Detecting a pulse train by a time-of-flight lidar system

Abstract

This document describes a time-of-flight lidar system configured to process pulse trains instead of individual pulses to improve range resolution and pixel throughput. Each pulse in a pulse train is output at a respective duration and intensity, which can vary to cause echoes with high intensity and low signal ambiguity, prevent heat buildup, or facilitate safe eye operation. An expected echo intensity as a function of time can be determined. By sampling reflections at the expected times and intensities, the lidar system can quickly identify corresponding lidar echoes despite lidar noise. Return times of the echoes can indicate distances or velocities associated with object pixels in a field of view. Processing pulse trains instead of individual pulses allows pixels to be scanned more quickly than using long duration or frame times, which also improves eye safety. The increased throughput is achieved using low-energy lasers and inexpensive hardware, which minimizes heat footprint.

Description

BACKGROUND

[0001] Automotive lidar systems use laser pulses to determine the speed and distance of stationary and moving objects (e.g., other vehicles, pedestrians, obstacles). To make these measurements, emitted lidar pulses are compared to their reflected lidar return signals. For some safety and autonomous driving applications, it is desirable to quickly and accurately detect lidar returns for identifying fast-moving targets or distant targets. Lidar systems can need to increase their laser power or accommodate longer frame times to capture some objects. Even so, some lidar systems struggle to detect objects within a range acceptable for automotive applications or to detect objects at a scan speed acceptable for automotive applications without increasing laser power or processing speed. SUMMARY

[0002] This document describes one or more aspects of detecting a burst of pulses by a time-of-flight (TOF) lidar system. In one example, a lidar system is configured to: emit a burst of pulses including a plurality of lidar pulses; determine, based on an intensity of at least one lidar pulse of the burst, an intensity at which to sample reflections of the burst; and identify a lidar return corresponding to the burst by sampling reflections at the intensity determined based on the intensity of the at least one lidar pulse of the burst. The lidar system is further configured to: output, based on analyzing the lidar return, an indication of at least one of a distance or a velocity associated with a pixel of an object in a field of view.

[0003] In another example, a method includes: emitting, by a lidar system, a burst of pulses including a plurality of lidar pulses; determining, by the lidar system, based on an intensity of at least one lidar pulse of the burst, an intensity at which to sample reflections of the burst; and identifying a lidar return corresponding to the burst by sampling reflections at the intensity determined based on the intensity of the at least one lidar pulse of the burst. The method further includes: outputting, by the lidar system, based on analyzing the lidar return, an indication of at least one of a distance or a velocity associated with a pixel of an object in a field of view.

[0004] In another example, a lidar system includes a driver and a laser configured to emit a pulse train including a first lidar pulse at a first intensity and a second lidar pulse at a second intensity, a photodetector configured to detect a reflection of the pulse train based on a combination of the first and second intensities, and a sampling unit configured to sample the reflection from the photodetector at the combination of the first and second intensities. The lidar system further includes a processor configured to determine at least one of a distance or a velocity associated with an object pixel in a field of view based on the reflection.

[0005] In addition to describing methods performed by the above-summarized lidar system and methods performed by other lidar systems set forth herein, this document also describes apparatuses for performing the above-summarized methods and other methods set forth herein.

[0006] This summary introduces simplified concepts of detecting a pulse train by a TOF lidar system, which will be further described below in the DETAILED DESCRIPTION and the accompanying drawings. This summary is not intended to identify essential features of the claimed subject matter, nor is it intended for use in determining the scope of the claimed subject matter. BRIEF DESCRIPTION OF DRAWINGS

[0007] One or more aspects of detecting a pulse train by a TOF lidar system are described in the detailed description in this document in reference to the following drawings. The same numbers are used in the drawings to reference like features and components.

[0008] Figure 1 An example environment in which a TOF lidar system configured to detect a pulse train can be implemented is shown.

[0009] Figure 2 An example implementation of a TOF lidar system as part of a vehicle is shown. Figure 1

[0010] Figure 3-1 An example transceiver of a TOF lidar system is shown. Figure 2

[0011] An example field of view scanned by a TOF lidar system is shown. Figure 3-2 Figure 2 An example transmitter of a TOF lidar system is shown.

[0012] Figure 3-3 Figure 2 An example receiver of a TOF lidar system is shown.

[0013] Figure 3-4 An example processor of a TOF lidar system is shown. Figure 2 ​​​an example readout module of a TOF lidar system.

[0014] Figure 4 An example method performed by a TOF lidar system configured to detect a pulse train is shown.

[0015] Figure 5-1 An example pulse train and corresponding echoes processed by a TOF lidar system are shown. Figure 2 Another example transceiver of a TOF lidar system.

[0016] Figure 5-2 An example pulse train and corresponding echoes processed by a TOF lidar system are shown.

[0017] Figure 6-1 Another example transceiver of a TOF lidar system. Figure 2 Another example transceiver of a TOF lidar system.

[0018] Figure 6-2 Another example method performed by a TOF lidar system configured to detect a pulse train is shown.

[0019] Figure 6-3 Additional example pulse trains processed by a TOF lidar system are shown.

[0020] Figure 7 Another example transceiver of a TOF lidar system. Figure 2 Another example transceiver of a TOF lidar system. DETAILED DESCRIPTION

[0021] SUMMARY

[0022] TOF lidar (also known as "light detection and ranging") can be used in automotive applications, in part to measure objects at long distances, whether stationary objects or high-speed moving objects. A TOF lidar illuminates a scene and detects backscattered echo signals. A light source (e.g., a laser) outputs a lidar signal comprising a single laser pulse; in response, a photodetector receives a corresponding echo signal (or more simply, an "echo"). From the time delay τ between the laser pulse and its resulting echo, the relative distance R to the target can be determined using the speed of light c, as shown in Equation 1:

[0023]

[0024] In an automobile, a lidar system can shoot laser pulses at every object pixel in the field of view, scanning the entire scene by using photodetectors to obtain a corresponding return for each laser pulse. The laser pulses include a defined duration, intensity, and repetition rate T. Each pulse can be output simultaneously with a start pulse that propagates to the photodetector as a time reference for determining a return time of the corresponding return based on a time delay t. When the corresponding return reaches the photodetector, it produces a specific response that is digitally processed as a return time, distance, or velocity when sampled based on the time reference using at least one digitizer (e.g., an analog-to-digital converter (ADC), a time-to-digital converter (TDC)).

[0025] To achieve long-range detection, some automotive lidar systems shoot laser pulses with long durations, or use high-power lasers to shoot laser pulses with high intensities; the former reduces pixel throughput and frame rate, while the latter also has other drawbacks. More powerful lasers are more expensive and require more energy to operate. Moreover, shooting high-intensity laser pulses requires additional safety and thermal considerations, which add complexity and cost. As autonomous driving automobiles become more prevalent, a lidar system on an automobile can receive interference from other lidar systems operating on the same or different automobiles. Interference from another lidar system can mask legitimate returns, or even be inadvertently processed as a corresponding return, which can cause the lidar system to falsely detect the interference.

[0026] In contrast to those lidar systems, this document describes a TOF lidar system configured to process pulse trains instead of individual pulses to improve range resolution and pixel throughput. A pulse train includes a series of lidar pulses that, upon reaching an object, reflect as a lidar echo whose intensity mimics that of the pulse train. A driver array and / or a laser array can be configured to emit a pulse train with little to no delay between pulses in the series. Each pulse in the pulse train is output with a respective duration and intensity (e.g., energy amount, power level), which is reflected in the intensity of the echo. The intensity is selected to elicit an echo with high intensity and low signal ambiguity, prevent heat buildup, or promote safe eye operation. Using a longer, more intense intensity pattern for pulses in a pulse train mitigates signal interference from other nearby lidar sources and also improves reliability. The intensity pattern can be modified from one object pixel to the next or from one frame to the next to improve safety. For example, the pattern can be determined randomly. An expected echo intensity can be determined as a function of time. By sampling for a reflection at the expected intensity, the lidar system can quickly identify a corresponding lidar echo despite external lidar noise. The return time of the echo can indicate a distance or velocity associated with an object pixel in the field of view. Processing pulse trains instead of individual pulses allows for scanning object pixels more quickly than using long duration or frame times, which also improves eye safety. Increased throughput is achieved using low energy lasers and inexpensive hardware, which minimizes heat footprint. These are just a few examples of how the techniques and systems described herein improve TOF lidar systems for automotive applications. Other examples and implementations are described in this document.

