CN103543443B - Two-way electropical scanning Orthoptic synthetic aperture laser imaging radar emission coefficient - Google Patents

Abstract

A kind of two-way electropical scanning Orthoptic synthetic aperture laser imaging radar emission coefficient, its formation comprises: laser instrument, half-wave plate, aperture diaphragm, the first polarization beam apparatus, the first electro-optic scanner, the first cylindrical mirror, the second polarization beam apparatus, the first quarter wave plate, the first catoptron, the 3rd polarization beam apparatus, the second quarter wave plate, the second catoptron, the second electro-optic scanner, the second cylindrical mirror, the 4th polarization beam apparatus, transmitter-telescope primary mirror, also has high-voltage power supply and signal generator in addition.The present invention can carry out electropical scanning to two-way light beam, finally realize the parabolic equipotential line corrugated phase differential of two polarized orthogonal light beams at far field objects place, for scanning target, and structure is simple, non-scan, the fast response time on electric light phase-modulation corrugated, reach nanosecond order, volume is little, lightweight, is particularly suitable for the emission coefficient of the Orthoptic synthetic aperture laser imaging radar on the high-speed cruising carrying platform such as airborne or spaceborne.

Description

Two-way electro-optical scanning direct-vision synthetic aperture laser imaging radar transmitting system

Technical Field

The invention relates to a laser radar, in particular to a two-way electro-optical scanning direct-view synthetic aperture laser imaging radar transmitting system which is used as an optical transmitting device in a direct-view synthetic aperture laser imaging radar. The method comprises the steps that double-path linear electro-optic scanning is carried out in the cross-track direction through an electro-optic scanner, linear item phase modulation of the cross-track direction target point transverse position is generated, phase modulation is carried out in the down-track direction through a cylindrical mirror, secondary item phase processes with the down-track direction target point longitudinal position as the center are generated, and finally, a polarization orthogonal parabolic equipotential line phase difference wave surface is obtained.

Background

The synthetic aperture laser imaging radar is based on the synthetic aperture radar principle in the radio frequency field, and is a unique optical imaging observation means capable of obtaining centimeter-level imaging resolution at a long distance. The traditional synthetic aperture laser imaging radar performs light wave transmission and data reception under the side-looking condition, adopts optical heterodyne reception, is greatly influenced by atmospheric disturbance, vibration of a moving platform, target speckle, phase change of a laser radar system and the like, and is difficult to practically apply because the initial phase of a beat signal is strictly synchronized and long-distance delay is required to control the phase change. In addition, the linear modulation of the frequency of the laser emission light source in the traditional synthetic aperture laser imaging radar mostly adopts mechanical modulation, and the modulation speed is limited.

The direct-view synthetic aperture laser imaging radar described in the prior art [1] (direct-view synthetic aperture laser imaging radar principle, optical science, vol.32,0928002-1 to 8,2012) and the prior art [2] (Liu Li people, direct-view synthetic aperture laser imaging radar, publication No. CN102435996) projects two coaxial concentric and polarization orthogonal light beams to a target by adopting a wave front transformation principle, receives the light beams by self-difference, performs spatial linear phase modulation in the cross-track direction, realizes one-dimensional Fourier transform focusing imaging, performs secondary phase history in the forward-track direction, and realizes conjugate secondary term phase matching filtering imaging. The motion direction of the radar carrying platform is the direction along the rail, and the orthogonal direction along the rail is the direction of crossing the rail.

The direct-view synthetic aperture laser imaging radar of the prior art [1] and [2] has the characteristics of being capable of automatically eliminating phase changes and interferences generated by atmosphere, a motion platform, a light radar system and speckles, allowing use of a low-quality receiving optical system, not needing an optical delay line, not needing real-time beat signal phase synchronization, enabling imaging without shadows, being capable of using various lasers with single-mode and single-frequency properties, simultaneously realizing complex demodulation of phases by adopting a space optical bridge, being simple in electronic equipment and the like. However, the transmitting system scheme proposed by the direct-view synthetic aperture laser imaging radar adopts two beam deflectors to perform opposite scanning on two beams to enable the light field distribution of an internal transmitting field to be in a space phase quadratic form, and linear phase modulation in the cross-track direction can be obtained only by maintaining accurate synchronization at the time, so that accurate synchronization of the opposite scanning of the two beams is difficult and complicated.

