High-precision area array 4D imaging optical method and system based on coherent detection

Abstract

The invention belongs to the technical field of intelligent sensors, and particularly relates to a high-precision area array 4D imaging optical method and system based on coherent detection. The method specifically comprises the following steps of: generating a step frequency signal by using an arbitrary waveform generator, loading the step frequency signal on an electro-optical modulator, and modulating a light beam output by a laser; the modulated laser is divided into reflected light and reference light, and the reflected light is reflected by an object to be detected and then enters the area array optical imaging device together with the reference light; the area array optical imaging device comprises a space bridge and a CCD (Charge Coupled Device) photosensitive area, the space bridge splits incident light into four paths through beam splitting control, and the space bridge regulates and controls the polarization state of the incident light, so that a phase difference exists between reference light and reflected light in each path of light beam; coherent processing is carried out on multiple frames of voltage data in each pixel, and the linear frequency modulation rate is calculated; and calculating the speed and position of each pixel target based on the linear frequency modulation rate to realize 4D high-precision imaging of the target.

Description

Technical Field

[0001] The present invention belongs to the technical field of intelligent sensors, and in particular relates to a high-precision area array 4D imaging optical method and system based on coherent detection. Background Art

[0002] With the continuous advancement of science and technology, the way of acquiring and displaying information has changed from 2D imaging to 3D imaging. Currently, 3D imaging technology is widely used in fields such as medicine, industrial manufacturing, cultural heritage protection, and virtual reality, achieving three-dimensional, realistic, and detailed imaging of targets. However, traditional 3D imaging technology lacks the ability to obtain dynamic information about targets changing over time, and cannot meet the needs of analyzing and understanding dynamic processes. 4D imaging technology captures the dynamic changes of targets in real time and extracts target speed information by adding a time dimension. Compared with 3D imaging technology, 4D imaging technology can achieve accurate perception of four-dimensional information of target distance, direction, height, and speed. In summary, the research of high-precision 4D imaging technology is of great significance to the fields of autonomous driving, medical diagnosis, and robotic vision.

[0003] Currently, high-precision 4D imaging technology is primarily based on the principle of coherent detection. This involves transmitting a frequency-modulated continuous wave (FMCW) signal and receiving the reflected signal from the target. The frequency variation between the transmitted and received signals is extracted, and through coherent processing, both the distance and velocity of the target object can be simultaneously determined. However, ideal FMCW signals are difficult to generate. Nonlinearities in the laser source or oscillator can cause distortion in the frequency modulation curve and inconsistent frequency slopes, which in turn leads to spectral broadening of the beat frequency signal and a degraded signal-to-noise ratio, making it difficult to accurately extract the target frequency. Stepped-frequency signals, on the other hand, utilize discrete frequency steps, with each sub-pulse occupying a fixed, narrow frequency band. This avoids the nonlinear accumulation effects of continuous frequency modulation. Furthermore, the frequency stepping is precisely controlled by an external arbitrary waveform generator, independent of the linearity of the continuous frequency modulation device. This significantly reduces the impact of nonlinear errors on system performance. Compared to FMCW, stepped-frequency signals can achieve a wider system bandwidth by synthesizing the equivalent bandwidth of N sub-pulses, thereby achieving higher range resolution and improving system measurement accuracy. However, 4D imaging technologies based on stepped-frequency signals have not yet been reported.

[0004] Currently, the primary optical imaging system based on coherent detection is lidar. Based on the amount of target information acquired and the implementation method, lidar is categorized into single-point lidar, scanning lidar, and area array lidar. Single-point lidar offers a long range and high accuracy, but it can only capture information from a single point, limiting its scope of application. To acquire information from multiple points on a target, scanning 3D lidar performs a two-dimensional scan on the imaging surface of the single-point lidar to acquire 3D information about the target. However, the scanning mechanism is complex, has low reliability, and echo delay increases the time required to capture a full frame. Area array lidar, on the other hand, can achieve high-resolution, high-frame-rate image acquisition, lacks a scanning structure, and enables fully solid-state beam control, making it a key development direction in lidar detection. Currently, the main detector arrays used in area array lidars include single-photon detector (APD) arrays and charge-coupled devices (CCDs). APD arrays are limited by pixel size and inter-pixel photoelectron crosstalk, while CCDs have reached the megapixel level through continuous development. Therefore, CCD-based area array optical imaging technology has certain development prospects for high-resolution 4D imaging. However, high-precision CCD area array 4D optical imaging methods and systems based on coherent detection have not yet been reported. Summary of the Invention

