Abstract

Optical phase-locked loops (OPLL's) are needed for synchronous homodyne receivers [l]–[4]. We constructed a stable optical phase-locked loop with miniature diode-pumped Nd:YAG ring lasers [5]. Using our loop, we demonstrated a 140 Mb/s PSK synchronous homodyne experiment with the sensitivity of 25 photons/bit¹. To the best of our knowledge this is the highest sensitivity demonstrated with any optical communication system to date². In addition, we demonstrated a 560 Mb/s PSK synchronous heterodyne experiment with the sensitivity of 124 photons/bit. We investigated, for the first time, the impact of the finite intermediate frequency (IF) on heterodyne system performance and show that an IF of at least twice the bit rate is needed for a neglibly small penalty.

© 1990 Optical Society of America