A laser three-dimensional imaging system and method based on receiving and transmitting dual-polarization modulation matching

Abstract

The application provides a laser three-dimensional imaging system and method based on receiving and transmitting dual-polarization modulation matching, which comprises the following steps: under the synchronous control of a transmitting unit controller, a single-wavelength linearly polarized pulsed laser is emitted by a pulsed laser, the linearly polarized direction of the laser is continuously rotated during the pulse duration, and finally the polarized modulated laser pulse is emitted to a target via a laser beam expander; in a receiving unit, the laser pulse returned from the target is received by a telescopic optical system, the beam width is narrowed, wavelength selection is performed by a wavelength filter, then the laser pulse is further decomposed into two orthogonal polarization directions by a polarization beam splitter via a receiving unit polarization modulator, and is imaged and received by two groups of imaging objectives and a surface array detector X and a surface array detector Y respectively; finally, the digital signals obtained by the two detectors are processed by a digital signal processor to obtain the distance information of each point on the two-dimensional image plane. The application realizes three-dimensional imaging at a farther distance, higher resolution and faster speed.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of laser three-dimensional imaging, and particularly relates to a laser three-dimensional imaging system and method based on receiving and transmitting dual-polarization modulation matching. BACKGROUND

[0002] Three-dimensional imaging laser radar is a new type of imaging technology, and is regarded as the next generation of technology products after passive optical imaging and active microwave imaging radar. Its technical means can fully integrate the advantages of both. Compared with passive optical imaging, because of its active illumination, it is convenient to modulate the transmitting and receiving signals, and thus it is more convenient to obtain target distance information and other reflection information, realize fast three-dimensional imaging and high-precision remote sensing inversion. Compared with microwave imaging radar, it has higher angular resolution, stronger anti-interference ability and faster imaging speed. At the same time, it has no requirements and restrictions on the relative motion of the target and the platform, and can perform high-resolution three-dimensional imaging in front of the moving platform, while the synthetic aperture radar (SAR) cannot do so.

[0003] Three-dimensional imaging laser radar can be divided into scanning and non-scanning modes according to the working mode. The laser imaging of the scanning mode obtains azimuth and range information by sequential scanning, and realizes three-dimensional imaging. The non-scanning laser imaging focuses the target area on the image plane through the optical system, and then uses a two-dimensional array detector to receive, directly obtains a two-dimensional image, and then obtains range information through demodulation and processing of the signal, and realizes three-dimensional imaging. The non-scanning laser three-dimensional imaging has the advantages of fast imaging speed and high resolution, and can be applied to moving target imaging. At the same time, it also avoids the cumbersome scanning mechanism, and can achieve smaller volume and weight.

[0004] The two-dimensional array detector used in non-scanning laser three-dimensional imaging is divided into two categories: one is a high-speed avalanche photodiode (APD) array, and the other is a visible light and infrared array imaging detector based on CCD or CMOS architecture. The difference between the two is that: the response and signal readout speed of the ADP array is very fast, which can reach tens of GHz, and can detect sub-nanosecond level high-speed modulated pulse waveform changes, so that the same technical means of microwave radar can be used to solve the distance information. Because the readout circuit is required to be high, the pixel size of the APD array is usually small, the spatial resolution that can be achieved is low, and the cost is extremely high. The optical imaging two-dimensional array detector reaches at most hundreds of Hz, and the detection result is the energy integration of the signal in at least microsecond level time, which is difficult to directly perceive the waveform of the echo signal. However, the overall technology level of the optical imaging two-dimensional array detector is relatively mature, the pixel size can be large, so that a very high spatial resolution can be achieved, and the cost is relatively low.

[0005] In the current common method of laser three-dimensional imaging using an optical imaging area array detector, the return time of the echo signal is usually mapped to the responsivity of the area array detector pixel, and then the distance information is inverted from the intensity information. The ranging accuracy of this method depends on the width of the signal pulse. The narrower the pulse width, the higher the ranging accuracy. In order to ensure that the detection receives sufficient light energy, if the total energy of a single pulse is constant, a smaller pulse width requires a higher instantaneous power within the pulse, which greatly increases the technical requirements and cost of the laser, and brings many problems such as volume, heat dissipation and the like. SUMMARY

[0006] In order to reduce the dependence on narrow pulse width and high energy of laser signals in laser three-dimensional imaging using an optical imaging area array detector, the application provides a laser three-dimensional imaging system and method based on receiving and transmitting dual polarization modulation matching.

