Scanning type single-photon laser radar system based on phase regulation and control

Abstract

The invention provides a scanning-type single-photon laser radar system based on phase regulation, and the system employs a reflection-type liquid crystal spatial light modulator to carry out the phase regulation of a laser beam, and achieves the long-distance fixed-point focusing through the modulation of laser wavefront. And echo signal detection is carried out by using a single-photon detector. Before the reflection type liquid crystal spatial light modulator is used for carrying out phase regulation and control on a laser beam, the laser beam is divided into reference light and detection light through the light splitting module, and then the divergence angle of the laser beam is reduced through the beam expanding module; after phase regulation and control, scanning of a laser beam in a target area is controlled through a reflector and a two-dimensional scanning galvanometer.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser radars, and in particular relates to a scanning single-photon laser radar system based on phase regulation. Background Art

[0002] Traditional laser radar systems determine the distance of target objects by emitting laser pulses and measuring the time of the return pulses. This process is called "time of flight" (ToF) ranging. Since the propagation of laser pulses in the air will be affected by factors such as scattering and absorption, especially at long distances or in severe weather conditions (such as fog, smoke, rain and snow), the echo intensity of the signal will be greatly weakened. The invention patent with publication number (CN 112130163 B) proposes a laser ranging system and ranging method based on single-photon detection. The light splitting module used splits the reference light and the detection light in a 1:1 ratio, which seriously reduces the detection light power, and the laser beam is in a divergent state after being emitted. The longer the propagation distance, the greater the attenuation of the echo signal, and the requirement for long-distance detection cannot be achieved. In addition, traditional laser radar systems usually rely on array detection technology, which means that the laser beam energy sensed by each detection unit needs to reach a large threshold to generate an effective signal, which will reduce the detection sensitivity of the system in low-light or strong noise environments. At the same time, the laser output power is high, which is not conducive to long-distance detection. For example, the invention patent with publication number (CN 109375237 B) proposes a fully solid-state array three-dimensional imaging laser radar system, which uses a CCD sensor array as an echo receiving sensor, and the detection range is only within tens of meters. Therefore, in view of the shortcomings of existing laser radar technology in long-distance, weak signal echo and complex scattering medium detection, a new solution suitable for long-distance single-point focusing detection in complex scattering environments and high-precision ranging of weak echo signals is urgently needed. Summary of the invention

[0003] In order to overcome the defects and shortcomings of the above-mentioned technical problems, the present invention provides a scanning single-photon laser radar system based on phase control, which uses phase control technology to achieve long-distance focusing of the laser beam and combines the innovative solution of the sensitivity of the single-photon detector to improve the detection range and accuracy of the system in complex environments. It is particularly suitable for long-distance single-point focusing detection and high-precision ranging of weak echo signals in complex scattering environments. The present invention introduces phase control technology to achieve high-precision dynamic focusing of the laser beam at a long distance, thereby significantly improving the detection capability of long-distance weak echo signals, and acquiring weak echo signals through the high sensitivity characteristics of single-photon detection technology. The system of the present invention has high-precision, long-distance, and complex environment detection capabilities, and is suitable for the detection and analysis of weak signal echoes.

[0004] The technical solution specifically adopted by the present invention to solve the technical problem is:

[0005] A scanning single-photon laser radar system based on phase control is characterized in that: a reflective liquid crystal spatial light modulator is used to control the phase of the laser beam, and long-distance fixed-point focusing is achieved by modulating the laser wavefront; and a single-photon detector is used to detect echo signals.

[0006] Furthermore, before the phase of the laser beam is adjusted by the reflective liquid crystal spatial light modulator, the laser beam is divided into reference light and detection light by a beam splitting module, and then passes through a beam expansion module to reduce the divergence angle of the laser beam; after the phase adjustment, the laser beam is controlled to scan the target area through a two-dimensional scanning galvanometer through a reflector.

[0007] Furthermore, by controlling the angle of the reflector, the modulated laser beam is emitted in the exact center direction of the X-axis deflection vibrator of the scanning galvanometer, and then the scanning voltage digital signal is converted into an analog signal through an acquisition card and transmitted to the galvanometer motor, thereby realizing two-dimensional scanning of the target area by the laser beam.