[0005] In view of this, the present invention provides a high-precision area array 4D imaging optical method and system based on coherent detection, which can perform 4D imaging on an object to be measured.

[0006] The technical solutions for implementing the present invention are as follows:

[0007] In a first aspect, the present invention provides a high-precision area array 4D imaging optical method based on coherent detection, the specific process of which is as follows:

[0008] An arbitrary waveform generator generates a stepped frequency signal, which is then loaded onto an electro-optical modulator to modulate the laser output beam. The modulated laser light is then divided into reflected light and reference light. After being reflected by the object to be detected, the reflected light and the reference light are incident on the area array optical imaging device.

[0009] The area array optical imaging device includes a spatial bridge and a CCD photosensitive area. The spatial bridge splits the incident light into four beams through beam splitting control, evenly distributing the four beams to different CCD photosensitive areas. The spatial bridge controls the polarization state of the incident light to ensure that the reference light and the reflected light in each beam have phase differences of 0°, 90°, 180°, and 270°. The reference light and the reflected light are mixed and beat in the CCD photosensitive area, converting the frequency change caused by the motion of the object to be measured into a voltage signal output.

[0010] After a set integral exposure time, different CCD photosensitive areas output voltage data of different phases, and coherent processing is performed on multiple frames of voltage data within each pixel to calculate the linear frequency modulation rate. The speed and position of the target in each pixel are calculated based on the linear frequency modulation rate to achieve 4D high-precision imaging of the target.

[0011] Optionally, the present invention sets the CCD exposure time and imaging frame rate f of the area array optical device frame , so that each frame is consistent with the step frequency switching time, the time t is:

[0012] t=t0+kΔt,k=0,1…,N-1 (5)

[0013] Where t0 is the time when the CCD starts working, N is the total number of frames measured, Δt is the step frequency switching time, and Δt=1 / f frame .

[0014] Optionally, the present invention combines four CCD integrated voltages of different phases to obtain a new voltage term:

[0015]

[0016] Among them, U1~U4 are the integrated voltages of four different phases.

[0017] The voltage is subjected to a discrete short-time Fourier transform to obtain a relationship between the signal frequency and time, ie, a linear frequency modulation rate r.

[0018] Optionally, the speed v and distance d of the target in the present invention are:

[0019]

[0020] Where r is the linear frequency modulation rate, f st is the starting frequency in the spectrum diagram, c is the speed of light, f0 is the starting frequency of the stepped frequency signal, and Δf is the step size of the stepped frequency signal.

[0021] Optionally, the present invention utilizes the optical fiber coupler 4 to split the input light into signal light and reference light according to a power ratio of 90:10.

[0022] In a second aspect, the present invention provides a high-precision area array 4D imaging optical system based on coherent detection, comprising:

[0023] Laser, electro-optical modulator, arbitrary waveform generator, reference optical path, signal optical path, array optical imaging device and controller; wherein,

[0024] A laser, for outputting a laser beam;

[0025] Arbitrary waveform generator, used to generate stepped frequency signal and load it onto the electro-optical modulator;

[0026] An electro-optical modulator is used to modulate the laser output beam and split it into reflected light and reference light after modulation;

[0027] The reflected light path is used to emit the modulated reflected light to the object to be detected, and then enter the area array optical imaging device after being reflected by the object to be detected;

[0028] Reference light path, used to inject the modulated reference light into the area array optical imaging device

[0029] The area array optical imaging device includes a spatial bridge and a CCD photosensitive area. The spatial bridge splits the incident light into four beams through beam splitting control, evenly distributing the four beams to different CCD photosensitive areas. The spatial bridge controls the polarization state of the incident light to ensure that the reference light and the reflected light in each beam have phase differences of 0°, 90°, 180°, and 270°. The reference light and the reflected light are mixed and beat in the CCD photosensitive area, converting the frequency change caused by the motion of the object to be measured into a voltage signal output.