[0007] In order to achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0008] The laser three-dimensional imaging system based on receiving and transmitting dual polarization modulation matching comprises a transmitting unit and a receiving unit.

[0009] The transmitting unit comprises:

[0010] A pulsed laser is used to generate a single-wavelength pulsed laser signal in linear polarization state.

[0011] A laser beam expander is used to adjust the width and divergence angle of the laser beam.

[0012] A transmitting unit polarization modulator is used to modulate the polarization state of the transmitted pulsed laser.

[0013] A transmitting unit controller is used to synchronously control the pulsed laser and the polarization modulator, and continuously modulate the laser polarization state within the laser pulse duration.

[0014] The receiving unit comprises:

[0015] A telescopic optical system is used to receive the laser signal scattered by the target and shrink the input beam width.

[0016] A wavelength filter is used to filter incident light other than laser wavelength and reduce the influence of natural light in the scene.

[0017] A receiving unit polarization modulator is used to polarization modulate the received laser signal.

[0018] A polarization beamsplitter is used to split the laser signal into two orthogonal polarization directions.

[0019] An imaging objective is used to image the laser beam on a two-dimensional image plane.

[0020] A face array detector X and a face array detector Y are used to convert the optical signal on the image plane into an electrical signal and further into a digital signal;

[0021] A receiving unit controller is used to synchronously control the polarization modulator and the face array detector, so as to ensure that the polarization modulation is matched with the imaging exposure;

[0022] A digital signal processor is used to calculate the depth information on each pixel from the two-dimensional digital image signal and obtain a three-dimensional image.

[0023] Further, the transmitting unit transmits a single-wavelength linearly polarized pulse laser from the pulse laser under the synchronous control of the transmitting unit controller, passes through a linear polarizer, then passes through the polarization modulator, continuously rotates the laser linear polarization direction during the pulse duration, and finally transmits the polarization-modulated laser pulse to the target via a laser beam expander.

[0024] Further, in the receiving unit, the laser pulse returned from the target is received by a telescopic optical system, is narrowed in width by a wavelength filter, and is received by the receiving unit polarization modulator, which has the same modulation rate and opposite deflection direction as the polarization of the transmitting unit.

[0025] Further, the laser pulse is converted from the continuously rotating polarization state during the pulse duration into a polarization state in a certain fixed direction, and the fixed direction maps the return time of the laser pulse, i.e., the distance of the target.

[0026] Further, the laser pulse is further decomposed into two orthogonal polarization directions by a polarization beam splitter, and is imaged and received by two sets of imaging objectives and the face array detector X and the face array detector Y.

[0027] Further, the digital signal processor calculates and processes the digital signals obtained by the face array detector X and the face array detector Y to obtain the distance information of each point on the two-dimensional image plane.

[0028] The application also provides a laser three-dimensional imaging method based on transmitting and receiving double-polarization modulation matching.

[0029] In step 1, in the transmitting unit of the laser three-dimensional imaging system based on transmitting and receiving double-polarization modulation matching, a pulse laser generates a linearly polarized laser pulse signal with a wavelength of , a pulse width of , and a pulse energy of ; under the synchronous control of the controller, the polarization modulator has a modulation rate of ; and during the duration from the beginning of the pulse to the end of the pulse, the polarization direction of the laser beam uniformly rotates ;

[0030] Step 2, obtaining two beams of light with orthogonal polarization directions in the receiving unit of the laser three-dimensional imaging system based on transmission and receiving dual-polarization modulation matching, and focusing and imaging on the area array detector X and the area array detector Y respectively;

[0031] Step 3, calculating the target distance according to the pulses returned by the area array detector X and the area array detector Y.

