  We present an active quenching application specific integrated circuit
(ASIC), for use in conjunction with InGaAs/InP avalanche photodiodes (APDs),
for 1550 nm single-photon detection. To evaluate its performance, we first
compare its operation with that of standard quenching electronics. We then test
4 InGaAs/InP APDs using the ASIC, operating both in the free-running and gated
modes, to study more general behavior. We investigate not only the standard
parameters under different working conditions but also parameters such as
charge persistence and quenching time. We also use the multiple trapping model
to account for the afterpulsing behavior in the gated mode, and further propose
a model to take account of the afterpulsing effects in the free-running mode.
Our results clearly indicate that the performance of APDs with an on-chip
quenching circuit significantly surpasses the conventional quenching
electronics, and makes them suitable for practical applications, e.g., quantum
cryptography.
