A laser doppler velocimetry system and method

Abstract

The application relates to the technical field of laser speed measurement, and discloses a laser Doppler speed measurement system and a speed measurement method. The system comprises a dual-frequency laser device, a first detection beam splitter, a second detection beam splitter, a first detection device, a second detection device and a signal processing device. The dual-frequency laser device is optically connected with the first detection beam splitter and the second detection beam splitter. The first detection beam splitter and the second detection beam splitter are respectively optically connected with the first detection device and the second detection device. The first detection device and the second detection device are optically connected with the signal processing device. The application constructs a set of optical path "cross pairing" dual-channel differential heterodyne interference systems, so that the interference optical path of each detection device simultaneously contains frequency components from two lasers. The inherent output frequencies of the two detection devices are equal in size and opposite in sign, have common mode rejection characteristics, effectively reduce the dependence of the system on the long-term stability of the core frequency shift device, and improve the measurement accuracy and reliability.

Description

Technical Field

[0001] This invention relates to the field of laser velocimetry technology, specifically to a laser Doppler velocimetry system and method. Background Technology

[0002] Laser Doppler Velocimetry (LDV) is a non-contact precision measurement technique based on the optical Doppler effect. When a laser beam irradiates a moving object or a tracer particle in a fluid, the frequency of the scattered or reflected light will shift proportionally to the object's velocity. By detecting this minute frequency change, the target's velocity can be obtained. With its outstanding advantages such as high spatial resolution, fast dynamic response, and no interference with the measured flow field, this technique is widely used in fields such as fluid mechanics, aerodynamics, biomedicine, and industrial process monitoring.

[0003] In laser Doppler velocimetry, one technique is heterodyne detection. Heterodyne detection introduces a fixed frequency shift in the optical path, creating a stable intermediate frequency carrier between the signal light and the reference light. The Doppler frequency shift information is modulated onto this carrier as a sideband. This method not only moves the signal spectrum away from the noisy low-frequency region, significantly improving the signal-to-noise ratio, but more importantly, by determining whether the output signal frequency is higher or lower than the fixed carrier frequency, it can, in principle, distinguish the direction of motion. Therefore, it has become the preferred solution for high-end applications with strict performance requirements.

[0004] However, although the heterodyne detection architecture theoretically possesses both high signal-to-noise ratio and direction discrimination capability, and is the cornerstone of high-performance laser Doppler velocimetry systems, it still faces a series of mutually restrictive technical defects in the pursuit of high precision, large range and strong robustness. The existing heterodyne detection architecture is extremely dependent on the long-term frequency stability of the generated laser, and any temperature drift or time drift will be directly mixed into the final velocimetry result as an error. Summary of the Invention

[0005] This invention provides a laser Doppler velocimetry system and method to solve the problem that any temperature drift or time drift will directly be mixed into the final velocimetry result as an error.

[0006] In a first aspect, the present invention provides a laser Doppler velocimetry system, the system comprising: A dual-frequency laser device is used to generate a first and a second probe laser with different frequencies. The first detection beam splitter is optically connected to the dual-frequency laser device and is used to split the first detection laser into a first signal light and a first reference light. The second detection beam splitter is optically connected to the dual-frequency laser device and is used to split the second detection laser into a second signal light and a second reference light. The first detection device is optically connected to the first detection beam splitter and the second detection beam splitter, respectively, and is used to generate a first detection signal by detecting an object with a first signal light and a second reference light. The second detection device is optically connected to the first detection beam splitter and the second detection beam splitter respectively, and is used to generate a second detection signal by detecting the object with the second signal light and the first reference light. A signal processing device, connected to the first detection device and the second detection device, is used to obtain a first Doppler frequency shift based on the first detection signal, obtain a second Doppler frequency shift based on the second detection signal, and calculate the detection speed based on the first Doppler frequency shift and the second Doppler frequency shift.

[0007] This invention constructs a dual-channel differential heterodyne interferometry system with "cross-paired" optical paths. This ensures that the interference optical path of each detection device simultaneously contains frequency components from two lasers. The inherent output frequencies of the two detection devices are equal in magnitude but opposite in sign, exhibiting common-mode rejection characteristics. This effectively reduces the system's dependence on the long-term stability of the core frequency shifting device and improves measurement accuracy and reliability.

