A dual-frequency polarization laser radar test system and method

Abstract

The present invention discloses a dual-frequency polarization laser radar test system and method. Through the cooperation of a laser, a beam splitter, a half-wave plate, a linear frequency modulation module, a beat frequency filtering module, a mixing module and a data processing module, the system can synchronously obtain the speed and distance information of a target object at the same time, thereby avoiding the measurement error caused by the parameter difference of different detection devices, reducing the use of separate devices, and reducing the complexity and cost of the system. At the same time, by utilizing the beat frequency filtering technology, the system can accurately separate the Doppler frequency shift information and the distance information, thereby solving the problem that the speed resolution and the distance resolution in the traditional distance measurement method are difficult to take into account at the same time.

Description

Technical Field

[0001] The present invention relates to the field of radar testing technology, and in particular to a dual-frequency polarization laser radar testing system and method. Background Art

[0002] LiDAR Ranging is a technology that determines the distance of a target object by emitting a laser pulse and measuring its return time. Specifically, the LiDAR device emits a laser beam, which is reflected back to the sensor after encountering an object. By calculating the time from the emission to the return of the laser, combined with the speed of light, the distance between the target object and the sensor can be accurately determined. LiDAR ranging technology is widely used in many fields such as autonomous driving, terrain mapping and environmental detection due to its high precision, high resolution and long-distance measurement.

[0003] In the existing linear frequency modulation continuous wave ranging system, Doppler frequency shift information and distance information often overlap in the spectrum. Although two detection systems can be used to collect speed information and distance information respectively, the system is expensive and complex in structure, and the differences between different detectors will affect the measurement accuracy. In addition, since the single-polarization laser depolarization ratio measurement is prone to reduced detection efficiency and large signal intensity deviation, the depolarization ratio of the detection light cannot be directly measured. Summary of the invention

[0004] The present invention provides a dual-frequency polarization laser radar test system and method, which can realize the measurement of speed, distance and depolarization ratio through a set of detection system, thereby reducing the measurement cost.

[0005] In order to solve the above technical problems, an embodiment of the present invention provides a dual-frequency polarization laser radar test system, including: a laser, a beam splitter, a half-wave plate, a linear frequency modulation module, an optical transceiver module, a beat frequency filtering module, a mixing module and a data processing module;

[0006] The laser is connected to the beam splitter, the beam splitter is connected to the half-wave plate and the first frequency shift module; the first frequency shift module is connected to the linear frequency modulation module; the linear frequency modulation module is connected to the optical transceiver module and the frequency mixing module; the optical transceiver module is connected to the beat frequency filter module; the half-wave plate is connected to the beat frequency filter module; the beat frequency filter module is connected to the frequency mixing module, and the frequency mixing module is connected to the data processing module;

[0007] The laser is used to emit linearly polarized light; the beam splitter is used to separate the linearly polarized light into a first light beam and a second light beam; the half-wave plate is used to generate an oscillator light signal according to the first light beam; the first frequency shift module is used to perform frequency shift processing on the second light beam, and the linear frequency modulation module is used to perform linear frequency modulation on the second light beam after frequency shifting, and generate a chirp signal; the optical transceiver module is used to generate an echo light signal; the beat frequency filtering module is used to generate a single frequency signal and a variable frequency signal according to the oscillator light signal and the echo light signal; the mixing module is used to generate a difference frequency signal according to the chirp signal and the variable frequency signal; the data processing module is used to obtain speed information according to the single frequency signal and obtain distance information according to the single frequency signal, the variable frequency signal and the difference frequency signal.

[0008] The present invention divides the linear polarized light emitted by the laser into a first light beam and a second light beam according to a beam splitter, rotates the polarization state of the first light beam according to a half-wave plate to generate a local oscillator light signal, modulates the second light beam according to a linear frequency modulation module to generate an echo light echo light signal, thereby extracting information from the local oscillator light signal and the echo light signal based on a beat frequency filtering module, obtaining a single frequency signal and a frequency conversion signal, and obtaining a difference frequency signal based on a frequency mixing module, so that a data processing module obtains speed information from the single frequency signal and obtains distance information according to the single frequency signal, the frequency conversion signal and the difference frequency signal; through the cooperation of the laser, the beam splitter, the half-wave plate, the linear frequency modulation module, the beat frequency filtering module, the frequency mixing module and the data processing module, the system can synchronously obtain the speed and distance information of the target object at the same time, avoids the measurement error caused by the parameter difference of different detection devices, reduces the use of separate devices, and reduces the complexity and cost of the system; at the same time, by using the beat frequency and mixing technology, the system can accurately separate the Doppler frequency shift information and the distance information, and solves the problem that the speed resolution and the distance resolution in the traditional distance measurement method are difficult to take into account.

