Pump phase-locking to fiber-transmitted QPSK phase-conjugated twin waves for non-degenerate phase-sensitive amplifier repeaters

Abstract

Pump phase-locking to fiber-transmitted quadrature phase-shift keying-phase-conjugated twin waves (QPSK-PCTWs) is experimentally demonstrated for the first time. First, we demonstrate pump phase-locking to 80-km fiber-transmitted 20-Gbit/s QPSK-PCTWs using a non-degenerate phase-sensitive optical amplifier (ND-PSA) repeater. Optical phase-locked loops assisted by sum-frequency and second-harmonic generation (SS-OPLL) enable pump phase-locking because optical parametric interaction between a signal and its phase-conjugated wave is observed at the ND-PSA output when the SS-OPLL is working. Then, the influence of optical noise on the SS-OPLL is investigated. The SS-OPLL is relatively robust for optical noise because the difference in the ND-PSA output signal quality was negligible for the cases of optical signal-to-noise ratios of 15 dB and 25 dB.