle. 
         FIG.  15    is a bottom view of the exemplary motorized optical scanner device according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     To provide a more thorough understanding of the present disclosure, the following description sets forth numerous specific details, such as specific configurations, parameters, examples, and the like. It should be recognized, however, that such description is not intended as a limitation on the scope of the present disclosure but is intended to provide a better description of the exemplary embodiments. 
     Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise: 
     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. 
     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. 
     The term “based on” is not exclusive and allows for being based on additional factors not described unless the context clearly dictates otherwise. 
     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. 
     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 surface could be termed a second surface and, similarly, a second surface could be termed a first surface, without departing from the scope of the various described examples. The first surface and the second surface can both be surfaces and, in some cases, can be separate and different surfaces. 
     In addition, throughout the specification, the meaning of “a”, “an”, and “the” includes plural references, and the meaning of “in” includes “in” and “on”. 
     Although some of the various embodiments presented herein constitute a single combination of inventive elements, it should be appreciated that the inventive subject matter is considered to include all possible combinations of the disclosed elements. As such, if one embodiment comprises elements A, B, and C, and another embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly discussed herein. Further, the transitional term “comprising” means to have as parts or members, or to be those parts or members. As used herein, the transitional term “comprising” is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. 
     Throughout the following disclosure, numerous references may be made regarding servers, services, interfaces, engines, modules, clients, peers, portals, platforms, or other systems formed from computing devices. It should be appreciated that the use of such terms is deemed to represent one or more computing devices having at least one processor (e.g., ASIC, FPGA, PLD, DSP, x 86 , ARM, RISC-V, ColdFire, GPU, multi-core processors, etc.) configured to execute software instructions stored on a computer readable tangible, non-transitory medium (e.g., hard drive, solid state drive, RAM, flash, ROM, etc.). For example, a server can include one or more computers operating as a web server, database server, or other type of computer server in a manner to fulfill described roles, responsibilities, or functions. One should further appreciate the disclosed computer-based algorithms, processes, methods, or other types of instruction sets can be embodied as a computer program product comprising a non-transitory, tangible computer readable medium storing the instructions that cause a processor to execute the disclosed steps. The various servers, systems, databases, or interfaces can 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 can be conducted over a packet-switched network, a circuit-switched network, the Internet, LAN, WAN, VPN, or other type of network. 
     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. 
     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, etc.). 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. 
     A LiDAR system often includes a polygon mirror for steering light pulses to a field-of-view (FOV). The polygon mirror is usually made from glass with multiple reflective surfaces (also referred to as facets) to reflect light pulses. The polygon mirror is mounted to a rotational shaft of a motor rotor body. A LiDAR system may be mounted to a vehicle and therefore may need to operate in a wide temperature range (e.g., −40° C. to 85° C.). The shaft of the motor rotor body rotates at a very high speed (e.g., a few thousand rounds-per-minute or rpm), thereby causing the polygon mirror to rotate at high speed as well. Due to various factors of manufacturing process, center of a polygon mirror may have a small angular deviation from its center of rotation. When center of a polygon mirror is not perfectly in-line with its center of rotation, tilt angles of polygon facets may change in the process of angular rotation, and the polygon mirror may wobble. This may affect the overall performance of the LiDAR system. Thus, there is a need to eliminate or reduce the impact caused by these conditions. 
     As used in this disclosure, total wobble of a rotating polygon mirror refers to the range of tilt angles between the polygon facets and the polygon&#39;s rotational axis. For better performance of a LiDAR system comprising a polygon mirror, it is often required for the polygon mirror to have a tight specification for total wobble. Without adjustment capability, errors or deviations from nominal values (e.g., tilt angles deviations) resulted from stacked up tolerances in the manufacturing process of a polygon mirror assembly may prevent the polygon mirror from meeting its wobble specifications. Total wobble can be the sum of two types of wobbles: repeatable wobble and random wobble. Repeatable wobble results from axial runout of mating surfaces. Random wobble is residual wobble after repeatable wobble is accounted for. Typical axial runout for a computer numerical control (CNC)-machined part is around ±0.05°, which almost consumes all of the allowable wobble that can be tolerated in typical LiDAR applications. 
     Embodiments of present disclosure are described below. In various embodiments of the present disclosure, an adjustment ring is used to adjust the tilt angle of the polygon mirror with respect to the rotor and rotational axis. A tilt angle refers to the angle between the normal direction of a reflective surface of the polygon mirror and the rotational axis of the polygon mirror. The adjustment ring can reduce the wobbling of the polygon mirror when it is rotating, thereby improving the performance and stability of the polygon mirror. A plurality of fastening mechanisms are also used to apply proper adjustment forces (e.g., pushing forces) to the adjustment ring. The fastening mechanisms may be fine-tuned to apply desired adjustment forces to different portions of the adjustment ring to tilt the polygon mirror. As a result, various embodiments of the present disclosure improve the stability and reliability of the polygon mirror, enhance the wobble adjustment capability of the polygon mirror, and improve the overall performance of the LiDAR system. 
       FIG.  1    illustrates one or more exemplary LiDAR systems  110  disposed or included in a motor vehicle  100 . 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&#39;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&#39;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. 
     In typical configurations, motor vehicle  100  comprises one or more LiDAR systems  110  and  120 A-F. Each of LiDAR systems  110  and  120 A-F can be a scanning-based LiDAR system and/or a non-scanning LiDAR system (e.g., a flash LiDAR). A scanning-based LiDAR system scans one or more light beams in one or more directions (e.g., horizontal and vertical directions) to detect objects in a field-of-view (FOV). A non-scanning based LiDAR 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. 
