A compact, flexible time-resolved single photon detection system based on an active quenched SPAD by FPGA tri-state...

We present a cost-effective, fully reconfigurable time-resolved single-photon detection system in which the active quenching circuit (AQC) is implemented using the tri-state gates of a field-programmable gate array (FTG-SPAD). By embedding the AQC within the FPGA, interfacing with discrete avalanche photodiodes (APDs), this design decouples the detector front end from the quenching and data processing circuits, enabling a rapid initialization of APDs into Geiger-mode single-photon detection. It has the advantages of firmware-level reconfigurability at fine temporal and spatial granularity, and flexibility to interchange APDs with different structures or operation wavelength for diverse applications. In addition to the quenching circuit, the FPGA back end implemented a time-to-digital converter (86.2 ps least significant bit), a 32-bit counter, and communication modules, forming a complete reconfigurable system for time-correlated single-photon counting. The FTG-SPAD with APDs of 23 µm diameter demonstrates a dark count rate of ∼12.2 cps at 3.2 V excess bias, a peak photon detection probability of 29.9% at 460 nm, and a single-photon time resolution of ∼234.6ps (FWHM) at 475 nm. These results verify that promising time-resolved single-photon detection can be achieved within this FPGA-based architecture, aiming to be a cost-effective, compact, flexible single-photon detection platform.