[0008] In one alternative embodiment, the dual-frequency laser device includes: A laser used to generate an initial laser beam; A laser beam splitter, optically connected to the laser, is used to split the initial laser into a first laser beam and a second laser beam. A first frequency shifter is optically connected to the laser beam splitter and is used to shift the frequency of the first split laser to form the first probe laser. The second frequency shifter is optically connected to the laser beam splitter and is used to shift the frequency of the second split laser to form the second probe laser.

[0009] By using two frequency shifters and a single laser source to generate two probe lasers, compared to a dual-frequency light source scheme that uses two independent lasers, the system structure of this invention is more compact, more reliable, and avoids the need for expensive and complex hardware such as high-bandwidth mixers.

[0010] In an optional embodiment, the first detection device includes: A first circulator, optically connected to the first detection beam splitter, is used to generate first scattered light by detecting with the first signal light; A first coupler, optically connecting the first circulator and the second probe beam splitter, is used to couple the first scattered light and the second reference light; A first balanced detector, optically connected to the first coupler, is used to convert the coupled first scattered light and the second reference light into the first detection signal; The second detection device includes: The second circulator, optically connected to the second detection beam splitter, is used to generate second scattered light by detecting with the second signal light; The second coupler, which optically connects the second circulator and the first probe beam splitter, is used to couple the second scattered light and the first reference light. The second balanced detector is optically connected to the second coupler and is used to convert the coupled second scattered light and the first reference light into the second detection signal.

[0011] During detection, the light from the first beam splitter is sent to the first circulator and the second coupler, and the light from the second beam splitter is sent to the second circulator and the first coupler. The signal light from the first circulator and the second circulator converges at the measuring body. The signal light output from the first circulator is scattered and returns to the first coupler to mix with the second reference light. After mixing, it is converted into an electrical signal by the first balanced detector. Similarly, the signal light output from the second circulator is scattered and returns to the second coupler to mix with the first reference light. After mixing, it is converted into an electrical signal by the second balanced detector. Finally, the outputs of the first balanced detector and the second balanced detector are sent to the digital signal processing unit to calculate the velocity, realizing dual-channel velocity detection.

[0012] In one alternative embodiment, the first detection device and the second detection device are arranged axially symmetrically.

[0013] When the first and second detection devices are arranged symmetrically, the detection angles of the first and second detection devices are the same when the speed measuring system is facing the object being detected, which can effectively simplify the calculation process and improve the detection speed.

[0014] Secondly, the present invention provides a laser Doppler velocimetry method, applied to the laser Doppler velocimetry system described above, the method comprising: The signal processing device acquires a first Doppler frequency shift based on a first detection signal and acquires a second Doppler frequency shift based on a second detection signal; The signal processing device calculates the detection velocity based on the first Doppler frequency shift and the second Doppler frequency shift.

[0015] By using two detectors whose inherent output frequencies are equal in magnitude but opposite in sign, common-mode rejection is achieved, effectively reducing the system's dependence on the long-term stability of the core frequency-shifting device and improving measurement accuracy and reliability.

[0016] In an optional embodiment, the signal processing device acquires a first Doppler frequency shift based on a first detection signal and a second Doppler frequency shift based on a second detection signal, specifically including: The signal processing device performs digital quadrature demodulation and frequency discrimination on the first detection signal to extract the first instantaneous frequency; The signal processing device performs digital quadrature demodulation and frequency discrimination on the second detection signal to extract the second instantaneous frequency; The signal processing device extracts the first Doppler frequency shift based on the first instantaneous frequency and extracts the second Doppler frequency shift based on the second instantaneous frequency.

[0017] By extracting the instantaneous frequencies from the first and second detection signals and performing simultaneous calculations on these instantaneous frequencies, the Doppler frequency shift can be extracted.

[0018] In an optional embodiment, the signal processing device calculates the detection velocity based on the joint solution of the first Doppler frequency shift and the second Doppler frequency shift, including: The signal processing device calculates the angle of the detection velocity based on the first Doppler frequency shift and the second Doppler frequency shift; The signal processing device calculates the absolute value of the detection velocity based on the first Doppler frequency shift and the second Doppler frequency shift.

