CN103543443A

CN103543443A - Bi-channel electrooptical scanning laser imaging radar transmitting system for down-looking synthetic aperture

Info

Publication number: CN103543443A
Application number: CN201310460508.5A
Authority: CN
Inventors: 卢智勇; 职亚楠; 孙建锋; 周煜; 刘立人; 张宁
Original assignee: Shanghai Institute of Optics and Fine Mechanics of CAS
Current assignee: Shanghai Institute of Optics and Fine Mechanics of CAS
Priority date: 2013-09-30
Filing date: 2013-09-30
Publication date: 2014-01-29
Anticipated expiration: 2033-09-30
Also published as: CN103543443B

Abstract

A dual-channel electro-optical scanning direct-looking synthetic aperture laser imaging radar transmission system, which consists of: a laser, a half-wave plate, an aperture stop, a first polarizing beam splitter, a first electro-optic scanner, a first cylindrical mirror, a second Two polarizing beam splitters, the first 1/4 wave plate, the first mirror, the third polarizing beam splitter, the second 1/4 wave plate, the second mirror, the second electro-optic scanner, and the second cylindrical mirror , the fourth polarizing beam splitter, the primary mirror of the transmitting telescope, in addition to the high-voltage power supply and signal generator. The invention can perform electro-optical scanning on two beams, and finally realize the parabolic equipotential wavefront phase difference of two polarized orthogonal beams at the far-field target, which is used to scan the target, and has simple structure, no mechanical scanning, and electro-optical phase modulation wavefront The response speed is fast, up to nanoseconds, small in size and light in weight, and is especially suitable for the launch system of direct-looking synthetic aperture imaging lidar on high-speed operating platforms such as airborne or spaceborne.

Description

Dual-channel electro-optic scanning direct-looking synthetic aperture imaging lidar launch system

技术领域technical field

本发明涉及激光雷达，特别是一种双路电光扫描直视合成孔径激光成像雷达发射系统，用作直视合成孔径激光成像雷达中的光学发射装置。通过电光扫描器在交轨向进行双路线性的电光扫描，产生交轨向目标点横向位置的线性项相位调制，通过柱面镜在顺轨向进行相位调制，产生顺轨向目标点纵向位置为中心的二次项相位历程，最终获得的偏振正交的抛物等位线相位差波面，是用以实现雷达二维平面目标成像的关键技术。The invention relates to a laser radar, in particular to a dual-channel electro-optical scanning direct-looking synthetic aperture laser imaging radar transmitting system, which is used as an optical transmitting device in a direct-looking synthetic aperture laser imaging radar. The electro-optic scanner performs dual-line linear electro-optic scanning in the cross-track direction to generate linear term phase modulation of the cross-track to the horizontal position of the target point, and performs phase modulation in the along-track direction through the cylindrical mirror to generate the longitudinal position of the target point along the track The quadratic term phase history centered on , and the finally obtained polarization orthogonal parabolic equipotential phase difference wavefront are the key technologies for realizing radar two-dimensional plane target imaging.

背景技术Background technique

合成孔径激光成像雷达的原理取之于射频领域的合成孔径雷达原理，是能够在远距离得到厘米量级成像分辨率的唯一的光学成像观察手段。传统的合成孔径激光成像雷达都是在侧视的条件下进行光波发射和数据接收，采用光学外差接收，受大气扰动、运动平台振动、目标散斑和激光雷达系统本身相位变化等影响很大，还要求拍频信号的初始相位严格同步并且需要长距离延时来控制相位的变化，在实际的应用中是很困难的。而且传统的合成孔径激光成像雷达中激光发射光源频率的线性调制大都采用机械调制，其调制速度受到限制。The principle of synthetic aperture laser imaging radar is taken from the principle of synthetic aperture radar in the radio frequency field, and it is the only optical imaging observation method that can obtain centimeter-level imaging resolution at long distances. Traditional synthetic aperture laser imaging radars transmit light waves and receive data under the condition of side view, and adopt optical heterodyne reception, which is greatly affected by atmospheric disturbance, vibration of moving platform, target speckle and phase change of the laser radar system itself. , it is also required that the initial phase of the beat frequency signal be strictly synchronized and a long-distance delay is required to control the change of the phase, which is very difficult in practical applications. Moreover, the linear modulation of the frequency of the laser emitting light source in the traditional synthetic aperture laser imaging radar mostly adopts mechanical modulation, and its modulation speed is limited.

在先技术[1]（直视合成孔径激光成像雷达原理，光学学报，Vol.32,0928002-1～8,2012）和先技术[2](刘立人，直视合成孔径激光成像雷达，公开号：CN102435996)所述的直视合成孔径激光成像雷达，采用波前变换原理对目标投射两个同轴同心且偏振正交的光束并且进行自差接收，在交轨向进行空间线性相位调制，实现一维傅里叶变换聚焦成像，在顺轨向进行二次相位历程，实现共轭二次项相位匹配滤波成像。其中，雷达搭载平台的运动方向为顺轨方向，顺轨的正交方向为交轨方向。Prior technology [1] (Principle of Direct-looking Synthetic Aperture Lidar Imaging Radar, Acta Optics Sinica, Vol.32, 0928002-1-8, 2012) and prior technology [2] (Liu Liren, Direct-looking Synthetic Aperture Lidar Imaging Radar, Publication No. : CN102435996) described direct-looking synthetic aperture laser imaging radar, adopts the principle of wavefront transformation to project two coaxial concentric and polarized light beams and carry out self-differential reception to the target, and carry out spatial linear phase modulation in the cross-track direction to realize One-dimensional Fourier transform focusing imaging, the quadratic phase history is carried out in the along-track direction, and the conjugate quadratic term phase-matched filtering imaging is realized. Among them, the moving direction of the radar carrying platform is the along-track direction, and the orthogonal direction along the track is the cross-track direction.

