This PDF file contains the front matter associated with SPIE Proceedings Volume 8906, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.

A design of a laser communications optical system with high transmitting and receiving performance is given. The traditional on-axis Cassegrain optical antenna has the default that the transmitting and receiving power decreased greatly because of the obscuration of the secondary mirror. Considering that the eccentric-pupil Cassegrain optical antenna is designed. The optical antenna system in transceiver has been designed by means of CODEV software. It improves the efficiency of transmitting and receiving power effectively. Its properties have been analyzed, such as gain, image quality, and transmission efficiency. Meanwhile, the materials of optical elements have been analyzed. The power decline curve has been obtained by means of the detailed analysis of antenna system in partial axis situation. The system includes transmitter channel, receiving channel and experiment channel. It can realize the functions of transmitter-receiver isolation and multi-light ways using dichroic mirrors and beam splitting prisms. The system volume and weight are reduced greatly. The complexity of conventional laser communication system is reduced enormously at the same time. It has important reference significance and application value.

Underwater wireless optical communication is a communication mode which uses light as an information carrier and water as transmission medium. As a result of the inherent characteristics of the light waves, underwater wireless optical communication has the advantages of high transmission rate, good security, and strong anti-interference ability. It is suitable for high-speed, short-range communication between underwater mobile vehicles. Underwater optical wireless communication system designed in this paper is composed of the omni-directional communication light source and the receiving system. In the omni-directional communication light source, the laser beams with small divergence angle of 532nm wavelength produced by modulated laser are expanded through a combination refraction-reflection solid and then obtain more than 2π space divergence angle. The paper use TRACEPRO simulation tool to help design a combination solid composed of the lens, conical reflector and parabolic reflector, and test in the air and underwater, the result shows that the effect is fine. Unlike in the air, light attenuation is heavy in the water and a large range of variations in light intensity at different distances appear during underwater optical communication. In order to overcome this problem, the paper use a small photomultiplier as the detection device, design the receiving system using the automatic gain control technique. Underwater wireless optical communication system designed in this paper has the characteristics of small size, low power dissipation and the omni-directional communication function, it is suitable for application in the UUV, AUV, Swimmer Delivery Vehicle (SDV) and other underwater mobile platform, it realizes point-to-point communications and point-to-multipoint communications.

In free space optical homodyne receiver that analyze Residual carrier COSTAS loop, in the pointing and communication phase with laser terminal analyze free space link optical power penalty and pointing power penalty. In the conforming bit error rate with BPSK homodyne receiver dues to the minimum receiver optical power, in the same way the relation between receiver optical power and homodyne locked phase error variance, and the relation between receiver optical power and homodyne optimum equivalent noise loop bandwidth, all the more loop filter design parameter is variable with receiver optical power. In simulation COSTAS loop homodyne locked phase error deviation and loop bandwidth, when the receiver power is more -50dBm and less -40dBm in the signal trace, COSTAS loop parameter is not appreciable on the whole. Locked phase loop is integrated in the relation between baseband phase error deviation and carrier frequency shift, when baseband phase error is 10 degree, carrier frequency shift about above 100MHz.

In the 40Gbps high-speed optical fiber communication system, chromatic dispersion of optical signal brings about to generation of inter-symbol interface which influences the quality of optical fiber communication. In order to solve the above questions in the 40Gbps differential quarter phase-shift keying (DQPSK) optical fiber communication system, a new method of chromatic dispersion compensation based on genetic algorithm is proposed according to the demodulation of DQPSK optical signal and the trait of chromatic dispersion. Result shows that the system’s receiving sensitivity has been enhanced up to six orders of magnitude.

The serious impact produced during the laser transmission in the atmospheric channel will degrade the performance of the communication system. Channel coding techniques can greatly improve the atmospheric channel. The low density parity check code (LDPC) is one of channel codes with excellent performance. we applied the LDPC code in the wireless optical communication system, built the model of the system, simulated and analyzed the application, and proved the improvement of the performance of wireless optical communication finally.

Free space laser communication based on airborne platforms will play a important role on the future space communications, high precision tracking system for airborne laser communication has been already the one of the best difficult problem. Because of diversity of maneuvering forms and high nonlinear problem, it is usual to adopt multiple models algorithm with a fixed structure for tracking system, which brings unnecessary inter-competition among the amount of models and calculation burden, in order to resolve this contradiction, a variable structure multiple-model (VSMM)based on digraph switching is presented, the particle filter (PF) can deal with nonlinear/non-Guassian problems, it can be introduced into VSMM framework. Simulation results show that the algorithm improves the accuracy of tracking by reducing the competition of the models as well as reducing the computation burden.

The spectrum of radar signal will be modulated by moving target or vibration and turning part of the target, this is called micro-Doppler effect. It is a new way of using micro-Doppler effect to realize the feature extraction and target recognition. Because the complex vibration target has more complicated frequency component than the single frequency target, so it is very useful to do the research of simulation and experiment of laser micro-Doppler effect for detecting complex vibration. In this paper, the research on simulation and experiment of laser micro-Doppler effect for detecting complex vibration of moving target was developed based on the simulation research of micro-Doppler effect in lidar. Firstly, the geometry of complex vibrating target detection in radar was established. Secondly, the simulation and experiment signal sources were compared and also the returned signals in radar of the simulation and experiment were compared, the compared results showed that the two complex signal sources were very similar, and the frequency change trend of returned signals in radar was the same. Thirdly, joint time-frequency analysis method of the reassigned smoothed pseudo Wigner-Ville distribution (RSPWVD) was introduced to analyze the signals. The results showed that in RSPWVD, the waveform of the vibration target, the target vibration period, the Doppler frequency shift and the target’s speed can be got. The simulation results and the experiment results got by the RSPWVD had the basically same frequency characteristics. So the RSPWVD can reflect very well the micro-Doppler characteristics of moving target’s complex vibration. In conclusion it proved the validity of the simulated model, also it proved that using this time-frequency method to analyze the micro-Doppler signal of complex vibration was correct. And it laid the foundation of further using lidar to realize the classification and identification of target.

An 4km optical link was established to examine the effect of beam wander on the scintillation characterization for multiple focus beams. Multiple beams that sample different portions of the atmosphere reduce the scintillation if the atmospheric turbulence each beam traverses is independent. How much the beam wander affects scintillation is determined by the number of the beams and the size of the beam wander variance. The number of mutually incoherent beams was 1, 3 or 6. Individual laser was launched from a separate region of the transmitter and focused on the flat screen with the horizontal distance of 4km by 350mm telescope. We recorded the illuminated flat screen with a CCD camera operating at 1kHz. We calculated the scintillation index of the illuminated area with the size of 8x8cm on the condition of untracked and tracked beams. A tracked beam generally refers to the situation in which the beam is tilt-corrected. However, There was no tilt-corrected in the experiment. Instead, the rms beam centroid of the area was aligned with the optical axis at each frame. Experimental results show that the scintillation index in tracked beam was larger than in the untracked beam case when the size of the Rytov variance σ²_R is the same for one beam case, but for three and six beams, the scintillation values are almost. It is the reason that the root mean square variance of wander angle decreases as the number of beams increases. So the effect of beam wander is not evident for three and six beams. And increasing the number of beams on the condition of untracked and tracked cases does reduce the scintillation index as predicted.

In the link of satellite to ground laser communication, light signals received by ground terminal receivers are susceptible to interference due to the impact of atmospheric turbulence, and it will result in the degradation of communication quality or even interruption. In this situation, the conventional communication detection device would not be able to analyze the link performance. Thus, it is necessary to develop a set of non-continuous optical signal recognition and storage devices which could work under adverse atmospheric conditions and do the online analysis of the impact of atmospheric on the link of satellite to ground laser. Since the interruption of the optical signal will cause the logical disorders of the high data rate storage system, which uses the CDR output clock as the system clock, general storage device cannot meet the demand of effective storage for communication. In this paper, the usage of FPGA optical signal recovered clock frequency discriminator identified the impact of non-continuous communication signal of atmospheric disturbances effectively. Through the optimization of the system hardware design and software control, we achieved the identification and storage of the laser communication optical signal data while the factor of atmospheric scintillation varying from 0 to 1.5 and the communication data rate being 600Mbps.

There are little research on the subject of probability density function of the phase fluctuations in turbulent atmosphere at present. There is still no analytical model under the most general case. Based on Born perturbation theory, the exact model of the phase fluctuation in Elliptical-Gaussian speckle filed was theoretically deduced. And then three approximate models (Circular-Gaussian approximation, Strong-Turbulence approximation and Strong-Turbulence- Circular-Gaussian approximation model) which are corresponding to the irradiance fluctuation models were deduced through appropriate simplification. Finally, the correlations of the models proposed were simulated analysed, and the results prove the accuracy of the exact model.

Based on electromagnetic wave radiation theory, the important parameters of the receiver antenna is analyzed, we analyze the relationship between the receiving antenna array characteristics and the method of improve antenna array gain. The receive performance is compared between a single receiver antenna and the antenna array. Based on the refractive index fluctuation of atmosphere follow the Kolmogorov power spectrum, the relationship between the receiving antenna array and improve coupling efficiency are analyzed in free-space optical communication systems through atmospheric turbulence. The simulations show that the receiving performance of antenna array is better than a single large aperture antenna. The optimum number of the sub-antennas and aperture diameter differ according to the area of the antenna array. In different atmospheric turbulent, the effect of improve coupling efficiency are analyzed between a single receiver antenna and the receiving antenna array. In the aspect of improve the coupling efficiency, the antenna array is better than optical antenna in medium, strong atmospheric turbulent.

An all-optical encryption system which can be used in fiber WDM system and directly encrypt multi-wave optical signals is proposed. This scheme achieves multi-wave signals encrypting by the technology of generating coherently multi-wave optical plain text, Key text and the technology of phase shift interference. The feasibility and validity of this encrypting scheme are verified by simulative experiment for multi-wave signals at 8x10Gbps with wavelength interval of 0.8nm, the simulative result shows that when the input Pi and Ki is Gauss pulse with duty cycle of 0.3, the bit error rate and Q factor of encryption output are 0 and 164 respectively. Theory analysis and simulative experiment shows the scheme is feasible and efficient.

