High-sensitivity direct-detection receiver with a 1.5 μm optical preamplifier

A 1.5 μn optical preamplifier was used to improve the sensitivity of a PINFET receiver by 12dB. The resonant optical amplifier provided 17dB of fibre-to-fibre gain including coupling losses in an isolator and a narrowband optical filter. The achieved sensitivity, -45.6 dBm at 500 Mbit/s, or 420 photons/bit, is the best reported for any direct-detection receiver and a factor of two better than previous results using optical amplifiers. However, the results are virtually identical to the best APD receiver results.