[0027] Operating Environment

[0028] Figure 1An example environment 100 in which a TOF lidar system 102 configured to detect a burst can be implemented is shown. The TOF lidar system 102 (simply referred to as "lidar system 102") is mounted to or integrated within a vehicle 104. The lidar system 102 is capable of detecting an object 108 (or multiple objects) proximate to the vehicle 104. Although shown as a car, the vehicle 104 can represent other types of motorized vehicles (e.g., motorcycles, buses, tractors, semi-trailers, construction equipment), non-motorized vehicles (e.g., bicycles), rail vehicles (e.g., trains, trolleys), watercraft (e.g., boats, ships), aircraft (e.g., airplanes, helicopters), or spacecraft (e.g., satellites). In some cases, the vehicle 104 can tow or include a trailer or other attachment. In general, a manufacturer can mount the lidar system 102 to any mobile platform, including mobile machinery or robotic devices.

[0029] In the depicted implementation, the lidar system 102 is mounted on a rear quarter of the vehicle 104 and provides a field of view 106 that illuminates the object 108 by emitting a burst 114 and receiving a corresponding return 116 (lidar return 116). The lidar system 102 can be mounted to or project the field of view 106 from any other portion or portions of the vehicle 104. For example, a vehicle manufacturer can integrate the lidar system 102 into a roof, bumper, side mirror, or any other internal or external location where detection of the distance or classification of an object 108 is desired. In some cases, the vehicle 104 includes multiple lidar systems 102, such as a first lidar system and a second lidar system that together provide a larger field of view 106 or input to other vehicle subsystems. In general, a vehicle manufacturer can select the location(s) of the lidar system 102 to provide a particular field of view 106 that encompasses a region of interest in which the object 108 can be present. The lidar system 102 divides the field of view 106 into object pixels (as shown) that represent a portion of the field of view 106. Figure 3-2

[0030] ​The object 108 is composed of one or more materials that reflect the lidar signals. Depending on the application, the object 108 can represent a target of interest. In some cases, the object 108 is a moving object 110, such as another vehicle 110-1, a semi-trailer 110-2, a person 110-3, an animal 110-4, a bicycle 110-5, or a motorcycle 110-6. In other cases, the object 108 represents a stationary object 112, such as a conical traffic marker 112-1, a concrete barrier 112-2, a guardrail 112-3, a fence 112-4, a tree 112-5, or a parked vehicle 112-6. The stationary objects 112 along a portion of the roadway can be continuous (e.g., the concrete barrier 112-2, the guardrail 112-3) or discontinuous (e.g., the conical traffic marker 112-1).

[0031] In contrast to other lidar systems, the lidar system 102 is configured to process the pulse train 114 instead of individual pulses to improve the range resolution and pixel throughput. As a TOF lidar system, the lidar system 102 emits and receives lidar signals, including pulses for each object pixel scanned in the field of view 106. The lidar system 102 measures the distance to the object 108 based on the time it takes for a pulse to travel from the lidar system 102 to the object 108 and for the reflection of the pulse to travel back to the lidar system 102 from the object 108. Instead of scanning each object pixel in the field of view 106 with a single pulse, the lidar system 102 scans each object pixel with the pulse train 114. The pulse train 114 includes a series of lidar pulses, each lidar pulse having a particular intensity. The duration of the lidar pulses in the pulse train 114 can be much shorter than the duration of a typical lidar pulse because the lidar system 102 does not wait for each previous pulse to return. When outputting the series of lidar pulses, the pulse train 114 has a time-varying intensity pattern from the intensity of one lidar pulse in the series to the intensity of the next lidar pulse in the series. The lidar system 102 is configured to detect the lidar return 116 by sampling for reflections at the expected intensity pattern of the pulse train 114. After detecting the lidar return 116, the lidar system 102 scans the next object pixel in the field of view 106 by firing another pulse train 114, analyzing its corresponding return 116.

[0032] The lidar system 102 can also measure the reflective properties of the object 108 based on the amount of intensity or energy of the return 116 (also referred to as a "reflection"). Information about this energy can be used to classify the object 108. As an example, the lidar system 102 can determine whether the object 108 is a parked vehicle 112-6, a lane marking, a road surface, or a person 110-3. The energy information also enables the lidar system 102 to determine properties of the object 108, such as the material composition of the object 108.

[0033] For each object pixel in the field of view 106, the lidar system 102 can fire the same or different pulse trains 114, which include several pulses in a short amount of time. Two or more pulses in a pulse train 114 can at least partially overlap in time; other pulses in a pulse train 114 can be output sequentially one after another, with or without a delay from one pulse to the next. In either case, the lidar system 102 can fire an entire pulse train 114 without having to wait for a return 116, which can shorten the amount of time it takes to scan an object pixel. This results in an improvement in pixel throughput.

[0034] After each emission or output of a pulse train 114, information is maintained about the timing and intensity of the pulse train 114, including the timing or intensity of each individual pulse. The lidar system 102 can configure the transceiver to use this information to resolve the return 116 for each pulse in the pulse train 114 in various ways. See Figure 2 The lidar system 102 and the vehicle 104 are further described.

[0035] Figure 2 The lidar system 102 is shown as part of the vehicle 104. The vehicle 104 includes a wired or wireless bus 206, and at least one vehicle-based system 202 communicatively coupled to the lidar system 102 via the bus 206. The vehicle-based system 202 or any other component connected to the bus 206 can rely on data output from the lidar system 102. For example, a vehicle control unit 204 is configured to manage a driver assist or autonomous driving system based on information about the object 108 received from the lidar system 102. Generally, the vehicle-based system 202 uses lidar data provided by the lidar system 102 to perform a function. For example, a driver assist system provides a blind spot warning for a potential collision with the object 108 when the object 108 enters the field of view 106. In this case, the lidar data from the lidar system 102 indicates when it is safe or unsafe to change lanes.

[0036] The lidar system 102 includes a communication interface 208 configured to transmit lidar data over the bus 206 to the vehicle-based system 202 or another component of the vehicle 104. Generally, the lidar data provided by the communication interface 208 is in a format usable by the vehicle-based system 202. In some implementations, the communication interface 208 can receive information from the vehicle-based system 202, such as an indication of the speed of the vehicle 104 or whether a turn signal is on or off. The lidar system 102 can use this information to properly configure itself. For example, the lidar system 102 can adjust its frame rate, scan speed, or intensity of the pulse train 114 based on the speed of the vehicle 104. Alternatively, the lidar system 102 can dynamically adjust the field of view 106 based on whether the right or left turn signal is on.

[0037] The lidar system 102 also includes transceiver(s) 210 configured to emit lidar signals and receive corresponding lidar returns. Although shown as a single component, the transceiver 210 can be multiple components, including shared or separate transmitter and receiver components, as shown in later figures. The transceiver 210 components can be incorporated together on the same integrated circuit (e.g., a transceiver integrated circuit) or separately on different integrated circuits. The transceiver 210 includes elements for emitting lidar signals, whether optical elements or other elements, and related components for directing the lidar signals.

[0038] The transceiver 210 can have a mono-static configuration with an optical design that shares a common deflector to scan the entire field of view 106 and steer the pulse train at a particular object pixel. The transceiver 210 can form steered or non-steered, wide or narrow beams. Steering and shaping can be obtained through analog beamforming or digital beamforming. The transceiver 210 includes one or more arrays of photodetectors (collectively, photodetectors) to detect the lidar returns 116. The photodetectors can be implemented as silicon photomultipliers (SiPMs), avalanche photodiodes (APDs), single-photon avalanche diodes (SPADs), photomultiplier tubes (PMTs), PIN diodes, and the like. A PIN diode includes an undoped intrinsic semiconductor region between p-type and n-type semiconductor regions.