[0009] Further, the half-wave plate is used to generate an oscillating light signal according to the first light beam, including:

[0010] The polarization state of the first light beam is rotated according to a preset deflection angle to generate an oscillating light signal.

[0011] Further, the first frequency shifting module includes a first frequency shifter and a spectroscope;

[0012] The first frequency shifter is connected to the beam splitter and the beam splitter; the beam splitter is connected to the linear frequency modulation module;

[0013] The first frequency shifter is used to modulate the frequency of the second light beam to generate a third light beam; and the beam splitter is used to split the third light beam into a fourth light beam and a fifth light beam.

[0014] Furthermore, the linear frequency modulation module includes a linear signal driving module, a second frequency shifter and a beam combining device;

[0015] The second frequency shifter is connected to the linear signal driving module, the beam combining device and the beam splitter; the beam combining device is connected to the beam splitter and the optical transceiver module; the linear signal driving module is connected to the mixing module

[0016] The second frequency shifter is used to modulate the fourth light beam to generate a sixth light beam; the beam combining device is used to generate a polarization orthogonal dual-frequency signal according to the fifth light beam and the sixth light beam; the linear signal driving module is used to generate a chirp signal and input the chirp signal into the second frequency shifter and the mixing module.

[0017] Furthermore, the optical transceiver module includes a relay module and a receiving and transmitting telescope module;

[0018] The relay module is connected to the beam combining device, the receiving and transmitting telescope module and the beat frequency filtering module;

[0019] The relay module is used to send the polarization orthogonal dual-frequency signal into the atmosphere, and receive and forward the echo light signal returned by the transmitting telescope module, and the receiving telescope module is used to receive the echo light signal in the atmosphere.

[0020] Further, the relay module includes a three-port circulator;

[0021] The three-port circulator is used to receive and forward the polarization orthogonal dual-frequency signal, and to receive and forward the echo optical signal.

[0022] Further, the beat frequency filtering module includes a photoelectric balance detector and a bandpass filter;

[0023] The photoelectric balanced detector is connected to the half-wave plate, the optical transceiver module and the bandpass filter;

[0024] The photoelectric balanced detector is used to beat the local oscillator light signal and the echo light signal to generate a single frequency signal and a variable frequency signal;

[0025] The filtering module is used to separate the single-frequency signal from the variable-frequency signal.

[0026] Furthermore, the frequency mixing module mixes the chirp signal and the frequency conversion signal based on a linear variation rule to generate a difference frequency signal.

[0027] Furthermore, the data processing module includes a speed measurement module, a distance measurement module and a depolarization ratio measurement module;

[0028] The speed measurement module is used to obtain Doppler frequency shift information according to the single-frequency signal, and calculate the speed information of the object based on the Doppler frequency shift information and the Doppler effect;

[0029] The distance measurement module is used to calculate the distance information of the object according to the difference frequency signal and the Doppler frequency shift information, and calculate the distance information of the object based on the object distance information, the bandwidth of the frequency shifter and the frequency modulation period;

[0030] The depolarization ratio measurement module is used to calculate the depolarization ratio information of the object according to the intensity ratio of the single-frequency signal and the variable-frequency signal.

[0031] In a second aspect, the present invention further provides a dual-frequency polarization laser radar testing method, comprising:

[0032] Based on the dual-frequency polarization laser radar test system, the speed information, distance information and depolarization ratio information of the object are calculated. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of the structure of a dual-frequency polarization laser radar test system provided in an embodiment of the present invention;

[0034] Figure 2 Another structural schematic diagram of a dual-frequency polarization laser radar test system provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0036] The terms "first" and "second" and the like in the specification, claims and drawings of this application are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device comprising a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products or devices.

[0037] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0038] Example 1

[0039] See also Figure 1 , Figure 1 The present invention provides a dual-frequency polarization laser radar test system according to an embodiment of the present invention. The present invention provides a dual-frequency polarization laser radar test system, including: a laser, a beam splitter, a half-wave plate, a first frequency shift module, a linear frequency modulation module, an optical transceiver module, a beat frequency filtering module, a mixing module and a data processing module;

[0040] The laser is connected to the beam splitter, the beam splitter is connected to the half-wave plate and the first frequency shift module; the first frequency shift module is connected to the linear frequency modulation module; the linear frequency modulation module is connected to the optical transceiver module and the frequency mixing module; the optical transceiver module is connected to the beat frequency filter module; the half-wave plate is connected to the beat frequency filter module; the beat frequency filter module is connected to the frequency mixing module, and the frequency mixing module is connected to the data processing module;

[0041] The laser is used to emit linearly polarized light; the beam splitter is used to separate the linearly polarized light into a first light beam and a second light beam; the half-wave plate is used to generate an oscillator light signal according to the first light beam; the first frequency shift module is used to perform frequency shift processing on the second light beam, and the linear frequency modulation module is used to perform linear frequency modulation on the second light beam after frequency shifting, and generate a chirp signal; the optical transceiver module is used to generate an echo light signal; the beat frequency filtering module is used to generate a single frequency signal and a variable frequency signal according to the oscillator light signal and the echo light signal; the mixing module is used to generate a difference frequency signal according to the chirp signal and the variable frequency signal; the data processing module is used to obtain speed information according to the single frequency signal and obtain distance information according to the single frequency signal, the variable frequency signal and the difference frequency signal.