Disclosure of Invention

The invention aims to solve the technical problem of overcoming the defects in the prior art, and provides a two-path electro-optical scanning direct-view synthetic aperture laser imaging radar transmitting system which adopts 4 polarization beam splitters, so that two light beams pass through the electro-optical scanner and have consistent polarization states, but the polarization states of the two light beams emitted by the system are orthogonal, the phase in the cross-track direction can be modulated by the electro-optical scanner, the phase of the wave surface in the along-track direction is modulated by a cylindrical mirror, the spatial linear phase item modulation related to the position in the cross-track direction of a target can be directly generated on a fast time axis, and the spatial quadratic phase course in the along-track direction of the target is generated on a slow time axis.

The technical solution of the invention is as follows:

a two-way electro-optical scanning direct-view synthetic aperture laser imaging radar transmitting system comprises a laser, a half-wave plate, an aperture diaphragm, a first polarization beam splitter, a first electro-optical scanner, a first cylindrical mirror, a second polarization beam splitter, a first 1/4 wave plate, a first reflector, a third polarization beam splitter, a second 1/4 wave plate, a second reflector, a second electro-optical scanner, a second cylindrical mirror, a fourth polarization beam splitter, a transmitting telescope primary mirror, a high-voltage power supply and a signal generator; the high-voltage pulse laser device comprises a first electro-optical scanner, a second electro-optical scanner, a signal generator, a first cylindrical mirror, a second cylindrical mirror, a first high-voltage power supply, a second high-voltage power supply, a signal generator and a second electro-optical scanner, wherein the emergent surface of the first electro-optical scanner is close to the first cylindrical mirror, the emergent surface of the second electro-optical scanner is close to the second cylindrical mirror, the first cylindrical mirror and the second cylindrical mirror are both located on the front focal plane of a primary mirror of a transmitting telescope, the high-voltage power supply is connected with the first electro-optical scanner and the second electro-optical scanner, the signal generator generates linear pulse signals to control the high-voltage power supply to generate linearly-changed voltage, the scanning directions of the first electro-optical. The positional relationship of the above components is as follows:

the polarized light beam output by the laser light source passes through the half-wave plate to obtain the required polarized light beam in the 45-degree direction, the polarized light beam passes through the aperture diaphragm and the first polarization beam splitter and is spatially polarized and decomposed into two horizontal polarized light beams and vertical polarized light beams with equal intensity and orthogonal polarization, the reflected polarized light beam is a vertical polarized light beam, the transmitted polarized light beam is a horizontal polarized light beam, the reflected vertical polarized light beam passes through the first electro-optical scanner and the first cylindrical mirror, is reflected by the second polarized beam splitter, enters the 1/4 wave plate and reaches the first reflector, then the light beam is reflected by the first reflector and enters the first 1/4 wave plate again, the polarization state of the vertical polarization light beam is rotated by 90 degrees at this time to become a horizontal polarization light beam, the light beam enters the second polarization beam splitter again to become a transmission light beam, then the transmitted horizontal polarized light beam is transmitted by a fourth polarization beam splitter and a primary mirror of a transmitting telescope; the horizontal polarization beam directly transmitted by the first polarization beam splitter enters the second 1/4 wave plate and the second reflector for reflection after passing through the third polarization beam splitter, the original horizontal polarization beam rotates 90 degrees in polarization state after the reflected beam enters the second 1/4 wave plate again to become a vertical polarization beam, the vertical polarization beam enters the third polarization beam splitter again to become a reflected beam, the reflected vertical polarization beam enters the second electro-optical scanner and the second cylindrical mirror and then is reflected by the fourth polarization beam splitter, the horizontal polarization beam and the vertical polarization beam are recombined into a coaxial concentric beam with orthogonal polarization by the fourth polarization beam splitter, and the beam is emitted to a target by the primary mirror of the emission telescope.

