Target transverse velocity measurement method and system based on composite modulation of polarization and orbital angular momentum

Abstract

The invention relates to a method and system for measuring the lateral velocity of a target based on composite modulation of polarization and orbital angular momentum, and belongs to the field of laser velocity measurement. The invention aims to solve the problem that existing laser lateral velocity measurement methods and technologies cannot accurately measure the lateral velocity of a moving target in atmospheric turbulence and determine the direction of the velocity. The method of the invention comprises the following steps: S1. Modulating a laser signal to generate a dual-mode vortex beam with 1st and 4th order superposition, compositely modulating the laser signal with polarization and orbital angular momentum with a Gaussian beam to generate a modulation signal, and irradiating the target object with atmospheric turbulence to generate an echo signal; S2. Using a wavefront sensor to obtain the distorted phase of the polarization component of the Gaussian beam, generating a compensation phase to perform phase correction on the dual-mode vortex beam; S3. Using an array detector to detect the polarization component of the dual-mode vortex beam after phase compensation correction, the polarization component of the dual-mode vortex beam is used to obtain three lateral Doppler effect spot areas of the echo light field, which are then detected and calculated by the array detector to determine the magnitude and direction of the lateral velocity of the moving target.

Description

Technical Field

[0001] The invention relates to a laser transverse velocity measurement technology and belongs to the field of laser velocity measurement. Background Art

[0002] Lateral velocity measurement can be used to measure the lateral velocity of a target and has broad application potential in industrial control, military, aerospace, and other fields. Currently, measuring target lateral velocity relies solely on post-processing algorithms such as multi-device, multi-point, and multi-angle measurement synthesis, differential velocity measurement, or image processing estimation. In actual velocity measurement, atmospheric turbulence can severely interfere with the transmission of the light beam. Existing laser lateral velocity measurement methods and technologies are unable to accurately measure the lateral velocity of a moving target in atmospheric turbulence and determine the direction of velocity. Summary of the Invention

[0003] In response to the problem that existing laser lateral velocity measurement methods and technologies are unable to accurately measure the lateral velocity of a moving target in atmospheric turbulence and determine the direction of the velocity, the present invention provides a target lateral velocity measurement method and system based on composite modulation of polarization and orbital angular momentum.

[0004] In one aspect of the present invention, a method for measuring the lateral velocity of a target based on composite modulation of polarization and orbital angular momentum is provided, the method comprising the following steps:

[0005] S1, modulating a laser signal to generate a dual-mode vortex beam with 1st and 4th order superposition, performing polarization and orbital angular momentum composite modulation on the dual-mode vortex beam and a Gaussian beam to generate a modulation signal, and irradiating the modulation signal on a target object through atmospheric turbulence to generate an echo signal, wherein the echo signal includes a phase-distorted dual-mode vortex beam polarization component and a Gaussian beam polarization component;

[0006] S2. Using a wavefront sensor to obtain the distortion phase of the polarization component of the Gaussian beam, generating a compensation phase to perform phase compensation correction on the polarization component of the dual-mode vortex beam;

[0007] S3. The polarization component of the dual-mode vortex beam after phase compensation correction is detected by an array detector to obtain the three transverse Doppler effect spot areas of the echo light field. The array detector performs Fourier transform on the timing signal of each spot area, extracts the Doppler frequency shift through an oscilloscope for detection, and calculates the transverse velocity and direction of the moving target through the transverse velocity solution module.

[0008] Preferably, the distortion phase of the polarization component of the Gaussian beam obtained by the wavefront sensor in S2 is , the compensation phase is generated as follows :

[0009]

[0010] Where, is the phase of a Gaussian beam propagating in free space without turbulence;

[0011] The compensation phase As the correction phase screen information to eliminate the influence of atmospheric turbulence in S1, the correction phase screen is loaded onto the spatial light modulator, thereby performing phase correction on the polarization component of the distorted dual-mode vortex beam.