     A LiDAR system is often an essential 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  120 A-F) 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  120 A-F. As shown in  FIG.  1   , in one embodiment, multiple LiDAR systems  110  and/or  120 A-F are attached to vehicle  100  at different locations of the vehicle. For example, LiDAR system  120 A is attached to vehicle  100  at the front right corner; LiDAR system  120 B is attached to vehicle  100  at the front center; LiDAR system  120 C is attached to vehicle  100  at the front left corner; LiDAR system  120 D is attached to vehicle  100  at the right-side rear view mirror; LiDAR system  120 E is attached to vehicle  100  at the left-side rear view mirror; and/or LiDAR system  120 F is attached to vehicle  100  at the back center. In some embodiments, LiDAR systems  110  and  120 A-F 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  120 A-F 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. 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  120 D and  120 E may be attached to the B-pillars of vehicle  100  instead of the rear-view mirrors. As another example, LiDAR system  120 B may be attached to the windshield of vehicle  100  instead of the front bumper. 
       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. 
     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 20-40 meters from the LiDAR sensor. Short-range LiDAR sensors can be used for, e.g., monitoring nearby moving objects (e.g., pedestrians crossing street in a school zone), parking assistance applications, or the like. A medium-range LiDAR sensor measures objects located up to about 100-150 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 150-300 meters. Long-range LiDAR sensors are typically used when a vehicle is travelling at high speed (e.g., on a freeway), such that the vehicle&#39;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. 
     With reference still to  FIG.  2   , in some embodiments, other vehicle onboard sensor(s)  230  are used 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 produces monochrome or color images and videos. Color information may be important in interpreting data for some situations (e.g., interpreting images of traffic lights). Color information may not be available from other sensors such as LiDAR or radar sensors. Camera(s)  232  can include one or more of 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. 
     Other vehicle onboard sensos(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&#39;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 nearby 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. 
     Other vehicle onboard sensor(s)  230  can also include ultrasonic sensor(s)  236 . Ultrasonic sensor(s)  236  use acoustic waves or pulses to measure object 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, check blind spot, identify parking spots, provide 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. 
     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 . 
     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 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 service for processing and then the processing results can be transmitted back to the vehicle perception and planning system  220 ). 
     With reference still to  FIG.  2   , in some embodiments, sensors onboard other vehicle(s)  250  are used to provide additional sensor data separately or together with LiDAR system(s)  210 . For example, two or more nearby vehicles may have their own respective LiDAR sensor(s), camera(s), radar sensor(s), ultrasonic sensor(s), etc. Nearby vehicles can communicate and share sensor data with one another. Communications between vehicles are also referred to as V2V (vehicle to vehicle) communications. For example, as shown in  FIG.  2   , sensor data generated by other vehicle(s)  250  can be communicated to vehicle perception and planning system  220  and/or vehicle onboard LiDAR system(s)  210 , via communication path  253  and/or communication path  251 , respectively. Communication paths  253  and  251  can be any wired or wireless communication links that can transfer data. 
     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 a 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 , thereby at least partially offloading the sensor fusion process performed by vehicle perception and planning system  220 . 
     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 V 21  (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 traffics in the opposite direction. In such a situation, sensors of intelligent infrastructure system(s)  240  can provide useful, and sometimes vital, 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. 
     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&#39;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 . 
     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. 
     Vehicle perception and planning system  220  further comprises an object classifier  223 . Using raw sensor data and/or correlated/fused data provided by sensor fusion sub-system  222 , object classifier  223  can 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). 
     Vehicle perception and planning system  220  further comprises a road detection sub-system  224 . Road detection sub-system  224  localizes the road and identifies objects and/or markings on the road. For example, based on raw or fused sensor data provided by radar sensor(s)  234 , camera(s)  232 , and/or LiDAR system(s)  210 , road detection sub-system  224  can build a 3D model of the road based on machine-learning techniques (e.g., pattern recognition algorithms for identifying lanes). Using the 3D model of the road, road detection sub-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). 
     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&#39;s posture. For example, using sensor data from LiDAR system(s)  210 , camera(s)  232 , and/or GPS data, localization and vehicle posture sub-system  225  can determine an accurate position of the vehicle on the road and the vehicle&#39;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&#39;s location. For instance, using the HD maps, localization and vehicle posture sub-system  225  can determine precisely the vehicle&#39;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&#39;s future positions. 
     Vehicle perception and planning system  220  further comprises obstacle predictor  226 . Objects identified by object classifier  223  can be stationary (e.g., a light pole, a road sign) or dynamic (e.g., a moving pedestrian, bicycle, another car). For moving objects, predicting their moving path or future positions can be important to avoid collision. Obstacle predictor  226  can predict an obstacle trajectory and/or warn the driver or the vehicle planning sub-system  228  about a potential collision. For example, if there is a high likelihood that the obstacle&#39;s trajectory intersects with the vehicle&#39;s current moving path, obstacle predictor  226  can generate such a warning. Obstacle predictor  226  can use a variety of techniques for making such a prediction. Such techniques include, for example, constant velocity or acceleration models, constant turn rate and velocity/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. 
     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 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&#39;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  223  and  271 , which include any wired or wireless communication links that can transfer data. 
     Vehicle control system  280  controls the vehicle&#39;s steering mechanism, throttle, brake, etc., to operate the vehicle according to the planned route and movement. 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  can communicate with vehicle perception and planning system  220 , for example, to obtain and display raw or fused sensor data, identified objects, vehicle&#39;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   . 
       FIG.  3    is a block diagram illustrating an exemplary LiDAR system  300 . LiDAR system  300  can be used to implement LiDAR system  110 ,  120 A-F, and/or  210  shown in  FIGS.  1  and  2   . In one embodiment, LiDAR system  300  comprises a laser source  310 , a transmitter  320 , an optical receiver and light detector  330 , a steering system  340 , and a control circuitry  350 . These components are coupled together using communications paths  312 ,  314 ,  322 ,  332 ,  343 ,  352 , and  362 . 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 laser 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). 
     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. 
     Laser source  310  outputs laser light for illuminating objects in a field of view (FOV). Laser 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), 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. 
     In some embodiments, laser source  310  comprises a master oscillator (also referred to as a seed laser) and power amplifier (MOPA). 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, laser 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 (Y 3 Al 5 O 12 ) laser crystals (i.e., Nd:YAG), or neodymium-doped vanadate (i.e., ND:YVO 4 ) laser crystals. 
