Lidar with light dynamic range

Abstract

A computer-implemented method for extending the dynamic range of a light detector of a LiDAR system is provided. A method includes receiving, using the light detector of the LiDAR system, one or more return pulse signals corresponding to a plurality of transmit pulse signals, wherein at least two transmit pulse signals of the plurality of transmit pulse signals have different power levels; selecting a return pulse signal from the one or more return pulse signals, wherein the selected return pulse signal is within the dynamic range of the photodetector; identifying a transmit pulse signal of the plurality of transmit pulse signals corresponding to the selected return pulse signal; and calculating a distance based on the selected return pulse signal and the identified transmit pulse signal.

Description

[0001] This application is a divisional application of the Chinese patent application with the invention name “LIDAR with large dynamic range”, the application date of October 18, 2018, and the application number of “201880081927.9”.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. Provisional Patent Application Serial No. 62 / 574,679, filed on October 19, 2017, entitled “LIDAR WITH LARGE DYNAMIC RANGE,” the contents of which are hereby incorporated by reference for all purposes.

[0004] This application is related to U.S. Provisional Patent Application No. 62 / 441,280, filed on December 31, 2016, entitled “COAXIAL INTERLACED RASTERSCANNING SYSTEM FOR LiDAR,” and U.S. Provisional Patent Application No. 62 / 529,955, filed on July 7, 2017, entitled “2D SCANNING HIGH PRECESION LiDAR USING COMBINATION OF ROTATING CONCAVE MIRROR AND BEAM STEERING DEVICES,” the contents of which are hereby incorporated by reference in their entirety for all purposes. Technical Field

[0005] The present disclosure relates generally to light detection and ranging (LiDAR) systems, and more particularly to systems and methods for extending the dynamic range of LiDAR systems. Background Art

[0006] LiDAR systems can be used to measure the distance between an object and the system. Specifically, the system can transmit a signal (e.g., by using a light source), record the returned signal (e.g., by using a photodetector), and determine the distance by calculating the delay between the returned signal and the transmitted signal. As an example, Figure 1 A LiDAR system 100 is depicted, having a transmitter 102 and a receiver 104. The LiDAR system transmits a pulse signal 106, receives a returned signal 108, and calculates the distance to an object 110 accordingly.

[0007] The accuracy of a typical LiDAR system is approximately 3-10 cm, which is limited by the pulse duration of the laser source and the response time of the receiver. Some techniques are used to improve the accuracy to a few centimeters, such as by comparing the returned signal with the corresponding original signal (i.e., a reference signal). Additional description of improving the accuracy of a LiDAR system is provided in U.S. Provisional Patent Application 62 / 529,955, "2D SCANNING HIGHPRECISION LiDAR USING COMBINATION OF ROTATING CONCAVE MIRROR AND BEAMSTEERING DEVICES", which is hereby incorporated by reference in its entirety.

[0008] LiDAR systems require a large dynamic range because the power level of the returned signal is inversely proportional to the square of the distance. For example, the return signal scattered from an object at a distance of 10 meters is typically 100 times stronger than the return signal scattered from an object at a distance of 100 meters. In addition, the scattered light for different objects can differ by hundreds of times or more. The dynamic range required for LiDAR systems is typically as large as 10^3-10^4. However, the dynamic range of a typical photodetector used to measure the power of the returned signal is only 10^2. Summary of the invention

[0009] A simplified summary of one or more examples is presented below to provide a basic understanding of the present disclosure. This summary is not an extensive overview of all contemplated examples, and is not intended to identify the key or decisive elements of all examples or to delineate the scope of any or all examples. Its purpose is to present some concepts of one or more examples in a simplified form as a preface to a more detailed description presented below.

[0010] According to some embodiments, a LiDAR scanning system is provided. The system includes a light source configured to provide a sequence of two or more light pulses (e.g., a sequential pulse train). The two or more light pulses have different peak powers and are separated from each other by a certain delay. The order of the sequential pulses follows the rule that weaker signals come out earlier than stronger signals. The system also includes one or more receivers to receive (multiple) return light pulses corresponding to the sequential light pulses. The power ratio between each pair of neighboring pulses of the light source can be as large as the dynamic range of the receiver, for example 10^2. Because the peak power of each sequential pulse in the sequential pulse train covers a wide range to 10^4, but not limited to 10^4, one of the pulses must return a signal that comfortably fits itself into the dynamic range of the receiver.

[0011] In some embodiments, a computer-implemented method for extending the dynamic range of a light detection and ranging (LiDAR) system includes: transmitting a sequence of pulse signals using a light source of the LiDAR system, wherein the sequence of pulse signals includes two or more increasingly stronger pulse signals; receiving one or more returned pulse signals corresponding to the sequence of transmitted pulse signals at a light detector of the LiDAR system, wherein the one or more returned pulse signals are above a noise level of the light detector; selecting a returned pulse signal from the one or more returned pulse signals, wherein the selected returned pulse signal is within the dynamic range of the light detector; identifying the transmitted pulse signal in the transmitted sequence corresponding to the selected returned pulse signal; and calculating a distance based on the selected returned signal and the identified transmitted signal.

[0012] In some embodiments, a light detection and ranging (LiDAR) system includes: a memory; a laser system configured to emit a sequence of pulse signals, wherein the sequence of pulse signals includes two or more increasingly stronger pulse signals; a light detector configured to receive one or more returned pulse signals corresponding to the sequence of emitted pulse signals, wherein the one or more returned pulse signals are above a noise level of the light detector; and one or more processors configured to: select a returned pulse signal from the one or more returned pulse signals, wherein the selected returned pulse signal is within a dynamic range of the light detector; identify the emitted pulse signal in the emitted sequence corresponding to the selected returned pulse signal; and calculate a distance based on the selected returned signal and the identified emitted signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For a better understanding of the various described embodiments, reference should be made to the following description of the embodiments in conjunction with the following drawings, in which like reference numerals refer to corresponding parts throughout the various figures.

