Regeneration of DQPSK signals using semiconductor optical amplifier-based phase regenerator

Amplification and simultaneous phase regeneration are considerably necessary for multi-level phase modulation format transmission system. In this paper, a phase regenerator for phase-noise degraded differential-quadrature-phase-shift-keying (DQPSK) signals is proposed by using semiconductor optical amplifier (SOA) as nonlinear medium with structure of nonlinear Mach-Zehnder interferometers (MZI). The formula of optical field distribution after input signals passing through phase regenerator is theoretically educed. For different input power of signal, the influence of signal-pump phase difference on signal power gain is studied. Furthermore, the optimal parameters of phase regenerator and relative phase of signal and pump are obtained. In this paper, we present the physical mechanism, which allowed us to design and optimize the phase regenerator, and compare the modeling and experimental results. In addition, the distributions of phase and intensity for both the non-regenerated and regenerated signals are simulated. The results demonstrate that nearly ideal phase regeneration can be achieved for the phase-noise degraded DQPSK signals using our SOA-based regenerator.