Patent ID: 12222456

DETAILED DESCRIPTION

Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

Embodiments of the present disclosure provide systems and methods for dynamically controlling the receiver gain in an optical sensing system (e.g., a LiDAR system). For example, the optical sensing system may include a transmitter configured to emit light beams (e.g., laser beams) at a plurality of vertical detection angles to scan an object. At smaller vertical detection angles, the detection distance is longer while at larger vertical detection angles, the detection distance shortens. The emitted light beams are reflected and returned from the object being scanned, and received by a receiver of the optical sensing system. For example, the receiver may include a detector that detects the returned light beams.

In some embodiments, the optical sensing system includes a controller configured to dynamically vary a gain of the detector for receiving the light beams emitted at the respective vertical detection angles. For example, the detector gain may be adjusted according to the detection distances at the various vertical detection angles, as light beams returned from shorter detection distances carry higher laser power and thus warrant using a lower gain. In some embodiments, the detector gain can be varied proportional to a square of the detection distances. In some further embodiments, the detector gain may be further adjusted by a ratio of the reflectivity of the object and the reflectivity of the ground. As another example, the controller may determine a threshold angle based on an elevation of the optical sensing system positioned above a ground and a threshold detection distance of the optical sensing system. The controller then reduces the detector gain when the vertical detection angle surpasses the threshold angle.

In some embodiments, the detector may further include a photodetector, a signal amplifier, and a signal conditioning circuit, and the gain of the detector can be varied by adjusting the gains of one or more of these individual components. For example, the controller can adjust the bias voltage of the photodetector in order to adjust the amplitude of the electrical signal generated by the photodetector in response to receiving a light beam. As another example, the controller can adjust the gain of the signal amplifier and/or signal conditioning circuit in order to adjust the signal amplitude.

In some embodiments, the detector gain control may be implemented with an open-loop or closed-loop method, or a hybrid version of the two. For example, in an open-loop control, the controller can look up a target gain of the detector for each vertical detection angle at which the light beam is emitted, and adjust the gain of the detector to the target gain. As another example, in a closed-loop control, a saturation detection circuit may be used to detect a saturation condition of the detector. When a saturation occurs, the controller may reduce the gain of the detector in response until the gain is reduced to a level that removes the saturation condition in the detector. In some embodiments, the saturation detection circuit may differentiate which component(s) of the detector causes the saturation and the controller may specifically adjust the again of that component(s) to address the saturation.

By dynamically and adaptively varying the receiver gain, embodiments of the present disclosure therefore improve the performance of an optical sensing system. For example, by avoiding saturation on the receiver end, the detection accuracy of the optical sensing system can be improved. On the other hand, reducing receiving power in the receiver also benefits thermal efficiency of the system. The improved optical sensing system can be used in many applications. For example, the improved optical sensing system can be used in advanced navigation technologies, such as to aid autonomous driving or to generate high-definition maps, in which the optical sensing system can be equipped on a vehicle.

For example,FIG.1illustrates a schematic diagram of an exemplary vehicle100equipped with an optical sensing system (e.g., a LiDAR system)102(hereinafter also referred to as LiDAR system102), according to embodiments of the disclosure. Consistent with some embodiments, vehicle100may be a survey vehicle configured for acquiring data for constructing a high-definition map or 3-D buildings and city modeling. Vehicle100may also be an autonomous driving vehicle.

As illustrated inFIG.1, vehicle100may be equipped with LiDAR system102mounted to a body104via a mounting structure108. Mounting structure108may be an electro-mechanical device installed or otherwise attached to body104of vehicle100. In some embodiments of the present disclosure, mounting structure108may use screws, adhesives, or another mounting mechanism. Vehicle100may be additionally equipped with a sensor110inside or outside body104using any suitable mounting mechanisms. Sensor110may include sensors used in a navigation unit, such as a Global Positioning System (GPS) receiver and one or more Inertial Measurement Unit (IMU) sensors. It is contemplated that the manners in which LiDAR system102or sensor110can be equipped on vehicle100are not limited by the example shown inFIG.1and may be modified depending on the types of LiDAR system102and sensor110and/or vehicle100to achieve desirable 3D sensing performance.