在先技术[1]和[2]所述的直视合成孔径激光成像雷达，具有能够自动消除大气、运动平台、光雷达系统和散斑产生的相位变化和干扰，允许使用低质量的接收光学系统，不需要光学延时线，无需进行实时拍频信号相位同步，成像无阴影，可以使用各种具有单模和单频性质的激光器，同时采用空间光桥接器实现相位的复数解调，电子设备简单等特点。但是该直视合成孔径激光成像雷达提出的发射系统方案是采用两个光束偏转器对两光束进行对向扫描使得内发射场的光场分布为空间相位二次项形式，这时只有要求保持精确同步才能获得交轨向的线性相位调制，要使两光束对向扫描的精确同步是比较困难和复杂的，同时，其光束偏转器一般采用机械偏转扫描，响应速度慢，转动惯量大，不利于机载等高速搭载平台上的应用。The direct-looking synthetic aperture lidar imaging radar described in the prior art [1] and [2] has the ability to automatically eliminate phase changes and interference generated by the atmosphere, moving platforms, lidar systems, and speckle, allowing the use of low-quality receiving optics The system does not require an optical delay line, does not need to perform real-time beat signal phase synchronization, and has no shadow in imaging. It can use various lasers with single-mode and single-frequency properties. The equipment is simple and so on. However, the emission system scheme proposed by the direct-looking synthetic aperture lidar is to use two beam deflectors to scan the two beams in opposite directions so that the light field distribution of the inner emission field is in the form of a quadratic spatial phase. Synchronization can obtain the linear phase modulation in the cross-track direction. It is difficult and complicated to make the precise synchronization of the two beams scanning oppositely. Applications on high-speed platforms such as airborne.

发明内容Contents of the invention

本发明要解决的技术问题是克服上述先技术在发射系统中存在的不足，提出一种双路电光扫描直视合成孔径激光成像雷达发射系统，该发射系统采用4个偏振分束器，使得两光束经过电光扫描器的偏振态一致但最终系统出射的两光束偏振态正交，这样可以通过电光扫描器对交轨向相位进行调制，通过柱面镜对顺轨向波面相位进行调制，就能直接在快时间轴上产生与目标交轨向位置有关的空间线性相位项调制，在慢时间轴上产生目标顺轨向的空间二次项相位历程。The technical problem to be solved by the present invention is to overcome the shortcomings of the above-mentioned prior art in the launch system, and propose a dual-channel electro-optical scanning direct-looking synthetic aperture laser imaging radar launch system. The launch system uses 4 polarization beam splitters, so that two The polarization states of the beams passing through the electro-optical scanner are the same, but the polarization states of the two beams emitted by the final system are orthogonal, so that the cross-track phase can be modulated by the electro-optic scanner, and the along-track wave surface phase can be modulated by the cylindrical mirror. It can directly generate the spatial linear phase term modulation related to the target cross-track position on the fast time axis, and generate the spatial quadratic phase history of the target along-track direction on the slow time axis.

本发明的技术解决方案如下：Technical solution of the present invention is as follows:

一种双路电光扫描直视合成孔径激光成像雷达发射系统，其构成包括激光器、半波片、孔径光阑、第一偏振分束器、第一电光扫描器、第一柱面镜、第二偏振分束器、第一1/4波片、第一反射镜、第三偏振分束器、第二1/4波片、第二反射镜、第二电光扫描器、第二柱面镜、第四偏振分束器、发射望远镜主镜，此外还有高压电源和信号发生器；所述的第一电光扫描器出射面紧靠第一柱面镜，所述的第二电光扫描器出射面紧靠第二柱面镜，所述的第一柱面镜和第二柱面镜均位于发射望远镜主镜的前焦面，所述的高压电源连接第一电光扫描器和第二电光扫描器，并由信号发生器产生线性脉冲信号用以控制高压电源产生线性变化的电压，所述的第一电光扫描器和第二电光扫描器扫描的方向符号相反，所述的第一电光扫描器和第二电光扫描器扫描方向为交轨向，第一柱面镜和第二柱面镜的调制波面为顺轨向。上述部件的位置关系如下：A two-way electro-optical scanning direct-looking synthetic aperture laser imaging radar launch system, which consists of a laser, a half-wave plate, an aperture stop, a first polarization beam splitter, a first electro-optic scanner, a first cylindrical mirror, a second Polarizing beam splitter, first 1/4 wave plate, first reflector, third polarizing beam splitter, second 1/4 wave plate, second reflector, second electro-optic scanner, second cylindrical mirror, The fourth polarization beam splitter, the primary mirror of the transmitting telescope, and a high-voltage power supply and a signal generator in addition; the exit surface of the first electro-optic scanner is close to the first cylindrical mirror, and the exit surface of the second electro-optic scanner Close to the second cylindrical mirror, the first cylindrical mirror and the second cylindrical mirror are located on the front focal plane of the main mirror of the transmitting telescope, and the high-voltage power supply is connected to the first electro-optic scanner and the second electro-optic scanner , and the signal generator generates a linear pulse signal to control the high-voltage power supply to generate a linearly changing voltage. The scanning directions of the first electro-optic scanner and the second electro-optic scanner have opposite signs, and the first electro-optic scanner and the The scanning direction of the second electro-optical scanner is the cross-track direction, and the modulated wavefronts of the first cylindrical mirror and the second cylindrical mirror are along the track direction. The positional relationship of the above components is as follows:

激光光源输出的偏振光束经过所述的半波片后获得所需的45°方向的偏振光束，该偏振光束通过孔径光阑和第一偏振分束器后在空间上被偏振分解为两个等强度的偏振正交的水平偏振光束和垂直偏振光束，所述的反射偏振光束为垂直偏振光束，透射的偏振光束为水平偏振光束，反射的垂直偏振光束经过第一电光扫描器和第一柱面镜后，由第二偏振分束器反射进入1/4波片到达第一反射镜，而后有第一反射镜反射再次进入第一1/4波片，这时的垂直偏振光束偏振态转动90°变为水平偏振光束，再次进入第二偏振分束器时为透射光束，然后该透射的水平偏振光束经过第四偏振分束器和发射望远镜主镜发射；所述的第一偏振分束器直接透射的水平偏振光束经过第三偏振分束器后，进入第二1/4波片和第二反射镜反射，反射光束再次进入第二1/4波片后，原来的水平偏振光束偏振态旋转90°变为垂直偏振光束，该垂直偏振光束再次进入第三偏振分束器为反射光束，该反射的垂直偏振光束进入第二电光扫描器和第二柱面镜，然后通过第四偏振分束器反射，由第四偏振分束器将水平偏振光束和垂直偏振光束重新组合为同轴同心且偏振正交的光束，由所述的发射望远镜主镜发射向目标。The polarized beam output by the laser light source passes through the half-wave plate to obtain the required polarized beam in the direction of 45°, and the polarized beam is spatially decomposed into two equal polarized beams after passing through the aperture stop and the first polarization beam splitter. Intensity polarized orthogonal horizontally polarized beams and vertically polarized beams, the reflected polarized beams are vertically polarized beams, the transmitted polarized beams are horizontally polarized beams, and the reflected vertically polarized beams pass through the first electro-optical scanner and the first cylinder After the mirror, it is reflected by the second polarizing beam splitter and enters the 1/4 wave plate to reach the first mirror, and then is reflected by the first mirror and enters the first 1/4 wave plate again. At this time, the polarization state of the vertically polarized beam is rotated by 90 ° becomes a horizontally polarized beam, which is a transmitted beam when entering the second polarized beam splitter again, and then the transmitted horizontally polarized beam is emitted through the fourth polarized beam splitter and the main mirror of the transmitting telescope; the first polarized beam splitter The directly transmitted horizontally polarized beam passes through the third polarization beam splitter, enters the second 1/4 wave plate and is reflected by the second mirror, and after the reflected beam enters the second 1/4 wave plate again, the polarization state of the original horizontally polarized beam Rotate 90° to become a vertically polarized beam, and the vertically polarized beam enters the third polarization beam splitter again as a reflected beam, and the reflected vertically polarized beam enters the second electro-optic scanner and the second cylindrical mirror, and then passes through the fourth polarization splitter The fourth polarized beam splitter recombines the horizontally polarized beam and the vertically polarized beam into a coaxial, concentric and orthogonally polarized beam, which is emitted to the target by the primary mirror of the transmitting telescope.

与现有技术相比，本发明具有以下技术效果：Compared with the prior art, the present invention has the following technical effects:

1、本发明采用四个偏振分束器对发射光波进行偏振分束与合束，在均为垂直偏振态的两支路上采用电光扫描器对两光束交轨向波面进行直接的线性相位调制，利用柱面镜对两偏振光束的顺轨向波面相位进行二次相位调制，使得交轨向的线性调制为单个电光扫描器的两倍，最终合束为两束偏振正交且同轴发射光束，整体器件更加简单紧凑，降低了发射系统的复杂性，便于控制。1. The present invention adopts four polarization beam splitters to carry out polarization beam splitting and beam combining on the emitted light waves, and uses an electro-optic scanner to directly perform linear phase modulation on the cross-track direction of the two beams to the wave surface on the two branches that are both vertically polarized. Use a cylindrical mirror to perform secondary phase modulation on the along-track wavefront phase of the two polarized beams, so that the linear modulation in the cross-track direction is twice that of a single electro-optic scanner, and the final beam combination is two beams with orthogonal polarizations and coaxial emission The light beam, the overall device is simpler and more compact, which reduces the complexity of the emission system and facilitates control.

2、本发明采用的电光扫描器调制交轨向的线性相位，控制简单，无机械扫描，无惯性，响应速度达纳秒量级，体积小，重量轻等优点，特别适用于机载或星载等高速运动的搭载平台。2. The electro-optical scanner used in the present invention modulates the linear phase of the cross-track direction, has the advantages of simple control, no mechanical scanning, no inertia, response speed of nanosecond level, small size, light weight, etc., and is especially suitable for airborne or satellite Loading and other high-speed sports carrying platform.

3、采用垂直偏振态的两路光束进行线性相位调制，可以充分利用垂直偏振下的大电光系数，实现水平方向的光束扫描。3. Two beams of vertical polarization are used for linear phase modulation, which can make full use of the large electro-optical coefficient under vertical polarization to realize beam scanning in the horizontal direction.

附图说明Description of drawings

图1是本发明双路电光扫描直视合成孔径激光成像雷达发射系统结构图。Fig. 1 is a structural diagram of the dual-channel electro-optical scanning direct-looking synthetic aperture imaging laser radar transmitting system of the present invention.

图2是本发明双路电光扫描直视合成孔径激光成像雷达发射系统中的一种四电极电光扫描器的结构图。Fig. 2 is a structural diagram of a four-electrode electro-optic scanner in the dual-channel electro-optic scanning direct-looking synthetic aperture laser imaging radar transmitting system of the present invention.

图3是本发明双路电光扫描直视合成孔径激光成像雷达发射系统中的两偏振光束抛物波面的干涉图。Fig. 3 is an interference diagram of parabolic wave surfaces of two polarized light beams in the dual-channel electro-optic scanning direct-looking synthetic aperture laser imaging radar transmitting system of the present invention.

具体实施方式Detailed ways

下面结合附图和实施例对本发明作进一步说明，但不应以此限制本发明的保护范围。The present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention should not be limited thereby.