[0012] Preferably, the specific process of S3 includes:

[0013] S31, three transverse Doppler effect spot areas of the echo light field, each area has a spot, namely spot 1, spot 2 and spot 3, and the center point of the echo light field points to the first spot. The line connecting the center points of the light spots is taken as Auxiliary direction vector, three velocity components of the lateral velocity of the moving target , Direction The auxiliary direction vector is in the reverse extension direction;

[0014] S32. Obtaining, through an oscilloscope, a light intensity timing signal of three transverse Doppler effect spot regions of the echo light field at each moment;

[0015] S33, perform Fourier transform on the light intensity timing signal obtained in step S32, and extract the Doppler frequency shift of the spot area ;

[0016] S34, according to the formula Get the three velocity components of the lateral velocity of the moving target The size of

[0017] Where, , is the wavelength of the laser signal, For the The order of orbital angular momentum in the spot area is For the The radius of the light spot;

[0018] is the frequency of the laser signal,

[0019] is the speed of light;

[0020] S35: Combine the direction determined in S31 and the magnitude determined in S34 to obtain the three velocity components of the lateral velocity of the moving target. , the solved 、 and Perform vector synthesis to obtain the magnitude and direction of the lateral velocity of the moving target.

[0021] Preferably, the process of determining the directions of the three velocity components of the lateral velocity of the moving target in step S31 is as follows:

[0022] There are three transverse Doppler effect spot areas in the echo light field. Each area has a spot, namely spot 1, spot 2 and spot 3. The center points of the three spots are A1, A2 and A3 respectively. The center point of the echo light field is O, so the three auxiliary vectors are 、 and , the auxiliary vector is The reverse extension direction is the velocity component of the lateral velocity of the moving target The direction of the auxiliary vector is The reverse extension direction is the velocity component of the lateral velocity of the moving target The direction of the auxiliary vector is The reverse extension direction is the velocity component of the lateral velocity of the moving target direction.

[0023] In another aspect of the present invention, a target lateral velocity measurement system based on composite modulation of polarization and orbital angular momentum is provided. The system is used to implement the method. The measurement system includes a laser 1, a first lens group 2, a beam splitter 3, a first spatial light modulator 4, a first half-wave plate 5, a second lens group 6, a first polarization beam splitter 7, a transmitting system 8, a first atmospheric turbulence simulator 9, a second atmospheric turbulence simulator 11, a moving object 10, a receiving system 12, a distortion correction module 13, a detection processing module 14, and a lateral velocity solution module 15.

[0024] The laser emitted by the laser 1 reaches the first lens group 2, which expands, collimates and polarizes the beam to form a beam of horizontally polarized light. The beam is split by the beam splitter 3, and one path is passed through the first spatial light modulator 4 for orbital angular momentum quantum control to generate a dual-mode vortex beam polarization component with 1st and 4th order superposition. The other path is passed through the first half-wave plate 5 and the second lens group 6 to adjust the polarization direction of the Gaussian beam and expand the beam to generate a Gaussian beam polarization component. The dual-mode vortex beam polarization component and the Gaussian beam polarization component are superimposed by the first polarization beam splitter 7 to achieve polarization and The orbital angular momentum is compound modulated, and the modulated signal beam generated is emitted by the transmitting system 8, irradiated by the moving object 10 through the No. 1 atmospheric turbulence simulator 9 to generate an echo signal, and then received by the receiving system 12 through the No. 2 atmospheric turbulence simulator 11. The distortion is corrected by the distortion correction module 13, and the signal of each lateral Doppler effect spot area is detected by the detection and processing module 14. The time series signal of the light intensity is obtained by the oscilloscope, and the Fourier transform is performed on it. The lateral velocity solution module 15 solves the lateral velocity and direction of the moving target.

[0025] Preferably, the modulation process of the polarization component of the dual-mode vortex light beam: the No. 1 spatial light modulator 4 is a polarization-dependent liquid crystal reflective phase modulator, which can modulate the horizontal X direction of the light field; the modulation process of the Gaussian mode laser signal requires loading the phase diagram of the 1st-order and 4th-order superimposed dual-mode vortex light onto the No. 1 spatial light modulator 4, and the dual-mode vortex light beam is generated by the laser incident on the No. 1 spatial light modulator 4.

[0026] Preferably, the modulation process of the polarization component of the Gaussian beam is as follows: the first half-wave plate 5 rotates the polarization component direction of the Gaussian beam so that the horizontal linear polarized light is generated. Phase delay, converting the polarization direction to the vertical Y direction;

[0027] The second lens group 6 is expanded by a 4F lens system so that the spot radius of its Gaussian beam is the same as the spot radius width of the propagating dual-mode vortex beam, thereby completing the modulation of the polarization component of the Gaussian beam.