Consistent with some embodiments, LiDAR system102and sensor110may be configured to capture data as vehicle100moves along a trajectory. For example, a transmitter of LiDAR system102may be configured to scan the surrounding environment. LiDAR system102measures distance to a target by illuminating the target with a pulsed laser beam and measuring the reflected/scattered pulses with a receiver. The laser beam used for LiDAR system102may be ultraviolet, visible, or near infrared. In some embodiments of the present disclosure, LiDAR system102may capture point clouds including depth information of the objects in the surrounding environment. As vehicle100moves along the trajectory, LiDAR system102may continuously capture data. Each set of scene data captured at a certain time range is known as a data frame.

In some embodiments, LiDAR system102may be mounted at a certain elevation (e.g., h0as shown inFIG.1) above the ground such that it can scan objects at a range of heights using laser beams emitted at different vertical detection angles. For example,FIG.1shows a field of view (FOV) consisting of a range of vertical detection angles to cover an object112up to hi in height above the ground. A vertical detection angle of a laser beam pointing upward relative to the horizontal direction (e.g., angle α as shown inFIG.1) may be referred to as a look-up angle, and a vertical detection angle of a laser beam pointing downward relative to the horizontal direction (e.g., angle θ as shown inFIG.1) may be referred to as a look-down angle.

In some embodiments, the vertical detection angle of LiDAR system102may be adjusted by mounting structure108and/or the scanner within LiDAR system102. In some embodiments, the vertical detection angle may also be impacted by the pose of vehicle100, e.g., whether vehicle100is traveling uphill or downhill. When the look-down angle θ is larger than a certain value, the laser beam emitted by LiDAR system102may impinge on the ground and the corresponding detection distance may be smaller than the maximum detection distance. In such cases, because the laser beam travels for a shorter distance, it is less attenuated and the remaining power in the returned laser beam is higher. Consistent with the present disclosure, LiDAR system102is configured to dynamically and adaptively adjust the receiver gain when receiving the laser beams during a scan, in a way to compensate for the shorter detection distances at larger vertical detection angles θ.

FIG.2illustrates a block diagram of an exemplary LiDAR system102, according to embodiments of the disclosure. LiDAR system102may include a transmitter202, a receiver204, and a controller206. Transmitter202may emit optical beams (e.g., laser beams) along multiple directions. Transmitter202may include one or more laser sources208and a scanner210. Transmitter202can sequentially emit a stream of pulsed laser beams in different directions within a scan FOV (e.g., a range in angular degrees), as illustrated inFIG.2.

Laser source208may be configured to provide a laser beam207(also referred to as “native laser beam”) to scanner210. In some embodiments of the present disclosure, laser source208may generate a pulsed laser beam in the ultraviolet, visible, or near infrared wavelength range. In some embodiments of the present disclosure, laser source208may include a pulsed laser diode (PLD), a vertical-cavity surface-emitting laser (VCSEL), a fiber laser, etc. For example, a PLD may be a semiconductor device similar to a light-emitting diode (LED) in which the laser beam is created at the diode's junction. In some embodiments of the present disclosure, a PLD includes a PIN diode in which the active region is in the intrinsic (I) region, and the carriers (electrons and holes) are pumped into the active region from the N and P regions, respectively. Depending on the semiconductor materials, the wavelength of incident laser beam207provided by a PLD may be smaller than 1,100 nm, such as 405 nm, between 445 nm and 465 nm, between 510 nm and 525 nm, 532 nm, 635 nm, between 650 nm and 660 nm, 670 nm, 760 nm, 785 nm, 808 nm, 848 nm, or 905 nm. It is understood that any suitable laser source may be used as laser source208for emitting laser beam207.

Scanner210may be configured to emit a laser beam209to an object212in a range of vertical detection angles (collectively forming the FOV of transmitter202such as shown inFIG.1). The vertical detection angles can be look-up angles (pointing upward from the horizontal direction) or look-down angles (pointing downward from the horizontal direction). In some embodiments, scanner210may also include optical components (e.g., lenses, mirrors) that can collimate pulsed laser light into a narrow laser beam to increase the scan resolution and the range to scan object212.

