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To perform the in-orbit test, verification and surveillance task, the laser simulation and test station must be constructed. Cooperated with the fixed laser communication ground station, we can not only test the main specifications of the laser communication terminals, but also test the performances of the laser backbone link. In this paper, we first give the basic theory of the in-orbit test. Then designed the laser simulation and test station, which consists of laser transmitter module, laser receiver module, and general test module. In the GEO-to-LEO laser communication terminal test progress, the laser simulation and test station responsible for the simulation of the LEO laser communication terminal. In the LEO-GEO-Ground laser link performance test progress, the laser simulation and test station simulate the LEO satellite, which transfer high date rate data flow to GEO satellite, then the GEO satellite route the data flow to the GEO-to-Ground laser communication terminal through optical router, finally GEO satellite transfer the LEO data down to fixed laser receiver on ground.

A 3 × 3 free-space optical router, which comprises optical switches and polarizing beam splitter (PBS) and based on crossbar network, is proposed in this paper. A control algorithm for the 3 × 3 free-space optical router is also developed to achieve rapid control without rearrangement. In order to test the performance of the network based on 3 × 3 free-space optical router and that of the algorithm developed for the optical router, experiments are designed. The experiment results show that the interconnection network based on the 3 × 3 free-space optical router has low cross talk, fast connection speed. Under the control of the algorithm developed, a non-block and real free interconnection network is obtained based on the 3 × 3 free-space optical router we proposed.

Down-looking synthetic aperture imaging ladar(SAIL) has overcome many difficulties in side-looking SAIL. However, it is inevitably impacted by the speckle effect. There is temporally varying speckle effect due to the angular deflecting of two coaxial polarization-orthogonal beams transmitted in the orthogonal direction of travel, and a spatial varying speckle effect in the travel direction. Under the coaxial heterodyne, phase variations caused by speckle effect are compensated, leaving the amplitude variations of speckle field. In this paper, the speckle effect in the down-looking SAIL is analyzed, expressions for two-dimensional data collection contained speckle effect are obtained and the two-dimensional image influenced by speckle effect is simulated.

Synthetic aperture radar interferometry (InSAR) can gain three-dimensional topography with high spatial resolution and height accuracy using across track interferometry[1]. Conventional InSAR produce three-dimensional images from SAR data. But when the working wavelength transit from microwave to optical wave, the transmission antenna and receive antenna become very sensitive to platform vibration and beam quality[2]. Through differential receive antenna formation, we can relax the requirement of platform and laser using synthetic aperture imaging ladar (SAIL) concept[3]. Line-of-sight motion constraints are reduced by several orders of magnitude. We introduce two distinctive forms of antenna formation according to the position of interferogram. The first architecture can simplify the interferogram processing and phase extraction algorithm under time-division multiplex operation. The second architecture can process the 2D coordinate and height coordinate at the same time. Using optical diffraction theory, a systematic theory of side-looking SAIL is mathematically formulated and the necessary conditions for assuring a correct phase history are established[4]. Based on optical transformation and regulation of wavefront, a side-looking SAIL of two distinctive architectures is invented and the basic principle, systematic theory, design equations and necessary conditions are presented. It is shown that high height accuracy can be reached and the influences from atmospheric turbulence and unmodeled line-of-sight motion can be automatically compensated.

Compared to synthetic aperture radar (SAR), synthetic aperture imaging ladar (SAIL) is more sensitive to the phase errors induced by atmospheric turbulence, undesirable line-of-sight translation-vibration and waveform phase error, because the light wavelength is about 3-6 orders of magnitude less than that of the radio frequency. This phase errors will deteriorate the imaging results. In this paper, an algorithm based on low-pass filtering to suppress the phase error is proposed. In this algorithm, the azimuth quadratic phase history with phase error is compensated, then the fast Fourier transform (FFT) is performed in azimuth direction, after the low-pass filtering, the inverse FFT is performed, then the image is reconstructed simultaneously in the range and azimuth direction by the two-dimensional (2D) FFT. The highfrequency phase error can be effectively eliminated hence the imaging results can be optimized by this algorithm. The mathematical analysis by virtue of data-collection equation of side-looking SAIL is presented. The theoretical modeling results are also given. In addition, based on this algorithm, a principle scheme of optical processor is proposed. The verified experiment is performed employing the data obtained from a SAIL demonstrator.

