Space Coherent Laser Data Transmission System And Multi-order Correction

With the development of spacecraft payloads, including optical and microwave remote sensing, electronic reconnaissance, space data transmission technology gives higher requirements in bandwidth and transmission rate.In the near future, high speed data transmission systems will use laser as an important data transmission carrier. Intensity modulation/direct detection of on-board laser data transmission system has been achieved, the phase modulation/homodyne detection of coherent laser data transmission system with advantages of high sensitivity, high-capacity, long distance and small-caliber, will become the advanced means of high-speed data transmission systems.Satellite coherent laser data transmission is a new subject, for the main reasons that link distribution and communication terminal design in the system level and coherence efficiency optimization of signal light and local oscillator light in the key technical level are all problems of space coherent laser system.This dissertation focuses on theoretical and experimental research of high-speed data transmission link which is applied to in-orbits or satellite-to-ground laser communication. Aimed at system design, subsystems and key technology decomposition, efficiency of optical coherence, theory of principles and methods of signal light multi-stage wave-front correction conducted a comprehensive study.Traditional space optical transmission link equation was supplemented and expanded to fit coherent and incoherent system, inter-satellite and satellite-ground links, which can be applied to coherent laser data transmission system with precision optical tracking, optical phase-locked loop and adaptive receiver. Combining with existing domestic laser communication terminal, successfully completed the experiments on first, second and higher-order wave-front mismatch correction which are essential in coherent laser data communication system. This provides a theoretical basis for the development of coherent laser data transmission system.Considering inter-satellite and satellite-to-ground high speed coherent laser transmission system as main research object, proposed system design scheme, completed key techniques decomposition. Coherent laser data transmission terminal generally has the acquisition, tracking, pointing subsystem and modem subsystems, according to the classical equation of space data link transmission power, proposed preliminary assumption, general idea and main design parameters of inter-satellite and satellite-to-ground system.The efficiency of optical coherence is a decisive condition of high sensitivity receiver. From the light field match theory, aiming at dynamic pointing error characteristics of space laser link, made an innovative and exploratory research on wave-front matching, efficiency of optical coherence and multi-stage optical wave-front mismatch correction. Mainly studies low order wave-front mismatch problem of signal light and local oscillator light, it is core issues to maximize the efficiency of light BPSK modulation/homodyne demodulation inter-satellite laser data transmission system. Wave-front mismatch impacts on coherent efficiency, thereby affects transmission performance of communication link characterized by bit error rate. After brief analysis of the general factors affecting coherent efficiency, put forward by Zernike polynomials to describe the wave-front mismatch of coherent laser communication system, and to define the low and the higher-order wave-front mismatch with Zernike polynomials.Directly affecting the performance of space laser data transmission link, optical coherence efficiency factor must be combined with coherent efficiency to revise and promote the classic link equations of long-distance space laser communications. From the ideal formula performance of BER, put OPLL random error, random optical axis pointing error of the antenna and the zero-order, first-order efficiency of coherent wave-front mismatch into classic link equation and research mathematical models of the zero-order and first order wave-front mismatch efficiency, coherent efficiency and BER of links.By experimental means, the feasibility of using the fast tracking technology of typical ATP to correct overall wave-front tilt was verified and the results agree well with theoretical simulation. It shows that in the coherent laser transmission system interfered by atmosphere, the technology of adaptive wave-front correction is the most suitable application in engineering to realize signal light match with local oscillator light. When inter-satellite and satellite-to-ground high speed data transmission links are closed, the state of channel wave-front corrector is different from conventional adaptive optics applied in astronomical imaging system. It can not only eliminate additional items of optical transmission caused by the atmosphere, but also adjust two coherent beams to a good wave-front matching state.