[0032] Further, the step 2 comprises: receiving the laser pulses returned from the target by the telescope optical system, narrowing the beam width, and then passing through the receiving unit polarization modulator, and the modulation rate is ; the pulses returned at different distances are modulated by the receiving unit polarization modulator and are in different linear polarization modulation directions; then passing through the polarization beamsplitter, the two beams of light with orthogonal polarization directions are decomposed and focused and imaged on the area array detector X and the area array detector Y respectively.

[0033] Further, the modulation starts from the time when the light beam returned from the nearest gated distance arrives.

[0034] Further, the step 3 comprises:

[0035] The distance is taken as the starting distance of the gated imaging, is the speed of light; the return time of the A pulse returned at the starting distance is ; the return time of the B pulse returned at the distance is .

[0036] Assuming that the linear polarization direction of the A pulse is the x direction, the angle between the linear polarization direction of the B pulse and the x axis is ; the energy ratio of the B pulse on a certain pair of pixels of the area array detector X and the area array detector Y is ; the digital signal processor calculates for each pixel, and then the distance corresponding to the pixel is obtained.

[0037] Based on the above technical solution, the present application has at least one of the following beneficial effects compared with the prior art:

[0038] (1) Compared with the microwave imaging radar, the present application has no limitation on the relative motion mode of the platform and the target, and can be used for forward-looking imaging under high-speed motion of the platform.

[0039] (2) Compared with the laser radar based on the APD array, the imaging receiving of the present application uses the area array optical detector based on the CCD or CMOS technology, and can have higher two-dimensional resolution. Compared with the scanning laser radar, the present application has higher imaging frame rate and can be used for a moving platform or a moving target.

[0040] (3) Compared with the laser imaging scheme using short pulse matching the response modulation of the area array detector, the application uses the receiving-transmitting dual polarization modulation matching method, the pulse width does not affect the distance resolution, so that long pulse laser light source can be used, under the condition of constant total pulse energy, the requirement for the peak power of the laser light source is reduced, the requirement for the sensitivity of the area array detector is reduced, and the requirement for the large aperture of the receiving optical system is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is a structural schematic diagram of a laser three-dimensional imaging system based on receiving and transmitting dual polarization modulation matching of the application;

[0042] Figure 2 is a schematic diagram of a transmitting and receiving beam polarization state modulation method of the application;

[0043] Figure 3 is a transmitting and receiving signal timing diagram of the application. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical scheme and advantages of the application clearer and more apparent, the application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the application and do not limit the application. In addition, the technical features involved in each embodiment of the application described below can be combined with each other as long as they do not conflict with each other.

[0045] In the description of the application, it should be understood that the terms "upper", "lower", "top", "bottom", "inner", "outer" and the like used in the application indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0046] In the application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection", "fixing" and the like should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0047] As Figure 1As shown, the laser three-dimensional imaging system based on the receiving and transmitting dual-polarization modulation matching of the application comprises a transmitting unit and a receiving unit.

[0048] Preferably, the transmitting unit comprises:

[0049] a pulsed laser for generating a single-wavelength pulsed laser signal in linear polarization state;

[0050] a laser beam expander for adjusting the width and divergence angle of the laser beam;

[0051] a transmitting unit polarization modulator for modulating the polarization state of the transmitted pulsed laser;

[0052] a transmitting unit controller for synchronously controlling the pulsed laser and the polarization modulator to continuously modulate the laser polarization state within the laser pulse duration.

[0053] Preferably, the receiving unit comprises:

[0054] a telescopic optical system for receiving the laser signal scattered by the target and shrinking the input beam width;

[0055] a wavelength filter for filtering the incident light other than the laser wavelength to reduce the influence of the natural light of the scene;

[0056] a receiving unit polarization modulator for polarization modulating the received laser signal;

[0057] a polarization beamsplitter for splitting the laser signal into two orthogonal polarization directions;

[0058] an imaging objective for imaging the laser beam on a two-dimensional image plane;

[0059] a face array detector X and a face array detector Y for converting the optical signal on the image plane into an electrical signal and further into a digital signal;

[0060] a receiving unit controller for synchronously controlling the polarization modulator and the face array detector to ensure that the polarization modulation is matched with the imaging exposure.

[0061] a digital signal processor for calculating the depth information on each pixel from the two-dimensional digital image signal to obtain a three-dimensional image.