The down-looking synthetic aperture imaging ladar (SAIL) with electro-optic modulation was proposed. The measurement uses electrically controlled scanner to produce beams with spatial parabolic phase difference, which consists of electro-optic crystal and cylindrical lens. Due to the high modulation rate without mechanical scanning, this technique has a great potential for applications in extensive synthetic aperture imaging ladar fields. The phase mapping of electrically controlled scanner under the different applied voltage is achieved and measured by the polarized digital holographic interferometry. The phase mappings of the scanner in the down-looking SAIL with the o-polarized light and e-polarized light are obtained. The linear phase distribution and the parabolic phase distribution are observed after applying the external electric field. The corresponding analyses and discussions are proposed to explain the phenomena.

Due to the restriction of the aperture effect and the aperture transverse delay, it is very difficult to get large instantaneous bandwidth under wide scan range for conventional phased array radar. Optical controlled beam forming network (OCBFN) technology can solve this problem. The key of the OCBFN is the optical true time delay line network. In this paper, we propose a new differential time delay line network based on the free-space integrated prism array technology. The new method can realize any linear time delay for the space multi-beam radar. Furthermore, the time delay can be adjusted very easily. In order to validate the new method, we design a 4×4 differential time delay line network, and the time delay ranges from 0 ps to 100 ps.

Atmospheric turbulence influences the wave-front, and reduces homodyne detection efficiency and bit error rate in the Satellite-to-Ground Laser Communication. Free-space differential interference structure based on differential phase shift keying (DPSK) is applied in the optical signal receiver. The free-space Mach-Zehnder delay interferometer without lens is suited for differential delay which is equal to the one bit period. Differential information is obtained by the subtraction of the two successive wave-front phases when made to interfere. Differential distance at the interference receiver is varied with transmission rate from satellite to ground. And through the receiving telescope, the spot size of incident signal light within the interference became small than before, which influences the interference efficiency of the two unequal branches. So that, it is significant for increasing homodyne efficiency to determine the optical signal rate and choose the magnification of receiving telescope. In this paper, the effect of the spot size of incident light and transmission data rate on homodyne detection efficiency is analysed. By the simulation result of efficiency in different spot size and transmission date of incident light, the homodyne efficiency will be predicted in the given data rate and light spot size on the basis of experiment setup. And application condition of free-space differential structure at DPSK differential receiver is proposed.

We investigate the random phase fluctuations of coherent laser propagate through the turbulent atmosphere, and introduce a model of its impact on optical heterodyne reception free space coherent laser optical communication (FSO) system. A polarization based shearing interferometer is used to detect the distorted laser wave-front and reconstruct the wave-front after propagate through a 1Km near-ground atmospheric channel. Further, the heterodyne efficiency of the heterodyne reception system would be given under special consideration of the mismatch between the signal field and the local oscillator. By analyzing the heterodyne efficiency data and the real-time atmospheric coherence length data, a mathematical model of the effects of atmospheric turbulence on FSO system performance is given.

Optimization of high fixed diffraction efficiency in LiNbO 3 :Ce:Cu is investigated. Holographic gratings are recorded using typical recording wavelengths including 488, 514 and 633 nm in LiNbO 3 :Ce:Cu for different doped concentration. Optimal switching from recording step to fixing step is taken into consideration. The experiment results can confirm the optimal recording wavelength and doped concentration for high fixed diffraction efficiency in LiNbO 3 :Ce:Cu crystal by optimal switching from holographic recording to fixing.

Phase-space optics has its advantage over the research of laser beam propagating through atmospheric turbulence channel due to its special joint space-spatial frequency representation, which can be used to describe the property of optical signals between variables that form a Fourier transform pair. In this paper, we introduce the effect of atmospheric turbulence in terms of matrix into the phase-space analysis of laser beam propagation through turbulence. The far field optical intensity in the channel will be given in terms of phase-space representation and the phase-space distribution of received optical intensity can be plotted. It may be a new method analyzing optical scintillation under the turbulent condition.

A new design and fabrication of flat optical lens by use of 90-degree volume holographic grating recording geometry is presented. It is recorded by the interference of a plane wave and a spherical wave in a Fe-doped LiNbO3. The flat optical lens can laterally transfer and focus the plane wave which perpendicularly incidents on the planar crystal surface. The optimal switching from recording to thermal fixing is taken into consideration in order to obtain the nonvolatile hologram with maximum fixing efficiency. The flat optical lens with different recording and reconstructing wavelength has also been discussed. The flat optical lens has the advantages of light weight, laterally transferring and focusing, small duty ratio, and easy for the microstructure integration. The testing results measured verify that the flat optical lens can successfully be used for the free space optical communication.

