Gated InGaAs detector characterization with sub-picosecond weak coherent pulses

We demonstrate a method to characterize a gated InGaAs single-photon detector (SPD). Ultrashort weak coherent pulses, from a mode-locked sub-picosecond pulsed laser, were used to measure photon counts, at varying arrival times relative to the start of the SPD gate voltage. The difference of detection probabilities for two gate windows with different widths, and the uneven detection probabilities within a gate window, were used to estimate the afterpulse probability with respect to the detector parameters: excess bias, width of gate window and hold-off time. We estimated an afterpulse decay time of 1.1 to 2.4μs using a power-law fit to the decay in afterpulse probability. Finally, we measure the timing jitter of the SPD, as 240 ps, using a time to digital converter with a resolution of 55 ps.