Blue-green Laser Submarine Communication Optical Channel Characteristics

The problem of Submarine Laser Communication is a hot issue in some countries which is so strong in submarine. Since the submarine was invented, every country has been trying to research new method suitable for Submarine Laser Communication. Therefore, it is imminent to develop the new Submarine Laser Communication system with higher data transfer rate and better crypticness. The blue-green Submarine Laser Communication system came to being under this background.Multiple scattering has influence on laser pulse transmission in the blue-green Submarine Laser Communication channel, which includes two aspects, in one hand, the signal power received by detector attenuates, in other hand, when the pulse carrying information arrivals at the receiver through scattering media, pulse will broaden in time. The later has affected the bandwidth and bit error rate of system severely and also has impact on Inter-Symbol and Inter-Code Interference. Thereby, the research on laser transmitting properties in channel is very important.To study this problem, be based on the studies of optical scattering channel, the channel is described as a multi-path in this dissertation. The optical channel models for airborne submarine laser communication are built and the received energy is discussed. In this propagation channel, sea has the most important impact on the power attenuation. Different water quality has affected the power attenuation differently.The multiple scattering characteristics of light propagation through clouds are described and the models of photo transferring in clouds are built. Based on the Mie scattering theory, the process of laser transferring through clouds is simulated by means of Monte Carlo, finally, the signal shape of the temporal broadening are studied. The results illustrate that it has a fast response at early times, followed by a long decaying tail, and the broadening shape is affected by some parameters such as asymmetry factor, clouds thickness, extinction coefficients, receiver field of view, typically, it is influenced strongly by asymmetry factor, clouds thickness.Applying the classical electron scattering theory to the photo scattering effects in the sea, the transmission delay of underwater laser pulse is investigated by small-angle approximation theory, caused by the scattering effects in the sea. To indicate the influences of the seawater properties on the transmission delay, some interrelated curves are displayed.The multi-path time spreading of signal pulse is studied. The waveform of received signals in receiver in submarine laser communication system is analyzed and simulated by use of Monte Carlo simulation. The results deduced by using Monte Carlo coincide with that simulated by using small-angle approximation theory.The study on Bit Error Rate caused by frequency selectivity decline support the practical theory for the system design. To improve the communication quality, it had better to adopt the frequency-domain filtering.Aiming at the practical communication system, conjunct with different factors, the simulation time broadening pulse is gained, which is closed to the practical environment, with certain innovation, has more effective guidance.The study methods and results in this dissertation provide the basic theory and experiment validation for improving performance of communication, detection and imaging under seawater.