Synthetic aperture laser imaging ladar’s optical receiver is a heterodyne detect system, so the atmosphere turbulence will affect the phase history of the ladar seriously. Unlike in conventional passive optical imaging system, both the wavefront distortion and piston term will decrease the imaging resolution. The distortion of the wavefrom decreases the heterodyne mixing efficient; the piston will cause the pulse-to-pulse phase errors. Multiaperture receiver technology can improve the heterodyne mixing efficient efficiently, but the pattern of multiaperture should be optimized according to different turbulence intensity. In this paper, we optimize a four-aperture receiver pattern in different turbulence environment. The simulation and experiment results are obtain in our ladar system.

The synthetic aperture imaging ladar (SAIL) systems typically generate large amounts of data difficult to compress with digital method. This paper presents an optical SAIL processor based on compensation of quadratic phase of echo in azimuth direction and two dimensional Fourier transform. The optical processor mainly consists of one phase-only liquid crystal spatial modulator(LCSLM) to load the phase data of target echo and one cylindrical lens to compensate the quadratic phase and one spherical lens to fulfill the task of two dimensional Fourier transform. We show the imaging processing result of practical target echo obtained by a synthetic aperture imaging ladar demonstrator. The optical processor is compact and lightweight and could provide inherent parallel and the speed-of-light computing capability, it has a promising application future especially in onboard and satellite borne SAIL systems.

As synthetic aperture imaging ladar employs the linear chirp laser signal, it is inevitably impacted by the space-time varying speckle effect. In many SAIL two-dimensional reconstructed images, the laser speckle effect severely reduces the image quality. In this paper, we analyze and simulate the influence of space-time speckle effect to the resolution element imaging both in range direction and in azimuth direction. Expressions for two-dimensional data collection contained space-time speckle effect are obtained, and computer simulation results of resolution degradation both in range direction and in cross-range direction are presented.

Laser communication links between satellite and ground remains a bottleneck problem that has not been solved in free space communication network now. Atmospheric disturbances have badly influenced the wave-front of signal light and destroyed the integrality of optical phase, so the bit error rate (BER) is increased at the receiving terminal in the space-to-ground laser communication. With conventional coherent reception, the contrast of coherent light increased dramatically, and transmission efficiency of Space to ground laser communication decreased. Receiving technology based on differential phase shift keying (DPSK) is proposed here to overcome the effects of atmosphere here. Differential phase shift keying without the integrality and compensation of the optical phases, is suited for high rate space to ground communication links due to its immunity of the wavefront of a beam passing atmosphere. A Mach-Zehnder delay interferometer is used for differential delay which is equal to the one bit period. The differential data information can be obtained from the optical phase changes. Differential phase modulation technique can be a promising optical receiving technology.

The high data-rate satellite-to-ground coherent optical communication link is limited because the phase integrity of a beam is impaired when passing through the atmospheric turbulence. Based on the interference of two successive data bits in an unequal arm-length Mach-Zehnder delay interferometer, the differential phase shift keying receiver is suited for high data-rate satellite-to-ground coherent optical communication links due to its immunity of the wave front impairment when passing through the atmospheric turbulence. In the time-delay self-homodyne interferometric detection used in 2×4 90 degree optical hybrid, the optical path difference corresponds to the duration of one bit. The optical path difference is stabilized to below one thousandth of the wavelength by moving a finely motorized platform with the close-loop control using the phase feedback from the outputs of the 90 degree hybrid. The 2.5 Gbps optical communication link has already been verified between two buildings over a distance of 2.4km in the worst-case atmospheric conditions. The design and experimental results are given in this paper.

In the inter-satellite laser communication, the laser beam transmitted from the optical terminals is required to be highly collimated and its divergence approaches diffraction-limit. For testing the diffraction-limit wavefront, a polarization phase-shifting cyclic Jamin shearing interferometer is proposed. It is composed of a Jamin plate with a PBS film coated on its front surface, a right-angle prism reflecting beams two times, a shearing plate shearing beams by its rotation and a polarization phase shifter. The laser beam to be test is incident on the Jamin plate and gives rise to two interference beams with mutually perpendicular polarization directions by the PBS film. The two beams falls on the right-angle prism before or after passing through the shearing plate. With reflection of the right-angle prism, a cyclic Jamin shearing interferometric light path is formed. Two emitted beams go into the polarization phase shifter to obtain phase-shifting interferograms. In this interferometer, the cyclic interferometric light path can eliminate error of the surface profile of the optical element and the effect of environment. The interferometer has polarization phase shifting function and its fringe visibility is high. Therefore the interferometer can obtain high accuracy with variable shearing amount. In experiments, phase-shifting interferograms are obtained and the usefulness of the interferometer is verified.