[0008] Furthermore, the light splitting module includes a short-focus near-infrared lens, a half-wave plate and a polarization beam splitter prism; the distance between the short-focus near-infrared lens and the output end of the laser fiber is less than the focal length of the short-focus lens, so that the divergent light spot at the output end of the optical fiber can be completely received by the short-focus infrared lens; the half-wave plate is used to adjust the polarization state of the polarization-maintaining pulse laser at the output end of the laser, and then pass through the polarization beam splitter prism to realize the free adjustment of the splitting ratio of the reference light and the detection light;

[0009] The beam expansion module is composed of two convex lens groups and is used to expand the diameter of the laser beam and improve the parallelism of the beam.

[0010] Furthermore, a pulsed laser is used to generate a laser beam, and the repetition frequency of the pulsed laser is set according to the measurement distance: d max =c / 2nf r , d max is the maximum detection distance, n is the refractive index of the laser propagating in the atmosphere; f r is the pulse repetition frequency of the laser, and c is the speed of light.

[0011] Furthermore, the echo light signal is converted into a parallel light signal by the echo collection module, transmitted through filtering and focusing by the echo transmission module, and finally converged at the optical fiber input port, and then the echo photons are photoelectrically converted by the optical fiber-coupled single-photon detector.

[0012] Furthermore, the echo receiving system for echo signal detection includes an echo collection module, an echo transmission module and a detection receiving module; the echo collection module is composed of a large-aperture objective lens and a small-aperture eyepiece; the echo transmission module is composed of two double convex lenses with different focal lengths and an infrared narrow-band filter, and the infrared narrow-band filter is arranged between the two double convex lenses to filter out echo light in non-receiving bands; the detector receiving module includes a module for receiving a reference light signal and generating a start time mark t start The avalanche photodetector is used to receive the target echo signal and generate the end time mark t end Single-photon avalanche photodetector.

[0013] Furthermore, an avalanche photodetector is used to receive a reference light signal and generate a start time mark; a single-photon avalanche photodetector is used to receive a target echo signal and generate an end time mark t end ;

[0014] The photons are time-stamped by a counter start and t end Perform time correlation calculation to obtain the target echo flight time and further calculate the target distance r0;

[0015] Then, according to the propagation distance of the laser beam from each pixel point to the target point Calculate the wavefront deviation and generate the corresponding phase compensation value: Where λ is the wavelength of the laser beam, L(x, y) is the actual distance from each pixel of the reflective liquid crystal spatial light modulator to the target, r0 is the target distance, and x, y are the coordinates of the pixel on the reflective liquid crystal spatial light modulator;

[0016] Finally, by controlling the X-axis and Y-axis deflection of the scanning galvanometer, a large-scale two-dimensional scanning of the target area by the laser beam is achieved.

[0017] Furthermore, the arrival time of each photon pulse is synchronously detected from the avalanche photodiode and the single-photon avalanche diode; the counter calculates the time stamp of the electrical pulse signal received by the two detectors and calculates the time interval between the signals; the calculation formula of the time interval Δt is: Δt = t end -t start After obtaining the time interval Δt data, a time axis is generated according to the size of the time interval Δt. The time on the axis and its corresponding count represent the number of times the time interval appears in the periodic cycle, which is represented by a histogram, thereby obtaining a photon time correlation distribution histogram. The time value corresponding to the maximum count value in the photon time correlation distribution histogram is the echo flight time of the target, thereby calculating the target distance: r0=c*Δt / 2, where c is the speed of light.

[0018] Furthermore, the actual distance from each pixel of the laser beam to the focus point is determined according to the calculated target distance r0. Thus, the wavefront deviation ΔL(x, y)=L(x, y)-r0 generated by the laser beam is calculated, and the corresponding phase compensation is calculated according to the wavefront deviation. The calculation formula is: Where λ is the wavelength of the laser beam, ΔL(x, y) is the wavefront error corresponding to each pixel point, and x, y are the coordinates of the pixel on the liquid crystal spatial light modulator; after obtaining the wavefront deviation, a corresponding phase pattern is generated as a control signal of the liquid crystal spatial light modulator, which is expressed as a two-dimensional array; each value in the array corresponds to a pixel point on the liquid crystal spatial light modulator, indicating the phase compensation value of the point; in order to pass the calculated phase compensation value to the liquid crystal spatial light modulator, the phase value 0 to 2π is mapped to a grayscale value between 0 and 255; since the laser beam in the system is continuously scanned, the corresponding phase pattern is updated in real time according to the distance of different scanning points and synchronously loaded onto the liquid crystal spatial light modulator to ensure that the laser beam achieves the best focusing effect at the new target point.