[0030] The controller is used to collect voltage data of different phases in different CCD photosensitive areas after a set integral exposure time, and coherently process multiple frames of voltage data in each pixel to calculate the linear frequency modulation rate; based on the linear frequency modulation rate, the speed and position of the target in each pixel are calculated to achieve 4D high-precision imaging of the target.

[0031] Optionally, the reflective light path of the present invention includes a second polarization controller 5 , a first collimator 6 and a first convex lens 7 which are arranged in sequence.

[0032] Optionally, the reference optical path of the present invention includes a third polarization controller 10, a second collimator 11, a second convex lens 12 and a pinhole filter 13, which are arranged in sequence.

[0033] Beneficial effects:

[0034] (1) The present invention adopts stepped frequency signal modulation, where each frequency step corresponds to a single time frame. Through sequential frequency scanning, coherent synthesis of multiple frames of received signals is performed to extract frequency domain peak information, thereby achieving high-precision depth and velocity information.

[0035] (2) This invention floods the entire scene with a stepped frequency modulated optical signal and converges the reflected light and reference light onto the CCD photosensitive area via a spatial bridge. This eliminates the need for mechanical scanning structures to control the beam and the need for complex phase control based on an optical phased array, achieving all-solid-state area array imaging, thereby improving system reliability and stability. Furthermore, the mature large-scale CCD provides technical support for high-resolution imaging.

[0036] (3) This invention uses a semiconductor laser as the light source and an electro-optical modulator for external intensity modulation to enhance the coherence length of the laser emission signal, thereby improving measurement stability and long-distance measurement performance. Furthermore, the use of a narrow-linewidth laser further enhances system coherence, ensuring high-precision 4D measurement at longer measurement distances.

[0037] (4) The present invention performs optical imaging based on the coherent detection principle, eliminates the interference of background light, improves the detection distance of the system and enhances the anti-interference ability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0039] Figure 1 This is a structural block diagram of the high-precision area array 4D imaging optical system based on coherent detection of the present invention.

[0040] Among them, 1-narrow linewidth laser, 2-first polarization controller (PC1), 3-electro-optic modulator (MZM), 4-fiber coupler (OC), 5-second polarization controller (PC2), 6-first collimator (COL1), 7-first convex lens (L1), 8-controller, 9-arbitrary waveform generator (AWG), 10-third polarization controller (PC3), 11-second collimator (COL2), 12-second convex lens (L2), 13-pinhole filter, 14-array optical imaging device, 15-target to be measured.

[0041] Figure 2 It is a 4D imaging point cloud map.

[0042] Figure 3 This is the velocity imaging result.

[0043] Figure 4 This is the range imaging result diagram. DETAILED DESCRIPTION

[0044] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0045] It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments may be combined with each other; and, based on the embodiments in this disclosure, all other embodiments obtained by persons of ordinary skill in the art without creative work are within the scope of protection of this disclosure.

[0046] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on this disclosure, it should be understood by those skilled in the art that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects described herein can be used to implement an apparatus and / or practice a method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this apparatus and / or practice this method.

[0047] like Figure 1 As shown, the embodiment of the present application is a high-precision area array 4D imaging optical method based on coherent detection, and the specific process is as follows:

[0048] First, an arbitrary waveform generator generates a stepped frequency signal and applies it to an electro-optical modulator to modulate the laser output beam. The modulated laser beam is then split into reflected light and reference light. After being reflected by the object to be detected, the reflected light and the reference light are incident on the area array optical imaging device.

[0049] Secondly, the area array optical imaging device includes a spatial bridge and a CCD photosensitive area. The spatial bridge splits the incident light into four beams through beam splitting control, evenly distributing the four beams to different CCD photosensitive areas. The spatial bridge controls the polarization state of the incident light to ensure that the reference light and the reflected light in each beam have phase differences of 0°, 90°, 180°, and 270°. The reference light and reflected light are mixed and beat in the CCD photosensitive area, converting the frequency change caused by the motion of the object to be measured into a voltage signal output.

