Active differential SAL imaging device with vibration self-compensation function

Abstract

The invention provides a vibration self-compensation active differential SAL imaging device. The vibration self-compensation active differential SAL imaging device comprises a half wave plate, a 1 / 4 wave plate, a polarization beam splitter, an MEMS rotating mirror, a reflecting mirror and a convex lens. According to the device, fixed differential synthetic aperture laser radar imaging can be received, and active synthetic aperture laser radar imaging can be carried out through modulation of a receiving branch rotating mirror under the condition that the radar and a target are kept static. According to the invention, two paths of echo signals and local oscillation signals are mixed and then phases are extracted, a first receiving branch is fixed to obtain a target stationary phase, a second receiving branch is modulated by an MEMS rotating mirror to obtain an azimuth secondary phase of a far-field target, and a far-field target two-dimensional image is obtained by combining frequency-modulated continuous wave coherent detection and synthetic aperture. The device compensates phase floating through receiving difference, is high in vibration resistance, compares and receives fixed difference SAL, does not need to reconstruct a secondary phase, can more stably image echo signals with low signal-to-noise ratio, and is higher in imaging sensitivity.

Description

TECHNICAL FIELD

[0001] The application relates to a synthetic aperture laser radar, in particular to a vibration self-compensated active differential SAL imaging transceiver. BACKGROUND

[0002] Synthetic aperture laser radar (SAL) is a way to realize long-distance high-resolution imaging, but the focusing in the azimuth direction needs to rely on a stable quadratic phase history, and the wavelength of laser is short, and the vibration of the return signal relative to the radar platform will cause serious phase disturbance. At the same time, long-distance imaging also means that the target scattering echo is usually small, and the detection ability of weak echo target is also very important.

[0003] In the invention patent (CN201410353015.6), differential synthetic aperture laser radar (DSAL) relies on two fixed receiving apertures to image the signals of the same position in turn, and needs complicated differential reconstruction phase processing to obtain a stable quadratic phase, and in the differential reconstruction process, both apertures are required to image the target, and the signal-to-noise ratio is required to be higher, which is not conducive to the imaging of weak echo signal target.

[0004] In the article (Li Minglei, Wu Jin, Bai Tao, et al. Strip pattern synthetic aperture laser radar imaging experiment under large random phase error [J]. China Optics, 2019, 12 (1): 8. DOI: CNKI: SUN: ZGGA.0.2019-01-012.), the SAL imaging under large random phase error is compensated by the phase gradient autofocus (PGA) algorithm of strip pattern imaging, but when the average power of laser is 30nW, the signal-to-noise ratio of the return image data is about 4dB, and the PGA phase error elimination capability loses its effect.

[0005] In the invention patent (CN200810037381.5), active synthetic aperture is realized by beam scanning, but due to the short wavelength of laser, even if the target and the radar platform are both in a stationary state, the imaging result is very sensitive to the common-mode phase error caused by beam scanning, and such common-mode phase error is not processed in the patent.

[0006] The article (Zhang Ning, Lu Zhiyong, Sun Jianfeng, et al. Image signal-to-noise ratio research of staring synthetic aperture laser imaging radar in sliding bunch mode [J]. Acta Optica Sinica, 2016 (8): 6. DOI:10.3788 / AOS201636.0828001.) obtains longer imaging time by adopting the sliding bunch working mode, and improves the detection ability of the system to weak signals. However, the sliding bunch working mode also means the extension of the imaging time and the substantial improvement of the motion control ability requirement of the radar. SUMMARY

[0007] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a vibration self-compensating active differential SAL imaging device, which can realize the imaging of the fixed differential synthetic aperture laser radar while also actively performing phase synthesis by relying on the rotation of the receiving end MEMS rotating mirror under the condition that the radar and the target are stationary. In particular, in the active modulation mode SAL imaging, the system has the following advantages:

[0008] The radar only needs to control the rotation of the MEMS rotating mirror, without complex motion control. In the system imaging, there is no need to perform secondary phase accumulation reconstruction, and the phase disturbance can be self-compensated by relying on the received phase floating, direct differential, strong anti-vibration ability, and simple data processing procedure. The radar and the target are both in a stationary state, the phase disturbance caused by vibration is small, and the pressure of system noise suppression is reduced. Moreover, when the target signal is seriously polluted by noise, the system can still stably image, and has higher imaging sensitivity than the received fixed differential SAL, and can stably image the weak echo target under the condition of large common-mode phase error. The weak echo signal with an average signal-to-noise ratio of 3.15dB of the range-compressed image can still be stably imaged.