At present inter-satellite laser communications have made great success, such as SILEX, TerraSAR-X LCT etc. But satellite to ground laser communications still at the experimental stages because of the atmosphere turbulence channel and the clouds. Once the satellite to ground laser communication technology obtains a breakthrough, the all laser spacebased communication era is coming. In this paper, we suggest a DPSK modulation/self-coherent homodyne reception scheme to overcome the atmosphere turbulence. The key in the scheme lies in the phase error compensation with the external environment change. In our experiment, we use two parallel plates rotating to compensate the phase error. The communication data rate reaches 2.5Gbps in the field experiment. The real time bit error rate was obtained with the variation of the communication channel’s turbulence.

The phase-space description of signals is a joint space-spatial frequency representation in local domain. It employ the phase-space representation functions to describe the property of optical signals between two variables that form a Fourier transform pair and provide a valuable analysis tool for signals when this new mathematical analysis tool applied to an optical system. This method can also be applied to the analysis of propagation of laser beam within free space or atmosphere condition. In this paper, we give the analytical formula of optical field distribution of laser beam after propagation within turbulence in the domain of phase-space. The results show an instructing aspect of optical signal propagation and are helpful to the future application of phase-space method to the laser communications.

The paper overviews various supporting ways for large-size movement mirrors, and the advantages and disadvantages of the support methods are summarized. Some valuable optimization methods to improve support effects are also introduced. As a case study, a radial segment-face contact support method is proposed to solve the support problem for a large-aperture rotating prism, and a two-step optimization method is implemented to improve the support effects. The surface deformations under different support separated angles are evaluated. The overview can be as good references for large-size mirror support design in similar opto-mechanical systems especially under movement conditions.

The cross-orbit scanning is very important for Fresnel telescope synthetic aperture imaging ladar system. This paper presents a design of large-angle high speed scanner based on electro-optic crystal for the cross-orbit scanning in Fresnel telescope synthetic aperture imaging ladar system. The designed scanner is based on the space-charge-controlled EO effect in KTN. In the experiment the crystal temperature should be kept a little higher above Tc to obtain a large EO effect and the polarization of the laser beam should be parallel to the direction of the driving electric field. Compared with other conventional EO crystal scanner, the new scanner can greatly improve the scanner angle by several times when maintains high speed and accuracy, which will have a great potential for cross-orbit scanning applications in Fresnel telescope synthetic aperture imaging ladar system.

A theoretical explanation of fixed holograms with high diffraction efficiency is given based on jointly solving the material equations and the coupled-wave equations. The dynamics of the recording and fixing diffraction efficiency can be effectively described and analyzed by using this method. The optimal recording wavelength for high fixed diffraction efficiency is discussed in detail. There is an optimal switching time for the maximum diffraction efficiency up to an ideal of 100%. Theoretical results can confirm the optimal recording wavelength for maximum diffraction efficiency of thermal fixing in Fe doped LiNbO 3 crystal.

The effect of dopants in doubly-doped LiNbO 3 crystals on persistence of two-center recording is investigated experimentally and theoretically in this paper. Six kinds of doubly-doped LiNbO 3 crystals are used in experiments with 633nm recording and 404nm sensitizing, the results show that LiNbO 3 :Ce:Cu crystal has the largest persistence. The dependence of persistence on bulk photo-voltaic coefficient and photo-excitation coefficient of deep center for recording light (K 12 and S 12 ) is discussed based on jointly solving the two-center material equations and the coupled-wave equations. The results show that both the increase of S 12 and the decrease of K 12 will result in the decrease of the persistence. When a holographic storage system is designed, the appropriate dopant will help to obtain the high persistence and dynamic range simultaneously.

During the signal acquisition for synthetic aperture imaging ladar, any phase error will deteriorate the phase-matched filtering results. The phase differential algorithm (PDA) is presented to correct the phase error. The quadratic spatial phase history can be reconstructed from the phase information submerged by the phase error from platform line-of-sight translation–vibration and nonlinear chirp. The theoretical modeling results and experimental results are presented.

