All-optical phase regeneration of multi-level amplitude and phase shift keyed signals

All-optical phase regeneration of multi-level phase shift keyed signals in fiber optic communications systems reduces the impact of phase noise induced by, e.g., self/cross-phase modulation of amplitude varying symbols, and has been previously simulated and experimentally demonstrated [1-3]. Phase regeneration is achieved through a judicious coherent addition of phase harmonics, bearing integer multiples of the signal phase, to the signal via four-wave mixing in a highly nonlinear fiber (HNLF), such that a staircase is realised in the signal phase transfer function of the HNLF. Phase regeneration may allow for greater transmission capacity and optical regeneration has the potential to work faster and consume less power than electronic compensation.