[0009] The technical solution of the present application is as follows:

[0010] A vibration self-compensating active differential synthetic aperture laser radar imaging device, characterized by comprising a transmitting collimating head, a transmitting polarization beam splitter, a 1 / 4 wave plate, a convex lens, a reflecting mirror, a half wave plate, a first polarization beam splitter, a second polarization beam splitter, a local oscillator collimating head, a first 2*2 optical bridge, a MEMS rotating mirror, a third polarization beam splitter, a second 2*2 optical bridge, and a signal generator, and the positional relationship of the above components is as follows:

[0011] The linearly polarized light beam output by the laser light source is collimated by the emission collimation head, and then is totally reflected by the emission polarization beam splitter, and then is sequentially passed through a 1 / 4 wave plate, a convex lens and a mirror to reach a far-field target; the target echo signal returns along the original path, is sequentially passed through the mirror, the convex lens and the 1 / 4 wave plate, and is transmitted by the emission polarization beam splitter, and the transmitted echo is divided into transmitted echo and reflected echo by the half wave plate and the first polarization beam splitter; the transmitted echo is transmitted by the second polarization beam splitter, and is combined with the same source coherent local oscillator light collimated by the local oscillator collimation head after being reflected by the second polarization beam splitter, and is transmitted to the first 2*2 optical bridge; the reflected echo is sequentially reflected by the MEMS mirror and the third polarization beam splitter, and is combined with the same source coherent local oscillator light collimated by the local oscillator collimation head after being sequentially transmitted by the second polarization beam splitter and the third polarization beam splitter, and is transmitted to the second 2*2 optical bridge;

[0012] The center of the rotation axis of the MEMS mirror is located on the front focal plane of the convex lens, and is used for controllable phase modulation of the reflected echo and introduction of azimuthal quadratic phase history; the first 2*2 optical bridge is used for collecting vibration reference signals of interference between the transmitted echo and the local oscillator light in the active modulation mode, and is used for collecting target imaging signals of interference between the transmitted echo and the local oscillator light in the fixed differential mode; the second 2*2 optical bridge is used for collecting target imaging signals of interference between the reflected echo modulated by the MEMS mirror and the local oscillator light; the signal generator is used for driving the MEMS mirror to periodically swing or fixedly deflect; the phase data of the two signals are processed by the phase differential algorithm, the vibration noise phase is eliminated, and the target phase information is extracted, and vibration self-compensation imaging can be realized in the active modulation mode.

[0013] The center of the convex lens is coaxially aligned with the main light beam of the emission laser, and the collimation of the light beam transmission is ensured.

[0014] The MEMS mirror modulates the phase of the reflected echo in the form of periodic swing or rotation in the active modulation mode, introduces azimuthal quadratic phase, and is used for synthetic aperture imaging.

[0015] The phase differential algorithm includes the following steps:

[0016] (1) In the fixed differential mode:

[0017] a) extract the phase from the target imaging signal collected by the first 2*2 optical bridge;

[0018] b) extract the phase from the target imaging signal collected by the second 2*2 optical bridge;

[0019] c) calculate the phase difference of the two signals;

[0020] d) reconstruct the azimuthal quadratic phase by accumulating the phase difference;

[0021] e) compensate the reconstructed phase based on the dual-aperture echo optical path difference;

[0022] f) convolve the compensated phase with the fixed differential mode matching signal to realize azimuthal focusing imaging;

[0023] (2) In the active modulation mode:

[0024] a) extract the phase from the vibration reference signal collected by the first 2x2 optical bridge;

[0025] b) extract the phase from the target imaging signal collected by the second 2x2 optical bridge (13);

[0026] c) calculate the real-time phase difference of the two signals;

[0027] d) take the real-time phase difference as the azimuthal secondary phase;

[0028] e) convolve the real-time phase difference with the active modulation mode matching signal to realize vibration self-compensation imaging.