[0019] Compared to single-channel laser velocimetry, dual-channel laser velocimetry has more information, which allows it to calculate the magnitude and direction of the target velocity in the measurement plane, providing richer motion information than single-point velocimetry.

[0020] In an optional embodiment, the signal processing device calculates the angle of the detection velocity based on the first Doppler frequency shift and the second Doppler frequency shift, specifically including: The signal processing device determines the direction angle of the detection velocity based on the geometric relationship between the first and second detection devices, and the absolute values ​​of the first and second Doppler frequency shifts.

[0021] By analyzing the two Doppler frequency shifts with a known spatial angle, the direction of the target velocity in the measurement plane can be calculated.

[0022] In an optional embodiment, the signal processing device determines the direction angle of the detection velocity based on the geometric relationship between the first and second detection devices and the absolute values ​​of the first and second Doppler frequency shifts, and then further includes: The signal processing device compares the first instantaneous frequency and the second instantaneous frequency. If the first instantaneous frequency is greater than the second instantaneous frequency, it determines that the direction of the detected velocity is along the direction angle approaching the speed measuring system. If the first instantaneous frequency is less than the second instantaneous frequency, then the direction of the detected velocity is determined to be away from the velocity measuring system along the direction angle.

[0023] This invention ensures that the direction determination is unaffected by the target speed. By using bidirectional symmetrical differential detection and joint calculation, it fundamentally solves the problem of directional ambiguity in traditional single-channel heterodyne laser velocimetry systems at high speeds.

[0024] In an optional embodiment, the signal processing device extracts the first Doppler frequency shift based on the first instantaneous frequency and extracts the second Doppler frequency shift based on the second instantaneous frequency, specifically including: Based on the first instantaneous frequency, extract the first Doppler frequency shift set; Based on the second instantaneous frequency, extract the second Doppler frequency shift set; Obtain the first Doppler frequency shift set and the second Doppler frequency shift set, and perform defuzzification calculation to obtain the first Doppler frequency shift and the second Doppler frequency shift.

[0025] In this embodiment, by performing defuzzification calculations, the unfuzzy speed measurement range is theoretically increased to be limited only by the detector bandwidth and processing algorithm, breaking through the bottleneck that the speed measurement upper limit of traditional dual-frequency systems is limited by the inherent frequency difference. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of a laser Doppler velocimetry system according to an embodiment of the present invention; Figure 2 This is another structural schematic diagram of a laser Doppler velocimetry system according to an embodiment of the present invention; Figure 3 This is a schematic flowchart of a laser Doppler velocimetry method according to an embodiment of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] It is understood that before using the technical solutions disclosed in the various embodiments of the present invention, users should be informed of the types, scope of use, and usage scenarios of the personal information involved in the present invention and their authorization should be obtained in accordance with relevant laws and regulations through appropriate means.

[0030] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0031] Please refer to Figure 1 The present invention provides a laser Doppler velocimetry system, the system comprising a dual-frequency laser device, a first detection beam splitter, a second detection beam splitter, a first detection device, a second detection device, and a signal processing device.

[0032] The dual-frequency laser device generates a first detection laser and a second detection laser with different frequencies. Both the first and second detection beamsplitters are optically connected to the dual-frequency laser device. The first detection beamsplitter splits the first detection laser into a first signal light and a first reference light. The second detection beamsplitter is also optically connected to the dual-frequency laser device, splitting the second detection laser into a second signal light and a second reference light. A first detection device is optically connected to both the first and second detection beamsplitters, generating a first detection signal by using the first signal light and the second reference light to detect an object. A second detection device is also optically connected to both the first and second detection beams, generating a second detection signal by using the second signal light and the first reference light to detect an object. A signal processing device is connected to both the first and second detection devices, acquiring a first Doppler frequency shift based on the first detection signal, acquiring a second Doppler frequency shift based on the second detection signal, and calculating the detection speed based on the first and second Doppler frequency shifts.

[0033] In this embodiment, the normal frequency of the first detection laser is used as... The normal frequency of the second detection laser is Please provide an explanation.

[0034] The first detection device uses a first detection laser as the signal light and a second detection laser as the reference light. Under normal conditions, the inherent frequency shift of the first detection device... for: ; Similarly, the inherent frequency shift of the second detection device, using the second detection laser as the signal light and the first detection laser as the reference light, is equal in magnitude but opposite in sign to the inherent frequency shift of the first detection device. Therefore, the inherent frequency shift of the second detection device is... .