[0019] Compared with the prior art, the core of the present invention and its preferred solution is to use a reflective liquid crystal spatial light modulator (LC-SLM) for phase control, and to achieve long-distance fixed-point focusing by modulating the laser wavefront. By precisely controlling the phase distribution of the laser, the laser can be focused to a single point at a long distance in a complex scattering environment, thereby enhancing the intensity of the echo signal, and combining with a single-photon detector for high-sensitivity signal detection.

[0020] The scanning galvanometer is used to quickly scan the laser beam over a large range, and the LC-SLM is used to perform fine phase modulation and beam shaping of the laser beam. The laser beam can be precisely focused at the target position, and full-view, high-sensitivity laser focusing can be achieved. It is suitable for target and medium echo detection in complex scattering medium environments. Combined with the high sensitivity of the single-photon detector and TCSPC technology, high-precision flight time measurement and target distance inversion can be achieved under extremely low photon counting conditions. The host computer user interface control and data acquisition functions are realized, and the collected data is displayed in real time on the GUI. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0022] Figure 1 is an overall design diagram of an embodiment of the present invention;

[0023] Figure 2 is a flowchart of an embodiment of the present invention;

[0024] Figure 3 This is a data collection flow chart of an embodiment of the present invention;

[0025] Figure 4 A phase generation flow chart of an embodiment of the present invention;

[0026] Figure 5 The figure is a schematic diagram of the front panel of the hardware control system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to make the features and advantages of the present invention more clearly understood, the following embodiments are specifically described in detail as follows:

[0028] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0029] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0030] The system structure of the present invention includes a laser emission module, an echo receiving module and a hardware control module. The core of the system is to use a reflective liquid crystal spatial light modulator (LC-SLM) for phase control, and to achieve long-distance fixed-point focusing by modulating the laser wavefront. By accurately controlling the phase distribution of the laser, the laser can be focused to a single point at a long distance in a complex scattering environment, thereby enhancing the intensity of the echo signal, and combining with a single-photon detector for high-sensitivity signal detection. The hardware control system is used to initialize system startup parameters and dynamic phase generation and loading. The laser emission system emits a wavefront modulated laser pulse. After passing through a complex scattering environment, the target echo signal light is received by the echo receiving system, and the received signal is subjected to time-correlated calculation to obtain a photon time-correlated distribution histogram (Time-Correlated Single Photon Counting, TCSPC).

[0031] Among them, the laser emission system includes a pulse laser, a spectroscopic module, a beam expansion module and an output control module. The pulse laser outputs a pulse laser signal of a specific wavelength through an optical fiber; the spectroscopic module includes a short-focus infrared lens, a half-wave plate, and a polarization spectroscopic prism. The short-focus infrared lens reduces the divergence angle of the original laser beam emitted by the laser, making the laser beam easy to perform spectroscopic operations. After passing through the spectroscopic module composed of a half-wave plate and a polarization spectroscopic prism, the laser beam is divided into a weak-power vertically polarized reference light and a strong-power horizontally polarized detection light; the beam expansion module is composed of two plano-convex lenses with different focal lengths, so that the laser beam is emitted as a nearly parallel beam, thereby reducing the divergence angle of the laser beam. The output control module controls the phase distribution of the laser beam and the deflection movement of the scanning galvanometer by controlling the LC-SLM loading phase map, so as to achieve long-distance fixed-point focusing of the detection laser and a wide range of coverage of the target area. Finally, the above system generates a pulsed laser with a small divergence angle, long-distance focusing and high time resolution characteristics, and realizes high-precision dynamic focusing of the laser beam over a long distance and a large range.

[0032] Among them, the echo receiving system includes an echo collection module, an echo transmission module and a detection receiving module. The echo collection module is composed of a large-aperture objective lens and a small-aperture eyepiece; the echo transmission module is composed of two double convex lenses with different focal lengths and an infrared narrow-band filter. The infrared narrow-band filter is placed between the two double convex lenses to filter out the echo light in the non-receiving band and improve the peak signal-to-noise ratio of the received light signal. The detector receiving module is composed of an avalanche photodetector (APD) and a single-photon avalanche photodetector (SPAD). The reference light is received by the APD and converted into an electrical signal as the photon starting time mark t start The target echo signal light is received by the SPAD and converted into an electrical signal as the photon end time mark t end , and then send the electrical signal obtained by the detector to the hardware control system.