[0028] Preferably, the No. 1 atmospheric turbulence simulator 9 and the No. 2 atmospheric turbulence simulator 11 are configured to load a random phase screen simulated by the power spectrum inversion method onto the transmissive spatial light modulator to replace the atmospheric turbulence process, and the light beam is distorted when passing through the transmissive spatial light modulator.

[0029] Preferably, the distortion correction module 13 includes a second half-wave plate 13-1, a second spatial light modulator 13-2, a third half-wave plate 13-3, a second polarization beam splitter 13-4, a wavefront sensor 13-5 and a feedback signal controller 13-6;

[0030] The second half-wave plate 13-1 rotates the polarization direction of the turbulence-distorted Gaussian beam in the echo signal by 90°, aligning the polarization direction of the Gaussian beam with the polarization direction of the second spatial light modulator 13-2.

[0031] The third half-wave plate 13-3 rotates the polarization direction of the turbulently distorted dual-mode vortex beam in the echo signal by 90°, so that the polarization direction of the dual-mode vortex beam is aligned with the polarization direction of the second spatial light modulator 13-2, so that the second spatial light modulator 13-2 performs phase correction on the dual-mode vortex beam.

[0032] The wavefront sensor 13-5 obtains the distorted phase of the polarization component of the Gaussian beam and loads the compensation phase to the second spatial light modulator 13-2 through the feedback signal controller 13-6, thereby correcting the polarization component of the dual-mode vortex beam;

[0033] The third half-wave plate 13 - 3 and the second polarization beam splitter 13 - 4 are further polarized to ensure that the polarization direction of the Gaussian beam points to the wavefront sensor 13 - 5 .

[0034] Preferably, the detection and processing module 14 includes a polarizer, an array detector and an oscilloscope. The polarizer is used to select the polarization component of the dual-mode vortex light beam, and the three transverse Doppler effect spot areas of the echo signal are detected by the array detector. The timing signal of the light intensity is obtained by the oscilloscope connected to the array detector, and a Fourier transform is performed on it to obtain the Doppler frequency shift of each area. The transverse velocity solution module 15 solves the magnitude and direction of the transverse velocity of the moving target.

[0035] Beneficial effects of the present invention: The present invention performs polarization multiplexing on the fundamental mode Gaussian light and the dual-mode vortex light beam, obtains the wavefront distortion of the Gaussian probe light beam through a wavefront sensor, loads the correction phase onto the spatial light modulator through a feedback controller, and recovers and corrects the phase of the vortex light beam. Through the detection and processing module, the array detector performs Fourier transform on the timing signal of each spot area of ​​the polarization component of the dual-mode vortex light beam, extracts the Doppler frequency shift amount for detection through an oscilloscope, and calculates the lateral velocity magnitude and direction of the moving target through the lateral velocity solution module. The present invention introduces a Gaussian probe light beam, performs polarization multiplexing on the vortex light beam, utilizes the characteristic that the wavefront sensor can obtain the distorted wavefront information of the Gaussian light beam, recovers and corrects the phase of the vortex light beam, and improves the precision measurement capability of the vortex light beam transmitted in atmospheric turbulence on the lateral velocity magnitude and direction of the moving target. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a block diagram of the target lateral velocity measurement system based on composite modulation of polarization and orbital angular momentum according to the present invention;

[0037] Figure 2 It is a structural diagram of the distortion correction module;

[0038] Figure 3 It is the atmospheric turbulence phase screen;

[0039] Figure 4 This is a schematic diagram of the effects of dual-mode vortex beam correction before and after; Figure 4 (a) is the intensity of the dual-mode vortex beam without turbulence, Figure 4 (b) is the intensity of the dual-mode vortex beam after turbulence. Figure 4 (c) The intensity of the dual-mode vortex beam after turbulence and correction;

[0040] Figure 5 It is a schematic diagram of the direction of the transverse velocity component of the echo light field. DETAILED DESCRIPTION

[0041] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0042] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other.