[0035] As can be seen, this invention constructs a dual-channel differential heterodyne interferometry system with "cross-paired" optical paths. This allows the interference optical path of each detection device to simultaneously contain frequency components from two lasers. The inherent output frequencies (net frequency shifts) of the two detection devices are equal in magnitude but opposite in sign, exhibiting common-mode suppression characteristics. This effectively reduces the system's dependence on the long-term stability of the core frequency shifting device and improves measurement accuracy and reliability.

[0036] Specifically, during detection, for the first detection device, frequency drift of the first detection laser due to various factors such as temperature drift and time drift is considered. The second detection laser generates frequency drift. In addition, the first Doppler frequency shift generated by the first detection device detecting the object. Then the beat frequency of the first detection device is: ; Similarly, for the second detection device, consider the second Doppler frequency shift generated by the second detection device detecting the object. The beat frequency of the second detection device is: ; It is not difficult to observe the drift terms of the two detection devices. and With equal magnitudes and opposite signs, the two signals can be differentially or fitted using joint digital signal processing, which can effectively cancel out this pair of common-mode drift errors.

[0037] In this embodiment, the dual-frequency laser device includes a laser, an isolator, a laser beam splitter, a first frequency shifter, and a second frequency shifter. The laser is optically connected to the laser beam splitter via the isolator. The laser beam splitter splits the initial laser generated by the laser into a first laser beam and a second laser beam. The laser beam splitter is optically connected to the first frequency shifter and the second frequency shifter. The first laser beam is sent to the first frequency shifter, which shifts the frequency of the first laser beam to form a first probe laser. The second laser beam is sent to the second frequency shifter, which shifts the frequency of the second laser beam to form a second probe laser.

[0038] This embodiment uses two frequency shifters and a single laser source to generate two probe lasers. Compared with the dual-frequency light source scheme that uses two independent lasers, the system structure of this invention is more compact, more reliable, and avoids the need for expensive and complex hardware such as high-bandwidth mixers.

[0039] Please refer to Figure 2 In this embodiment, the first detection device includes a first circulator, a first coupler, and a first balanced detector, and the second detection device includes a second circulator, a second coupler, and a second balanced detector.

[0040] The first circulator is optically connected to the first detector beamsplitter, which uses the first signal light to generate the first scattered light. The first coupler is optically connected to the first circulator and the second detector beamsplitter, and the first coupler couples the first scattered light and the second reference light. The first balanced detector is optically connected to the first coupler, which converts the coupled first scattered light and the second reference light into the first detection signal.

[0041] The second circulator is optically connected to the second detector beamsplitter, which uses the second signal light to generate the second scattered light. The second coupler is optically connected to the second circulator and the first detector beamsplitter, and the second coupler couples the second scattered light and the first reference light. The second balanced detector is optically connected to the second coupler, which converts the coupled second scattered light and the first reference light into the second detection signal.

[0042] During detection, the light from the first beam splitter is sent to the first circulator and the second coupler, and the light from the second beam splitter is sent to the second circulator and the first coupler. The signal light from the first circulator and the second circulator converges at the measuring body. The signal light output from the first circulator is scattered and returns to the first coupler to mix with the second reference light. After mixing, it is converted into an electrical signal by the first balanced detector. Similarly, the signal light output from the second circulator is scattered and returns to the second coupler to mix with the first reference light. After mixing, it is converted into an electrical signal by the second balanced detector. Finally, the outputs of the first balanced detector and the second balanced detector are sent to the digital signal processing unit to calculate the speed.

[0043] Among them, the first detection device The first detection signal output at any time It should be: ; In the formula, This represents the amplitude of the first balanced detector. This indicates the random phase of the first detection device.

[0044] Second detection device The second detection signal output at time It should be: ; In the formula, This indicates the amplitude of the second balanced detector. This indicates the random phase of the second detection device.

[0045] Based on the first detection device and its output, the first Doppler frequency shift can be effectively extracted. Second Doppler frequency shift Then, the detection speed can be calculated.

[0046] In one alternative embodiment, the first detection device and the second detection device are arranged symmetrically.

[0047] Consider a case where the two devices are not axially symmetrically arranged, such as the detection angle of the first detection device. The detection angle of the second detection device is The relative angle between the two is .