[0014] Figure 1 An exemplary LiDAR system having a light source and a receiver is depicted in accordance with some embodiments.

[0015] Figure 2 Depicted is an exemplary sequence of pulsed signals from a light source according to some embodiments.

[0016] Figure 3A Depicted is a received return signal scattered from a relatively nearby object in accordance with some embodiments.

[0017] Figure 3B Depicted is a received return signal scattered from a relatively mid-range object in accordance with some embodiments.

[0018] Figure 3C Depicted is a received return signal scattered from a relatively distant object in accordance with some embodiments.

[0019] Figure 4 Depicted is an exemplary process for extending the dynamic range of a LiDAR system in accordance with some embodiments.

[0020] Figure 5 Depicted is an exemplary schematic diagram of a fiber laser in accordance with some embodiments.

[0021] Fig. 6A Depicted are exemplary configurations for implementing sequential pulsing of light sources in accordance with some embodiments.

[0022] Figure 6B Depicted are exemplary configurations for implementing sequential pulsing of light sources in accordance with some embodiments.

[0023] Figure 6C Depicted are exemplary configurations for implementing sequential pulsing of light sources in accordance with some embodiments.

[0024] Fig.6D Depicted are exemplary configurations for implementing sequential pulsing of light sources in accordance with some embodiments.

[0025] Figure 7 Depicted is an exemplary configuration for implementing a reference beam with sequential pulses in accordance with some embodiments. DETAILED DESCRIPTION

[0026] As discussed above, LiDAR systems require a large dynamic range because the power level of the returned signal is inversely proportional to the square of the distance. The dynamic range required for LiDAR systems is typically as large as 10^3-10^4. However, the dynamic range of a typical photodetector used to measure the power of the returned signal is only 10^2.

[0027] In order to increase the dynamic range of the system, several techniques can be used. If the laser source is a semiconductor laser, the driving current of the laser source can be modulated to adjust the output power so that a small signal is sent to detect a nearby object and a large signal is sent to detect a distant object. However, this technique requires predicting the environment based on the previous frame and increases the complexity of the computational load and the control circuit. In addition, this technique cannot be used for certain laser sources, such as erbium-doped fiber lasers, for which the active doping has a long fluorescence time of 3-10 milliseconds. The output power from such a laser cannot be adjusted from pulse to pulse because the time scale of the laser response is usually in the region of a few microseconds. Some other techniques can be applied to such lasers, including, for example, adjusting the pulse duration of the laser source, tuning the supply voltage of the photodetector, and using multiple sets of photodetectors. However, none of these techniques can effectively increase the dynamic range of the photodetector from 10^2 to 10^4, and the cost may be high. The present disclosure introduces an efficient and cost-saving method to realize a LiDAR system with a large dynamic range of 10^4 but not limited to 10^4.

[0028] The following description is presented to enable those of ordinary skill in the art to make and use various embodiments. The description of specific equipment, technology and application is provided only as an example. Various modifications to the examples described herein will be easily apparent to those of ordinary skill in the art, and the general principles defined herein can be applied to other examples and applications without departing from the spirit and scope of the various embodiments. Thus, the various embodiments are not intended to be limited to the examples described and shown herein, but to be given a scope consistent with the claims.

[0029] In the following description of the examples, reference is made to the accompanying drawings, which form a part of the description and in which are shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the disclosed examples.

[0030] Although the following description uses the terms "first", "second" and the like to describe various elements, these elements should not be limited by the terms. These terms are only used to distinguish one element from another. For example, the first pulse signal can be referred to as the second pulse signal, and similarly, the second pulse signal can be referred to as the first pulse signal, without departing from the scope of the various embodiments. Both the first pulse signal and the second pulse signal are pulse signals, but they may not be identical pulse signals.

[0031] The terms used in the description of the various described embodiments herein are only for the purpose of describing specific embodiments and are not intended to be limiting. As used in the description of the various described embodiments and in the appended claims, the singular forms "one", "an" and "the" are intended to also include the plural forms, unless the context clearly indicates otherwise. It will also be understood that the term "and / or" as used herein refers to and includes any and all possible combinations of one or more associated listed items. It will also be understood that the terms "include", "comprising", "including" and / or "comprising" when used in this specification specify the presence of the claimed features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0032] The term "if" is optionally interpreted to mean "when" or "upon" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrases "if it is determined" or "if [a stated condition or event] is detected" are optionally interpreted to mean "upon determining" or "in response to determining" or "upon detecting [a stated condition or event]" or "in response to detecting [a stated condition or event]," depending on the context.

[0033] The present disclosure describes a method for increasing the dynamic range of a LiDAR system to (but not limited to) 10^4 by using a standard photodetector. A typical photodetector has a dynamic range where the amplified electronic signal is linearly proportional to the incident power, up to 10^2. However, in order to determine the distance between an object and a LiDAR system with an accuracy of a few centimeters, the receiver should be able to measure the returned signal with a dynamic range of 10^4. In order to extend the dynamic range of a LiDAR system, sequential pulses of a light source are manipulated to illuminate an object in the field of view. The returned signal is measured by a typical photodetector, as discussed below.