In some embodiments, object212may be made of a wide range of materials including, for example, non-metallic objects, rocks, rain, chemical compounds, aerosols, clouds and even single molecules. In some embodiments, at each time point during the scan, scanner210may emit laser beam209to object212in a direction within a range of scanning angles by rotating a deflector, such as a micromachined mirror assembly.

In some embodiments, receiver204may be configured to detect a returned laser beam211returned from object212. The returned laser beam211may be in a different direction from laser beam209. Receiver204can collect laser beams returned from object212and output electrical signals reflecting the intensity of the returned laser beams. Upon contact, laser light can be reflected/scattered by object212via backscattering, such as Rayleigh scattering, Mie scattering, Raman scattering, and fluorescence. As illustrated inFIG.2, receiver204may include a lens214and a detector216. Lens214may be configured to collect light from a respective direction in the receiver field of view (FOV) and converge the light beam to focus on detector216. At each time point during the scan, returned laser beam211may be collected by lens214. Returned laser beam211may be returned from object212and have the same wavelength as laser beam209.

Detector216may be configured to detect returned laser beam211returned from object212and converged by lens214. In some embodiments, detector216may convert the laser light (e.g., returned laser beam211) converged by lens214into an electrical signal218(e.g., a current or a voltage signal). Detector216may have a gain defined as a ratio between the power of electrical signal218and power of the light beam received by detector216. The higher the gain is, the higher amplitude electrical signal218has. Consistent with the present disclosure, the gain of detector216can be dynamically varied at different vertical detection angles of the light beams.

In some embodiments, detector216may include several stages and the gain of detector216may be adjusted at one or more of the stages. For example,FIG.3illustrates a schematic diagram of an exemplary detector300in a receiver of a LiDAR system, according to embodiments of the disclosure. As shown inFIG.3, detector300may include three stages: a photodetector302, a signal amplifier304, and a signal conditioning circuit306. Each stage has its own gain defined as a ratio between the output power and input power, and the overall gain of detector300is a product of the gains of the individual stages.

Photodetector302may include a photodiode that converts light into an electrical current (also known as photocurrent). In some embodiments, photodetector302may include a PIN detector, an avalanche photodiode (APD) detector, a single photon avalanche diode (SPAD) detector, a silicon photo multiplier (SiPM) detector, or the like. The photocurrent is generated when photos are absorbed in the photodiode. The ratio of photocurrent generated from incident light to the power of the incident light (known as responsivity of a photodiode) can be manipulated by adjusting the bias voltage of the photodiode. Therefore, the gain of detector300can be adjusted by varying the bias voltage of photodetector302.

Signal amplifier304may amplify the electrical signal generated by photodetector302. In some embodiments, signal amplifier may be a transimpedance amplifier. Signal conditioning circuit306may further condition the electrical signal. In some embodiments, signal conditioning circuit306may be a limiting amplifier, a log amplifier, a comparator, an analog-to-digital converter (ADC), or a time-to-digital converter (TDC). The gain of detector300can be alternatively or additionally adjusted by varying the gains of signal amplifier304and/or signal conditioning circuit306.

In some embodiments, saturation may occur at one or more stages of detector300. For example, one or more of photodetector302, signal amplifier304, and signal conditioning circuit306may be saturated. In some embodiments, a saturation detection circuit310may be coupled with each of photodetector302, signal amplifier304, and signal conditioning circuit306to detect the saturation condition. In some embodiments, the gain of the saturated component may be reduced to remove the saturation condition.

Returning toFIG.2, electrical signal218may be transmitted to a data processing unit, e.g., signal processor220of LiDAR system102, to be processed and analyzed. For example, signal processor220may determine the distance of object212from LiDAR system102based on electrical signal218and data of laser beam209. In some embodiments, signal processor may be a field-programmable gate array (FPGA), a microcontroller unit (MCU), a central processing unit (CPU), a digital signal processor (DSP), etc. In some embodiments, signal processor220may be part of controller206.

