Laser Doppler velocity measurement device and velocity measurement method based on multi-core optical fiber and vortex light field

Abstract

The invention provides a laser Doppler velocity measurement device based on a multi-core optical fiber and a vortex light field, and belongs to the technical field of vortex light field velocity measurement. The system comprises a laser, an optical splitter, a phase modulator, a multi-core optical fiber fan-in and fan-out device, a multi-core optical fiber, a gradient refractive index lens, an optical beam splitter, a photoelectric detector, an analog-to-digital converter, an upper computer, a controller and a driving circuit, the optical path design is simplified, direct generation of vortex light is achieved through the multi-core optical fiber, the optical path design is simplified, and the power consumption is reduced. The Doppler probe is formed by the gradient refractive index lens and the multi-core optical fiber, the light beam focusing characteristic is optimized, the quality of a vortex light field is ensured, meanwhile, the flexibility of a system is improved, the advantages of being compact in structure, high in integration level and high in precision are achieved, a stable vortex field can be formed at the position with the short emitting distance, and the requirement for the working environment is lowered. And a more efficient solution is provided for measuring the speed of the compound motion.

Description

Technical Field

[0001] This invention relates to the field of optical velocimetry, and in particular to a laser Doppler velocimetry device and method based on multi-core optical fiber and vortex optical field. Background Technology

[0002] Laser Doppler Velocimetry (LDV) is a non-contact flow velocity measurement method based on the Doppler effect, widely used in fluid mechanics, biomedicine, and industrial process monitoring. Traditional LDV systems calculate velocity by detecting the laser frequency shift caused by scattering particles, but they are mainly limited to measuring a single velocity and cannot simultaneously measure translational and angular velocities.

[0003] In recent years, vortex light fields have offered new insights into composite motion velocimetry due to their ability to carry orbital angular momentum. The helical wavefront structure and phase gradient of vortex light can enhance sensitivity to particle axial motion. However, the generation of vortex light in existing technologies typically relies on complex optical devices, such as spatial light modulators or helical phase plates. These methods are not only highly complex but also susceptible to damage under high-power environments. For example, spatial light modulators rely on liquid crystal cells to control the wavefront phase; at milliwatt-level laser power, the liquid crystal layer may fail due to thermal effects. Furthermore, they require more than ten discrete optical components, such as polarization controllers and beam expanders, resulting in a large system size and low calibration tolerance. While helical phase plates avoid the complexity of electronic control, minute depth errors in the etching process can significantly reduce the purity of orbital angular momentum, and the fixed phase structure cannot dynamically adapt to different measurement scenarios. In addition, although multi-beam interferometry can generate vortex light, it requires sub-micron level displacement precision to control the beam spacing and micro-radian level tilt angle. Environmental temperature drift or mechanical vibration will directly disrupt the phase matching conditions, leading to vortex nucleus distortion or even topological charge reversal, resulting in poor system stability. Summary of the Invention

[0004] In view of this, the present invention provides a laser Doppler velocimetry device and method based on multi-core optical fiber and vortex optical field. The vortex optical field is directly generated by multi-core optical fiber, simplifying the optical path design. A Doppler probe is formed by a gradient refractive index lens and multi-core optical fiber, optimizing the beam focusing characteristics. This ensures the quality of the vortex optical field while improving the system's flexibility. It has the advantages of compact structure, high integration, and high precision. It can form a stable vortex field at a relatively short emission distance, reducing the requirements for the working environment and providing a more efficient solution for measuring the speed of composite motion.

[0005] The technical solution adopted by the embodiments of the present invention to solve its technical problem is as follows:

[0006] A laser Doppler velocimetry device based on multi-core optical fiber and vortex optical field includes: a laser (1), an optical splitter (2), a set of phase modulators, a multi-core optical fiber fan-in fan-out unit (6), a multi-core optical fiber (7), a gradient refractive index lens (8), and an optical beam splitter (9) connected in sequence by optical fibers along the optical path; a first photodetector (10), a first analog-to-digital converter (12), and a host computer (13) connected in sequence by electrical connection; and a second photodetector (11), a second analog-to-digital converter (14), a controller (15), a digital-to-analog converter (16), and a driving circuit (17) connected in sequence by electrical connection.

