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 was 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 13.° when the received signal power P _s is -65 dBm. For signal powers P_s⩾-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 a phase-locked loop, phase-shift keying homodyne transmission is demonstrated at 140 Mb/S and 2 single-moded fiber is -62.8 dBm, corresponding to 25 photons/b