In order to realize the all-optical encryption for multi-wave and ultra-high speed, an all-optical encryption scheme is proposed, which is based on pockels effect of LiNbO3 waveguide and optical-time-division-multiplexing (OTDM) in LibNO3 waveguide. The coherently ultra-high speed plaintext and key are generated by OTDM in LibNO3 waveguide and the XOR operation of optical plaintext and key are achieved by direct light interference. The feasibility and validity of this scheme is verified by simulative experiment at 8 x 80Gbps with wavelength interval of 2nm.

The space coherent laser communication is a very potential mean for high-speed laser communication in the future, because the excellent receiver sensitivities can be achieved by coherent detection techniques. The best coherent receiver sensitivity amounts to -59.4dBm at a data rate of 10Gbit/s and a bit error rate of 10^-9, which is obtained with phase-shift keying modulation in combination with homodyne detection. In this paper, we investigated optical homodyne detection based on Costas phase-locked loop in the space coherent laser communication system. We obtain optimum loop bandwidth of Costas phase-locked loop and the maximum permissible laser line width based on Costas phase locked loop.

The space coherent laser communication is a very potential and attractive mean as it allows higher speed communication between satellites. The space coherent laser communication makes use of local oscillator laser power to improve the power of received optical signal by mixing local oscillator laser and optical signal together. However, the power of the local laser oscillator can not be increased infinitely, too large but reduces the detection sensitivity. In this paper, starting from the principle of the signal-to-noise ratio of the space coherent laser communication, we found the optimum local oscillator laser power was 28.174mw, under the condition of the selected photodetector specific parameters. It is a great significant for high detection sensitivity and low data error of the actual coherent detection system.

The application of orthogonal frequency division multiplexing (OFDM) in atmospheric laser communication is not as wildly as expected. This is should be owing to several problems rooted in OFDM system and the incompatibility between IM and OFDM. Aiming to analyze the major problems and propose optimized solutions, in the first part of this paper, we introduce the application of fast Hartley transform (FHT), as a suitable alternative to FFT, in asymmetrically clipped (AC) OFDM Atmospheric laser communication system. Then we demonstrate the problem of high PAPR embedded in such system. In the following part of this paper, we firstly review and analyze the performance of some standard methods, namely, Clipping, Companding, Selective Mapping (SLM), Partial Transmit Sequence (PTS), used to reduce the high peak to average power ratio (PAPR) caused by OFDM. And then we make some modifications on those methods so that they could be applied on DHT based AC-OFDM atmospheric laser communication system with more effectiveness. Finally, we propose and compare four different PAPR reduction techniques obtained by serialization of those modified methods. And by using Matlab simulation we demonstrate the feasibility of the proposed methods.

Improving the bandwidth of fast steering mirror is the important premise when adaptive optics is applied to space communication. In this paper, based on the fast steering mirror structure, the resonance frequency and its vibration model of the mirror, driving elements and bend-board of fast steering mirror (FSM) are analyzed in detail by use of finite element analysis. It is concluded that the unreasonable structure of the bend-board which fixes and supports the fast steering mirror is the main reason why the fast steering mirror has lower resonance and the resonance frequency of the bend-board has the great influence of the parts of the whole fast steering mirror. In addition, the optimized design to improve the resonance frequency of the FSM mounting is put forward.

Based on the cat-eye effect of optical system, free space optical communication based on cat-eye modulating retro-reflector can build communication link rapidly. Compared to classical free space optical communication system, system based on cat-eye modulating retro-reflector has great advantages such as building communication link more rapidly, a passive terminal is smaller, lighter and lower power consuming. The incident angle is an important factor of cat-eye effect, so it will affect the retro-reflecting communication link. In this paper, the principle and work flow of free space optical communication based on cat-eye modulating retro-reflector were introduced. Then, using the theory of geometric optics, the equivalent model of modulating retro-reflector with incidence angle was presented. The analytical solution of active area and retro-reflected light intensity of cat-eye modulating retro-reflector were given. Noise of PIN photodetector was analyzed, based on which, bit error rate of free space optical communication based on cat-eye modulating retro-reflector was presented. Finally, simulations were done to study the effect of incidence angle to the communication. The simulation results show that the incidence angle has little effect on active area and retro-reflected light intensity when the incidence beam is in the active field angle of cat-eye modulating retro-reflector. With certain system and condition, the communication link can rapidly be built when the incidence light beam is in the field angle, and the bit error rate increases greatly with link range. When link range is smaller than 35Km, the bit error rate is less than 10^-16.

High precision acquisition, tracking, pointing (ATP) system is one of the key techniques of laser communication. The spot-detecting camera is used to detect the direction of beacon in laser communication link, so that it can get the position information of communication terminal for ATP system. The positioning accuracy of camera decides the capability of laser communication system directly. So the spot-detecting camera in satellite-to-earth laser communication ATP systems needs high precision on target detection. The positioning accuracy of cameras should be better than ±1μ rad . The spot-detecting cameras usually adopt centroid algorithm to get the position information of light spot on detectors. When the intensity of beacon is moderate, calculation results of centroid algorithm will be precise. But the intensity of beacon changes greatly during communication for distance, atmospheric scintillation, weather etc. The output signal of detector will be insufficient when the camera underexposes to beacon because of low light intensity. On the other hand, the output signal of detector will be saturated when the camera overexposes to beacon because of high light intensity. The calculation accuracy of centroid algorithm becomes worse if the spot-detecting camera underexposes or overexposes, and then the positioning accuracy of camera will be reduced obviously. In order to improve the accuracy, space-based cameras should regulate exposure time in real time according to light intensity. The algorithm of adaptive-exposure technique for spot-detecting camera based on metal-oxide-semiconductor (CMOS) detector is analyzed. According to analytic results, a CMOS camera in space-based laser communication system is described, which utilizes the algorithm of adaptive-exposure to adapting exposure time. Test results from imaging experiment system formed verify the design. Experimental results prove that this design can restrain the reduction of positioning accuracy for the change of light intensity. So the camera can keep stable and high positioning accuracy during communication.

In this paper we study the acquisition technology with the antenna scanning in satellite-ground laser links by theoretical analysis and practical experiment. Based on the satellite-ground laser communication system, we first set up the theoretical model and deduce the mathematic expressions of acquisition probability and acquisition time according to the raster-spiral scanning scheme. Then, we analyze factors which might influence the acquisition probability. Different with other research, our study explores the impact of fixed offset errors as well as the impact of the scanning step and scanning speed on the acquisition system in detail. Further, we optimize the average acquisition time by numerical analysis. Finally, we examine the theoretical model in a real acquisition, tracking and pointing (ATP) system. The experimental results showed that the proposed analysis can improve the acquisition performance.

Sand dust aerosol is the main component of aerosol in troposphere atmosphere of East Asia, which can produce the extensive influence on the ecosystem, atmosphere environment and atmosphere chemistry through intensive sand dust weather process. For investigation of the aerosol optical depth (AOD) and its temporal-spatial evolution over this area, a series of observation experiments were carried out by a sun photometer CE-318 located at Beifang University of Nationality( 106°E, 38°29'N ), Yinchuan Ningxia province of China from September 2012 to April 2013 and many direct solar radiation datum were obtained. The experiments results were analyzed in detail and some conclusions are obtained as follows: (1) For daily evolution of AOD, the variation trend are divided into four types: ①the AOD values are relatively steady in whole day; ② the AOD values increase from morning to afternoon; ③ the AOD values are greater at noon than that in the morning and afternoon; ④there is a peak in the variation trends of AOD from 9:00~12:00 in the morning, but it is small at other time. (2) For month evolution, the minimum AOD average value appears in September and the maximum one appears in April. (3) For the seasonal changes trend, the average AOD values in the April are bigger than that in the autumn. (4) In addition, during the observation period, one dust weather process was observed and the change characteristic of AOD of dust aerosol was obtained and analyzed.

Photon Detection technology is a hot area in low light detection field. The paper introduces the working principle, basic structure and performance characteristics of SPM detection device, focuses on two components of the photon detection system: Optical-electric conversion circuit and Detector bias circuit. In order to verify the photon detection performance and photon distinguish ability of SPM detector, designed SPM photon detection circuit using high speed transconducance amplifier, and executed photon detection experimental research.

2.0μm emission properties of Ho³⁺-Yb³⁺ co-doped tellurite oxy-halide glass exited by 980nm LD is reported. Mid-infrared transmittance property of glass was investigated by Fouriertransform infrared (FTIR) spectrometer. The Judd-Ofelt intensity parameters Ω_t)t=2,4,6) , spontaneous radiative transition probabilities, branching ratios and radiative lifetime of Ho3+ were calculated according to the absorption spectra by using Judd-Ofelt theory. The absorption, emission cross-sections and gain coefficient of Ho³⁺:⁵I₇→⁵I₈ are calculated based on the McCumber and Reciprocity theories. Results indicate that the maximum 2.0μm emission intensity of Ho³⁺ was achieved at 0.15mol% Ho₂O₃ and 1.5mol% Yb2O3 concentrations in tellurite oxy-halide glass. The maximum absorption and stimulated emission cross-section of Ho³⁺ near 1944nm are 6.37 x 10^-210cm² at 2.0μm and 10.94 x 10^-21cm² respectively. The results suggest Ho³⁺-Yb³⁺ co-doped tellurite oxy-halide glass is a good candidate for efficient 2.0μm laser.

We present simulation results for a 5 Gb/s optically pre-amplified, differential phase shift keying communication system achieving -48.1 dBm (about 24.7 photons/bit) receiver sensitivity at 10^-9 bit-error-rate and using an optical delay line interferometer made by ourselves with 1 bit delay as the demodulator. The system is also experimental tested and sensitivity of the receiver is -36.5 dBm (about 106.6 photons/bit). The experimental results have some penalty in sensitivity comparing to the results in the simulation because the 1 bit delay interferometer is sensitive to the environment such as temperature, tremble and so on. To our knowledge if the interferometer is well designed and optimized, the experimental results can correspond with the simulative results and an optically pre-amplified direct detection DPSK receiver with high sensitivity can be realized.

It is the key of realizing high speed, large capacity fiber information transmission that achieve ultrashort optical pulse by optical pulse compression. At present, the compression method that is achieving parabolic pulse with linear chirp and compensating the linear chirp is paid more attention. Based on the two schemes for the parabolic pulse with linear chirp by the normal dispersion decreasing fiber or the fiber amplifier with a normal dispersion, more study on the characteristics of the parabolic pulse with linear chirp in the different dispersion decreasing profiles (such as cosine, Gaussian, linear, exponential and hyperbolic) is showed; the results show that, for different dispersion decreasing profiles, the good linear chirp and parabolic shapes that are good for pulse compression can be generated. Moreover, a novel scheme for the parabolic pulse, which is achieved by a dispersion decreasing fiber amplifier with a normal dispersion, is presented. Numerical simulations show that, compared with the parabolic pulses generated in the normal dispersion decreasing fiber or the fiber amplifier, the parabolic pulse generated by the novel scheme has the better linear chirp and the more pulse energy; the gain has an obviously effect on the intensity and quality of the linear chirp, which is that the output pulse has a smaller pulse width and higher pulse power after the chirp is compensated.