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0044] Specific implementation method 1: Figures 1 to 5 This embodiment describes a method for measuring the target transverse velocity based on composite modulation of polarization and orbital angular momentum, comprising the following steps:

[0045] S1, modulating a laser signal to generate a dual-mode vortex beam with 1st and 4th order superposition, performing polarization and orbital angular momentum composite modulation on the dual-mode vortex beam and a Gaussian beam to generate a modulation signal, and irradiating the modulation signal on a target object through atmospheric turbulence to generate an echo signal, wherein the echo signal includes a phase-distorted dual-mode vortex beam polarization component and a Gaussian beam polarization component;

[0046] S2. Using a wavefront sensor to obtain the distortion phase of the polarization component of the Gaussian beam, generating a compensation phase to perform phase compensation correction on the polarization component of the dual-mode vortex beam;

[0047] S3. The polarization component of the dual-mode vortex beam after phase compensation correction is detected by an array detector to obtain the three transverse Doppler effect spot areas of the echo light field. The array detector performs Fourier transform on the timing signal of each spot area, extracts the Doppler frequency shift through an oscilloscope for detection, and calculates the transverse velocity and direction of the moving target through the transverse velocity solution module.

[0048] The distortion phase of the polarization component of the Gaussian beam obtained by the wavefront sensor in S2 is: , the compensation phase is generated as follows :

[0049]

[0050] Where, is the phase of a Gaussian beam propagating in free space without turbulence;

[0051] The compensation phase As the correction phase screen information to eliminate the influence of atmospheric turbulence in S1, the correction phase screen is loaded onto the spatial light modulator, thereby performing phase correction on the polarization component of the distorted dual-mode vortex beam.

[0052] Working Principle: This embodiment utilizes the unique phase characteristics of a vortex beam. Because the vortex beam contains an angular Poynting vector component rotating about the optical axis, the direction of photon motion is offset from the optical axis. After the beam is reflected by the target, a transverse Doppler shift is generated, which can be used for lateral velocity measurement. A Gaussian beam and a distortion correction module are used to obtain a corrected phase for the vortex beam, correcting the distorted vortex beam after passing through atmospheric turbulence. This enables simple and effective precise measurement of the target's transverse velocity in atmospheric turbulence.

[0053] The dual-mode vortex beam and the expanded Gaussian beam are coaxial and co-beamed in an orthogonal polarization manner. They pass through the same turbulence and are subjected to the same phase perturbation, and therefore the same phase distortion.

[0054] The wavefront sensor uses a Shack–Hartmann wavefront sensor. When the incident light wave is an ideal plane wave, a uniform, regularly distributed set of focal points is obtained at the focal point of the microlens array on the sensor. However, when the incident light wave exhibits wavefront distortion, the array image obtained at the focal plane of the microlens array is no longer uniformly distributed but is offset from the focal point of the ideal wavefront. This offset is the wavefront slope, and the wavefront phase distribution can be reconstructed from this wavefront slope using a wavefront restoration algorithm. Because the vortex beam has a spiral phase structure, if the wavefront slope of the vortex beam is directly detected using a Shack–Hartmann wavefront sensor, the measured wavefront slope cannot be directly used to calculate the corrector's driving information. Therefore, Gaussian light is introduced as a beacon light. The distorted phase of the Gaussian beam is measured to correct the phase of the dual-mode vortex beam. The wavefront sensor detects the wavefront distortion of the Gaussian beam.

[0055] The specific process of S3 includes:

[0056] S31, three transverse Doppler effect spot areas of the echo light field, each area has a spot, namely spot 1, spot 2 and spot 3, and the center point of the echo light field points to the first spot. The line connecting the center points of the light spots is taken as Auxiliary direction vector, three velocity components of the lateral velocity of the moving target , Direction The auxiliary direction vector is in the reverse extension direction;

[0057] S32. Obtaining, through an oscilloscope, a light intensity timing signal of three transverse Doppler effect spot regions of the echo light field at each moment;

[0058] S33, perform Fourier transform on the light intensity timing signal obtained in step S32, and extract the Doppler frequency shift of the spot area ;

[0059] S34, according to the formula Get the three velocity components of the lateral velocity of the moving target The size of

[0060] Where, , is the wavelength of the laser signal, For the The order of orbital angular momentum in the spot area is For the The radius of the light spot;

[0061] is the frequency of the laser signal,

[0062] is the speed of light;

[0063] S35: Combine the direction determined in S31 and the magnitude determined in S34 to obtain the three velocity components of the lateral velocity of the moving target. , the solved 、 and Perform vector synthesis to obtain the magnitude and direction of the lateral velocity of the moving target.