[0050] Finally, after the set integral exposure time, different CCD photosensitive areas output voltage data of different phases, and coherent processing is performed on multiple frames of voltage data in each pixel to calculate the linear frequency modulation rate. The speed and position of each pixel target are calculated based on the linear frequency modulation rate, achieving 4D high-precision imaging of the target.

[0051] This embodiment uses a stepped frequency signal for intensity modulation. The narrow linewidth signal output by the laser serves as a carrier input to an electro-optical modulator (in this embodiment, the electro-optical modulator can be a Mach-Zehnder modulator). An arbitrary waveform generator generates a stepped frequency signal, which is then applied to the Mach-Zehnder modulator for modulation, achieving highly stable and coherent stepped frequency modulation. The modulated laser signal is then split into reflected light and reference light by a fiber coupler. These two beams travel through a spatial optical path through a planar array optical imaging device. By controlling the phase variation of the light, voltage data of different phases is output on four CCDs. Coherent processing of multiple frames of voltage data within each pixel enables precise extraction of target velocity and distance information, achieving high-precision 4D imaging of the target. Compared to traditional laser imaging systems, this method can achieve 4D imaging of the target, simultaneously acquiring the target's velocity field image, distance, azimuth, and altitude information, with imaging accuracy reaching the millimeter level. Furthermore, the CCD-based flash active imaging system also achieves high image resolution using a fully solid-state scanning method.

[0052] like Figure 1 As shown, this embodiment provides a high-precision area array 4D imaging optical system based on coherent detection, including: a laser, an electro-optical modulator, an arbitrary waveform generator, a reference optical path, a signal optical path, an area array optical imaging device, and a controller; wherein,

[0053] Laser, electro-optic modulator, arbitrary waveform generator, fiber coupler, reference optical path, signal optical path, array optical imaging device and controller; wherein,

[0054] A laser, for outputting a laser beam;

[0055] Arbitrary waveform generator, used to generate stepped frequency signal and load it onto the electro-optical modulator;

[0056] An electro-optical modulator, used to modulate the laser output beam;

[0057] A fiber coupler is used to split the modulated light into reflected light and reference light;

[0058] The reflected light path is used to emit the modulated reflected light to the object to be detected, and then enter the area array optical imaging device after being reflected by the object to be detected;

[0059] Reference light path, used to inject the modulated reference light into the area array optical imaging device

[0060] The area array optical imaging device includes a spatial bridge and a CCD photosensitive area. The spatial bridge splits the incident light into four beams through beam splitting control, evenly distributing the four beams to different CCD photosensitive areas. The spatial bridge controls the polarization state of the incident light to ensure that the reference light and the reflected light in each beam have phase differences of 0°, 90°, 180°, and 270°. The reference light and the reflected light are mixed and beat in the CCD photosensitive area, converting the frequency change caused by the motion of the object to be measured into a voltage signal output.

[0061] The controller is used to collect voltage data of different phases in different CCD photosensitive areas after a set integral exposure time, and coherently process multiple frames of voltage data in each pixel to calculate the linear frequency modulation rate; based on the linear frequency modulation rate, the speed and position of the target in each pixel are calculated to achieve 4D high-precision imaging of the target.

[0062] The laser in this embodiment is a narrow-linewidth laser 1. The output optical path of the narrow-linewidth laser 1 is further provided with a first polarization controller 2, an electro-optical modulator 3, and a fiber coupler 4. The reflected optical path includes a second polarization controller 5, a first collimator 6, and a first convex lens 7 arranged in sequence. The reference optical path includes a third polarization controller 10, a second collimator 11, a second convex lens 12, and a pinhole filter 13 arranged in sequence. That is, the photoelectric imaging system includes: a narrow-linewidth laser 1, a first polarization controller 2, an electro-optical modulator 3, a fiber coupler 4, a second polarization controller 5, a first collimator 6, a first convex lens 7, a controller 8, an arbitrary waveform generator 9, a third polarization controller 10, a second collimator 11, a second convex lens 12, a pinhole filter 13, and a planar array optical imaging device 14, and a target to be measured 15. The planar array optical imaging device 14 includes. The connection relationship is as follows:

[0063] The narrow linewidth laser 1 is connected to the first polarization controller 2 through an optical fiber, the output end of the first polarization controller 2 is connected to the input end of the electro-optical modulator 3 through an optical fiber, the output end of the electro-optical modulator 3 is connected to the input end of the fiber coupler 4 through an optical fiber, the two output ends of the fiber coupler 4 are respectively connected to the second polarization controller 5 and the third polarization controller 10 through optical fibers, the second polarization controller 5 is connected to the first collimator 6, and the third polarization controller 10 is connected to the second collimator 11 through an optical fiber.

[0064] The output light of the first collimator 6 is received by the first convex lens 7, and the output light of the first convex lens 7 covers and illuminates the target 15 to be measured. The target 15 to be measured reflects the light signal in a moving state, and the reflected light is transmitted through the optical path and received by the spatial bridge inside the area array optical imaging device 14.

[0065] The output light of the second collimator 11 is received by the second convex lens 12 , and the output light of the second convex lens 12 is spatially filtered by the pinhole filter 13 . The filtered light signal enters the spatial bridge inside the area array optical imaging device 14 for further processing.

[0066] The area array optical imaging device 14 is connected to the controller 8 via a circuit. The controller 8 is connected to the narrow linewidth laser 1 and the arbitrary waveform generator 9 via a circuit respectively. The arbitrary waveform generator 9 is connected to the electro-optical modulator 3 via a circuit.

[0067] In another embodiment of the present application, the controller 8 controls the arbitrary waveform generator 9 to emit a linearly increasing stepped frequency modulation signal, which is loaded on the electro-optical modulator 3. External intensity modulation is used to modulate the narrow linewidth laser with a long coherence distance, which is beneficial for imaging long-distance targets. To ensure system stability and reduce the influence of high-order sidebands, the electro-optical modulator 3 operates under small signal modulation conditions, that is, the output voltage of the arbitrary waveform generator 9 is much lower than the half-wave voltage V of the electro-optical modulator. π .

[0068] After the modulated light enters the fiber coupler 4, it is divided into two signals: reference light and signal light. In this embodiment, the fiber coupler 4 divides the input light into signal light and reference light at a power ratio of 90:10. After being split by the fiber coupler 4, the signal light is polarized by the second polarization controller 5 and sent to the first collimator 6 to be coupled from the optical fiber into the spatial light path. The signal light coupled into the space is expanded by the first convex lens 7, and the field of view covers the target to be measured 15. Assume that the target to be measured 15 in this embodiment includes a rabbit and a turtle. The rabbit and the turtle move in a straight line at a uniform speed of v1 and v2, respectively, and at the same time reflect the irradiated light to the array optical imaging device 14.

[0069] Meanwhile, the reference light undergoes polarization adjustment by a third polarization controller 10 and is then sent to a second collimator 11 for coupling into the spatial optical path. The reference light then passes through a second convex lens 12 and is focused at the center of the pinhole in a pinhole filter 13. This spatially filters the input light, removing high-frequency components and eliminating stray light, improving beam quality and, consequently, imaging quality. The filtered reference light then enters an area array optical imaging device 14.

[0070] The area array optical imaging device 14 is composed of a spatial optical bridge and a CCD. The spatial optical bridge introduces reference light and reflected light, and the formula is expressed as:

[0071]

[0072] Among them, A l and A e are the reference light and signal light intensities respectively, ω is the frequency of the narrow linewidth laser emission, τ is the round-trip time delay, is the phase change caused by the electro-optic modulator.

[0073] By controlling the polarization state of light and beam splitting, the incident light beam is split into four paths, evenly distributing the reference light and reflected light to different CCD photosensitive areas. This special beam splitting method ensures that the phase differences between the reference light and reflected light in each path are 0°, 90°, 180°, and 270°, respectively.