Compared with the prior art, the invention has the following technical effects:

1. the invention adopts four polarization beam splitters to carry out polarization beam splitting and beam combining on the emitted light wave, adopts the electro-optic scanner to carry out direct linear phase modulation on the wave surface in the cross-track direction of the two light beams on two branches in the vertical polarization state, and utilizes the cylindrical mirror to carry out secondary phase modulation on the phase of the wave surface in the along-track direction of the two polarized light beams, so that the linear modulation in the cross-track direction is twice of that of a single electro-optic scanner, and finally the combined beam is two beams of polarization orthogonal and coaxial emitted light beams.

2. The electro-optical scanner adopted by the invention modulates the linear phase in the cross-track direction, has the advantages of simple control, no mechanical scanning, no inertia, response speed reaching nanosecond level, small volume, light weight and the like, and is particularly suitable for carrying platforms which move at high speed, such as airborne or satellite borne platforms and the like.

3. Two paths of light beams in a vertical polarization state are adopted for linear phase modulation, so that the large electro-optic coefficient under vertical polarization can be fully utilized, and light beam scanning in the horizontal direction is realized.

Drawings

FIG. 1 is a diagram of a two-way electro-optical scanning direct-view synthetic aperture laser imaging radar transmitting system of the present invention.

Fig. 2 is a structural diagram of a four-electrode electro-optical scanner in a two-way electro-optical scanning direct-view synthetic aperture laser imaging radar transmitting system of the present invention.

Fig. 3 is an interference diagram of the parabolic wave surfaces of two polarized light beams in the two-way electro-optical scanning direct-view synthetic aperture laser imaging radar transmitting system of the invention.

Detailed Description

The invention is further illustrated with reference to the following figures and examples, which should not be construed as limiting the scope of the invention.

Referring to fig. 1, fig. 1 is a structural diagram of a two-way electro-optical scanning direct-view synthetic aperture laser imaging radar transmitting system according to the present invention. As can be seen from the figure, the two-way electro-optical scanning direct-view synthetic aperture laser imaging radar transmitting system comprises 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 close to the first cylindrical mirror 6, the emergent surface of the second electro-optical scanner 13 is close to the second cylindrical mirror 14, the first cylindrical mirror 6 and the second cylindrical mirror 14 are both positioned on the front focal plane of the 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, a signal generator 18 generates linear pulse signals to control the high-voltage power supply 17 to generate linearly-changed voltage, the first electro-optical scanner 5 and the second electro-optical scanner 13 both adopt electro-optical deflectors with four-curved-surface electrode structures, the crystals are cut in the 45-degree direction to generate linear gradient electric fields in the cross-track direction to realize cross-track position-related linear phase modulation, and the signs scanned by the first electro-optical scanner 5 and the second electro-optical scanner 13 are opposite. 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 the required polarized light beam in the 45-degree direction, the polarized light beam passes through the aperture stop 3 and the first polarization beam splitter 4 and is spatially polarization-decomposed into two horizontal polarized light beams and vertical polarized light beams of equal intensity and polarization orthogonality, the reflected polarized light beam is a vertical polarized light beam, the transmitted polarized light beam is a horizontal polarized light beam, the reflected vertical polarized light beam passes through the first electro-optical scanner 5 and the first cylindrical mirror 6, reflected by the second polarizing beam splitter 7 into 1/4 wave plate 8 to the first mirror 9, and then reflected by the first mirror 9 to enter the first 1/4 wave plate 8 again, where the polarization state of the vertically polarized light beam is rotated by 90 degrees to become a horizontally polarized light beam, and then to enter the second polarization beam splitter 7 again as a transmitted light beam, the transmitted horizontally polarized beam is then transmitted through a fourth polarizing beam splitter 15 and a primary mirror 16 of the transmitting telescope; the horizontal polarization beam directly transmitted by the first polarization beam splitter 4 passes through the third polarization beam splitter 10, enters the second 1/4 wave plate 11 and the second reflector 12 for reflection, the original horizontal polarization beam is rotated by 90 ° after the reflected beam enters the second 1/4 wave plate 11 again, and then becomes a vertical polarization beam, the vertical polarization beam enters the third polarization beam splitter 10 again as a reflected beam, the reflected vertical polarization beam enters the second electro-optical scanner 13 and the second cylindrical mirror 14, and then is reflected by the fourth polarization beam splitter 15, the horizontal polarization beam and the vertical polarization beam are recombined into a concentric and polarized orthogonal beam by the fourth polarization beam splitter 15, and the concentric and polarized orthogonal beam is emitted to a target by the primary mirror 16 of the emission telescope.

