Efficient phase regeneration of DPSK signal by sideband‐assisted dual‐pump phase‐sensitive amplifier

A high phase sensitivity of 25 dB at the nonlinear phase shift of 0.8 rad in a sideband‐assisted dual‐pump phase‐sensitive amplifier is achieved. Here the sidebands play an important role to evoke larger phase‐sensitive attenuations for achieving higher phase sensitivity at such a lower nonlinear phase shift. This feature is utilised to improve the efficiency in the phase regeneration of 21.5 Gbit/s DPSK signals. The phase error of 22.6° was squeezed to 2.5° by operating such a sideband‐assisted dual‐pump phase‐sensitive amplifier at 0.8 rad nonlinear phase shift. The operations at low nonlinear phase shift enable utilisation of the state‐of‐the‐art silica‐based highly nonlinear fibre with low noise and low dispersion slope by avoiding stimulated Brillouin scattering induced by higher pump power.