[0074] Set the CCD exposure time and imaging frame rate so that each frame is consistent with the step frequency switching time. In each time frame, a single photosensitive unit (pixel) is exposed, and the reference light and reflected light are mixed and beat-frequencyed in the photosensitive area, converting the frequency change caused by the object movement into a voltage signal output. The mixed beat-frequency signal can be expressed as:

[0075]

[0076] in, is the responsivity of the CCD.

[0077] Since electro-optical modulation contains multiple sidebands, only the DC term and the first-order sideband are retained due to the bandwidth limitation of the CCD, and all other high-frequency terms are filtered out. Therefore, when the Mach-Zehnder modulator operates at a small modulation index, the output voltage after the signal light and the reflected light are mixed in the CCD photosensitive area can be expressed as the superposition of the DC term and the first-order sideband:

[0078]

[0079] Among them, U DC Indicates DC voltage, f m is the stepped frequency signal output by the arbitrary waveform generator, f m =f0+Δf·t, where f0 is the starting frequency of the stepped frequency signal, Δf is the step size of the stepped frequency signal, β is the modulation index of the electro-optic modulator, v is the target velocity, d is the target distance, c is the speed of light, and J1(β) is a first-order Bessel function.

[0080] The signal light and reflected light with different phase differences are mixed in the CCD photosensitive area and then pass through the T exp The integrated exposure time is calculated by combining the CCD integrated voltages of four different phases, U1 to U4, to obtain a new voltage term:

[0081]

[0082] The DC voltage term U of U(t) can be eliminated by equation (4): DC , eliminate the influence of background light or external environment interference on measurement, and improve the system's anti-interference ability.

[0083] When the area array optical imaging device 14 starts working, the frame rate f of the CCD is adjusted. frame Keeping consistent with the frequency switching of the step frequency signal, the time t is:

[0084] t=t0+kΔt,k=0,1…,N-1 (5)

[0085] Where t0 is the time when the CCD starts working, N is the total number of frames measured, Δt is the time per frame (step frequency switching time), and Δt=1 / f frame .

[0086] Switch the step frequency and collect the voltage signals of the four CCDs in different time frames in real time, and transmit them to the controller 8. Combining equations (4) and (5), we can get:

[0087]

[0088] And perform discrete short-time Fourier transform on equation (6) to obtain the relationship between the signal frequency and time, that is, the linear frequency modulation rate r, and obtain the time-frequency relationship diagram and spectrum diagram of the signal, and calculate the speed and distance of the target:

[0089]

[0090] Among them, r is the linear frequency modulation rate, that is, the slope of the step frequency signal changing with time, f st is the starting frequency in the spectrum graph.

[0091] In actual situations, the above operations are performed in each pixel of the CCD, and the distance and speed information of the target corresponding to each pixel can be calculated at the same time, which not only realizes single-target 4D imaging, but also simultaneously images the velocity field in the measurement scene, and can realize multi-target 4D imaging in the scene to be measured, such as Figure 2-4 shown.

[0092] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-precision area array 4D imaging optical method based on coherent detection, characterized in that: The specific process is: An arbitrary waveform generator generates a stepped frequency signal, which is then loaded onto an electro-optical modulator to modulate the laser output beam. The modulated laser light is then divided into reflected light and reference light. After being reflected by the object to be detected, the reflected light and the reference light are incident on the area array optical imaging device. The area array optical imaging device includes a spatial bridge and a CCD photosensitive area. The spatial bridge splits the incident light into four beams through beam splitting control, evenly distributing the four beams to different CCD photosensitive areas. The spatial bridge controls the polarization state of the incident light to ensure that the reference light and the reflected light in each beam have phase differences of 0°, 90°, 180°, and 270°. The reference light and the reflected light are mixed and beat in the CCD photosensitive area, converting the frequency change caused by the motion of the object to be measured into a voltage signal output. After a set integral exposure time, different CCD photosensitive areas output voltage data of different phases, and coherent processing is performed on multiple frames of voltage data within each pixel to calculate the linear frequency modulation rate. The speed and position of the target in each pixel are calculated based on the linear frequency modulation rate to achieve 4D high-precision imaging of the target.