The laser emitted from the laser source 1 passes through the half-wave plate 2 to generate a polarized beam with 45 degree polarization, the aperture stop 3 is used to limit the amplitude width of the polarized beam, and then the polarized beam is split into a horizontal polarized beam and a vertical polarized beam by the first polarization beam splitter 4, wherein the vertical polarized beam directly enters the first electro-optical scanner 5 and the first cylindrical mirror 6, and then passes through the second polarization beam splitter 7 and the 1/4 wave plate 8 twice to be converted into the horizontal polarized beam, while the horizontal polarized beam transmitted by the first polarization beam splitter 4 passes through the third polarization beam splitter 10 and then passes through the 1/4 wave plate 11 twice to be converted into the vertical polarized beam to enter the second electro-optical scanner 13 and the second cylindrical mirror 14, so the polarization states of the two beams entering the first electro-optical scanner 5 and the second electro-optical scanner 13 are the same, and the linear phases of the modulation are the same, since the first electro-optical scanner 5 and the second scanner 13 employ a four-electrode lithium niobate crystal electro-optical deflector, as shown in fig. 2, if light propagates along the y direction, when the z axis of the crystal is the polarization state direction of the vertically polarized light beam (depending on the placement of the crystal), then for the horizontally polarized light beam, the polarization state is perpendicular to the z axis of the crystal, which is o light of the crystal; when the z axis of the crystal is the polarization state direction of the horizontal polarization light beam, the polarization state of the horizontal polarization light beam is parallel to the z axis of the crystal and is e light of the crystal, and different refractive index changes are generated at two placing positions of the crystal and correspond to different electro-optic deflection angles.

When the polarization state is o light of the electro-optical scanner, the refractive index changes to

$\left\{\begin{array}{c}{n}_1=n_o+\frac{1}{2}{n}_o^3{\mathrm{\γ}}_{13}{E}_3\left(y\right)=n_o+\mathrm{\Δ}{n}^{\′}\\ n_2=n_o-\frac{1}{2}{n}_o^3{\mathrm{\γ}}_{13}{E}_3\left(y\right)=n_o-{\mathrm{\Δn}}^{\′}\end{array}\right.$

Wherein,n_ois the refractive index of the o light of the crystal, E₃For electric fields applied across the clear aperture of the crystal, gamma₁₃Is the electro-optic coefficient in that direction. At this time, after passing through the two electro-optical scanners, the phase delay in the x direction is

φ(x)＝kxθ+kLn_o

Wherein,is the scan angle of the electro-optical scanner.

Therefore, when the horizontally polarized light beams are emitted from the first electro-optical scanner 5 and the first cylindrical mirror 6, the second electro-optical scanner 13 and the second cylindrical mirror 14, the position is the front focal plane of the primary mirror 16 of the transmitting telescope, and the emission field is

$e_H^{\mathrm{in}}(x,y)=\mathrm{Crect}\left(\frac{x}{L_x^{\mathrm{in}}}\right)\mathrm{rect}\left(\frac{y}{L_y^{\mathrm{in}}}\right)\exp \left\{j\frac{2\mathrm{\π}}{\mathrm{\λ}}\right[x\·\mathrm{\θ}+{\mathrm{Ln}}_o+\frac{y^2}{{2f}_1}\left]\right\}$

