Search

CN-122017864-A - Laser Doppler speed measurement device and method based on multi-core optical fiber and vortex optical field

CN122017864ACN 122017864 ACN122017864 ACN 122017864ACN-122017864-A

Abstract

The invention provides a laser Doppler velocity measurement device based on a multicore 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 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, wherein the optical path design is simplified, the direct generation of vortex rotation is realized through the multi-core optical fiber, the optical path design is simplified, a Doppler probe is formed through the gradient refractive index lens and the multi-core optical fiber, the focusing characteristic of a light beam is optimized, the quality of a vortex light field is ensured, the flexibility of the system is improved, the system has the advantages of compact structure, high integration level and high precision, a stable vortex field can be formed at a position with a shorter emergent distance, the requirement on the working environment is reduced, and a more efficient solution is provided for measuring the speed of compound motion.

Inventors

  • MA XIN
  • LI GUILONG
  • SONG JIANGTAO

Assignees

  • 宁夏大学

Dates

Publication Date
20260512
Application Date
20260122

Claims (9)

  1. 1. The laser Doppler speed measuring device based on the multi-core optical fiber and the vortex optical field is characterized by comprising a laser (1), an optical divider (2), a group of phase modulators, a multi-core optical fiber fan-in fan-out device (6), a multi-core optical fiber (7), a gradient refractive index lens (8) and an optical beam splitter (9), wherein the laser, the optical divider, the multi-core optical fiber fan-in fan-out device, the gradient refractive index lens (8) and the optical beam splitter are sequentially connected with each other through optical fibers, a first photoelectric detector (10), a first analog-to-digital converter (12) and an upper computer (13), and a second photoelectric detector (11), a second analog-to-digital converter (14), a controller (15), a digital-to-analog converter (16) and a driving circuit (17) are sequentially connected with each other through electrical wires; Laser emitted by the laser (1) is split by the optical splitter (2) and then enters N groups of phase modulators respectively for phase modulation, the debugged light beams enter each fiber core of the multi-core optical fiber (7) for positioning and emergent through the multi-core optical fiber fan-in fan-out device (6), focused by the gradient refractive index lens (8) and emergent, each emergent beam of detection light is split into two directions by the optical splitter (9) and is used for measurement, detection light facing the detection area is used for measurement, scattered light is generated after particles (18) pass through a vortex light field formed by the detection area, the scattered light after frequency change enters a coupling lens of the first photoelectric detector (10), and frequency information of the light beams is transmitted to the upper computer (13) after being converted by the first analog-digital converter (12); The detection light facing the non-detection area enters a coupling lens of a second photoelectric detector (11), the phase information of the light beam is converted into a digital signal through a second analog-to-digital converter (14) and then is transmitted to a controller (15), the controller (15) performs phase locking control, randomly transmits a group of crosstalk signal factors, the crosstalk signal factors are converted into an analog voltage signal through a digital-to-analog converter (16) and then enter a driving circuit (17), and the driving circuit (17) controls a phase modulator to perform phase compensation according to the received analog voltage signal; The speed calculation mode of the particles (18) passing through the vortex light field is that the upper computer (13) carries out frequency spectrum analysis on the digital signal, selects a vortex light ring on a plane where a focusing center is located, and calculates the angular speed, the transverse speed component and the longitudinal speed component of the particles (18) according to the radial distance, the topological load size and the Doppler frequency shift quantity of the vortex light ring.
  2. 2. The laser Doppler velocimetry apparatus based on the multicore fiber and the vortex light field as claimed in claim 1, wherein the phase-locked control process performed by the controller (15) is that the controller (15) controls the driving circuit (17) to randomly transmit a set of crosstalk signal factors to each phase modulator each time to compensate, so that each beam of light is in phase.
  3. 3. The laser Doppler speed measuring device based on the multi-core optical fiber and the vortex light field according to claim 2, wherein the phase locking control process of the controller (15) comprises the steps that the controller (15) transmits a group of voltage signals with the same length as the number of the phase modulators to the driving circuit, the driving circuit correspondingly controls the phase modulators to conduct phase compensation according to the voltage signals so as to enable the light beams to obtain the phase compensation, the first photoelectric detector (11) detects the superimposed light beams after the phase compensation and outputs illumination intensity information of the superimposed light beams to the controller (15), the controller (15) analyzes the influence of the last adjustment on the illumination intensity according to the historical illumination intensity information, the next voltage signal for the phase compensation is adjusted with the illumination intensity increased as a target, and the iteration process is continued until the illumination intensity reaches a maximum value, the light beams are represented in phase, and a stable vortex light field with a plurality of topological nuclei is formed at an output end.