先参阅图1，图1为本发明双路电光扫描直视合成孔径激光成像雷达发射系统结构图。由图可见，本发明双路电光扫描直视合成孔径激光成像雷达发射系统由激光器1、半波片2、孔径光阑3、第一偏振分束器4、第一电光扫描器5、第一柱面镜6、第二偏振分束器7、第一1/4波片8、第一反射镜9、第三偏振分束器10、第二1/4波片11、第二反射镜12、第二电光扫描器13、第二柱面镜14、第四偏振分束器15、发射望远镜主镜16，此外还有高压电源17和信号发生器18；所述的第一电光扫描器5出射面紧靠第一柱面镜6，所述的第二电光扫描器13出射面紧靠第二柱面镜14，所述的第一柱面镜6和第二柱面镜14均位于发射望远镜主镜16的前焦面，所述的高压电源17连接第一电光扫描器5和第二电光扫描器13，并由信号发生器18产生线性脉冲信号用以控制高压电源17产生线性变化的电压，所述的第一电光扫描器5和第二电光扫描器13均采用四曲面电极结构电光偏转器，晶体采用45o方向切割，产生交轨方向的线性梯度电场，实现交轨向位置有关的线性相位调制，所述的第一电光扫描器5和第二电光扫描器13所扫描的符号相反。上述部件的位置关系如下：Referring to Fig. 1 first, Fig. 1 is a structural diagram of the dual-channel electro-optical scanning direct-looking synthetic aperture imaging laser radar transmitting system of the present invention. As can be seen from the figure, the dual-channel electro-optic scanning direct-looking synthetic aperture laser imaging radar transmitting system of the present invention consists of a laser 1, a half-wave plate 2, an aperture stop 3, a first polarization beam splitter 4, a first electro-optic scanner 5, a first Cylindrical mirror 6, second polarizing beam splitter 7, first 1/4 wave plate 8, first mirror 9, third polarizing beam splitter 10, second 1/4 wave plate 11, second mirror 12 , the second electro-optic scanner 13, the second cylindrical mirror 14, the fourth polarizing beam splitter 15, the transmitting telescope main mirror 16, in addition to high voltage power supply 17 and signal generator 18; described first electro-optic scanner 5 The outgoing surface is close to the first cylindrical mirror 6, and the outgoing surface of the second electro-optical scanner 13 is close to the second cylindrical mirror 14, and the first cylindrical mirror 6 and the second cylindrical mirror 14 are both located at the emission The front focal plane of the telescope main mirror 16, the high-voltage power supply 17 is connected to the first electro-optic scanner 5 and the second electro-optic scanner 13, and the linear pulse signal is generated by the signal generator 18 to control the high-voltage power supply 17 to produce linear changes Voltage, the first electro-optic scanner 5 and the second electro-optic scanner 13 both use electro-optic deflectors with a four-curved electrode structure, and the crystal is cut in a 45o direction to generate a linear gradient electric field in the cross-rail direction to realize cross-rail position-related For linear phase modulation, the signs scanned by the first electro-optic scanner 5 and the second electro-optic scanner 13 are opposite. The positional relationship of the above components is as follows:

激光光源1输出的偏振光束经过所述的半波片2后获得所需的45°方向的偏振光束，该偏振光束通过孔径光阑3和第一偏振分束器4后在空间上被偏振分解为两个等强度的偏振正交的水平偏振光束和垂直偏振光束，所述的反射偏振光束为垂直偏振光束，透射的偏振光束为水平偏振光束，反射的垂直偏振光束经过第一电光扫描器5和第一柱面镜6后，由第二偏振分束器7反射进入1/4波片8到达第一反射镜9，而后由第一反射镜9反射再次进入第一1/4波片8，这时的垂直偏振光束偏振态转动90°变为水平偏振光束，再次进入第二偏振分束器7时为透射光束，然后该透射的水平偏振光束经过第四偏振分束器15和发射望远镜主镜16发射；所述的第一偏振分束器4直接透射的水平偏振光束经过第三偏振分束器10后，进入第二1/4波片11和第二反射镜12反射，反射光束再次进入第二1/4波片11后，原来的水平偏振光束偏振态旋转90°变为垂直偏振光束，该垂直偏振光束再次进入第三偏振分束器10为反射光束，该反射的垂直偏振光束进入第二电光扫描器13和第二柱面镜14，然后通过第四偏振分束器15反射，由第四偏振分束器15将水平偏振光束和垂直偏振光束重新组合为同轴同心且偏振正交的光束，由所述的发射望远镜主镜16发射向目标。The polarized beam output by the laser light source 1 passes through the half-wave plate 2 to obtain the required polarized beam in the direction of 45°, and the polarized beam is spatially decomposed by polarization after passing through the aperture stop 3 and the first polarizing beam splitter 4 It is two equal-intensity polarized orthogonal horizontally polarized beams and vertically polarized beams, the reflected polarized beam is a vertically polarized beam, the transmitted polarized beam is a horizontally polarized beam, and the reflected vertically polarized beam passes through the first electro-optic scanner 5 After the first cylindrical mirror 6, it is reflected by the second polarizing beam splitter 7 and enters the 1/4 wave plate 8 to reach the first reflector 9, and then is reflected by the first reflector 9 and enters the first 1/4 wave plate 8 again , the polarization state of the vertically polarized beam at this time is rotated by 90° to become a horizontally polarized beam, which is a transmitted beam when entering the second polarized beam splitter 7 again, and then the transmitted horizontally polarized beam passes through the fourth polarized beam splitter 15 and the transmitting telescope The main mirror 16 emits; the horizontally polarized beam directly transmitted by the first polarizing beam splitter 4 passes through the third polarizing beam splitter 10, enters the second 1/4 wave plate 11 and the second mirror 12 for reflection, and the reflected beam After entering the second 1/4 wave plate 11 again, the polarization state of the original horizontally polarized light beam is rotated by 90° to become a vertically polarized light beam, and the vertically polarized light beam enters the third polarization beam splitter 10 again as a reflected light beam, and the reflected vertically polarized light beam The light beam enters the second electro-optical scanner 13 and the second cylindrical mirror 14, and then is reflected by the fourth polarizing beam splitter 15, and the fourth polarizing beam splitter 15 recombines the horizontally polarized beam and the vertically polarized beam into a coaxial and concentric and The light beams with orthogonal polarization are sent to the target by the main mirror 16 of the transmitting telescope.