[0034] Figure 2 Two exemplary sequences of pulse signals (i.e., two sequential pulse groups) generated by a light source are illustrated. Each of the two sequences of pulse signals includes two or more sequential optical pulse signals. In each sequence, the peak power of each pulse signal is different, and adjacent pulses are separated by a certain delay. In each sequence, the order of the sequential pulse signals follows the following rule: weaker signals come out earlier than stronger signals. Figure 2 As depicted in FIG. 1 , each exemplary sequential pulse group includes pulse signals P1, P2, . . . , P n The sequence of T pRepresents the period between the sequence of pulse signals and is the inverse of the repetition rate of the laser. The pulse signals in the sequential pulse group can have the same pulse duration or different pulse durations. The delays between neighboring pulse signals (e.g., between P1 and P2, between P2 and P3) can be the same or different.

[0035] Figure 3A -C illustrates an exemplary scenario in which the LiDAR system transmits two sequential pulse groups and receives two groups of returned signals scattered from a relatively close object, a relatively mid-range object, and a relatively far-away object, respectively. The received returned signals (annotated as R1, R2, ..., R n ) correspond to P1, P2, ..., P n .

[0036] refer to Figure 3A , the transmitted sequential pulse groups are scattered by nearby objects, resulting in the return signals R1, R2, ..., R n Due to the short distance and thus strong return signal, only R1 stays within the dynamic range of the photodetector and all other signals are saturated. The saturated signal is later discarded by the software that processes the measured return signal. Therefore, R1 (together with P1) is used to determine the distance between the object and the LiDAR system.

[0037] refer to Figure 3B , the transmitted sequential pulse groups are scattered by mid-range objects, resulting in the measured returned signals R1, R2, ..., R n Some return signals (such as R1 corresponding to P1) are hidden below the noise level of the photodetector and cannot be analyzed. n R n ) saturates the photodetector and is later discarded. The returned signal of the mid-range pulse (R3 corresponding to P3) stays in the dynamic range of the photodetector and is used to analyze the distance between the mid-range object and the LiDAR system.

[0038] refer to Figure 3C , the transmitted sequential pulse groups are scattered by distant objects, resulting in the measured returned signals R1, R2, ..., R n Due to the long distance and thus weak return signal, only R n stays within the dynamic range of the photodetector, and all other signals are below the noise level of the system. n Used to analyze the distance between distant objects and the LiDAR system.

[0039] Figure 4 A process 400 for providing a large dynamic range for a LiDAR system according to various examples is illustrated. The process 400 is performed, for example, using a LiDAR system having a light source (e.g., a fiber laser), a light detector, a memory, and one or more processors. Although portions of the process 400 are described herein as being performed by specific components of the LiDAR system, it will be appreciated that the process 400 is not so limited. In the process 400, some boxes are optionally combined, the order of some boxes is optionally changed, and some boxes are optionally omitted. In some examples, additional steps may be performed in conjunction with the process 400. Therefore, the operations as illustrated (and described in more detail below) are exemplary in nature and should not be considered limiting as such.

[0040] At block 402, a LiDAR system transmits a sequence of pulse signals (e.g., Figure 2 The sequential pulse groups P1, P2, ..., P n ). The sequence of pulse signals includes two or more increasingly stronger pulse signals. For example, Figure 2 As depicted in , P1 is transmitted before P2, and the power level of P1 is lower than the power level of P2. In some examples, the power ratio between two adjacent pulse signals (eg, P1 and P2) in the sequence of pulse signals does not exceed the dynamic range of the detector.

[0041] At block 404, the LiDAR system receives one or more returned pulse signals corresponding to the sequence of transmitted pulse signals using a light detector of the LiDAR system. The one or more returned pulse signals are above the noise level of the light detector. For example, Figure 3A As depicted in FIG. 1 , the LiDAR system receives n returned pulse signals (R1, R2, ..., R n ), which corresponds to the transmitted pulse signal (P1, P2, ..., P n ) sequence. In addition, all n returned pulse signals (P1, P2, ..., P n ) is above the noise level of the photodetector. As another example, Figure 3B In , the LiDAR system receives less than n returned pulse signals above the noise level of the photodetector because the first return signal R1 received by the LiDAR system is hidden below the noise level of the photodetector and cannot be analyzed.

[0042] At block 406, the LiDAR system selects a returned pulse signal from the one or more returned pulse signals. The selected returned pulse signal is within the dynamic range of the photodetector (e.g., not saturated and not below the noise level of the photodetector). Figure 3B As depicted in , the LiDAR system selects R3, which is within the dynamic range of the photodetector and will be used to analyze the distance between the mid-range object and the LiDAR system. In this example, R n (corresponding to P n ) is a saturated signal and is therefore not selected.

[0043] In some examples, to select the returned pulse signal, the LiDAR system identifies the last received pulse signal among the returned signals that is not a saturation signal. Figure 3B , the system can identify R3 as the last received pulse signal that is not a saturated signal, because R4-R n All are saturated signals. Therefore, R3 is selected.

[0044] In some examples, there is only one returned pulse signal that corresponds to the transmitted pulse signal sequence that is within the dynamic range of the photodetector. Therefore, that one returned pulse signal is selected.

[0045] In some examples, the LiDAR system transmits multiple pulse signal sequences, and for each of the multiple pulse signal sequences, the system receives at least one returned pulse signal within the dynamic range of the light detector. For example, if the system transmits two sequential pulse groups (such as Figure 2 ), and the first group is scattered by a nearby object and the second group is scattered by a distant object, the system may be able to receive (a plurality of) returned pulse signals within the dynamic range of the light detector for both the first group and the second group, as in Figure 3A and 3C As shown in the figure.

