We have developed single-photon detectors at 1550 nm using electrically cooled InGaAs/InP avalanche photodiodes. The avalanche photodiode was sinusoidally gated and the undesired signal due to the gating that set the discrimination level in the photon detection was completely removed by filtering, which enabled us to detect avalanche pulses in the thermal noise limited sensitivity. The detection efficiency of 10.5% was obtained with a dark count probability of 6.1 × 10^–7 and an afterpulsing probability of 3.4%. The figure of merit of the single-photon detector was 1.2 × 10⁶ which is comparable to that of the superconducting single-photon detector.

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