Amplitude noise suppression of quadrature phase-shift keyed signals based on non-degenerate phase-sensitive optical amplification with phase-rotation

This study investigates the amplitude noise suppression of 20-Gbit/s quadrature phase-shift keyed phase-conjugated twin waves (PCTWs) by frequency non-degenerate phase-sensitive optical amplification. The amplitude fluctuations of PCTWs are converted into phase fluctuations through the optical Kerr effect in transmission optical fibers. The average phases of transmitted PCTWs are then phase-locked to the pump phase and subsequently phase-rotated by an appropriate amount. This sequence results in amplitude noise suppression through optical parametric processing when the appropriate phase rotation is applied. Numerical simulations investigate the signal-to-noise ratio (SNR) of transmitted PCTWs with optical noise simulating the noise conditions of multi-relay transmissions, in a single-span transmission model. The SNR improvement is observed irrespective of whether the optical noises between PCTWs are correlated or not.