Based on non-regenerative relays, the bit error probability expressions of CSI-assisted relay and fixed-gain relays for high altitude platform multi-hop optical communication is given. The effect of the factors, including atmospheric turbulence pointing error and relay node position, on the performance of multi-hop optical links is analyzed. The simulation results show that the influence of atmospheric turbulence on optical links is greater than that of pointing error. The improvement of average SNR per hop and transmit power on multi-hop optical communications may be restricted by pointing error. Compared to CSI-assisted relay, fixed-gain relay is suited to more hops links with the condition of high average SNR per hop.

Research on characteristics of atmospheric communication link becomes a subject of current interest, and often mainly focuses on some fading parameters including the probability of fade, the mean fade number and the mean fade time. The contribution of false alarm to bit error rate has been considered, however, the temporal characteristic is rarely mentioned., To make up the deficiency, parameters integrating the influence of false alarm and fading were defined. On one hand, the laser communication link were modeled for Gamma-Gamma distribution of irradiance fluctuation subjected to weak atmospheric turbulence. Accordingly the mathematical expressions of these parameters were deduced. On the other hand, characteristic of the parameters were obtained by numerical simulation with various channel environment parameters, such as mean signal-to-noise ratio (SNR), zenith angle and detection threshold. Compared with other researches on fade characteristic, some different conclusions can be drawn from simulation results. With the same SNR and zenith angle, there is an optimum value of detection threshold corresponding to the minimum mean error number, which deviates obviously from that obtained according to the minimum error probability. Either increasing SNR or decreasing zenith angle can reduce mean error number and the optimum threshold. Different from mean error number, mean error time is slightly influenced with channel environment parameters and constant at the order of milliseconds.

Polarized laser has been widely used in free space optical communication, laser radar, and laser ranging system because of its advantages of good performance in recent years. The changes of laser polarization properties in the process of transmission in atmospheric turbulence have a certain impact on the system performance. The paper research on the rule of polarization properties changes of Gauss Schell model beam in turbulent conditions. And analysis the main factors to affect the polarization properties by numerical simulation using MATLAB software tools. The factors mainly including: initial polarization, coherence coefficient, spot size and the intensity of the atmospheric turbulent. The simulation results show that, the degree of polarization will converge to the initial polarization when the beam propagation in turbulent conditions. The degrees of polarization change to different value when initial polarization of beam is different in a short distance. And, the degrees of polarization converge to the initial polarization after long distance. Beam coherence coefficient bigger, the degree of polarization and change range increases bigger. The change of polarization more slowly for spot size is bigger. The change of polarization change is faster for longer wavelength. The conclusion of the study indicated that the light source parameters effect the changes of polarization properties under turbulent conditions. The research provides theory basis for the polarization properties of the laser propagation, and it will plays a significant role in optical communication and target recognition.

We demonstrate a multi-wavelength fiber laser with Brillouin cavity loop. Brillouin-Erbium fiber laser (BEFL) integrates Brillouin and Erbium gains in the resonate cavity to produce high power multi-wavelength fiber laser. The Brillouin gain loop connects with main ring cavity by port2 of the circulator1. A coil of SMF with a length of 10 km is employed by 3-dB fiber coupler as Brillouin gain medium, and pumped by Brillouin pump (BP), a tunable laser with a maximum output power of 15 dBm to generate Stokes light. The measured results were extracted from the laser system by using 90/10 coupler where 10% power is used for monitoring and measurement purpose while the 90% power is feedback into the laser cavity. A 1550 nm tunable laser diode (LD) provided the BP that can be tuned from 1470 nm to 1580 nm (110 nm tuning range). Two fiber circulators are used as the fiber reflection loops at both ends of the linear cavity. The effect of the erbium-doped fiber amplifier (EDFA) locating at different locations in the cavity BEFL on Stokes wave is experimentally studied. In the experiment, with EDFA in position A, the tunable range and the output power of the multi-wavelength laser were limited by gain saturation of the signals and the self-lasing cavity modes. The self-lasing cavity modes were suppressed without EDFA, but the tunable wavelength range was narrower because of the low gain. By using EDFA at the total reflective side of the linear cavity, more Stokes waves and wider tunable range was observed because the more powerful Stokes feedback light was amplified twice by the EDFA. The peak power of -1.8dBm and the tuning range of 60 nm were obtained. It has many important applications, such as dense wavelength division multiplexing (DWDM) systems, distributed fiber sensing, slow light, and microwave photonics, etc.

Currently, the atmospheric wireless optical communication generally uses intensity modulation/direct detection (IM/DD) systems. There are typical modulation schemes such as on-off keying (OOK), pulse position modulation (PPM), differential pulse position modulation (DPPM), differential pulse interval modulation (DPIM) and dualheader-pulse interval modulation (DH-PIM) for atmospheric wireless optical communications. For the high packet error rate and low information transmission rate of wireless optical communication intensity modulations presently, which is caused by atmospheric turbulence and scintillation on the laser beam, a new modulation scheme--Polarization Shift Keying is proposed. The modulation structures, bandwidth requirement, transmission capacity, power requirement and packet error rate performance over weak turbulence are compared between several intensity modulation schemes (including OOK, DPPM, DPIM, DH-PIM) and PolSK modulation. Theoretical analysis and simulation results show that OOK offers the highest bandwidth efficiency and transmission capacity. However, the average transmission power and bit error rate is both high. The reliability of DPPM and DH-PIM is better, while the bandwidth efficiency is low. CPolSK offers the highest bandwidth efficiency and the lowest bit error rate and packet error rate, which are very important in the atmospheric wireless optical communication. CPolSK has stronger anti-interference ability compared to intensity modulation scheme, because the polarization seems to be the most stable characteristic of a laser beam while propagating through the atmosphere. Hence, CPolSK is superior in the atmospheric laser communication.

Optical satellite communication with the advantages of broadband, large capacity and low power consuming broke the bottleneck of the traditional microwave satellite communication. The formation of the Space-based Information System with the technology of high performance optical inter-satellite communication and the realization of global seamless coverage and mobile terminal accessing are the necessary trend of the development of optical satellite communication. Considering the resources, missions and restraints of Data Relay Satellite Optical Communication System, a model of optical communication resources scheduling is established and a scheduling algorithm based on artificial intelligent optimization is put forwarded. According to the multi-relay-satellite, multi-user-satellite, multi-optical-antenna and multi-mission with several priority weights, the resources are scheduled reasonable by the operation: “Ascertain Current Mission Scheduling Time” and “Refresh Latter Mission Time-Window”. The priority weight is considered as the parameter of the fitness function and the scheduling project is optimized by the Genetic Algorithm. The simulation scenarios including 3 relay satellites with 6 optical antennas, 12 user satellites and 30 missions, the simulation result reveals that the algorithm obtain satisfactory results in both efficiency and performance and resources scheduling model and the optimization algorithm are suitable in multi-relay-satellite, multi-user-satellite, and multi-optical-antenna recourses scheduling problem.

Cat-eye effect has been widely used in active laser detection, optical target identification and free space optical (FSO) communication, but atmospheric turbulence makes laser beam fluctuate, which limits the use of cat-eye effect. The optical aperture has the aperture averaging effect to the detecting laser, which can be used to identify optical targets. Using the flashing theory of spherical wave in the weak atmospheric turbulence, the circular aperture filter function and the Kolmogorov power spectrum, the analytic expression of the echo scintillation index of the cat-eye target of the horizontal path two-way transmission was given in which the cat-eye target were equivalent to a combination of two circular apertures and the detector of cat-eye target was equivalent to a reflecting plane with the reflectivity η when the light is normal incidence. Then the impact of turbulence inner and outer scales to the echo scintillation index and the analytic expression of the echo scintillation index at the receiving aperture were presented using the modified Hill spectrum and the modified Von Karman spectrum. The simulation results show that scintillation index of considering the inner scale is larger compared with that of without considering the inner and outer scales and considering the inner and outer scales. Echo scintillation index shows the tendency of decreasing with the target aperture increases. The echo scintillation index increases with the transmission distance increasing.

A polarization phase shifting lateral shearing interferometer based on a polarization beam splitting plate(PBSP) is proposed. The front surface of the PBSP is coated with polarization beam splitting film and its back surface is coated with total reflection film. The beam to be tested is split by the PBSP with an incidence angle of 45° and divided into two mutually perpendicular linearly polarization beams. Phase shifting can be introduced to the interferometer when the PBSP is combined with a polarzation temporal or spatial phase shifter. A polarizaiton temporal phase shifting lateral shearing interferometer system is built up both with the ASAP software and the experiments. The usefulness of the interferometer is verified.

Lots of researches have simulated performance of optical system based on plane wave or spherical wave model, but optical field is Gauss distribution in real optical communication system. So we derive the relationships between the signal-to-noise ratio (SNR), bit error rate (BER), channel capacity (C) and the transmission distance of the space laser communication system, which is obtained by the Gaussian beam propagation model for on-off keying (OOK) modulated signal under horizontal link. We numerically study the influence of atmospheric turbulence on system performance. we get the conclusions: Under weak turbulence intensity, as the turbulence intensity increases, the C and SNR for OOK modulated space laser communication system decrease while the BER increase; In the case of strong turbulence intensity, the intensity scintillation and the BER dramatically increase with the increase of transmission distance, and then become saturated; In the condition of turbulence intensity and transmission distance are both constant, the longer the wavelength results in greater C, higher SNR and lower BER. Selecting longer communication wavelength can mitigate the impact of the atmosphere turbulence on the communication system in some extent.