[0048] Since the Doppler frequency shift and the detection velocity have a definite geometric relationship, in this case, the relationship between the first Doppler frequency shift and the detection velocity is: ; The relationship between the second Doppler frequency shift and the detection velocity is as follows: ; in, Indicates the detection speed. Indicates the laser wavelength.

[0049] Since the first and second detection devices are arranged symmetrically, when the speed measuring system is directly facing the object being detected, the detection angles of the first and second detection devices are the same. In this embodiment, the detection angles of the first and second detection devices are set to be the same. .

[0050] Then the first Doppler frequency shift Second Doppler frequency shift They should be equal for calculating the Doppler frequency shift. : ; This approach can effectively simplify the calculation process and improve the detection speed.

[0051] Please refer to Figure 3 According to an embodiment of the present invention, a laser Doppler velocimetry method is provided that can be used in the above-mentioned laser Doppler velocimetry system. The method includes: S201. The signal processing device obtains a first Doppler frequency shift based on the first detection signal and a second Doppler frequency shift based on the second detection signal; S202, The signal processing device calculates the detection velocity based on the first Doppler frequency shift and the second Doppler frequency shift.

[0052] Since the Doppler frequency shift and the detection velocity have a definite geometric relationship, the relationship between the first Doppler frequency shift and the detection velocity is as follows: ; The relationship between the second Doppler frequency shift and the detection velocity is as follows: ; The detection velocity is obtained by combining the relationships between the first Doppler frequency shift and the detection velocity, and the relationships between the second Doppler frequency shift and the detection velocity.

[0053] In one optional embodiment, the signal processing device acquires a first Doppler frequency shift based on a first detection signal and acquires a second Doppler frequency shift based on a second detection signal, specifically including: The signal processing device performs digital quadrature demodulation and frequency discrimination on the first detection signal to extract the first instantaneous frequency; The signal processing device performs digital quadrature demodulation and frequency discrimination on the second detection signal to extract the second instantaneous frequency; The signal processing device extracts the first Doppler frequency shift based on the first instantaneous frequency and extracts the second Doppler frequency shift based on the second instantaneous frequency.

[0054] First detection device The first detection signal output at any time for: ; Second detection device The second detection signal output at time for: ; The signal processing device processes the first detection signal. Second detection signal Synchronous acquisition is performed, and the first instantaneous frequency is extracted through digital quadrature demodulation and frequency discrimination. Second instantaneous frequency : ; ; The signal processing device uses the first instantaneous frequency Second instantaneous frequency The first and second Doppler frequency shifts can be obtained, and thus the detection velocity can be obtained.

[0055] In this embodiment, digital quadrature demodulation is specifically performed using the Hilbert method.

[0056] In one optional embodiment, the signal processing device calculates the detection velocity based on a joint solution of a first Doppler frequency shift and a second Doppler frequency shift, including: The signal processing device calculates the angle of the detection velocity based on the first Doppler frequency shift and the second Doppler frequency shift; The signal processing device calculates the absolute value of the detection velocity based on the first Doppler frequency shift and the second Doppler frequency shift.

[0057] Since the Doppler frequency shift and the detection velocity have a definite geometric relationship, the relationship between the first Doppler frequency shift and the detection velocity is as follows: ; The relationship between the second Doppler frequency shift and the detection velocity is as follows: ; It can be seen that the magnitude and direction of the detection velocity are uncertain, but other parameters are known. Therefore, the direction and magnitude of the detection velocity can be obtained by solving the above equations simultaneously, providing richer motion information than single-point velocity measurement.

[0058] In one optional embodiment, the signal processing device calculates the angle of the detection velocity based on the first Doppler frequency shift and the second Doppler frequency shift, specifically including: The signal processing device determines the direction angle of the detection velocity based on the geometric relationship between the first and second detection devices, and the absolute values ​​of the first and second Doppler frequency shifts.

[0059] In this embodiment, by analyzing the two Doppler frequency shift information with known spatial angles, the magnitude and direction of the target velocity in the measurement plane can be calculated.