[0046] In some examples, the system may determine that all of the returned pulse signals are saturated signals (ie, none of the returned pulse signals are within the dynamic range of the photodetector). This may indicate that: the transmitted pulse signal (eg Figure 2 P1, P2, ..., P n) is not appropriate for the environment being surveyed. Therefore, the LiDAR system can be adjusted so that a different sequence of pulse signals is generated and then transmitted. The new sequence of pulse signals can differ from the previous sequence in the number of pulses, the peak power level of the pulses, or a combination thereof. In some examples, the LiDAR system is adjusted by a human operator who manually changes the configuration of the LiDAR system. In some examples, the LiDAR system is adjusted automatically by one or more processors of the system.

[0047] At block 408, the LiDAR system identifies the transmitted pulse signal in the transmitted sequence that corresponds to the selected returned pulse signal. At block 410, the LiDAR system calculates a distance based on the selected returned signal and the identified transmitted signal.

[0048] An exemplary process for selecting a returned signal and identifying a transmitted pulse signal corresponding to the selected returned pulse signal is provided below. In this example, the LiDAR system transmits a sequence of pulse signals, which includes three increasingly strong pulse signals, and receives one or more returned signals corresponding to the transmitted sequence.

[0049] If the LiDAR system receives only one returned signal above the noise level, the system selects the returned signal (assuming that the signal is within the dynamic range of the photodetector) and determines that the returned signal corresponds to the third / last pulse signal in the transmitted sequence. The system thus calculates the distance based on the one returned pulse signal and the third pulse signal in the transmitted pulse signal sequence.

[0050] If the LiDAR system receives two returned signals that are above the noise level of the photodetector, the system selects the earlier received returned signal of the two (assuming that the earlier signal is within the dynamic range of the photodetector) and determines that the selected returned signal corresponds to the second pulse signal in the transmitted sequence. The system then calculates the distance based on the earlier received pulse signal and the second pulse signal in the transmitted pulse signal sequence.

[0051] If the LiDAR system receives three returned signals above the noise level of the photodetector, the system selects the earliest received returned signal of the three (assuming that the earliest signal is within the dynamic range of the photodetector) and determines that the selected returned signal corresponds to the first pulse signal in the transmitted sequence. Thus, the system calculates the distance including calculating the distance based on the earliest received pulse signal and the first pulse signal in the transmitted pulse signal sequence.

[0052] Various exemplary configurations for implementing sequential pulses of a light source are disclosed herein. In some embodiments, a LiDAR system uses a fiber laser as a light source. Fiber lasers have their unique advantages, including perfect beam profiles, stability from pulse to pulse, eye safety if a 1550nm wavelength is used, and so on. However, fiber lasers also have their disadvantages. For example, the fluorescence time of active ions in a fiber laser is several milliseconds, thus preventing the laser from adjusting power from pulse to pulse. Therefore, methods of increasing dynamic range by adjusting laser power cannot be easily implemented in standard fiber lasers. Described below is a technique for generating sequential pulse groups in a fiber laser that provides a practical and efficient way to increase dynamic range.

[0053] Figure 5 An exemplary schematic diagram of a fiber laser is illustrated. The seed source is amplified by one or more preamplifiers and / or booster amplifiers to achieve the desired output power. If the system is a nanosecond laser, the seed can be a DFB laser with pulse duration and repetition rate controlled by external circuitry. If the system is a picosecond laser or shorter, the seed can be a mode-locked fiber laser with pulse duration and repetition rate controlled by the laser cavity. The present disclosure discusses nanosecond fiber lasers as an example, but it should be appreciated that the disclosed techniques can be applied to any type of laser.

[0054] Figures 6A-6D An exemplary configuration for implementing a sequential pulse train is shown. Figures 6A-6D Each configuration depicted in generates a 2-pulse sequential pulse train, but the configuration can be extended to achieve sequential pulse trains with any number of pulses.

[0055] refer to Fig. 6A , the laser system 610 includes a laser splitter C1 having an input port 612, a first output port 614, and a second output port 616. The laser splitter is configured to receive a laser beam via the input port 612 (e.g., from a preamplifier), and based on the received laser beam, provide a first split laser beam via the first output port 614, and provide a second split laser beam via the second output port 616.

[0056] The laser system 610 further comprises a laser combiner C2 having a first input port 618, a second input port 620 and an output port 622. The laser combiner is configured to receive the first split laser beam and the second split laser beam via the two input ports, and to provide a sequence of pulse signals via the output port, which comprises a first pulse signal corresponding to at least a portion of the first split beam, and at least a portion of the second pulse signal corresponding to the second split beam.

[0057] In some examples, the laser combiner is a coupler having two output ports, one of which is output port 622. Specifically, the coupler is configured to emit a portion (e.g., 10%) of the first split laser beam to output port 622, and the rest of the first split laser beam to the other output port, and to emit a portion (e.g., 90%) of the second split laser beam to output port 622, and the rest of the second split laser beam to the other output port. In this example, the laser beam output via the other output port is discarded. In addition, the laser beam output via output port 622 will be a sequence of pulse signals having a first pulse signal corresponding to a portion (e.g., 10%) of the first split beam, and a second pulse signal corresponding to a portion (e.g., 90%) of the second split beam.

[0058] In some examples, the laser combiner includes a polarization beam splitter. The polarization beam splitter is configured to: receive a first beam having a linear polarization and a second beam having a polarization perpendicular to the first beam; combine the first beam and the second beam into a third beam; and provide the third beam to an output port of the laser combiner. Therefore, if the first split laser beam and the second split laser beam have polarizations as described above, the polarization beam splitter can combine the first split laser beam and the second laser beam into a sequence of pulse signals having a first pulse signal corresponding to 100% of the first split beam and a second pulse signal corresponding to 100% of the second split beam.

