Research On Ultraviolet Communication System Based On Geiger Mode APD

Ultraviolet communication is a new communication mode,which uses ultraviolet light as carrier,atmosphere as channel,and light scattering in the air to realize information transmission.It has potential application prospects in the field of short-distance communication.Ultraviolet communication has the characteristics of high confidentiality,non-line-of-sight,strong anti-interference and electromagnetic silence.It can provide all-weather and all-round secure communication in a variety of complex environments.It has potential application prospects in information security field.Compared with other communication modes,ultraviolet communication has its unique performance and attracts much attention from domestic and foreign research institutions.Early ultraviolet communication mainly relied on gas discharge lamp,photomultiplier tube and other devices.It has many disadvantages,such as large volume,fragile,inconvenient to carry,and it is difficult to get practical application.With the development of semiconductor technology,ultraviolet light emitting diodes and ultraviolet avalanche photodiodes are gradually used as emission sources and reception detectors in ultraviolet communication.The detection circuit of the ultraviolet communication system based on APD mainly includes linear mode and Geiger mode.The former has low sensitivity and small system bandwidth,which makes it difficult to achieve long-distance and high-speed communication.Therefore,this paper studies the ultraviolet communication system based on Geiger mode APD,and tests the performance of detection circuit and communication system.(1)The active quenching circuit based on Geiger mode APD is designed and built,including passive quenching module,signal amplification module,pulse amplitude discrimination module,quenching signal and recovery signal generation module.Dead time is an important parameter of quenching circuit,which directly affects the counting upper limit and detection performance of the circuit.Dead time includes avalanche quenching time and voltage recovery time.In theory,quenching time and recovery time of active quenching circuit are determined by quenching signal pulse width t1 and recovery signal pulse width t2.However,experiments show that when the recovery signal pulse width t2 is small,the recovery time becomes longer,and is affected by APD port capacitance and resistance.In addition,a photon counting system is designed based on FPGA.The dark counting and photon counting under passive quenching circuit and active quenching circuit are tested.The effects of bias,dead time and irradiance on photon counting are studied and analyzed,which can provide reference for further improving the detection performance of SPAD Geiger mode circuit.(2)On the basis of Geiger mode circuit,the ultraviolet communication system is built,including the hardware and software design of each module of transmitter and receiver.The main function of the transmitter is to amplify the audio signal properly,generate digital signal through analog-to-digital conversion module,then reduce the data transmission rate by speech compression coding,then extract the effective data from the speech compression data by using FPGA and make simple modulation,finally output the ultraviolet light signal through the ultraviolet LED driver module.The main tasks of the receiver are similar to those of the transmitter,including photon detection module,optical signal restoration and demodulation module,decoding module,digital-to-analog conversion module and speaker driver module.The basic method of recovering the optical signal from the optical counting pulse is proposed in the experiment,and the ultraviolet voice communication is preliminarily realized.In addition,a bit error rate test system is designed by using FPGA and LabVIEW software,and the transmission performance of ultraviolet communication system is studied.