$e_V^{\mathrm{in}}(x,y)=\mathrm{Crect}\left(\frac{x}{L_x^{\mathrm{in}}}\right)\mathrm{rect}\left(\frac{y}{L_y^{\mathrm{in}}}\right)\exp \left\{j\frac{2\mathrm{\π}}{\mathrm{\λ}}\right[-x\·\mathrm{\θ}+{\mathrm{Ln}}_o-\frac{y^2}{{2f}_2}\left]\right\}$

Wherein,is the amplitude width of the incident beam, L is the length of the crystal, f₁Is the focal length, f, of the first cylindrical mirror 6₂The focal length of the second cylindrical lens 14.

Then one of the two horizontal polarized beams passes through the second polarization beam splitter 7 and then passes through the second 1/4 wave plate 8 twice to be converted into a vertical polarized beam, the beam is recombined with the other horizontal polarized beam by the fourth polarization beam splitter 15 to be a coaxial concentric polarization orthogonal beam, and the beam is emitted to a far field target by the emission telescope primary mirror 16, wherein after an internal emission field is emitted by the emission telescope primary mirror 16, the light field of the internal emission field at the far field target is the amplified light field of the internal emission field, the amplification factor is M = (Z-F)/F, Z is the distance from the emission telescope primary mirror 16 to the far field target surface, and F is the focal length of the emission telescope primary mirror. The horizontally polarized illumination wavefront now formed on the target surface is:

$e_H^T(x,y)=\mathrm{Crect}\left(\frac{x}{L_x}\right)\mathrm{rect}\left(\frac{y}{L_y}\right)\exp \left\{j\frac{2\mathrm{\π}}{\mathrm{\λ}}\right[\frac{x}{M}\·\mathrm{\θ}+{\mathrm{Ln}}_o+\frac{{(y-v_y{t}_x)}^2}{{2R}_1}\left]\right\}\exp \left\{j\frac{\mathrm{\π}}{\mathrm{\λZ}}\right[x^2+{(y-v_y{t}_s)}^2\left]\right\}$

$e_V^T(x,y)=\mathrm{Crect}\left(\frac{x}{L_x}\right)\mathrm{rect}\left(\frac{y}{L_y}\right)\exp \{-j\frac{2\mathrm{\π}}{\mathrm{\λ}}[\frac{x}{M}\·\mathrm{\θ}-{\mathrm{Ln}}_o-\frac{{(y-v_y{t}_x)}^2}{{2R}_2}\left]\right\}\exp \left\{j\frac{\mathrm{\π}}{\mathrm{\λZ}}\right[x^2+{(y-v_y{t}_s)}^2\left]\right\}$

in the formula,R₁＝M²f₁，R₂＝M²f₂，t_sis a slow time, v_yFor the slow-time movement speed on the aircraft flight line, the phase quadratic term related to Z in the last term in the formula is a far-field background phase quadratic term generated by emission beam Fraunhofer diffraction propagation. The common area of illumination of the two polarized beams is the effective illumination swath, at this time, the spatial phase difference of the effective illumination spots has parabolic equipotential lines:

in the formula, 1/R₃＝1/R₂+1/R₁In general, R is used in design₂＝R₁. Due to the fact thatThe four-electrode electro-optical deflector can realize that the deflection angle linearly changes along with the voltage, so that the linear phase modulation with high response speed can be obtained by applying linear voltage, and the linear term phase modulation at the transverse position of a target point in the direction of an intersection rail can be obtained.

When the polarization state is e-light of electro-optical scanner, its refractive index changes

$\left\{\begin{array}{c}{n}_1=n_e+\frac{1}{2}{n}_e^3{\mathrm{\γ}}_{33}{E}_3\left(y\right)=n_e+\mathrm{\Δn}\\ n_2=n_e-\frac{1}{2}{n}_e^3{\mathrm{\γ}}_{33}{E}_3\left(y\right)=n_e-\mathrm{\Δn}\end{array}\right.$

Wherein,n_eis the refractive index of E light of crystal, E₃Is the electric field in the clear aperture of the crystal, gamma₃₃Is the electro-optic coefficient in that direction. After passing through the electro-optical scanner, the phase delay in the x direction is