[0059] The laser system 610 further includes: a first fiber 624 configured to relay a first split beam from a first output port 614 of the laser splitter to a first input port 618 of the laser combiner; and a second fiber 626 configured to relay a second split beam from a second output port 616 of the laser splitter to a second input port 620 of the laser combiner. The first fiber and the second fiber are configured to induce a delay to the second split laser beam relative to the first split laser beam. In some examples, the length of the second fiber is longer than the length of the first fiber to introduce a delay. In some examples, the laser system 610 further includes a preamplifier and / or a boost amplifier, such as Fig. 6A As depicted in .

[0060] exist Fig. 6A Specific quantities are provided in order to illustrate an exemplary implementation of a sequential pulse group. As depicted, the final preamplifier power Wpre is 30 mW, and the output power W of the fiber laser is out is 1000mW. Splitter C1 is positioned between the final preamplifier and the boost amplifier to divide Wpre Split into two split laser beams. The split laser beam from port 616 has a power level of 20mW and is fed to a boost amplifier to generate a 1000mW output. The split laser beam from port 614 has a power level of 10mW. Combiner C2 combines the two split beams to form a sequential pulse group. During the combination process, if the input is polarized and maintained, a polarization beam splitter can be used. For the case of an unpolarized system, a coupler with a certain ratio (e.g., 90:10) can be used, but at the expense of a certain power loss. The length of fiber 624, 626, and / or 630 can be controlled to limit the delay between a small pulse and a large pulse. The pulse intensity ratio between a small pulse and a large pulse is approximately 10^2, which is designed to match the dynamic range of a photodetector. As discussed above, the returned signal corresponding to the small pulse is used to determine a short distance, and the one corresponding to the large pulse is used to determine a long distance. By using a combination of two pulses, the final dynamic range can reach 10^2*10^2=10^4.

[0061] In some examples, the laser splitter is implemented by using a circulator and a reflector. Figure 6B Another exemplary configuration for implementing a sequential pulse group is illustrated. As depicted, a circulator is used after the boost amplifier. The circulator is configured to receive a laser beam via an input port 636 and provide the received laser beam to the input port of a partial reflector via an output port 632 of the circulator. A partial reflector (e.g., a 1% reflector) reflects a small amount (e.g., 1%) of the pulse back to the circulator. The circulator is directionally aware and is configured to propagate any laser beam traveling into an output port 632 via port 634. The remainder of the pulse (i.e., that which is not reflected by the reflector) is output by the reflector.

[0062] and Fig. 6A A combiner similar to the one in combines a small pulse from port 634 with a large pulse leaving the circulator. The intensity ratio between the large pulse and the small pulse can be controlled by the reflectivity of the reflector. The fiber length in the configuration (e.g., from port 634 and port 632) is controlled to determine the delay between the small pulse and the large pulse. If a 1% reflector is used, the intensity ratio of the large pulse to the small pulse is about 10^2, matching a photodetector whose dynamic range is 10^2. The final dynamic range is 10^4, as with respect to Fig. 6A As described in the technique.

[0063] In some examples, a LiDAR system includes a laser combiner having a first input port, a second input port, and two output ports; and the laser combiner is configured to provide two sequences of pulse signals via the two output ports. Figure 6C-6D Two exemplary configurations for achieving sequential pulse bursts for a system with two laser beams as light sources are illustrated. As depicted, a 50:50 coupler is used to combine a small beam with a large beam. At the output of the coupler, each of the two ports gets 50% of the large beam and 50% of the small beam. Thus, for a fiber laser with an output power of 1000 mW, two laser sources are provided as light sources, each of which contains a small pulse (5 mW) and a large pulse (500 mW).

[0064] In order to determine the distance of an object with a high accuracy of several centimeters, a reference beam is needed for analysis. Additional description of improving the accuracy of LiDAR systems is provided in U.S. Provisional Patent Application 62 / 529,955 "2D SCANNING HIGH PRECISION LIDAR USING COMBINATION OF ROTATING CONCAVE MIRROR AND BEAM STEERING DEVICES", which is hereby incorporated by reference in its entirety. The reference beam can be provided by a coupler (e.g., in a fiber laser), such as Figure 7 A small portion of the main pulse is propagated into the reference arm via a coupler and recorded by a photodetector. The pulse shape and beam profile of the reference signal are identical to the sequence of transmitted pulse signals. By analyzing the pulse shape of the reference beam and the returned signal, the distance between the object and the LiDAR system can be calculated more accurately.

[0065] In some examples, a reference beam is provided to a light detector of the LiDAR system, and the system causes a delay between the provision of the reference signal and the emission of the pulse signal sequence so that the measured signal of the reference beam does not interfere with any signal in the returned signal. For example, the fiber length of the reference arm is arranged to cause such a delay. When calculating the distance based on the reference signal and the returned signal(s), the system takes the delay into account (e.g., by using software to correct for the delay).

[0066] It is important for the LiDAR system to distinguish its own signal from those of others through encoding and decoding techniques. Implementing sequential pulse groups can provide such encoding and decoding functions. By using different delays between pulses and different amplitude ratios between pulses, the LiDAR system associates a unique signature and can therefore distinguish itself from others. For example, after the LiDAR system transmits a sequence of pulse signals, the system can receive a plurality of returned signals in the dynamic range of the photodetector. However, only some of the returned signals are generated by the transmitted sequence scattered by the object. The LiDAR system can identify a subset of the plurality of returned signals as corresponding to the transmitted pulse signal sequence based on the known delays between neighboring pulse signals in the transmitted pulse signal sequence. Additionally or alternatively, the LiDAR system can identify a subset of the plurality of returned signals as corresponding to the transmitted pulse signal sequence based on the known amplitude differences between neighboring pulse signals in the transmitted pulse signal sequence.

