Geiger Mode Ultraviolet Counting System Based On Avalanche Photodiode

Communication plays a vital role in modern society,especially in military aspect,which requires higher adaptability and can be used in more complex environment.The solar blind ultraviolet light has a relatively clean background near the surface,as a result,the UV communication system based on solar blind ultraviolet has high signal to noise ratio.Because of the scattering and absorption of ultraviolet light,the communication will be greatly restricted.Therefore,the ultraviolet counting system based on geiger mode is of great importance.With high gain and counting,the weak light can be effectively detected and quantitative analysis is carried out to reach the level of single photon detection,thus reducing limit of communication distance.A high voltage bias power supply with low ripple,which can be adjusted by a potentiometer,is designed in the experiment.The power supply of the chip is designed by DC-DC power supply and LDO.At the same time,an active quenching and fast recovery circuit is designed for quenching time sequence and strictly independent recovery time sequence.Under the illumination of ultraviolet LED,the ultraviolet counting system is used to count,besides,the result is analyzed,which provides data reference for the development of Geiger mode ultraviolet communication system.In this paper,the UV light source is designed first,visible blind 365nm ultraviolet LED is used.In this project,we need to simulate the scene of single photon source,so the light source needs to be weakened.When the distance of single photon avalanche photodiode?SPAD?and LED is 400mm,by an attenuation of filter with 1570 times,the irradiance of visible blind 365nm ultraviolet LED can achieve 0.6 nW/cm².Next is the power of this project.It includes the adjustable high voltage bias power of 250V,which provides high voltage bias for SPAD,the power ripple is less than19.5mV,the ripple coefficient is 10^-5;the DC-DC power supply for the chip is less than 10mV;the LDO for the delay device,the ripple less than 9 mV.The smaller ripple can keep the potential stable,especially for SPAD,the tiny potential fluctuation causes the drastic change of counting.The following is the design of the active quenching and fast recovery circuit,which is mainly characterized by two feedback of quenching signal and recovery signal,controlling the bias voltage of the avalanche photodiode at both ends respectively.The two feedback signals are required to be completely independent on the time series,and the recovery signal is not available during the quenching period,and the delay module is not available.The existence of the two feedback signals can completely isolate the rising and falling edges of the feedback signals.Active fast recovery circuit can effectively control the voltage at both ends of SPAD,thereby protecting SPAD and improving the counting rate.Finally is the building of the experimental platform and the counting module.In this experiment,a test platform is set up for the designed circuit.The background noise is shielded by the dark box.Under the condition of no light,the number of ultraviolet SPAD counts for reference is tested.In the case of ultraviolet light,the quenching time,recovery time and photon count of the active recovery circuit are tested.The dead time of passive Geiger mode was tested at the beginning of the test.In this project,the dead time in the passive Geiger mode circuit is about 1?s,the counting upper limit is 1MHz,the dead time of the active recovery circuit is 100.2ns,and the counting upper limit is raised to 10MHz.The single chip microcomputer is used to count at the fixed interval and upload the data to the serial port.Under the condition of0.6 nW/cm² with the reverse bias voltage of 211.5V,the photon counts can be the resolution of 10⁵ level.At the same time,by changing the angle of LED emission and counting the photon counts,we explored the relationship between optical counts and angles,which provided a theoretical preparation for increasing the communication distance.