High-sensitivity semiconductor optically preamplified Q-PPM receiver

An optically preamplified receiver for 980-nm laser intersatellite communications is reported. A record sensitivity of 330 photons/bit for a semiconductor optically preamplified receiver is obtained at 50 Mb/s with quaternary pulse-position-modulation (Q-PPM). The experimental results are shown to be in excellent agreement with a novel exact calculation of the optically preamplified receiver Q-PPM bit-error rate (BER). Calculated performance based on these results shows that with an improved optical transmitter the receiver attains 1.5 dB higher sensitivity than previously achieved at this wavelength.