[0067] To achieve different delays, in some examples, you can adjust Figure 7 To achieve different amplitude ratios, in some examples, the length of the fiber delay line can be adjusted Figure 7 In addition, one or more power ratios between adjacent pulses in the sequence are set to be lower than the dynamic range of the photodetector so that the system can receive multiple returned signals within the dynamic range of the photodetector, thereby obtaining the delays between these returned signals to be used in the above analysis.

[0068] Exemplary methods, non-transitory computer-readable storage media, systems, and electronic devices are set forth in example implementations of the following items.

[0069] Item 1. A computer-implemented method for extending the dynamic range of a light detection and ranging (LiDAR) system having a light source and a light detector, the method comprising:

[0070] By using a light source of the LiDAR system to emit a sequence of pulse signals, wherein the sequence of pulse signals includes two or more increasingly stronger pulse signals;

[0071] receiving one or more returned pulse signals corresponding to the sequence of transmitted pulse signals using a photodetector of the LiDAR system, wherein the one or more returned pulse signals are above a noise level of the photodetector;

[0072] selecting a returned pulse signal from the one or more returned pulse signals, wherein the selected returned pulse signal is within a dynamic range of the photodetector;

[0073] identifying a transmitted pulse signal in the transmitted sequence corresponding to the selected returned pulse signal; and calculating a distance based on the selected returned signal and the identified transmitted signal.

[0074] Item 2. The method of Item 1, wherein the power ratio between two adjacent pulse signals in the sequence of transmitted pulse signals does not exceed the dynamic range of the detector.

[0075] Item 3. The method of any one of Items 1-2, wherein the selected returned pulse signal is a first returned pulse signal, wherein the one or more returned pulse signals further include a second returned pulse signal received after the first returned pulse signal, wherein the second returned pulse signal is a saturated signal.

[0076] Item 4. The method of any of Items 1-2, further comprising: receiving a returned signal below a noise level of the light detector before receiving the one or more returned signals above a noise level of the light detector.

[0077] Item 5. The method of any one of Items 1-4 further comprises: transmitting a plurality of pulse signal sequences; and for each of the plurality of pulse signal sequences, receiving at least one returned pulse signal within the dynamic range of the light detector.

[0078] Item 6. The method of any one of Items 1-5, wherein selecting the returned pulse signal from the one or more returned pulse signals includes: identifying the last received pulse signal in the one or more returned signals that is not a saturation signal.

[0079] Item 7. The method of any one of Items 1-5, wherein selecting a returned pulse signal from the one or more returned pulse signals includes: determining that there is only one returned pulse signal that corresponds to the sequence of emitted pulse signals and is above the noise level of the light detector.

[0080] Item 8. A method according to any one of Items 1-7, wherein the sequence of transmitted pulse signals is a first sequence, and the method further comprises: determining that each of the one or more returned pulse signals is a saturated signal; and after the determination, sending a second sequence of pulse signals that is different from the first sequence in the following aspects: the number of pulses, the peak power level of the pulses, or a combination thereof.

[0081] Item 9. The method of any one of Items 1-8, wherein the sequence of emitted pulse signals includes a first pulse signal, a second pulse signal emitted after the first pulse signal and stronger than the first pulse signal, and a third pulse signal emitted after the second pulse signal and stronger than the second pulse signal.

[0082] Item 10. The method of Item 9, wherein the one or more returned pulse signals include a returned pulse signal above a noise level, wherein the one returned pulse signal is the selected returned signal, and wherein calculating the distance includes calculating the distance based on the one returned pulse signal and a third pulse signal in a sequence of transmitted pulse signals.

[0083] Item 11. The method of Item 9, wherein the one or more returned pulse signals include two returned signals above a noise level, wherein the earlier received returned signal of the two is the selected returned signal, and wherein calculating the distance includes calculating the distance based on the earlier received pulse signal and a second pulse signal in a sequence of transmitted pulse signals.

[0084] Item 12. The method of Item 9, wherein the one or more returned pulse signals include three returned signals, wherein the earliest received returned signal among the three is the selected returned signal, and wherein calculating the distance includes calculating the distance based on the earliest received pulse signal and the first pulse signal in the sequence of transmitted pulse signals.

[0085] Item 13. The method of any one of Items 1-12 further includes: receiving a plurality of returned signals within the dynamic range of the optical detector; identifying a subset of the plurality of returned signals as corresponding to a sequence of emitted pulse signals, wherein the identification is based on one or more delays between adjacent pulse signals in the sequence of emitted pulse signals.

[0086] Item 14. The method of any one of Items 1-12 further includes: receiving a plurality of returned signals within the dynamic range of the light detector; identifying a subset of the plurality of returned signals as corresponding to a sequence of emitted pulse signals, wherein the identification is based on one or more amplitude differences between adjacent pulse signals in the sequence of emitted pulse signals.

[0087] Item 15. The method of any one of Items 1-14, further comprising: providing a reference signal to the light detector via a light source, wherein a pulse shape and a beam profile of the reference signal are the same as the sequence of the emitted pulse signals.

[0088] Item 16. The method of Item 15, further comprising: causing a delay between the provision of the reference signal and the transmission of the sequence of pulse signals, wherein the distance is calculated based on the delay.

[0089] Item 17. The method of any one of Items 1-16, wherein the light source comprises a fiber laser.

[0090] Item 18. The method of any one of Items 1-17, wherein the light source comprises a beam splitter, a combiner, and at least two fibers of different lengths.