[0042] In this embodiment, the linearly polarized light emitted by the laser is divided into a first light beam and a second light beam according to a beam splitter, the polarization state of the first light beam is rotated according to a half-wave plate to generate an oscillating light signal, and the second light beam is modulated according to a linear frequency modulation module to generate an echo light signal, so that the oscillating light signal and the echo light signal are extracted based on the beat frequency filtering module to obtain a single frequency signal and a variable frequency signal, and a difference frequency signal is obtained based on a mixing module, so that the data processing module obtains speed information from the single frequency signal and obtains distance information based on the single frequency signal, the variable frequency signal and the difference frequency signal; through the cooperation of the laser, the beam splitter, the half-wave plate, the linear frequency modulation module, the beat frequency filtering module, the mixing module and the data processing module, the system can synchronously obtain the speed and distance information of the target object at the same time, avoiding the measurement error caused by the parameter difference of different detection devices, reducing the use of separate devices, and reducing the complexity and cost of the system; at the same time, by using the beat frequency and mixing technology, the system can accurately separate the Doppler frequency shift information and the distance information, solving the problem that the speed resolution and the distance resolution in the traditional distance measurement method are difficult to take into account.

[0043] In this embodiment, the half-wave plate is used to generate an oscillating light signal according to the first light beam, including:

[0044] The polarization state of the first light beam is rotated according to a preset deflection angle to generate an oscillating light signal.

[0045] In this embodiment, the half-wave plate is a phase retarder, which is an optical element and is usually made of a birefringent material. It can change the phase of light passing through it so that a phase difference of half a wavelength is generated between two orthogonal polarization components in the light beam. The materials of the half-wave plate include crystal quartz, lithium niobate and mica lamp.

[0046] In this embodiment, the main function of the half-wave plate is to rotate the polarization state of the incident light. When the first light beam passes through the half-wave plate, its polarization direction will be rotated, and the rotation angle is twice the angle between the polarization direction of the incident light and the optical axis of the wave plate. If the polarization direction of the incident light forms an angle θ with the optical axis of the half-wave plate, after passing through the half-wave plate, the polarization direction of the light will rotate by an angle of 2θ. Therefore, by accurately controlling the rotation angle of the half-wave plate, accurate control of the polarization state of the first light beam can be achieved.

[0047] In this embodiment, the half-wave plate is used to rotate the polarization state of the first light beam, and its deflection angle is 45°. The laser emits linearly polarized light, which is split into two beams after passing through the beam splitter: the first light beam and the second light beam. The half-wave plate rotates the polarization state of the first light beam by 45°, thereby generating a local oscillation light signal.

[0048] In this embodiment, the first frequency shifting module includes a first frequency shifter and a spectroscope;

[0049] The first frequency shifter is connected to the beam splitter and the beam splitter; the beam splitter is connected to the linear frequency modulation module;

[0050] The first frequency shifter is used for modulating the frequency of the second light beam to generate a third light beam; and the beam splitter is used for splitting the third light beam into a fourth light beam and a fifth light beam.

[0051] In this embodiment, the first frequency shifter is connected after the beam splitter to directly process the second light beam separated by the beam splitter. The frequency of the second light beam is f0. Its main function is to modulate the frequency of the second light beam so that the frequency of the second light beam produces a specific shift. This is equivalent to generating a new light beam, i.e., the third light beam, whose frequency is f0+f1.

[0052] In this embodiment, the beam splitter is connected after the first frequency shifter, and its main function is to further split the third light beam into the fourth light beam and the fifth light beam. The function of the beam splitter is the same as that of the beam splitter, but the difference is that it splits a single light beam (the third light beam) into two parts instead of separating two parts from the original light beam. In other words, the frequency of the fourth light beam and the fifth light beam is equal to that of the third light beam, and their frequency is also f0+f1.

[0053] In this embodiment, the linear frequency modulation module includes a linear signal driving module, a second frequency shifter and a beam combining device;

[0054] The second frequency shifter is connected to the linear signal driving module, the beam combining device and the beam splitter; the beam combining device is connected to the beam splitter and the optical transceiver module; the linear signal driving module is connected to the frequency mixing module;

[0055] The second frequency shifter is used to modulate the fourth light beam to generate a sixth light beam; the beam combining device is used to generate a polarization orthogonal dual-frequency signal according to the fifth light beam and the sixth light beam; the linear signal driving module linear frequency modulation module is used to generate a chirp signal and input the chirp signal into the second frequency shifter and the mixing module.