[0029] The device has two working modes:

[0030] Fixed differential mode, when the target and the radar relative motion, the target surface and the radar distance is Z, the MEMS rotating mirror is driven by the direct current signal generated by the signal generator, and the fixed deflection angle is maintained to ensure that the reflection echo light path matches the transmission light path. The optical path difference of the first 2x2 optical bridge and the second 2x2 optical bridge satisfies the phase relationship of synthetic aperture sampling. If the pulse repetition period is dt, the echo is arranged by the trigger signal of pulse repetition, and the original echo signal is subjected to fast Fourier transform for distance focusing, then the distance coordinate of the target is obtained by frequency modulation continuous wave ranging. C is the speed of light, and B is the chirp bandwidth, then the distance resolution is:

[0031]

[0032] The phase spectrum and amplitude spectrum A0 of the two focusing images (frequency domain signals) obtained by the dual aperture are calculated respectively, and the linear differential phase is accumulated to recover the secondary phase The echo secondary phase for matching and the matching signal phase need to be complex conjugate, and the reconstructed secondary phase is compensated by the known dual-aperture echo optical path difference d in the optical path building and data processing: if the relative motion speed is v, the azimuthal sampling step dy = v·dt, then the compensated accumulated recovered secondary phase is Finally, the reconstructed secondary phase is restored to the focused frequency domain signal Convolution of the fixed differential mode matching signal ha0 of the SAL imaging strip mode is azimuth focusing, and an image is obtained. In the imaging time T, m represents the sequence number of the pulse repetition period, and satisfies m∈{-M0,…,-1,0,1,…,M0}, wherein M0 is an integer, M=2M0+1 is the total number of periods, and M is the maximum odd number satisfying M≤T / dt. The fixed differential mode matching signal ha0 is determined by the following formula:

[0033]

[0034] Wherein λ is the wavelength of the laser, and j is the imaginary unit.

[0035] Further, the optical path difference d of the first 2×2 optical bridge and the second 2×2 optical bridge is equal to the azimuth sampling step dy, and the accumulated recovered quadratic phase is the target azimuth quadratic phase at this time, and the fixed differential mode matching signal ha0 can be determined by the following formula:

[0036]

[0037] The azimuth resolution Δy in the synthetic aperture laser radar is defined as the full width of the coherent point spread function L is the effective synthetic aperture length, which can be determined by the distance of the target moving in the imaged area jointly determined by the imaging time and the receiving field of view.

[0038] Active modulation mode, when the target and the radar are relatively static, the MEMS rotating mirror is driven by a periodic electric signal output by a signal generator to periodically swing, and the reflected echo spot is scanned in the plane perpendicular to the optical axis to form the azimuth quadratic phase history required by the synthetic aperture; combined with the vibration reference signal collected by the first 2×2 optical bridge, the active synthetic aperture imaging with vibration compensation is realized.

[0039] Further, the periodic electric signal, the driving current of which has a linear relationship with the rotation angle of the MEMS rotating mirror, rotates and modulates the reflected echo, so that the reflected echo spot is displaced in the plane perpendicular to the optical axis. Define the distance direction (optical axis direction) as z direction, and the azimuth direction (horizontal direction) as y direction, the x direction can be defined by the right-handed rectangular coordinate system, the coordinate projection of the target in the main plane is (x n ,y b ,z n ), and the target distance direction coordinate z n is obtained by frequency modulation continuous wave ranging. C is the speed of light, and B is the chirp bandwidth, and the distance direction resolution is:

[0040]

[0041] The derivation process of the matching signal ha is described below. The frequency-modulated continuous wave (FMCW) is transmitted to a stationary target in the far field through a convex lens. The key phase in the transmitting single optical path is has:

[0042]

[0043] where λ is the wavelength, F t is the transmitting equivalent curvature radius. The echo of the far-field target is coherent with the local signal, and the transmitted echo signal is the stationary target signal. r is the receiving equivalent curvature radius. The key phase in the receiving single optical path of the transmitted echo is has:

[0044]

[0045] The key phase of the transmitted echo data is the stationary target phase φ0 through the radar equation derivation. has:

[0046]

[0047] where φ0 is the stationary target phase, and φd is the disturbance phase caused by factors other than MEMS. The total equivalent curvature radius F has the formula: Substituting F into the formula, we get:

[0048]

[0049] For a determined stationary target, if the disturbance phase φd is constant, then the stationary target phase φ0 is constant.

