Abstract

In any direct detection measurement system the highest sensitivities are reached by using a high efficiency photon counting system. Silicon single photon counting avalanche photo-diodes (SPAD's) have been studied since the early 1980's [1]. Present commercially available devices show low dark counts, high quantum efficiencies and timing jitter below 300ps. With such a device the effective sensitivity is only limited by the detector dark count which when cooled can be as low as a few tens of counts per second. A good silicon SPAD module with a 50% efficiency and 50 counts per second has a noise equivalent power (NEP) of less than 4.10^-18W/Hz^1/2. In comparison best PIN diode based receivers have NEP's of 16.10^-15W /Hz^1/2 and are based on high impedance amplifiers which severely limit their bandwidth. Thus to obtain the ultimate sensitivity coupled with an extremely low timing jitter we must rely on single photon counting detectors. The sensitivity of silicon APD's falls off beyond 1 micron wavelength and cannot extend to the eyesafe wavelengths, at 1.54 microns and beyond. For a variety of applications including fibre based optical time domain reflectometry (OTDR), sensitive eye-safe rangefinding and quantum cryptography there is a pressing need for a practical 1.0-1.6um single photon counting detector.

© 2000 IEEE