A Study Of Dual-channel SPAD Single-photon Detector Based On Lens Coupling

Single Photon Avalanche Diode(SPAD)is widely used in quantum information,laser radar,spectrum detection,biophotonics and other fields because of its single photon detection sensitivity and picosecond time resolution.However,due to the thermal excitation effect,SPAD with larger photosensitive area is usually accompanied by higher dark counting phenomenon,which restricts its limit detection ability and seriously affects its application in the field of single photon detection.Therefore,it is of great significance to develop SPAD single photon detector with large photosensitive area and low dark counting level(i.e.high limit detection capability).Based on the optical coupling technology and free photon counting technology,this paper develops a lens-coupled dual-channel SPAD single photon detector with high detection limit,which lays a foundation for the application of two-photon coincidence measurement and multi-channel weak light detection in the future.The specific work is as follows:(1)Aiming at the shortage of SPAD photosensitive area,two different coupling modes,lens coupling and multimode fiber coupling,are designed,which can realize the focusing of large area incident spot into small area SPAD active area.In view of the simulation of Light Tools optical software,the energy utilization and uniformity of the two coupling modes under different light sources are analyzed.The results show that,in the case of an ideal parallel light source,the linear distribution of the light spot in a large area can be obtained by using the lens coupling system,which has high energy utilization and uniformity,and is conducive to focusing the incident light spot in a large area into the SPAD active area in a small area.Therefore,the SPAD single photon detector can obtain a larger photosensitive area through front-end coupling.(2)Based on the principle and performance parameters of SPAD single photon detector,combined with simulation,the design of single/double channel free photon counting circuit is completed,including high voltage power supply circuit,passive quenching circuit,signal amplification circuit,pulse discrimination shaping circuit and FPGA photon counting circuit.And the single/double channel free photon counting circuit was developed according to SAP500 S SPAD,OPA5657 amplifier chip and TLV3501 comparator chip.(3)A lens coupling dual-channel SPAD single photon detector is developed on the basis of lens coupling and free photon counting circuit and a corresponding test platform was built to characterize its characteristics.The experimental results show that the developed lens-coupled dual-channel SPAD single-photon detector has good dual-channel independent counting ability,and compared with SAP500 S SPAD,its weak light detection limit is increased by nearly 30 times,the dynamic range is 42 d B,the working period is 100 ns,and the time resolution is only 38.9 ps,which has a great application prospect in the fields of two-photon entangled state detection and future multi-channel spectrum detection.