[0050] Taking the rotation of the MEMS mirror around the x-axis as an example, the MEMS will cause the deflection of the reflected echo beam, so that the echo spot is scanned along the horizontal direction. The phase surface of the reflected echo is tilted, and the phase surfaces of different angles are coupled into the second 2x2 optical bridge. Assuming that the driving electrical signal generated by the signal generator is a triangular wave with a period of T e , the driving electrical signal needs to be a linear signal during imaging. In order to obtain a larger synthetic aperture length, the imaging time T = 0.5T e and T >> dt. During the imaging time T, m represents the sequence number of the pulse repetition period, which satisfies m ∈ {-M0,…,-1,0,1,…,M0}, where M0 is an integer, M = 2M0 + 1 is the total number of periods, and M is the maximum odd number that satisfies M ≤ T / dt. The driving electrical signal voltage in the pulse repetition period with sequence number m within the imaging time T is:

[0051] ​​​

[0052] U0 is the driving electric signal amplitude, dt is the pulse repetition period, the relationship between the driving electric signal voltage U and the MEMS rotating mirror rotation angle θ is:

[0053] θ = ηU

[0054] wherein η is the conversion coefficient of the driving electric signal voltage and the rotation angle, then the MEMS rotating mirror rotation angular velocity (unit: radian) is:

[0055]

[0056] Then the light ray angle change through the rotating mirror is The radar equation derived from the diffraction law is that the key phase of the reflection echo receiving single light path is has:

[0057]

[0058] wherein Z is the radar and target distance, mΔL1 is the y coordinate position of the reflection receiving port, and mΔL2 is the y coordinate position of the receiving field center at the target distance. Since the radar is stationary, mΔL1 = 0; the MEMS rotating mirror rotation axis center is on the convex lens front focal plane, combined with the MEMS rotating mirror angular velocity ω and the convex lens focal length f, then mΔL2 = f·tan(m·2ω·dt). The key phase of the reflection echo data is has:

[0059]

[0060] Substituting it is obtained:

[0061]

[0062] Wherein the quadratic phase history for the azimuth direction matching focusing is is:

[0063]

[0064] Then the matching signal ha of the active modulation mode is composed of the complex conjugate of the quadratic phase history :

[0065]

[0066] Let the sampling rate be fs, when processing echo data, the time domain signals received by the two 2*2 optical bridges are respectively divided into M segments of length dt, and arranged into two dt*fs rows M columns of echo matrix, the row dimension of the matrix corresponds to the azimuth direction, and the column dimension corresponds to the range direction. First, the distance direction is focused by fast Fourier transform to obtain the frequency peak, and then the phase of the azimuth direction is calculated respectively, so that the phase of the stationary target and the secondary phase modulated by the MEMS rotating mirror are obtained, and the amplitude spectrum A is obtained by taking the modulus of the FFT result of the reflected echo Restored to the focused frequency domain signal Further matched with ha in the azimuth direction.

[0067] The azimuth resolution Δy in the synthetic aperture laser radar is defined as the full width of the coherent point spread function L is the effective synthetic aperture length, which can be determined by the distance that the target moves in the imaged area jointly determined by the spot and the receiving field of view during imaging.

