Research On APD Based Underwater Optical Communications With Blue-Green Light

With the development of ocean exploitation,the demand of underwater communication technology has been put forward with high standard.Therefore,the research of low cost and high performance underwater blue-green light communication equipment is of great significance.In this paper,an underwater blue-green light communication system is designed and implemented on the basis of analyzing the propagation loss of the channel and simulating the link model of underwater optical communication.The main work is as follows.(1)Transmitter design:One circuit is designed to realize high speed and high power modulation of blue-green laser,and achieves the output optical power of 62m W and 68m W respectively for the green and blue laser.In addition,another circuit is designed by thermistor and semiconductor cooler to control the temperature at the transmitter.(2)Receiver design:As the large photosensitive surface APD is adopted to increase the robustness of the system,a photoelectric conversion circuit consisting of APD and TIA is designed,with a posterior amplification,which can further improve the gain.The sensitivity of the system receiver is up to-36d Bm.A negative bias circuit with temperature compensation is designed to ensure the stability of APD output gain.(3)System implementation and experiment:A whole duplex communication system is implemented,including a FPGA as data processing platform.The system is tested in three different environments,dark box environment,indoor environment and underwater environment.Dual-band devices of the system achieved stable full-duplex communication with a rate of 50Mbps at a distance of more than 30 meters underwater.Experiments show that the transmitter is characteristic of high speed and high power,and the receiver has the characteristics of high sensitivity and high bandwidth.The system can realize underwater medium and long distance communication.Within the scope of effective communication distance,the full-duplex communication system can achieve a rate of 50Mbps,with the error rate lower 10^-13.When distance limit is reached,the bit error rate will increase rapidly with the increase of the distance.