[0064] The process of determining the directions of the three velocity components of the moving target's lateral velocity in step S31 is as follows:

[0065] There are three transverse Doppler effect spot areas in the echo light field. Each area has a spot, namely spot 1, spot 2 and spot 3. The center points of the three spots are A1, A2 and A3 respectively. The center point of the echo light field is O, so the three auxiliary vectors are 、 and , the auxiliary vector is The reverse extension direction is the velocity component of the lateral velocity of the moving target The direction of the auxiliary vector is The reverse extension direction is the velocity component of the lateral velocity of the moving target The direction of the auxiliary vector is The reverse extension direction is the velocity component of the lateral velocity of the moving target The direction of Figure 5 shown.

[0066] Specific implementation method 2: Combined with the following Figures 1 to 5 This embodiment describes a target lateral velocity measurement system based on composite modulation of polarization and orbital angular momentum. The measurement system includes a laser 1, a first lens group 2, a beam splitter 3, a first spatial light modulator 4, a first half-wave plate 5, a second lens group 6, a first polarization beam splitter 7, a transmitting system 8, a first atmospheric turbulence simulator 9, a second atmospheric turbulence simulator 11, a moving object 10, a receiving system 12, a distortion correction module 13, a detection processing module 14, and a lateral velocity calculation module 15.

[0067] The laser emitted by the laser 1 reaches the first lens group 2, which expands, collimates and polarizes the beam to form a beam of horizontally polarized light. The beam is split by the beam splitter 3, and one path is passed through the first spatial light modulator 4 for orbital angular momentum quantum control to generate a dual-mode vortex beam polarization component with 1st and 4th order superposition. The other path is passed through the first half-wave plate 5 and the second lens group 6 to adjust the polarization direction of the Gaussian beam and expand the beam to generate a Gaussian beam polarization component. The dual-mode vortex beam polarization component and the Gaussian beam polarization component are superimposed by the first polarization beam splitter 7 to achieve polarization and The orbital angular momentum is compound modulated, and the modulated signal beam generated is emitted by the transmitting system 8, irradiated by the moving object 10 through the No. 1 atmospheric turbulence simulator 9 to generate an echo signal, and then received by the receiving system 12 through the No. 2 atmospheric turbulence simulator 11. The distortion is corrected by the distortion correction module 13, and the signal of each lateral Doppler effect spot area is detected by the detection and processing module 14. The time series signal of the light intensity is obtained by the oscilloscope, and the Fourier transform is performed on it. The lateral velocity solution module 15 solves the lateral velocity and direction of the moving target.

[0068] Modulation process of the polarization component of the dual-mode vortex beam: The spatial light modulator No. 1 is a polarization-dependent liquid crystal reflective phase modulator that can modulate the horizontal X direction of the light field. The modulation process of the Gaussian mode laser signal requires loading the phase diagram of the dual-mode vortex light superimposed by the 1st and 4th orders onto the spatial light modulator No. 1, and the dual-mode vortex beam is generated by the laser incident on the spatial light modulator No. 1.

[0069] The modulation process of the polarization component of the Gaussian beam is as follows: the first half-wave plate 5 rotates the polarization component direction of the Gaussian beam so that the horizontal linear polarized light is generated. Phase delay, converting the polarization direction to the vertical Y direction;

[0070] The second lens group 6 is expanded by a 4F lens system so that the spot radius of its Gaussian beam is the same as the spot radius width of the propagating dual-mode vortex beam, thereby completing the modulation of the polarization component of the Gaussian beam.

[0071] The first polarization beam splitter 7 superimposes the polarization component of the dual-mode vortex beam in the X direction and the polarization component of the Gaussian beam in the Y direction into a modulated signal, which is then transmitted by the transmitting system 8 .

[0072] Atmospheric turbulence simulator No. 1 9 and atmospheric turbulence simulator No. 2 11 are to load a random phase screen simulated by the power spectrum inversion method onto a transmissive spatial light modulator to replace the atmospheric turbulence process, and the light beam is distorted when passing through the transmissive spatial light modulator.