[0068] Compared with the prior art, the present application has the following technical effects:

[0069] The device can realize fixed differential synthetic aperture laser radar imaging, and can also actively synthesize phases by relying on the rotation of the MEMS rotating mirror on the reflected echo receiving path when the radar and the target remain stationary. In particular in the active modulation mode SAL imaging, the system has the following advantages:

[0070] The radar only needs to control the rotation of the MEMS rotating mirror, without complex motion control. In the system imaging, there is no need to perform secondary phase accumulation reconstruction, but rely on the received phase floating to directly difference the phase disturbance Self-compensating, strong anti-vibration ability, and simple data processing flow. The radar and the target are both in a stationary state, so the phase disturbance caused by vibration is small, reducing the pressure of system noise suppression. And when the target signal is severely polluted by noise, the system can still image stably, and has higher imaging sensitivity than the received fixed differential SAL, and can realize stable imaging of weak echo targets in the case of large common mode phase error. The weak echo signal with an average signal-to-noise ratio of 3.15dB in the range compressed image can still be imaged stably. BRIEF DESCRIPTION OF DRAWINGS

[0071] Figure 1 is a structure schematic diagram of a vibration self-compensating active differential SAL imaging device of the present application;

[0072] Figure 2 is an imaging result graph of a vibration self-compensating active differential SAL imaging embodiment of the present application;

[0073] Figure 3 is a non-compensated imaging result figure of one vibration self-compensated active differential SAL imaging embodiment of the present application;

[0074] Figure 4 is an imaging result figure of one target moving fixed differential synthetic aperture lidar embodiment of the present application;

[0075] The figure mark is explained: 1-emitting collimating head, 2-emitting polarization beam splitter, 3-1 / 4 wave plate, 4-convex lens, 5-mirror, 6-half wave plate, 7-first polarization beam splitter, 8-second polarization beam splitter, 9-local oscillation collimating head, 10-first 2x2 optical bridge, 11-MEMS rotating mirror, 12-third polarization beam splitter, 13-second 2x2 optical bridge, 14-signal generator. DETAILED DESCRIPTION

[0076] The present application is further explained in conjunction with the drawings and embodiments, but the protection scope of the present application should not be limited by this.

[0077] Referring to the drawings, Figure 1 The present application proposes a vibration self-compensated active differential SAL imaging device, including emitting collimating head 1, emitting polarization beam splitter 2, 1 / 4 wave plate 3, convex lens 4, mirror 5, half wave plate 6, first polarization beam splitter 7, second polarization beam splitter 8, local oscillation collimating head 9, first 2x2 optical bridge 10, MEMS rotating mirror 11, third polarization beam splitter 12, second 2x2 optical bridge 13, signal generator 14.

[0078] Embodiment 1: the radar platform and the target are both in a static state, the MEMS rotating mirror periodically swings, referring to the drawings, Figure 1 The optical path system is built, the convex lens is three-dimensionally adjusted, so that the center position of the emitting main light beam remains unchanged whether it passes through the convex lens or not, the center of the convex lens is coaxially aligned with the emitting laser main light beam. The focal length f of the convex lens is 277mm, the reference parallel light can be used, the position of the convex lens is adjusted so that the light spot converges at the center of the MEMS rotating mirror rotating shaft. The relationship between the driving electric signal and the MEMS rotating mirror rotating angle is η=0.5° / V, the optical path is adjusted so that when the driving electric signal voltage U(mdt)=0V, the MEMS rotating mirror will reflect the echo light spot center to be coupled to the second 2x2 optical bridge. The signal generator generates a triangular wave driving electric signal with a period T e =0.25s and an amplitude U0=6V, which is connected to the x-axis driving input end of the MEMS rotating mirror, so that the imaging time T=0.5T e= 0.125s, the driving electrical signal voltage linearly changes. M is the maximum odd number satisfying M≤2000, then M0=9999, and the pulse repetition period sequence number m∈{-9999,…,-1,0,1,…,9999}. Referring to Figure 1 , the MEMS rotating mirror rotates linearly around the x-axis in the horizontal direction, and the MEMS rotating mirror rotation angle θ linearly changes within the imaging time T. The rotating mirror rotation angular velocity , then the echo deflection angular velocity The half-wave plate is set to make the reflection echo and the transmission echo have a 1:1 light splitting ratio. The laser wavelength λ=1550nm, the frequency-modulated continuous wave period dt=1 / 160000s, the convex lens distance from the target surface is Z=12.634m, the reflection receiving curvature radius F r =5.6913m. The transmitting and receiving collimating head apertures are both 0.45mm, the target illumination spot diameter is 2.12cm, the receivable range diameter is 3.49cm, and the receiving field of view scanning range is 2.90cm, so the effective synthetic aperture length is L=2.12cm. The chirp bandwidth is B=4.6×10 9 HZ, c is the light speed, and the range resolution is The system parameters can be used to obtain the active modulation mode matching signal for azimuth focusing , wherein