[0039] The transceiver 210 is configured to emit the entire laser radar pulse train 114 in an amount of time that is less than the amount of time that some other laser radar systems can emit a single laser radar pulse. By varying the timing or intensity of the laser radar pulse train 114 and maintaining information about the variation after the emission of the pulse train 114, the transceiver 210 can immediately resolve the echoes 116 resulting from the emission of the laser radar pulse train 114. Identification of the echoes 116 occurs despite noise, including noise from other laser radar systems, in part because of the intensity of the pulses in the pulse train 114. Thus, objects pixels can be scanned with higher reliability in a shorter amount of time compared to using other transceivers that wait to emit each subsequent laser radar pulse until the echoes of the most recent laser radar pulse are resolved.

[0040] The laser radar system 102 also includes a readout module 212. The readout module 212 provides an interface between the transceiver 210 and the processor 214. In some implementations, the readout module 212 is incorporated within the transceiver 210 and implemented on the same integrated circuit. However, the readout module 212 can be separate from the transceiver 210 and implemented on a different integrated circuit (or multiple integrated circuits), and in some implementations, at least a portion of the readout module 212 can be implemented by the processor 214.

[0041] In general, the readout module 212 extracts information from the analog signals output by the transceiver 210 and generates digital information for the processor 214. This information can include information about the intensity of the echoes and provide an intensity readout function. The readout module 212 can include a timing function that generates timing data related to the TOF of the echoes, such as the time associated with a voltage or current of a pulse in the echo signal being greater than, equal to, or less than a threshold set for determining the time of return.

[0042] The readout module 212 can maintain information about the timing and intensity of the pulse train 114, including information about the individual widths, timings, intensities, or number of pulses in the pulse train. These pulse level timing and intensity characteristics can be compared to the timing and intensity characteristics of the echoes 116. From this comparison, the readout module 212 can identify each individual laser radar echo 116 corresponding to the pulse train 114 and eliminate external noise due to other laser radar systems. Laser radar echoes 116 that do not match the expected timing or intensity associated with the pulse train 114 are discarded, while the remaining laser radar echoes 116 that have timing or intensity characteristics that conform to the expected pattern are sampled.

[0043] The lidar system 102 also includes one or more processors 214 and a computer-readable storage medium (CRM) 216. The processor 214 can be implemented as a microprocessor or a system on a chip. The processor 214 executes instructions stored in the CRM 216. As an example, the processor 214 can determine a position of the object 108 relative to the lidar system 102 (e.g., determine a slant range, an azimuth, and an elevation to the object 108), determine a material composition of the object 108, or classify the object 108. In particular, the processor 214 determines the characteristics of the object 108 based on information provided by the transceiver 210 or the readout module 212. The processor 214 can generate lidar data for the vehicle-based system 202. Figure 1

[0044] Example Architecture

[0045] Figure 3-1 A transceiver 210-1 is shown, which is an example of the transceiver 210 of the lidar system 102. The transceiver 210-1 is configured to scan each of the object pixels 318 in the field of view 106, which in this case aligns with the object 108. For reference, Figure 3-2 The object pixels 318 are shown as being arranged in a grid that is X pixels wide by Y pixels high and being individually scanned, one row (or column) at a time, in the order indicated by the arrows. Other orders for scanning the object pixels 318 are possible.

[0046] Referring back to Figure 3-1 , the transceiver 210-1 includes a transmitter 300, a beamsplitter 302, a deflector 304, and a receiver 306. Within the transmitter 300, the transceiver 210-1 includes a driver 308, a laser 310, and a lens 312. The receiver 306 includes a photodetector 314.

[0047] Figure 3-1 Also shown in FIG. 3A is an optional feedback loop 320-1 or 320-2; either of which enables controlling the intensity of the pulse train 114 based on the position of the deflector 304 or the intensity of the echo 116. For example, as later described with respect to Figure 7 ​The strength of the echo 116 from nearby objects 108 can be unnecessarily high as described for eye safety in the 608 nm band; reducing the strength of the burst 114 can provide sufficient detection for object ranging and classification while emitting light within the limits of eye safety.

[0048] The laser 310 is focused through the lens 312 and the beamsplitter 302 and focused onto a spot of the deflector 304 that is aligned with an object pixel 318. The emitter 300 is configured to emit the burst 114 by driving the laser 310. The driver 308 fires the laser 310 to output the burst 114 through the lens 312. The beamsplitter 302 directs the burst 114 to the spot on the deflector 304. The beamsplitter 302 also outputs an indication of the burst 114 to the receiver 306. The photodetector 314 is configured to extract the echo 116 from the beamsplitter 302 as the beamsplitter 302 receives the echo 116 from the deflector 304.

[0049] The photodetector 314 is configured to identify a matching echo 116 based on a particular timing pattern and strength pattern of the burst 114. From one object pixel to the next in the field of view 106, the burst 114 can change, and the photodetector 314 is configured to accommodate such changes. For example, scanning a first pixel can include emitting a first burst that includes a first set of pulses directed at a first object pixel in the field of view 106. Subsequently after receiving a corresponding echo 116, the deflector 304 moves to a next object pixel in the field of view 106, where the emitter 300 is configured to emit the same or a different burst 114 that includes a second series of pulses directed at the next object pixel in the field of view 106.

[0050] Figure 3-3 Emitters 300-1, 300-2, and 300-3 are shown as examples of emitters 300 that are transceivers 210-1. Each of the emitters 300-1, 300-2, and 300-3 is configured to output a burst 114 from the lens 312. The difference between the emitters 300-1, 300-2, and 300-3 is the number of drivers and the number of lasers each used to generate the burst 114.

[0051] Each of the emitters 300-1, 300-2, and 300-3 implements individual frames of a fast-scanning object pixel 318 while reducing signal interference, especially from external lidar systems. The emitters 300-1, 300-2, and 300-3 use multiple lasers or multiple drivers to emit a lidar signal with an intensity shaped for each particular pixel. By using several lasers or drivers, the time between two pulses within the pulse train 114 can be very short. Using an array of lasers or drivers overcomes the limited pixel throughput and signal interference problems that some other TOF lidar systems have.

[0052] The emitted light of the pulse train 114 is deflected via a deflector 304, which is a common deflector within the single station optical path from the lens 312 and through the beam splitter 302. The returned light of the echo 116 is detected by a photodetector 314, which can be a shared photodetector array. The photodetector 314 is configured to match the echo 116 to the respective pulse train 114 of the particular pixel 318 from which the echo 116 originally originated. The emitters 300-1, 300-2, and 300-3 use multiple lasers or drivers, which allows the transceiver 210-1 to output pulses within the pulse train 114 within a very short time period and, by varying the intensity of the pulse train 114, to aim multiple pixels in the same angle using the deflector 304.

[0053] The emitter 300-1 includes multiple drivers 308-1 through 308-n (where n is any integer greater than 2) coupled to a single laser 310. The drivers 308-1 through 308-n can be collectively referred to as a “driver array 308.” Each of the multiple drivers 308-1 through 308-n drives the laser 310 to a respective intensity level. The emitter 300-1 is configured to emit the pulse train 114 with a particular intensity pattern by selectively driving the laser 310 with different drivers from the multiple drivers 308-1 through 308-n.

[0054] The emitter 300-2 includes a single driver 308 coupled to multiple lasers 310-1 through 310-m (where m is any integer greater than two). The lasers 310-1 through 310-n can be collectively referred to as a “laser array 310.” Each of the multiple lasers 310-1 through 310-m is driven by the driver 308. The emitter 300-2 is configured to emit the pulse train 114 by selectively driving a combination of one or more of the lasers 310-1 through 310-m over time to achieve a particular intensity pattern.

[0055] Transmitter 300-3 is a combination of transmitters 300-1 and 300-2. Transmitter 300-3 includes driver arrays 308-1 through 308-n coupled to laser arrays 310-1 through 310-m. Transmitter 300-3 is configured to emit pulse train 114 by selectively driving a combination of one or more lasers 310-1 through 310-m using different drivers from multiple drivers 308-1 through 308-n over time to achieve a particular intensity pattern.