激光光源1出射的激光经过半波片2后产生45°偏振的偏振光束，采用孔径光阑3用以限制该偏振光束的振幅宽度，而后该偏振光束被第一偏振分束器4分束为水平偏振光束和垂直偏振光束，其中垂直偏振光束直接进入第一电光扫描器5和第一柱面镜6，而后经过第二偏振分束器7和两次的1/4波片8后转为水平偏振光束，而由第一偏振分束器4透射的水平偏振光束先经过第三偏振分束器10后，两次经过1/4波片11转换为垂直偏振光束进入到第二电光扫描器13和第二柱面镜镜14，因此两光束进入第一电光扫描器5和第二电光扫描器13的偏振态相同，调制的线性相位相同，可为晶体的o光，也可以是晶体的e光，由于第一电光扫描器5和第二扫描器13采用四电极铌酸锂晶体电光偏转器，如图2所示，若光沿着y方向传播，当晶体的z轴为垂直偏振光束的偏振态方向（取决于晶体的放置）时，则对于水平偏振光束，其偏振态垂直于晶体z轴，为晶体的o光；当晶体的z轴为水平偏振光束的偏振态方向，则对于水平偏振光束，其偏振态平行于晶体z轴，为晶体的e光，晶体的两种放置位置产生不同的折射率变化，对应不同的电光偏转角度。The laser light emitted by the laser light source 1 passes through the half-wave plate 2 to generate a polarized beam of 45° polarization. The aperture stop 3 is used to limit the amplitude width of the polarized beam, and then the polarized beam is split by the first polarizing beam splitter 4 into Horizontally polarized light beams and vertically polarized light beams, wherein the vertically polarized light beams directly enter the first electro-optic scanner 5 and the first cylindrical mirror 6, and then pass through the second polarizing beam splitter 7 and twice the 1/4 wave plate 8 and turn into Horizontally polarized beam, and the horizontally polarized beam transmitted by the first polarizing beam splitter 4 first passes through the third polarizing beam splitter 10, then passes through the 1/4 wave plate 11 twice to be converted into a vertically polarized beam and enters the second electro-optical scanner 13 and the second cylindrical mirror 14, so the polarization states of the two light beams entering the first electro-optic scanner 5 and the second electro-optic scanner 13 are the same, and the linear phase of the modulation is the same, which can be the o light of the crystal or the crystal e light, since the first electro-optic scanner 5 and the second scanner 13 use a four-electrode lithium niobate crystal electro-optic deflector, as shown in Figure 2, if the light propagates along the y direction, when the z-axis of the crystal is a vertically polarized light beam When the polarization state direction of the crystal (depending on the placement of the crystal), then for a horizontally polarized beam, its polarization state is perpendicular to the z-axis of the crystal, which is the o light of the crystal; when the z-axis of the crystal is the polarization state direction of the horizontally polarized beam, then for The horizontally polarized light beam, whose polarization state is parallel to the z-axis of the crystal, is the e-ray of the crystal. The two placement positions of the crystal produce different refractive index changes, corresponding to different electro-optical deflection angles.

当偏振态为电光扫描器的o光时，其折射率变化为When the polarization state is the o light of the electro-optic scanner, its refractive index changes as

$\{\begin{matrix} {n no}_{11} = = {n no}_{o o} + + \frac{11}{22} {n no}_{o o}^{33} {γ γ}_{1313} {E E.}_{33} ((y the y)) = = {n no}_{o o} + + Δ Δ {n no}^{' '} \\ {n no}_{22} = = {n no}_{o o} - - \frac{11}{22} {n no}_{o o}^{33} {γ γ}_{1313} {E E.}_{33} ((y the y)) = = {n no}_{o o} - - {Δn Δn}^{' '} \end{matrix}$

其中，

n_o为晶体o光折射率，E₃为施加在晶体通光孔径上的电场，γ₁₃为在该方向上的电光系数。此时，经过两个电光扫描器后，其x方向的相位延迟为in,

n _o is the refractive index of crystal o light, E ₃ is the electric field applied to the clear aperture of the crystal, and γ ₁₃ is the electro-optic coefficient in this direction. At this time, after passing through two electro-optic scanners, the phase delay in the x direction is

φ(x)＝kxθ+kLn_o φ(x)=kxθ+kLn _o

其中，

为电光扫描器的扫描角度。in,

is the scanning angle of the electro-optical scanner.

因此当水平偏振光束从第一电光扫描器5和第一柱面镜6、第二电光扫描器13和第二柱面镜14后，该位置同为发射望远镜主镜16的前焦面，其发射场为Therefore when the horizontally polarized light beam is behind the first electro-optic scanner 5 and the first cylindrical mirror 6, the second electro-optic scanner 13 and the second cylindrical mirror 14, this position is the same as the front focal plane of the main mirror 16 of the transmitting telescope, which The launch site is

${e e}_{H h}^{in in} ((x x,, y the y)) = = Crect Crect ((\frac{x x}{{L L}_{x x}^{in in}})) rect rect ((\frac{y the y}{{L L}_{y the y}^{in in}})) exp exp {{j j \frac{22 π π}{λ λ} [[x x \cdot \cdot θ θ + + {Ln ln}_{o o} + + \frac{{y the y}^{22}}{{22 f f}_{11}}]]}}$

${e e}_{V V}^{in in} ((x x,, y the y)) = = Crect Crect ((\frac{x x}{{L L}_{x x}^{in in}})) rect rect ((\frac{y the y}{{L L}_{y the y}^{in in}})) exp exp {{j j \frac{22 π π}{λ λ} [[- - x x \cdot \cdot θ θ + + {Ln ln}_{o o} - - \frac{{y the y}^{22}}{{22 f f}_{22}}]]}}$

其中，为入射光束的振幅宽度，L为晶体的长度，f₁为第一柱面镜6的焦距，f₂为第二柱面镜14的焦距。in, is the amplitude width of the incident beam, L is the length of the crystal, f ₁ is the focal length of the first cylindrical lens 6 , and f ₂ is the focal length of the second cylindrical lens 14 .