[0007] The laser emitted by the laser (1) is split by the optical splitter (2) and enters N sets of phase modulators for phase modulation. The adjusted beam enters each core of the multi-core fiber (7) through the multi-core fiber fan-in fan-out device (6) for positioning and emission. After being focused by the gradient refractive index lens (8), the beams of probe light are split into two directions by the optical beam splitter (9). The probe light facing the probe area is used for measurement. The particles (18) generate scattered light after passing through the vortex light field formed in the probe area. The scattered light after the frequency change enters the coupling lens of the first photodetector (10). The frequency information of the beam is converted by the first analog-to-digital converter (12) and transmitted to the host computer (13).

[0008] The probe light facing the non-detection area enters the coupling lens of the second photodetector (11). The phase information of the beam is converted into a digital signal by the second analog-to-digital converter (14) and then transmitted to the controller (15). The controller (15) performs phase-locked control and randomly transmits a set of crosstalk signal factors. The crosstalk signal factors are converted into analog voltage signals by the digital-to-analog converter (16) and then enter the driving circuit (17). The driving circuit (17) controls the phase modulator to perform phase compensation according to the received analog voltage signal. The compensated beam enters the optical path for measurement and compensation control, and iterative optimization is performed until the beam is in phase.

[0009] The velocity of particle (18) passing through the vortex light field is calculated as follows: The host computer (13) performs spectrum analysis on the digital signal, selects the vortex light ring on the plane where the focus center is located, and calculates the angular velocity, transverse velocity component and longitudinal velocity component of particle (18) based on the radial distance, topological charge, and Doppler frequency shift of the vortex light ring.

[0010] Preferably, the phase-locked loop control process performed by the controller (15) is as follows: each time the controller (15) controls the drive circuit (17) to randomly transmit a set of crosstalk signal factors to each phase modulator for compensation, so that each beam of light is in phase.

[0011] Preferably, the phase-locked control process of the controller (15) includes: the controller (15) transmits a set of voltage signals with the same length as the number of phase modulators to the drive circuit, and the drive circuit controls each phase modulator to perform phase compensation according to the voltage signals, so that the beam is phase compensated; the photodetector (11) detects the superimposed beam after phase compensation and outputs the illumination intensity information of the superimposed beam to the controller (15); the controller (15) analyzes the influence of the previous adjustment on the illumination intensity according to the historical illumination intensity information, and adjusts the voltage signal used for phase compensation next time with the goal of increasing the illumination intensity, and continues the iterative process until the illumination intensity reaches the maximum value, which represents that the beam is in phase and forms a stable vortex light field with multiple topological nuclei at the output end.

[0012] Preferably, the number of phase modulators is not less than 3, and the fiber cores used for transmitting laser in the multi-core fiber (7) form a single equilateral triangle structure or multiple equilateral triangle structures of different sizes. The outgoing light in phase is coherently superimposed to form a vortex light field with multiple topological cores.

[0013] Preferably, the multi-core optical fiber (5) and the gradient refractive index lens (6) are connected by fusion splicing to form a Doppler probe.

[0014] Preferably, the laser Doppler velocimetry device includes a first phase modulator (3), a second phase modulator (4), and a third phase modulator (5); the three modulated beams are positioned and emitted from the three cores (7-4), (7-5), and (7-6) of the multi-core fiber (7) which are in an equilateral triangular structure, and are focused at the focusing center (0,0) by the gradient refractive index lens (8); the host computer (13) calculates the velocity of the particle (18) passing through the vortex light field as follows:

[0015] Selecting vortex rings A(0,a), B(a,0), and C(0,-a) with the same radial distance a, the Doppler frequency shifts of vortex rings A, B, and C are obtained through spectral analysis of digital signals. , , angular velocity of particle (18) lateral velocity component along the x-axis longitudinal velocity component along the y-axis The calculation formula is:

[0016] ;

[0017] ;

[0018] ;

[0019] In the formula, L represents the topological load size.