       FIG.  4    is a block diagram illustrating an exemplary 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 laser source  310  depicted in  FIG.  3   . In some embodiments, fiber-based laser source  400  comprises a seed laser  402  to generate initial light pulses of one or more wavelengths (e.g., 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 20-30 dB gain). In some embodiments, pre-amplifier(s)  408  are low noise amplifiers. Pre-amplifier(s)  408  output to a 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 pulses to a booster amplifier  414 , which produces output light pulses via optical fiber  410 . The booster amplifier  414  provides further amplification of the optical signals. The outputted light pulses can then be transmitted to transmitter  320  and/or steering mechanism  340  (shown in  FIG.  3   ). It is understood that  FIG.  4    illustrates one exemplary 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.  4    and/or other components not shown in  FIG.  4    (e.g., other components such as power supplies, lens, filters, splitters, combiners, etc.). 
     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. 
     Referencing  FIG.  3   , typical operating wavelengths of laser source  310  comprise, for example, about 850 nm, about 905 nm, about 940 nm, about 1064 nm, and about 1550 nm. 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 laser source  310  can be characterized by its peak power, average power, and the pulse energy. 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. The PRR typically corresponds to the maximum range that a LiDAR system can measure. Laser 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. Laser 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 key 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 laser source  310  and/or designing laser delivery systems for vehicle-mounted LiDAR applications. 
     It is understood that the above descriptions provide non-limiting examples of a laser source  310 . Laser 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. 
     With reference back to  FIG.  3   , LiDAR system  300  further comprises a transmitter  320 . Laser source  310  provides laser light (e.g., in the form of a laser beam) to transmitter  320 . The laser light provided by laser 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 laser 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 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. 
     Laser beams provided by laser source  310  may diverge as they travel to transmitter  320 . Therefore, transmitter  320  often comprises a collimating lens 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 M 2  factor) 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 M 2  factor represents a degree of variation of a beam from an ideal Gaussian beam. Thus, the M 2  factor 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, laser source  310  and/or transmitter  320  can be configured to meet, for example, a scan resolution requirement while maintaining the desired M 2  factor. 
     One or more of the light beams provided by transmitter  320  are scanned by steering mechanism  340  to a FOV. Steering mechanism  340  scans light beams in multiple dimensions (e.g., in both the horizontal and vertical dimension) to facilitate LiDAR system  300  to map the environment by generating a 3D point cloud. 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 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, focus, 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. 
     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 exemplary 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&#39;s capability of maintaining linear relationship between input optical signal power and the detector&#39;s output. A detector having good linearity can maintain a linear relationship over a large dynamic input optical signal range. 
     To achieve desired detector characteristics, configurations or customizations can be made to the light detector&#39;s structure and/or the detector&#39;s material system. Various detector structure can be used for a light detector. For example, a light detector structure can be a PIN based structure, which has a 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, a APD (avalanche photodiode) based structure, a PMT (photomultiplier tube) based structure, a SiPM (Silicon photomultiplier) based structure, a SPAD (single-photon 5  avalanche diode) base 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 . 
     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&#39;s internal gain. Common types of noise include signal shot noise, dark current shot noise, thermal noise, and amplifier noise (TIA). 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 TIA-transimpedance amplifier, 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 implement 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. 
       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 referred to as a raster mechanism or a scanning mechanism. Scanning light beams in multiple directions (e.g., in both the horizontal and vertical directions) facilitates a LiDAR system to map the environment by generating an image or a 3D point cloud. A steering mechanism can be based on mechanical scanning and/or solid-state scanning. Mechanical scanning uses rotating mirrors to steer the laser beam or physically rotate the LiDAR transmitter and receiver (collectively referred to as transceiver) to scan the laser beam. Solid-state scanning directs the laser beam to various positions through the FOV without mechanically moving any macroscopic components such as the transceiver. Solid-state scanning mechanisms include, for example, optical phased arrays based steering and flash LiDAR based steering. In some embodiments, because solid-state scanning mechanisms do not physically move macroscopic components, the steering performed by a solid-state scanning mechanism may be referred to as effective steering. A LiDAR system using solid-state scanning may also be referred to as a non-mechanical scanning or simply non-scanning LiDAR system (a flash LiDAR system is an exemplary non-scanning LiDAR system). 
     Steering mechanism  340  can be used with the 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), 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 two devices combined to realize two-dimensional scanning. 
     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) 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. 
     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. 
     Some implementations of steering mechanism  340  comprise one or more optical redirection elements (e.g., mirrors or lens) 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). 
     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 laser source  310  to obtain desired laser pulse timing, 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/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. 
     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 a transmitted light pulse; determines the direction (e.g., horizontal and/or vertical information) for a transmitted/return light pulse; determines the estimated range in a particular direction; and/or determines any other type of data relevant to LiDAR system  300 . 
     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 humidifies, 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 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), 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. 
     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. 
     These components shown in  FIG.  3    are coupled together using communications paths  312 ,  314 ,  322 ,  332 ,  342 ,  352 , and  362 . These communications paths represent communication (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, busses, 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 exemplary 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). 
     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.  5 A , an exemplary LiDAR system  500  includes a laser light source (e.g., a fiber laser), a steering system (e.g., a system of one or more moving mirrors), and a light detector (e.g., a photon detector 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 system 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 system of the LiDAR system  500  is a pulsed-signal steering system. 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. 
     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 generate a return light pulse  508 . Return light pulse  508  may return to system  500  along light path  510 . 
     The time from when transmitted light pulse  502  leaves LiDAR system  500  to when return light pulse  508  arrives back at LiDAR system  500  can be measured (e.g., by a processor or other electronics, such as control circuitry  350 , within the LiDAR system). This time-of-flight combined with the knowledge of the speed of light can be used to determine the range/distance from LiDAR system  500  to the portion of object  506  where light pulse  502  scattered or reflected. 
     By directing many light pulses, as depicted in  FIG.  5 B , 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.  5 C , 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 generated 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). 
     If a corresponding light pulse is not received for a particular transmitted light pulse, then it may be determined 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.  5 B , light pulse  526  may not have a corresponding return light pulse (as illustrated in  FIG.  5 C ) 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 . 