[0073] The distortion correction module 13 includes a second half-wave plate 13-1, a second spatial light modulator 13-2, a third half-wave plate 13-3, a second polarization beam splitter 13-4, a wavefront sensor 13-5 and a feedback signal controller 13-6;

[0074] The second half-wave plate 13-1 rotates the polarization direction of the turbulence-distorted Gaussian beam in the echo signal by 90°, aligning the polarization direction of the Gaussian beam with the polarization direction of the second spatial light modulator 13-2.

[0075] The third half-wave plate 13-3 rotates the polarization direction of the turbulently distorted dual-mode vortex beam in the echo signal by 90°, so that the polarization direction of the dual-mode vortex beam is aligned with the polarization direction of the second spatial light modulator 13-2, so that the second spatial light modulator 13-2 performs phase correction on the dual-mode vortex beam.

[0076] The wavefront sensor 13-5 obtains the distorted phase of the polarization component of the Gaussian beam, and loads the compensation phase to the second spatial light modulator 13-2 through the feedback signal controller 13-6, thereby correcting the polarization component of the dual-mode vortex beam; the feedback signal controller 13-6 is connected and feedback is performed between the second spatial light modulator 13-2 and the wavefront sensor 13-5, and provides a phase correction mode as a control signal.

[0077] The third half-wave plate 13 - 3 and the second polarization beam splitter 13 - 4 are further polarized to ensure that the polarization direction of the Gaussian beam points to the wavefront sensor 13 - 5 .

[0078] The correction information, the wavefront sensor 13-5 obtains the wavefront information of the polarization component of the distorted Gaussian beam ; Phase of a Gaussian beam propagating in free space without turbulence minus , the correction phase screen information for correcting the vortex beam can be obtained, and the correction phase screen is loaded onto the second spatial light modulator 13-2 to correct the distorted vortex beam. The correction result is as follows: Figure 4 As shown, (a) the intensity of the dual-mode vortex beam in the absence of turbulence, (b) the intensity of the dual-mode vortex beam in the presence of turbulence, and (c) the intensity of the dual-mode vortex beam in the presence of turbulence and correction.

[0079] The distortion correction module 13, upon obtaining a turbulently distorted beam correction pattern, rotates the third half-wave plate 13.3 by 90°, aligning the polarization of the dual-mode vortex beam with the polarization direction of the second spatial light modulator 13-2. This allows the dual-mode vortex beam to be phase-corrected by the second spatial light modulator 13-2. The operating principle is as follows: the second half-wave plate 13-1 is adjusted to rotate the polarization direction of the beam, aligning the polarization of the Gaussian beam with the polarization direction of the second spatial light modulator 13-2. The third half-wave plate 13-3 and the second polarization beam splitter 13-4 are further polarized to ensure that the polarization direction of the Gaussian beam is directed toward the wavefront sensor 13-5. The wavefront sensor 13-5 detects the wavefront distortion of the Gaussian beam. The feedback signal controller 13-6 provides a phase correction pattern as a control signal based on the wavefront distortion, and the second spatial light modulator 13-2 corrects the polarization component of the dual-mode vortex beam.

[0080] The detection and processing module 14 includes a polarizer, an array detector and an oscilloscope. The polarizer is used to select the polarization component of the dual-mode vortex light beam. The array detector detects the three transverse Doppler effect spot areas of the echo signal, and the oscilloscope connected to the array detector obtains the time series signal of the light intensity. The Fourier transform is performed on it to obtain the Doppler frequency shift of each area. The transverse velocity solution module 15 solves the transverse velocity magnitude and direction of the moving target.

[0081] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the invention. It should be understood that many modifications may be made to the illustrative embodiments, and that other arrangements may be devised, without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in ways other than those described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in conjunction with other described embodiments.