[0020] A second aspect of this invention provides a laser Doppler velocimetry method based on multi-core optical fiber and vortex optical field, comprising the following steps:

[0021] Step S1: Start the laser Doppler velocimetry device and start the controller to perform phase-locked control. The controller randomly transmits a set of crosstalk signal factors and inputs them into each phase modulator for compensation, so that each beam of light is in phase and forms a stable vortex light field with multiple topological nuclei at the output end.

[0022] In step S2, the particle passes through the vortex light rings at different positions in the vortex light field, and the first photodetector converts the frequency shift information of each vortex light ring into a digital signal and transmits it to the host computer.

[0023] Step S3, the host computer (13) performs spectrum analysis on the digital signal and calculates the particle's angular velocity, transverse velocity component and longitudinal velocity component based on the radial distance, topological charge size and Doppler frequency shift of the vortex ring.

[0024] Preferably, the phase-locked loop control process includes: the controller transmitting a set of voltage signals with the same length as the number of phase modulators to the drive circuit; the drive circuit controlling each phase modulator to perform phase compensation according to the voltage signals, so that the beam is phase compensated; the photodetector detecting the superimposed beam after phase compensation, and outputting the illumination intensity information of the superimposed beam to the controller; the controller analyzing the impact of the previous adjustment on the illumination intensity based on the historical illumination intensity information, and adjusting the voltage signal used for the next phase compensation with the goal of increasing the illumination intensity, and continuing the iterative process until the illumination intensity reaches a maximum value, representing that the beam is in phase, and forming a stable vortex light field with multiple topological nuclei at the emission end.

[0025] Preferably, the laser Doppler velocimetry device includes a first phase modulator, a second phase modulator, and a third phase modulator; the three modulated beams are positioned and emitted from three fiber cores in a multi-core optical fiber with an equilateral triangular structure, and focused at the focal center (0,0) by a gradient refractive index lens; the host computer calculates the velocity of the particle passing through the vortex light field as follows:

[0026] Selecting vortex rings A(0,a), B(a,0), and C(0,-a) with the same radial distance a, the Doppler frequency shifts of vortex rings A, B, and C are obtained through spectral analysis of digital signals. , , angular velocity of particle (18) lateral velocity component along the x-axis longitudinal velocity component along the y-axis The calculation formula is:

[0027] ;

[0028] ;

[0029] ;

[0030] In the formula, L represents the topological load size.

[0031] As can be seen from the above technical solution, the laser Doppler velocimetry device and method based on multi-core optical fiber and vortex optical field provided by the embodiments of the present invention consists of a laser, an optical splitter, a phase modulator, a multi-core optical fiber fan-in / fan-out unit, a multi-core optical fiber, a gradient refractive index lens, an optical beam splitter, a photodetector, an analog-to-digital converter, a host computer, a controller, and a drive circuit. This simplifies the optical path design and achieves direct generation of vortex light through multi-core optical fiber, ensuring the quality of the vortex optical field while improving the system's flexibility. Compared with existing technologies, this solution significantly improves the system's reliability, practicality, and flexibility while being able to measure translational velocity and angular velocity, providing a more efficient solution for measuring the velocity of composite motion. This invention is based on the propagation effects of radio wave technology (such as the Doppler effect) for velocity measurement, belonging to the category of radio wave velocimetry. The solution has the advantages of compact structure, high integration, and high precision, and can form a stable vortex field at a relatively short emission distance, greatly reducing the requirements for the working environment and the complexity of experimental setup. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the laser Doppler velocimetry device based on multi-core optical fiber and vortex optical field of the present invention.

