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Afterpulsing-free 80MHz single-photon detection at 1550 nm using an InGaAs/InP avalanche photodiode operated with sinusoidal gating

A single-photon detector (SPD) at 1550 nm is essential for quantum key distribution (QKD) based on optical fiber links. A cooled InGaAs/InP avalanche photodiode (APD) is a candidate for the SPD, because it has a high detection efficiency with a low dark count probability. However, the maximum detection speed was very slow (<10 MHz), which is due to the afterpulsing phenomenon. Recently we proposed the sinusoidal gating scheme and demonstrated the high-speed (500-800MHz) single-photon detection with a low afterpulsing probability. In the scheme, the overall afterpulsing probability is somewhat high when the gating frequency is lower than 100MHz. In this paper, we report on the afterpulsing-free (<1%) 80MHz single-photon detection using the sinusoidal gating. The 80MHz mode-locked titanium sapphire laser emits ~90 fs optical pulses at 810 nm. The wavelength of the optical pulses is converted into 1550 nm by the optical parametric oscillator (OPO). The 1550 nm optical pulses (~120 fs) are attenuated to the single-photon level and led to the APD (EPITAXX EPM239BA) cooled to -35 degrees Celsius. The cooled APD was operated with sinusoidal gating.