A 1320-NM EXPERIMENTAL OPTICAL PHASE-LOCKED LOOP - PERFORMANCE INVESTIGATION AND PSK HOMODYNE EXPERIMENTS AT 140 MB/S AND 2 GB/S

An experimental balanced optical phase-locked loop (OPLL) has been constructed using two 1320-nm diode-laser-pumped miniature Nd : YAG lasers. With a natural frequency of 13.5 kHz and a damping factor of 0.6, the loop phase error is less than 1.3° when the received signal power Ps is −65 dBm. For signal powers Ps ≥ −62 dBm, the phase error is 0.3° and is virtually independent of the signal power. When the natural frequency is 74 kHz, the damping factor is 0.03, and the dc gain is 68 MHz, the loop exhibits a chaotic behavior: it maintains the frequency lock, but not the phase lock. Using our phase-locked loop, we demonstrated phase-shift keying homodyne transmission at 140 Mb/s and 2 Gb/s. The receiver sensitivity at 140 Mb/s over 28.6 km of single-mode fiber is −62.8 dBm, corresponding to 25 photons/b. This is the highest sensitivity obtained to date with any optical communication system. The receiver sensitivity at 2 Gb/s is −40 dBm, corresponding to 332 photons/b. © 1990 IEEE