[0056] In this embodiment, the linear signal driving module is the core of the linear frequency modulation module, and its main function is to generate a linear frequency modulation signal (chirp signal). The chirp signal is a signal whose frequency changes linearly with time, and is widely used in radar systems to improve the distance resolution. The chirp signal generated by the linear signal driving module is not only input into the second frequency shifter (for modulating the fourth light beam), but also input into the mixing module to provide a basic signal for subsequent speed and distance information processing. Through the modulation of the chirp signal, the second frequency shifter modulates the frequency of the fourth light beam into a linear change to generate a sixth light beam, whose frequency is f0+f1+f2+ut, so that the spectrum characteristics of the sixth light beam meet the system's requirements for distance information extraction.

[0057] Wherein, f0 is the center frequency of the linearly polarized light emitted by the laser, that is, the frequency of the original laser signal. f1 is the frequency offset generated by the first frequency shifter after frequency modulation of the second light beam. The frequencies of the third light beam, the fourth light beam and the fifth light beam are all increased by f1. f2+ut is the frequency offset generated by the second frequency shifter after frequency modulation of the fourth light beam. The frequency of the sixth light beam is further increased by f2+ut on the basis of f0+f1. u is the frequency change rate of the chirp signal, which indicates the rate at which the frequency of the chirp signal changes linearly with time. t is time.

[0058] In this embodiment, the frequency of the second light beam is f0. The frequency of the third light beam is f0+f1. The frequency of the fourth light beam is f0+f1. The frequency of the fifth light beam is f0+f1. The frequency of the sixth light beam is f0+f1+f2+ut.

[0059] In this embodiment, the linear signal driving module is a linear frequency modulated signal generator (LFM Signa l Generator for short), which is a device that can generate a signal whose frequency changes linearly with time. This signal is usually called a chirp signal. The characteristic of a chirp signal is that its frequency changes linearly from a low frequency to a high frequency, or from a high frequency to a low frequency within a certain period of time.

[0060] In this embodiment, the linear frequency modulation signal generator is connected to the second frequency shifter, and its main function is to generate a chirp signal and input the signal into the second frequency shifter, so that the frequency of the sixth light beam generated by the second frequency shifter changes linearly with time. The generated chirp signal is input into the second frequency shifter to frequency modulate the fourth light beam separated by the second beam splitter. The second frequency shifter changes according to the frequency of the chirp signal, so that the frequency of the fourth light beam also changes linearly with time, thereby generating the sixth light beam.

[0061] In this embodiment, the second frequency shifter receives the chirp signal generated by the linear signal driving module and applies it to the fourth light beam, thereby modulating the fourth light beam to generate the sixth light beam. The modulation process causes the frequency of the sixth light beam to change linearly with time, forming a chirped light beam.

[0062] In this embodiment, both the first frequency shifter and the second frequency shifter are acousto-optic frequency shifters. An acousto-optic frequency shifter is an optical device that uses the acousto-optic effect to change the frequency of a light beam. It is used to modulate the frequency of a light beam to shift its frequency. By controlling the frequency and intensity of the sound wave, the frequency shift of the light beam can be accurately adjusted.

[0063] In an alternative embodiment, the acousto-optic frequency shifter is often made of acousto-optic materials, including fused silica, lithium niobate, tellurium dioxide, and germanium.

[0064] In this embodiment, an anisotropic acousto-optic crystal is used to prepare the acousto-optic frequency shifter, such as tellurium dioxide, so that the polarization angle of the diffracted light and the incident light is 90°. Isotropic acousto-optic crystals, such as quartz, germanium, indium phosphide, etc., can also be used, and a wave plate is installed at the output end of the acousto-optic device to change the polarization state of the diffracted light to make it perpendicular to the polarization state of the incident light.

[0065] In this embodiment, by introducing sound waves, the frequency of the second light beam is changed based on the first frequency shifter so that it contains a specific frequency offset, and the fourth light beam separated by the second spectroscope is frequency modulated for the second time. Based on another frequency shift of the second frequency shifter, the sixth light beam has a different frequency component, and generates a polarization orthogonal dual-frequency signal together with the fifth light beam.

[0066] In this embodiment, a sawtooth wave linear frequency modulation signal, i.e., a chirp signal, is used during the ranging process. The sawtooth wave linear frequency modulation signal causes the frequency of the sixth light beam generated by the second frequency shifter to change linearly with time, and the change pattern of the echo light signal is the same. By analyzing the frequency change of the echo light signal, the distance of the target object can be accurately measured.