[0062] The working process of the laser three-dimensional imaging system based on the receiving and transmitting dual-polarization modulation matching of the application is as follows: under the synchronous control of the transmitting unit controller, the transmitting unit transmits a single-wavelength linearly polarized pulse laser by the pulse laser, passes through a linear polarizer, then passes through a polarization modulator, continuously rotates the laser linear polarization direction during the pulse duration, and finally transmits the polarization-modulated laser pulse to the target via a laser beam expander; in the receiving unit, the laser pulse returned from the target is received by a telescopic optical system, passes through a wavelength filter to narrow the beam width, and then passes through a receiving unit polarization modulator, which has the same modulation rate as the polarization of the transmitting unit but has an opposite deflection direction. After the laser pulse passes through the receiving unit polarization modulator, the polarization state continuously rotates in the pulse duration is changed into a polarization state with a certain fixed direction, and the polarization direction maps the return time of the laser pulse, that is, the distance of the target. The laser pulse is further decomposed into two orthogonal polarization directions by a polarization beam splitter, and is imaged and received by two groups of imaging objectives and a face array detector X and a face array detector Y. Finally, the digital signal processor receives the digital signals obtained by the face array detector X and the face array detector Y under the unified coordination of the controller, and performs calculation and processing to obtain the distance information of each point on the two-dimensional image plane.

[0063] The imaging method of the application comprises:

[0064] The pulse laser transmits a linearly polarized laser pulse signal with a wavelength of , a pulse width of , and a pulse energy of . The pulse laser exit light pulse first passes through a linear polarizer to ensure that the polarization direction is aligned, assuming that the linear polarization direction is along the y direction. Then it passes through a polarization modulator to modulate the linear polarization direction of the pulse, as shown in Figure 2 . Target A and target B are two targets with different distances, wherein target A is located at the nearest detection distance of the system and has a distance of from the receiving unit, c is the speed of light, and T is the gating time, that is, the return time of the echo signal at target A. The distance of target B is farther than that of target A, and the time difference between the echo signals returned by the same exit beam pulse reflected by the two targets when reaching the receiving unit is , so the distance difference between target A and target B is . The return time difference of the two pulses is , and the polarization angle difference of the linearly polarized light generated after the modulation of the receiving end polarization modulator is . The polarization modulator can adopt at least two methods, namely, magnetic rotation effect or electric birefringence effect combined with a 1 / 4 wave plate.

[0065] When the magnetic rotation effect is used, the rotation angle The magnetization M is proportional to the magnetic field H and the distance l, that is: Where, M is the saturation magnetization, F is the Faraday rotation coefficient. M can be controlled by the current of the electromagnetic coil, so that the rotation angle The electrical modulation is realized.

[0066] When the electric birefringence effect is used with a 1 / 4 wave plate, the propagation direction of the pulsed laser is along the coordinate z direction, the polarization direction is along the coordinate y direction, and the optical wave electric vector E is expressed as , is the optical wave complex amplitude, i is the imaginary unit, is the optical wave angular frequency, is the time, is the initial phase. The direction of the fast axis f of the electro-optic birefringence crystal is 45° to the coordinate x axis and y axis, and the phase difference introduced by the direction of the fast axis f and the slow axis s is At this time, the light emitted from the birefringence crystal is decomposed into:

[0067] The optical wave electric vector of the f direction is:

[0068] ;

[0069] The optical wave electric vector of the s direction is:

[0070] .

[0071] Add a 1 / 4 wave plate, the fast axis direction of the wave plate is along the coordinate x axis direction, and the slow axis is along the y direction. Decompose the above and into x axis direction and y axis direction respectively, and express them as: , , , :

[0072] ;

[0073] ;

[0074] ;

[0075] ;

[0076] The optical wave electric vector in the x direction is:

[0077] ;

[0078] The optical wave electric vector in the y direction For:

[0079] ;

[0080] To and Take the real part can be:

[0081] ;

[0082] ;

[0083] It can be seen that the x-axis and y-axis direction phase is the same, the amplitude is and , that is, the polarization direction compared to the incident light deflection angle is . The voltage applied to the electro-optic crystal is determined, thereby realizing the electrical modulation of the deflection angle.