[0056] Referring back to Figure 3-1 In accordance with the indication of pulse train 114, receiver 306 is configured to determine an intensity of the reflection sampled. Receiver 306 adjusts photodetector 314 to sample the reflection at the same or similar intensity as pulse train 114. In response to pulse train 114 reflecting off object 108 and the intensity of lidar return 116 matching the expected intensity, receiver 306 is configured to output the indication of pulse train 114 and lidar return 116 to a readout module.

[0057] Receiver 306 includes at least one photodetector 314. Although not explicitly shown, receiver 306 can include other elements such as amplifiers. Photodetector 314 detects reflected return 116 by collecting photons. Photodetector 314 converts the photons into an analog current. In the case where photodetector 314 is an APD or SPAD, photodetector 314 pulls electrons created by photon absorption into a multiplication region where photon-induced electrons are amplified to create a breakdown avalanche of multiplied electrons. In the linear output region of photodetector 314, the output of the photodetector increases linearly based on the number of incident photons in a portion of return 116. As the number of photons incident on photodetector 314 increases, the output of the photodetector becomes non-linear and does not scale with the number of received photons. In the non-linear region of photodetector 314, the accuracy of distance determination and reflectivity determination by lidar system 102 decreases as lidar system 102 can not be able to determine TOF or intensity information of return 116.

[0058] Receiver 306 adjusts the sensitivity of photodetector 314 by changing the bias voltage of photodetector 314 to detect photons in echo 116. Increasing the bias voltage increases the sensitivity of photodetector 314 to echoes 116 with low energy (e.g., reflected by objects 108 that are far from lidar system 102 or have low reflectivity). Similarly, decreasing the bias voltage decreases the sensitivity of photodetector 314 to echoes 116 with high energy. Receiver 306 can adjust the sensitivity of photodetector 314 to detect photons in echoes 116 with intensity patterns corresponding to the intensity patterns of pulse train 114.

[0059] Figure 3-4 It was shown as coming from Figure 2 Example of read module 212-1. Figure 3-4 It is from Figure 3-1 The background of transceiver 210-1 is described.

[0060] Readout modules 212-21 extract information from the analog current output of receiver 306 and generate digital information for processor 214. (Refer to the above text.) Figure 2 As described, the readout module 212-1 can be incorporated as part of the transceiver 210 or implemented as a separate component in the lidar system 102. The readout module 212-1 may include a filter 324, a hold circuit 326, and a converter 328.

[0061] Filter 324 can be a low-pass filter coupled between receiver 306 and hold circuit 326, or filter 324 can be coupled between hold circuit 326 and converter 328. Filter 324 attenuates high-frequency noise. By attenuating noise, filter 324 improves the measurement accuracy of lidar system 102.

[0062] A hold circuit 326 is coupled between receiver 306 and converter 328. The hold circuit 326 samples the analog signal. Specifically, the hold circuit 326 holds the analog signal and samples it for a specified duration. The hold duration and sampling rate of the hold circuit 326 can be pre-programmed or controlled by processor 214. The hold circuit 326 can be implemented as, for example, an integral and hold circuit, or a peak and hold circuit. An integral and hold circuit measures the amount of charge in the echo (e.g., measures the amount of current changing over time, measures the amount of voltage changing over time) and generates a voltage representing the energy of the echo. A peak and hold circuit measures the peak amplitude of current or voltage across the echo and generates a voltage representing the energy of the echo.

[0063] The converter 328 can include a digital converter (e.g., ADC, TDC) and be coupled between the holding circuit 326 and the processor 214. The converter 328 is high speed to resolve each pulse in the pulse train 114 and increase the range resolution of the lidar system 102. The converter 328 collects one or more samples of the output voltage from the holding circuit 326 and generates data indicative of the time or intensity of the return. For example, the data can represent a scaled number of photons received by the photodetector 314 within the return for a particular time. The data can be output to the processor 214 as a merged signal for each of the object pixels 318. For example, the data can be collected by the converter 328 or another component of the readout module 212-1, such as a buffer, into a merged signal for the return 116 and then sent to the processor 214 once the data has been collected for each of the object pixels 318.

[0064] The processor 214 analyzes the data output from the readout module 212-1 to detect the object 108. The processor 214 can use the intensity data to determine the material composition of the object 108 and / or classify the object 108. Further, the processor 214 can use the timing data to measure the distance between the lidar system 102 and the object 108. Information about the distance and classification of the object 108 can be provided as lidar data to Figure 2 the vehicle-based system 202.

[0065] During operation, the receiver 306 receives the return 116 and provides it to the photodetector 314. The return 116 includes a plurality of pulses, where each pulse corresponds to one of the pulses of the pulse train 114. The photodetector 314 converts the photons in the pulses into pulse data. The pulse data represents the analog current response of the photodetector 314 to the pulses in the time domain.

[0066] The pulse data can be filtered by the filter 324. The pulse data or the filtered pulse data is input to the holding circuit 406. The holding circuit 326 samples the pulse data or the filtered pulse data and outputs the sampled pulse data to the converter 328. The converter 328 converts the sampled pulse data into digital data indicative of the intensity of the return 116 over time.

[0067] Example methods

[0068] Figure 4An example method 400 performed by a lidar system configured to detect a burst is shown. The method 400 is shown as a plurality of sets of operations (or actions) performed, but is not necessarily limited to the order or combinations of operations shown herein. Further, any of one or more of the operations can be repeated, combined, or reorganized to provide other methods. In the following discussion, reference is made to the environment 100 and entities detailed in Figure 1 Figures 1 to 3-4 The techniques are not necessarily limited to being performed by one entity or multiple entities.

[0069] At 402, the lidar system 102 emits a burst comprising a plurality of lidar pulses. For example, the transceiver 210 outputs a lidar signal comprising the burst 114, which includes a series of pulses that overlap in time or have little delay between pulses.

[0070] At 404, the lidar system 102 determines an intensity at which to sample reflections of the burst based on an intensity of at least one lidar pulse in the burst. The indication of the burst 114 is received by the receiver 306 and the readout module 212-1. The readout module 212-1 determines an intensity of the burst 114 based on intensity data inferred from the indication of the burst 114. For example, the burst 114 can include a first pulse at a low intensity level and a second pulse at a high intensity level. The readout module 212-1 determines an expected intensity of a first portion of the echo 116 based on the low intensity level of the first pulse and an expected intensity of a second portion of the echo 116 based on the high intensity level of the second pulse. The readout module 212-1 can configure the receiver 306 or photodetector 314 to sample reflections at or near the expected intensity of the echo 116.

[0071] At 406, the lidar system 102 identifies a lidar echo corresponding to the burst by sampling reflections at an intensity determined based on an intensity of at least one lidar pulse in the burst. For example, with the receiver 306 or photodetector 314 tuned by the readout module 212-1, the receiver 306 receives reflections at or near the expected intensity of the echo 116 when the deflector receives the echo 116. The readout module 212-1 samples data received in response to the reflections to determine an intensity and a time of the echo 116.

[0072] ​At 408, the lidar system 102 outputs an indication of a distance or velocity associated with an object pixel in the field of view based on analyzing the lidar returns. For example, the readout module 212-1 outputs the intensity and time data associated with the returns 116 to the processor 214. The processor 214 determines a return time based on the intensity and time data of the returns 116, and determines a distance or velocity of one of the object pixels 318 in the field of view 106 from the return time.

[0073] Example pulse trains

[0074] Figure 5-1 A transceiver 210-2 is shown, which is another example transceiver of the lidar system 102. The transceiver 210-2 is the same as the transceiver 210-1 except that the transmitter 300 is replaced by a transmitter 300-4. The transmitter 300-4 includes four drivers 308-1 through 308-4, each of which is configured to drive one of four lasers 310-1 through 310-4. The driver 308-1 and the laser 310-1 emit light at a first intensity level through the lens 312. The driver 308-2 and the laser 310-2 emit light at a second intensity level through the lens 312. The driver 308-3 and the laser 310-3 emit light at a third intensity level through the lens 312. The driver 308-4 and the laser 310-4 emit light at a fourth intensity level through the lens 312. Two or more of the drivers 308-1 through 308-4 and the lasers 310-1 through 310-4 can emit light at the same or different intensity levels. The transmitter 300-4 can emit the pulse train 114 based on light emitted by any combination of the lasers 310-1 through 310-4.