[0091] Item 19. A light detection and ranging (LiDAR) system comprising:

[0092] Memory;

[0093] A laser system configured to emit a sequence of pulse signals, wherein the sequence of pulse signals comprises two or more increasingly stronger pulse signals;

[0094] a photodetector configured to receive one or more returned pulse signals corresponding to the sequence of transmitted pulse signals, wherein the one or more returned pulse signals are above a noise level of the photodetector; and

[0095] One or more processors configured to:

[0096] selecting a returned pulse signal from the one or more returned pulse signals, wherein the selected returned pulse signal is within a dynamic range of the photodetector;

[0097] identifying a transmitted pulse signal in the transmitted sequence corresponding to the selected returned pulse signal; and calculating a distance based on the selected returned signal and the identified transmitted signal.

[0098] Item 20. The system of Item 19, wherein the laser system includes a beam splitter having an input port, a first output port, and a second output port, wherein the beam splitter is configured to receive a laser beam via the input port, and based on the received laser beam, provide a first split laser beam via the first output port and provide a second split laser beam via the second output port.

[0099] Item 21. The system of Item 20, wherein the beam splitter includes a circulator; and a reflector, wherein the circulator is configured to provide the received laser beam to an input port of the reflector via an output port of the circulator, wherein the reflector is configured to reflect a first portion of the received laser beam back to the output port of the circulator and to emit a second portion of the received laser beam via the output port of the reflector.

[0100] Item 22. The system of Item 21, wherein the first portion of the received laser beam corresponds to a first split laser beam, and wherein the second portion of the received laser beam corresponds to a second split laser beam.

[0101] Item 23. A system of any one of Items 20-22, wherein the laser system includes a laser combiner having a first input port, a second input port, and an output port; wherein the laser combiner is configured to provide a sequence of pulse signals via the output port, comprising a first pulse signal corresponding to at least a portion of the first split beam and a second pulse signal corresponding to at least a portion of the delayed second split beam.

[0102] Item 24. The system of Item 23, wherein the laser combiner comprises a coupler having a first output port and a second output port, and wherein the output port of the laser combiner is one of the first output port and the second output port of the coupler.

[0103] Item 25. The system of Item 23, wherein the laser combiner includes a polarization beam combiner, which is configured to: receive a first beam having a linear polarization and a second beam having a polarization perpendicular to the first beam; combine the first beam and the second beam into a third beam; and provide the third beam to an output port of the laser combiner, wherein the third beam includes a sequence of pulse signals.

[0104] Item 26. A system of any one of Items 19-22, wherein the laser system includes a laser combiner having a first input port, a second input port, a first output port, and a second output port; wherein the laser combiner is configured to provide a first sequence of pulse signals via the first output port of the laser combiner, and to provide a second sequence of pulse signals via the second output port of the laser combiner.

[0105] Item 27. A system of any one of Items 19-26, wherein the laser system further comprises: a first fiber configured to relay a first split beam from a first output port of a beam splitter to a first input port of a laser combiner; and a second fiber configured to relay a second split beam from a second output port of the beam splitter to a second input port of the laser combiner, wherein the first fiber and the second fiber are configured to induce a delay to the second split laser beam relative to the first split laser beam.

[0106] Item 28. The system of Item 27, wherein the length of the first fiber is different from the length of the second fiber.

[0107] Item 29. The system of any one of Items 19-28, wherein the laser system further comprises a preamplifier.

[0108] Item 30. The system of any one of Items 19-29, wherein the laser system further comprises a boost amplifier.

[0109] Item 31. The system of any one of Items 19-30, wherein the laser system is further configured to provide a reference signal to the light detector, wherein the pulse shape and beam profile of the reference signal are identical to the sequence of emitted pulse signals.

[0110] Although the present disclosure and examples have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications will be understood to be included within the scope of the present disclosure and examples as defined by the claims.

[0111] The foregoing description for explanation purposes has been described with reference to specific embodiments. However, the above illustrative discussion is not intended to be exhaustive or to limit the invention to the exact form disclosed. In view of the above teachings, many modifications and variations are possible. The embodiments are selected and described in order to best explain the principles of the technology and its practical application. This enables others skilled in the art to best utilize the technology and various embodiments, with various modifications as appropriate for the specific use contemplated.

Claims

1. A computer-implemented method for extending the dynamic range of a light detector of a light detection and ranging LiDAR system, the method include: receiving, using the light detector of the LiDAR system, one or more return pulse signals corresponding to a plurality of transmit pulse signals, wherein at least two of the plurality of transmit pulse signals have different power levels; selecting a return pulse signal from the one or more return pulse signals, wherein the selected return pulse signal is within the dynamic range of the photodetector; identifying a transmit pulse signal among the plurality of transmit pulse signals corresponding to the selected return pulse signal; as well as The distance is calculated based on the selected return pulse signal and the identified transmit pulse signal.

2. The method according to claim 1, in, A power ratio between two adjacent pulse signals among the plurality of transmit pulse signals does not exceed the dynamic range of the photodetector.

3. The method according to claim 1 or 2, in, The selected return pulse signal is a first return pulse signal, wherein the one or more return pulse signals further include a second return pulse signal that exceeds the dynamic range of the optical detector.

4. The method according to claim 1 or 2, in, The one or more return pulse signals are above a noise level of the photodetector.

5. The method according to claim 1 or 2, in, Selecting a return pulse signal from the one or more return pulse signals comprises: A last received return pulse signal of the one or more return pulse signals that is not a saturation signal is identified.

6. The method according to claim 1 or 2, in, Selecting a return pulse signal from the one or more return pulse signals comprises: It is determined that there is only one return pulse signal corresponding to the plurality of transmit pulse signals and above a noise level of the photodetector.