[0033] The hardware control system uses LabView as the main development platform, and integrates the data acquisition module into the LabView submodule to realize the user interface development. The data operation process in the hardware control system is as follows: the photon start time mark t start and end time marker t end Perform time-dependent counting: Δt = t end -t start,. After obtaining these time interval data, the system generates a time axis according to the size of the time interval Δt. The time on the axis and its corresponding count represent the number of times the time interval appears in the periodic cycle, which is represented by a histogram to obtain the time-correlated single photon counting (TCSPC) distribution histogram. The time value corresponding to the maximum count in TCSPC is the echo flight time of the target. The target distance information is further parsed out: r = c * Δt / 2. According to the obtained target distance, the phase pattern is updated to achieve laser focusing at the target. When the laser beam is deflected once by the scanning galvanometer, the target distance and the corresponding phase pattern are updated again to achieve dynamic focusing of the whole process. Finally, the hardware control system is integrated into the superior graphical user interface (GUI). It meets the hardware control and real-time data collection requirements of the scanning single-photon lidar system based on phase regulation.

[0034] like Figure 1 As shown, the overall design provided by the embodiment of the present invention includes a laser emitting system, an echo receiving system and a hardware control system; in the optical design part, along the optical axis direction of laser propagation, the laser emitting system includes: a pulse laser, a spectrometer module, a beam expansion module, and an emission control module in sequence; the echo receiving system converts the optical signal into an electrical signal and includes: an echo collection module, a detector receiving module in sequence; the hardware control system mainly includes: counter parameter control, galvanometer motion trajectory control, loading of dynamic phase patterns, data acquisition and real-time data display.

[0035] Among them, the laser is used as a laser source to emit a laser of a specific wavelength. The spectroscopic module includes a short-focus lens, a half-wave plate and a polarization splitter prism assembly, which divides the laser beam into a detection light and a reference light. The detection light is used for target detection, and the reference light is detected by the APD in the detector receiving module to generate the start time of the optical signal. The beam expansion module is composed of two convex lens groups, which are used to expand the diameter of the laser beam, improve the parallelism of the beam, reduce the spot divergence angle, and improve the spatial resolution of the laser beam. The output control module: includes a reflector, a spatial light modulator (LC-SLM) and a scanning galvanometer. The laser beam is dynamically phased through the LC-SLM. The LC-SLM acts as a real-time dynamic zoom lens to achieve precise focusing of the laser beam at a long distance. Then control the angle of the reflector so that the modulated laser beam is emitted in the exact center direction of the X-axis deflection oscillator of the scanning galvanometer, and then convert the scanning voltage digital signal into an analog signal through the acquisition card and transmit it to the galvanometer motor, thereby realizing the two-dimensional scanning of the target area by the laser beam. The echo collection module is composed of a large-aperture objective lens and a small-aperture eyepiece, and the echo transmission module is composed of two convex lenses with different focal lengths and an infrared narrow-band filter. The echo light signal is converted into a parallel light signal by the module, and then transmitted through the filtering and focusing of the echo transmission module, and finally converged at the optical fiber input port, and then the echo photons are converted into photoelectricity by the optical fiber-coupled single-photon detector.

[0036] like Figure 2 As shown, it is a specific workflow diagram of an embodiment of the present invention. First, turn on the power of the laser, counter, detector, liquid crystal spatial light modulator (LC-SLM) and two-dimensional galvanometer and other equipment in turn to ensure that each hardware module works normally. After the hardware initialization is completed, set the emission power and pulse width of the laser, the counter trigger voltage, time width and gate number settings, the integration time and number of cycles of single-point acquisition and other parameters, and specify the data storage location. After completing the settings, start the LabView hardware control program and start running to control each module for data acquisition and processing. During the operation, the system will monitor the program status in real time to determine whether it is running normally. If the program runs abnormally, the system will return the cause of the error and prompt the user to modify or restart the program; if the program runs normally, the counter will perform time-related calculations on the received detector end signal to obtain the time difference of the detection signal. According to the time difference, the system further calculates the target distance. After the distance calculation is completed, the system generates a corresponding phase pattern according to the target distance, and the pattern is loaded in real time through the LC-SLM, thereby adjusting the wavefront of the laser beam so that the beam is focused at the target distance. When the data acquisition is completed, the system checks whether the number of cycles reaches the preset value. If the number of cycles does not reach the set value, the system will repeat the above process and continue to the next round of data collection; if the number of cycles reaches the set value, the system will end the operation and save all collected data.