[0067] In this embodiment, the beam combining device receives the fifth light beam from the beam splitter and the sixth light beam modulated by the second frequency shifter. Its main function is to combine the two light beams to generate a polarization orthogonal dual-frequency signal. This dual-frequency signal contains information of the fifth light beam and the sixth light beam, and has different polarization characteristics.

[0068] In this embodiment, the linear frequency modulation module includes a plurality of cascaded acousto-optic frequency shifters, and the bandwidth is expanded by the plurality of cascaded acousto-optic frequency shifters to improve the ranging accuracy.

[0069] In another optional embodiment, the linear frequency modulation module includes three cascaded acousto-optic frequency shifters, each of which provides frequency shifts of Δf1, Δf2 and Δf3, and the total frequency shift range becomes Δf_total=Δf1+Δf2+Δf3.

[0070] In this embodiment, by cascading multiple acousto-optic frequency shifters, the final output optical signal has a larger frequency offset range, which can effectively expand the bandwidth, thereby improving the ranging resolution and speed measurement accuracy. Not only can the frequency resolution of the system be improved, but the signal-to-noise ratio of the signal can also be enhanced, thereby achieving higher-precision ranging and speed measurement.

[0071] In this embodiment, the optical transceiver module includes a relay module and a transceiver telescope module;

[0072] The relay module is connected to the beam combining device, the receiving and transmitting telescope module and the beat frequency filtering module;

[0073] The relay module is used to send the polarization orthogonal dual-frequency signal into the atmosphere, and receive and forward the echo light signal returned by the transmitting telescope module, and the receiving telescope module is used to receive the echo light signal in the atmosphere.

[0074] In this embodiment, the relay module includes a three-port circulator;

[0075] The three-port circulator is used to receive and forward the polarization orthogonal dual-frequency signal, and to receive and forward the echo optical signal.

[0076] In this embodiment, the three-port circulator is a multi-port non-reciprocal optical or microwave device, in which the signal can only be transmitted in a fixed direction. After the signal enters from a certain port, it can only be output from the next port and will not return to the previous port. The input signal enters the first port and can only be output from the second port. At this time, the second port can receive both the signal from the first port and other external signals (such as echo signals). The signal received by the second port can only be output from the third port. The third port can receive the signal from the second port, but will not feed the signal back to the second port or the first port.

[0077] In this embodiment, the third port circulator is used to receive and forward the polarization orthogonal dual-frequency signal, and receive and forward the echo optical signal. The polarization orthogonal dual-frequency signal is sent to the first port of the third port circulator. The circulator forwards the signal from the second port, enters the subsequent optical system or transmission module, and finally transmits it to the target object. When the echo optical signal is reflected back from the target object, the echo signal enters the circulator through the second port. The circulator outputs the received echo signal from the third port and sends it to the receiving module for processing.

[0078] In this embodiment, the circulator based on the third port can effectively isolate the signal paths of transmission and reception, and prevent crosstalk between the transmission signal and the echo signal. Due to the non-reciprocal characteristics of the circulator, the transmission signal will not be directly fed back into the receiving path, thereby protecting the receiver from damage by high-power transmission signals. By preventing the transmission signal from reflecting back to the receiver, the circulator can improve the stability and reliability of the system and reduce measurement errors caused by signal crosstalk or reflection.

[0079] In this embodiment, the beat frequency filtering module includes a photoelectric balance detector and a bandpass filter;

[0080] The photoelectric balanced detector is connected to the half-wave plate, the optical transceiver module and the bandpass filter;

[0081] The photoelectric balanced detector is used to beat the local oscillator light signal and the echo light signal to generate a single frequency signal and a variable frequency signal;

[0082] The filtering module is used to separate the single-frequency signal from the variable-frequency signal.

[0083] In this embodiment, the photoelectric balance detector is a high-sensitivity, high-precision photoelectric detector, which is usually used to measure the difference of weak light signals. It consists of two or more photoelectric detector units, and eliminates common mode noise and improves the signal-to-noise ratio by measuring the difference of the output signals of the two detectors.

[0084] In this embodiment, the photoelectric balanced detector includes two photodiodes. The photoelectric balanced detector receives a local oscillator light signal and an echo light signal. The two light beams have similar frequencies, so interference occurs during the photoelectric conversion process to form a beat signal. The frequency of the beat signal is the frequency difference of the light beams.

[0085] In this embodiment, the photoelectric balanced detector receives the local oscillator light signal from the half-wave plate and the echo light signal from the linear frequency modulation module, and the generated beat frequency signal includes the single frequency signal A1 and the variable frequency signal A2.

[0086] In this embodiment, the bandpass filter is a filter that allows signals within a certain frequency range to pass (ie, signals near a center frequency) and suppresses signals outside the frequency range.

