Single photon detection of degenerate photon pairs at 1.55 μm from a periodically poled lithium niobate parametric downconverter

The performance of a communication system that uses 1.55 mum correlated photon pairs is analysed experimentally in terms of achievable coincidence rates, optimal pump rates, and the performance of custom-built photon-counting detectors at 1.55 mm. The testbed considered in this study uses standard telecom fibre, twin photons, and photon-counting detectors. Degenerate cw time-frequency entangled photon pairs are produced via quasi-phase-matched spontaneous parametric downconversion in bulk periodically poled lithium niobate. The photon pairs are efficiently collected into a single-mode fibre and are sent to a pair of custom-built InGaAs photon-counting avalanche photodiodes that are passively quenched, gated in Geiger mode, and thermoelectrically cooled to temperatures as low as -60degreesC. Reliable photon-counting operation with a quantum efficiency of 20% at a dark count probability of 0.04% per gate (20 ns) and negligible afterpulses is reported.