     In  FIG.  5 B , 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.  5 B  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.  5 B , 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. A point cloud or image from a 1-dimensional transmission of light pulses (e.g., a single horizontal line) can generate 2-dimensional data (e.g., (1) data from the horizontal transmission direction and (2) the range or distance to objects). Similarly, a point cloud or image from a 2-dimensional transmission of light pulses can generate 3-dimensional data (e.g., (1) data from the horizontal transmission direction, (2) data from the vertical transmission direction, and (3) the range or distance to objects). In general, a LiDAR system performing an n-dimensional transmission of light pulses generates (n+1) dimensional data. This is because the LiDAR system can measure the depth of an object or the range/distance 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. 
     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 with a higher pulse repetition rate (PRR) is needed. 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. 
     To illustrate, consider an exemplary LiDAR system that can transmit laser pulses with a 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 conventional LiDAR design, the farthest distance the LiDAR system can detect may be 300 meters and 150 meters for 500 kHz and 1 MHz, respectively. The density of points of a LiDAR system with 500 kHz repetition rate is half of that with 1 MHz. Thus, this example demonstrates that, if the system cannot correctly correlate return signals that arrive out of order, increasing the repetition rate from 500 kHz to 1 MHz (and thus improving the density of points of the system) may reduce the detection range of the system. Various techniques are used to mitigate the tradeoff between higher PRR and limited detection range. For example, multiple wavelengths can be used for detecting objects in different ranges. Optical and/or signal processing techniques are also used to correlate between transmitted and return light signals. 
     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. 
     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. 
     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  FIG.  14   , 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. 
     A high-level block diagram of an exemplary apparatus that may be used to implement systems, apparatus and methods described herein is illustrated in  FIG.  6   . Apparatus  600  comprises a processor  610  operatively coupled to a persistent storage device  620  and a main memory device  630 . Processor  610  controls the overall operation of apparatus  600  by executing computer program instructions that define such operations. The computer program instructions may be stored in persistent storage device  620 , or other computer-readable medium, and loaded into main memory device  630  when execution of the computer program instructions is desired. For example, processor  610  may be used to implement one or more components and systems described herein, such as control circuitry  350  (shown in  FIG.  3   ), vehicle perception and planning system  220  (shown in  FIG.  2   ), and vehicle control system  280  (shown in  FIG.  2   ). Thus, at least some of the method steps of  FIG.  14    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 at least some of the method steps of  FIG.  14   . Accordingly, by executing the computer program instructions, the processor  610  executes an algorithm defined by the method steps of  FIG.  14   . 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.). 
     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). 
     Persistent storage device  620  and main memory device  630  each comprise a tangible non-transitory computer readable storage medium. Persistent storage device  620 , and main memory device  630 , may each include high-speed random access memory, such as dynamic random access memory (DRAM), static random access memory (SRAM), double data rate synchronous dynamic random access memory (DDR RAM), or other random access solid state memory devices, and may include non-volatile memory, such as one or more magnetic disk storage devices such as internal hard disks and removable disks, magneto-optical disk storage devices, optical disk storage devices, flash memory devices, semiconductor memory devices, such as erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM), digital versatile disc read-only memory (DVD-ROM) disks, or other non-volatile solid state storage devices. 
     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 . 
     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. 
     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. 
       FIG.  7    illustrates a top view of an exemplary motorized optical scanner device  700 .  FIG.  8    illustrates a bottom view of the exemplary motorized optical scanner device  700 .  FIG.  9    illustrates a cross-sectional view of motorized optical scanner device  700  along the cross-section position A-A′ shown in  FIGS.  7  and  8   .  FIGS.  10 - 11    illustrate perspective views of motorized optical scanner device  700 .  FIG.  12    illustrates a cut-off view of the exemplary motorized optical scanner device according to some embodiments.  FIG.  13    illustrates an exploded view of motorized optical scanner device  700 .  FIGS.  7 - 13    are described together and the same elements are referred to by using the same numbers in  FIGS.  7 - 13   . Motorized optical scanner device  700  can be, for example, a part of steering mechanism  340  shown in  FIG.  3   . 
     Referencing  FIGS.  7 - 13   , motorized optical scanner device  700  comprises a glass-based optical reflector  702 . Optical reflector  702  can be, for example, a polygon mirror. In one embodiment, glass-based optical reflector  702  comprises a polygon-shaped top surface  705 , a polygon-shaped bottom surface  802 , and a plurality of reflective surfaces  704 A-E (collectively as  704 ). Reflective surfaces  704  form outer side surfaces of optical reflector  702 . Reflective surfaces  704  reflect light and are also referred to as facets of optical reflector  702 . Top surface  705  and bottom surface  802  may or may not be reflective. The top view of optical reflector  702  in  FIG.  7    shows a pentagon-shaped top surface  705 . In one embodiment, top surface  705  may be a flat or substantially flat surface comprising five edges. Top surface  705  may also be a curved surface having chamfered or beveled corners such as corner  708 . The five edges of top surface  705  form a pentagon shape. The edges of top surface  705  may be straight edges or curved edges. It is understood that glass-based optical reflector  702  can have a polygon-shaped top surface comprising any number of edges (e.g., 3, 4, 5, 6, 7, 8, etc.). Correspondingly, optical reflector  702  can have a triangle-, square-, pentagon-, hexagon-, heptagon-, or octagon-shaped top surface  705 ; and 3, 4, 5, 6, 7, 8 side surfaces, respectively. 
     The bottom view of optical reflector  702  in  FIG.  8    illustrates a pentagon-shaped bottom surface  802 . In  FIG.  8   , bottom surface  802  is a flat or substantially flat surface comprising five edges. Bottom surface  802  may also be a curved surface. The five edges of bottom surface  802  form a pentagon shape. The edges of the bottom surface  802  may be straight edges or curved edges. It is understood that glass-based optical reflector  702  can have a polygon-shaped bottom surface comprising any number of edges (e.g., 3, 4, 5, 6, 7, 8, etc.). Correspondingly, glass-based optical reflector  702  can have a triangle-, square-, pentagon-, hexagon-, heptagon-, or octagon-shaped bottom surface. As shown in  FIGS.  8  and  9   , polygon-shaped bottom surface  802  includes threaded holes  930  into which a plurality of fastening mechanisms  804  may be inserted during a wobble adjustment process. In some embodiments, a plurality of fastening mechanisms  804  may be adjustment screws. Polygon-shaped bottom surface  802  also includes through holes  806  for gluing an adjustment ring  908 . Through holes  806  can be round-shaped holes or any other shaped holes (e.g., rectangle, square, polygon, oval, or the like). 