In order to ensure the reliable performance of a high-speed optical fiber communication system, it is vital that all optical components are characterized, such as connectors, couplers, switches and detectors. Among the component characteristics, backreflection in the laser propagation system will cause high bit error rate resulting from multipath interference, degrade optical signal-to-noise ratio (OSNR) and induce transmitter instability. The measurement of optical return loss (ORL), which quantifies this backreflection characteristic, is necessary. Optical continuous wave reflectometer (OCWR) and optical reflection discrimination (ORD) are widely used to measure ORL of optical devices in laser propagation system. These two techniques have different application effect, so to select suited technique to measure ORL is very important. This paper will describe their measurement principle and application issue of these two techniques. By comparison, it can be found that OCWR technique has the advantage of measurement accuracy, but ORD technique has the advantage of simplicity of implementation due to no mandrel wrap and increased dynamic range. As for the laser propagation system, ORL of entire optical link should be measured using OCWR technique to ensure good status; otherwise, ORL of individual optical device should be measured quickly using ORD technique. Conclusions of this paper can be guidance for selecting proper optical return loss meter in the laser propagation system.

Ultraviolet (UV) scattering communication is a broadcast communication mode of information transmission by particles in the atmosphere scattering effect on the blind band ultraviolet light, there are many advantages such as unaffected by electromagnetic radiation, good confidentiality, non-line-of sight communication. This type communication mainly used in a short distance, secure communication, which was superior to no line communication in aspect of anti-jamming and secrecy. Firstly the military requirement of UV scattering communication is analyzed in this paper, The development trend is introduced, then the composition and working principle of ultraviolet scattering communication system are also discussed, The key influential factors of UV communication system path transmission loss effects on parameters such as receiver, transmitter and received beam divergence angle, pitch angle and the communication distance were analyzed. Attenuation was quantitatively simulated under different atmospheres, communication patterns and structure parameters. The results show that: transmission distance increases with increasing beam divergence angle and decreasing field angle. And the received view angle of influence on the communication distance is far greater than the emission beam divergence angle; transmission distance increases with increasing beam divergence angle and decreasing field and field angle effects on communication distance is greater than beam divergence angle.

Free space optical communication is one of the best approaches in future communications. Laser beam's acquisition, pointing and tracking are crucial technologies of free space optical communication. Fine tracking system is important component of APT (acquisition, pointing and tracking) system. It cooperates with the coarse pointing system in executing the APT mission. Satellite platform vibration and disturbance, which reduce received optical power, increase bit error rate and affect seriously the natural performance of laser communication. For the characteristic of satellite platform, an active disturbance rejection controller was designed to reduce the vibration and disturbance. There are three major contributions in the paper. Firstly, the effects of vibration on the inter satellite optical communications were analyzed, and the reasons and characters of vibration of the satellite platform were summarized. The amplitude-frequency response of a filter was designed according to the power spectral density of platform vibration of SILEX (Semiconductor Inter-satellite Laser Experiment), and then the signals of platform vibration were generated by filtering white Gaussian noise using the filter. Secondly, the fast steering mirror is a key component of the fine tracking system for optical communication. The mechanical design and model analysis was made to the tip/tilt mirror driven by the piezoelectric actuator and transmitted by the flexure hinge. The transfer function of the fast steering mirror, camera, D/A data acquisition card was established, and the theory model of transfer function of this system was further obtained. Finally, an active disturbance rejection control method is developed, multiple parallel extended state observers were designed for estimation of unknown dynamics and external disturbance, and the estimated states were used for nonlinear feedback control and compensation to improve system performance. The simulation results show that the designed controller not only accurately estimates and compensates the disturbances, but also realizes the robustness to estimation of unknown dynamics. The controller can satisfy the requirement of fine tracking accuracy for free space optical communication system.

In this paper, a novel design of laser monitoring and sound localization system is proposed. It utilizes laser to monitor and locate the position of the indoor conversation. In China most of the laser monitors no matter used in labor in an instrument uses photodiode or phototransistor as a detector at present. At the laser receivers of those facilities, light beams are adjusted to ensure that only part of the window in photodiodes or phototransistors received the beams. The reflection would deviate from its original path because of the vibration of the detected window, which would cause the changing of imaging spots in photodiode or phototransistor. However, such method is limited not only because it could bring in much stray light in receivers but also merely single output of photocurrent could be obtained. Therefore a new method based on quadrant detector is proposed. It utilizes the relation of the optical integral among quadrants to locate the position of imaging spots. This method could eliminate background disturbance and acquired two-dimensional spots vibrating data pacifically. The principle of this whole system could be described as follows. Collimated laser beams are reflected from vibrate-window caused by the vibration of sound source. Therefore reflected beams are modulated by vibration source. Such optical signals are collected by quadrant detectors and then are processed by photoelectric converters and corresponding circuits. Speech signals are eventually reconstructed. In addition, sound source localization is implemented by the means of detecting three different reflected light sources simultaneously. Indoor mathematical models based on the principle of Time Difference Of Arrival (TDOA) are established to calculate the twodimensional coordinate of sound source. Experiments showed that this system is able to monitor the indoor sound source beyond 15 meters with a high quality of speech reconstruction and to locate the sound source position accurately.

As human beings expand the research in unknown areas constantly, the deep space exploration has become a hot research topic all over the world. According to the long distance and large amount of information transmission characteristics of deep space exploration, the space laser communication is the preferred mode because it has the advantages of concentrated energy, good security, and large information capacity and interference immunity. In a variety of laser source, fibre-optical pulse laser has become an important communication source in deep space laser communication system because of its small size, light weight and large power. For fiber lasers, to solve the contradiction between the high repetition rate and the peak value power is an important scientific problem. General Q technology is difficult to obtain a shorter pulse widths, This paper presents a DFB semiconductor laser integrated with Electro-absorption modulator to realize the narrow pulse width, high repetition rate of the seed source, and then using a two-cascaded high gain fiber amplifier as amplification mean, to realize the fibre-optical pulse laser with pulse width 3ns, pulse frequency 200kHz and peak power 1kW. According to the space laser atmospheric transmission window, the wavelength selects for 1.06um. It is adopted that full fibre technology to make seed source and amplification, pumping source and amplification of free-space coupled into fiber-coupled way. It can overcome that fibre lasers are vulnerable to changes in external conditions such as vibration, temperature drift and other factors affect, improving long-term stability. The fiber lasers can be modulated by PPM mode, to realize high rate modulation, because of its peak power, high transmission rate, narrow pulse width, high frequency stability, all technical indexes meet the requirements of the exploration of deep space communication technology.

Build theory model of intensity scintilla characteristics of laser atmospheric transmission. Under the analysis of the model, focus on theory model simulation of effect model simulation of laser transmission characteristics. And simulation results show that: the laser scintilla caused by atmospheric turbulence increased with the transmission distance and turbulence intensity increased; The longer wavelengths of light intensity, the smaller intensity scintilla; The plane waves of laser scintilla is smaller than spherical wave and so on. Finally research of the laser transmission characteristics in the atmosphere is prospected.

We demonstrate a distributed feedback (DFB) random fiber laser based on Rayleigh scattering. Amplified spontaneous emission is produced by using a segment of erbium doped fiber (EDF) pumped by 980 nm laser diode (LD). An 50km-long single-mode fiber (SMF) and a fiber bragg grate (FBG) are used as random resonate cavity and wavelength output at 1550 nm is observed which can be amplified through the erbium-doped fiber amplifier. Evaluations on the spectral evolution and power development are also performed from the results obtained.

An ultra-narrow linewidth multiwavelength Brillouin fiber laser is demonstrated. Erbium-doped fiber amplifier with linear gain is not used in the structure to avoid the signal broaden. Multiwavelength output with identical interval and ultra-narrow linewidth will be obtained through the experiment. Because the whole system works with a simple structure, it can work stably and has a good application performance in the future. A one-way feedback multiwavelength Brillouin fiber laser structure has been designed. A 2x2 3dB coupler, a 8 km-long single-mode fiber (SMF), a distributed feedback(DFB) semiconductor laser and two optical circulators are included in the structure. A segment of 8 km-long single-mode fiber (SMF) between the two ports of a 2x2 3 dB coupler is used as Brillouin gain loop. A distributed feedback semiconductor laser works as the Brillouin pump (BP). Laser output and feedback are realized by two optical circulators. We adopt the Brillouin pump power at 80 mW. Seven Stokes signals can be observed excluding BP. The Brillouin frequency shift is 0.088 nm compares with the wavelength of BP. We have measured multiwavelength Brillouin fiber laser spectrum ten times in 50 minutes. The experiment result shows that the multiwavelength output of Brillouin fiber laser is very stable. The 3 dB linewidth of the output laser is 5 kHz measured by the frequency spectrum analyzer.

In order to reduce the impacts of atmospheric turbulence and background light etc. factors to atmospheric laser communication system performance, the atmospheric laser communication system using circular polarization modulation technology is adopted and researched. This system uses polarization shift keying modulation (PloSK), which is a new standard digital modulation technique in optical communication field. In this modulation, two rotation states of the circle polarization light (left handed and right handed) representation logic signal ' 0 ' and ' 1 ', are used to information loaded and data transmission. In the receiver, the modulation optical signal is detected with dual differential probe method. Under the OptiSystem system simulation environment, several direct detection system model based on OOK intensity modulation, single rode circular polarization modulation and circular polarization modulation with balanced detection is constructed, and compares and analysis of the various communication system performance. The results show that: at the same parameter conditions, bit error rate of CPolSK system with balanced detection lower about two orders of magnitude than the OOK system and single rode CPolSK system, the eye diagram and the waveform chart are also significantly better than OOK system’s. It can be seen, based on circular polarization shift keying (CPolSK) laser communication system with dual differential detection is superior on anti-interference of atmospheric interference, and reducing error rate, and will be easy to implement.

In this paper, we study influences of inherent optical properties (IOP) of seawater and parameters of laser pulse on characteristic of laser pulse after underwater propagation. Besides, achievable transmission distances under different conditions are simulated. Regard single pulse energy, initial duration and far field divergence angle of the transmitted laser pulse as inputs, and energy, temporal and spatial distribution on receive plane as outputs, underwater optical channel can be treated as a linear time invariant (LTI) system. The response of the underwater optical channel to the laser pulse with unit energy, far-field divergence angle of 0 and duration of 0 is impulse response. For different inputs, corresponding outputs are the convolution of the inputs and impulse response. Firstly, by using Monte Carlo method, the impulse responses of the underwater optical channel after transmission under a series of seawater performance conditions are studied. Through convolution, the influences of initial duration and far field divergence angle on temporal and spatial distribution are simulated. Simulation results show that influences of initial duration and far-field divergence angle of transmitted laser pulse are not obvious. And, the effects of IOP of seawater, such as absorption coefficient, scattering coefficient and asymmetry factor, on energy value, temporal and spatial distribution on receive plane are analyzed and compared. At last, according to proposed reasonable receive condition and detection threshold, achievable transmission distance of different parameters of laser pulse and different IOP of seawater are simulated. Simulation results show that, achievable transmission distance depends mostly on IOP of seawater, less on parameters of laser pulse. Simulation results provide a certain reference for underwater optical communication.