Claims

1. A target lateral velocity measurement system based on composite modulation of polarization and orbital angular momentum, characterized in that: The measurement system includes a laser (1), a lens group No. 1 (2), a beam splitter (3), a spatial light modulator No. 1 (4), a half-wave plate No. 1 (5), a lens group No. 2 (6), a polarization beam splitter No. 1 (7), a transmitting system (8), an atmospheric turbulence simulator No. 1 (9), an atmospheric turbulence simulator No. 2 (11), a moving object (10), a receiving system (12), a distortion correction module (13), a detection processing module (14), and a transverse velocity solution module (15); The laser light emitted by the laser (1) reaches the first lens group (2), and the first lens group (2) expands, collimates and polarizes the light beam to form a beam of horizontal linear polarized light, which is split by the beam splitter (3). One path passes through the first spatial light modulator (4) to perform orbital angular momentum quantum control to generate a double-mode vortex beam polarization component with the first and fourth orders superimposed. The other path passes through the first half-wave plate (5) and the second lens group (6) to adjust the polarization direction of the Gaussian beam and expand the beam to generate a Gaussian beam polarization component. The double-mode vortex beam polarization component and the Gaussian beam polarization component are superimposed by the first polarization beam splitter (7) to achieve polarization and The orbital angular momentum is compositely modulated, and the modulated signal beam generated is emitted by the transmitting system (8), irradiated by the moving object (10) via the atmospheric turbulence simulator No. 1 (9) to generate an echo signal, and then received by the receiving system (12) via the atmospheric turbulence simulator No. 2 (11), and the distortion is corrected by the distortion correction module (13), and the signal of each transverse Doppler effect spot area is detected by the detection processing module (14), and the time series signal of the light intensity is obtained by the oscilloscope, and the Fourier transform is performed on the signal, and the transverse velocity calculation module (15) calculates the transverse velocity and direction of the moving target; The measurement method implemented using this system includes the following steps: S1, modulating a laser signal to generate a dual-mode vortex beam with 1st and 4th order superposition, performing polarization and orbital angular momentum composite modulation on the dual-mode vortex beam and a Gaussian beam to generate a modulation signal, and irradiating the modulation signal on a target object through atmospheric turbulence to generate an echo signal, wherein the echo signal includes a phase-distorted dual-mode vortex beam polarization component and a Gaussian beam polarization component; S2. Using a wavefront sensor to obtain the distortion phase of the polarization component of the Gaussian beam, generating a compensation phase to perform phase compensation correction on the polarization component of the dual-mode vortex beam; S3. The polarization component of the dual-mode vortex beam after phase compensation correction is detected by an array detector to obtain the three transverse Doppler effect spot areas of the echo light field. The array detector performs Fourier transform on the timing signal of each spot area, extracts the Doppler frequency shift through an oscilloscope for detection, and calculates the transverse velocity and direction of the moving target through the transverse velocity solution module.

2. The target lateral velocity measurement system based on polarization and orbital angular momentum composite modulation according to claim 1, characterized in that: Modulation process of polarization components of dual-mode vortex beam: the first spatial light modulator (4) is a polarization-dependent liquid crystal reflective phase modulator, which modulates the horizontal X direction of the light field; the modulation process of the Gaussian mode laser signal requires loading the phase diagram of the first-order and fourth-order superimposed dual-mode vortex light onto the first spatial light modulator (4), and the laser is incident on the first spatial light modulator (4) to generate a dual-mode vortex beam.

3. The target lateral velocity measurement system based on polarization and orbital angular momentum composite modulation according to claim 1, characterized in that: The modulation process of the polarization component of the Gaussian beam is as follows: the first half-wave plate (5) rotates the polarization component direction of the Gaussian beam, so that the horizontal linear polarized light produces a phase delay of π / 2, and the polarization direction is converted into the vertical Y direction; The second lens group (6) is expanded by a 4F lens system so that the spot radius of the Gaussian beam is the same as the spot radius width of the propagating dual-mode vortex beam, thereby completing the modulation of the polarization component of the Gaussian beam.

4. The target lateral velocity measurement system based on composite modulation of polarization and orbital angular momentum according to claim 1, characterized in that: Atmospheric turbulence simulator No. 1 (9) and atmospheric turbulence simulator No. 2 (11) are to load a random phase screen simulated by the power spectrum inversion method onto a transmission type spatial light modulator to replace the atmospheric turbulence process, and the light beam is distorted when passing through the transmission type spatial light modulator.