     In some embodiments, motor assembly  910  has threaded holes  930  on its perimeter, each of which can be lined up with the center of a corresponding facet. Through holes  806  can be distributed evenly on its perimeter. In other embodiments, the threaded holes  930  can be disposed to line up with other locations of the facets in any desired manner. In some embodiments, motor assembly  910  has threaded holes  930  and through holes  806  alternatively distributed on its perimeter. For example, a threaded hole  930  is distributed between two through holes  806 , and a through hole  806  is distributed between two threaded holes  930 . In some embodiments, a quantity of the plurality of fastening mechanisms  804  may be the same as a quantity of the plurality of reflective surfaces of the glass-based optical reflector. During the wobble adjustment process, at least two of the plurality of fastening mechanisms  804  are inserted into threaded holes  930  and are tightened such that the adjustment ring  908  is supported by two of the plurality of fastening mechanisms  804  and a portion of the glass-based optical reflector  702  that is opposite to a mid-portion between the two fastening mechanisms  804 . As shown in  FIG.  9   , in particular, adjustment ring  908  can be in contact with flange  902  of the optical reflector  702  through a first mounting surface  922 . Thus, the portion of the optical reflector  702  that is opposite to a mid-portion between the two inserted fastening mechanisms  804  can be a portion of flange  902  that is contact with adjustment ring  908  and is opposite in position to the two inserted fastening mechanisms  804 . As one example shown in  FIG.  8   , if the low point is identified to be between the two reflective surfaces  704 D and  704 E, two fastening mechanisms  804  may be inserted into the threaded holes  930  corresponding to these two surfaces. The portion of the optical reflector  702  that is opposite to a mid-portion between the two inserted fastening mechanisms  804  can thus be located somewhere between the reflective surfaces  704 B and  704 C, or  704 A and  704 B. 
     In one example of a wobble adjustment process, a low point of a glass-based optical reflector  702  may be identified when measuring wobble using a fixture. In some embodiments, the low point may be identified by, for example, measuring the tilt angles of the plurality of reflective surfaces  704  of the optical reflector  702 . At least two of the plurality of fastening mechanisms  804  can be selected based on the identified low point. For example, if the low point is identified to be positioned between two adjacent threaded holes  930 , these two adjacent threaded holes  930  may be selected. If the low point is identified to be positioned very close (e.g., right next to) a particular threaded hole  930 , then this particular threaded hole  930  may be selected. An adjacent threaded hole  930  located on either side of this particular threaded hole  930  can be also selected. In some cases, three or more threaded holes  930  may be selected. During the wobble adjustment process, at least two fastening mechanisms  804  (e.g., adjustment screws) may be installed into at least two selected threaded holes  930  in motor assembly  910  to apply adjustment forces (e.g., pushing forces) to an adjustment ring to reduce wobble associated with rotation of glass-based optical reflector  702 . The at least two selected threaded holes may be adjacent threaded holes in most cases or spaced one threaded hole apart in case that the low point is aligned with the edge between two reflective surfaces. It is understood that any number of adjustment mechanisms  804  may be selected to perform the wobble adjustment by applying forces to the adjustment ring. The forces applied by different adjustment mechanisms  804  may be the same or different. The forces may be pushing forces or in some case, pulling forces. In some embodiments, the inserting of different fastening mechanisms  804  to the threaded holes  930  may be performed alternately between the different fastening mechanisms  804 . For instance, using  FIG.  8    as an illustrating, if fastening mechanisms located corresponding to reflective surfaces  704 A and  704 B are used to apply force to adjustment ring  908 , the two fastening mechanisms can be inserted in an alternating manner (e.g., a first fastening mechanism is inserted only half way, the second fastening mechanism is then inserted half way, the first fastening mechanism is then inserted further, and so on). In some embodiments, the installing of the fastening mechanisms are guided by the measured wobble of the optical reflector  702 . The measurement may be repeated one or more times until the installing of the fastening mechanisms reduces the wobble to be within a threshold or within a specification. 
     In some embodiments, after at least two of the plurality of fastening mechanisms  804  are inserted into respective threaded holes  930 , adhesive materials may be injected into one or more of a plurality of through holes  806  to secure the adjustment ring and/or the inserted fastening mechanisms in position. In some embodiments, adhesive materials may also be injected into respective threaded holes  930  to secure the plurality of fastening mechanisms in position. 
     Referencing  FIGS.  8 - 13   , optical reflector  702  comprises a plurality of reflective surfaces (e.g., surfaces  704 A-E) forming its outer side surfaces. The side surfaces share their top edges with top surface  705  and share their bottom edges with bottom surface  802 . In some embodiments, a side surface has a trapezoidal-type shape. Using reflective surface  704 B as an example, the top edge of reflective surface  704 B is longer than its bottom edge, thereby forming a trapezoidal-type shape. Similarly, in some embodiments, other reflective surfaces may also have longer top edges and shorter bottom edges. As a result, at least one of reflective surfaces  704 A-E (collectively  704 ) forms a tilt angle with respect to the rotational axis of optical reflector  702 . A tilt angle can be between 0-90 degrees (e.g., 27 degrees). A tilt angle is also referred to as a facet angle. In other words, one or more of reflective surfaces  704  are not parallel with the rotational axis of optical reflector  702 . Such a rotational axis is shown as axis  907  in  FIG.  9   . Rotational axis  907  of optical reflector  702  is parallel or substantially parallel to motor shaft  906 . As illustrated in  FIG.  9   , reflective surface  704 B and rotational axis form a tilt angle. Similarly, other reflective surfaces  704  may also form their respective tilt angles with rotational axis  907 . The tilt angles of different reflective surfaces  704 A-E may or may not be the same. 
