A simple and flexible FPGA based autocorrelator for afterpulse characterization of single-photon detectors

Single Photon Avalanche Diodes (SPADs) are widely employed for photon counting and timing in a variety of scientific and industrial applications. However they are affected by the afterpulsing effect, which can significantly increase the effective dark count rate of the detector. Being correlated with previous photon pulses, afterpulses can cause sharp distortions in photon correlation experiments. In this paper we exploit autocorrelation to characterize the afterpulsing of SPADs. A FPGA based autocorrelator has been specifically designed to this purpose, featuring a lag-time range from 10ns to more than 10ms, covering a range well beyond the longest expected trapped carrier lifetime.