Balanced single-photon detectors using InGaAs/InP avalanche photodiodes with transformer-based spike cancellation

We demonstrate balanced single-photon detectors at 1550 nm with InGaAs/InP avalanche photodiodes by using transformer-based spike cancellation. The spike cancellation makes it possible to shorten the gate pulse width and to decrease the threshold of the discriminator. With a 4-ns gate, we obtain a dark-count probability of 8.5 × 10^-5 per pulse at the detection efficiency of 10%. An after-pulse probability of 8.9 × 10^-5 is obtained after 1-μs interval. Owing to its low after-pulse probability, the ratio of the dark count probability to the detection efficiency per pulse is about 7.5 × 10^-4 while the repetition frequency ranges from 100 to 800 kHz.