Search

3D coherent imaging ladar based on frequency modulated continuous wave (FMCW) technology is proposed. The triangle wave is used to modulate chirped laser. The distance information is detected by optical heterodyne technique. Meanwhile, the beam scanning is realized by rotation double-prism. And the 3D target image is obtained. The 3D coherent imaging ladar has advantages of anti-background interference, high sensitivity and long-detected distance. Under the condition of the strongly sunlight background, the targets outdoor are scanned and high resolution images are achieved. This technique has a great potential for applications in extensive imaging ladar fields.

Down-looking synthetic aperture imaging ladar have bidirectional (positive and negative direction) modulation in the orthogonal direction of travel during phase modulation. The return signal can be also collected in the two directions. The imaging processing with bidirectional modulation is used and demonstrated. The signal-to-noise ratio can be enhanced in this mode synthetic aperture imaging ladar. Meanwhile, the velocity of carrying-platform can be faster. In the experiment, the return signals with bidirectional modulation are stacked and rebuilt. Compared to the unidirectional modulation imaging, the faster and clearer imaging is realized with bidirectional modulation. This technique has a great potential for applications in extensive synthetic aperture imaging ladar fields.

Active polarization imaging technology has recently become the hot research field all over the world, which has great potential application value in the military and civil area. By introducing active light source, the Mueller matrix of the target can be calculated according to the incident light and the emitted or reflected light. Compared with conventional direct detection technology, optical heterodyne detection technology have higher receiving sensitivities, which can obtain the whole amplitude, frequency and phase information of the signal light. In this paper, an active polarization imaging system will be designed. Based on optical heterodyne balanced receiver, the system can acquire the horizontal and vertical polarization of reflected optical field simultaneously, which contain the polarization characteristic of the target. Besides, signal to noise ratio and imaging distance can be greatly improved.

In the inter-satellite laser communication, the diffraction-limit wavefront is required. To test the wavefront, we have developed a Jamin double-shearing interferometer. The interferometer is consists of two Jamin plates to form lateral shearing and four wedge plates to divide the aperture. The laser beam to be test is incident on the first Jamin plate and gives rise to two beams. One is reflected from the front surface of the first Jamin plate, then passes two wedge plates and is reflected from the rear surface of the second Jamin plate. The other is reflected from the rear surface of the first Jamin plate, then passes other two wedge plates and is reflected from the front surface of the second Jamin plate. The two beams are recombined to form the interferogram. For the interferometer, simple phase-shifting method to improve the measurement accuracy of the wavefront by moving four wedge plates is proposed in this paper. When the wedge plates are moved along its surface or in the incidence direction of the interferometer, the optical path difference of two interferometric beams is changed to form phase shift. The added optical path difference introduced by the movement of wedge plates is liner function of displacement, thus the phase-shifting amount is easy to be control. Wedge plates can be moved in four steps with interval of quarter wavelength and the phase can be unwrapped using the four-step phase-shifting algorithm. In experiments, phase-shifting interferograms are obtained. The usefulness of the phase-shifting methods is verified.

Space to ground laser communication is limited by the effects of atmosphere. Differential phase shift keying (DPSK) is suited for high data rate space to ground communication links due to its immunity of the wave front of a beam passing atmospheric turbulence, which carry the information in optical phase changes between bits. The benefit of DPSK over OOK is the 3 dB lower optical signal to noise ratio to reach a given bit error rate (BER) using a balanced receiver. An aperture-matched phase-compensated DPSK receiver with a 90° hybrid is proposed here. The receive optics are based on free-space optics. A Mach-Zehnder delay interferometer is used for differential delay which is equal to the bit period. The input pupil is imaged onto the same place by two afocal systems composed of 4f imaging lenses. The optical path difference is stabilized to a faction of the wavelength with a fine phase adjustment which is measured by a 2×4 90° optical hybrid and closed loop electric circuit. The design and experiments are given in this paper. optical hybrid and closed loop electric circuit. The design and experiments are given in this paper. optical hybrid and closed loop electric circuit. The design and experiments are given in this paper.

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.