Controller206may be configured to control transmitter202and/or receiver204to perform detection/sensing operations. In some embodiments consistent with the present disclosure, controller206may dynamically determine an appropriate gain for detector216based on the vertical detection angle of LiDAR system102and adjust the gain to the appropriate level. For example, controller206may use a predetermined look-up table (LUT) to determine the target gains for detector216corresponding to the various vertical detection angles. In some embodiments, the target gain can be proportional to a square of the detection distances calculated for the respective vertical detection angles. In some further embodiments, the target gain is also proportional to a ratio of the reflectivity of object212and the reflectivity of the ground. For example, controller206may determine the reflectivity of object212based on the returned laser beams received by receiver204. In another example, controller206may determine a threshold angle based on an elevation of LiDAR system102positioned above the ground and a threshold detection distance of LiDAR system102. Controller206may reduce the gain when the vertical detection angle surpasses the threshold angle. In yet another example, controller206may reduce the gain when saturation detection circuit310detects a saturation condition from detector216.

In some embodiments, controller206may generate and send a command signal to detector216to adjust its gain. For example, controller206may send the command signal to photodetector302to adjust its bias voltage, thus adjusting the photocurrent it generates. As another example, controller206may send the command signal to signal amplifier304and/or signal conditioning circuit306to adjust the respective gains.

For example,FIG.4illustrates a schematic diagram of an exemplary controller206for adjusting laser power of a LiDAR system, according to embodiments of the disclosure. As shown byFIG.4, controller206may include a communication interface402, a processor404, a memory406, and a storage408. In some embodiments, controller206may have different modules in a single device, such as an integrated circuit (IC) chip (e.g., implemented as an application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA)), or separate devices with dedicated functions. In some embodiments, one or more components of controller206may be located in a cloud or may be alternatively in a single location (such as inside a mobile device) or distributed locations. Components of controller206may be in an integrated device or distributed at different locations but communicate with each other through a network (not shown). Consistent with the present disclosure, controller206may be configured to dynamically control the gain of detector216based on the different vertical detection angles of the emitted laser beams. In some embodiments, controller206may also perform various other control functions of other components of LiDAR system102.

Communication interface402may send signals to and receive signals from components of transmitter202and receiver204(such as detector216and components therein) via wired communication methods, such as Serializer/Deserializer (SerDes), Low-voltage differential signaling (LVDS), Serial Peripheral Interface (SPI), etc. In some embodiments, communication interface402may optionally use wireless communication methods, such as a Wireless Local Area Network (WLAN), a Wide Area Network (WAN), wireless networks such as radio waves, a cellular network, and/or a local or short-range wireless network (e.g., Bluetooth™), etc. Communication interface402can send and receive electrical, electromagnetic or optical signals in analog form or in digital form.

Consistent with some embodiments, communication interface402may receive scanning parameters, such as vertical detection angles of emitted laser beams, from transmitter202. Communication interface402may additionally receive detection results from saturation detection circuit310. Communication interface402may provide command signals to detector216to dynamically adjust its gain. Communication interface402may also receive acquired signals from and provide control signals to various other components of LiDAR system102.

Processor404may include any appropriate type of general-purpose or special-purpose microprocessor, digital signal processor, or microcontroller. Processor404may be configured as a separate processor module dedicated to LiDAR emitting power control, e.g., dynamically determining a target gain for detector216for receiving light beams of different vertical detection angles and generating command signals to adjust the gain of detector216to that target gain. Alternatively, processor404may be configured as a shared processor module for performing other functions of LiDAR controls.

Memory406and storage408may include any appropriate type of mass storage provided to store any type of information that processor404may need to operate. Memory406and storage408may be a volatile or non-volatile, magnetic, semiconductor, tape, optical, removable, non-removable, or other type of storage device or tangible (i.e., non-transitory) computer-readable medium including, but not limited to, a ROM, a flash memory, a dynamic RAM, and a static RAM. Memory406and/or storage408may be configured to store one or more computer programs that may be executed by processor404to perform functions disclosed herein. For example, memory406and/or storage408may be configured to store program(s) that may be executed by processor404for dynamic receiver gain control in a LiDAR. In some embodiments, memory406and/or storage408may further store a predetermined look-up table that maps various vertical detection angles to corresponding pre-calculated target gains. In some embodiments, memory406and/or storage408may also store intermediate data such as threshold vertical detection angle, detection distances corresponding to the different vertical detection angles, reflectivity of the object being scanned, desired gains for the respective vertical detection angles, etc.

