High-repetition-frequency high-flux single-photon laser radar system and data processing method

Abstract

The invention belongs to the field of laser radars, and provides a high-repetition-frequency high-flux single-photon laser radar system and a data processing method, and the system comprises a signal light path part and a signal collection and processing part. The signal light path part comprises a high repetition frequency laser, a transmitting lens, a perforated reflector, a light beam direction control unit, a receiving lens, a synchronous detector and a single photon detector; the signal acquisition and processing part comprises a time-to-digital converter, a control and data processing unit and a digital-to-analog conversion module; the method comprises the steps of signal acquisition, signal interpolation, waveform construction, waveform correction and three-dimensional point cloud processing. According to the method, the data volume of galvanometer synchronization is reduced in a down-sampling or key point coding mode, and storage, transmission and calculation resources consumed by galvanometer synchronization signals are reduced; the distortion waveform caused by the dead time is corrected, the inversion precision of the intensity and depth data of the single-photon detection laser radar system is improved, and the method has the advantages of being easy to operate and wide in application range.

Description

Technical Field

[0001] The present invention relates to the field of laser radar, and in particular to a high-repetition-rate and high-throughput single-photon laser radar system and a data processing method. Background Art

[0002] Single-photon detectors can respond to single photons, reaching the theoretical limit of photon detection. With the advantage of weak light detection, single-photon lidar is used in target detection, earth resource mapping, and autonomous driving. Single-photon detection lidar requires a long time to accumulate information because of the small amount of information in each echo. However, due to the influence of the dead time of the single-photon detector, the signal waveform will be distorted. The degree of distortion is directly related to the signal flux. The higher the signal flux, the higher the degree of distortion. Researchers have proposed the classic "5% criterion", which is to attenuate the probability of signal detection to an extremely low level below 5%.

[0003] Low flux means that it takes a longer time to acquire enough photon information, which greatly limits the real-time measurement of the system. The low-repetition-rate lidar system cannot fully utilize the performance of the single-photon detector. There are still some signal-free time intervals in a single pulse cycle that are not in the dead zone state. Therefore, there is still a lot of room for improvement in detection speed. On the basis of high signal flux, increasing the laser repetition rate can further increase the photon information acquisition rate and increase the detection speed. However, at the same time, the use of high-repetition-rate and high-throughput detection methods brings about the problem of generating a large amount of data in a short period of time, as well as the problem of inaccurate signal strength and signal depth inversion caused by the shielding effect coupling caused by the dead zone time between adjacent cycles. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a high-repetition-rate and high-throughput single-photon lidar system and a data processing method, which can improve the photon information acquisition rate by means of high repetition-rate and high-throughput, so as to improve the system detection speed, and improve the data processing speed and signal inversion accuracy by proposing a data processing method suitable for high repetition-rate and high-throughput.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A high repetition rate and high flux single photon laser radar system, comprising: a signal optical path part and a signal acquisition and processing part; the signal optical path part comprises: a high repetition rate laser, a transmitting lens, a perforated reflector, a beam direction control unit, a receiving lens, a synchronous detector and a single photon detector; the signal acquisition and processing part comprises: a time-to-digital converter, a control and data processing unit and a digital-to-analog conversion module;

[0007] The high repetition rate laser is connected to the synchronous detector and the transmitting lens respectively; the receiving lens is connected to the single photon detector; the single photon detector is connected to the time digital converter; the synchronous detector is connected to the time digital converter; the time digital converter is connected to the control and data processing unit and the digital-to-analog conversion module respectively; the digital-to-analog conversion module is connected to the control and data processing unit and the beam direction control unit respectively;