Synthetic aperture laser ladar is one of the most possible long-distance super-resolution active imaging methods. Many institutes have obtained two-dimensional synthetic aperture laser ladar’s reconstructed images. However, in these images, the laser speckle effect severely reduces the image quality. In the paper, we use mutli-receiver and multinoncoherent image superposition methods to reduce the impact of the laser speckle. According to the scalar diffraction theory, we deduced reconstructed image with the multi-receiver and the multi-noncoherent image superposition methods.

In this paper, we present a laboratory demonstration of Fresnel telescope imaging ladar system for imaging the faraway objects with high resolution. Two concentric and coaxial quadratic wavefront with orthogonal polarization are used as scanning beams to illuminate the target. The scattered light from the target is heterodyne detected by a 90 degree 2×4 optical hybrid with two balanced receivers. The target image can be reconstructed by digital processing of the output signals of the balanced receivers. Point targets 4.3m away are reconstructed with high resolution in experiments.

Volume holographic gratings (VHG) are of wide interest in many applications because of their properties of high diffraction efficiency, excellent wavelength selectivity and angular selectivity. Recently, because of more free parameters, multi-layer volume holographic gratings (MVHG) have become an ideal candidate for various promising technological applications such as optical interconnects, pulse shaping and optical filters. Therefore, some knowledge of the diffraction behaviors of such system would be very valuable for characterizing and optimizing such volume diffractive optical elements. In this paper, we extend the coupled wave theory of multi-layer gratings to study the Bragg diffraction properties of continuous wave, ultrashort laser pulse and chirped ultrashort pulse, and present a systematically theoretical analysis on the spectrum distribution of the diffracted intensities, the diffraction bandwidth of a system of MRVHG. The system of MRVHG is composed of multiple layers of reflection VHG separated by intermediate layers. The comparisons of the diffraction characteristics for these beams are investigated.

An efficient technique of utilizing Dammann grating and phase plate to get high power and high brightness laser beam from phase-locked laser array is presented. The conjugate Dammann grating and the phase plate are placed in the back and front focal plane of a Fourier lens respectively. In order to improve the beam combining efficiency, Continuous grating of high diffraction efficiency is used to replace the Dammann grating. Analysis shows that the Continuous grating which has a higher diffraction of efficiency is also suitable for beam combining of the presented system.

The phase perturbations due to propagation effects can destroy the high resolution imagery of Synthetic Aperture Imaging Ladar (SAIL). Some autofocus algorithms for Synthetic Aperture Radar (SAR) were developed and implemented. Phase Gradient Algorithm (PGA) is a well-known one for its robustness and wide application, and Phase Curvature Algorithm (PCA) as a similar algorithm expands its applied field to strip map mode. In this paper the autofocus algorithms utilized in optical frequency domain are proposed, including optical PGA and PCA respectively implemented in spotlight and strip map mode. Firstly, the mathematical flows of optical PGA and PCA in SAIL are derived. The simulations model of the airborne SAIL is established, and the compensation simulations of the synthetic aperture laser images corrupted by the random errors, linear phase errors and quadratic phase errors are executed. The compensation effect and the cycle index of the simulation are discussed. The simulation results show that both the two optical autofocus algorithms are effective while the optical PGA outperforms the optical PCA, which keeps consistency with the theory.

Based on the computer vision theory, this article researched the algorithm for the location of laser beam cutting. This article combines Canny operator and thresheolding image. It overcomes the inaccuracy of edge detection and clutter jamming problem which are caused by the poor quality of acquired images. Collecting the key points of target edge, making B-spline curves fitting, it solved the problem that target edge is jagged. And it uses interpolation algorithm to locate the point for laser beam cutting. At last, we developed corresponding and prefessional software system which is based on Visual Stdio2003 and C#.

Fresnel telescopy full-aperture synthesized imaging ladar is a new high resolution active laser imaging technique. In the operational mode with moving target by beam scanning, spatial distributions of the complex data of the returned signals are not regular or uniform. In order to use fast Fourier transform (FFT) algorithm in signal processing, algorithm for Fresnel telescopy imaging system should include resampling interpolation step to change sampling data into uniform and quadratic spatial distribution. We choose suitable resampling interpolation algorithm for Fresnel telescopy, and get computer simulation of area target. The work is found to have substantial practical value and offers significant practical benefit for high resolution imaging in Fresnel telescopy imaging ladar.