As shown inFIG.4, processor404may include multiple modules, such as a detection distance determination unit442, a gain determination unit444, a saturation detection unit446, and a command signal generation unit448, and the like. These modules can be hardware units (e.g., portions of an integrated circuit) of processor404designed for use with other components or software units implemented by processor404through executing at least part of a program. The program may be stored on a computer-readable medium, and when executed by processor404, it may perform one or more functions. AlthoughFIG.4shows units442-448all within one processor404, it is contemplated that these units may be distributed among different processors located closely or remotely with each other.

In some embodiments, detection distance determination unit442may calculate the detection distances corresponding to various vertical detection angles within the transmitter FOV. For example,FIG.5illustrates vertical detection angles used during a LiDAR scan and corresponding detection distances, according to embodiments of the disclosure. As shown inFIG.5, LiDAR system102may locate at an elevation of h0above the ground plane. For example, LiDAR system102may be mounted on vehicle100and therefore lifted above the ground. LiDAR system102may have maximum detection distance dmax(also referred to as a threshold detection distance), which corresponds to the horizontal distance between object112and LiDAR system102.

In some embodiments, the detection distance may be calculated as a function of the vertical detection angle (e.g., look-down angle θ as shown inFIG.5). For example, the vertical detection angles may be determined based on the vertical scanning angles of scanner210, the tilt angle of LiDAR system102(e.g., by mounting structure108), and the elevation angle if the vehicle on which LiDAR system102is mount is traveling on a slope (e.g., uphill or downhill). In some embodiments, the vertical scanning angles of scanner210may be stored in controller206or obtained from another controller that controls the scanning of laser beams. The tilt angle and/or the elevation angle, if non-zero, are subtracted from the vertical scanning angles to obtain the vertical detection angles. For example, if the vertical scanning angle is 40°, LiDAR system102is mounted to be tilted upward for 10°, and vehicle100is traveling downhill on a slope of 15° (i.e., a −15° elevation angle), the vertical detection angle is determined as 40°−10°−(−) 15°=45°.

In some embodiments, the detection distances may be calculated differently for vertical detection angles in two ranges: a first range of [0, θa], where θais a threshold angle, and a second range of [θa, 90°). In some embodiments, the threshold angle θamay be determined according to Equation (1):

θa=sin-1⁡(h⁢⁢0dmax)(1)
where h0is the elevation of LiDAR system102above the ground plane, and dmaxis the maximum detection distance.

When the vertical detection angle (e.g., look-down angle θ as shown inFIG.5) is smaller than θa(i.e., in the first range), the detection distance remains dmax. When the look-down angle θ is larger than θa(i.e., in the second range), the detection distance do becomes smaller. In some embodiments, the detection distance can be determined using Equation (2):

dθ=h⁢⁢0sin⁢⁢θ.(2)

Based on the determined detection distances, gain determination unit444may calculate the target gain for detector216. In some embodiments, for detection distances dθshorter than the maximum detection distance dmax(i.e., for vertical detection angles θ larger than the threshold angle θa), gain determination unit444may reduce the detector gain from the maximum gain Gmaxto a smaller but sufficient level. In some embodiments, the target gain may be proportional to a square of the respective detection distances. In some further embodiments, the target gain is proportional to a ratio of a first reflectivity of the target object and a second reflectivity of the ground. For example, gain determination unit444may calculate the target gain (Go) at look-down angle θ according to Equation (3):

Gθ=(dθdmax)2·ρobjectρground·Gmax(3)
where Gmaxis the maximum gain of detector216, ρobjectis the reflectivity of target object and ρgroundis the reflectivity of ground plane, dθis the detection distance at look-down angle θ, and dmaxis the maximum detection distance. In some embodiments, the reflectivity of ground plane may be predetermined and preprogramed into controller206. In some embodiments, the reflectivity of the target object (e.g., object112) may be determined dynamically based on returned laser beam signals received by receiver204in real-time.

In some embodiments, the target gains Gθscorresponding to various vertical detection angles θSof the light beams may be calculated offline, e.g., by a separate processor, according to Equations (1)-(3). The mapping between the target gains and the vertical detection angles may be recorded in a look-up table and preprogramed in controller206. For example, the look-up table may be stored in memory406or storage408of controller206. According to such embodiments, the calculations performed by detection distance determination unit442described above may be skipped. Gain determination unit444may determine the target gain by looking up the vertical detection angles θ in the look-up table.