[0008] The high repetition rate laser is used to generate laser pulses and synchronously transmit the laser pulses to the synchronous detector and the transmitting lens; the transmitting lens is used to transmit the input laser pulses to the beam direction control unit through the perforated reflector; the beam direction control unit is used to scan the target object using the input laser pulses according to the direction adjustment instruction sent by the digital-to-analog conversion module, receive the return signal of the target object, and transmit the return signal to the single photon detector through the perforated reflector and the receiving lens in sequence; the single photon detector is used to convert the return signal into an electrical signal and transmit the electrical signal to the time digital converter; the time digital converter is used to encode the electrical signal according to the input of the synchronous detector to obtain a timestamp signal; the control and data processing unit is used to pre-program the scanning trajectory, obtain a pre-programmed instruction, and transmit the pre-programmed instruction to the digital-to-analog conversion module; the digital-to-analog conversion module is used to convert the pre-programmed instruction into a direction adjustment instruction and provide a galvanometer synchronization signal to the time digital converter by downsampling or key point encoding.

[0009] Preferably, the single-photon detector is any one of a superconducting nanowire single-photon detector, a photomultiplier tube, and a Geiger-mode avalanche photodiode.

[0010] Preferably, a high repetition rate and high throughput single photon laser radar data processing method comprises:

[0011] Collecting the galvanometer synchronization signal and the timestamp signal;

[0012] Using the nearest neighbor method to interpolate the spatial position of the timestamp signal according to the photon recording time sequence to obtain an interpolated signal;

[0013] The galvanometer synchronization signal and the interpolation signal are subjected to waveform construction by means of statistical accumulation to obtain an original photon waveform signal;

[0014] Correcting the original photon waveform signal using a pre-designed high repetition rate single photon detection waveform correction model to obtain a corrected waveform;

[0015] The three-dimensional point cloud signal of the correction waveform is obtained by the centroid method and pulse area integration, and the three-dimensional point cloud signal is processed by a three-dimensional point cloud processing algorithm to obtain a laser radar detection image; the three-dimensional point cloud signal includes: signal depth information and signal strength information.

[0016] Preferably, the expression of the high repetition rate single photon detection waveform correction model includes:

[0017] and

[0018]

[0019] Among them, P M (t i ) is the detection probability of the i-th bin; m is the number of whole cycles spanned by the dead time; d is the number of bins occupied by the dead time; r is the number of bins occupied by the pulse cycle time; P N (t j ) is the probability of suppressing the detection of the jth bin; Λ j is the jth distortion-free signal strength.

[0020] The present invention discloses the following technical effects:

[0021] The present invention provides a high-repetition-rate and high-throughput single-photon laser radar system and a data processing method, which reduces the amount of data for galvanometer synchronization by downsampling or key point encoding, thereby solving the problem of large consumption of storage, transmission and computing resources in conventional single-photon laser radar systems, and achieving more efficient acquisition of photon information; by correcting the distorted waveform caused by dead time, the problem of signal-free time intervals in some non-dead time states still existing within a single pulse cycle is solved, thereby achieving improved measurement accuracy of depth and intensity data of the single-photon detection laser radar system. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0023] Figure 1 A structural diagram of a high-speed and high-precision single-photon laser radar detection and imaging system provided by an embodiment of the present invention;

[0024] Figure 2 A high-speed and high-precision single-photon laser radar detection and imaging flow chart provided by an embodiment of the present invention;

[0025] Figure 3 A structural diagram of system data transmission provided by an embodiment of the present invention;

[0026] Figure 4 A diagram illustrating the principle of a high repetition rate single photon detection waveform correction model provided in an embodiment of the present invention.

[0027] Description of reference numerals:

[0028] 1- high repetition rate laser, 2- transmitting lens, 3- synchronous detector, 4- perforated reflector, 5- beam direction control unit, 6- receiving lens, 7- single photon detector, 8- time digital converter, 9- control and data processing unit, 10- digital-to-analog conversion module. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The purpose of the present invention is to provide a high-repetition-rate and high-throughput single-photon lidar system and a data processing method, which can improve the photon information acquisition rate by means of high repetition-rate and high-throughput, so as to improve the system detection speed, and improve the data processing speed and signal inversion accuracy by proposing a data processing method suitable for high repetition-rate and high-throughput.