In this paper, we propose a new method that can acquire the complex hologram of a 3D object for optical scanning holography (OSH) by using polarized optical elements and a 90 degrees 2×4 optical hybrid. The 3D object is scanned by a wave front combined by a plane and spherical wave with orthogonal polarization. The transmitted/reflected signal light is divided into two beams by a polarized beamsplitter (PBS). Then after the polarization control, the two separated beams are heterodyne detected by a 90 degrees 2×4 optical hybrid with two balanced detectors. The 3D object can be reconstructed from the complex hologram acquired from the balanced detectors. Compared with the conventional OSH, the acousto-optic modulator and complex electronic system are not needed in this method. Another advantage of this method lies in its high efficiency since there is almost no energy loss in the generation of the scanning beam by using the polarized optical elements. This method should be used for 3D holographic microscopy and 3D holographic television.

Fresnel telescopy (short for Fresnel telescopy full-aperture synthesized imaging ladar) is a new high resolution active laser imaging technique. This technique is a variant of Fourier telescopy and optical scanning holography, which uses Fresnel zone plates to scan target. Compare with synthetic aperture imaging ladar(SAIL), Fresnel telescopy avoids problem of time synchronization and space synchronization, which decreasing technical difficulty. In one-dimensional (1D) scanning operational mode for moving target, after time-to-space transformation, spatial distribution of sampling data is non-uniform because of the relative motion between target and scanning beam. However, as we use fast Fourier transform (FFT) in the following imaging algorithm of matched filtering, distribution of data should be regular and uniform. We use resampling interpolation to transform the data into two-dimensional (2D) uniform distribution, and accuracy of resampling interpolation process mainly affects the reconstruction results. Imaging algorithms with different resampling interpolation algorithms have been analysis and computer simulation are also given. We get good reconstruction results of the target, which proves that the designed imaging algorithm for Fresnel telescopy imaging system is effective. This work is found to have substantial practical value and offers significant benefit for high resolution imaging system of Fresnel telescopy laser imaging ladar.

This paper presents imaging result of computer simulation using a modified Radon-Fourier transform algorithm to reconstruct images from reflective tomography data. Since the signal returned is reflected off the illuminated outer surface of an opaque target, only information about the exterior of the target can be obtained, and the images reconstructed using reflective tomography techniques is an outline view of the target cross section. The projection p(r,φ ) and p(r,φ + 180°) contain different information about the target surface, and will lead different Fourier estimates along the same line through the origin based on the standard Fourier-Slice tomography theorem. Here, using the functional similarity between transmission tomography and reflective tomography, we add the collinear reflective projections to become corresponding transmissive projections before Fourier transform. Then the target can be reconstructed from the Fourier domain using the same operations in transmission tomography. The computer simulation result demonstrates the effectiveness of this modified algorithm to reconstruct image in reflective tomography using the diffuse reflection model (lamberts body). Future research will include the development of image reconstruction based on this modified algorithm for targets with much more complicated reflective characters.

In order to study the influence of the time-varying turbulence to facular orientation precision when the facula is moving during the pointing and tracking process, a random phase screen is generated using modified inverse fourier transform to simulate atmospheric turbulence. And then the orientation deviation of the facular barycenter, the relation between the deviation and the facular position in the detector and the orientation precision of the facula is analyzed under different atmospheric turbulence intensity. The results indicate that at the presence of time-varying atmospheric turbulence, there is a deviation between actual translational amount of the facular barycenter and that of the barycenter detected by the charge-coupled device and it relates with the atmospheric turbulence intensity. And the dynamic facular orientation precision is found that it relates to the atmospheric turbulence intensity and the facular position in the detector.

In this paper, a concept of spotlight-mode incoherently-synthetic aperture imaging ladar (SAIL) is proposed on the basis of computer tomography (CT). This incoherent SAIL has three operations of conventional, inverse and CT spotlight-modes with two sensing techniques of range and Doppler resolutions, and supplies a variety of dimensional transformations for 2-D range- and Doppler-resolved imaging of 2-D objects and for 3-D range-resolved imaging or in the depth compressed 2-D range- and Doppler-resolved imaging of 3-D objects. Due to the simplification in both the construction and the algorithm the difficulties in the signal collection and data processing are importantly relaxed. The incoherent SAIL provides a great potential for applications in the extensive fields. The paper gives the detailed analysis.