The time-delay self-homodyne interferometric detection used in 2×4 90° optical hybrid for free-space optical communication is presented. An asymmetric Mach-Zehnder interferometer splits the received signal into two paths and recombines these two signals after a optical path difference. A balanced receiver follows the interferometer as a multiplier. The modulation contrast in the interferometer depends on the interference of identical wave-fronts, not on the quality of the wave-front itself. So it does not require wave-front compensation techniques, a local oscillator laser nor does it need frequency locking. The scheme can eliminate the effect of wave-front deformation on coherent detection in free-space optical communication effectively.

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.

The design of an optical birefringent 90° hybrid for coherent receiver in free-space optical communication system is presented. The bulk optical design of 2×4 90° hybrid is a six-port device with two inputs and four outputs. For the balanced receiver configuration two pairs of 180° phase shifted outputs are obtained and one pair has a phase shift of 90° with respect to the other. The optical birefringent 90° hybrid includes two pairs of birefringent plates, an analyser plate and a λ/8 wave plate. The scheme of phase compensation is also presented.

A fully 2-D synthetic aperture imaging ladar (SAIL) demonstrator is designed and being fabricated to experimentally investigate and theoretically analyze the beam diffraction properties, antenna function, imaging resolution and signal processing algorithm of SAIL. The design details of the multi-purpose SAIL demonstrator are given and, as the first phase, a laboratory-scaled SAIL system based on bulk optical elements has been built to verify the principle of design, which is similar in construction to the demonstrator but without the major antenna telescope. The system has the aperture diameter of about 1mm and the target distance of 3.2m.

The instantaneous preferential domain nucleation effect of the z-cut hafnium-doped congruent LiNbO 3 crystal is investigated. 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 digital holographic interferometry is used in investigating the visible laser-induced domain nucleation in hafnium-doped congruent LiNbO 3 crystal, and reconstructs the phase shift of new domain. From the investigation of phase shift induced by the domain inversion, the analysis of domain nucleation is performed. When the electric field exceeds a certain threshold value, the preferential domain nucleation is achieved instantaneously at the focal spot during the combined actions of irradiation and external fields. The nucleation fields have a systematic decrease with increasing laser intensity, and reach an effective saturation at higher intensities. The reduction proportions obtained in the second scheme are lower than those in the first one with the same intensity, and the saturation values at higher intensities are the same in both schemes. We attribute the instantaneous effect of laser-induced domain nucleation to the space charge field, and the saturation value at higher intensities is related to the saturation of the space charge field. The formation of instantaneous effect and corresponding physical explanation based on space charge field are present.

The phase-mapping of domain wall kinetics under the uniform st eady-state electric field is achieved and investigated in the LiNbO 3 crystals by the digital holographic interferometry. We obtained the sequences of reconstructed three-dimensional and two-dimensional wave-field phase distributions during the electric poling in the congruent and near stoichiometric LiNbO 3 crystals. The phase-mapping of domain wall mo tions in the two crystals are obtained. Both the phase relaxation and the pinning-depinning mechanism are observed during the domain wall motion. The residual phase distribution is observed after the high-speed domain wall motion. The corresponding analyses and discussions are proposed to explain the phenomena. Keywords: phase-mapping, domain wall kinetics, lithium ni obate, digital holographic interferometry 1. Introduction With the large electro-optic and nonlinear optical coefficients, lithium niobate has become one of the most important and widely applied optical materials. The domain engineering in the LiNbO

A method to measure the frequency change of the tunable laser based on a Jamin shearing interferometer is proposed. The Jamin shearing interferometer is composed of two Jamin plates, two shearing plates and a retardation plate. The tunable laser beam is split into two beams by one Jamin plate. The retardation plate is placed in one of two beams to provide additional phase retardation. Two beams pass two shearing plates, respectively, and are combined by the other Jamin plate to form lateral shearing interferogram. In course of tuning, interference fringes are shifted as a whole and its spacing is kept constant. By detecting displacement of fringes, the frequency change of the laser is obtained. In experiments, we observed that interference fringes were shift periodically when the laser diode was modulated sinusoidally. A series of interferogram in which fringes are shifted as a whole with the variation of the frequency are obtained. The feasibility of the method is verified.