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] Figure 1 The structure diagram of the high-speed and high-precision single-photon laser radar detection imaging system provided by the embodiment of the present invention is as follows: Figure 1 As shown, the present invention provides a high repetition rate and high flux single photon laser radar system, comprising: a signal optical path part and a signal acquisition and processing part; the signal optical path part comprises: a high repetition rate laser 1, a transmitting lens 2, a perforated reflector 4, a beam direction control unit 5, a receiving lens 6, a synchronous detector 3 and a single photon detector 7; the signal acquisition and processing part comprises: a time-to-digital converter 8, a control and data processing unit 9 and a digital-to-analog conversion module 10;

[0033] The high repetition rate laser 1 is connected to the synchronous detector 3 and the transmitting lens 2 respectively; the receiving lens 6 is connected to the single photon detector 7; the single photon detector 7 is connected to the time digital converter 8; the synchronous detector 3 is connected to the time digital converter 8; the time digital converter 8 is connected to the control and data processing unit 9 and the digital-to-analog conversion module 10 respectively; the digital-to-analog conversion module 10 is connected to the control and data processing unit 9 and the beam direction control unit 5 respectively;

[0034] The high repetition rate laser 1 is used to generate laser pulses and synchronously transmit the laser pulses to the synchronous detector 3 and the transmitting lens 2; the transmitting lens 2 is used to transmit the input laser pulses to the beam direction control unit 5 through the perforated reflector 4; the beam direction control unit 5 is used to scan the target object using the input laser pulses according to the direction adjustment instruction sent by the digital-to-analog conversion module 10, receive the return signal of the target object, and transmit the return signal to the single photon detector 7 through the perforated reflector 4 and the receiving lens 6 in turn; the single photon detector 7 is used to convert the return signal into an electrical signal and transmit the electrical signal to the time digital converter 8; the time digital converter 8 is used to encode the electrical signal according to the input of the synchronous detector 3 to obtain a timestamp signal; the control and data processing unit 9 is used to pre-program the scanning trajectory, obtain a pre-programmed instruction, and transmit the pre-programmed instruction to the digital-to-analog conversion module 10; the digital-to-analog conversion module 10 is used to convert the pre-programmed instruction into a direction adjustment instruction and provide a galvanometer synchronization signal to the time digital converter 8 by downsampling or key point encoding.

[0035] Optionally, the single-photon detector 7 is any one of a superconducting nanowire single-photon detector 7, a photomultiplier tube, and a Geiger-mode avalanche photodiode.

[0036] refer to Figure 2 , a high repetition rate and high throughput single photon laser radar data processing method, comprising:

[0037] Collect galvanometer synchronization signal and timestamp signal;

[0038] The spatial position of the time stamp signal is interpolated according to the photon recording time sequence using the nearest neighbor method to obtain an interpolated signal;

[0039] The waveform of the galvanometer synchronization signal and the interpolation signal is constructed by statistical accumulation to obtain the original photon waveform signal;

[0040] The original photon waveform signal is corrected using a pre-designed high repetition rate single photon detection waveform correction model to obtain a corrected waveform;

[0041] The three-dimensional point cloud signal of the correction waveform is obtained by the centroid method and pulse area integration, and the three-dimensional point cloud signal is processed by the three-dimensional point cloud processing algorithm to obtain the laser radar detection image; the three-dimensional point cloud signal includes: signal depth information and signal strength information.

[0042] Specifically, the expression of the high repetition rate single photon detection waveform correction model includes:

[0043] and

[0044]

[0045] Among them, P M (t i ) is the detection probability of the i-th bin; m is the number of whole cycles spanned by the dead time; d is the number of bins occupied by the dead time; r is the number of bins occupied by the pulse cycle time; P N (t j ) is the probability of suppressing the detection of the jth bin; Λ j is the jth distortion-free signal strength.

