Research On Single Photon Avalanche Photodiode Calibration System

The single photon avalanche photodiode is the core device of the receiver detector of quantum private communication,and its performance is very important to the effect of quantum private communication.At present,there are few studies on SPAD performance calibration equipment specifically for single-photon detector applications.Therefore,this paper has developed a SPAD calibration system.The system adopts an integrated design.It integrates SPAD working environment configuration,avalanche signal identification and extraction,and performance parameter calculation and calibration in a test host,which greatly improves the calibration efficiency and accuracy of SPAD.This paper fully analyzes the working characteristics and the key performance parameters of SPAD single photon avalanche photodiodes.Based on the test volume concerned by the calibration system,a design scheme for SPAD calibration system is developed.The system uses a high-precision DAC chip to achieve the precise setting of the reverse bias voltage.A constant current source compensation scheme is proposed to monitor weak bias current changes.Through the design of avalanche signal discrimination extraction,pulse stretching,level conversion,etc.the problems of small amplitude and large jitter of the avalanche pulse signal generated by SPAD are overcome.In addition,according to the actual calibration needs,an FPGA-based system signal processing flow is designed.The light source driving signals,gated signals,and coincident gate signals are generated.The avalanche signals and gate signals are adjusted through the gated differential signal scanning and delayed scanning functions.Control the relative delay position of the coincidence gate signal,extract the statistical information at the maximum value of the avalanche pulse count,and use the double coincidence gate count method to effectively separate the SPAD light count,dark count,and post pulse count,and finally calculate the performance of the collected data Calibration results.The experimental results prove that the SPAD calibration system design scheme can accurately calibrate the performance parameters such as SPAD's detection efficiency,post-pulse,dark count,optimal working voltage,and bias current.