Synthetic aperture imaging ladar (SAIL) used a series of pulses in which the optical frequency was swept linearly in time over a bandwidth greater than several gigahertz. The linearity of such broadly tunable sources is often poor which is leading to phase errors. Many methods are adopted to correct for quadratic and higher-order phase errors such as the reference channel or algorithm for unmatched channel of Aerospace and the reference interferometer of Naval Research Laboratory. If the real value of frequency swept quasi-linearly is measured another direct way to mitigate the waveform linearity problem can be developed. At first the frequency curve is measured with Fabry Perot fiber interferometer. Experiment and results are explained in detail in this paper. The quadratic and higher-order terms of frequency swept are calculated. They may be used to deduce the phase errors directly later. At the same time the wavefront is also measured by a Jamin shearing interferometer through the fringe analysis.

The double threshold effect of ultraviolet laser-induced preferential domain nucleation in near stoichiometric LiTaO3 is observed. The continuous ultraviolet laser beam (351 nm) is focused on the -z surface of the wafer, and the homogeneous electric field is applied simultaneously antiparallel to the direction of spontaneous polarization along the z axis. The double threshold effect includes both the primary and the secondary thresholds. The primary threshold is the minimum intensity to achieve the instantaneous preferential domain nucleation within the focus by the combined action of irradiation and electric fields. Below the dark nucleation field, the instantaneous preferential domain nucleation is achieved within the illuminated area when the intensity exceeds the primary threshold. The experiments prove that the domain inversion can be locally controlled by the laser irradiation. The secondary threshold is the minimum intensity to achieve the memory effect without any irradiation within the original focus. The memory effect of preferential nucleation is observed when the intensity is below the primary threshold and above the secondary threshold. The preferential domain nucleation of memory effect is investigated. The different physical explanations are presented for the instantaneous effect and memory effect. The space charge field created by the photoionization carriers is thought to be responsible for the instantaneous effect. The explanation based on the formation and transformation of extrinsic defect is presented for the memory effect.

There is transmitting optics of 250mm aperture with about 8 microradians in SILEX system. This is often large aperture and diffraction-limited laser beam in the laser communications. Large-Optics white light interferometer using double-shearing structure has been submitted to analysis the laser wavefront before. Six optical plates of 490 millimeters apertures are manufactured now one of which is also aperture-divided so that the precision of measured wave front is higher than the full aperture design. It is suitable for measurement of minimum diffraction-limited laser wave front and any wavelength. The interference is happened between equal optical path of the reflection and the other. The plates are the basic structures which are precisely parallel or perpendicular needed for either two plates. There are several tools equipped with the interferometer including white light test source and collimators and so on to confirm the precision of several seconds angle. The apparatus and application is explained in detail in this paper. The adjustment is important for the realization of white light test.

Due to the improved receiver sensitivity and wavelength selectivity, coherent detection became an attractive alternative to direct detection in inter-satellite laser communications. A novel method to coherent detection of position errors information is proposed. Coherent communication system generally consists of receive telescope, local oscillator, optical hybrid, photoelectric detector and optical phase lock loop (OPLL). Based on the system composing, this method adds CCD and computer as position error detector. CCD captures interference pattern while detection of transmission data from the transmitter laser. After processed and analyzed by computer, target position information is obtained from characteristic parameter of the interference pattern. The position errors as the control signal of PAT subsystem drive the receiver telescope to keep tracking to the target. Theoretical deviation and analysis is presented. The application extends to coherent laser rang finder, in which object distance and position information can be obtained simultaneously.

In the inter-satellite laser communication, the laser wavefront reaches the diffraction limit. For the test of the diffraction-limited wavefront, we have developed a Jamin double-shearing interferometer of which the detectable wave-front height is in the order of 0.1 wavelengths. Based on this interferometer, a polarization phase-shifting double-shearing interferometer is proposed to improve the performance. The existing Jamin double-shearing interferometer is consists of two Jamin plates to form lateral shearing and four wedge plates to divide the aperture. The polarization phase shifter is composed of three polarizers, a quarter-wave plate and an analyzer. The first polarizer is placed in front of the first Jamin plate. The second and third polarizers are placed behind the wedge plates and their transmission axes are parallel and perpendicular to the incident plane of the Jamin plates, respectively. The fast axis of the quarter-wave plate has an angle of 45 degrees to the transmission axis of the second and third polarizers. By rotating the analyzer, the phase-shift interferogram is obtained. In the interferometer, the polarization phase shifter is simple to be inserted and the phase shifting is easy to realize. The interferometer is kept as an equal optical path system and still suits wavefront testing of the low coherent light. In experiments, phase-shifting interferograms are obtained and the usefulness of the interferometer is verified.