[0084] After the polarization modulation of the laser pulse, it is emitted to the target area through the laser beam expander.

[0085] The returned laser beam is received by the telescope optical system. The function of the telescope optical system is to make the light beam from a certain target point parallel incident and parallel out, and the light beam width is contracted, which is opposite to the effect of the beam expander.

[0086] The parallel light beam emitted by the telescope optical system then passes through the wavelength filter to reduce the influence of ambient light. Then it enters the receiving unit polarization modulator, which modulates from the time when the light beam from the nearest gating distance arrives. The pulses returned at different distances will be in different linear polarization modulation directions after being modulated by the receiving unit polarization modulator, as shown in Figure 2 Then through the polarization beam splitter, it is decomposed into two beams of light with orthogonal polarization directions (x direction, y direction), which are focused and imaged on the area array detector X and the area array detector Y through the imaging objective lens, respectively.

[0087] Preferably, the receiving unit polarization modulator can also use the two modulation methods of magnetic rotatory effect and electric birefringence effect. Assuming that the light intensity of the light beam incident on the receiving unit polarization modulator is The receiving unit polarization modulator starts to modulate from the time when the light beam from the nearest gating distance arrives.

[0088] If the electric birefringence effect modulation method is used, let the crystal fast axis along the x-axis and the slow axis along the y-axis, is the angle between the incident light polarization direction and the x-axis, is the angle between the polarization direction received by the area array detector and the x-axis, and the light intensity incident on the modulator is , The phase difference generated by the fast and slow axes of the crystal, then the light intensity received by the area array detector can be expressed as:

[0089]

[0090] If the two-way area array detector and the crystal x-axis are 45° and -45°, respectively, that is The laser pulse width is The emission end optical modulation rate and the receiving end crystal modulation rate are That is , The echo time difference of the light pulse between target A and target B.

[0091] In order to facilitate subsequent integration, taking the time when each light pulse reaches the receiving end electro-optic crystal as the 0 time point, then the above formula can be written as:

[0092]

[0093]

[0094] Among them, And The light intensity on the corresponding pixels of the area array detector X and the area array detector Y, respectively. Integrate the above formula in the pulse duration , The total light energy received by the corresponding pixels of the area array detector X and the area array detector Y in the exposure time can be obtained, which are represented by And

[0095]

[0096]

[0097] Among them, C is a constant.

[0098] If , that is, the signal intensity ratio of the corresponding pixels of the area array detector X and the area array detector Y is m, then Can be calculated:

[0099]

[0100]

[0101] If a magnetic rotatory crystal is used as a polarization modulator, the light intensity , Finally incident on the area array detector X and the area array detector Y is:

[0102]

[0103] ​​​​​​​​​ ;

[0104] The ratio of the response values of the two area array detectors is:

[0105] ;

[0106] wherein, is the new signal intensity ratio.

[0107] Thus, the distance of the target can be obtained is:

[0108] ;

[0109] The distance of the target can be further calculated:

[0110] The distance of the target corresponding to each pixel can be calculated , and the distance of the pixel is . Wherein, c is the speed of light, and T is the gating time, i.e. the arrival time of the echo of the target at the predetermined nearest detection distance.

[0111] The timing of the signal transmission and reception, and the mapping relationship between the time and the polarization state are shown in Figure 3 , and echo A and echo B correspond to the echoes of target A and target B shown in Figure 2 . It can be seen that the distance information of the target is mapped to the proportional information of the responses of the two corresponding pixels on the two detectors, so that the distance information of the target is detected.