而后两水平偏振光束中的一支透过第二偏振分束器7后两次经过第二1/4波片8使其偏转态转变为垂直偏振光束，由第四偏振分束器15重新与另一水平偏振光束合束为同轴同心偏振正交的光束，由发射望远镜主镜16发射至远场目标处，其中内发射场经过发射望远镜主镜16的发射后，其在远场目标处的光场为内发射场光场的放大光场，其放大倍数是M=(Z-F)/F，Z是发射望远镜主镜16到远场目标面的距离，F是发射望远镜主镜的焦距。这时在目标面上形成水平偏振照明波前为：Then one of the two horizontally polarized light beams passes through the second polarization beam splitter 7 and then passes through the second 1/4 wave plate 8 twice so that its deflection state is converted into a vertically polarized light beam, which is reconnected with the fourth polarization beam splitter 15 Another horizontally polarized light beam is combined into a coaxial concentric polarization orthogonal beam, which is emitted to the far-field target by the main mirror 16 of the transmitting telescope. The light field is the amplified light field of the inner emission field light field, and its magnification is M=(Z-F)/F, Z is the distance from the main mirror 16 of the transmitting telescope to the far field target surface, and F is the focal length of the main mirror of the transmitting telescope. At this time, the horizontally polarized illumination wavefront formed on the target surface is:

${e e}_{H h}^{T T} ((x x,, y the y)) = = Crect Crect ((\frac{x x}{{L L}_{x x}})) rect rect ((\frac{y the y}{{L L}_{y the y}})) exp exp {{j j \frac{22 π π}{λ λ} [[\frac{x x}{M m} \cdot \cdot θ θ + + {Ln ln}_{o o} + + \frac{{((y the y - - {v v}_{y the y} {t t}_{x x}))}^{22}}{{22 R R}_{11}}]]}} exp exp {{j j \frac{π π}{λZ λZ} [[{x x}^{22} + + {((y the y - - {v v}_{y the y} {t t}_{s the s}))}^{22}]]}}$

${e e}_{V V}^{T T} ((x x,, y the y)) = = Crect Crect ((\frac{x x}{{L L}_{x x}})) rect rect ((\frac{y the y}{{L L}_{y the y}})) exp exp {{- - j j \frac{22 π π}{λ λ} [[\frac{x x}{M m} \cdot &Center Dot; θ θ - - {Ln ln}_{o o} - - \frac{{((y the y - - {v v}_{y the y} {t t}_{x x}))}^{22}}{{22 R R}_{22}}]]}} exp exp {{j j \frac{π π}{λZ λZ} [[{x x}^{22} + + {((y the y - - {v v}_{y the y} {t t}_{s the s}))}^{22}]]}}$

式中，

R₁＝M²f₁，R₂＝M²f₂，t_s为慢时间，v_y为飞机航线上慢时间的运动速度，公式中最后一项与Z有关的相位二次项是发射光束夫琅禾费衍射传播产生的远场背景相位二次项。两偏振光束的照明的公共区域为有效的照明条幅，此时，有效照明光斑的空间相位差具有抛物等位线：In the formula,

R ₁ ＝M ² f ₁ , R ₂ ＝M ² f ₂ , t _s is the slow time, v _y is the moving speed of the slow time on the flight route, the last item in the formula is the phase quadratic term related to Z is the emitted beam Far-field background phase quadratic term due to Fraunhofer diffractive propagation. The common area illuminated by the two polarized light beams is the effective illumination strip. At this time, the spatial phase difference of the effective illumination spot has a parabolic equipotential line:

式中，1/R₃＝1/R₂+1/R₁，一般设计时采用R₂＝R₁。由于采用四电极电光偏转器可以实现偏转角度随电压线性变化，因此通过施加线性电压可获得高响应速度的线性相位调制，这样就可以获得交轨向目标点横向位置的线性项相位调制，顺轨向目标点纵向位置为中心的二次项相位历程，是用以实现雷达二维平面目标成像的关键抛物波面相位。In the formula, 1/R ₃ =1/R ₂ +1/R ₁ , and R ₂ =R ₁ is generally used in design. because The four-electrode electro-optical deflector can realize the linear change of the deflection angle with the voltage, so the linear phase modulation with high response speed can be obtained by applying a linear voltage, so that the linear phase modulation of the cross-track to the lateral position of the target point can be obtained, and the along-track direction The quadratic term phase history centered on the longitudinal position of the target point is the key parabolic wave surface phase used to realize the radar two-dimensional plane target imaging.

当偏振态为电光扫描器的e光时，其折射率变化为When the polarization state is the e-ray of the electro-optical scanner, its refractive index changes as

$\{\begin{matrix} {n no}_{11} = = {n no}_{e e} + + \frac{11}{22} {n no}_{e e}^{33} {γ γ}_{3333} {E E.}_{33} ((y the y)) = = {n no}_{e e} + + Δn Δn \\ {n no}_{22} = = {n no}_{e e} - - \frac{11}{22} {n no}_{e e}^{33} {γ γ}_{3333} {E E.}_{33} ((y the y)) = = {n no}_{e e} - - Δn Δn \end{matrix}$

其中，n_e为晶体e光折射率，E₃为晶体通光孔径内的电场，γ₃₃为在该方向上的电光系数。经过电光扫描器后，其x方向的相位延迟为in, n _e is the optical refractive index of the crystal e, E ₃ is the electric field in the clear aperture of the crystal, and γ ₃₃ is the electro-optic coefficient in this direction. After passing through the electro-optical scanner, the phase delay in the x direction is

φ(x)＝-kx·θ+kLn_e φ(x)=-kx·θ+kLn _e

同样当水平偏振光束从第一电光扫描器5和第一柱面镜6、第二电光扫描器13和第二柱面镜14后，该位置同为发射望远镜主镜16的前焦面，其发射场为Equally when the horizontally polarized light beam is behind the first electro-optic scanner 5 and the first cylindrical mirror 6, the second electro-optic scanner 13 and the second cylindrical mirror 14, this position is the same as the front focal plane of the main mirror 16 of the transmitting telescope. The launch site is

${e e}_{H h}^{in in} ((x x,, y the y)) = = Crect Crect ((\frac{x x}{{L L}_{x x}^{in in}})) rect rect ((\frac{y the y}{{L L}_{y the y}^{in in}})) exp exp {{j j \frac{22 π π}{λ λ} [[x x \cdot &Center Dot; θ θ + + {Ln ln}_{e e} + + \frac{{y the y}^{22}}{22 {f f}_{11}}]]}}$