[0087] In this embodiment, the bandpass filter receives the beat frequency signal (including the single frequency signal A1 and the variable frequency signal A2) output from the photoelectric balance detector, and the filter selectively passes through different frequency ranges to separate the single frequency signal A1 and the variable frequency signal A2. The separated single frequency signal A1 and the variable frequency signal A2 contain different information. The single frequency signal A1 corresponds to the distance information of the target object, and the variable frequency signal A2 corresponds to the speed information of the target object.

[0088] In this embodiment, the photoelectric balance detector is mainly responsible for receiving the local oscillator light signal and the echo light signal, and performing beat frequency detection on them to generate a beat frequency signal including a single frequency signal and a variable frequency signal, thereby improving the signal-to-noise ratio of the system. The bandpass filter is responsible for frequency separation of the beat frequency signal, extracting the single frequency signal and the variable frequency signal, which are respectively used for extracting the distance and speed information of the target object, thereby improving the purity and analyzability of the signal.

[0089] In this embodiment, the frequency mixing module mixes the chirp signal and the frequency conversion signal based on a linear variation rule to generate a difference frequency signal.

[0090] In this embodiment, the frequency mixing module includes a mixer. A mixer is an electronic device used to mix two signals of different frequencies to generate a new frequency component, such as a difference frequency signal.

[0091] In this embodiment, the mixer mixes the chirp signal from the linear frequency modulation module and the frequency conversion signal from the beat frequency filtering module. During the mixing process, the chirp signal and the frequency conversion signal interact in the mixer to generate a new signal, namely, the difference frequency signal.

[0092] In this embodiment, when two signals with different frequencies are multiplied in the mixer, two new signals are generated: one is the sum of the frequencies of the two input signals (sum frequency signal), and the other is the difference between the frequencies of the two input signals (difference frequency signal). Since the frequency of the chirp signal changes linearly with time, the frequency conversion signal also has a specific frequency characteristic, and the difference frequency signal after mixing will reflect the distance information of the target object. By analyzing the frequency characteristics of the difference frequency signal, the distance information of the target object can be accurately extracted.

[0093] In this embodiment, the data processing module includes a speed measurement module, a distance measurement module and a depolarization ratio measurement module;

[0094] The speed measurement module is used to obtain Doppler frequency shift information according to the single-frequency signal, and calculate the speed information of the object based on the Doppler frequency shift information and the Doppler effect;

[0095] The distance measurement module is used to calculate the distance information of the object according to the difference frequency signal and the Doppler frequency shift information, and calculate the distance information of the object based on the object distance information, the bandwidth of the frequency shifter and the frequency modulation period;

[0096] The depolarization ratio measurement module is used to calculate the depolarization ratio information of the object according to the intensity ratio of the single-frequency signal and the variable-frequency signal.

[0097] In this embodiment, the difference frequency signal generated by the frequency mixing module is transmitted to the data processing module, and the data processing module extracts the distance information of the target object according to the frequency characteristics of the difference frequency signal. At the same time, the data processing module also uses the single frequency signal (from the beat frequency filtering module) to obtain the speed information of the target object.

[0098] In this embodiment, according to the Doppler effect, when light is incident on a moving object, a frequency shift will occur in the speed measurement module, and the object's speed v r and the optical frequency shift Δf d The relationship is:

[0099]

[0100] The Doppler frequency shift information can be obtained from the single-frequency beat signal A1, thereby calculating the relative speed of the object.

[0101] In this embodiment, in the ranging module, due to the sawtooth wave linear frequency modulation signal, the frequency of the ranging light, that is, the sixth light beam generated based on the second frequency shifter, changes linearly with time, and the change law of the echo light signal is the same, that is, there is a time difference t between the sixth light beam and the echo light. r , the difference frequency signal f can be obtained by mixing the two b .f b The Doppler frequency shift Δf d , by f b -Δf d Get f containing only the distance information of the object R , and calculate the target distance:

[0102]

[0103] Where B is the bandwidth of the AOM and T is the period of the linear frequency modulation. The distance resolution is defined as:

[0104]

[0105] In this embodiment, in the depolarization ratio measurement module, the intensity ratio of the light polarization state of the backscattered echo to the orthogonal direction is calculated according to the intensity ratio of the single-frequency signal and the variable-frequency signal, and the depolarization ratio is calculated according to the intensity ratio, that is, the depolarization ratio is:

[0106]

[0107] Where p is the intensity ratio of the backscattered echo whose light polarization state changes to the orthogonal direction.

[0108] In this embodiment, the intensity ratio of the beat frequency signals A1 and A2 is assumed to be r. r0 is the test constant of the lidar system, which can be obtained during calibration, because in this system, the depolarization ratio can be expressed as:

[0109]

[0110] That is, by measuring the intensity ratio of the beat frequency signals A1 and A2 in the echo signal, the depolarization ratio information can be obtained.

