The Key Technology Of Optical Communication Research Based On Ultraviolet Laser

Ultraviolet (UV) communication is a new kind of communication, in order toreduce the impact of the background noise, the communication system select thewavelength range from200nm to280nm as its wave band. UV communication hasmany advantages such as flexibility、good concealment、good secrecy and stronganti-interference ability.This paper analyze the influence of the absorption、Rayleigh scattering、Miescattering toward UV communication. It also analyze LOS and NLOS model of UVcommunication system. It analyze the overall framework of UV communicationsystem, including the choice of the UV light source、photoelectric detector、modulatorand demodulator and coding and decoding.The system using modified2FSK modulation method, with adjustable duty ratiosquare wave as carrier signal, can drive the laser more stable and load the signal toachieve data transmission. At the receiving, the UV communication system demodulateby using pulse counting detection method. In order to reduce the error rate, channelcoding use cyclic redundancy check coding, which is able to achieve feedbackretransmission error correction. The modulation and demodulation、 coding anddecoding achieved by programming with Verilog HDL language andQuartusⅡ software in hardware platform of FPGA.The process of the whole communication system is: At the transmitting terminal,data is sampled、coding and modulation processing that access on TTL level of theinput which is outside the laser. At the receiving terminal, the photomultiplier detectthe transmitted photon, after processing I-V switching circuit and Voltageamplification circuit,it is converted to high and low level, the voltage signal that canmatch sampling requirement.then, after sampling、demodulation and decoding,it issend to the PC serial port to complete data communication.This paper constructs UV communication prototype, and test for many times. Itcompares simplex data communication within2m indoor with half duplex which hasthe CRC error correction function. The latter can reduce error rate well. After testingmany times we find that, when the transmission rate is600bit/s and1200bit/s, the errorrate is below E-6. When the transmission rate reaches2400bit/s,the error rate is below2E-6,at the same time, the system also change error data with special characters to display, and can locate and analyze the error data,which can reduce the influence oferror data to the use of transmit data. The system also completes simplex datacommunication outdoor in different distance, the transmission rate is600bit/s.Itanalyzes the error rate. The system laid a good foundation for the practical applicationof high rate of UV communication system.