7. The method according to claim 1 or 2, in, The plurality of transmit pulse signals are a first plurality of transmit pulse signals, and the one or more return pulse signals are a first return pulse signal, and the method further comprises: receiving one or more second return pulse signals corresponding to a second plurality of transmit pulse signals; determining that none of the one or more second return pulse signals is within the dynamic range of the optical detector; and After determining, a third plurality of transmit pulse signals are transmitted, the third plurality of transmit pulse signals being different from the second plurality of transmit pulse signals in one or more of the following: number of pulses, peak power level of the pulses, or a combination thereof.

8. The method according to claim 1 or 2, in, The plurality of transmit pulse signals form a sequence of transmit pulse signals having increasingly stronger power levels.

9. The method according to claim 8, in, The selected return pulse signal is the only return pulse signal among the one or more return pulse signals that is above a noise level of the optical detector.

10. The method according to claim 8, in, The one or more return pulse signals include two or three return pulse signals above a noise level, wherein the earliest received return pulse signal among the two or three return pulse signals is the selected return pulse signal.

11. The method according to claim 1 or 2, in, The plurality of transmit pulse signals are encoded using different delays between at least some adjacent transmit pulse signals in the plurality of transmit pulse signals.

12. The method according to claim 11, further comprising: include: The plurality of return pulse signals are decoded based on the different delays to identify the one or more return pulse signals corresponding to the plurality of transmit pulse signals.

13. The method of claim 12, further comprising discarding return signals associated with one or more other LiDAR systems based on the decoding results.

14. The method according to claim 1 or 2, in, The plurality of transmit pulse signals are configured to have power level differences between at least some adjacent transmit pulse signals among the plurality of transmit pulse signals.

15. The method according to claim 14, further comprising: include: The plurality of return pulse signals are decoded based on the power level differences to identify the one or more return pulse signals corresponding to the plurality of transmit pulse signals.

16. The method according to claim 1 or 2, further comprising: include: A reference signal is provided to the optical detector, wherein calculating the distance is further based on a delay between providing the reference signal and transmitting the plurality of transmit pulse signals.

17. A light detection and ranging LiDAR system, include: a photodetector operable to receive one or more return pulse signals corresponding to a plurality of transmit pulse signals, wherein at least two of the plurality of transmit pulse signals have different power levels; Memory; and One or more processors configured to: selecting a return pulse signal from the one or more return pulse signals, wherein the selected return pulse signal is within a dynamic range of the photodetector; identifying a transmit pulse signal among the plurality of transmit pulse signals corresponding to the selected return pulse signal; as well as The distance is calculated based on the selected return pulse signal and the identified transmit pulse signal.

18. The system according to claim 17, in, A power ratio between two adjacent pulse signals among the plurality of transmit pulse signals does not exceed the dynamic range of the photodetector.

19. The system according to claim 17 or 18, in, The selected return pulse signal is a first return pulse signal, wherein the one or more return pulse signals further include a second return pulse signal that exceeds the dynamic range of the optical detector.

20. The system according to claim 17 or 18, in, The one or more return pulse signals are above a noise level of the photodetector.

21. The system according to claim 17 or 18, in, The one or more processors are configured to select a return pulse signal from the one or more return pulse signals by: A last received return pulse signal of the one or more return pulse signals that is not a saturation signal is identified.

22. The system according to claim 17 or 18, in, The one or more processors are configured to select a return pulse signal from the one or more return pulse signals by: It is determined that there is only one return pulse signal corresponding to the plurality of transmit pulse signals and above a noise level of the photodetector.

23. The system according to claim 17 or 18, in, The plurality of transmit pulse signals are a first plurality of transmit pulse signals, and the one or more return pulse signals are first return pulse signals, the optical detector being operable to: receiving one or more second return pulse signals corresponding to a second plurality of transmit pulse signals; The one or more processors are further configured to: determining that no second return pulse signal of the one or more second return pulse signals is within the dynamic range of the optical detector; and After determining, a third plurality of transmit pulse signals are transmitted, the third plurality of transmit pulse signals being different from the second plurality of transmit pulse signals in one or more of the following: number of pulses, peak power level of the pulses, or a combination thereof.

24. The system according to claim 17 or 18, in, The plurality of transmit pulse signals form a sequence of transmit pulse signals having increasingly stronger power levels.

25. The system of claim 24, the selected return pulse signal being the only return pulse signal of the one or more return pulse signals that is above a noise level of the photodetector.

26. The system according to claim 24, in, The one or more return pulse signals include two or three return pulse signals above a noise level, wherein the earliest received return pulse signal among the two or three return pulse signals is the selected return pulse signal.

27. The system according to claim 17 or 18, in, The one or more processors are further configured to encode the plurality of transmit pulse signals using different delays between at least some adjacent transmit pulse signals in the plurality of transmit pulse signals.

28. The system according to claim 27, in, The one or more processors are further configured to: The plurality of return pulse signals are decoded based on the different delays to identify the one or more return pulse signals corresponding to the plurality of transmit pulse signals.

29. The system according to claim 28, in, The one or more processors are further configured to discard return signals associated with one or more other LiDAR systems based on the decoding results.

30. The system according to claim 17 or 18, in, The plurality of transmit pulse signals are configured to have power level differences between at least some adjacent transmit pulse signals among the plurality of transmit pulse signals.

31. The system according to claim 30, in, The one or more processors are further configured to: The plurality of return pulse signals are decoded based on the power level differences to identify the one or more return pulse signals corresponding to the plurality of transmit pulse signals.

32. The system according to claim 17 or 18, in, The one or more processors are configured to calculate the distance further based on delays associated with a reference signal and the plurality of transmit pulse signals.

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