2. The high-precision area array 4D imaging optical method based on coherent detection according to claim 1, characterized in that: Set the CCD exposure time and imaging frame rate f of the area array optical device frame , so that each frame is consistent with the step frequency switching time, the time t is: t=t0+kΔt,k=0,1...,N-1 Where t0 is the time when the CCD starts working, N is the total number of frames measured, Δt is the step frequency switching time, and Δt=1 / f frame .

3. The high-precision area array 4D imaging optical method based on coherent detection according to claim 2, characterized in that: Combining the CCD integrated voltages of four different phases, we get a new voltage term: Among them, U1~U4 are the integrated voltages of four different phases. The voltage is subjected to a discrete short-time Fourier transform to obtain a relationship between the signal frequency and time, ie, a linear frequency modulation rate r.

4. The high-precision area array 4D imaging optical method based on coherent detection according to claim 3, characterized in that: The speed v and distance d of the target are: Where r is the linear frequency modulation rate, f st is the starting frequency in the spectrum diagram, c is the speed of light, f0 is the starting frequency of the stepped frequency signal, and Δf is the step size of the stepped frequency signal.

5. The high-precision area array 4D imaging optical method based on coherent detection according to claim 1, characterized in that: The input light is split into signal light and reference light at a power ratio of 90:10 using a fiber coupler 4 .

6. A high-precision area array 4D imaging optical system based on coherent detection, characterized in that: include Laser, electro-optical modulator, arbitrary waveform generator, reference optical path, signal optical path, array optical imaging device and controller; wherein, A laser, for outputting a laser beam; Arbitrary waveform generator, used to generate stepped frequency signal and load it onto the electro-optical modulator; An electro-optical modulator is used to modulate the laser output beam and split it into reflected light and reference light after modulation; The reflected light path is used to emit the modulated reflected light to the object to be detected, and then enter the area array optical imaging device after being reflected by the object to be detected; Reference light path, used to inject the modulated reference light into the area array optical imaging device The area array optical imaging device includes a spatial bridge and a CCD photosensitive area. The spatial bridge splits the incident light into four beams through beam splitting control, evenly distributing the four beams to different CCD photosensitive areas. The spatial bridge controls the polarization state of the incident light to ensure that the reference light and the reflected light in each beam have phase differences of 0°, 90°, 180°, and 270°. The reference light and the reflected light are mixed and beat in the CCD photosensitive area, converting the frequency change caused by the motion of the object to be measured into a voltage signal output. The controller is used to collect voltage data of different phases in different CCD photosensitive areas after a set integral exposure time, and coherently process multiple frames of voltage data in each pixel to calculate the linear frequency modulation rate; based on the linear frequency modulation rate, the speed and position of the target in each pixel are calculated to achieve 4D high-precision imaging of the target.

7. The high-precision area array 4D imaging optical system based on coherent detection according to claim 6, characterized in that: The reflective light path includes a second polarization controller, a first collimator and a first convex lens which are arranged in sequence.

8. The high-precision area array 4D imaging optical system based on coherent detection according to claim 6 or 7, characterized in that: The reference optical path includes a third polarization controller, a second collimator, a second convex lens and a pinhole filter which are arranged in sequence.

9. The high-precision area array 4D imaging optical system based on coherent detection according to claim 6, characterized in that: Combining the CCD integrated voltages of four different phases, we get a new voltage term: Among them, U1~U4 are the integrated voltages of four different phases. The voltage is subjected to a discrete short-time Fourier transform to obtain a relationship between the signal frequency and time, ie, a linear frequency modulation rate r.

10. The high-precision area array 4D imaging optical system based on coherent detection according to claim 9, characterized in that: The speed v and distance d of the target are: Where r is the linear frequency modulation rate, f st is the starting frequency in the spectrum diagram, c is the speed of light, f0 is the starting frequency of the stepped frequency signal, and Δf is the step size of the stepped frequency signal.

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