[0079]

[0080] The sampling rate fs=500MHZ, after the collected time domain signal is rearranged into an echo matrix, the range is subjected to fast Fourier transform to obtain a range compressed image. The transmission echo and the reflection echo phases and the reflection echo amplitude A are respectively obtained, and the differential phase is further obtained. The phase disturbance is compensated Finally, the differential self-compensated signal is convoluted with the active modulation mode matching signal ha to obtain a final image.

[0081] In the imaging process, if other errors are not considered, the theoretical azimuth resolution In the range compressed echo spectrum, when the range compressed image average signal-to-noise ratio is 3.15dB, the first example of the system imaging result of the multi-angle pyramid target surface after the vibration self-compensation is shown in Figure 2 From the figure, it can be seen that when the signal-to-noise ratio is 3.15dB, the vibration self-compensation algorithm can still clearly image, verifying the stability of the system in imaging weak signals.

[0082] For a determined stationary target, the stationary target phase reflects the phase disturbance. The maximum static phase disturbance amplitude in this embodiment is 2.59π. If the same imaging process is performed on the reflected echo of the multi-angle pyramid target surface alone, the azimuth direction cannot be focused, as shown in FIG. 6, which is an imaging result without vibration compensation. The azimuth direction is defocused due to the phase disturbance, verifying the necessity of the self-compensation algorithm. Figure 3 As shown in FIG. 6, the azimuth direction is defocused due to the phase disturbance, verifying the necessity of the self-compensation algorithm.

[0083] Embodiment 2: The target moves, the MEMS rotating mirror is fixedly deflected, and the radar platform and the MEMS rotating mirror are in a static state, that is, the driving electrical signal of the signal generator is U(mdt) = 0V, and the other optical path systems are built in the same way as in Embodiment 1. In the system, the system parameters of Z, λ, fs, dt, f, B, T, the collimating head aperture, and the half-wave plate splitting ratio are the same as in Embodiment 1. The target moves in the y direction at a speed of v = 181mm / s, the optical path difference d of the first 2x2 optical bridge and the second 2x2 optical bridge is 600um, and the azimuth direction sampling step dy = vdt = 1131.25um, so the cumulative reconstruction phase The second phase opening needs to be corrected Finally, the focused frequency domain signal is restored Convolution with the fixed differential mode matching signal ha0 to perform azimuth direction matching focusing:

[0084]

[0085] Similarly, the imaging resolution is:

[0086] In the distance-compressed echo spectrum, when the average signal-to-noise ratio of the distance-compressed image in the echo signal is 11.01dB, the second example of the imaging result of the multi-angle pyramid target surface is Figure 4 As shown in FIG. 10, when the radar and the target move relative to each other, the system can also realize SAL imaging in the fixed differential mode by only changing the MEMS deflection state.