[0046] Specifically, the laser pulses emitted by the high repetition rate laser 1 are divided into two optical signals, one of which is received by the synchronous detector 3 as a signal synchronization path, and the other is emitted through the transmitting lens 2 as a signal detection path. The laser of the signal detection path passes through the perforated reflector 4 to reach the beam direction control unit 5. The beam direction control unit 5 can control the emission direction of the laser to scan the target object. The returned signal light passes through the beam direction control unit 5 to reach the perforated reflector 4. The perforated reflector 4 reflects the echo signal to the receiving lens 6, and then couples it to the receiving multimode optical fiber. The single photon detector 7 converts the reflected photon signal into an electrical signal. The arrival time of the electrical signal is encoded as a timestamp signal through the time digital converter 8. The control and data processing unit 9 uses a digital-to-analog conversion device to pre-program the scanning trajectory of the galvanometer. Another channel of the digital-to-analog conversion device is used as a galvanometer synchronization channel, which is connected to the time digital converter 8 for synchronization with the measured photon signal.

[0047] refer to Figure 3In this embodiment, the system uses the control and data processing unit 9 as the signal processing and control center. On the one hand, it exchanges data with the time digital converter 8 and controls the start and stop and parameter configuration of the time digital converter 8. On the other hand, the control and data processing unit 9 encodes the galvanometer scanning signal and outputs it to the beam direction control unit 5 through the digital-to-analog conversion module 10, thereby controlling the scanning mode of the beam direction control unit 5. The single-photon detection signal is input to the time digital converter 8, and the digital-to-analog conversion module 10 inputs the galvanometer synchronization signal to the time digital converter 8. The signal synchronization between the beam direction control unit 5 and the measured photon signal is ensured by the digital-to-analog conversion device.

[0048] refer to Figure 2 , the measured photon timestamp signal and the galvanometer synchronization timestamp signal are received through the time-to-digital converter 8, and the timestamp data is transmitted to the control and data processing unit 9. The galvanometer synchronization timestamp signal corresponds to the galvanometer voltage one by one, and then the nearest neighbor method is used to interpolate the spatial position according to the photon recording time sequence. The interpolated photon signal obtains the photon waveform signal by statistical accumulation, and the proposed high-repetition-rate single-photon detection waveform correction model corrects the accumulated waveform. The corrected waveform can obtain the signal depth information and signal intensity information by the centroid method and integration of the pulse area, and finally the three-dimensional point cloud signal is processed using the three-dimensional point cloud processing algorithm in combination with the spatial position information corresponding to each photon.

[0049] refer to Figure 4 The proposed high repetition rate single photon detection waveform correction method is as follows: the dead time of the general near-infrared single photon detector 7 is in the order of microseconds. In order to increase the amount of echo photon information, the high repetition rate method can effectively increase the amount of echo information, but at the same time, the long single photon dead time will affect the detection probability of multiple cycles in the future, thus causing the problem of multi-cycle photon signal coupling. It can be seen from the forward steady-state model of single photon detection that the signal flux of the jth bin of the echo is The undistorted signal strength Λ in the jth bin j It can be obtained by the following formula:

[0050]

[0051] Among them, P N (t j ) is the probability of not detecting a signal within the previous dead time, P M (t j ) is the detection probability of the jth bin, which can be obtained by the following formula:

[0052]

[0053] Among them, N jis the accumulated number of signal photons, f r Laser pulse repetition frequency, T a The accumulated time for each pixel can be obtained by the synchronization time difference of adjacent galvanometers. The probability P of detecting a signal in the d bins before the jth bin is N (t j )

[0054]

[0055] Where d is the number of bins occupied by the dead time.

[0056] Since the single-photon detection process can reach stability in a short time, when the detection finally reaches stability, the high-repetition-rate detection waveform is equivalent to a multi-pulse laser, and the pulse period is extended to the original m=ceil(t d / t r ) times, and the number of pulses is m. Therefore, it is believed that in the high repetition rate detection process, the signal inversion can be directly performed through the steady-state model, and the following formula can be derived from the above formula:

[0057]

[0058]

[0059] The above formula can be used to obtain the accumulated photon number of the jth bin of the correction. By cyclically correcting each bin within the period of the correction cycle, a distortion-free waveform can be obtained.