[0111] Please refer to Figure 2 , Figure 2 Another structural schematic diagram of a dual-frequency polarization laser radar test system provided in an embodiment of the present invention.

[0112] In this embodiment, a dual-frequency polarization lidar test system includes a laser, a beam splitter, a half-wave plate, a first frequency shifter, a second frequency shifter, a second beam splitter, a beam combining device, a linear frequency modulation signal generator, a three-port circulator, a receiving and transmitting telescope module, a photoelectric balanced detector, a bandpass filter, a mixer and a data processing module.

[0113] In this embodiment, the linearly polarized light with a frequency of f0 emitted by the laser is divided into a first light beam and a second light beam by a beam splitter. Among them, the half-wave plate is used to rotate the polarization state of the first light beam by 45° and input it into the photoelectric balanced detector as a local oscillator signal. The second light beam is used to generate a detection beam. The second light beam passes through the first acousto-optic frequency shifter to obtain a third light beam with a frequency of f0+f1. The third light beam is divided into two paths through the second beam splitter, namely the fourth light beam and the fifth light beam. The fifth light beam is directly input into the beam combining device as a speed measurement beam, and the fourth light beam passes through the second acousto-optic frequency shifter. The second acousto-optic frequency shifter is controlled by the chirp signal to linearly modulate the input optical signal and output a continuously frequency modulated optical signal with a frequency of f0+f1+f2+μt, that is, the sixth light beam, which is input into the beam combining device as a ranging beam. The polarization states of the fifth light beam and the sixth light beam are orthogonal, and the frequencies are different. After being combined by the beam combining device, a beam of polarized orthogonal dual-frequency signal light is output, that is, the seventh light beam. The orthogonal dual-frequency signal light passes through the annular beam splitter and is emitted into the atmosphere through the transmitting and receiving telescope. The echo light signal generated by the atmospheric action is received by the receiving and transmitting telescope and input into the photoelectric balanced detector through the three-port circulator. The local oscillator light signal and the echo light signal beat in the photoelectric balanced detector to generate a single-frequency beat signal A1 and a frequency conversion signal A2. A1 and A2 can be separated through a bandpass filter, and the distance and speed information can be extracted from the two signals according to the data processor.

[0114] The embodiment of the present invention also provides a dual-frequency polarization laser radar testing method, including:

[0115] Based on the dual-frequency polarization laser radar test system, the speed information, distance information and depolarization ratio information of the object are calculated.

[0116] In this embodiment, the linearly polarized light emitted by the laser is divided into a first light beam and a second light beam according to a beam splitter, the polarization state of the first light beam is rotated according to a half-wave plate to generate an oscillating light signal, and the second light beam is modulated according to a linear frequency modulation module to generate an echo light signal, so that the oscillating light signal and the echo light signal are extracted based on the beat frequency filtering module to obtain a single frequency signal and a variable frequency signal, and a difference frequency signal is obtained based on a mixing module, so that the data processing module obtains speed information from the single frequency signal and obtains distance information based on the single frequency signal, the variable frequency signal and the difference frequency signal; through the cooperation of the laser, the beam splitter, the half-wave plate, the linear frequency modulation module, the beat frequency filtering module, the mixing module and the data processing module, the system can synchronously obtain the speed and distance information of the target object at the same time, avoiding the measurement error caused by the parameter difference of different detection devices, reducing the use of separate devices, and reducing the complexity and cost of the system; at the same time, by using the beat frequency and mixing technology, the system can accurately separate the Doppler frequency shift information and the distance information, solving the problem that the speed resolution and the distance resolution in the traditional distance measurement method are difficult to take into account.

[0117] In this embodiment, a set of detection equipment is used to complete the measurement of speed, distance, and depolarization ratio information. The measurement error caused by the parameter differences of different detection equipment is avoided; the synchronous measurement in the true sense is realized; the complexity of the system is reduced while the cost is saved. At the same time, a dual-frequency orthogonal polarization laser radar system is used to realize the distance measurement and speed measurement in different polarization states. The distance measurement system uses the Doppler effect, and the speed measurement principle is based on the frequency modulated continuous wave speed measurement theory, which avoids the situation in traditional pulse laser radar where both the speed resolution and the distance resolution depend on the pulse width and are difficult to take into account.