[0060] In an optional embodiment, the signal processing device determines the direction angle of the detection velocity based on the geometric relationship between the first and second detection devices and the absolute values ​​of the first and second Doppler frequency shifts, and then further includes: The signal processing device compares the first instantaneous frequency and the second instantaneous frequency. If the first instantaneous frequency is greater than the second instantaneous frequency, it determines that the direction of the detection speed is along the direction angle approaching the speed measuring system. If the first instantaneous frequency is less than the second instantaneous frequency, then the direction of the detected velocity is determined to be away from the velocity measuring system along the direction angle.

[0061] Specifically, in traditional heterodyne laser velocimetry systems, a heterodyne system based on a single acousto-optic frequency shifter splits a laser beam into two paths, introducing a fixed frequency shift only into one of the paths using a single acousto-optic frequency shifter. While this method is relatively simple in structure, it inherently suffers from velocity direction ambiguity. When the target's reverse motion is too fast, causing the absolute value of the Doppler frequency shift to exceed the frequency shift of the acousto-optic frequency shifter, the system's output frequency will "fold," making it impossible to distinguish between high-speed forward and reverse motion, thus severely limiting the velocimetry range.

[0062] In this invention, unambiguous direction discrimination can be achieved by comparing the first Doppler frequency shift and the second Doppler frequency shift. Specifically, the comparison... and You can know Sign (direction of velocity). If ,but If the object being detected is close to the detection device, then it is close to the detection device; otherwise, it is close to the detection device. ,but If the detected object is far away from the detection device, it means that the detected object is far away from the detection device.

[0063] Its direction determination is not affected by the target's speed.

[0064] In an optional embodiment, the absolute value of the detection velocity is calculated based on the first Doppler frequency shift and the second Doppler frequency shift, specifically including: The absolute value of the detection velocity is obtained by jointly calculating the first and second Doppler frequency shifts.

[0065] Based on the definite geometric relationship between Doppler frequency shift and detection velocity, the absolute value of the detection velocity can be determined by combining the first Doppler frequency shift and the second Doppler frequency shift.

[0066] In an optional embodiment, the signal processing device extracts the first Doppler frequency shift based on the first instantaneous frequency and extracts the second Doppler frequency shift based on the second instantaneous frequency, specifically including: Based on the first instantaneous frequency, extract the first Doppler frequency shift set; Based on the second instantaneous frequency, extract the second Doppler frequency shift set; Obtain the first Doppler frequency shift set and the second Doppler frequency shift set, and perform defuzzification calculation to obtain the first Doppler frequency shift and the second Doppler frequency shift.

[0067] Traditional single-channel systems Speed ​​ambiguity occurs immediately; in this invention, even if... Much larger ,lead to or Even if the values ​​are numerically close or even identical due to periodicity, the system can uniquely determine the true value by analyzing the phase relationship between the two signals or by using their symmetry for unenvelopment processing. value.

[0068] For example, when At a frequency of 200 MHz, with detection velocities of +50 m / s and -250 m / s, a forward frequency shift of 100 MHz and a reverse frequency shift of 500 MHz were obtained. Since both are 300M, the direction and magnitude of the velocity cannot be distinguished at this point. Regarding the dual-channel system in this embodiment: For the first detection device, if the velocity is +50 m / s and its positive component is 100 M, then The value is 300M. At this point, for the second detection device, its positive component is 200M. Similarly, for -250m / s, its reverse component is 500M, then It is 300M, but .

[0069] In this embodiment, by performing defuzzification operations, the unfuzzy velocity measurement range is theoretically increased to be limited only by the detector bandwidth and processing algorithm.

[0070] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A laser Doppler velocimetry system, characterized in that, The system includes: A dual-frequency laser device is used to generate a first and a second probe laser with different frequencies. The first detection beam splitter is optically connected to the dual-frequency laser device and is used to split the first detection laser into a first signal light and a first reference light. The second detection beam splitter is optically connected to the dual-frequency laser device and is used to split the second detection laser into a second signal light and a second reference light. The first detection device is optically connected to the first detection beam splitter and the second detection beam splitter, respectively, and is used to generate a first detection signal by detecting an object with a first signal light and a second reference light. The second detection device is optically connected to the first detection beam splitter and the second detection beam splitter respectively, and is used to generate a second detection signal by detecting the object with the second signal light and the first reference light. A signal processing device, connected to the first detection device and the second detection device, is used to obtain a first Doppler frequency shift based on the first detection signal, obtain a second Doppler frequency shift based on the second detection signal, and calculate the detection speed based on the first Doppler frequency shift and the second Doppler frequency shift.

