SINGLE-PHOTON DETECTOR MODULE APPLICATION NOTE Single-photon detection with InGaAs/InP avalanche photodiodes

When most people think of detecting single-photons, photomultiplier tubes probably spring to their mind. Indeed, for a long time these were the detectors of choice in ultrasensitive detection and spectroscopy. Today, however other types of detectors allow to reach a single-photon sensitivity. Special semiconductor devices called singlephoton avalanche diodes (SPAD) have been developed, optimised for this regime and are commercially available. Silicon SPADs exhibit very good performance between 400 and 900 nm: quantum efficiencies for detecting single photons around 60%, dark counts in the absence of light below 100 counts per second and sub-nanosecond timing resolution. The excellent performance of silicon SPADs has enabled significant progresses in luminescence studies, astronomy, sensor applications and fundamental research in physics. However, if one wishes to pursue photon counting at the longer telecom wavelengths of 1300 nm and 1550 nm, the situation is no longer so easy. Although near-infrared photomultiplier tubes having a spectral response extending to 1700 nm exist, their quantum efficiency does not exceed a fraction of a percent. For 1300 nm photons, germanium APD’s have been extensively studied. In order to have a reasonable dark count rate, these detectors must be cooled, usually with liquid nitrogen, to a temperature below 150 K, making them impractical for most applications. Furthermore, the cut-off wavelength of these APD’s when cooled is around 1450 nm, making them unsuitable for use as photon counters for 1550 nm photons. More recently new approaches employing superconducting materials have been proposed and tested. However, because of their cooling requirements – 4 K or lower – these detectors are impractical for most applications. The 0.73 eV bandgap of InGaAs, lattice matched to an InP substrate makes single-photon sensitivity possible up to a wavelength of 1650 nm. Quite a few groups have therefore turned their attention to using commercially available InGaAs/InP APD’s, originally developed for optical communication applications, for photon counting at 1300 nm and 1550 nm. This research has proved quite fruitful, and there are many applications emerging in optical metrology, in eye-safe range finding, and in future quantum technologies. ID Quantique brought the first commercial single-photon detection system employing InGaAs/InP APD’s into laboratories in 2001. This application note describes the principle of singlephoton detection using InGaAs/InP APD’s. It presents then the id210 Single-Photon Detection System launched in 2011 and finally mentions applications.