[0033] Figure 2 This is a schematic diagram of the vortex optical field structure and the phase of the vortex optical field.

[0034] Figure 3 This is a schematic diagram of the end face of a multi-core optical fiber.

[0035] Figure 4 This is a flowchart of the laser Doppler measurement method based on multi-core optical fiber and vortex optical field of the present invention.

[0036] Figure 1In Figure (2): Laser (1), Optical splitter (2), First phase modulator (3), Second phase modulator (4), Third phase modulator (5), Multi-core fiber fan-in fan-out (6), Multi-core fiber (7), Gradient refractive index lens (8), Optical beam splitter (9), First photodetector (coupled lens) (10), Second photodetector (coupled lens) (11), First analog-to-digital converter (12), Host computer (13), Second analog-to-digital converter (14), Controller (15), Digital-to-analog converter (16), Drive circuit (17), Particle (18); In Figure (2): Multi-core fiber protective shell (7-1), Multi-core fiber coating (7-2), Multi-core fiber cladding (7-3), Multi-core fiber core (7-4), Multi-core fiber core (7-5), Multi-core fiber core (7-6). Detailed Implementation

[0037] The technical solution and effects of the present invention will be further described in detail below with reference to the accompanying drawings.

[0038] This invention proposes a laser Doppler velocimetry device and method based on multi-core optical fiber and vortex optical field. It achieves direct generation of vortex light through multi-core optical fiber, eliminating the need for complex external modulation devices. (Reference) Figure 1 As shown, the laser Doppler velocimetry device based on multi-core optical fiber and vortex optical field of the present invention includes:

[0039] The laser (1), optical splitter (2), a set of phase modulators, multi-core fiber fan-in fan-out unit (6), multi-core fiber (7), gradient refractive index lens (8), and optical beam splitter (9) are connected in sequence according to the optical path. The multi-core fiber (5) and gradient refractive index lens (6) are connected by fusion splicing technology to form a Doppler probe. The first photodetector (coupled lens) (10), the first analog-to-digital converter (12), and the host computer (13) are connected in sequence. The second photodetector (coupled lens) (11), the second analog-to-digital converter (14), the controller (15), the digital-to-analog converter (16), and the drive circuit (17) are connected in sequence.

[0040] The laser emitted by the laser (1) is split by the optical splitter (2) and enters N sets of phase modulators for phase modulation. The adjusted beam enters each core of the multi-core fiber (7) through the multi-core fiber fan-in fan-out device (6) for positioning and emission. After being focused by the gradient refractive index lens (8), the beams of probe light are split into two directions by the optical beam splitter (9). The probe light facing the probe area is used for measurement. The particles (18) generate scattered light after passing through the vortex light field formed in the probe area. The scattered light after the frequency change enters the coupling lens of the first photodetector (10). The frequency information of the beam is converted by the first analog-to-digital converter (12) and transmitted to the host computer (13).

[0041] The probe light facing the non-detection area enters the coupling lens of the second photodetector (11). The phase information of the beam is converted into a digital signal by the second analog-to-digital converter (14) and then transmitted to the controller (15). The controller (15) performs phase-locked control and randomly transmits a set of crosstalk signal factors. The crosstalk signal factors are converted into analog voltage signals by the digital-to-analog converter (16) and then enter the driving circuit (17). The driving circuit (17) controls the phase modulator to perform phase compensation according to the received analog voltage signal. The compensated beam enters the optical path for measurement and compensation control, and iterative optimization is performed until the beam is in phase.

[0042] The velocity of particle (18) passing through the vortex light field is calculated as follows: The host computer (13) performs spectrum analysis on the digital signal, selects the vortex light ring on the plane where the focus center is located, and calculates the angular velocity, transverse velocity component and longitudinal velocity component of particle (18) based on the radial distance, topological charge, and Doppler frequency shift of the vortex light ring.