2. The system according to claim 1, characterized in that, The dual-frequency laser device includes: A laser, used to generate the initial laser beam; A laser beam splitter, optically connected to the laser, is used to split the initial laser into a first laser beam and a second laser beam. A first frequency shifter is optically connected to the laser beam splitter and is used to shift the frequency of the first split laser to form the first probe laser. The second frequency shifter is optically connected to the laser beam splitter and is used to shift the frequency of the second split laser to form the second probe laser.

3. The system according to claim 1 or 2, characterized in that, The first detection device includes: A first circulator, optically connected to the first detection beam splitter, is used to generate first scattered light by detecting with the first signal light; A first coupler, optically connecting the first circulator and the second probe beam splitter, is used to couple the first scattered light and the second reference light; A first balanced detector, optically connected to the first coupler, is used to convert the coupled first scattered light and the second reference light into the first detection signal; The second detection device includes: The second circulator, optically connected to the second detection beam splitter, is used to generate second scattered light by detecting with the second signal light; The second coupler, which optically connects the second circulator and the first probe beam splitter, is used to couple the second scattered light and the first reference light. The second balanced detector is optically connected to the second coupler and is used to convert the coupled second scattered light and the first reference light into the second detection signal.

4. The system according to claim 1, characterized in that, The first detection device and the second detection device are arranged axially symmetrically.

5. A laser Doppler velocimetry method, characterized in that, The method, applied to the system of any one of claims 1 to 4, comprises: The signal processing device acquires a first Doppler frequency shift based on a first detection signal and acquires a second Doppler frequency shift based on a second detection signal; The signal processing device calculates the detection velocity based on the first Doppler frequency shift and the second Doppler frequency shift.

6. The method according to claim 5, characterized in that, The signal processing device acquires a first Doppler frequency shift based on a first detection signal and a second Doppler frequency shift based on a second detection signal, specifically including: The signal processing device performs digital quadrature demodulation and frequency discrimination on the first detection signal to extract the first instantaneous frequency; The signal processing device performs digital quadrature demodulation and frequency discrimination on the second detection signal to extract the second instantaneous frequency; The signal processing device extracts the first Doppler frequency shift based on the first instantaneous frequency and extracts the second Doppler frequency shift based on the second instantaneous frequency.

7. The method according to claim 5 or 6, characterized in that, The signal processing device calculates the detection velocity based on the joint solution of the first Doppler frequency shift and the second Doppler frequency shift, including: The signal processing device calculates the angle of the detection velocity based on the first Doppler frequency shift and the second Doppler frequency shift; The signal processing device calculates the absolute value of the detection velocity based on the first Doppler frequency shift and the second Doppler frequency shift.

8. The method according to claim 7, characterized in that, The signal processing device calculates the angle of the detection velocity based on the first Doppler frequency shift and the second Doppler frequency shift, specifically including: The signal processing device determines the direction angle of the detection velocity based on the geometric relationship between the first and second detection devices, and the absolute values ​​of the first and second Doppler frequency shifts.

9. The method according to claim 8, characterized in that, The signal processing device determines the direction angle of the detection velocity based on the geometric relationship between the first and second detection devices, and the absolute values ​​of the first and second Doppler frequency shifts, and then further includes: The signal processing device compares the first instantaneous frequency and the second instantaneous frequency. If the first instantaneous frequency is greater than the second instantaneous frequency, it determines that the direction of the detected velocity is approaching the speed measuring system along the direction angle. If the first instantaneous frequency is less than the second instantaneous frequency, then the direction of the detected velocity is determined to be away from the velocity measuring system along the direction angle.

10. The method according to claim 6, characterized in that, The signal processing device extracts the first Doppler frequency shift based on the first instantaneous frequency and extracts the second Doppler frequency shift based on the second instantaneous frequency, specifically including: Based on the first instantaneous frequency, extract the first Doppler frequency shift set; Based on the second instantaneous frequency, extract the second Doppler frequency shift set; Obtain the first Doppler frequency shift set and the second Doppler frequency shift set, and perform defuzzification calculation to obtain the first Doppler frequency shift and the second Doppler frequency shift.

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