[0037] It is worth noting that Figure 1 The figure only shows the positional relationship between the components; the dimensions on the figure and the proportional relationship between the components do not constitute a specific limitation on this solution.

[0038] Based on the above design, a more preferred solution provided by the embodiment of the present invention is:

[0039] The laser wavelength is selected in the 1550nm near-infrared band, which has stronger penetration. The laser pulse width is 8ns, and the repetition frequency is set according to the measurement distance. Based on the distance ambiguity problem in time-of-flight ranging, the relationship between the repetition frequency of the pulsed laser and the maximum detection distance is defined, and its mathematical expression is d max =c / 2nf r , d max is the maximum detection distance, n is the refractive index of the laser propagating in the atmosphere; f r is the pulse repetition frequency of the laser, and c is the speed of light. The spectroscopic module includes a short-focus lens, a half-wave plate, and a polarization beam splitter prism. The distance between the short-focus near-infrared lens and the output end of the laser fiber should be less than the focal length of the short-focus lens, so that the divergent light spot at the output end of the optical fiber can be completely received by the short-focus infrared lens, reducing the divergence angle of the light spot. The half-wave plate adjusts the polarization state of the polarization-maintaining pulsed laser at the output end of the laser, and then passes through the polarization beam splitter prism to achieve free regulation of the reference light and the detection light splitting ratio. The output control module preferably uses a dielectric film high-reflection mirror, which can achieve a reflectivity of up to 99% for a specific band, thereby maximizing the power of the detection light. The galvanometer scanner is preferably a Sorebo GVS012-M scanning galvanometer, which includes an X-axis mirror, a Y-axis mirror, and its corresponding drive motor and drive card. By converting the scanning voltage signal in the hardware control system into an analog signal through a data acquisition card, precise control of the position and range of the galvanometer scanning field of view can be achieved. The liquid crystal spatial light modulator is preferably a pure phase liquid crystal spatial light modulator from Meadowlark Optics, which has a high resolution of 1920*1152, a high fill rate of 95.7%, a high refresh rate of 845Hz, and a response speed of up to 5ms in the 1550nm band, which can meet the system phase control hardware performance requirements. Finally, the above module generates a pulsed laser with a small divergence angle, long-distance focusing and high time resolution characteristics, and realizes high-precision dynamic focusing of the laser beam at a long distance.

[0040] The echo collection module is composed of a large-aperture objective lens and a small-aperture eyepiece. The parallel light signals reflected from the distant target are collected through a lens combination, output through a small-aperture eyepiece, and then pass through the echo transmission module. The more preferred components are the Sorebo LB1761-C lens and the FBH1550-12 bandpass filter. The LB1761-C lens increases the transmittance of the target echo light signal by adding a near-infrared anti-reflection film. The peak signal-to-noise ratio of the echo light signal is further increased by passing through the FBH1550-12 bandpass filter corresponding to the laser wavelength, thereby improving the detection sensitivity and efficiency of the system. After passing through the echo transmission module, the echo light signal is gathered to the single-photon avalanche photodetector in the detection and receiving module for photoelectric signal conversion to form the starting time mark t of the photon corresponding to the electrical signal. start and end time marker t end The avalanche detector and the single photon avalanche detector will record the time stamp t start and t end The data are input into the counter for single photon time correlation calculation. More preferably, the counter can select Time Tagger 20, which has 8 receiving channels, a dead time as low as 6ns, and a maximum data receiving rate of up to 8.5M tags / s.

[0041] The specific steps for data collection are as follows: Figure 3 As shown, first, the data acquisition process starts with the avalanche photodiode (APD) and the single photon avalanche diode (SPAD) synchronously detecting the arrival time of each photon pulse. APD and SPAD are highly sensitive photon detectors, and their function is to detect the arriving photons and generate corresponding electrical pulse signals. In this process, the system obtains the pulse electrical signals at the start and end of the photons. Next, the counter calculates the time stamps of the electrical pulse signals received by the two detectors and calculates the time interval between the signals. The calculation formula for the time interval Δt is: Δt = t end -t start , where t start and t end Respectively represent the start and end time marks of the photon arrival. After obtaining these time interval Δt data, the system generates a time axis according to the size of the time interval Δt. The time on the axis and its corresponding count represent the number of times the time interval size appears in the cycle, which is represented by a histogram, thereby obtaining the photon time correlation distribution histogram (TCSPC). The time value corresponding to the maximum count in TCSPC is the target echo flight time, so as to calculate the target distance: r0 = c*Δt / 2, where c is the speed of light.