[0043] In order to coherently superimpose and form a vortex optical field with multiple vortex rings, the number of phase modulators in the device is not less than 3. The fiber cores used to transmit lasers in the multi-core fiber (7) should form a single equilateral triangle structure or multiple equilateral triangle structures of different sizes. The outgoing light in phase is coherently superimposed to form a vortex optical field with multiple topological nuclei. Figure 1 The paper provides a specific scheme in which the laser emitted by the laser (1) is split into three equal paths by the optical splitter (2). The three equally split beams enter the first phase modulator (3), the second phase modulator (4), and the third phase modulator (5) respectively for phase modulation. Then, the beam after initial adjustment enters the cores (7-4), (7-5), and (7-6) of the multi-core fiber (7) through the fan-in fan-out ... x V y and angular velocity V w After the particles (18) pass through the vortex light field formed by the detection area, they will generate scattered light. The frequency of the scattered light will change. The changed light enters the first photodetector (10) of the coupling lens, and then the frequency information of the beam is converted by the first analog-to-digital converter (12) and transmitted to the host computer (13) for velocity calculation.

[0044] The other part of the probe light after beam splitting enters the second photodetector (11) of the coupling lens. The second photodetector (11) extracts the phase information of the outgoing beam, and then converts it into a digital signal through the second analog-to-digital converter (14) and transmits it to the controller (15). The controller (15) performs phase-locked operation. The phase-locked control process of the controller (15) is as follows: the controller (15) controls the drive circuit (17) to randomly transmit a set of crosstalk signal factors to each phase modulator for compensation, so that each beam of light is in phase. The specific implementation process is as follows: the controller (15) transmits a set of voltage signals with the same length as the number of phase modulators to the drive circuit (for example, transmitting three independent crosstalk signal factors of +1 or -1). The signal factors are converted into analog voltage signals by the digital-to-analog converter (16) and then enter the drive circuit (17). The drive circuit controls the phase modulators (3), (4), and (5) to perform phase compensation according to the received analog voltage signals, so that the beam is phase compensated. The compensated beam then propagates to the second photodetector (11) of the coupling lens as described above. The photodetector (11) detects the superimposed beam after phase compensation. The output superimposed beam's illumination intensity information is sent to the controller (15). The controller (15) analyzes the impact of the previous adjustment on the illumination intensity based on the historical illumination intensity information. It adjusts the voltage signal used for phase compensation next time with the goal of increasing the illumination intensity (specifically, it can be that each variable is adjusted one by one, and the illumination intensity of the three superimposed beams is the highest. If the illumination intensity is weakened after transmitting +1 voltage information to one of the phase modulators, then -1 voltage signal is transmitted to it next time). The process continues iterating until the illumination intensity reaches a maximum value, which means that the beams are in phase and a stable vortex light field with multiple topological nuclei is formed at the output end.

[0045] The laser Doppler velocimetry device includes a first phase modulator (3), a second phase modulator (4), and a third phase modulator (5); the three modulated beams are positioned and emitted from three cores (7-4), (7-5), and (7-6) of a multi-core fiber (7) that are in an equilateral triangular structure, and are focused at the focal center (0,0) by a gradient refractive index lens (8); the host computer (13) calculates the velocity of the particle (18) passing through the vortex light field as follows:

[0046] Selecting vortex rings A(0,a), B(a,0), and C(0,-a) with the same radial distance a, the Doppler frequency shifts of vortex rings A, B, and C are obtained through spectral analysis of digital signals. , , angular velocity of particle (18) lateral velocity component along the x-axis longitudinal velocity component along the y-axis The calculation formula is:

[0047] (1)

[0048] (2)

[0049] (3)

[0050] In the formula, L represents the topological load size.

[0051] like Figure 2 As shown, the vortex light field is composed of multiple vortex beams. The wavefront of each vortex beam has a phase singularity at its center, resulting in zero light intensity at the center. Therefore, the intensity distribution of the vortex beam is ring-shaped, with zero intensity at the center, forming a hollow ring. The phase structure of the vortex beam is spirally distributed; the phase of the vortex beam changes L times per revolution around the center. .