     In some embodiments, reflective surfaces  704  comprise mirrors for reflecting or redirecting light. In other embodiments, reflective surfaces  704  comprises semiconductor wafer based reflectors (e.g., a polished piece of semiconductor wafer). The mirrors or semiconductor wafer based reflectors are disposed at the outer side surfaces of glass-based optical reflector  702 . In some embodiments, optical reflector  702  is made from a glass material and the side surfaces of optical reflector  702  are coated with reflective materials to make them reflective. In some embodiments, reflective surfaces  704  can also be made reflective by mechanically or adhesively attaching mirrors or semiconductor wafer based reflectors to the side surfaces of optical reflector  702 . In some embodiments, the outer side surfaces of the optical reflector  702  are integral parts of optical reflector  702 . For example, the entire optical reflector  702  can be made with reflective material so that each of the outer side surfaces (e.g., reflective surfaces  704 ) of optical reflector  702  is reflective. In some embodiments, only the outer side surfaces of optical reflector  702  are made reflective but other parts of optical reflector  702  are not made reflective. 
     As shown in the cross-sectional view of  FIG.  9   , optical reflector  702  has an inner opening  920 , within which at least a part of motor assembly  910  is disposed. Motor assembly  910  comprises a motor rotor body  904 . Motor rotor body  904  can be a metal-based piece formed by using aluminum, titanium, iron, copper, steel, an alloy, and/or any other desired metal-based materials. In one embodiment, motor rotor body  904  is made from aluminum, which has a CTE of about 22×10 −6 /° K. 
     As shown in  FIG.  9   , motor rotor body  904  is at least partially disposed within inner opening  920  of optical reflector  702  and mounted to optical reflector  702 .  FIG.  9    illustrates one embodiment where motor rotor body  904  is mechanically mounted to optical reflector  702  using a flange  902  of optical reflector  702 . Flange  902  can be an integral part of optical reflector  702 . Flange  902  may also be a detachable part that is mechanically mounted or attached to optical reflector  702 . In one embodiment, flange  902  extends from an inner sidewall  912  of optical reflector  702  towards motor rotor body  904 . In some embodiments, flange  902  includes a first mounting surface  922  that is in contact with a first surface  924  of an adjustment ring  908 . Adjustment ring  908  can have a ring shape as shown in  FIG.  13   . Flange  902  further includes a second mounting surface that is in contact with an elastomer piece  928 . Elastomer piece  928  can have a ring shape as shown in  FIGS.  12  and  13   . Elastomer piece  928  or a substantial portion thereof can be disposed on, and in contact with, flange  902 . In some embodiments, a clamp mechanism  942  is in contact with elastomer piece  928  and is configured to compress elastomer piece  928 . Elastomer piece  928  is thus disposed between clamping mechanism  942  and flange  902 . Clamping mechanism  942  may be, for example, a clamping ring. 
     As shown in  FIGS.  9  and  13   , clamping mechanism  942  compresses elastomer piece  928  to flange  902 , which in turn applies compression force to motor rotor body  904 . This way, optical reflector  702 , via flange  902 , is secured to motor rotor body  904  by the friction generated by the compression force. The amount of the compression can be configured to be sufficient under many foreseeable operating conditions (e.g., high speed rotation, temperature variation, humidity variations, road conditions, or the like). In one embodiment, clamping mechanism  942  is a clamping ring. In some embodiments, clamping mechanism  942  comprises one or more fastening mechanisms  944  (e.g., screws with or without lock washers). Fastening mechanisms  944  are used to apply compression forces to elastomer piece  928 . In operation of the LiDAR system, the movement of the metal-based motor rotor body  904  causes the glass-based optical reflector  702  to rotate at a very high speed in a range of about 2000-9000 revolutions per minute (rpm). Thus, clamping mechanism  942  may need to be configured to apply a proper compression force to secure optical reflector  702  to motor rotor body  904  under all or most of the foreseeable operating conditions. 
       FIG.  9    illustrates that adjustment ring  908  has a first surface  924  and a second surface  926 . First surface  924  can be the top surface of the ring-shaped adjustment ring  908 . Second surface  926  can be the bottom surface of the ring-shaped adjustment ring  908 . As shown in  FIG.  9   , first surface  924  of adjustment ring  908  is in contact with first mounting surface  922  of flange  902 . Second surface  926  of adjustment ring  908  is at least partially in contact with a motor rotor body  904 . When a fastening mechanism  804  is inserted into a threaded hole  930 , tip of a fastening mechanism  804  may be at least partially in contact with second surface  926  of adjustment ring  908  and is configured to apply adjustment forces to adjustment ring  908 . A plurality of fastening mechanisms  804  may be adjustment screws with hard ball, oval, or round shaped tip. As illustrated in  FIG.  9   , adjustment ring  908  is thus disposed between fastening mechanism  804  and flange  902 . 
     Referencing  FIGS.  9  and  13   , motor assembly  910  further comprises a motor shaft  906  disposed in one or more bearings  954  and  956 . Bearings  954  and  956  are disposed inside motor rotor body  904 . Motor assembly  910  further comprises a motor stator  958  and a magnetic ring  960 . Motor stator  958  has electrical windings. When motor assembly  910  is provided with electricity, magnetic forces are generated via the electrical windings mounted on motor stator  958 . The rotation of motor rotor body  904  causes optical reflector  702  to rotate. 
     Referencing  FIGS.  9  and  13   , in one embodiment, the glass-based optical reflector  702  and the metal-based motor rotor body  904  are substantially concentric with respect to a rotational axis (e.g., axis  907 ) along a longitudinal direction of motor shaft  906 . For example, the error of concentricity can be controlled to be less than a preconfigured threshold (e.g., about  20 - 25  pm). If the error of concentricity is larger than the threshold, the rotation of the optical reflector  702  may be imbalanced (e.g., off-centered) because the weight center of optical reflector  702  is shifted with respect to that of motor rotor body  904 . Such a shift may or may not impact the LiDAR scanning performance but may affect the overall robustness and reliability of optical reflector device  700 . 