5. The target lateral velocity measurement system based on polarization and orbital angular momentum composite modulation according to claim 1, characterized in that: The distortion correction module (13) includes a second half-wave plate (13-1), a second spatial light modulator (13-2), a third half-wave plate (13-3), a second polarization beam splitter (13-4), a wavefront sensor (13-5) and a feedback signal controller (13-6); The second half-wave plate (13-1) rotates the polarization direction of the turbulence-distorted Gaussian beam polarization component in the echo signal by 90 degrees, and aligns the polarization direction of the Gaussian beam with the polarization direction of the second spatial light modulator (13-2); The third half-wave plate (13-3) rotates the polarization direction of the polarization component of the dual-mode vortex beam that has undergone turbulence distortion in the echo signal by 90 degrees, so that the polarization direction of the dual-mode vortex beam is aligned with the polarization direction of the second spatial light modulator (13-2), so that the second spatial light modulator (13-2) performs phase correction on the dual-mode vortex beam; The wavefront sensor (13-5) obtains the distorted phase of the polarization component of the Gaussian beam and loads the compensation phase to the second spatial light modulator (13-2) through the feedback signal controller (13-6), thereby correcting the polarization component of the dual-mode vortex beam; The third half-wave plate (13-3) and the second polarization beam splitter (13-4) are further polarized to ensure that the polarization direction of the Gaussian beam points to the wavefront sensor (13-5).

6. The target lateral velocity measurement system based on polarization and orbital angular momentum composite modulation according to claim 1, characterized in that: The detection and processing module (14) includes a polarizer, an array detector and an oscilloscope. The polarizer is used to select the polarization component of the dual-mode vortex light beam. The array detector is used to detect the three transverse Doppler effect spot areas of the echo signal, and the oscilloscope connected to the array detector is used to obtain the time series signal of the light intensity. The Fourier transform is performed on the signal to obtain the Doppler frequency shift of each area. The transverse velocity calculation module (15) calculates the transverse velocity size and direction of the moving target.

7. The target lateral velocity measurement system based on polarization and orbital angular momentum composite modulation according to claim 1, characterized in that: The distortion phase of the polarization component of the Gaussian beam obtained by the wavefront sensor in S2 is: , the compensation phase is generated as follows : Where, is the phase of a Gaussian beam propagating in free space without turbulence; The compensation phase As the correction phase screen information to eliminate the influence of atmospheric turbulence in S1, the correction phase screen is loaded onto the spatial light modulator, thereby performing phase correction on the polarization component of the distorted dual-mode vortex beam.

8. The target lateral velocity measurement system based on polarization and orbital angular momentum composite modulation according to claim 1, characterized in that: The specific process of S3 includes: S31, three transverse Doppler effect spot areas of the echo light field, each area has a spot, namely spot 1, spot 2 and spot 3, and the center point of the echo light field points to the first spot. The line connecting the center points of the light spots is taken as Auxiliary direction vector, three velocity components of the lateral velocity of the moving target , Direction The auxiliary direction vector is in the reverse extension direction; S32. Obtaining, through an oscilloscope, a light intensity timing signal of three transverse Doppler effect spot regions of the echo light field at each moment; S33, perform Fourier transform on the light intensity timing signal obtained in step S32, and extract the Doppler frequency shift of the spot area ; S34, according to the formula Get the three velocity components of the lateral velocity of the moving target The size of Where, , is the wavelength of the laser signal, For the The order of orbital angular momentum in the spot area is For the The radius of the light spot; is the frequency of the laser signal, is the speed of light; S35: Combine the direction determined in S31 and the magnitude determined in S34 to obtain the three velocity components of the lateral velocity of the moving target. , the solved 、 and Perform vector synthesis to obtain the magnitude and direction of the lateral velocity of the moving target.

9. The target lateral velocity measurement system based on polarization and orbital angular momentum composite modulation according to claim 8, characterized in that: The process of determining the directions of the three velocity components of the moving target's lateral velocity in step S31 is as follows: There are three transverse Doppler effect spot areas in the echo light field. Each area has a spot, namely spot 1, spot 2 and spot 3. The center points of the three spots are A1, A2 and A3 respectively. The center point of the echo light field is O, so the three auxiliary vectors are 、 and , the auxiliary vector is The reverse extension direction is the velocity component of the lateral velocity of the moving target The direction of the auxiliary vector is The reverse extension direction is the velocity component of the lateral velocity of the moving target The direction of the auxiliary vector is The reverse extension direction is the velocity component of the lateral velocity of the moving target direction.

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