A demonstrator of synthetic aperture imaging ladar (SAIL) is constructed with the maximum aperture O300mm of antenna telescope. This demonstrator can be set with a rectangular aperture to produce a rectangular footprint suitable for scanning format with a high resolution and a wide strip. Particularly, the demonstrator is designed not only for the farfield application but also for the verifying and testing in the near-field in the laboratory space. And a 90 degree optical hybrid is used to mitigate the external phase errors caused by turbulence and vibration along line of sight direction and the internal phase errors caused by local fiber delay line. This paper gives the details of the systematic design, and the progresses of the experiment at a target distance around 130m.

A control software experiment system of synthetic aperture imaging ladar is developed based on multithreading parallel mechanism of Labview8.6 and SCPI (standard commands for programmable instruments) protocol. Firstly, hardware composition and software function requirement of the system are analyzed. Then, the control module of the laser and stepper motor and the data communication module of oscillograph are developed separately and the three modules are integrated to realize the gather and compute of the return signal. Finally, by the result of experiment, the control software worked steady and real timely and it can operate the laser, stepper motor and oscillograph successfully.

The laser-induced domain nucleation effect is investigated in the 3mol% hafnium-doped congruent lithium niobate crystal. The beam from an Ar-ion laser with 514 nm wavelength is focused on z surface. Two incidence schemes are performed: (1) irradiating near and focusing on the +z surface; (2) irradiating near and focusing on the -z surface. The formed space charge field is observed by the in-situ phase mapping during the laser-induced domain nucleation. The variations of phase distributions are reconstructed by the digital holographic interferometry. The light intensity dependence of the measured photovoltaic current density j phv is described. The space charge field along -z direction is thought to be an important mechanism for the laser-induced domain nucleation. According to these experimental results, we present a qualitative model on the laser-induced domain nucleation process in lithium niobate crystal.

A new method of high resolution laser imaging is developed in this paper, which is denoted as Fresnel telescopy. It creates Fresnel zone plate (FZP) fringe at the detected target, then makes relative motion between Fresnel zone plate and the target to accomplish the encoding process, namely, to achieve the convolution between target reflection function and the Fresnel zone plate intensity distribution function. The design scheme of the proposed system is presented. The proposed technique offers significant practical benefit for ground-based imaging of objects in many important military applications.

A novel type of electro-optic scanner is presented which can satisfy the requirements for high speed and large-angle. It is a two-stage cascade system which consists of a fine scanning system implemented by using voltage-controlled refraction-based electro-optic deflectors and a coarse scanning using several LiNbO 3 electro-optic switch and polarization beam splitter system. The deflection angle can be enlarged by using the coarse-fine cascaded system. We demonstrate the design scheme of the proposed large-angle optical beam scanner. The system is analyzed and simulated theoretically. It is shown that proper design of the parameters of coarse-fine cascaded two-stage system can lead to an optimal beam scanner with enhanced performance of large angle and high speed. The analysis and observations will be valuable for the accurate design and fabrication of the novel optical scanning devices based on electro-optic effect.

We proposed a novel beam combining technique for coherent laser arrays that uses a conjugate Dammann grating (CDG) and a phase plate. By using this technique, a coherent laser array can be not only coherently combined to a single beam but also aperture filled to a far field single central lobe beam by means of phase compensation in theory. The aperture size and power density of the combined beam can be conveniently changed. Moreover, the technique applies for both binary and continuous amplitude profiles emitted from an individual laser of laser arrays, especially Gaussian beam. An verified experiment with a simulated 5×5 coherent laser array using an aperture mask was performed that effectively verified the feasibility of the proposed concept. This new method has the potential for scaling to much higher output powers with good beam quality by coherent combination and aperture filling of coherent laser arrays in practical applications.

The phase errors due to the nonlinear chirp of a tunable laser reduce the range resolution in Synthetic Aperture Imaging Ladar (SAIL). The analogue and digital image processing algorithms were developed, and all the image processing algorithms employed matched or nonmatched optical delay line. In this paper a theory of equiarm delay line to compensate the nonlinear chirp phase errors is proposed. This image processing algorithm includes three methods with different compensation precision and implementation difficulties, and promotes the application flexibility. Firstly, we derive the theory that the impact of the nonlinear chirp is suppressed with decreasing the delay time difference of the echo signal and the LO signal. Based on the theory, we propose three methods to establish the equiarm delay line: establishing matched target LO path, establishing reference path and dual coherent detections, establishing reference path and phase shifting calculation. Then the construction of the signal processing system and the mathematical flow of the algorithm are established. The simulations of the airborne synthetic aperture imaging ladar model approve that three methods suppress the phase errors of the nonlinear chirp to various extent, and improve the range resolution. The characteristics and the applicabilities of three methods are discussed finally.