[0118] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A dual-frequency polarization laser radar test system, characterized in that: include: Laser, beam splitter, half-wave plate, linear frequency modulation module, optical transceiver module, beat frequency filter module, mixing module and data processing module; The laser is connected to the beam splitter, the beam splitter is connected to the half-wave plate and the first frequency shift module; the first frequency shift module is connected to the linear frequency modulation module; the linear frequency modulation module is connected to the optical transceiver module and the frequency mixing module; the optical transceiver module is connected to the beat frequency filter module; the half-wave plate is connected to the beat frequency filter module; the beat frequency filter module is connected to the frequency mixing module, and the frequency mixing module is connected to the data processing module; The laser is used to emit linearly polarized light; the beam splitter is used to separate the linearly polarized light into a first light beam and a second light beam; the half-wave plate is used to generate an oscillating light signal according to the first light beam; the first frequency shift module is used to perform frequency shift processing on the second light beam, and the linear frequency modulation module is used to perform linear frequency modulation on the frequency-shifted second light beam and generate a chirp signal; the optical transceiver module is used to generate an echo light signal; The beat frequency filtering module is used to generate a single frequency signal and a variable frequency signal according to the local oscillator light signal and the echo light signal; the mixing module is used to generate a difference frequency signal according to the chirp signal and the variable frequency signal; the data processing module is used to obtain speed information according to the single frequency signal and obtain distance information according to the single frequency signal, the variable frequency signal and the difference frequency signal.

2. A dual-frequency polarization laser radar test system as claimed in claim 1, characterized in that: The half-wave plate is used to generate an oscillating light signal according to the first light beam, including: The polarization state of the first light beam is rotated according to a preset deflection angle to generate an oscillating light signal.

3. A dual-frequency polarization laser radar test system as claimed in claim 1, characterized in that: The first frequency shifting module includes a first frequency shifter and a spectroscope; The first frequency shifter is connected to the beam splitter and the beam splitter; the beam splitter is connected to the linear frequency modulation module; The first frequency shifter is used for modulating the frequency of the second light beam to generate a third light beam; and the beam splitter is used for splitting the third light beam into a fourth light beam and a fifth light beam.

4. A dual-frequency polarization laser radar test system as claimed in claim 3, characterized in that: The linear frequency modulation module includes a linear signal driving module, a second frequency shifter and a beam combining device; The second frequency shifter is connected to the linear signal driving module, the beam combining device and the beam splitter; the beam combining device is connected to the beam splitter and the optical transceiver module; the linear signal driving module is connected to the frequency mixing module; The second frequency shifter is used to modulate the fourth light beam to generate a sixth light beam; the beam combining device is used to generate a polarization orthogonal dual-frequency signal according to the fifth light beam and the sixth light beam; the linear signal driving module is used to generate a chirp signal and input the chirp signal into the second frequency shifter and the mixing module.

5. A dual-frequency polarization laser radar test system as claimed in claim 4, characterized in that: The optical transceiver module includes a relay module and a receiving and transmitting telescope module; The relay module is connected to the beam combining device, the receiving and transmitting telescope module and the beat frequency filtering module; The relay module is used to send the polarization orthogonal dual-frequency signal into the atmosphere, and receive and forward the echo light signal returned by the transmitting telescope module, and the receiving telescope module is used to receive the echo light signal in the atmosphere.

6. A dual-frequency polarization laser radar test system as claimed in claim 5, characterized in that: The relay module includes a three-port circulator; The three-port circulator is used to receive and forward the polarization orthogonal dual-frequency signal, and to receive and forward the echo optical signal.

7. A dual-frequency polarization laser radar test system as claimed in claim 1, characterized in that: The beat frequency filtering module includes a photoelectric balance detector and a bandpass filter; The photoelectric balanced detector is connected to the half-wave plate, the optical transceiver module and the bandpass filter; The photoelectric balanced detector is used to beat the local oscillator light signal and the echo light signal to generate a single frequency signal and a variable frequency signal; The filtering module is used to separate the single-frequency signal from the variable-frequency signal.

8. A dual-frequency polarization laser radar test system as claimed in claim 3, characterized in that: The frequency mixing module is used to mix the chirp signal and the frequency conversion signal based on a linear variation rule to generate a difference frequency signal.

9. A dual-frequency polarization laser radar test system according to any one of claims 1 to 8, characterized in that: The data processing module includes a speed measurement module, a distance measurement module and a depolarization ratio measurement module; The speed measurement module is used to obtain Doppler frequency shift information according to the single-frequency signal, and calculate the speed information of the object based on the Doppler frequency shift information and the Doppler effect; The distance measurement module is used to calculate the distance information of the object according to the difference frequency signal and the Doppler frequency shift information, and calculate the distance information of the object based on the object distance information, the bandwidth of the frequency shifter and the frequency modulation period; The depolarization ratio measurement module is used to calculate the depolarization ratio information of the object according to the intensity ratio of the single-frequency signal and the variable-frequency signal.

10. A dual-frequency polarization laser radar testing method, characterized in that: include: Based on a dual-frequency polarization laser radar test system as described in any one of claims 1 to 9, the speed information, distance information and depolarization ratio information of the object are calculated.

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