CMOS is a good candidate tracking detector for satellite optical communications systems with outstanding feature of sub-window for the development of APS (Active Pixel Sensor) technology. For inter-satellite optical communications it is critical to estimate the direction of incident laser beam precisely by measuring the centroid position of incident beam spot. The presence of detector noise results in measurement error, which degrades the tracking performance of systems. In this research, the measurement error of CMOS is derived taking consideration of detector noise. It is shown that the measurement error depends on pixel noise, size of the tracking sub-window (pixels number), intensity of incident laser beam, relative size of beam spot. The influences of these factors are analyzed by numerical simulation. We hope the results obtained in this research will be helpful in the design of CMOS detector satellite optical communications systems.

The roughness of sea surface affects the optical property of the exiting upward laser, which constrains the application of the LIDAR and Laser Communication in ocean. The paper designs one pool test to study the influence of sea-air interfaces and develops a corresponding geometric optical model. It analyzes the optical property of the upward laser through the sea-air interface systematic. Results show that the roughness of wavy sea surface will affect beam spreading, pointing and scintillation when transmitting through the boundary. Further, experiment results in one water tank with man-made wave show that the incident angle and divergence angle are very important to the upward laser on the real-time and statistics change. Selecting one appropriate incident angle and divergence angle will get one stabilized performance, which is useful to the laser practical application on the marine areas.

Study the laser pulses transmission time characteristics in discrete random medium using the Monte Carlo method. Firstly, the medium optical parameters have been given by OPAC software. Then, create a Monte Carlo model and Monte Carlo simulation of photon transport behavior of a large number of tracking, statistics obtain the photon average arrival time and average pulse broadening case, the calculation result with calculation results of two-frequency mutual coherence function are compared, the results are very consistent. Finally, medium impulse response function given by polynomial fitting method can be used to correct discrete random medium inter-symbol interference in optical communications and reduce the rate of system error.

This paper investigates the performances of 16×100Gbit/s return-to-zero differential quadrature phase shift keying (RZDQPSK) coded modulation signals in dense wavelength division multiplexing (DWDM) system and compares three different dispersion compensation fiber (DCF) methods. The performance has been evaluated by using Q value as the major parameter along with the variation of the input power for different channels with different dispersion compensation schemes. It is observed that symmetrical compensation of DCF is more excellent than pre-compensation and post-compensation methods. Corresponding to symmetrical compensation of DCF method, the maximum values of Q factor are 11.7026, 10.5128 and10.5138 for channel NO.1, channel NO.8, and channel NO.16, respectively. Meanwhile, the eye diagram shape of symmetrical compensation method is superior to the others.

By establishing the model of chemical laser cavity, the eigen mode of laser and the phase distribution of output beam have been simulated numerically, and the influence of inhomogeneous gain on phase characteristics of output beam has been discussed detailedly by analyzing the power spectral density of wavefront phase. The results show that the inhomogeneous gain of chemical laser gives rise to the phase distortion of output wavefront and the obvious increase of high-frequency phase in distortion wavefront; in addition, the degree of high-frequency phase distortion is influenced by the ratio of each component in gain mediums. Therefor, the key factor that resulting in the distortion of high-frequency phase is the inhomogeneous gain.

One key technology of laser active jamming effect is that the jamming laser is accurately controlled to reach laser seeker ahead of the target indicating laser. And it is sure that the jamming laser must be in the gate of laser seeker. In this paper, many factors are synthetically considered such as the gate of laser seeker, the jitter time of guiding laser, the jitter time of jamming laser, the optical path difference revising time of jamming laser and so on. And a probability model is put forward that the jamming laser reach laser seeker ahead of the target indicating laser. A simulating experiment is done, and the optimum ahead time range is gotten.

Space Laser communication is a new technology in recent years of optical communications, optical antenna is a communications front receiving system, compose of the optical antenna receiver, optical fiber coupling lenses. Optical antenna to receive as much as possible the signal light from the target of free space, In this paper, 10.6μm wavelength of infrared light for communication wave, we use spherical mirror and aspheric lens combination of the system, Design of large diameter concave mirror to collect more laser energy, After another spherical convex mirror reflection again to aspherical lens, then coupled into the fiber. The aspheric lens can be a good feature to correct aberration, so this design has less transmission loss and high coupling efficiency. Using Zemax software, we setting reasonable energy analysis and image quality evaluation, design spherical mirrors and aspherical refractive lenses optical system, has good optical performance and economy, can be apply on the atmospheric Laser communication the receiving device.

Most previous transmission characteristics analysis did not consider whole characteristic of the atmospheric-seawater channel and model of underwater optical power attenuation was applied only to the horizontal communication links. Optical power attenuation model in slant path is built based on seawater optical properties and idea of seawater stratification. Power attenuation of downlink is analyzed with simulation in the conditions of pure atmospheric and calm sea. The results show that, when communicating in the South China Sea and the receiver sensitivity is -55.3dBm, the communication distance can reach underwater 54.4m to 66.5 m.

The deployment of advanced hyperspectral imaging and other Earth sensing instruments onboard Earth observing satellites is driving the demand for high-data rate communications. Space laser communications technology offers the potential for significantly increasing in data return capability from space to Earth. Compared to the current state of the art radio frequency communications links, lasercom links operate at much higher carrier frequencies. The use of higher carrier frequencies implies a much smaller diffraction loss, which in turn, results in a much higher efficiency in delivering the signal energy. Optical communications meet the required data rates with small, low-mass, and low-power communications packages. The communications optical system assembly typically consists of a front aperture, reflection or refraction type telescope, with or without a solar rejection filter, aft optics, fine-pointing mirrors, and array detectors. Optical system used in space laser communications usually has long focal length, large aperture compared with common optical systems. So the reflective optical system is widely used. An unobstructed four-mirror anastigmatic telescope system was proposed, which was modified based on the theory about geometry optics of common-axis three-mirror systems. Intermediate image was between secondary and tertiary mirror. In order to fold the optical path, four-mirror was designed by adding the plane reflective mirror at intermediate image. The design was analyzed, then a system with effective aperture of 200mm and field of view of 1.0°x1.0° was designed, total length and magnification are 700mm and 20, respectively. The system has advantages of large magnification, relative short physical size and loose manufacturing tolerances.

The limited quantization digit of voltage and the effect of fringing field between adjacent electrodes (phased-array controlling units) limit the deflection efficiency when a Liquid-Crystal Phased Array (LCPA) is used for beam steering. In this paper, an optimization algorithm named pattern search is proposed to improve the diffraction efficiency. This algorithm directly optimizes the step phase slope to obtain high diffraction efficiency, rather than discussing the complex relationship between the diffraction efficiency and various influence factors. Besides, other optimization algorithms based on phase retrieval, such as GS, need the entire energy distribution; however, it is hard to obtain in practical. Our algorithm need only the energy of the target diffraction point and it can be easily realized. Firstly, we construct the model for beam steering, and point out that the deformation of the phase slope by influence factors is the reason why conventional method can not realize high diffraction efficiency. Secondly, we construct an optimization model for the issues and apply the pattern search algorithm to optimize the diffraction efficiency. The simulation results show high performance of our algorithm comparing with the conventional steering method. Finally, a set of beam steering experiments were performed with a one-dimensional LCPA being set both according to the un-optimized and the optimized recipe, and the results were in very good agreement with the theoretical predictions. We show that the deflection efficiency can be drastically improved.

With the development of optical fiber communications, especially the maturity of the optical amplifiers and the WDM technology, space optical communication at 1550 nm becomes a promising solution for future high speed satellite communication. Receiving technology with optical amplifiers and coupling space light into single mode fiber are key technologies in space optical communication at 1550 nm. Free-space-to-fiber coupling technique investigated in this paper is the first challenge of applying fiber communication techniques to free space optical communications. We analyzed the factors that affect the efficiency of free-space-to single-mode-fiber coupling based on mode-matching theory of electromagnetic fields. On this objective, in this paper, the theoretical analysis of the effect of atmospheric turbulence on the space light-single mode fiber coupling efficiency is discussed. On this basis, the short-distance experiment coupling space light into single mode fiber is carried out. 1. The main factors affecting the process coupling space light into single mode fiber are analyzed. This paper introduced the statistical theory of atmospheric turbulence and gave out the main turbulence parameters and meteyard based on the theory of the space light-single mode fiber coupling efficiency under ideal conditions. 2. The influence of atmospheric turbulence on the space light-single mode fiber coupling efficiency is analyzed and simulated. In the weak turbulence condition, mathematical model of the mean coupling efficiency and its fluctuation variance was given. And the fluctuation variance of coupling efficiency was simulated studied under the atmospheric conditions. The influences on the average coupling efficiency was theoretically studied, which were induced by the structure constant of atmospheric refractive index, the diameter of coupling lens and the single-mode fiber mode field radius. 3. Validating the theoretical model by a experiment under a short link coupling condition. The results of this paper lay the theoretical and experimental foundation for indeed establishing the efficient space light-single mode fiber coupling systems.

Space laser communication is researched by more and more countries. Space laser communication deserves to be researched. We can acquire higher transmission speed and better transmission quality between satellite and satellite, satellite and earth by setting up laser link. But in the space laser communication system，the reliability is under influences of many factors of atmosphere，detector noise, optical platform jitter and other factors. The intensity of the signal which is attenuated because of the long transmission distance is demanded to have higher intensity to acquire low BER. The channel code technology can enhance the anti-interference ability of the system. The theory of channel coding technology is that some redundancies is added to information codes. So it can make use of the checkout polynomial to correct errors at the sink port. It help the system to get low BER rate and coding gain. Reed-Solomon (RS) code is one of the channel code, and it is one kind of multi-ary BCH code, and it can correct both burst errors and random errors, and it is widely used in the error-control schemes. The new method of the RS encoder and interleaving based on the FPGA is proposed, aiming at satisfying the needs of the widely-used error control technology in the space laser communication field. An improved method for Finite Galois Field multiplier of encoding is proposed, and it is suitable for FPGA implementation. Comparison of the XOR gates cost between the optimization and original, the number of XOR gates is lessen more than 40% .Then give a new structure of interleaving by using the FPGA. By controlling the in-data stream and out-data stream of encoder, the asynchronous process of the whole frame is accomplished, while by using multi-level pipeline, the real-time transfer of the data is achieved. By controlling the read-address and write-address of the block RAM, the interleaving operation of the arbitrary depth is synchronously implemented. Compared with the normal method, it could reduce the complexity of the channel encoder and the hardware requirement effectively.