Nearly diffraction-limited laser beam in the laser communications is often to be evaluated by the interferometers. A series of wave fronts sensors are manufactured which are designed as over 500 millimeters apertures and three kinds of thickness of 50, 100 and 200 millimeters according to different need of shearing amount. They are suitable for measurement of diffraction-limited laser wave front or the larger aberrations. The plate and the wedge are the basic structures for the sensors which are shearing interference between the forward surface reflection and the backward. These simple plates will make the mechanical design and adjustment easier. The wedge of aperture-divided is so designed that the precision of measured wave front is higher than the full aperture design for that the error comes from the material and optical manufacture is reduced through compare the up part and the down part each other. The method is explained in detail in this paper. Some experiment interferograms are analyzed and the wave heights are deduced.

In this paper, within the spectrum range from 351 nm to 799 nm, the different reductions of nucleation field induced by the focused continuous irradiation with different light intensity are achieved in congruent LiNbO 3 crystals. The reduction proportion increases exponentially with decreasing the irradiation wavelength, and decreases exponentially with increasing the irradiation wavelength. Basing on photo-excited effect, we propose a proper model to explain the mechanism of light-induced domain nucleation in congruent LiNbO 3 crystals.

It is necessary, on the ground in a laboratory, to test the technical parameters and to verify the working performance for the optical pointing, acquisition and tracking (PAT) of an inter-satellite lasercom terminal. In this paper, we report a completed PAT test-bed for this aim. The test-bed works in a fully physical way and is an integration of a 2D optical scanner of two rotating prisms, a 2D fine beam deflector of two tilting optical wedges and a double-focus laser collimator, the overall aperture is about Φ440mm. The optical scanner is designed to scan the beam in the range of 30° with an accuracy of 100μrad and used to simulate the mutual movement between two satellites. The fine beam deflector has the maximum beam deviation of about 1mrad with a step of 0.5μrad and is used to measure the tracking error of a terminal. The collimator has the double focal lengths, respectively, of 1.5m and 10m, the former provides a wide view of field for the use in the acquisition process of the terminal and the latter a narrow view of field for the use in the tracking process. In this paper, the design and fabrication considerations of the PAT test-bed as well as the main specifications of the completed integrated test-bad are given.

Recent successful demonstrations of laser communications have demonstrated the feasibility of some of the key aspects of this technology. The demonstrations can not success without the full-up ground test and validation. So an integrate test-bed was build in build to test the technical parameters and to verify the working performance for the optical pointing, acquisition and tracking (PAT) of various inter-satellite lasercom terminals. In this paper, we detail the test technical scheme (TTS) and the corresponding experiments. The integrate test-bed is a high quality optical system that will measure the key characteristics of lasercom terminals, such as point error, tracking error, acquisition possibility etc.. The test-bed can operate over the relative wavelength range. Through quantitative tests, the terminal could be optimized base on the test results.

The original scanner of tilting orthogonal double prisms is studied for testing the tracking performance in inter-satellite laser communications. Two prisms respectively rotate around the horizontal axle and the vertical one within the admissible range to determine the corresponding orientation and position of the passing beam, therefore the high accuracy deviation angle of passing beam can be performed. The test experiments performed with autocollimator and interferometer, as well as the theoretical analysis, indicates that the scanner can meet the requirements of the deviation accuracy superior to 0.5 μrad with the deviation range greater than 500 μrad, which accords to our design requirements.

The dynamic and static measurements of phase variation induced by domain inversion are performed in congruent lithium niobate crystal by the digital holographic interferometry. The existence of ridge-shape phase distribution adjacent to 180° domain wall is observed. During the domain wall motion, the phase variations are not uniform but have obvious relaxations. In the static measurement, the ridge elevation can vary linearly with the uniform electric field. The reasonable assumptions are proposed to explain these effects. The phase contrast across the crystal thickness induced by the internal field is also measured by the digital holographic interferometry just after the congruent lithium niobate crystal is partially poled. The direction of applied external field is antiparallel to that of internal field, and the measured phase contrast varies linearly with the applied external field. A new internal field is obtained by this method, and named effective internal field. The distinct discrepancy between effective and equivalent internal fields is observed. We attribute this effect to the new macroscopic representation of elastic dipole components of defect complex in the crystal.