  4. 4. The laser doppler velocity measurement device based on the multi-core optical fiber and the vortex optical field as set forth in claim 3, wherein the number of the phase modulators is not less than 3, and the cores for transmitting laser in the multi-core optical fiber (7) form a single regular triangle structure relationship or a plurality of regular triangle structure relationships with different sizes, and the in-phase emergent light is coherently superimposed to form the vortex optical field with a plurality of topological cores.
  5. 5. The laser doppler velocimetry device based on a multicore fiber and a vortex light field according to claim 4, characterized in that the multicore fiber (5) and the gradient index lens (6) are connected by fusion technique, forming a doppler probe.
  6. 6. The laser Doppler velocimetry device based on the multi-core optical fiber and the vortex optical field according to claim 5 is characterized in that the laser Doppler velocimetry device comprises a first phase modulator (3), a second phase modulator (4) and a third phase modulator (5), three beams of modulated light are positioned and emergent by three fiber cores (7-4), (7-5) and (7-6) in regular triangle structural relation in the multi-core optical fiber (7), and focused on a focusing center (0, 0) through a gradient refractive index lens (8), and the speed of particles (18) passing through the vortex optical field is calculated by an upper computer (13) in the following way: Vortex light rings A (0, a), B (a, 0) and C (0-a) with the same radial distance a are selected, and the Doppler frequency shift of the vortex light ring A, B, C is obtained by carrying out frequency spectrum analysis on the digital signals 、 、 Angular velocity of particles (18) Transverse velocity component along the x-axis Longitudinal velocity component along y-axis The calculation formula of (2) is as follows: ; ; ; Wherein L is the topological charge size.
  7. 7. The laser Doppler velocity measurement method based on the multi-core optical fiber and the vortex optical field is characterized in that an implementation main body is the laser Doppler velocity measurement device of any one of claims 1 to 6, and the method comprises the following steps: step S1, starting a laser Doppler velocity measuring device, starting a controller to perform phase locking control, randomly transmitting a group of crosstalk signal factors by the controller, respectively inputting the crosstalk signal factors into each phase modulator to compensate, enabling each beam of light to be in phase, and forming a stable vortex light field with a plurality of topological cores at an exit end; S2, particles pass through vortex light rings at different positions in a vortex light field, and the first photoelectric detector converts frequency shift information of each vortex light ring into a digital signal and transmits the digital signal to an upper computer; And S3, performing spectrum analysis on the digital signal by the upper computer (13), and calculating the angular velocity, the transverse velocity component and the longitudinal velocity component of the particles according to the radial distance, the topological charge size and the Doppler frequency shift of the vortex light ring.
  8. 8. The laser Doppler velocimetry method based on the multi-core optical fiber and the vortex light field of claim 7, wherein the phase-locked control process comprises the steps that the controller transmits a group of voltage signals with the same length as the number of the phase modulators to the driving circuit, the driving circuit correspondingly controls the phase modulators to conduct phase compensation according to the voltage signals to enable the light beams to obtain phase compensation, the first photoelectric detector detects the superimposed light beams after the phase compensation and outputs illumination intensity information of the superimposed light beams to the controller, the controller analyzes the influence of last adjustment on the illumination intensity according to the historical illumination intensity information, adjusts the voltage signals for phase compensation next time with the illumination intensity increased as a target, and continues the iterative process until the illumination intensity reaches a maximum value, the phase compensation is achieved, and a stable vortex light field with a plurality of topological nuclei is formed at an emitting end.
  9. 9. The laser Doppler velocimetry method based on the multi-core optical fiber and the vortex optical field according to claim 8 is characterized in that the laser Doppler velocimetry device comprises a first phase modulator, a second phase modulator and a third phase modulator, three modulated light beams are positioned and emergent by three fiber cores in a regular triangle structural relationship in the multi-core optical fiber and are focused on a focusing center (0, 0) through a gradient refractive index lens, and the calculation mode of the speed of particles through the vortex optical field by an upper computer is as follows: Vortex light rings A (0, a), B (a, 0) and C (0-a) with the same radial distance a are selected, and the Doppler frequency shift of the vortex light ring A, B, C is obtained by carrying out frequency spectrum analysis on the digital signals 、 、 Angular velocity of particles (18) Transverse velocity component along the x-axis Longitudinal velocity component along y-axis The calculation formula of (2) is as follows: ; ; ; Wherein L is the topological charge size.