[0112] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A laser three-dimensional imaging system based on receiving and transmitting dual-polarization modulation matching, characterized in that, The transmitting unit and the receiving unit are included; The transmitting unit includes: a pulsed laser for generating a single-wavelength pulsed laser signal in linear polarization state; a laser beam expander for adjusting the width and divergence angle of the laser beam; a transmitting unit polarization modulator for modulating the polarization state of the transmitted pulsed laser; a transmitting unit controller for synchronously controlling the pulsed laser and the polarization modulator to continuously modulate the laser polarization state within the laser pulse duration; The receiving unit includes: a telescopic optical system for receiving the laser signal scattered by the target and narrowing the input beam width; a wavelength filter for filtering the incident light other than the laser wavelength to reduce the influence of the natural light in the scene; a receiving unit polarization modulator for polarization modulating the received laser signal; a polarization beamsplitter for splitting the laser signal into two orthogonal polarization directions; an imaging objective for imaging the laser beam on a two-dimensional image plane; a face array detector X and a face array detector Y for converting the optical signal on the image plane into an electrical signal and further into a digital signal; a receiving unit controller for synchronously controlling the polarization modulator and the face array detector to ensure that the polarization modulation is synchronized and matched with the imaging exposure; a digital signal processor for calculating the depth information of each pixel from the two-dimensional digital image signal to obtain a three-dimensional image; Under the synchronous control of the transmitting unit controller, the transmitting unit transmits a single-wavelength linearly polarized pulsed laser from the pulsed laser, passes through a linear polarizer, and then passes through a polarization modulator, which continuously rotates the linear polarization direction of the laser within the pulse duration. Finally, the polarization-modulated laser pulse is transmitted to the target via the laser beam expander. In the receiving unit, the laser pulse returned from the target is received by the telescopic optical system, and after the beam width is narrowed by the wavelength filter, the polarization-modulated laser pulse is received by the receiving unit polarization modulator, which has the same modulation rate as the polarization of the transmitting unit but opposite deflection direction.

2. The laser three-dimensional imaging system based on receiving and transmitting dual-polarization modulation matching according to claim 1, characterized in that, After passing through the receiving unit polarization modulator, the laser pulse is converted from the continuously rotating polarization state within the pulse duration to a fixed direction polarization state, which maps the return time of the laser pulse, i.e., the distance of the target.

3. The laser three-dimensional imaging system based on receiving and transmitting dual-polarization modulation matching according to claim 2, characterized in that, The laser pulse is further split into two orthogonal polarization directions by the polarization beamsplitter and imaged and received by the two sets of imaging objectives and the face array detector X and the face array detector Y, respectively.

4. The laser three-dimensional imaging system based on receiving and transmitting dual-polarization modulation matching according to claim 3, characterized in that, The digital signal processor calculates and processes the digital signals obtained by the face array detector X and the face array detector Y to obtain the distance information of each point on the two-dimensional image plane.

5. The method according to any one of claims 1-4, wherein, The steps include: Step 1, in the transmitting unit of the laser three-dimensional imaging system based on transmitting and receiving dual-polarization modulation matching, a pulsed laser generates linearly polarized laser pulse signals with a wavelength of , a pulse width of , and a pulse energy of ; under the synchronous control of the controller, the polarization modulator has a modulation rate of ; and the polarization direction of the laser beam rotates uniformly at a speed of from the beginning of the pulse to the end of the pulse within the duration Step 2: In the receiving unit of the laser three-dimensional imaging system based on the transmitting and receiving dual-polarization modulation matching, two beams of light with orthogonal polarization directions are obtained and focused and imaged on the face array detector X and the face array detector Y, respectively; Step 3: The target distance is calculated according to the pulses returned by the face array detector X and the face array detector Y.

6. The method of claim 5, wherein, The step 2 comprises: receiving the laser pulse returned from the target by the telescopic optical system, narrowing the beam width, and then passing through the receiving unit polarization modulator, and the modulation rate is ; the pulses returned at different distances are modulated by the receiving unit polarization modulator, and are in different linear polarization modulation directions; then passing through the polarization beam splitter, and being decomposed into two beams of light with orthogonal polarization directions, and being focused and imaged on the surface array detector X and the surface array detector Y respectively.

7. The method of claim 6, wherein, The modulation starts from the time when the light beam returns from the nearest gating distance.

8. The method of claim 5, wherein, The step 3 includes: at a distance as a start distance for gated imaging, is the speed of light; the return time of the B-pulse returned at a distance is ; where T is the gating time, is the return time difference; Assuming the linear polarization direction of the A pulse is the x direction, the angle between the linear polarization direction of the B pulse and the x axis is ; the energy ratio of the B pulse on a certain pair of pixels of the area array detector X, area array detector Y is ; the digital signal processor calculates for each pixel, and then obtains the distance corresponding to the pixel.

Images