[0042] The specific steps of the phase pattern dynamic modulation process are as follows: Figure 4As shown in Figure 1, this part is the core part of realizing dynamic focusing of the laser beam. The specific process includes: determining the actual distance from each pixel of the laser beam to the focusing point based on the calculated target distance r0 Thus, the wavefront deviation ΔL(x, y)=L(x, y)-r0 generated by the laser beam is calculated, and the corresponding phase compensation is calculated according to the wavefront deviation. The calculation formula is as follows: Where λ is the wavelength of the laser beam, ΔL(x, y) is the wavefront error corresponding to each pixel, and x, y are the coordinates of the pixel on the LC-SLM. After obtaining the wavefront deviation, the system generates a corresponding phase pattern, wherein the phase pattern is the control signal of the LC-SLM, which is expressed as a two-dimensional array. Each value in the array corresponds to a pixel on the LC-SLM, representing the phase compensation value of the point. In order to pass the calculated phase compensation value to the LC-SLM, the phase value of 0 to 2π is mapped to a grayscale value between 0 and 255. Since the laser beam in the system is continuously scanned, the present invention will update the corresponding phase pattern in real time according to the distance of different scanning points and load it to the LC-SLM synchronously to ensure that the laser beam achieves the best focusing effect at the new target point.

[0043] The hardware control system is developed based on the LabView software platform. By developing a software package for hardware instruments and combining data analysis, the hardware control of the scanning single-photon laser radar system based on phase control and its real-time data collection and analysis requirements are realized. Figure 5 The hardware control interface of the embodiment of the present invention shown initializes the parameters of each device, including the time gate width binwidth and the number of time gates n_bins of the counter, which define the time resolution and measurement range of photon detection. As well as voltage settings, data acquisition channel selection, start delay and integration time, etc. The system performs scanning measurement of the target surface through phase control to obtain accurate distance and reflectivity data. The interface displays the collected data in real time, including photon detection intensity and target distance information, can automatically calculate the target distance, and provide real-time phase control feedback. The data collected by the system will be saved to the specified path for subsequent analysis and processing. The entire hardware control system realizes a high-precision phase-controlled scanning and focusing function, which can adapt to the single-photon lidar measurement requirements in complex environments.

[0044] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0045] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

[0046] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of a scanning single-photon laser radar system based on phase control under the inspiration of the present invention. All equal changes and modifications made within the scope of the invention application of the present invention should be covered by the present invention.

Claims

1. A scanning single-photon laser radar system based on phase control, characterized in that: The reflective liquid crystal spatial light modulator is used to control the phase of the laser beam, and long-distance fixed-point focusing is achieved by modulating the laser wavefront; and the echo signal is detected using a single-photon detector.

2. The scanning single-photon laser radar system based on phase control according to claim 1, characterized in that: Before the reflective liquid crystal spatial light modulator is used to adjust the phase of the laser beam, the laser beam is divided into reference light and detection light by a beam splitting module, and then passes through a beam expansion module to reduce the divergence angle of the laser beam; After phase adjustment, the laser beam is scanned in the target area through a two-dimensional scanning galvanometer via a reflector.

3. The scanning single-photon laser radar system based on phase control according to claim 2, characterized in that: By controlling the angle of the reflector, the modulated laser beam is emitted in the exact center direction of the X-axis deflection vibrator of the scanning galvanometer, and then the scanning voltage digital signal is converted into an analog signal through an acquisition card and transmitted to the galvanometer motor, thereby realizing two-dimensional scanning of the target area by the laser beam.

4. The scanning single-photon laser radar system based on phase control according to claim 2, characterized in that: The light splitting module includes a short-focus near-infrared lens, a half-wave plate and a polarization light splitting prism; The distance between the short-focus near-infrared lens and the output end of the laser optical fiber is smaller than the focal length of the short-focus lens, so that the divergent light spot at the output end of the optical fiber can be completely received by the short-focus infrared lens; The half-wave plate is used to adjust the polarization state of the polarization-maintaining pulse laser at the output end of the laser, and then passes through the polarization beam splitter prism to achieve free adjustment of the splitting ratio of the reference light and the detection light; The beam expansion module is composed of two convex lens groups and is used to expand the diameter of the laser beam and improve the parallelism of the beam.