A laser collimator is necessary for the testing and verification of the PAT performance of inter-satellite laser communication terminals. However, the terminals mostly have a large field of view for the acquisition and a high angular accuracy for the fine tracking needed to be examined. A single collimator has the conflict to reach at both a large field of view and a fine resolution. To compromise, a double-focus laser collimator is proposed. The collimator is mainly composed of a primary lens, a beam splitter, a secondary lens and some reflectors. The primary lens with a 9.9m focal length directly forms the long focal length arm of the collimator. The combination of the primary lens and the secondary lens has a new focal length of 1.3m and constructs the short focal length arm of the collimator. With two CMOS imaging sensors, the collimator can realize a 1.1mrad field of view with a

The propagation of laser beam in inter-satellite laser communications belongs to the far-field diffraction, but in the optical test and verification of pointing, acquisition and tracking (PAT) function on the laboratory the beam from a terminal propagates within the near-field. In this paper, in terms of the Fresnel diffraction theory the inherent difference is found that in the far-field diffraction the optical tracking position error is resulted from both the mutual movement between two laser communication terminals and the tilting of the receiver terminal, but the tilting of the transmitter has no effect on the error position; and that in the near-field diffraction the position error is caused by the tilting of the transmitter or the receiver, but the mutual movement has no effect. It is furthermore found that the use of a beam scanner in the test in the near-field can simulate exactly the mutual movement of satellites in the far-field, and the trajectory formula for the beam scanning is deduced that is the same as the mutual angular trajectory from one satellite to another. Therefore a practical PAT test bed of a double-focus laser collimator, a beam scanner and a fine beam steering device is developed by us to test and verify the PAT function of inter-satellite laser communication terminals. The optical aperture is about φ440mm for this use. And a test bed for concurrent test and verification of both PAT function and communication performance is also demonstrated. The test bed consists of a conventional laser collimator, an optical scanner and a far-field beam transmission simulator, which is a combination of a Fourier-transform lens an a followed multiple-stage imaging amplifier. The details of configurations are given. It is clear that these test beds can be also used to test and verify the functions of laser radar, passive optical tracker, and so on.

The scanner of orthogonally tilting double prisms is researched for testing the performance of tracking performance in inter-satellite laser communications for the first time. With the reduction ratio of more than a hundred times from the change rate of deviation angle of beam to that of tilting angle of each prism, the scanner can reach the scanning accuracy of sub-microradian order but facilitates the mechanical structure design. The theoretical analysis performed, as well as the validation experiment, indicates the scanner can meet the requirements of the scanning accuracy superior to 0.5 μrad with the scanning range greater than 500 μrad.

The domain inversion and electrochromism in congruent RuO 2 :LiNbO 3 crystals are investigated at room temperature, and the relations between them are proposed. During electric poling process, the electrochromism accompanies the ferroelectric domain inversion simultaneously, and is localized to the same region with domain inversion. As domain inversion, the electrochromism is completely reversible when the domain is inverted from the reverse direction. The properties, coincidence and localization, between domain inversion and electrochromism are proved solidly by the digital holographic interferometry, the real-time measurement of optical transmittance change and poling current, and the micrographic analysis after being etched in hydrofluoric acid. The influences of annealing conditions on electrochromism are also discussed. We provide the reasonable assumptions and analyses that the charge redistribution within the crystal caused by domain inversion is the source for electrochemically oxidation and reduction of Ru ion, and the intervalence electron transference between Ru 4+ and Ru 3+ plays a key role in the spectrum shift within different spectral range by the change of the photon absorption.

The volume holograms recorded by use of 90-degree geometry with reference and signal beams entering orthogonal crystal faces, have been widely used in fields such as waveguide couplers, holographic lenses, high-density holographic data storage. They posses the peculiar advantageous of small volume, ease of integrating and cascading. In fabrication of volume holograms are capable of converting various wavefronts into each other with high efficiency. But most of the researches were based on on-axis holographic optical elements such as cylindrical lens or spherical lens but not 90-degree geometry. In this paper, we investigate the properties of holographic lenses capable of converting plane waves into spherical waves in a perpendicular direction. Our research submits an analytical integral solution for the wavefront conversion problem in 90-degree geometry. The results can be of great practical importance in the design of volume holographic optical elements.