[0075] Figure 5-2 Example pulse trains and corresponding returns processed by the lidar system 102 using the transceiver 210-2 are shown. Figure 5-2 The pulse trains shown in FIG. 6 are some example pulse trains, and other variations and combinations can also be used. In general, the characteristics of the pulse trains (e.g., pulse width, pulse duration, number of pulses) are selected to enable fast scanning of individual frames of the field of view 106 while reducing signal ambiguity. The intensity from each pulse in the pulse train adds up to an amount of energy sufficient to detect a remote target at a long distance in the returns 116 with sufficient intensity. The longer the pulse duration, the greater the pulse width, or the greater the number of pulses, the more energy associated with the pulse train.

[0076] Figure 5-2A portion 500-1 of the burst 114 output by the lasers 310-1 through 310-4 is shown, as is a corresponding portion 502-1 of the echo 116 received at the input of the receiver 306. Another portion 500-2 of the burst 114 output by the lasers 310-1 through 310-4 is shown, as is another corresponding portion 502-2 of the echo 116 received at the input of the receiver 306. Finally, Figure 5-2 A portion 500-3 of the burst 114 output by the lasers 310-1 through 310-4 is shown, as is a corresponding portion 502-3 of the echo 116 received at the input of the receiver 306. The transceiver 210-2 outputs each pulse in the burst 114 with a respective duration and intensity, which can vary to: induce the echo 116 with high intensity and low signal ambiguity, prevent heat buildup, or facilitate safe eye operation.

[0077] The timing of the pulses in the burst 114 and the intensity of each pulse can be specifically adjusted for each object pixel 318 to introduce a specific emission pattern in a frame. The time between two pulses in the burst 114 can be very short by using several lasers or using separate drivers for one laser. The pattern is resolved by the receiver 306, photodetector 314, or readout module 212, any of which can be configured to identify the object pixel 318 from which the echo originated.

[0078] The portion 500-1 of the burst 114 includes four pulses of equal width and amplitude, with little delay between the four pulses. The transceiver 210-2 is configured to output the portion 500-1 between times 0 and t4, with the laser 310-1 outputting a pulse before time ti, the laser 310-2 outputting a pulse before time t2, and so on. The portion 502-1 of the received echo 116 is at an expected intensity 504 determined based on the intensity of the burst 114.

[0079] The portion 500-2 of the pulse train 114 includes four time periods or pulse groups between times 0 and t4, where each time period includes four pulses of equal width and amplitude with little to no delay between the four pulses. Each time period or pulse group contains a time and intensity pattern that likely causes the echo 116 to have a high intensity level and little signal interference. The transceiver 210-2 is configured to output the portion 500-2 between times 0 and t4 with the laser 310-1 outputting four pulses before time tl, the laser 310-2 outputting four lower energy pulses before time t2, the laser 310-3 outputting four medium energy pulses before time t3, and the laser 310-4 outputting four higher energy pulses before time t4. The portion 502-2 of the echo 116 that is initially received is at an expected intensity 504 that is determined based on the intensity of the first four pulses in the pulse train 114.

[0080] According to the portion 500-2 of the emitted pulse train 114, the total intensity of the echo 116 is proportional to the sum of the intensities of all the pulses within the pulse train 114. The signal-to-noise ratio of the echo 116 can be increased by emitting a pulse train 114 with a greater amount of energy in the pulses. This allows for an accurate estimation of the return time of the pulse train 114.

[0081] Finally, the portion 500-3 of the pulse train 114 includes two time periods between time 0 and t2, where each time period includes four low-energy pulses of equal width and amplitude with little to no delay between the four low-energy pulses. The transceiver 210-2 is configured to output the portion 500-3 between time 0 and t2. The portion 502-3 of the received echo 116 at an expected intensity 504 is determined based on the intensity of the low-energy pulses in the corresponding portion 500-3 of the pulse train 114. The amount of intensity or energy associated with the echo 116 at the portion 502-3 is proportional to the energy of the pulse train 114 at the corresponding portion 500-3. The total energy of the pulse train 114 is the sum of the individual energy outputs from each of the four lasers 310-1 to 310-4. The intensity of the corresponding portion 502-3 of the echo 116 is approximately four times the intensity of the echo obtained if only one of the four lasers 310-1 to 310-4 was used. In this approach, each pulse in the pulse train 114 hits the photodetector 314, which has a certain response that is sampled using a single or stacked high-speed ADC and / or TDC. These guarantee a high time resolution, enabling accurate determination of the return time, and thus the time delay, distance, or velocity to the object 108. The timing of the echo 116 is compared to the timing pattern of the pulse train 114, and the timing of the echo 116 is adjusted if necessary, for example, to mitigate errors caused by timing jitter. The intensity of each pulse or the total intensity of all pulses in the pulse train 114 is based on the amount of energy required to induce the echo 116, which has sufficient intensity to exceed external noise and come from a target at a distance.

[0082] Thermal protection

[0083] Figure 6-1 A transceiver 210-3 is shown as another example transceiver of the lidar system 102. The transceiver 210-3 is the same as the transceiver 210-2 except for a temperature sensor 600. The temperature sensor 600 monitors the temperature of the emitter 300-4. The output of the temperature sensor 600 is used by a temperature controller (not shown) to selectively control whether the emitter 300-4 receives active heating 602 (e.g., from a heat source) or active cooling 604 (e.g., from a cooling source), if at all. Logic in the receiver 306 or input from the processor 214 can enable the active heating 602 or the active cooling 604 by performing the method 402-1.

[0084] The pulse train 114, which for example includes a combination of high-energy pulses, can cause the transmitter temperature (e.g., the junction temperature of one or more laser diodes) to rise. The pulses in the pulse train 114 emit light that generates energy that is released as heat to the laser diodes and other parts of the transceiver 210-3. The temperature can rise to a level that exceeds the operating limits of the transmitter. The transceiver 210-3 enables the lidar system 102 to provide temperature control, maintaining the temperature of the transceiver 210-3 at one or more different temperature regions, such as a low ambient temperature region and a high ambient temperature region.

[0085] By individually adjusting each laser 310-1 through 310-m and / or each driver 308-1 through 308-n, the transceiver 210-3 is configured to scale the power and resulting heat output. The transceiver 210-3 can adjust laser parameters including the number of active lasers 310-1 through 310-m or the number of active drivers 308-1 through 308-n, and the transceiver 210-3 can switch between natural convection and active heating or cooling when above or below a nominal ambient temperature or outside a nominal range. Laser parameters can include output power, intensity level of a pulse train, energy level of a pulse train, number of pulses in a pulse train, width or duration of pulses in a pulse train, and the like. In this way, the characteristics of the pulse train are tightly controlled to maintain the temperature measured by the temperature sensor 600 within a nominal range. The nominal temperature range can vary between lidar systems depending on the physical arrangement and packaging of the components that make up the lidar system 102.

[0086] Figure 6-2 A method 402-1 is shown, which corresponds to step 402 of the method 400. When performing step 402 of the method 400, the lidar system 102 can emit a pulse train including a plurality of lidar pulses by performing the method 402-1. The method 402-1 is shown as a plurality of groups of operations (or actions) performed, but is not necessarily limited to the order or combinations of operations employed by the operations shown herein. Moreover, any of one or more of the operations can be repeated, combined, or re-ordered to provide other methods.

[0087] At 606, a temperature of the lidar system 102 is determined. For example, the temperature sensor 600 outputs an indication of the temperature of the transmitter 300-4.

[0088] At 608, it is determined whether the temperature is within the nominal range. For example, if the temperature sensor indicates that the emitter 300-4 is at a temperature below the nominal range, then at 612, active heating 602 is enabled to raise the temperature into the nominal range. A heater can be energized to increase the temperature measured by the temperature sensor 600. In some examples, a heating element is activated to maintain the temperature at or above a minimum temperature. In addition to or in lieu of active heating at step 612, the emitter 300-4 can increase the amount of power associated with the pulse train 114, increase the width of any of the pulses in the pulse train 114, or increase the number of pulses in the pulse train 114 to raise the temperature into the nominal range at 616. For example, turning back to Figure 6-3 .