[0052] Figure 3 The fiber core selection shown is one feasible embodiment. Further, the measurement of this device can be performed with more fiber cores, but the selected fiber cores must be three or more and must be able to form an equilateral triangle. Alternatively, multiple equilateral triangles can be stacked together.

[0053] based on Figure 1 The laser Doppler velocimetry device shown in the invention provides a laser Doppler velocimetry method based on multi-core optical fiber and vortex optical field, the steps of which include:

[0054] Step S1: Start the laser Doppler velocimetry device and start the controller to perform phase-locked control. The controller randomly transmits a set of crosstalk signal factors and inputs them into each phase modulator for compensation, so that each beam of light is in phase and forms a stable vortex light field with multiple topological nuclei at the output end.

[0055] In step S2, the particle passes through the vortex light rings at different positions in the vortex light field, and the first photodetector converts the frequency shift information of each vortex light ring into a digital signal and transmits it to the host computer.

[0056] Step S3, the host computer (13) performs spectrum analysis on the digital signal and calculates the particle's angular velocity, transverse velocity component and longitudinal velocity component based on the radial distance, topological charge size and Doppler frequency shift of the vortex ring.

[0057] The phase-locked loop (PLL) control process includes: the controller transmits a set of voltage signals with the same length as the number of phase modulators to the drive circuit; the drive circuit controls each phase modulator to perform phase compensation according to the voltage signals, so that the beam is phase compensated; the photodetector detects the superimposed beam after phase compensation and outputs the illumination intensity information of the superimposed beam to the controller; the controller analyzes the impact of the previous adjustment on the illumination intensity based on the historical illumination intensity information, and adjusts the voltage signal used for the next phase compensation with the goal of increasing the illumination intensity. This iterative process continues until the illumination intensity reaches a maximum value, which represents that the beam is in phase and forms a stable vortex light field with multiple topological nuclei at the emission end.

[0058] As an optional implementation, the laser Doppler velocimetry device includes a first phase modulator, a second phase modulator, and a third phase modulator; the three modulated beams are positioned and emitted from three fiber cores in a multi-core optical fiber with an equilateral triangular structure, and focused at the focal center (0,0) by a gradient refractive index lens; the host computer calculates the velocity of the particle passing through the vortex light field as follows:

[0059] Selecting vortex rings A(0,a), B(a,0), and C(0,-a) with the same radial distance a, the Doppler frequency shifts of vortex rings A, B, and C are obtained through spectral analysis of digital signals. , , (For the specific implementation process of obtaining the Doppler frequency shift through spectral analysis, please refer to existing technologies.) Angular velocity of particle (18) lateral velocity component along the x-axis longitudinal velocity component along the y-axis The calculation formula is:

[0060] ;

[0061] ;

[0062] ;

[0063] In the formula, L represents the topological load size.

[0064] This invention proposes a laser Doppler velocimetry device based on multi-core optical fiber and vortex optical field, employing multi-core optical fiber, vortex optical field, and active phase modulation technology. Compared to the traditional method of combining multiple independent LDV systems, this scheme highlights its advantages: First, by utilizing the parallel transmission characteristics of multi-core optical fibers, and dynamically compensating for optical path differences through a phase modulator and feedback phase-locked loop algorithm, it ensures that multiple beams are strictly in phase, automatically forming a stable vortex optical field at the probe end. This eliminates the need for complex optical path alignment, significantly improving system stability and anti-interference capabilities. Second, by fusing multi-core optical fiber and a gradient refractive index lens into a single miniature probe, it achieves a high degree of integration of beam emission, focusing, and scattered light collection. The compact structure and small size greatly reduce the requirements for the working environment and the complexity of assembly and adjustment, making it suitable for transient measurement of single-point composite motion velocities in space-constrained scenarios. Third, by using the orbital angular momentum and topological kernel structure of the vortex optical field, it simultaneously analyzes the particle angular velocity and linear velocity, achieving simultaneous measurement of multiple velocity vectors at a single point with high time resolution, overcoming the fundamental limitation of traditional schemes that cannot acquire composite motion velocity information in real time.