In this paper, the theory model in which both the two-center material equations and two-dimensional two-wave coupled equations were solved jointly based on two-center holographic recording method is presented to analysis the dynamic formation of the crossed-beam photorefractive gratings in two doped LiNbO 3 crystals. The influence of the light intensity on the basic holographic properties of the crossed-beam photorefractive gratings in LiNbO 3 :Fe:Mn crystals is explored. The numerical simulation results are presented. The investigation yields quantitative predictions of the expected behavior of the dynamics of these gratings, which can be useful for the design of finite boundary photorefractive holographic optical elements.

Two-dimensional phase unwrapping (PhU) is one of the most important processing steps in optical phase-shifting interferometry. It aims to reconstruct the continuous phase field, but in fact, it becomes very difficult to perform the PhU due to the existence of noise, low modulation, under sampling, discontinuities or other defects. For solving the problem, we present a new PhU method which is based on the local parameter-guided fitting plane. It relies on the basic plane-approximated assumption for phase value of local pixels and is guided by our proposed parameter map- Modulation-Gradient and Pseudo-Correlation (MGPC) parameter map. This new map is the combination of fringe modulation and wrapped phase, thus it's reliable in estimating the quality or goodness of phase data. Meanwhile, the adoption of fitting plane for the 3×3 window of pixels makes the process of PhU very fast. In applications, we offer the simulated and the experimental data to compare our method with the two previously reported path-following unwrapping algorithms. The unwrapped results show our proposed PhU method not only is efficient, but also has higher noise robustness in recovering the true phase field.

In order to obtain the two dimensional distribution of the refractive index changes due to the domain inversion in the RuO 2 :LiNbO 3 crystal, we make use of the Mach-Zehnder interferometer system to record holograms, with the object light transmitting through the poling RuO 2 :LiNbO 3 crystal, and then filter the spectrum in the frequency domain to get the object light spectrum for numerically reconstructing the object wavefront. The results confirm that the electro-chromic effect region well agrees with the domain inversion region in RuO 2 :LiNbO 3 crystal.

The characteristics of the terminals for the inter-satellite laser communication must be tested and verified on ground before flight test. A pair of terminals for inter-satellite laser communications was developed for principle demonstration. A terminal has two main subsystems. The first is one for the laser communications and the second one for acquisition, pointing and tracking (APT). The optical methods and related system test-beds to measure and verify the performance of the terminals in the lab room. In these programs, several novel ideas are proposed. With these ideas, whole programs can be tested on ground in near-contacted field. The dynamic APT performances of an inter-satellite laser communication terminal can be tested and verified by the combination of satellite trajectory simulator and a collimator-like laser communication.

The 90-degree recording geometry has special advantages in suppressing holographic scattering and can be used for designing of compact volume grating components, but the main drawbacks are low diffraction efficiency and small sensitivity. In this paper, we optimized the components and oxidation states of LiNbO 3 :Fe crystals for high diffraction efficiency during 90-degree holographic recording. The experimental results show that the samples with moderately doped components of Fe ions and high oxidation states have high diffraction efficiency.

Significant improvements of photorefractive properties such as diffraction efficiency with 90-degree holographic recording geometry have been obtained by the application of external electric fields. Experimental results show that the highest diffraction efficiency can be obtained at least 3 times than without external electric field in Fe-doped LiNbO 3 crystals. The vectorial Kukhtarev equations are modified in single center model taking into account the directions of optical axis and external electric field. The photorefractive properties of single doped LiNbO 3 :Fe crystal using 90-degree storage geometry are theoretically investigated by jointly solving the vectorial material equations and the two dimensional coupled wave equations. The variation trends of the theoretical results are similar to the experimental results.

A Bragg grating focusing device composed of electro-optically induced refractive index grating in periodically poled lithium niobate was designed for integrated optics systems. The device are induced and controlled by the application of an external electric field. The theoretical analysis of the proposed optical device is carried out using two-dimensional coupled wave theory. The focusing properties and the diffraction intensity are investigated at the focal plane. It is shown that the designed device has good performance of focusing when a plane wave incidents on it at a certain angle. This type of Bragg diffraction devices can be act as a focusing lens and will have many potential applications such as in integrated optics and opto-electronics.