     In some embodiments, optical reflector  702  and motor rotor body  904  are assembled in a manner to minimize wobbling during the rotation of optical reflector  702 . As shown in  FIG.  9   , to prevent wobbling, motor rotor body  904  includes threaded holes  930  extending from polygon-shaped bottom surface  802  toward the adjustment ring  908 . A plurality of fastening mechanisms  804  may be inserted into the threaded holes  930  during wobble adjustment. In some embodiments, a plurality of fastening mechanisms  804  may be adjustment screws. Motor rotor body  904  also includes through holes  806  for gluing an adjustment ring  908 . Through holes  806  may also extend from Polygon-shaped bottom surface  802  toward adjustment ring  908 . In some embodiments, motor assembly  910  has threaded holes  930  on its perimeter lined up with the center of each facet and through holes  806  distributed evenly on its perimeter. In some embodiments, motor assembly  910  has threaded holes  930  and through holes  806  alternatively distributed on its perimeter. For example, as described above, a threaded hole  930  is distributed between two through holes  806 , and a through hole  806  is distributed between two threaded holes  930 . During wobble adjustment, at least two of the plurality of fastening mechanisms  804  are inserted into threaded holes  930  and are tightened such that adjustment ring  908  is supported by two of the plurality of fastening mechanisms  804  and a portion of the glass-based optical reflector that is opposite to a mid-portion between the two fastening mechanisms. For example, a low point of a glass-based optical reflector  702  may be identified when measuring wobble using a fixture. During wobble adjustment, two adjustment screws may be installed into two selected threaded holes  930  in motor assembly  910  to apply adjustment forces to an adjustment ring to reduce wobble associated with rotation of glass-based optical reflector  702 . Adjustment ring  908  facilitates distributing the adjustment forces of a plurality of fastening mechanisms  804  to a large area on optical reflector  702 . In some embodiments, adjustment ring  908  are made from hard steel materials (e.g., full hard H 302  steel material). In some embodiments, after the plurality of fastening mechanisms are inserted into threaded holes  930 , adhesive materials may be injected into a plurality of through holes  806  to secure the plurality of fastening mechanisms  804 . In some embodiments, adhesive materials may also be injected behind the plurality of fastening mechanisms to secure them. 
     As shown in  FIGS.  11 - 12   , the compression force can be applied by using a plurality of fastening mechanisms  804  disposed under adjustment ring  908 . In  FIG.  10   , for example, fastening mechanisms  804  include two adjustment screws. For example, a low point of a glass-based optical reflector  702  may be identified when measuring wobble using a fixture. As described above, during wobble adjustment, in one embodiment, two adjustment screws may be installed into two selected threaded holes in motor assembly  910  to apply adjustment forces to an adjustment ring to reduce wobble associated with rotation of glass-based optical reflector  702 . The two adjustment screws may be in adjacent threaded holes in most cases or spaced one threaded hole apart in case that the low point is aligned with the edge between two facets. In some embodiments, the two screws are tightened such that the same or substantially the same amount of adjustment forces are applied to adjustment ring  908 . In some embodiments, the two screws are adjustable individually or as a group such that optical reflector  702  is secured and capable of rotating without wobbling (or within a tolerable wobbling range). For example, some screws may be tightened more than the others to fine tune the amount of adjustment forces applied at any given point of adjustment ring  908 . Wobbling can be eliminated or substantially reduced by such fine tuning of the adjustment forces using the fastening mechanisms  804 . It is understood that motor assembly  910  may include any number of fastening mechanisms  804  distributed in any manner to satisfy the performance requirements of optical reflector  702 . 
     Referencing  FIG.  13   , optical reflector device  700  further comprises a Hall-effect sensor and processing circuitry  1312 . The Hall-effect sensor and processing circuitry  1312  detects the presence and the magnitude of a magnetic field using the Hall effect. The output voltage of the Hall-effect sensor is directly proportional to the strength of the field. Thus, the Hall-effect sensor and processing circuitry  1312  can be used to detect the angular position, rotational speed, and phases, rotational directions, etc. of optical reflector  702 . For example, one or more magnets (not shown) can be installed in optical reflector device  700  to rotate together with optical reflector  702 . When the magnets passing through Hall-effect sensor and processing circuitry  1312 , electrical signals are generated and processed to compute various parameters of optical reflector  702 . In some embodiments, a Hall-effect sensor is more sensitive and accurate than an index encoder. And therefore, optical reflector device  700  may use only the Hall-effect sensor during operation. The index encoder can be used, for example, during calibration of the LiDAR system. In some embodiments, optical reflector device  700  can use both the index encoder and the Hall-effect sensor for position encoding. 
     Referencing  FIG.  13   , in some embodiments, optical reflector device  700  further comprises a fairing  1302 . Fairing  1302  is disposed around the optical reflector  702  to at least partially enclose optical reflector  702  and other components of motor assembly  910 . In one embodiment, fairing  1302  comprises a housing, walls, covers, and/or other structures to at least partially enclose optical reflector  702  and motor assembly  910 . In one embodiment, fairing  1302  comprises at least a portion of a cylinder or a cone. An axial direction of fairing  1302  is substantially parallel to an axial direction of optical reflector  702 . Fairing  1302  can be concentric or eccentric to optical reflector  702 . Fairing  1302 , alone or in combination with motor base  1314 , encloses the optical reflector  702  to form a housing. The enclosing of optical reflector  702  by using one or both of fairing  1302  and motor base  1314  reduces the air friction caused by the high-speed rotation of optical reflector  702 , thereby effectively generating a local vacuum surrounding optical reflector  702 . The housing formed by fairing  1302  and/or motor base  1314  thus facilitates a smoother rotation of optical reflector  702  (e.g., reduces the variations of speed between rotations caused by air friction or turbulence). In turn, the smoother rotation improves the overall light scanning performance and energy efficiency of optical reflector  702 . 