With the rapid development of modern science and technology in astronomical imaging, optical communications, optical radar, optical information processing, high-precision ranging, tracking, guidance, and remote sensing, light waves propagating in the medium, especially in the turbulent atmosphere spread more and more important. Atmospheric turbulence is one of the main factors which have influence on the performance of a laser communication system. Adaptive optics technology is an important means to solve the problem of atmospheric turbulence. This paper states how adaptive optics technique can be used in space laser communication system to compensate atmospheric turbulence when laser beam transmission through it. The core content of adaptive optics is correct laser beam wave-front disturbance in real-time，with it to enhance optical system imaging quality and the next aim is reach the level of diffraction limitation. Adaptive optics system consists of wave-front detection， wave-front control and wave-front correction . The demo platform including: atmospheric turbulence simulation unit、adaptive correction unit、signal transmitting and receiving unit. Liquid crystal spatial light modulator applications in adaptive optics system and the turbulence simulation system introduced. And used zernike polynomials method to produce atmospheric turbulence phase screen simulation analysis. Simulation results show that: in the low spatial frequency components, the atmospheric turbulence phase screen generated by Zernike polynomial method consistent with the theoretical values, but in the high spatial frequency components, the simulation results with large difference between the theoretical values. In addition, the simulation results also show that: we can change the distribution of turbulence in the atmospheric turbulence phase screen by increasing the Zernike polynomials of orders or change the receiving apertures, but to calculate the large calculate the complex and other shortcomings. If adaptive optics technique can be applied in space laser communication system and is proved by practice， must make a space laser communication system performance has greatly improved.

Compared with the edge emission laser, the vertical-cavity surface-emitting laser (VCSEL) with better beam quality can be performed more efficiently coupling with optical fiber. The 650nm~670nm wavelength VCSEL can be widely used in plastic optical fiber (POF) network source. This paper introduces a new kind VCSEL with new structure, of which the thermal characteristic is better than tradition device. In the special structure of the laser, the thickness of the substrate under the active region is lower, the heat generated by the laser can be faster transferred to the heat sink and the cooling effect is enhanced. In addition, the series resistance of the device is smaller and the heat produced by the device is further reduced. Through comparative test with the traditional VCSEL, the light output power of the device with new structure is increased by more than 20%.

Space laser communication is moving in a wider bandwidth, greater distances, is more accurate and more narrow laser communication beam direction, faster bandwidth as well as communication interface chip high-speed clock more demanding requirements of the low frequency noise, and good reliability, small size and low power consumption characteristics. Production of ADI's ADF4350 integrated voltage-controlled oscillator (VCO) bandwidth frequency synthesizer just to meet this requirement clock frequency This paper describes the basic principles and operating characteristics of the broadband frequency synthesizer. In this paper we use CPLD to control the ADF4350 and give a control electric circuit with CPLD structure and based on Verilog program. Simulation and experimental results show that the lock-in effect is good, easy to control, and reliable performance. It is able to generate stable clock, suitable for applications in laser communication.

In this paper, a real-time on-line performance evaluation processor based on graphic processing unit (GPU) for adaptive optics (AO) system is presented, aiming to monitor the 127-element AO system during its close-loop work by quantifying its correction results, which can provide reference to improve the performance of the system. Since there is a contradiction between the heavy computation burden and the real-time processing requirement, we modified operations and algorithms to fit the CPU-GPU heterogeneous environment, in which GPU is used to handle the complex computation but simple logicality, and CPU is assigned to undertake data transportation between internal storage and video memory，as well as some small-scale computations. In the real-time processor, performance parameters to be computed include peak-valley (PV) and root-mean-square (RMS) of near-field wavefront phase, point spread function (PSF), full width half maximum (FWHM) of far-field image，modulation transfer function (MTF) and Strehl ratio (SR). And the inputs are residual slopes obtained from Hartmann wavefront sensor of 127-element AO system. By computation 4096 frames of parameters, the average rate by single precision is 4.11ms/frame.

This paper gives the introduction about a new measuring device which is to measure th e atmospheric coherence length by using the differential movement principle.The system can observe the edge of the sun in the day time, and also observe planets at night. This system can measure the atmospheric coherence length in both horizontal and slant directions. The measurement in the day time requests the assistance of the attenuator and beacon beam of the atmospheric coherence length in the direction of the slant path.The working principle is the laser beam scattered by atmospheric turbulence through into the receiving optical system. Because the receiving system which is consists of two completely symmetrical telephoto optical system. Therefore，two optical channels in turbulence device are completely identical. After passing through the optical channels, the beam focusing is finished. By adjusting the optical system manually or automatically, two light point images can be formed on the photosensitive element of the CCD. Atmospheric turbulence can cause phase fluctuation of wave front. After aggregation by the receiving lens, The photosensitive element of CCD can collect the relative jitter of the two imaging optical centroid positions we require, and researchers can obtain relative changes from the two centroid positions by the calculations of computer software, as the result, the atmospheric coherence length is obtained. By means of the simulation of the optical system and the imaging quality optimization by Code V, researchers can rather achieve transfer function diagram, the circle of confusion value in different views and energy distribution. From above, researchers can examine whether the optical system is being qualified, or the method is leading to a better observation effect. At end of this dissertation, the limitations of this system will be analyzed, and the improvement methods and suggestions will be provided.

In order to analyze the effect of atmospheric turbulence along Earth-space path on the performance of laser communication system, the change of Kolmogorov spectrum with altitude is taken into account on the basis of the relation of turbulence structure constant with altitude. The scintillation index under the condition of the different coherent degree for optical source are discussed from weak to strong turbulence regime for a partially coherent Gaussian beam (PCB) propagating through turbulent atmosphere. The relation of the scintillation index with elevation is analyzed on Earth-space path. The expressions for the Log-normal and the Gamma-Gamma turbulence channel of irradiance fluctuations are given. The mathematical expression for the evaluation of the average capacity is shown for a Kolmogorov turbulent atmosphere channel. The average capacity of a PCB is calculated under the condition of different coherent length, aperture, on the horizontal and Earth-space path, respectively. The results of scintillation index show that the difference among plane, spherical, and beam wave are obvious from weak to moderate turbulence regime, at strong regime, the results tend to saturation. The degradation of optical source coherence causes scintillation depression at weak turbulence regime. At moderate regime, the scintillation is little increase. The effect of source partially coherence on scintillation is disappear at stronger regime. Based on the Log-normal model in weak turbulent fade channel and the Gamma-Gamma model from weak to strong turbulence fade channel, the average capacities for different initial Gaussian beam radius, partially coherent degree beam are estimated, respectively. The results show that at weak turbulence, the difference between the capacities by Log-normal and Gamma-Gamma distribution is small, and from moderate to strong regime, the difference is gradually increase. At weak regime, the average capacity of partially coherent beam is greater than the coherent beam. On the contrary, at stronger regime, the average capacity of coherent beam is slightly greater than the partially coherent. At saturation regime, the capacity is not improved by means of partially coherent optical source. Hence, it is shown that in weak turbulence, the suppression of scintillation index and the improvement of average capacity is effective by means of partially coherent source.

The liquid crystal beam steering technology with low driving voltage, high diffraction efficiency and without the effect of mechanical inertia，is regard as a potential technology in the field of non-mechanical beam steering. Liquid crystal spatial light modulator (LCSLM) can be applied as a beam steering control device in laser communication, and it can realize the programmable control in real time. And compared with fast steering mirror (FSM), which is widely used at present, LCSLM is smaller, lighter and lower power consumptive in a non-mechanical way, so it’s convenient to control. But the system bandwidth is a restricted problem in the research. In this article, the principle of beam steering with LCSLM is introduced firstly. A beam steering bench is set up using reflective pure-phase LCSLM from BNS. The offset of beam spot is detected by the CCD and a classic PI close-loop control experiment is designed to test the system bandwidth. And then the factors which restricted the control bandwidth are analyzed. Considering the effect of the CCD’ frame rate, the PSD with higher frame rate is used in the control system and the data model of the liquid crystal is tested. A controller is designed based on the data model and the bandwidth is improved observably.

Space laser communication and space quantum communication are all space optical communication, they are similar in communication links, high accuracy tracking and pointing, ground testing etc. The characters of space optical communication determine the necessity of testing and verifying communication terminals, for example, the laser beam reach diffraction limit in space laser communication, weak light detection or single photon detection should be carried out in space quantum communication, communication terminals are relatively moving refer to the ground station, and the terminals should have high quality in tracking target and pointing laser beam, so good system should be used in testing and verifying communication terminals. In this paper we did research on ground testing and verifying systems, we developed optical paths and two ground testing and verifying systems which are compatible with space laser communication and space quantum communication, the two systems contain one laboratory used system and one portable outfield used system. The laboratory used system mainly contains optical communication terminal, two dimensional (2D) simulation turntable, collimator and rear optical path, it can simulate the moving environment, transmission channel and relative motion of the satellite to ground or inter-satellite optical communication, it can also fully test the condition and performance of the optical communication terminals. The portable outfield used system mainly contains opto-mechanical subsystem, 2D turntable, electronic cabinet. The opto-mechanical subsystem is installed on the 2D turntable, it contains front and rear optical path. Electronic cabinet contains industry computer, turntable controller, GPS radio and optical controller, it mainly executes data acquisition, receiving and transmitting command. The portable outfield used system can be used in outfield, to help testing and verifying space-borne equipment. The design breaks through several difficulties, and improved the integrated degree of the system. Theory analysis and experiment shows the system can work properly.

The communication ways nowadays has highly developed, but because of its using limitation, the application is restricted, especially under the emergency situations. Using infrared laser non line of sight atmosphere scattering can solve the difficult problem effectively, and achieve the function of “minimizing communication support”. The article try to study the 1.06μm laser atmosphere scattering communication, first, we introduce the laser scattering communication technique and principle, and then describe the system composition and work route. In the way of building the laser atmosphere scattering communication system math model, the article analyze the relations between the laser receiving rate and the following elements: laser beam emission angle, receiving field vision, detector sensitivity, emission inclination angle, receiver inclination, atmosphere attenuation, laser launch rate, and communication distance. Based on the simulations, the field experiment showed, that the 1.06μm infrared laser signals transmission has the probability to achieve the long distance atmosphere scattering communication under certain atmosphere conditions.

