Research On The Modulation Technology Of Underwater Wireless Optical Communication For Deep Sea Applications

Underwater wireless optical communication has become a research hotspot for underwater wireless communication in recent years,due to its advantages and potential applications such as high transmission rate,flexible mobility,and better confidentiality.In particular,this communication method is very suitable for use in the dark and clean water of the deep sea.Therefore,in this thesis,according to the characteristics of the deep-sea environment and the communication needs of high-capacity short and medium-distance transmission,research is carried out on the blue-green light signal modulation problem faced by deep-sea optical communication.The following work was mainly accomplished.The modulation technology route of deep-sea wireless optical communication is designed.Firstly,the principle and symbol structure of OOK,PPM,and DPIM modulation is analyzed and simulated for comparison.The results show that OOK modulation has the advantages of simple implementation,small required bandwidth,large transmission capacity,and strong antiinterference capability,and it is more suitable for application in the deep sea.Then,based on summarizing the luminescence principles of light-emitting diodes,semiconductor lasers,and super-radiant laser diodes,the technical route of directly modulating light-emitting diodes and laser diodes to generate communication optical signals is determined.Based on the LED array with the central wavelength of 478 nm,the blue-green light signal modulation technology research has been carried out.The OOK modulation which is adaptable to the deep sea is adopted as the communication modulation format,and the modulation circuit of underwater wireless optical communication is designed with the direct modulation method.Then the modulation characteristics of the blue LED circuit were tested,and the highest modulation rate of the circuit was measured up to 26 Mbps.The output radiation flux of LED was measured by integrating sphere,and the emitted light power was 1.13 W at the modulation rate of 20 Mbps.Finally,a communication experiment system was built based on blue LED modulation circuit,and the demonstration and verification of video transmission service were carried out in air and water medium respectively.The LD with the central wavelength of 450 nm is used as the communication light source,and the blue light LD modulation circuit is developed by OOK modulation format and direct modulation method,and the highest modulation rate can reach more than 100 Mbps.And the test results show that the emitted optical power is 10.8m W at the modulation rate of 50 Mbps.Based on this modulation circuit,video transmission service is demonstrated and verified in air and water respectively.