Phase sensitive amplifier using frequency-shift free optical phase conjugation for phase-regeneration of DPSK signals

We propose and numerically verify a scheme of phase-sensitive amplifier (PSA) using frequency-shift free optical phase conjugation. PSA is obtained by combining the conjugated wave with original signal. The frequency-shift free operation of phase conjugation helps in preserving the frequency of input signal during phase-sensitive amplification The expression for PSA signal output and PSA gain are derived and it is analytically shown that PSA provides high gain for in-phase component and almost cancellation for quadrature-phase component of signal relative to pump phase under low pump power approximation. We prove theoretically that the proposed PSA provides 0 dB noise-figure with high gain-extension ratio. We study the performance of PSA under the effects of pump-signal detuning, amplifier length, input signal phase and signal power. Simulation results shows that PSA output is forced to attain 0 or π phase regardless of large variation of phase in input signal. Nonlinear phase noise reduction of 40 Gbps DPSK signal transmitted over 1000 km standard single mode fiber confirms phase-regeneration by PSA.