In some embodiments, saturation detection unit446may determine whether a saturation condition has occurred based on the detection results provided by saturation detection circuit310. In some embodiments, if a saturation condition is detected, saturation detection unit446may additionally determine where the saturation condition has occurred, e.g., in photodetector302, signal amplifier304and/or signal conditioning circuit306.

Command signal generation unit448may generate a command signal to adjust the gain of detector216according to the determination by gain determination unit444and/or saturation detection unit446. In some embodiments, when open-loop control is used, the command signal may be generated based on the target gain determined by gain determination unit444in order to adjust the gain of detector216to the target gain. The open-loop control method will be described in more details in connection withFIG.6. In some alternative embodiments, when closed-loop control used, the command signal may be generated to reduce the gain of detector216when a saturation condition is detected, until the gain is reduced to a level that the saturation condition no longer exists. The closed-loop control method will be described in more details in connection withFIG.7. In yet some alternative embodiments, a hybrid control method can be used. For example, gain determination unit444may first generate an initial command signal to adjust the gain of detector216to the target gain determined by gain determination unit444, and then generate another command signal to fine tune the gain until saturation condition disappears from detector216.

In some embodiments, the command signal may adjust the gains of one or more stages in detector216. For example, it may adjust the bias voltage of photodetector302, and/or the gains of signal amplifier304and/or signal conditioning circuit306. In some embodiments, based on where the saturation condition occurs, as determined by saturation detection unit446, the command signal may be provided to the respective component to adjust its gain in order to remove the saturation condition.

FIG.6is a flow chart of an exemplary open-loop control method600for adjusting a receiver gain of a LiDAR system, according to embodiments of the disclosure. In some embodiments, method600may be performed by various components of LiDAR system102, e.g., receiver204and controller206. In some embodiments, method600may include steps S602-618. It is to be appreciated that some of the steps may be optional. Further, some of the steps may be performed simultaneously, or in a different order than shown inFIG.6.

In step S602, controller206may determine the vertical detection angle for the current scanning angle. In some embodiments, controller206may receive the current scanning angle used by transmitter202. In some embodiments, controller206may be the same controller that determines the scanning parameters and therefore have the parameters saved in its memory/storage. Therefore, controller206may retrieve the scanning angle from its own memory/storage. Otherwise, controller206may receive it from an external source. In some embodiments, detection distance determination unit442may first determine the current vertical detection angle based on the scanning angle, as adjusted by the tilt angle of LiDAR system102, and the elevation angle if the vehicle is traveling on a slope.

In step S604, controller206may then calculate the detection distance corresponding to the current vertical detection angle. For example, when the vertical detection angle θ is smaller than a threshold angle θacalculated, e.g., according to Equation (1), detection distance determination unit342may determine the detection distance remains the maximum detection distance dmax. When the angle θ surpasses than θa, detection distance determination unit342may determine the detection distance using the elevation h0and a trigonometry of the angle θ, e.g., according to Equation (2).

In step S606, controller206may determine the detector gain for receiving the light beam emitted at the current scanning angle based on the detection distance determined in step S604. In some embodiments, for detection distances dθshorter than the maximum detection distance dmax, gain determination unit444may reduce the gain from the maximum gain Gmaxto a smaller but sufficient level. In some embodiments, the target gain may be proportional to a square of the respective detection distances. In some further embodiments, the emitting power level is proportional to a ratio of a first reflectivity of the target object and a second reflectivity of the ground. For example, gain determination unit344may calculate the target gain according to Equation (3).

In step S608, controller206may generate a command signal corresponding to the target gain determined in step S606. In some embodiments, the command signal may be generated to adjust the bias voltage of photodetector302, and/or the gains of signal amplifier304and/or signal conditioning circuit306. In step S610, controller206may supply the command signal to the respective components of detector216to adjust the gain to the target gain.