Two-wave coupling in LiNbO 3 :Fe:Ru crystals is investigated experimentally and theoretically in this paper. The dependence of gain coefficient on doped concentration, as well as the light intensity ratio between pump beam and signal is experimentally investigated, the maximal gain coefficient 9.2cm -1 is found while the ratio is 2.2, light gain cannot be observed in the reduced sample because of fan effect. Effect of phase difference between light modulation and the refractive index grating on two-wave coupling is investigated based on jointly solving the two-center material equations and the coupled wave equations, the variation of phase difference is obvious in the crystals with reduced process or high doped concentration.

Characteristic of electro-optic modulation of light propagating near the optic axis in a uniaxial crystal is well known but not for the cases of propagating bias the optic axis. In this paper, two pairs of LiNbO 3 crystal plates with the same sizes consist of an optical system in where the sum of geometrically optical length of o-ray and e-ray is equal. And then the characteristics of electro-optic modulation of light propagating bias the optic axis in LiNbO 3 are studied experimentally through a coherent received system. The additional phase shift caused by electro-optic effect is measured. The relation of phase shift varying with applied electric-field is reported when the angle between incident beam and the optic axis is 45o. Based on above experiments, a new 90o optical hybrid will be developed. Key words: LiNbO 3 crystal; electro-optic modulation; phase shift 1. INTRODUCTION The electro-optic effect of crystal is the basic of many electro-optic devices [1-4] . It plays an important role in the fields of optical information processing and optical communication. The properties of electro-optic modulation along optical axis are well known

There is large aperture and diffraction-limited laser beam in the space laser applications such as laser communication. Laser wavefront can be measured by shearing interferometer or Shark-Hartmann sensor etc. Large-Optics shearing interferometer based on Mach-Zehnder plate structure has been manufactured to differentially analyze the laser wavefront from two parts of aperture-divided fringes. One of six optical plates of the interferometer is divided to the up part and the down. The precision of measurement is higher than the full aperture design. It is suitable for the diameter below 290mm with the changeable shear amount from 1mm to 150mm. There are two sets of collimators used for the parallel of the plates. Another single-mode 635nm laser collimator which is measured through double-shearing plate before is serving as a standard wavefront of 150mm diameter. One path of the interference is changed with precise adjustment unit in several microns that the interference may be happened between equal optical path reflection and the other. It can be used for widely tunable laser and other laser system which has short coherent length. The apparatus and the experiments are explained in detail in this paper. Many systems of different quality and diameter and coherent length are measured by the large-optics shearing interferometer. The experimental wavefront results are fitted to Zernike polynomial and the Zernike coefficients are derived.

Based on Fourier transform of heterodyne signal and linear fitting of phase time-evolution, a nonlinearity-induced phase error correction technique for synthetic aperture ladar is experimentally studied. The problem of beat frequency matching in the conventional method for nonlinearity-induced phase error correction in target channel by designing a reference channel and phase shift equations is practically analyzed, and its limitation on application under the condition of large time delay in target channel is verified. According to this problem, a new method of directly nonlinearity-induced phase error correction by linear fitting of phase time-evolution in target channel is proposed. In experiments, the rang resolution of 2 mm is gained at 1.5 μm wavelength, which is coincident well with theory. The results show that this technique can overcome the problem of beat frequency matching in two channels and is effective for practical applications with different time delay in target channel.

The phase errors due to the nonlinear chirp of tunable laser reduce the range resolution in synthetic aperture imaging ladar(SAIL). The compensating algorithms establishing matched and nonmatched reference paths were developed, and the phase errors were compensated in the whole echo pulse. In this paper a compensating algorithm by scan filtering is proposed. Compared to the compensation in the whole echo pulse, this compensating algorithm promotes precision and range resolution. Every echo pulse includes different echo components from all target points in footprint. The heterodyne signals of these different echoes are scan filtered from the heterodyne signal of one whole echo pulse in the spectrum. The phase errors of these heterodyne signals are measured by phase shifting algorithm in nonmatched reference path and compensated separately. Then the compensated signals are combined into whole heterodyne pulse and compressed in range. After all echo pulses are compressed in range the azimuth compensation and compression is followed. The mathematical flow of this algorithm is established. The simulation of the airborne SAIL model validates the feasibility, and the BW of range compression decreases obviously. The effects of width of the scan filter and nonlinear chirp are discussed. The conclusion of adequate width of the scan filter is given finally.