Experimental characterization of after-pulsing probability in InGaAs/InP-based single-photon avalanche photodiodes.

We present an automated, software-driven instrument for rapid and precise characterization of after-pulsing probability (PAP) in single-photon avalanche diodes (SPADs). The system replaces subjective manual analysis with a robust algorithm that separates correlated after-pulses from uncorrelated noise in inter-arrival time histograms. Using this instrument, we systematically map PAP as a function of dead time (1-80 μs) and detection efficiency (2.5%-25%) for commercial InGaAs/InP SPADs in free-running and gated modes. For the ID210 detector at 10% efficiency, PAP decreases from 12.8% to 3.2% as dead time increases from 1 to 20 μs. Gated operation further reduces PAP to 0.8%, a fourfold improvement. The instrument achieves measurement repeatability better than 1% and reduces analysis time from hours to minutes. This tool enables data-driven optimization of SPADs for quantum communications, LiDAR, and time-resolved spectroscopy.