In the field of intersatellite communication, laser beam transmitted from the optical terminal is required to be highly collimated with diffraction-limit divergence. Then, the maximal wavefront aberration at the edge of exit pupil is about 0.3λ. In order to measure the diffraction-limit wavefront, we present a whole-field double-shearing interferometer based on double-shearing theory. In this paper, firstly, the principle and configuration of the interferometer is introduced. Then the theory of double shearing is discussed. At the same time, we extend the applications of the interferometer. Lastly, we present the simulations of interference fringes with different primary aberrations and give the experimental results for the measurement of diffraction-limit wavefront.

In this paper, we give the far-field diffraction theory for calculating the divergence by using the superposition of Gaussian beams instead of the aperture function and obtain the explicit express for calculating the beam divergence. We analyze in detail the influence of the diffraction adding defocus aberrations upon the transmitter's divergence and get the simulated result. These researches are useful to system design and give us some suggestions of avoiding the influence of the aberrations and the diffractions on the transmitter.

The 90-degree recording geometry in photorefractive often suffers low diffraction efficiency and small sensitivity. For the low diffraction efficiency, previous researches considered it mainly come from larger K-vector. But in experiments the diffraction efficiency in 90-degree geometry is so low that the large K-vector can't explain the origin of low diffraction efficiency. We think the main reason of low diffraction efficiency in 90-degree geometry comes from the coupling between the incident light and diffraction light. The volume grating formatted in 90-degree geometry must be volume grating with finite size and follow the diffraction characteristic of crossed-beam volume gratings. When the refractive index change Δn>1×10 -4 , the diffractive efficiency in 90-degree recording geometry would be comparable with that in transmission geometry. However narrow grating space in 90-degree recording geometry makes it is more sensitive to ambient disturbs and leads to low effective modulation depth. That is why we can't obtain high diffraction efficiency for 90-degree geometry in experiments. For obtaining high diffraction efficiency in 90-degree geometry experimentally an active stabilization system is necessary.

In this paper, effect of polarization of light on photorefractive grating formulation with any light modulation in birefringent photorefractive material is studied in detail. The diffraction efficiency with various modulations and different polarization mode is calculated. Theoretical analytic results are presented. It is shown that both the ratio of the initial intensity and the incident angle of the writing waves are selective when the polarization of mode of the readout wave and that of diffracted wave are different. But these two recording conditions are not selective for the isotropic diffraction. On the other hand, it is also found that the length of the grating is selective for anisotropic diffraction.

Dopants in doubly doped lithium niobate crystals are crucial for properties of nonvolatile holographic recording. In our experiments, a series of possible doubly doped congruent LiNbO3:Fe:X (X=Mn, Cu, Rh, Ru, Ni) are proposed and investigated for nonvolatile holographic recording. The experimental results demonstrate that the dopants with different distances of energy band to conduction band have different recording efficiency. Further analysis approve that the dopants which have moderate energy-band distance to conduction band can perform recording with both high diffraction efficiency and long lifetime. The compared results show that LiNbO3:Fe:Ni is promising for nonvolatile holographic recording, and its recording conditions are optimized.

Holographic recording experiments of doubly-doped LiNbO 3 :Fe:Ni crystals were conducted by three kinds of different two-color recording schemes. The results show that the saturation diffraction efficiency, the fixing diffraction efficiency, and the recording sensitivity of oxidized LiNbO 3 :Fe:Ni crystal are higher than those of other reported doubly-doped LiNbO 3 crystals. Based on the doped energy-band diagram, the effect of microcosmic optical parameter of the deep trap center on holographic recording properties of doubly-doped LiNbO 3 is analyzed theoretically. LiNbO 3 :Fe:Ni has the potential of being a new highly efficient nonvolatile holographic recording material.

In this paper, a prototype of intersatellite laser communication terminal for a principle demonstration is reported, and the corresponding ground support equipments are described, too. The terminal has two main subsystems, the first is one for the laser communication and the second for the pointing, acquisition and tracking. Laser diodes are used for the communication link, and with the average laser power of more than 200mW and the data-rate up to 600Mbps. The PAT unit consists of a fine pointing mechanism and a coarse pointing assemble, which reaches a tracking accuracy of ~5μrad. The on-ground test equipments are included in a communication test bed with a long-distance beam propagation simulator, a PAT test bed with an optical satellite trajectory simulator, and a wavefront test bed with deferent lateral-shearing interferometers.