       FIG.  14    illustrates an exemplary method  1400  for adjusting a motorized optical scanner device to reduce wobble according to some embodiments of the present disclosure. In some examples, at least some of these operations are performed by a system including a processor executing a set of codes to control functional elements of an apparatus. Additionally or alternatively, certain processes are performed by a human operator. Generally, these operations are performed according to the methods and processes described in accordance with aspects of the present disclosure. In some cases, the operations described herein are composed of various substeps, or are performed in conjunction with other operations. 
     As shown in  FIG.  14   , method  1400  is an exemplary method for adjusting a motorized optical scanner device to reduce wobble. At step  1405 , a system or human operator assembles a motorized optical scanner device. The device may be motorized optical scanner  700  as described with reference to  FIG.  7   . The motorized optical scanner device may comprise a glass-based optical reflector including a plurality of reflective surfaces, an adjustment ring, and a metal-based motor rotor body at least partially disposed in an inner opening of the glass-based optical reflector. 
     At step  1410 , a system or human operator measures wobble of a motorized optical scanner device. In some embodiments, measuring the wobble of the motorized optical scanner device includes identifying a low point of the glass-based optical reflector. For instance, a low point may be identified using a fixed laser source. A fixed laser source may emit light to a plurality of reflective surfaces (e.g., surfaces  704 A-D) of a glass-based optical reflector (e.g., reflector  702 ). The glass-based optical reflector may be rotated such that each of the plurality of reflective surfaces may reflect the light emitted from the fixed laser source. The reflected light may be received by an optical detector such as a quadrant detector which generates electric signals based on received reflected light. In some embodiments, when the tilt angles of the reflective surfaces are different from one another, light reflected from the reflective surfaces are received at different positions of detector elements of the optical detector. As such, the electrical signals generated by the detector elements of the optical detector based on the reflected light can indicate tilt angles, or tile angle differences, of the plurality of reflective surfaces. A low point can therefore be identified based on comparisons of the tilt angles or their differences using the electrical signals. As described above, due to various factors of manufacturing process, center of a polygon mirror may have a small angular deviation from its center of rotation. When center of a polygon mirror is not perfectly in-line with its center of rotation, tilt angles of the polygon facets may change in the process of angular rotation, and the polygon mirror may wobble. 
     At step  1415 , a system or human operator selects at least two adjustment positions with respect to the adjustment ring based on the measured wobble. In some embodiments, to select the adjustment positions, step  1415  determines whether a position of the low point is between two reflective surfaces of the plurality of reflective surfaces of the optical reflector. If the position of the low point is determined to be between two adjacent reflective surfaces of the plurality of reflective surfaces, then two threaded holes of a plurality of threaded holes corresponding to the two adjacent reflective surfaces may be selected as the at least two adjustment positions. For example, for a motorized optical scanner device  700  illustrated in  FIG.  8   , a position of a low point may be between reflective surface  704 D and reflective surface  704 E. As described above, each of threaded holes  930  may be lined up with the center of a corresponding reflective surface. When the position of a low point is determined to be between reflective surface  704 D and reflective surface  704 E, threaded holes  930  which are lined up with the centers of reflective surface  704 D and reflective surface  704 E respectively may be selected to be the adjustment positions. Fastening mechanisms can thus be inserted to these selected threaded holes  930 . 
     In some embodiments, to select the adjustment positions, step  1415  determines whether a position of the low point may be within a threshold angle to a particular threaded hole of a plurality of threaded holes  930 . As shown in  FIG.  15   , a threshold angle may be represented by angle α. Angle α can be a predetermined angle measured from the line connecting the center of rotation of the optical reflector and a particular threaded hole for inserting fastening mechanism  804 . A threshold angle may be, for example, 10 degrees. It is understood that the threshold angle can be configured to be any desired number. For example, for a motorized optical scanner device  700  illustrated in  FIG.  15   , if the position of the low point is determined to be within a threshold angle to a threaded hole for inserting fastening mechanism  804  corresponding to reflective surface  704 C, then two adjacent threaded holes, (in this case, threaded holes for inserting fastening mechanisms  804  corresponding to reflective surface  704 B and reflective surface  704 D respectively, are selected as adjustment positions. 
     In some embodiments, to select the adjustment positions, step  1415  determines whether a position of the low point may be aligned with an edge between two reflective surfaces of the plurality of reflective surfaces. If the position of the low point is determined to be aligned with an edge between two reflective surfaces of the plurality of reflective surfaces, then two threaded holes of the plurality of threaded holes corresponding to the two reflective surfaces at an end of the edge may be selected as the at least two adjustment positions. For example, for a motorized optical scanner device  700  illustrated in  FIG.  8   , a position of the low point may be determined to be aligned with the edge of reflective surface  704 A between two reflective surfaces  704 B and  704 E. Then threaded holes  930  which are lined up with the centers of reflective surface  704 B and reflective surface  704 E respectively may be selected to be two adjustment positions. 
     With reference still to  FIG.  14   , at step  1420 , a system or human operator installs a plurality of fastening mechanisms to apply adjustment forces to the adjustment ring at the at least two selected adjustment positions. In some embodiments, a plurality of fastening mechanisms may be inserted into adjustment positions individually. In some embodiments, a plurality of fastening mechanisms may be fine tuned to apply predetermined adjustment forces. In some embodiments, wobble of the motorized optical scanner device may be re-measured. More fastening mechanisms of the plurality of fastening mechanisms may be inserted after remeasurement of wobble. In some embodiments, a motorized optical scanner device comprises a plurality of through holes. Adhesive materials (e.g., glue) may be injected into the plurality of through holes to secure at least one of the adjustment ring. Adhesive materials may also be injected at the selected adjustment positions to secure the plurality of fastening mechanisms. 
     Various exemplary embodiments are described herein. Reference is made to these examples in a non-limiting sense. They are provided to illustrate more broadly applicable aspects of the disclosed technology. Various changes may be made, and equivalents may be substituted without departing from the true spirit and scope of the various embodiments. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process act(s) or step(s) to the obj ective(s), spirit or scope of the various embodiments. Further, as will be appreciated by those with skill in the art, each of the individual variations described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the various embodiments.