Description

Laser Doppler speed measurement device and method based on multi-core optical fiber and vortex optical field Technical Field The invention relates to the technical field of optical speed measurement, in particular to a laser Doppler speed measurement device and a speed measurement method based on a multi-core optical fiber and a vortex light field. Background The laser Doppler velocimetry (Laser Doppler Velocimetry, LDV) is a non-contact flow velocity measurement method based on Doppler effect, and is widely applied to the fields of fluid mechanics, biomedicine, industrial process monitoring and the like. The conventional LDV system calculates the velocity by detecting the laser frequency shift caused by the scattering particles, but is mainly limited to measurement of a single velocity, and it is difficult to simultaneously achieve simultaneous measurement of the translational velocity and the angular velocity. In recent years, the vortex light field provides a new thought for speed measurement of compound motion due to the characteristic of carrying orbital angular momentum. The helical wavefront structure and phase gradient of eddy currents can enhance sensitivity to axial movement of particles, however, generation of eddy currents in the prior art typically relies on complex optics such as spatial light modulators or helical phase plates, which are not only complex in systems but also vulnerable to damage in high power environments. For example, the spatial light modulator needs to rely on a liquid crystal unit to regulate the wave front phase, the liquid crystal layer is likely to be invalid due to the thermal effect under the milliwatt laser power, and meanwhile, more than ten discrete optical elements such as a polarization controller, a beam expander and the like are needed to be matched, so that the system is huge in volume and low in calibration tolerance. While the spiral phase plate can avoid the complexity of electric control, the tiny depth error of the etching process can lead to the reduction of the orbital angular momentum purity, and the fixed phase structure cannot be dynamically adapted to different measurement scenes. In addition, although the multi-beam interference method can generate vortex rotation, submicron displacement accuracy is required to control the beam spacing and micro radian level inclination. Environmental temperature drift or mechanical vibration can directly destroy phase matching conditions, so that vortex nuclear distortion and even topological charge overturning are caused, and the system stability is poor. Disclosure of Invention In view of the above, the invention provides a laser Doppler velocity measurement device and a velocity measurement method based on a multi-core optical fiber and a vortex optical field, which realize the direct generation of the vortex optical field through the multi-core optical fiber, simplify the optical path design, form a Doppler probe through a gradient refractive index lens and the multi-core optical fiber, optimize the focusing characteristic of a light beam, ensure the quality of the vortex optical field, improve the flexibility of a system, have the advantages of compact structure, high integration level and high precision, can form a stable vortex optical field at a position with a shorter emergent distance, reduce the requirement on the working environment, and provide a more efficient solution for measuring the speed of compound motion. The technical scheme adopted by the embodiment of the invention for solving the technical problems is as follows: A laser Doppler speed measuring device based on a multi-core optical fiber and a vortex optical field comprises a laser (1), an optical splitter (2), a group of phase modulators, a multi-core optical fiber fan-in fan-out device (6), a multi-core optical fiber (7), a gradient refractive index lens (8) and an optical beam splitter (9), wherein the laser, the optical splitter (2), the group of phase modulators, the multi-core optical fiber fan-in fan-out device, the multi-core optical fiber fan-out device, the gradient refractive index lens (8) and the optical beam splitter (9) are sequentially and electrically connected, a first photoelectric detector (10), a first analog-to-digital converter (12) and an upper computer (13), and a second photoelectric detector (11), a second analog-to-digital converter (14), a controller (15), a digital-to-analog converter (16) and a driving circuit (17) are sequentially and electrically connected; Laser emitted by the laser (1) is split by the optical splitter (2) and then enters N groups of phase modulators respectively for phase modulation, the debugged light beams enter each fiber core of the multi-core optical fiber (7) for positioning and emergent through the multi-core optical fiber fan-in fan-out device (6), focused by the gradient refractive index lens (8) and emergent, each emergent beam of detection light is split into two directions by t