Fiber Coupled And Optically Preamplified Satellite-to-Ground Bidirectional Laser Communication Systems And Its Key Technologies

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 1550nm. In this dissertation, the technologies of space optical communication systems with optical amplified receivers, including the aspects of coupling space light into single mode fiber, characteristics of fading channel and anti-fading technologies are studied.Coupling space light into single mode fiber is a key technology in optically preamplified space optical communication systems. Based on matrix optics method, a model for coupling free space light into single mode fiber is established. The influences of fiber assembing misalignments,aberration of optical systems,material dispersion of lens,pointing error and atmospheric turbulence on coupling efficiency are analyzed. Active coupling experiments are also demonstrated by using of fiber nutation tracking techniques. Turbulence-induced fading of coupled optical power is investgated by simulating distorted optical wave-front, and the coupling performance with adaptive optics is alse analyzed. For angle-tracked coupling systems, an gaussian template matching tracking algorithm is proposed to reduce signal fading depth in the situation of strong turbulence.The influence of pointing error on communication performance is analyzed in fiber coupled and optically preamplified space optical communication systems. Considering the pointing errors of transmitter and receiver, a model for optimizing optically preamplified satellite optical communication systems are established according to average bit error rate or burst error rate, and the optimal antenna parameters are given.Anti-fading technologies are studied in satellite-to-ground optical downlink. The parameter of distance between sub-apertures is introduced in multi-aperture receiver, and a distributed multi-aperture receiver array is proposed to reduce the fading induced by pointing error of transmitter. The performance of distributed multi-aperture optically preamplified receiver array is analyzed. Signal combining methods are also studied. When the actual rms pointing error is larger than the optimal designed value in traditional centralized array, the signal fading depth can be reduced greatly by changing the traditional centralized array into distributed array.Characteristics of fading channel for ground-to-satellite optical uplink is studied based on numerical simulation and beam wander scintillation mechanism. The influence of anisoplanatism error due to point-ahead angle is also analyzed. For multiple-beam uplink, because of the strong spatial correlation of turbulence-induced wave-front tilt, beam wander of sub-beam is strong correlative, the influence of this correlation on the anti-fading performance of multiple-beam uplink is analyzed.