We demonstrate the methods for increasing the observed squeezing level in the generation of squeezed states of light at 1064 nm with periodically poled KTiOPO4 (PPKTP) crystal. We analyze the technical limits to the reduction of noise in the squeezed quadrature theoretically, including the intra-cavity loss of the optical parametric amplifier (OPA) cavity, the normalized amplitude, the detection frequency, and the mode matching on the balanced homodyning stage. To observe a high degree of squeezing, we improve the quality of mode matching into the OPA cavity and the mode cleaning (MC) cavity experimentally. By optimizing mode matching of the light into cavities, the finesse of the cavities would be higher in practice and the desirable spatial mode can be realized. As the intensity noise of the laser light reach the shot noise limit above the frequency of 1 MHz, which is sufficient for our experiment, so the MC cavity is incorporated to filter higher-order transverse modes of the local oscillator (LO) beam for the balanced homodyne detection. The experimental and theoretical results show that it is essential to optimize the mode matching efficiency to generate and detect high degree of squeezing otherwise an inefficiency mode matching will throw away the squeezing and transform the squeezed field into a vacuum field.

Laser satellite communication has become especially attractive in recent years. However, because the laser beam is very narrow and there is a long distance between satellites, the laser communication channel is very sensitive to vibrations of the optical platform. These vibrations cause optical jitter, leading to the reduction of received signals and bit-error rate degradation. Consequently, optical jitter control with PAT (pointing acquisition and tracking) subsystems is a critical problem in laser satellite communication. To compensate for the platform vibration effectively in realtime, in this paper, an adaptive feedback control technique based on Youla-parameterization is presented, which can adapt to the current disturbance acting on the laser beam by adjusting its parameters in realtime to maintain optimal performance. The main idea is to use the well-known Youla parameterization formula to construct a feedback control scheme with the guaranteed closed loop stability, and the feedback controller is a function of plant coprime factors and a free parameter Q. For adaptive disturbance estimation, the free parameter Q is set to an adaptive finite impulse response (FIR) filter, the coefficients of which are updated by a recursive least-squares (RLS) algorithm in realtime. It is shown in experiment that the adaptive feedback control technique based on Youla-parameterization can reject the optical jitter caused by satellite platform vibration effectively and improve the performance of the system.

Electro-optical stabilization and tracking system is critical and difficult issue in satellite laser communication. Moreover, line-of-sight stabilized system is the kernel of implementing electro-optical stabilization and tracking system, which can be used to isolate the vibration of the moving platform of the satellite and the disturbance of the space environment. In this paper, we propose a new method, which using H∞ mix sensitivity based on generalized internal model controller (GIMC), to design the control system of the electro-optical stabilized platform. It is well known that there is an intrinsic conflict between performance and robustness in the standard feedback framework. Generalized internal model controller is a new architecture which can separate the performance and robustness design in controller design. This architecture has two parts: a high performance controller, say K₀,which is designed by PI controller in this paper, and then a robustification controller, say Q, which is designed to improve the ability of the anti disturbance by using H-infinity mix sensitivity controller design method. In this paper, we also present the steps of controller design by using this method to make it easier to use. Based on the proposed method, numerical simulation and experiment are both carried out for a gyro stabilized platform of electro-optical tacking system. Both the numerical simulated and the experimental results show that the electro-optical stabilized platform using the H-infinity mix sensitivity controller design method based on GIMC is accurate and effective. Comparing with the same PI controller in standard feedback framework, the proposed method can guarantee the high tracking performance as same as the PI controller and improve the external disturbance restraining ability a lot. In conclusion, H-infinity mix sensitivity controller design method based on GIMC is a new approach for gyro stabilized platform of electro-optical stabilization and tracking system and might be used easily in practical.

Cassegrain antenna is commonly used in Free Space Optic communication system. The double reflection structure determines the system has a shade problem. In this paper, the off-axis emission (semi-aperture lighting) method is applied to solve the shade problem caused by the secondary mirror. This method is simple both in structure an implement. ZEMAX software and Fourier optics are used to analyze the Cassegrain antenna theoretically. We can improve the performance of Cassegrain antenna under the guidance of the analytical results. Some experiment has been carried out. The results showed that the percentage of exit-pupil power effectively increased from 9% to 53%, the diameter of spot was not exceeding 200mm at the distance of 600m.It is significant for engineering applications.

A kind of portable atmosphere laser communication system based on fiber technology is designed by using Ethernet transceiver terminal and video-audio transceiver terminal with diode laser module and PIN diode, while a flexible connection is built between the terminal and the optical antenna connected by laser fiber. The application of EDFA technology, which realizes the amplification of the power of the 1550nm laser diode module, brings forth a more stable structure and easier deployment and testing in wild environment, and the communication distance can reach 2 kilometers with a transmission bandwidth of 100 MBit/s. Prototype experiments prove the good communication performance of this system.

The sight-axis alignment can be accomplished by the quick acquisition operation between two laser communication terminals, which is the premise of establishing a free-space optical communication link. Especially for the laser communication links of LEO (Low Earth Orbit)-Ground and LEO-GEO (Geostationary Earth Orbit), since the earth would break the transmission of laser and break the communication as well, so the effective time for each communication is very shot (several minutes~ dozens of minutes), as a result the communication terminals have to capture each other to rebuild the laser communication link. In the paper, on the basis of the analysis of the traditional methods, it presents a new idea that using the long beacon light instead of the circular beacon light; thereby the original of two-dimensional raster spiral scanning is replaced by one-dimensional scanning. This method will reduce the setup time and decrease the failure probability of acquisition for the LEO-GEO laser communication link. Firstly, the analysis of the external constraint conditions in the acquisition phase has been presented in this paper. Furthermore, the acquisition algorithm models have been established. The optimization analysis for the parameters of the acquisition unit has been carried out, and the ground validation experiments of the acquisition strategy have also been performed. The experiments and analysis show that compared with traditional capturing methods, the method presented in this article can make the capturing time be shortened by about 40%, and the failure probability of capturing be reduced by about 30%. So, the method is significant for the LEO-GEO laser communication link.

Quantum entanglement is the main resource to endow the field of quantum information processing with powers that exceed those of classical communication and computation. Due to low absorption and negligible nonbirefringent character in atmosphere, optical free space therefore serves as the most promising channel for large-scale quantum communication by use of satellites and ground stations. The acquisition, tracking and pointing (ATP) system is one of the most important parts of quantum experiment system, and it controls a transmitting and receiving laser beam within a few micro radians jitter because of using an extremely narrow beam divergence of several micro radians. This paper introduces the cascade ATP systems for 100km quantum entanglement distribution experiment among Charlie, Bob and Alice station. The specification and optical diagram of each ATP system are presented. The ATP system of Alice station is described in detail，it has coarse, fine and ultra-fine loop. In the 100km quantum entanglement distribution experiment, a tracking error of 4μrad is achieved for 70Hz bandwidth. The ATP strategy in this experiment can be used in the prospective satellite-to-ground quantum distribution.

For laser communication performance which carried by airplane or airship, due to high-speed platform movement, the air has two influences in platform and laser communication terminal window. The first influence is that aerodynamic effect causes the deformation of the optical window; the second one is that a shock wave and boundary layer would be generated. For subsonic within the aircraft, the boundary layer is the main influence. The presence of a boundary layer could change the air density and the temperature of the optical window, which causes the light deflection and received beam spot flicker. Ultimately, the energy hunting of the beam spot which reaches receiving side increases, so that the error rate increases. In this paper, aerodynamic theory is used in analyzing the influence of the optical window deformation due to high speed air. Aero-optics theory is used to analyze the influence of the boundary layer in laser communication link. Based on this, we focused on working on exploring in aerodynamic and aero-optical effect suppression method in the perspective of the optical window design. Based on planning experimental aircraft types and equipment installation location, we optimized the design parameters of the shape and thickness of the optical window, the shape and size of air-management kit. Finally, deformation of the optical window and air flow distribution were simulated by fluid simulation software in the different mach and different altitude fly condition. The simulation results showed that the optical window can inhibit the aerodynamic influence after optimization. In addition, the boundary layer is smoothed; the turbulence influence is reduced, which meets the requirements of the airborne laser communication.

We investigate the sensitivity of fiber amplifiers to radiations and present an approach to design radiation hardened rare-earth doped fiber amplifiers. This paper includes testing experiments on comparing the radiation responses (200krad electron irradiation) of fiber amplifiers made with same lengths of different rare-earth doped fibers. Simulation tools can also be used to improve the tolerance of the fiber amplifiers by helping identifying the best performance for operation in harsh environment, simulation analysis figured that fiber length of the amplifier should be optimized to reduce the radiation-induced losses around the signal wavelength that strongly impact the fiber response. By using this particular approach, fiber amplifiers with little insensitivity to radiations could be manufactured in the future.

The propagation characteristic of a Gaussian beam through turbulent atmosphere have been studied in the past several years. The main advantage of Gaussian beam wave model is that the infinite plant wave and a spherical wave are being included. Non-Kolmogorov spectrum can describe generalized turbulent atmosphere environment. The propagation properties of Gaussian beam propagating through the turbulent atmosphere described by non-Kolmogorov spectrum are studied on slant path. The scintillation index is analyzed with the Gaussian beam of different turbulent strength, zenith angle, φ , and the spectral exponent, α, of non-Kolmogorov, respectively. The effect of the turbulent structure constant on the ground on sicntillation is notable. The scintillation index reduces remarkably with zenith angle and structure parameter decrease. At weak turbulenc, scintillation index increases as spectral exponent decreases. The bit error rate (BER) of a Gaussian beam propagating in non-Kolmogorov atmospheric turbulence channel is estimated on Earth-space slant path. By comparing the effect of the spectral power with the structure constant on BER at moderate and strong turbulence, the effect of the spectral power change on BER is small. With turbulence weakening , at the order of 10^-15m^-2/3 , the relative effect of the spectral power on BER is gradually increase. Hence, at the small structure constant on the ground, or weak turbulence, the effect of the turbulent spectral power on BER is required to take into account.