φ(x)＝-kx·θ+kLn_e

Similarly, when the horizontally polarized beam comes from the first electro-optical scanner 5 and the first cylindrical mirror 6, the second electro-optical scanner 13 and the second cylindrical mirror 14, the position is the front focal plane of the primary mirror 16 of the transmitting telescope, and the transmitting field is

$e_H^{\mathrm{in}}(x,y)=\mathrm{Crect}\left(\frac{x}{L_x^{\mathrm{in}}}\right)\mathrm{rect}\left(\frac{y}{L_y^{\mathrm{in}}}\right)\exp \left\{j\frac{2\mathrm{\π}}{\mathrm{\λ}}\right[x\·\mathrm{\θ}+{\mathrm{Ln}}_e+\frac{y^2}{2f_1}\left]\right\}$

$e_V^{\mathrm{in}}(x,y)=\mathrm{Crect}\left(\frac{x}{L_x^{\mathrm{in}}}\right)\mathrm{rect}\left(\frac{y}{L_y^{\mathrm{in}}}\right)\exp \left\{j\frac{2\mathrm{\π}}{\mathrm{\λ}}\right[-x\·\mathrm{\θ}+{\mathrm{Ln}}_e-\frac{y^2}{{2f}_2}\left]\right\}$

The same reasoning holds for forming a horizontally polarized illumination wavefront on the target surface:

$e_H^T(x,y)=\mathrm{Crect}\left(\frac{x}{L_x}\right)\mathrm{rect}\left(\frac{y}{L_y}\right)\exp \left\{j\frac{2\mathrm{\π}}{\mathrm{\λ}}\right[\frac{x}{M}\·\mathrm{\θ}+{\mathrm{Ln}}_e+\frac{{(y-v_y{t}_s)}^2}{{2R}_1}\left]\right\}\exp \left\{j\frac{\mathrm{\π}}{\mathrm{\λZ}}\right[x^2+{(y-v_y{t}_s)}^2\left]\right\}$

$e_V^T(x,y)=\mathrm{Crect}\left(\frac{x}{L_x}\right)\mathrm{rect}\left(\frac{y}{L_y}\right)\exp \{-j\frac{2\mathrm{\π}}{\mathrm{\λ}}[\frac{x}{M}\·\mathrm{\θ}-{\mathrm{Ln}}_e-\frac{{(y-v_y{t}_x)}^2}{{2R}_2}\left]\right\}\exp \left\{j\frac{\mathrm{\π}}{\mathrm{\λZ}}\right[x^2+{(y-v_y{t}_s)}^2\left]\right\}$

in the formula,R₁＝M²f₁，R₂＝M²f₂，t_sis a slow time, v_yFor the slow-time movement speed on the flight line of the aircraft, formulaThe last phase quadratic term in Z is the far field background phase quadratic term generated by the propagation of the fraunhofer diffraction of the emitted beam. The common area of illumination of the two polarized beams is the effective illumination swath, at this time, the spatial phase difference of the effective illumination spots has parabolic equipotential lines:

in the formula, 1/R₃＝1/R₂+1/R₁In general, R is used in design₂＝R₁. Due to the fact thatThe deflection angle of the electro-optic scanner is in a linear relation with voltage in the light-passing aperture, so that linear phase modulation with high response speed can be obtained by applying linear voltage, linear item phase modulation crossing the rail to the transverse position of a target point can be obtained, and a quadratic item phase process taking the longitudinal position of the rail to the target point as the center is a key parabolic wave surface phase for realizing radar two-dimensional plane target imaging. FIG. 3 is an interference diagram of two polarized beams having parabolic wave surface phase difference and passing through an analyzer.