${e e}_{V V}^{in in} ((x x,, y the y)) = = Crect Crect ((\frac{x x}{{L L}_{x x}^{in in}})) rect rect ((\frac{y the y}{{L L}_{y the y}^{in in}})) exp exp {{j j \frac{22 π π}{λ λ} [[- - x x \cdot &Center Dot; θ θ + + {Ln ln}_{e e} - - \frac{{y the y}^{22}}{{22 f f}_{22}}]]}}$

这时在目标面上形成水平偏振照明波前同理为：At this time, the horizontally polarized illumination wavefront is formed on the target surface, and the same reasoning is as follows:

${e e}_{H h}^{T T} ((x x,, y the y)) = = Crect Crect ((\frac{x x}{{L L}_{x x}})) rect rect ((\frac{y the y}{{L L}_{y the y}})) exp exp {{j j \frac{22 π π}{λ λ} [[\frac{x x}{M m} \cdot \cdot θ θ + + {Ln ln}_{e e} + + \frac{{((y the y - - {v v}_{y the y} {t t}_{s the s}))}^{22}}{{22 R R}_{11}}]]}} exp exp {{j j \frac{π π}{λZ λZ} [[{x x}^{22} + + {((y the y - - {v v}_{y the y} {t t}_{s the s}))}^{22}]]}}$

${e e}_{V V}^{T T} ((x x,, y the y)) = = Crect Crect ((\frac{x x}{{L L}_{x x}})) rect rect ((\frac{y the y}{{L L}_{y the y}})) exp exp {{- - j j \frac{22 π π}{λ λ} [[\frac{x x}{M m} \cdot &Center Dot; θ θ - - {Ln ln}_{e e} - - \frac{{((y the y - - {v v}_{y the y} {t t}_{x x}))}^{22}}{{22 R R}_{22}}]]}} exp exp {{j j \frac{π π}{λZ λZ} [[{x x}^{22} + + {((y the y - - {v v}_{y the y} {t t}_{s the s}))}^{22}]]}}$

式中，

式中，1/R₃＝1/R₂+1/R₁，一般设计时采用R₂＝R₁。由于

其中电光扫描器的偏转角度在通光口径内与电压成线性关系，因此通过施加线性电压可获得高响应速度的线性相位调制，这样就可以获得交轨向目标点横向位置的线性项相位调制，顺轨向目标点纵向位置为中心的二次项相位历程，是用以实现雷达二维平面目标成像的关键抛物波面相位。图3为两偏振光束具有抛物波面相位差经过检偏器后的干涉图。In the formula, 1/R ₃ =1/R ₂ +1/R ₁ , and R ₂ =R ₁ is generally used in design. because

Among them, the deflection angle of the electro-optical scanner has a linear relationship with the voltage within the aperture, so the linear phase modulation with high response speed can be obtained by applying a linear voltage, so that the linear term phase modulation of the cross track to the lateral position of the target point can be obtained. The quadratic term phase history centered on the longitudinal position of the along-track target point is the key parabolic wave surface phase used to realize the radar two-dimensional planar target imaging. Fig. 3 is the interferogram of two polarized light beams with parabolic phase difference after passing through the analyzer.

成像分辨率采用相干点扩散函数最小值半宽度来表达，由于照明光斑在交轨向的角度扫描范围为(-kθ_max,kθ_max)，k≤0.5为光束中心偏转的可能设计值，且目标面上可成像的有效条幅为L_x，积分范围为2kθ_max，因此交轨向的分辨率为The imaging resolution is expressed by the minimum half-width of the coherent point spread function. Since the angular scanning range of the illumination spot in the cross-track direction is (-kθ _max , kθ _max ), k≤0.5 is the possible design value of the deflection of the beam center, and the target The effective swath that can be imaged on the surface is L _x , and the integration range is 2kθ _max , so the cross-track resolution is

${d d}_{x x} = = \frac{λM λ M}{44 k k {θ θ}_{max max}}$

同理，顺轨向的分辨率为Similarly, the along-track resolution is

${d d}_{y the y} = = \frac{λ λ {R R}_{33}}{{L L}_{y the y}} = = \frac{Mλ Mλ {R R}_{33}^{in in}}{{L L}_{y the y}^{in in}}$

一般情况下，设计x，y方向的分辨率相等，有d_x＝d_y，

理想的设计最大偏向角为

θ_{\max} = \frac{L_{y}^{in}}{{4 kR}_{3}^{in}},

当k=0.5时，

θ_{\max} = \frac{L_{y}^{in}}{2 R_{3}^{in}} .

In general, the resolutions in the design x and y directions are equal, d _x = d _y ,

The ideal design maximum deflection angle is

θ_{\max} = \frac{L_{the y}^{in}}{{4 kR}_{3}^{in}},

When k=0.5,

θ_{\max} = \frac{L_{the y}^{in}}{2 R_{3}^{in}} .

由此可见，表示成像分辨率的顺轨向的相干点扩展函数最小值半宽度由内发射光场的相对口径所决定，随工作距离增长而增大；而交轨向的相干点扩展函数最小值半宽度由内发射光场的相对口径和其电光晶体长厚比和晶体性质与所施加的电场所决定，同样随工作距离增长而增大。It can be seen that the minimum half-width of the coherent point spread function in the along-track direction of the imaging resolution is determined by the relative aperture of the internal emission light field, and increases with the increase of the working distance; while the coherent point spread function in the cross-track direction is the smallest The value half-width is determined by the relative aperture of the internal emission light field, the aspect ratio of the electro-optic crystal, the crystal properties and the applied electric field, and it also increases with the working distance.

图1是本发明最佳实施例的结构示意图，其具体结构和参数如下：Fig. 1 is the structural representation of preferred embodiment of the present invention, and its concrete structure and parameter are as follows:

本实施例性能指标要求为：飞机机载观察，平台运动速度为40m/s；观察高度Z=5km，要求激光照明有效条幅宽度为25m×25m，且分辨率全宽度为有d_x＝40mm，d_y＝40mm。The performance index requirements of this embodiment are: aircraft airborne observation, platform movement speed is 40m/s; observation height Z=5km, the effective banner width of laser lighting is required to be 25m×25m, and the full resolution width is _dx =40mm, d _y =40mm.

