Research On Ultraviolet Communication Modulation And Detection Technology Based On Low Pressure Mercury Lamp

Ultraviolet communication is a new type of communication mode,which is more secure than traditional communication mode,more resistant to third-party interference,and does not occupy radio frequency band resources.It has been rapidly favored by many scientific researchers.However,as many different communication needs are proposed,the disadvantages of ultraviolet laser such as large volume and weight,portability and low power of ultraviolet LED are also exposed,which lead to the limitation of related applications.First of all,aiming at the low transmission rate of low-voltage mercury lamp modulated by2 FSK in solar-blind ultraviolet communication,this paper proposes a scheme of modulating low-voltage mercury lamp by multi-band frequency shift keying(MFSK).The detector uses ultraviolet enhanced APD.A multi-system modulation system based on low-voltage mercury lamp is designed.Compared with the binary frequency shift keying modulation,the transmission rate of low-voltage mercury lamp is doubled.To solve the problem of low responsiveness of direct detection of solar-blind ultraviolet light,a scheme of receiving ultraviolet light communication based on wavelength down-conversion of fluorescent materials is proposed.Fluorescent materials absorb 280 nm photons and generate fluorescence emission at 500-650 nm,thus realizing visible detection of solar-blind band.The main research contents are as follows:Firstly,the scattering,absorption and atmospheric turbulence of ultraviolet light in the transmission process are analyzed.MODTRAN is used to simulate and analyze the transmittance of ultraviolet light in several common weather conditions.Secondly,the key components of the system transceiver are analyzed and compared,and the low-voltage mercury lamp is chosen as the light source,which can ensure the light power of the light source to Watt level.In view of the low transmission rate of the low-voltage mercury lamp,a4 FSK modulation mode is proposed,and the detection terminal uses APD to detect.Then,the transmission modulation terminal circuit is analyzed and designed,and the 4FSK modulation is completed by using half-bridge driver chip and half-bridge resonant switch circuit.At the receiving end,the demodulation is carried out by using FPGA,and the tail processing module is added to ensure the accuracy of demodulation.Finally,the maximum data transmission rate of the system can reach 30 kbit/s,which is higher than the current reports.Finally,aiming at the low responsiveness of direct detection solar-blind ultraviolet detectors,ascheme is proposed to improve the responsiveness of detectors by utilizing the characteristics of detectors that have higher responsiveness to visible light than solar-blind ultraviolet light and using fluorescent down-conversion materials to convert solar-blind ultraviolet light into visible light.Considering the radiation wavelength and fluorescence lifetime,three kinds of fluorescence down-conversion materials were selected and tested from the angles of detection response voltage,response current and response gain bandwidth.The results show that this scheme can improve the response of the detector to varying degrees,up to 2.7 times.