Claims

1. A vibration self-compensating active differential SAL imaging device, characterized in that: The optical fiber optical system comprises an emission collimator (1), an emission polarization beam splitter (2), a quarter wave plate (3), a convex lens (4), a reflector (5), a half wave plate (6), a first polarization beam splitter (7), a second polarization beam splitter (8), a local oscillator collimator (9), a first 2×2 optical bridge (10), a MEMS rotating mirror (11), a third polarization beam splitter (12), a second 2×2 optical bridge (13), and a signal generator (14). The positional relationship of the above components is as follows: The linearly polarized light beam output by the laser light source is collimated by the emission collimator (1) and then completely reflected by the emission polarization beam splitter (2), and then passes through a quarter wave plate (3), a convex lens (4) and a reflector (5) in sequence to reach a far-field target; The target echo signal returns along the original path, passes through the reflector (5), convex lens (4), and 1 / 4 wave plate (3) in sequence, and is transmitted by the transmitting polarization beam splitter (2). The transmitted echo is divided into two paths, a transmitted echo and a reflected echo, by the half-wave plate (6) and the first polarization beam splitter (7); the transmitted echo is transmitted by the second polarization beam splitter (8), and then is combined with the cognate coherent local oscillator light collimated by the local oscillator collimator head (9) after being reflected by the second polarization beam splitter (8), and then is transmitted to the first 2×2 optical bridge (10); the reflected echo is reflected by the MEMS rotating mirror (11) and the third polarization beam splitter (12), and then is combined with the cognate coherent local oscillator light collimated by the local oscillator collimator head (9) after being transmitted by the second polarization beam splitter (8) and the third polarization beam splitter (12), and then is transmitted to the second 2×2 optical bridge (13); The center of the rotating axis of the MEMS rotating mirror (11) is located on the front focal plane of the convex lens (4), and is used to perform controllable phase modulation on the reflected echo and introduce a secondary phase process in the azimuth direction; the first 2×2 optical bridge (10) is used to collect the vibration reference signal of the interference between the transmitted echo and the local oscillator light in the active modulation mode, and is used to collect the target imaging signal of the interference between the transmitted echo and the local oscillator light in the fixed differential mode; the second 2×2 optical bridge (13) is used to collect the target imaging signal of the interference between the MEMS modulated reflected echo and the local oscillator light; the signal generator (14) is used to drive the MEMS rotating mirror (11) to perform periodic swing or fixed deflection; the phase data of the two signals are processed by a phase differential algorithm to eliminate the vibration noise phase and extract the target phase information, so that vibration self-compensation imaging can be achieved in the active modulation mode.

2. The vibration self-compensating active differential SAL imaging device according to claim 1, characterized in that: The center of the convex lens (4) is coaxially aligned with the main beam of the emitted laser, thereby ensuring the collimation of the beam transmission.

3. The vibration self-compensating active differential SAL imaging device according to claim 1, characterized in that: The phase difference algorithm includes the following steps: (1) In fixed differential mode: a) extracting a phase from a target imaging signal collected by a first 2×2 optical bridge (10); b) extracting a phase from a target imaging signal collected by a second 2×2 optical bridge (13); c) Calculate the phase difference between the two signals; d) reconstructing the azimuth secondary phase by accumulating phase differences; e) compensating the reconstructed phase based on the optical path difference of the dual-aperture echo; f) convolving the compensated phase with the fixed differential pattern matching signal to achieve azimuth focused imaging; (2) In active modulation mode: a) extracting a phase from a vibration reference signal collected by a first 2×2 optical bridge (10); b) extracting a phase from a target imaging signal collected by a second 2×2 optical bridge (13); c) Calculate the real-time phase difference between the two signals; d) using the real-time phase difference as the secondary phase in azimuth; e) Convolving the real-time phase difference with the active modulation pattern matching signal to achieve vibration self-compensation imaging.

4. The vibration self-compensating active differential SAL imaging device according to claim 3, characterized in that: In the active modulation mode, the signal generator (14) outputs a periodic electrical signal to drive the MEMS mirror (11) to oscillate periodically; In a fixed differential mode, the signal generator (14) outputs a DC signal to keep the MEMS mirror (11) at a fixed deflection angle.

5. The vibration self-compensating active differential SAL imaging device according to claim 4, characterized in that: In the active modulation mode, the MEMS mirror (11) performs linear periodic rotation, so that the reflected echo light spot generates a scanning displacement in a plane perpendicular to the optical axis, thereby forming an azimuth secondary phase process required for synthetic aperture.

6. The vibration self-compensating active differential SAL imaging device according to claim 5, characterized in that: In the active modulation mode, the driving current of the periodic electrical signal is linearly related to the rotation angle of the MEMS mirror (11).

7. The vibration self-compensating active differential SAL imaging device according to claim 4, characterized in that: In the fixed differential mode, the optical path difference between the first 2×2 optical bridge (10) and the second 2×2 optical bridge (13) is equal to the azimuth sampling step length.

Images