[0065] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the above-described embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A laser Doppler velocimetry device based on multi-core optical fiber and vortex optical field, characterized in that, include: The laser (1), optical splitter (2), a set of phase modulators, multi-core fiber fan-in fan-out unit (6), multi-core fiber (7), gradient refractive index lens (8), and optical beam splitter (9) are connected in sequence according to the optical path. The first photodetector (10), the first analog-to-digital converter (12), and the host computer (13) are connected in sequence. The second photodetector (11), the second analog-to-digital converter (14), the controller (15), the digital-to-analog converter (16), and the driving circuit (17) are connected in sequence according to the optical path. The laser emitted by the laser (1) is split by the optical splitter (2) and enters N sets of phase modulators for phase modulation. The adjusted beam enters each core of the multi-core fiber (7) through the multi-core fiber fan-in fan-out device (6) for positioning and emission. After being focused by the gradient refractive index lens (8), the beams of probe light are split into two directions by the optical beam splitter (9). The probe light facing the probe area is used for measurement. The particles (18) generate scattered light after passing through the vortex light field formed in the probe area. The scattered light after the frequency change enters the coupling lens of the first photodetector (10). The frequency information of the beam is converted by the first analog-to-digital converter (12) and transmitted to the host computer (13). The probe light facing the non-detection area enters the coupling lens of the second photodetector (11). The phase information of the beam is converted into a digital signal by the second analog-to-digital converter (14) and then transmitted to the controller (15). The controller (15) performs phase-locked control and randomly transmits a set of crosstalk signal factors. The crosstalk signal factors are converted into analog voltage signals by the digital-to-analog converter (16) and then enter the driving circuit (17). The driving circuit (17) controls the phase modulator to perform phase compensation according to the received analog voltage signal. The compensated beam enters the optical path for measurement and compensation control, and iterative optimization is performed until the beam is in phase. The velocity of particle (18) passing through the vortex light field is calculated as follows: The host computer (13) performs spectrum analysis on the digital signal, selects the vortex light ring on the plane where the focus center is located, and calculates the angular velocity, transverse velocity component and longitudinal velocity component of particle (18) based on the radial distance, topological charge, and Doppler frequency shift of the vortex light ring.

2. The laser Doppler velocimetry device based on multi-core optical fiber and vortex optical field as described in claim 1, characterized in that, The phase-locked control process of the controller (15) is as follows: each time the controller (15) controls the drive circuit (17) to randomly transmit a set of crosstalk signal factors to each phase modulator for compensation, so that each beam of light is in phase.

3. The laser Doppler velocimetry device based on multi-core optical fiber and vortex optical field as described in claim 2, characterized in that, The phase-locked control process of the controller (15) includes: the controller (15) transmits a set of voltage signals with the same length as the number of phase modulators to the drive circuit. The drive circuit controls each phase modulator to perform phase compensation according to the voltage signal, so that the beam is phase compensated. The first photodetector (11) detects the superimposed beam after phase compensation and outputs the illumination intensity information of the superimposed beam to the controller (15). The controller (15) analyzes the influence of the previous adjustment on the illumination intensity according to the historical illumination intensity information, and adjusts the voltage signal used for phase compensation next time with the goal of increasing the illumination intensity. The process continues iterating until the illumination intensity reaches the maximum value, which represents that the beam is in phase and forms a stable vortex light field with multiple topological nuclei at the output end.