[0060] The beneficial effects of the present invention are as follows:

[0061] The present invention reduces the amount of galvanometer synchronization data by downsampling or key point encoding, thereby reducing the storage, transmission and computing resources consumed by the galvanometer synchronization signal; by correcting the distorted waveform caused by the dead time, the inversion accuracy of the intensity and depth data of the single-photon detection laser radar system is improved, and the invention has the advantages of easy operation and wide application range.

[0062] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0063] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A high repetition rate and high throughput single photon laser radar system, characterized in that: include: Signal optical path part and signal acquisition and processing part; The signal optical path part includes: a high repetition rate laser, a transmitting lens, a perforated reflector, a beam direction control unit, a receiving lens, a synchronous detector and a single photon detector; the signal acquisition and processing part includes: a time-to-digital converter, a control and data processing unit and a digital-to-analog conversion module; The high repetition rate laser is connected to the synchronous detector and the transmitting lens respectively; the receiving lens is connected to the single photon detector; the single photon detector is connected to the time digital converter; the synchronous detector is connected to the time digital converter; the time digital converter is connected to the control and data processing unit and the digital-to-analog conversion module respectively; the digital-to-analog conversion module is connected to the control and data processing unit and the beam direction control unit respectively; The high repetition rate laser is used to generate laser pulses and synchronously transmit the laser pulses to the synchronous detector and the transmitting lens; the transmitting lens is used to transmit the input laser pulses to the beam direction control unit through the perforated reflector; the beam direction control unit is used to scan the target object using the input laser pulses according to the direction adjustment instruction sent by the digital-to-analog conversion module, receive the return signal of the target object, and transmit the return signal to the single photon detector through the perforated reflector and the receiving lens in sequence; the single photon detector is used to convert the return signal into an electrical signal and transmit the electrical signal to the time digital converter; the time digital converter is used to encode the electrical signal according to the input of the synchronous detector to obtain a timestamp signal; the control and data processing unit is used to pre-program the scanning trajectory, obtain a pre-programmed instruction, and transmit the pre-programmed instruction to the digital-to-analog conversion module; the digital-to-analog conversion module is used to convert the pre-programmed instruction into a direction adjustment instruction and provide a galvanometer synchronization signal to the time digital converter by downsampling or key point encoding.

2. A high repetition rate and high throughput single photon laser radar system according to claim 1, characterized in that: The single-photon detector is any one of a superconducting nanowire single-photon detector, a photomultiplier tube, and a Geiger-mode avalanche photodiode.

3. A high repetition rate and high throughput single photon laser radar data processing method, characterized in that: A high repetition rate and high throughput single photon laser radar system applied to any one of claims 1 and 2, the method comprising: Collecting the galvanometer synchronization signal and the timestamp signal; Using the nearest neighbor method to interpolate the spatial position of the timestamp signal according to the photon recording time sequence to obtain an interpolated signal; The galvanometer synchronization signal and the interpolation signal are subjected to waveform construction by means of statistical accumulation to obtain an original photon waveform signal; Correcting the original photon waveform signal using a pre-designed high repetition rate single photon detection waveform correction model to obtain a corrected waveform; The three-dimensional point cloud signal of the correction waveform is obtained by the centroid method and pulse area integration, and the three-dimensional point cloud signal is processed by a three-dimensional point cloud processing algorithm to obtain a laser radar detection image; the three-dimensional point cloud signal includes: signal depth information and signal strength information.

4. The high repetition rate and high throughput single photon laser radar data processing method according to claim 1, characterized in that: The expression of the high repetition rate single photon detection waveform correction model includes: Among them, P M (t i ) is the detection probability of the i-th bin; m is the number of whole cycles spanned by the dead time; d is the number of bins occupied by the dead time; r is the number of bins occupied by the pulse cycle time; P N (t j ) is the probability of suppressing the detection of the jth bin; Λ j is the jth distortion-free signal strength.

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