HF532 Laser In Underwater Optical Communication Research On DPIM Modulation Technology

There are abundant resources in the ocean,and it is a natural barrier to ensure the invisibility of underwater navigation.In the commercial field,we hope to explore the ocean further,fully develop and make use of the seabed resources;in the military field,the future underwater operations require that submarines should cooperate well with land,sea and air systems,both of which make greater demands for underwater wireless communication technology.The traditional underwater radio communication technology and underwater acoustic communication technology have some shortcomings,such as low transmission rate and limited communication bandwidth.Instead,the underwater wireless optical communication technology has the advantages of high communication rate,wide frequency bandwidth and good confidentiality,which attracts the attention of researchers all over the world.Diode Pumped Solid State Laser(DPSS)has the characteristics of high peak power,good beam quality,high conversion efficiency and narrow line width.Therefore,based on the analysis of sea water channel,the DPIM modulation technology of semiconductor pumped solid-state laser HF532 is studied in this paper.The principle of DPIM modulation is analyzed and compared with OOK and PPM modulation.It is concluded that DPIM modulation technology has high power utilization,high bandwidth utilization and strong anti-interference,and it does not need symbol synchronization.The influence of DPIM modulation technology on the modulation performance of HF532 laser is studied particularly.The protection period,laser pulse width and modulation bits in DPIM information frame are analyzed.The DPIM modulation system scheme with FPGA as the control core and the electro-optic Q-switching driving circuit are proposed.Finally,the hardware test of DPIM modulation system is carried out.The results of the test shows that the system can realize DPIM modulation pulse with a pulse width of 3 ns,which meets the requirements of practical application of HF532 laser with a pulse width of 2-3 ns and a repetition frequency of 70 kHz-100 kHz.