In step S612, receiver204may detect the light beam returned by the target object using detector216. For example, receiver204may detect a returned laser beam211returned from object212. Receiver204can collect laser beams returned from object212and output electrical signals reflecting the intensity of the returned laser beams, as adjusted by the gain. In step S614, controller206may determine the reflectivity of the target object based on the intensity of the returned laser beams. The reflectivity of the object may be used in step S606to determine the target gain. For example, the target gain may be further adjusted by a ratio of the reflectivity of the target object and the reflectivity of the ground.

In step S616, controller206may determine whether all scanning angles of scanner210have been covered, and if not (S616: NO), method600proceeds to step S618to determine and adjust the detector gain for the next scanning angle, for example, by repeating steps S602-S616. Method600concludes after scanner210goes through all the scanning angles (S616: YES).

In some embodiments, steps S604-S606may be performed offline for all the vertical detection angles to determine the corresponding target gains. The results may be recorded in a look-up table and saved with controller206. In real-time execution, method600may skip S604and S606, and instead, method600may include a step where controller206looks up the target gain for the current vertical detection angle from the predetermined look-up table. By using a look-up table, computation cost can be significantly reduced.

FIG.7is a flow chart of an exemplary closed-loop control method700for adjusting a receiver gain of a LiDAR system, according to embodiments of the disclosure. In some embodiments, method700may be performed by various components of LiDAR system102, e.g., receiver204and controller206. In some embodiments, method600may include steps S702-714. It is to be appreciated that some of the steps may be optional. Further, some of the steps may be performed simultaneously, or in a different order than shown inFIG.7.

In step S702, controller206may detect a saturation condition of detector216based on detection results provided by saturation detection circuit310. In some embodiments, if a saturation condition is detected, controller206may additionally determine where the saturation condition has occurred, e.g., in photodetector302, signal amplifier304and/or signal conditioning circuit306.

In step S704, controller206may generate a command signal to reduce the gain of detector216. In some embodiments, to reduce the overall gain of detector216, the command signal may be generated to adjust the bias voltage of photodetector302, and/or the gains of signal amplifier304and/or signal conditioning circuit306. In step S706, controller206may supply the command signal to the respective components of detector216to adjust the gain to the target gain.

In step S708, receiver204may detect the light beam returned by the target object using detector216. In step S710, controller206may determine whether the saturation condition has disappeared. Reducing the gain of detector216helps reduce the electrical signal generated by detector216, thus bringing detector216outside the saturation zone. If the saturation condition has not disappeared (S710: NO), method700returns to steps S704-S706to continue generating and supplying the command signal to further reduce the gain. If the saturation condition has disappeared (S710: YES), method700may proceed to step S712, where controller206determines whether all scanning angles of scanner210have been covered. If not (S712: NO), method700proceeds to step S714to adjust the detector gain for the next scanning angle, for example, by repeating steps S702-S712. Method700concludes after scanner210goes through all the scanning angles (S712: YES).

In some embodiments, a hybrid control method may be implemented by combining certain steps of method600and method700. For example, for each scanning angle, controller206may first perform the open-loop control of steps S602-S614to adjust the gain to a determined target gain. Then controller206may perform the closed-loop control of steps S702-S710to fine tune the gain to ensure no saturation condition still exists.

In some embodiments, the systems and methods described in the current disclosure may be combined with those described in U.S. application Ser. No. 16/920,650, which is incorporated by reference herein. For example, both the emitter power level and the receiver gain may be adjusted to collectively compensate for the change of detection distance at different vertical detection angles of the LiDAR system.

Although the disclosure is made using a LiDAR system as an example, the disclosed embodiments may be adapted and implemented to other types of optical sensing systems that use receivers to receive optical signals not limited to laser beams. For example, the embodiments may be readily adapted for optical imaging systems or radar detection systems that use electromagnetic waves to scan objects.

Another aspect of the disclosure is directed to a non-transitory computer-readable medium storing instructions which, when executed, cause one or more processors to perform the methods, as discussed above. The computer-readable medium may include volatile or non-volatile, magnetic, semiconductor-based, tape-based, optical, removable, non-removable, or other types of computer-readable medium or computer-readable storage devices. For example, the computer-readable medium may be the storage device or the memory module having the computer instructions stored thereon, as disclosed. In some embodiments, the computer-readable medium may be a disc or a flash drive having the computer instructions stored thereon.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system and related methods. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed system and related methods.

It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.