[0089] Figure 6-3 Additional example pulse trains 620-1 through 620-3 processed by the lidar system 102 are shown. The pulse train 620-1 includes four wide pulses above the energy level 622, the pulse train 620-2 includes four narrower pulses at the energy level 622, and the pulse train 620-3 includes three pulses below the energy level 622. When the temperature sensor 600 indicates that the temperature is below the nominal range, the emitter 300-4 can output the pulse train 620-1 to maximize the heat generated by the lasers 310-1 through 310-4. When the temperature sensor 600 indicates that the temperature is above the nominal range, the emitter 300-4 can output the pulse train 620-3 to minimize the heat generated by the lasers 310-3 through 310-4.

[0090] Returning to Figure 6-2 At 614, if the temperature sensor indicates that the emitter 300-4 is at a temperature greater than the nominal range, then at 614, active cooling 604 is enabled to lower the temperature into the nominal range. For example, a fan can be enabled to increase air circulation near the emitter 300-4 and lower the temperature measured by the temperature sensor 600. In some examples, a thermoelectric cooler is activated to maintain the temperature at or below a maximum temperature.

[0091] In addition to or in lieu of active cooling at step 614, the emitter 300-4 can decrease the amount of power associated with the pulse train 114, decrease the width of any of the pulses in the pulse train 114, or decrease the number of pulses in the pulse train 114 to lower the temperature into the nominal range at 618. For example, turning back to Figure 6-3 The pulse train 620-3 includes three narrow pulses below the energy level 622. When the temperature sensor 600 indicates that the temperature is above the nominal range, the emitter 300-4 can output the pulse train 620-3 to minimize the heat generated by the lasers 310-3 through 310-4.

[0092] In some examples, the transceiver 210-3 provides precise temperature control to maintain the temperature of the transceiver 210-3 within one of a plurality of different temperature regions (e.g., a low ambient temperature region and a high ambient temperature region). For example, a nominal range can include a first threshold set to a low ambient temperature and a second threshold set to a high ambient temperature, the high ambient temperature being greater than the low ambient temperature and the first threshold. The active cooling can be activated in response to the temperature from the temperature sensor 600 exceeding the first threshold in the nominal range at step 614. In addition, the processor 214, the readout module 212, or the receiver 306 can adjust the intensity of one or more pulses in the pulse train to reduce power output and heat generation in response to the temperature exceeding the second threshold in the nominal range. The processor 214, the readout module 212, or the receiver 306 can adjust the characteristics of the pulse train 114 in other ways (e.g., by modifying the number of pulses in the pulse train 114 in response to the temperature even exceeding the high ambient temperature or the nominal range) to prevent thermal damage. The transceiver 210-3 can avoid outputting one or more pulses in the pulse train to reduce the power of the pulse train and prevent temperature increase. Similar steps can be taken for the case where the temperature is below the nominal range, for example, enabling an active heating element or increasing the power associated with the pulse train 114.

[0093] At 610, in response to determining that the temperature is within the nominal range, the active heating 602 and the active cooling 604 can be disabled. For example, the heater and the fan are disabled to maintain the temperature measured by the temperature sensor 600. The transmitter 300-4 can adjust the amount of power associated with the pulse train 114, adjust the width of any of the pulses in the pulse train 114, or adjust the number of pulses in the pulse train 114 based on the heat generated by the lasers 310-1 to 310-4 to raise or lower the temperature within the nominal range. The transmitter 300-4 can output the pulse train 620-2 when the temperature sensor 600 indicates that the temperature is within the nominal range. The method 402-1 ends by entering step 404 of the method 400 after active compensation or no compensation for the heat generated by the lasers 310-1 to 310-4.

[0094] Eye safety

[0095] Figure 7A transceiver 210-4 is shown as another example transceiver of the lidar system 102. The transceiver 210-4 is the same as the transceiver 210-1 except that the optional feedback loop 320-1 is replaced by a position controller 700 and a velocity controller 702, which enable control of the intensity of the pulse train 114 based on the position or velocity of the deflector 304 or the intensity of the return 116. The position controller 700 is configured to adjust the position of the deflector 304 based on feedback from the driver 308 of the transmitter 300. The velocity controller 702 is configured to modify the velocity at which the deflector 304 changes position using feedback from the driver 308. The position controller 700 and the velocity controller 702 work together to aim the deflector 304 at different pixels 318 in the field of view 106.

[0096] The transceiver 210-4 can use information about the intensity of the return 116 obtained by the receiver 306 to modify the light emitted by the laser 310 so that the pulse train 114 is emitted under safe ocular conditions. For example, the intensity of the return 116 from a nearby object 108 can be unnecessarily high; reducing the intensity of the pulse train 114 can provide sufficient detection for ranging and classification of the object 108 while emitting light within the limits of eye safety, e.g., the eye safety standard IEC 60825-1, which provides a recommended amount of energy that can enter the eye without causing harm to the eye. The maximum permissible exposure (MPE) is defined as a function of the exposure time of a fully open pupil and the laser emission wavelength. The MPE is also a function of the energy, which in a TOF design is affected by the pulse duration and frequency.

[0097] To ensure safer ocular operation, other lidar systems can use a combination of different wavelengths (e.g., 905 nm and 1550 nm). By using a combination of two laser wavelengths, a higher allowed total laser power in its field of view is achievable without posing a threat to the human eye. At the receiver, these systems require separate photodetectors to receive the reflected light of the two different wavelengths, which adds cost over a single deflector design.

[0098] In other lidar systems, the intensity of the laser is adaptively controlled to ensure eye safety based on careful monitoring of the position of the deflector. For example, the deflector includes a guard region that uses a lower intensity laser relative to other regions that use a high intensity laser. These other lidar systems include additional protection against system failure conditions where the deflector fails or stops working; if allowed to emit high intensity laser light while inadvertently positioned within the guard region, these lidar systems can cause harm to the eye. Unlike these other systems, the position controller 700 and the velocity controller 702 in combination provide eye safety monitoring and failure mode protection for the transceiver 210-4.

[0099] The position controller 700 monitors the position of the deflector 304 throughout the field of view 106 and provides the position to the driver 308. Depending on the spatial distribution of the object pixels 318 within the field of view 106, the position controller 700 can signal the emitter 300 to change the laser-firing-pattern to emit less energy and meet the eye safety threshold. For example, a scanning pattern including raster scanning, Lissajous scanning, etc. can have some areas of the field of view 106 with a higher density of object pixels 318. The position controller 700 senses when the deflector 304 reaches the higher density portions of the field of view 106 and mitigates the situation by changing the firing pattern or reducing the power. For example, the emitter 300 determines the density of the object pixel regions in the field of view and, based on the density of the object pixel regions, adjusts the driver 308 to emit pulse trains including lower intensity pulses if the density of the object pixel regions exceeds a safety threshold. The processor 214, receiver 306, or emitter 300 can instruct the driver 308 to stop emitting pulse trains 114 with the laser 310 in response to the density exceeding the safety threshold.

[0100] The speed controller 702 monitors the movement of the deflector 304 within each scan period or frame and provides feedback to the driver 308. In the event of a failure condition of the deflector 304 (e.g., the deflector 304 fails to align with a particular object pixel 318), the driver 308 can stop the emission of the pulse train 114 in order to prevent injury to the eye. For example, if the speed of the deflector 304 is too slow, there is an increased risk of the pulse train 114 over-exciting and damaging the eye if the speed is below a threshold speed. In this case, the speed controller 702 can output a signal to the driver 308 to stop the laser 310 from emitting to mitigate the risk of damaging the eye.

[0101] In this way, the lidar system 102 can implement eye safety without needing to define a protection zone. It dynamically controls the laser 310 based on whether the speed and position of the deflector 304 are accurate and reduces the intensity of the laser 310 output when necessary (e.g., in high pixel density areas or when the intensity of the return 116 indicates a nearby object).