4. The laser Doppler velocimetry device based on multi-core optical fiber and vortex optical field as described in claim 3, characterized in that, The number of phase modulators is not less than 3. In the multi-core fiber (7), the fiber cores used to transmit lasers form a single equilateral triangle structure or multiple equilateral triangle structures of different sizes. The outgoing light in phase is coherently superimposed to form a vortex light field with multiple topological nuclei.

5. The laser Doppler velocimetry device based on multi-core optical fiber and vortex optical field as described in claim 4, characterized in that, The multi-core optical fiber (5) and the gradient refractive index lens (6) are connected by fusion splicing to form a Doppler probe.

6. The laser Doppler velocimetry device based on multi-core optical fiber and vortex optical field as described in claim 5, characterized in that, The laser Doppler velocimetry device includes a first phase modulator (3), a second phase modulator (4), and a third phase modulator (5); the three modulated beams are positioned and emitted from three cores (7-4), (7-5), and (7-6) of a multi-core fiber (7) that are in an equilateral triangular structure, and are focused at the focal center (0,0) by a gradient refractive index lens (8); the host computer (13) calculates the velocity of the particle (18) passing through the vortex light field as follows: Selecting vortex rings A(0,a), B(a,0), and C(0,-a) with the same radial distance a, the Doppler frequency shifts of vortex rings A, B, and C are obtained through spectral analysis of digital signals. , , angular velocity of particle (18) lateral velocity component along the x-axis longitudinal velocity component along the y-axis The calculation formula is: ; ; ; In the formula, L represents the topological load size.

7. A laser Doppler velocimetry method based on multi-core optical fiber and vortex optical field, characterized in that, The implementing entity is the laser Doppler velocimetry device according to any one of claims 1-6, and the steps include: Step S1: Start the laser Doppler velocimetry device and start the controller to perform phase-locked control. The controller randomly transmits a set of crosstalk signal factors and inputs them into each phase modulator for compensation, so that each beam of light is in phase and forms a stable vortex light field with multiple topological nuclei at the output end. In step S2, the particle passes through the vortex light rings at different positions in the vortex light field, and the first photodetector converts the frequency shift information of each vortex light ring into a digital signal and transmits it to the host computer. Step S3, the host computer (13) performs spectrum analysis on the digital signal and calculates the particle's angular velocity, transverse velocity component and longitudinal velocity component based on the radial distance, topological charge size and Doppler frequency shift of the vortex ring.

8. The laser Doppler velocimetry method based on multi-core optical fiber and vortex optical field as described in claim 7, characterized in that, The phase-locked loop (PLL) control process includes: the controller transmits a set of voltage signals with the same length as the number of phase modulators to the drive circuit; the drive circuit controls each phase modulator to perform phase compensation according to the voltage signals, so that the beam is phase compensated; the first photodetector detects the superimposed beam after phase compensation and outputs the illumination intensity information of the superimposed beam to the controller; the controller analyzes the impact of the previous adjustment on the illumination intensity based on the historical illumination intensity information, and adjusts the voltage signal used for the next phase compensation with the goal of increasing the illumination intensity. This iterative process continues until the illumination intensity reaches a maximum value, which represents that the beam is in phase and forms a stable vortex light field with multiple topological nuclei at the emission end.

9. The laser Doppler velocimetry method based on multi-core optical fiber and vortex optical field as described in claim 8, characterized in that, The laser Doppler velocimetry device includes a first phase modulator, a second phase modulator, and a third phase modulator. The three modulated beams are positioned and emitted from three cores of a multi-core optical fiber arranged in an equilateral triangle structure, and focused at the focal center (0,0) by a gradient refractive index lens. The host computer calculates the velocity of the particle passing through the vortex light field as follows: Selecting vortex rings A(0,a), B(a,0), and C(0,-a) with the same radial distance a, the Doppler frequency shifts of vortex rings A, B, and C are obtained through spectral analysis of digital signals. , , angular velocity of particle (18) lateral velocity component along the x-axis longitudinal velocity component along the y-axis The calculation formula is: ; ; ; In the formula, L represents the topological load size.

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