In this paper two-beam interference experiments are performed to investigate the diffraction characteristics of volume gratings in Fe:LiNbO 3 crystals (0.15wt% Fe 2 O 3 ), the results show that the dependence of the diffraction characteristics on the oxidization-reduction state and the oscillatory diffraction can be found in the reduced crystals. The theoretical analysis shows that the strongest space charge field can be formed in the reduced crystals, which induce the strong refractive index change, and because of the sin 2 relation between refractive index change and diffraction efficiency, the oscillatory diffraction can be found in the reduced crystals. In application for high diffraction efficiency the oxidized treatment should be performed for Fe:LiNbO 3 crystals so that the depth integral of saturated refractive index change is equal to π/2.

For on-ground performances testing and verification for intersatellite laser communication systems, a compact and multi-function optical testbed and a 2-D sub-micro-radian beamsteerer were designed. The testbed consists mainly of an optical simulator for long-distance propagation of laser beams, two CCD detectors, an autocollimation system, an interferometer, and a noise light source, for the uses is to measure far-field beam characteristics, transmitting powers, the wavefront errors and to evaluate the communication performances of any lasercom terminals with a aperture less than 280 mm in link level. The range of beam propagation distance of the optical simulator is from 2.8km to 3,5000km. An angular deviation yielded by the beamsteerer is to simulate the pointing error caused by all error sources. And a light source is to provide the noise-like illumination of changeable levels. Combined the testbed with the beamsteerer, it can measure the pointing errors and the tracking errors of the lasercom terminals, and estimates dynamic communication performances in the presence of random angular jitter. So the testbed has the potential to become all-purpose and tests the optical, communication and track performances for intersatellite lasercom terminals (ISLTs).

In this paper, a very effective recording technique of optimal recording/fixing switching time induced by high-coupling effect is considered for high diffraction efficiency of local nonvolatile holographic gratings in LiNbO3:Ce:Cu crystals. The fixed diffraction efficiencies gained by optimal switching time are up to 100% in theoretical simulations and 78% in experiments. It provides a new idea to obtain high persistent diffraction efficiency. Finally, as one of examples for design of 3-D optical integrations by local nonvolatile holographic gratings, a new type of volume holographic grating lenses for converting a plane wave to a lateral-spread spherical wave and vice versa, is illustrated.

In this paper, an oscillatory characteristic of diffraction is observed in a weakly oxidized LiNbO 3 :Ce:Cu crystal during the holographic recording. Experiment indicates that, after the first diffraction maximum, there exists an optimal switching time from the recording step to the fixing step which can produce a high diffraction of fixed hologram. High diffraction efficiency of 70% is observed in LiNbO 3 :Ce:Cu crystal. For theoretical simulation, the time-space dynamic evolution of the nonvolatile holographic recording in doubly doped LiNbO 3 crystals by jointly solving the two-center material equations and the coupled-wave equations is performed. The results show that the optimal switching will lead theoretically the fixed diffraction up to 100 % with a suitable switching time. This method provides us a new idea to obtain high persistent diffraction efficiency. The relationship between the optimal switching and the crystal thickness is studied. Keywords: LiNbO 3 :Ce:Cu crystals, nonvolatile holographic storage, diffraction efficiency.

It is required for the laser communication that laser beam transmitted from the optical terminal must be highly parallel. Optical diffraction limit angle is the minimum divergence the beam can obtain while limited by the definite aperture under ideal conditions, here wavefront still has an error of 0.3 wave. This paper introduces a new method for wavefront analysis. In this method a circular aperture diaphragm used to sample the tested wavefront, a focusing lens, a microscope objective and a fiber optic probe are arranged coaxial. Axial intensity profile behind the focusing lens is plotted by registering the positions of the microscope objective on the axis and the readings of the radiometer. The sampled wavefront height is estimated from the distance between two symmetrical positions along the axis where the intensity is zero. The tested wavefront height is calculated from the sampled wavefront height. The theory and the simulation results are given. It can be applied in coarse measurement of any wavelength laser wavefront. Due to simplicity of the method and its low cost, it is a promising method for checking the collimation of a laser beam.