其中发射激光波长采用0.532μm，第一电光扫描器5和第二电光扫描器13均采用LiNbO₃晶体，他们的尺寸均为10mm×10mm×50mm，通光口径为5mm×5mm，四曲面电极采用双曲面电极，产生通光口径内的x方向的线性梯度电场，施加的最大电压为8000V，因此其可获得的最大线性调制角度为θ_max＝0.034rad，发射望远镜主镜16的焦距设计为F=1m，因此距离放大倍数为M=5×10³，发射望远镜主镜16口径大约为100mm，目标面有效照明光斑尺寸为50m×50m。第一电光扫描器5和第二电光扫描器13的扫描范围为(-0.5θ_max,0.5θ_max)，据此，其成像分辨率的设计为d_x＝40mm，设计x，y方向的分辨率相等，有d_x＝d_y，则

这时第一柱面镜6与第二柱面镜14的焦距为f₁＝147mm，f₂＝-147mm。据此，可获得我们所需的成像分辨率、有效条幅宽度与电光调制的抛物等位相差，用以直视合成孔径激光成像雷达的自差接收。The emission laser wavelength is 0.532 μm, the first electro-optic scanner 5 and the second electro-optic scanner 13 both use LiNbO ₃ crystals, their dimensions are 10mm×10mm×50mm, the aperture of the light is 5mm×5mm, and the four-curved surface electrode adopts The hyperboloid electrode produces a linear gradient electric field in the x direction in the light aperture, and the applied maximum voltage is 8000V, so the maximum linear modulation angle it can obtain is _θmax =0.034rad, and the focal length of the primary mirror 16 of the transmitting telescope is designed to be F =1m, so the distance magnification is M=5×10 ³ , the aperture of the primary mirror 16 of the transmitting telescope is about 100mm, and the effective illumination spot size of the target surface is 50m×50m. The scanning range of the first electro-optic scanner 5 and the second electro-optic scanner 13 is (-0.5θ _max , 0.5θ _max ), accordingly, the design of its imaging resolution is d _x =40mm, and the resolution of x and y directions is designed rates are equal, d _x = d _y , then

At this time, the focal lengths of the first cylindrical lens 6 and the second cylindrical lens 14 are f ₁ =147mm, f ₂ =-147mm. According to this, we can obtain the required imaging resolution, effective swath width and parabolic equipotential phase difference of electro-optical modulation, which can be used to directly look at the self-differential reception of synthetic aperture imaging lidar.

Claims

1. A two-way electro-optical scanning direct-view synthetic aperture laser imaging radar transmitting system is characterized by comprising a laser (1), a half-wave plate (2), an aperture diaphragm (3), a first polarization beam splitter (4), a first electro-optical scanner (5), a first cylindrical mirror (6), a second polarization beam splitter (7), a first 1/4 wave plate (8), a first reflecting mirror (9), a third polarization beam splitter (10), a second 1/4 wave plate (11), a second reflecting mirror (12), a second electro-optical scanner (13), a second cylindrical mirror (14), a fourth polarization beam splitter (15), a transmitting telescope main mirror (16), a high-voltage power supply (17) and a signal generator (18); the emergent surface of the first electro-optical scanner (5) is closely attached to a first cylindrical mirror (6), the emergent surface of the second electro-optical scanner (13) is closely attached to a second cylindrical mirror (14), the first cylindrical mirror (6) and the second cylindrical mirror (14) are both positioned on the front focal plane of a primary mirror (16) of the transmitting telescope, the high-voltage power supply (17) is connected with the first electro-optical scanner (5) and the second electro-optical scanner (13) and generates a linear pulse signal by a signal generator (18) to control the high-voltage power supply (17) to generate linearly-changed voltage, the scanning directions of the first electro-optical scanner (5) and the second electro-optical scanner (13) are opposite in sign, the scanning directions of the first electro-optical scanner (5) and the second electro-optical scanner (13) are in an intersecting direction, and the modulation wave surfaces of the first cylindrical mirror (6) and the second cylindrical mirror (14) are in an ascending direction, the positional relationship of the above components is as follows:

the polarized light beam output by the laser light source (1) passes through the half-wave plate (2) to obtain a polarized light beam in a required 45-degree direction, the polarized light beam passes through the aperture diaphragm (3) and the first polarization beam splitter (4) and is spatially polarized and decomposed into two horizontal polarized light beams and vertical polarized light beams which are orthogonal in polarization and have equal intensity, the reflected polarized light beam is vertical polarized light beam, the transmitted polarized light beam is horizontal polarized light beam, the reflected vertical polarized light beam passes through the first electro-optical scanner (5) and the first cylindrical mirror (6), is reflected by the second polarization beam splitter (7) to enter the first 1/4 wave plate (8) to reach the first reflecting mirror (9), and then is reflected by the first reflecting mirror (9) to pass through the first 1/4 wave plate (8) again, and the polarization state of the vertical polarized light beam at this time is rotated by 90 degrees to be a horizontal polarized light beam, the beam enters the second polarization beam splitter (7) again to be a transmission beam, and then the transmission horizontal polarization beam is transmitted by a fourth polarization beam splitter (15) and a primary mirror (16) of a transmitting telescope; the horizontal polarization light beam directly transmitted by the first polarization beam splitter (4) enters a second 1/4 wave plate (11) and a second reflector for reflection (12) after passing through a third polarization beam splitter (10), the original horizontal polarization light beam is rotated by 90 degrees to become a vertical polarization light beam after the reflected light beam enters a second 1/4 wave plate (11) again, the vertical polarization light beam enters the third polarization beam splitter (10) again to become a reflected light beam, the reflected vertical polarization light beam enters a second electro-optical scanner (13) and a second cylindrical mirror (14), then the reflected vertical polarization light beam is reflected by a fourth polarization beam splitter (15), the horizontal polarization light beam and the vertical polarization light beam are recombined into a coaxial concentric light beam with orthogonal polarization by the fourth polarization beam splitter (15), and the coaxial concentric light beam with the orthogonal polarization light beam is emitted to a target by the main transmitting telescope mirror (16).