[0102] Examples

[0103] In the following sections, examples are provided.

[0104] Example 1. A lidar system configured to: emit a burst comprising a plurality of lidar pulses; determine, based on an intensity of at least one lidar pulse in the burst, an intensity at which to sample reflections of the burst; identify, by sampling reflections at the intensity determined based on the intensity of the at least one lidar pulse in the burst, a lidar return corresponding to the burst; and output, based on analyzing the lidar return, an indication of at least one of a distance or a velocity associated with an object pixel in a field of view.

[0105] Example 2. The lidar system of any of the preceding examples, wherein: the lidar system comprises a laser focused on an object pixel in a field of view; and the lidar system is configured to emit the burst by driving the laser.

[0106] Example 3. The lidar system of any of the preceding examples, wherein: the lidar system further comprises a beam splitter and a deflector; and the lidar system is further configured to: focus the laser through the beam splitter and to a spot of the deflector; align the spot of the deflector with an object pixel in a field of view; and identify the lidar return by sampling reflections from the beam splitter.

[0107] Example 4. The lidar system of any of the preceding examples, wherein the lidar system comprises a driver configured to: drive the laser at a first intensity during a first pulse in the burst; and drive the laser at a second intensity during a second pulse in the burst.

[0108] Example 5. The lidar system of any of the preceding examples, wherein the lidar system comprises an array of laser diodes comprising: a first laser diode configured to emit a first pulse in the burst at a first intensity; and a second laser diode configured to emit a second pulse in the burst at a second intensity.

[0109] Example 6. The lidar system of any of the preceding examples, wherein the driver comprises: a first driver configured to energize the laser to a first intensity during a first pulse in the burst; and a second driver configured to energize the laser to a second intensity during a second pulse in the burst.

[0110] Example 7. The lidar system of any of the preceding examples, wherein the lidar system comprises an array of laser diodes: the first driver is configured to energize the first laser diode to a first intensity during a first pulse of the pulse train; and the second driver is configured to energize the second laser diode to a second intensity during a second pulse of the pulse train.

[0111] Example 8. The lidar system of any of the preceding examples, wherein the lidar system is configured to determine the intensity at which to sample reflections of the pulse train by determining a first intensity of a first pulse of the pulse train and determining a second intensity of at least one second pulse of the pulse train.

[0112] Example 9. The lidar system of any of the preceding examples, wherein the lidar system is configured to identify lidar returns corresponding to the pulse train by: adjusting a sensitivity of the photodetector to the first intensity and the second intensity; and sampling the lidar returns from the adjusted photodetector.

[0113] Example 10. The lidar system of any of the preceding examples, wherein the photodetector comprises at least one of: a photodiode, a silicon photomultiplier, an avalanche photodiode, a single-photon avalanche diode, a photomultiplier, or a PIN diode.

[0114] Example 11. The lidar system of any of the preceding examples, wherein the lidar system further comprises at least one of: an analog-to-digital converter or a time-to-digital converter configured to sample the lidar returns from the adjusted photodetector.

[0115] Example 12. The lidar system of any of the preceding examples, wherein the lidar system is further configured to: determine a return time of the pulse train in response to sampling the lidar returns; and determine at least one of a distance or a velocity associated with an object pixel in the field of view based on the return time of the pulse train.

[0116] Example 13. The lidar system of any of the preceding examples, wherein the plurality of lidar pulses in the pulse train comprises three or more pulses.

[0117] Example 14. A method comprising: emitting, by a lidar system, a pulse train comprising a plurality of lidar pulses; determining, by the lidar system, an intensity at which to sample reflections of the pulse train based on an intensity of at least one lidar pulse in the pulse train; identifying, by the lidar system, a lidar return corresponding to the pulse train by sampling the reflections at the intensity determined based on the intensity of the at least one lidar pulse in the pulse train; and outputting, by the lidar system, an indication of at least one of a distance or a velocity associated with a pixel of an object in a field of view based on analyzing the lidar return.

[0118] Example 15. The method of any of the preceding examples, further comprising: focusing, by the lidar system, a laser through a beam splitter and to a spot of a deflector; aligning, by the lidar system, the spot of the deflector with a pixel of an object in a field of view; and identifying, by the lidar system, the lidar return by sampling reflections from the beam splitter.

[0119] Example 16. The method of any of the preceding examples, further comprising: emitting, by the lidar system, a first pulse in the pulse train at a first intensity; and emitting, by the lidar system, a second pulse in the pulse train at a second intensity.

[0120] Example 17. The method of any of the preceding examples, wherein determining the intensity at which to sample the reflections of the pulse train comprises: determining a first intensity of a first pulse in the pulse train and determining a second intensity of at least one second pulse in the pulse train.

[0121] Example 18. The method of any of the preceding examples, wherein identifying the lidar return corresponding to the pulse train comprises at least one of: adjusting a sensitivity of a photodetector to the first intensity and the second intensity; and sampling the lidar return from the adjusted photodetector.

[0122] Example 19. The method of any of the preceding examples, further comprising: determining, by the lidar system, a return time of the pulse train in response to sampling the lidar return; and determining, by the lidar system, a distance or a velocity associated with the pixel of the object in the field of view based on the return time of the pulse train.

[0123] Example 20. A lidar system comprising: a driver and a laser configured to emit a pulse train comprising a first lidar pulse at a first intensity and a second lidar pulse at a second intensity; a photodetector configured to detect a reflection of the pulse train based on a combination of the first and second intensities; a sampling unit configured to sample the reflection from the photodetector at the combination of the first and second intensities; and a processor configured to determine at least one of a distance or a velocity associated with an object pixel in a field of view based on the reflection.

[0124] Example 21. The lidar system of any of the preceding examples, wherein the driver comprises: a first driver configured to drive the laser to the first intensity during the first lidar pulse; and a second driver configured to drive the laser to the second intensity during the second lidar pulse.

[0125] Example 22. The lidar system of any of the preceding examples, wherein the laser comprises: a first laser configured to emit the first lidar pulse at the first intensity; and a second laser configured to emit the second lidar pulse at the second intensity.

[0126] Example 23. The lidar system of any of the preceding examples, wherein the driver comprises: a first driver configured to drive the first laser to the first intensity during the first lidar pulse; and a second driver configured to drive the second laser to the second intensity during the second lidar pulse.

[0127] Example 24. The lidar system of any of the preceding examples, wherein: the lidar system further comprises: a temperature sensor configured to obtain a temperature of the laser; and active cooling enabled in response to the temperature of the laser exceeding a first threshold in a nominal range; and the processor is further configured to adjust the first intensity of the first pulse and the second intensity of the second pulse in response to the temperature of the laser exceeding a second threshold greater than the first threshold in the nominal range.

[0128] Example 25. The lidar system of any of the preceding examples, wherein: the lidar system further comprises: a deflector configured to align a spot with an object pixel in a field of view; and a beam splitter configured to focus the laser to the spot of the deflector; and the photodetector is further configured to detect the reflection of the pulse train from the beam splitter.

[0129] Example 26. The lidar system of any of the preceding examples, wherein the pulse train comprises a first pulse train, and the processor is further configured to: determine a density of object pixel regions in the field of view; based on the density of object pixel regions, adjust the driver to fire a second pulse train comprising third lidar pulses at a third intensity and fourth lidar pulses at a fourth intensity.

[0130] Example 27. The lidar system of any of the preceding examples, wherein if the density of object pixel regions exceeds a safety threshold, the third intensity is less than the first intensity and the fourth intensity is less than the second intensity.

[0131] Example 28. The lidar system of any of the preceding examples, wherein the processor is further configured to: in response to the density exceeding the safety threshold, direct the driver to stop firing pulse trains with the laser.

[0132] Example 29. The lidar system of any of the preceding examples, wherein the processor is further configured to: in response to the temperature of the laser exceeding a third threshold value that is greater than the second threshold value, direct the driver to avoid firing the second lidar pulse.

[0133] Example 30. The lidar system of any of the preceding examples, further comprising: means for performing the method of any of the preceding examples.

