Coherent Optical Communication Homodyne Bpsk System Design

Free space optics (FSO) communication involves the use of modulated laser beams to send telecommunication information through free space or the atmosphere. FSO is recognized as a next-generation technique for meeting the ever-increasing needs for high data rate transfer. The advantage over equivalent RF systems in weight, power, and volume is prominent when applied to hybrid fiber and RF communications networks. In nearly three decades, FSO system experiments are widely conducted between variable platforms, such as satellites, vehicles, ships, airplanes, high altitude balloons, and optical ground stations, etc. The general goal of FSO R&Ds is to realize reliable communication links to establish a high-speed, RF-immune, transparent optical wireless networks, via airborne, spaceborne and terrestrial FSO backbones.As people had recognized that the advantages of the space optical communication such as high data rating, low power consumption, good security assurance, small size, less weight, anti-jamming etc. are so attractive, the application of the space optical communication became the research focus in communication field. Traditional FSO communication systems are based on the time-honored modulation/demodulation scheme called intensity modulation and direct detection(IM/DD). However, in recent years, integration of coherent technology into FSO communication systems has become popular due to several advantages it offers. The primary advantage is receiving sensitivity, an important property of a communication system. And now, there are many key technologies and problems which need to be solved in the space optical communication. Being the key technology, Optical Phase Locked Loop(OPLL) has become the focus.Free space optics communication is one of the most promising methods complement to optical fiber and RF Communication networks. Optical coherent receiver has prominent advantages in FSO system for its high sensitivity performance. Based on principles and mathematical models, key technologies of inter-satellites coherent optical communication systems are thoroughly analyzed, including optical modulation/demodulation schemes, spatial coherent methods, optical phase locked loops, and free-space-to-fiber coupling technology. The design and realization of OPLL are mainly discussed, and the impacts of line-of-sight pointing error on receiver performances, especially on optical homodyne detection, are discussed. Further more, the coherent system experiments are carried out on the module level. The system design philosophy and top-level specifications are presented, which founded the preliminary benchmark of inter-satellite optical coherent communication links. These results provide some benchmarks for FSO coherent communication system design in the potential applications to integrate FSO into transparent Optical Networks. The research indicates that high speed coherent optical systems are capable of application to satellite communication scenarios.