In the space laser communication terminal with rotation-mirror, course- tracking system achieves APT (Alignment Pointing and Tracking) function by a two-axis rotation-mirror and reduces the weight and power dissipation of the system. Image rotation will be exist, if the photoelectric-detect unit is fixed and not rotate with rotation-mirror. Rotation of mirror will make revolution between coordinates of mirror and detector, in which mirror’s adjust-angle is not linear to detection-angle. In the paper, firstly math model of rotation-mirror course-tracking system for laser communication terminal based on the vector theory of optical reflection is established and deduces the adjust formulation of mirror tracking the beacon laser, figuring out relation between adjust-angle and detection-angle. As a result, the formulation is very complex and is not desired for system. To optimize computed efficiency, the relationship between rotation-mirror angle and the detector’s elevation and azimuth is analyzed in detail. The calculating formulation to eliminate image-rotation's affection is simplified, while the angle error of this method has been got. Analytical result shows the maximum calculating error is 3.9μrad, being satisfied with the need of course-tracking accuracy. The paper presents the adjust-angle formulation for the two-axis rotation mirror course-tracking system used for laser communication terminal, is useful for the design of tracking system.

With the highlights of the high transmission rate, large capacity, strong anti-interference and anti-capture ability, good security and small light, space laser communication becomes an important hotspot. At present, the focus of research of the laser communication system is point to point communication structure. However, from the application point of view, both the realization of space laser communication among multiple points and the establishment of the information transmission network can really have the practical value. Aiming at the problem of space laser communication network, this article puts forward the general idea about optical antenna to achieve multiple tracking goals at the same time. Through the analysis of the optical antenna, and the comparing of the current commonly used mirror driving mechanism, a new mirror driving mechanism is designed. The azimuth motion, containing circular grating feedback, is driven by torque motor，voice coil motor of fan produces pitch motion that has fan-shaped grating feedback, so that compression of the structure size to improve the efficiency of the reflector assembly. Through the establishment of the driving mechanism and the kinematic model of 3D entity, the relationship between the single drive azimuth and pitch angle following the angle of incident light is explained. The biggest ideal view area affecting the optical antenna is obtained by the simulation analysis of the kinematics model using MATLAB. The several factors of field overlap area and blind area offers a theoretical basis for structure optimization and control system for the subsequent optical antenna design.

A novel pulse modulation method is proposed to improve the data transmission rate and expand the applications of indoor visible light communication. In our communication system, Red, Green and Blue LEDs are used as the optical source. Combining with the simplicity of Space Shift Key and the energy efficiency of Pulse Position Modulation, we propose an optimized Space Pulse Position Modulation (SPPM) for the special optical source. Its fundamental purpose is to use Red Green and Blue LEDs to carry different data and then to transmit one of the colors as a pulse signal in each time slot. We introduce this method in realizing a high capacity and data rate wireless light communication system with the less average optical power. The experiment results show that Red, Green and Blue LEDs with the proposed SPPM has higher data transmission rate than that of White LED under the same optical power.

The purpose of this paper is to present a real time basis-deviation measurement system based on BB84 module. As BB84 module is the essential module in QKD receiver system, the basis-deviation measurement system can be directly implanted into the QKD receiver system to detect the polarization of photon current in real time during quantum key distribution. BB84 module distributes the incident photon current into four photon currents with the polarization of H (Horizontal), V (Vertical), + (+45°) and - (-45°). Their energies can be detected by four APD photon-detectors. Basis-deviation compute equation is deduced with the Stocks-vector of the optical devices path in BB84 module. The energies of the four distributed photon currents are collected in real time and then input to basis-deviation compute equation to calculate the basis-deviation. There is error bears on the effects produced by the optical elements in the BB84 module, so we built a set of software module to foundation the process of the real time polarization measurement system working. Thus we can see how all the parameters of the optical elements effects the calculation results. At last, we built a polarization photon current generator which can produce photon current with continuous changing polarization and a real time basis-deviation measurement system based on BB84 module in laboratory.

Based on the theory of optical wave propagation in the slant path and the ITU-R turbulence structure constant model which is dependent on altitude, the on-axis scintillation index of the flat-topped Gaussian beam at the receiver plane in slant path turbulence was given by using Kolmogorov atmospheric turbulence power spectrum model. The influences of the link altitudes, atmospheric refractive index structure constant C₀ at the ground，the source size and the beam order on scintillation index of the flat-topped Gaussian beam are discussed in detail. The result shows that the scintillation index increased first and then decreased with the increase of the beam order. The advantage of a flat-topped Gaussian beam over a single Gaussian beam is restricted to small source sizes, which is consistent with the case of the horizontal path. To find the average bit error rate under weak slant path turbulence, the log-normal distribution model of the intensity fluctuation was used. The influence of beam order and source size on BER was discussed. The result indicates that the smaller sized flat-topped Gaussian beam will bring average bit error rate advantage over the same size Gaussian beam. Our results correctly reduce to the result of the horizontal path with atmospheric structure constant fixed.

A multi-wavelength Erbium-doped fiber (EDF) laser based on four-wave-mixing is proposed and experimentally demonstrated. The 5km single mode fiber in the cavity enhances the four-wave-mixing to suppress the homogenous broadening of the erbium-doped fiber and get the stable multi-wavelength comb. The lasing stability is investigated. When the pump power is 300mW, the fiber laser has 5-lasing lines and the maximum fluctuation of the output power is about 3.18dB. At the same time, a laser with 110m high nonlinear fiber (HNFL) is demonstrated. When the pump power is 300mW, it has 7-lasing lines (above -30dBm) and the maximum fluctuation is 0.18dB.

A novel angular magnification method based on a telescope system is proposed in this paper to achieve liquid crystal optical phased array (LCOPA) wide-angle deflection. The optics transfer matrix of telescope is studied and the angle magnification effect is derived. The transformation formulas of a Gaussian beam through the telescope system are also derived by using the ABCD law. Simulation and experiment have been done to magnify the angle that deflected by a LCOPA. This method is feasible and convenient to obtain wide-angle steering for a LCOPA.

High-frequency laser will be able to enter the enemy laser signal processing systems without encoded identification and a copy. That makes it one of the research directions of new interference sources. In order to study the interference mechanism of high-frequency laser to laser guided weapons. According to the principle of high-frequency laser interference, a series of related theoretical models such as a semi-active laser seeker coded identification model, a time door model, multi-signal processing model and a interference signal modulation processing model are established. Then seeker interfere with effective 3σ criterion is proposed. Based on this, the study of the effect of multi-source interference and signal characteristics of the effect of high repetition frequency laser interference are key research. According to the simulation system testing, the results show that the multi-source interference and interference signal frequency modulation can effectively enhance the interference effect. While the interference effect of the interference signal amplitude modulation is not obvious. The research results will provide the evaluation of high-frequency laser interference effect and provide theoretical references for high-frequency laser interference system application.

Adaptive optics system can work with beacon produced by illumination the dim target with laser beam. But atmospheric turbulence distributed over the entire propagation path produces intensity scintillation of the illumination laser beam. The multi-beam illumination approach can improve the intensity uniformity by adding different intensity distributions produced by separate illumination beams passing through independent atmospheric paths. A 4 km horizontal propagation path was established to examine the illumination effect with multi-beam on the target. Individual laser beams were launched from a separate region of the transmitter telescope. The far-field irradiance profile was received by target-plane and recorded with a CCD camera operating in 1k Hz placed in front of the target-plane. The uniformity of target area was determined by the number of the illuminating beams and the turbulence strength. Data were recorded with 1, 3 or 6 incoherence lasers illumination and for a range of R0 parameter. We calculated the irradiance of a 8x8 cm² area in the target-plane to characterize uniformity of illumination. Results show a good reduction in intensity variance with number of illumination beams increasing and that the uniformity of illumination on target turns to worse when the atmosphere turbulence became worse. The back backscatter from the target-plane was received by another telescope nearby the transmitter side and imaged by a CCD camera. The images of the rough reflector showed that the image resolution and the illumination effects improved with the number of illuminating beams increasing.

With the developing of the space laser communication link, the performance index including higher transfer speed, extending transfer distance, and environmental adaptability, all ask the system accuracy and indexes improving. Special the developing near space platform, its environmental is extremes, the near space drone and other airplane flight speed is very quickly from the subsonic to supersonic. The aero optics effect caused by high speed will generate a thin turbulent air layer. It affects the performance of laser communication optical system by laser light vibration, deviation and so on, further more affects the performance of laser communication system working performance, even can’t communication. Therefore, for achieving optical system indexes, we need do more research in optical system near space aero optics environmental adaptability. In this paper, near space link environmental characteristic are researched. And on the base of the aero optics theory, computer simulating method is applied to analyze the relationship among the altitude, the flight speed and the image dispersion. The result shows that, the aero optics effect cannot be ignored when the terminal is in low altitude or is moving with supersonic speed. The effect must be taken into considered from overall design. The result will provide the basis of research design.

Using the extended Huygens-Fresnel principle and the altitude-dependent model of the ITU-R atmospheric turbulence structure constant model, we derive an expression for the intensity correlation function of a partially coherent beam wave through the slant turbulent medium. The result shows that as compared to Gaussian beam, intensity correlation of partially coherent beam wave is found smaller; with the inner-scale decreases, wavelength increases and turbulent strength increases, the intensity correlation tends to decrease.

With the wide application of laser beams in the atmosphere, such as optical communications, the propagation of high-power laser beams and laser ranging, the propagation of laser beams in turbulent atmosphere has been studied extensively for many years. The atmospheric turbulence severely influences the beam quality and therefore the efficiency of the technology. Up to now, there have been many studies in random effects on laser beams propagation through atmosphere. Typically, M² factor which is a very important parameter for characterizing the laser beam quality is widely investigated. In this paper, energy Strehl ratio was utilized to characterize the laser beam quality. The propagation of a collimated Gaussian beam through atmospheric paths was numerically simulated using phase screens by the FFT method. And the effects of various factors such as atmosphere turbulent parameter C²_n, the inner scale, the outer scale and meteorological parameters on energy Strehl ratio were analyzed by means of probability statistics. The results show that the mean of energy Strehl ratio decreases with the transmission distance increasing, and it is the same with strong refractive index fluctuation. However, the beam quality may be improved in shorter distance when energy Strehl ratio is larger than 1. The energy density of the laser beam after propagating through turbulent atmosphere in the radius of that in vacuum can be calculated by energy Strehl ratio. It may represent the accepting states of the laser beam in a short distance.