[0134] CONCLUSION

[0135] While various embodiments of the present disclosure have been described above, it should be understood that they have been presented by way of example only, and not limitation. Numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the spirit or scope of the disclosure. Indeed, various modifications can be made to the embodiments described herein, and changes can be made without departing from the scope of the claims as described herein and their equivalents. Although the disclosed embodiments have been largely described with reference to examples in which the present disclosure is implemented in a lidar system, it should be understood that the present disclosure is not limited to such implementations, but can be implemented in any suitable system.

[0136] The use of “or” and the like, as used herein, indicates a non-exclusive or, unless explicitly indicated otherwise. As used herein, the phrase “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of a, b, or c” is intended to cover a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

Claims

1. A lidar system configured to: emit a burst comprising a plurality of lidar pulses having different intensities, an intensity pattern modified from one object pixel to the next; determine an intensity at which to sample reflections of the burst based on an intensity of at least one lidar pulse in the burst; identify a lidar return corresponding to the burst by sampling reflections at the intensity determined based on the intensity of the at least one lidar pulse in the burst; and output an indication of at least one of a distance or a velocity associated with an object pixel in a field of view based on analyzing the lidar return.

2. The lidar system of claim 1, wherein: the lidar system comprises a laser focused on the object pixel in the field of view; and the lidar system is configured to emit the burst by driving the laser.

3. The lidar system of claim 2, wherein: the lidar system further comprises a beam splitter and a deflector; and the lidar system is further configured to: focus the laser through the beam splitter and to a spot of the deflector; align the spot of the deflector with the object pixel in the field of view; and identify the lidar return by sampling reflections from the beam splitter. the lidar system comprises a driver configured to:

4. The lidar system of claim 2, wherein, drive the laser at a first intensity during a first pulse in the burst; and drive the laser at a second intensity during a second pulse in the burst. the laser comprises a laser diode array comprising:

5. The lidar system of claim 4, wherein, a first laser diode configured to emit the first pulse in the burst at the first intensity; and a second laser diode configured to emit the second pulse in the burst at the second intensity. the driver comprises:

6. The lidar system of claim 4, wherein, a first driver configured to energize the laser to the first intensity during the first pulse in the burst; and a second driver configured to energize the laser to the second intensity during the second pulse in the burst. the laser comprises a laser diode array:

7. The lidar system of claim 6, wherein, the first driver is configured to energize a first laser diode to the first intensity during the first pulse in the burst; and the second driver is configured to energize a second laser diode to the second intensity during the second pulse in the burst. the lidar system is configured to determine an intensity at which to sample reflections of the burst by determining a first intensity of a first pulse in the burst and determining a second intensity of at least one second pulse in the burst.

8. The lidar system of claim 1, wherein, ​ 9. The lidar system of claim 8, wherein, The lidar system is configured to identify the lidar returns corresponding to the pulse train by: adjusting sensitivity of a photodetector to the first intensity and the second intensity; and sampling the lidar returns from the adjusted photodetector.

10. The lidar system of claim 9, wherein, The photodetector comprises at least one of: a photodiode, a silicon photomultiplier, an avalanche photodiode, a single-photon avalanche diode, a photomultiplier, or a PIN diode.

11. The lidar system of claim 9, wherein, The lidar system further comprises at least one of: an analog-to-digital converter or a time-to-digital converter configured to sample the lidar returns from the adjusted photodetector.

12. The lidar system of claim 1, wherein, The lidar system is further configured to: determine a return time of the pulse train in response to sampling the lidar returns; and determine the at least one of a distance or a velocity associated with the object pixels in the field of view based on the return time of the pulse train.

13. The lidar system of claim 1, wherein, The plurality of lidar pulses in the pulse train comprises three or more pulses.

14. A method for a lidar system, the method comprising: firing, by the lidar system, a pulse train comprising a plurality of lidar pulses having different intensities, an intensity pattern modified from one object pixel to a next object pixel; determining, by the lidar system, an intensity at which to sample reflections of the pulse train based on an intensity of at least one lidar pulse in the pulse train; identifying, by the lidar system, lidar returns corresponding to the pulse train by sampling reflections at the intensity determined based on the intensity of the at least one lidar pulse in the pulse train; and outputting, by the lidar system, an indication of at least one of a distance or a velocity associated with object pixels in a field of view based on analyzing the lidar returns.

15. The method of claim 14, wherein, further comprising: focusing, by the lidar system, a laser through a beamsplitter and to a spot of a deflector; aligning, by the lidar system, the spot of the deflector with the object pixels in the field of view; and identifying, by the lidar system, the lidar returns by sampling reflections from the beamsplitter.

16. The method of claim 15, wherein, further comprising: firing, by the lidar system, a first pulse in the pulse train at a first intensity; and firing, by the lidar system, a second pulse in the pulse train at a second intensity.

17. The method of claim 14, wherein, Determining an intensity at which to sample reflections of the pulse train comprises determining a first intensity of a first pulse in the pulse train and determining a second intensity of at least one second pulse in the pulse train.

18. The method of claim 17, wherein, Identifying the lidar returns corresponding to the pulse train comprises at least one of: adjusting sensitivity of a photodetector to the first intensity and the second intensity; and sampling the lidar returns from the adjusted photodetector.

19. The method of claim 14, wherein, further comprising: determining, by the lidar system, a return time of the pulse train in response to sampling the lidar returns; and determining, by the lidar system, the distance or velocity associated with the object pixel in the field of view based on the return time of the pulse train.

20. A lidar system comprising: a driver and a laser configured to emit a pulse train, the pulse train comprising a first lidar pulse at a first intensity and a second lidar pulse at a second intensity, wherein an intensity pattern is modified from one object pixel to a next object pixel; a photodetector configured to detect a reflection of the pulse train based on a combination of the first and second intensities; a sampling unit configured to sample the reflection from the photodetector at the combination of the first and second intensities; and a processor configured to determine at least one of a distance or velocity associated with an object pixel in a field of view based on the reflection.

21. The lidar system of claim 20, wherein, the driver comprises: a first driver configured to drive the laser to the first intensity during the first lidar pulse; and a second driver configured to drive the laser to the second intensity during the second lidar pulse.

22. The lidar system of claim 20, wherein, the laser comprises: a first laser configured to emit the first lidar pulse at the first intensity; and a second laser configured to emit the second lidar pulse at the second intensity.

23. The lidar system of claim 22, wherein, the driver comprises: a first driver configured to drive the first laser to the first intensity during the first lidar pulse; and a second driver configured to drive the second laser to the second intensity during the second lidar pulse.

24. The lidar system of claim 20, wherein: the lidar system further comprises: a temperature sensor configured to obtain a temperature of the laser; and active cooling enabled in response to the temperature of the laser exceeding a first threshold in a nominal range; and the processor is further configured to adjust the first intensity of the first lidar pulse and the second intensity of the second lidar pulse in response to the temperature of the laser exceeding a second threshold greater than the first threshold in the nominal range.

25. The lidar system of claim 20, wherein: the lidar system further comprises: a deflector configured to align a spot with the object pixel in the field of view; and a beam splitter configured to focus the laser to the spot of the deflector; and the photodetector is further configured to detect a reflection of the pulse train from the beam splitter.

26. The lidar system of claim 20, wherein, The burst includes a first burst, and the processor is further configured to: determine a density of an object pixel region in the field of view; and adjust the driver to fire a second burst of laser radar pulses based on the density of the object pixel region, the second burst including a third laser radar pulse at a third intensity and a fourth laser radar pulse at a fourth intensity.

27. The lidar system of claim 26, wherein, The third intensity is less than the first intensity and the fourth intensity is less than the second intensity if the density of the object pixel region exceeds a safety threshold.

28. The lidar system of claim 27, wherein, The processor is further configured to direct the driver to stop firing the burst of laser radar pulses with the laser in response to the density exceeding the safety threshold.

29. The lidar system of claim 20, wherein, The processor is further configured to direct the driver to avoid firing the second laser radar pulse in response to a temperature of the laser exceeding a third threshold value that is greater than a second threshold value.

Images