100 Mcount/s InGaAs/InP single-photon detector

Recently there has been considerable effort to develop photon-counting detectors for the near-infrared wavelength range (up to 1700 nm). However, a practical detector, which can be employed in many real applications and has both high count rates and low noise, is still not available. Here we show a novel technique to operate InGaAs/InP single-photon avalanche diodes (SPADs) in a free-running equivalent mode at high count rate. The photodetector is enabled with a 915 MHz sinusoidal gate signal: by keeping the SPAD gate signal unlocked from the synchronization reference of the optical waveform to be reconstructed, a free-running equivalent mode is obtained, that we called gate-free. An extensive experimental characterization has shown how the SPAD performance improves compared with a classical square-wave gating scheme, especially for non-periodic high-throughput applications. The resulting single-photon detector achieves a maximum count rate of 100 Mcount/s, an afterpulsing probability below 0.3 %, a photon detection efficiency of 3 % at 1550 nm, a temporal resolution of 150 ps (Full-Width Half Maximum) and a dark count rate below 2000 count/s (the SPAD is cooled at 220 K).