5. The working method of a scanning single-photon laser radar system based on phase control according to claim 1, characterized in that: A pulsed laser is used to generate a laser beam, and the repetition frequency of the pulsed laser is set according to the measurement distance: d max =c / 2nf r , d max is the maximum detection distance, n is the refractive index of the laser propagating in the atmosphere; f r is the pulse repetition frequency of the laser, and c is the speed of light.

6. The working method of a scanning single-photon laser radar system based on phase control according to claim 1, characterized in that: The echo light signal is converted into a parallel light signal by the echo collection module, transmitted through filtering and focusing by the echo transmission module, and finally converged at the optical fiber input port, and then the echo photons are converted into photoelectricity by the optical fiber-coupled single-photon detector.

7. The working method of a scanning single-photon laser radar system based on phase control according to claim 1, characterized in that: The echo receiving system for echo signal detection includes an echo collection module, an echo transmission module and a detection receiving module; the echo collection module is composed of a large-aperture objective lens and a small-aperture eyepiece; the echo transmission module is composed of two double convex lenses with different focal lengths and an infrared narrow-band filter, and the infrared narrow-band filter is arranged between the two double convex lenses to filter out the echo light in the non-receiving band; the detector receiving module includes a module for receiving a reference light signal and generating a start time mark t start The avalanche photodetector is used to receive the target echo signal and generate the end time mark t end Single-photon avalanche photodetector.

8. The working method of a scanning single-photon laser radar system based on phase control according to claim 1, characterized in that: The reference light signal is received by an avalanche photodetector and a start time mark is generated; the target echo signal is received by a single photon avalanche photodetector and an end time mark is generated. end ; The photons are time-stamped by a counter start and t end Perform time correlation calculation to obtain the target echo flight time and further calculate the target distance r0; Then, according to the propagation distance of the laser beam from each pixel point to the target point Calculate the wavefront deviation and generate the corresponding phase compensation value: Where λ is the wavelength of the laser beam, L(x, y) is the actual distance from each pixel of the reflective liquid crystal spatial light modulator to the target, r0 is the target distance, and x, y are the coordinates of the pixel on the reflective liquid crystal spatial light modulator; Finally, by controlling the X-axis and Y-axis deflection of the scanning galvanometer, a large-scale two-dimensional scanning of the target area by the laser beam is achieved.

9. The working method of a scanning single-photon laser radar system based on phase control according to claim 8, characterized in that: The arrival time of each photon pulse is synchronously detected from the avalanche photodiode and the single-photon avalanche diode. The counter calculates the time stamp of the electrical pulse signal received by the two detectors and calculates the time interval between the signals. The calculation formula of the time interval Δt is: Δt = t end -t start After obtaining the time interval Δt data, a time axis is generated according to the size of the time interval Δt. The time on the axis and its corresponding count represent the number of times the time interval appears in the periodic cycle, which is represented by a histogram, thereby obtaining a photon time correlation distribution histogram. The time value corresponding to the maximum count value in the photon time correlation distribution histogram is the echo flight time of the target, thereby calculating the target distance: r0=c*Δt / 2, where c is the speed of light.

10. The working method of a scanning single-photon laser radar system based on phase control according to claim 9, characterized in that: According to the calculated target distance r0, determine the actual distance from each pixel of the laser beam to the focus point Thus, the wavefront deviation ΔL(x, y)=L(x, y)-r0 generated by the laser beam is calculated, and the corresponding phase compensation is calculated according to the wavefront deviation. The calculation formula is: Where λ is the wavelength of the laser beam, ΔL(x, y) is the wavefront error corresponding to each pixel point, and x, y are the coordinates of the pixel on the liquid crystal spatial light modulator; after obtaining the wavefront deviation, a corresponding phase pattern is generated as a control signal of the liquid crystal spatial light modulator, which is expressed as a two-dimensional array; each value in the array corresponds to a pixel point on the liquid crystal spatial light modulator, indicating the phase compensation value of the point; in order to pass the calculated phase compensation value to the liquid crystal spatial light modulator, the phase value 0 to 2π is mapped to a grayscale value between 0 and 255; since the laser beam in the system is continuously scanned, the corresponding phase pattern is updated in real time according to the distance of different scanning points and synchronously loaded onto the liquid crystal spatial light modulator to ensure that the laser beam achieves the best focusing effect at the new target point.

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