Research On Modulation Technology Of PL450B Laser For Underwater Laser Communication

As an important strategic space for human sustainable development,the ocean not only provides sufficient natural gas,oil and other material energy for human life,but also an important strategic commanding point in the military development of the world recently,and is a strategic strategy for demonstrating national power and strategic place to maintain national security.In order to achieve marine environmental monitoring and deep sea exploration in military use,underwater high-resolution imaging systems,ocean-aware networks,and autonomous underwater submersible?AUV?are continuously updated,and at the mean time,the real-time communication and large-capacity data transmit between underwater terminal devices are realized.The transmission has gradually become a research hotspot for human exploration of the ocean.Underwater laser communication,with its advantages of high transmission rate,small delay,small size,low power consumption,good confidentiality and strong anti-disturbance ability,has gradually become the main way to solve the problem of underwater large-capacity data transmission.In view of that the underwater communication need of long distance and large-capacity data transmission,this paper has carry out an analysis on the characteristics of optical transmission underwater,the principle of laser modulation,the light source and the performance analysis of optical modulating technology.First,study the optical properties of three types of water quality and their effects on optical communication systems,from the loss factor,the pulse broadening,the background noise,and accomplish the optical power budget of underwater optical communication link.Through the analysis of the laser direct modulation,set up the model for the small signal and the big signal of the semiconductor laser,and design the modulation system.And according to the channel characteristics of underwater optical communication,this paper analysis the symbol structures of several common modulations bandwidth requirements,peak power,error characteristics and other technical properties of choosing switching keying?OOK?modulation with better channel adaptability and pulse amplitude?PAM?modulation with better bandwidth utilization.Design the laser direct modulation system of PL450B for underwater optical communication,design the temperature automatic control circuit of PL450B laser to restrain the change of wavelength and power caused by temperature drift;design the PL450B laser power automatic control circuit to prevent power decline caused by device aging.Finally,experimental platform is built to test the function of the underwater optical communication system.Based on the analysis of classic triode common emitter single-ended drive methods,proposed the method of differential drive for ECL circuit structure,achieved high power,high speed drive,through the experiment measure the communication bandwidth is reach to40MHz,laser emit power reach to 81.5mW,the bit error is less than 10^-6 and through the video transmission,experiment,verified the system has capability of transmitting high speed stably transmission.By the calculation of the maximum communication distance,equivalent the maximum communication distance can reach to 60m.