The imaging resolution is expressed by adopting the minimum half width of a coherent point spread function, and the angular scanning range of the illumination light spot in the cross-track direction is (-k theta)_max,kθ_max) K is less than or equal to 0.5, which is a possible design value of the central deflection of the light beam, and the effective strip width capable of being imaged on the target surface is L_xIntegration range of 2k theta_maxThus the resolution in the cross-track direction is

$d_x=\frac{\mathrm{\λM}}{4k{\mathrm{\θ}}_{\max }}$

For the same reason, the resolution in the down-track direction is

$d_y=\frac{\mathrm{\λ}{R}_3}{L_y}=\frac{\mathrm{M\λ}{R}_3^{\mathrm{in}}}{L_y^{\mathrm{in}}}$

In general, the resolution in the x, y directions is designed to be equal, with d_x＝d_y，The desired design maximum deflection angle is ${\mathrm{\θ}}_{\max }=\frac{L_y^{\mathrm{in}}}{{4\mathrm{kR}}_3^{\mathrm{in}}},$ When k =0.5, the number of the bits is set to k =0.5, ${\mathrm{\θ}}_{\max }=\frac{L_y^{\mathrm{in}}}{2R_3^{\mathrm{in}}}.$

therefore, the half width of the minimum value of the forward-orbit coherent point spread function representing the imaging resolution is determined by the relative aperture of the internal transmitting light field and is increased along with the increase of the working distance; the half width of the minimum value of the coherent point spread function in the cross-track direction is determined by the relative caliber of an internal emission light field and the length-thickness ratio and crystal property of an electro-optic crystal thereof and an applied electric field, and also increases along with the increase of the working distance.

FIG. 1 is a schematic structural diagram of the preferred embodiment of the present invention, the specific structure and parameters of which are as follows:

the performance indexes of the embodiment are that the aircraft is observed on board, the platform moving speed is 40m/s, the observation height Z =5km, the effective width of a laser illumination swath is 25m × 25m, and the resolution full width is d_x＝40mm，d_y＝40mm。

Wherein the wavelength of the emitted laser light is 0.532 μm, and the first electro-optical scanner 5 and the second electro-optical scanner 13 are both LiNbO₃The size of the crystal is 10mm × 10mm × 50mm, the light-passing aperture is 5mm × 5mm, the four-curved-surface electrode adopts a hyperboloid electrode, a linear gradient electric field in the x direction in the light-passing aperture is generated, the maximum applied voltage is 8000V, and therefore the maximum linear modulation angle obtained by the crystal is theta_maxAt 0.034rad, the focal length of the transmit telescope primary mirror 16 is designed to be F =1M, so the range magnification is M =5 × 10³The aperture of the primary mirror 16 of the transmitting telescope is about 100mm, the effective illumination spot size of the target surface is 50m × 50m, and the scanning ranges of the first electro-optical scanner 5 and the second electro-optical scanner 13 are (-0.5 theta)_max,0.5θ_max) According to this, the imaging resolution is designed to be d_x40mm, equal resolution in x, y directions, with d_x＝d_yThen, thenThe focal length of the first cylindrical mirror 6 and the second cylindrical mirror 14 is f₁＝147mm，f₂-147 mm. Accordingly, the imaging resolution, effective swath width and parabolic equipotential phase difference of the electro-optic modulation required by us can be obtainedWith direct view synthetic aperture laser imaging radar homodyne reception.

Claims (1)

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 source (1) passes through the half-wave plate (2) to obtain the required polarized light beam in the direction of 45 degrees, the polarized light beam passes through an aperture diaphragm (3) and a first polarization beam splitter (4) and is spatially polarized and decomposed into two horizontal polarized light beams and vertical polarized light beams which have the same intensity and are orthogonal in polarization, after the reflected vertical polarized light beam passes through the first electro-optic scanner (5) and the first cylindrical mirror (6), reflected by the second polarization beam splitter (7) into a first 1/4 wave plate (8) to a first mirror (9), then the light is reflected by the first reflector (9) and passes through the first 1/4 wave plate (8) again, the polarization state of the vertical polarization beam is rotated by 90 degrees at this time to become a horizontal polarization beam, and the horizontal polarization beam enters the second polarization beam splitter (7) again to become a transmission beam, then the transmitted horizontal polarized light 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).