Phase Preserving Amplitude Saturation Through Tone Synthesis Assisted Saturated Four-Wave Mixing

Abstract

When processing a data carrying signal with amplitude saturation in a fibre-optic parametric amplifier, the signal can be subject to a deleterious conversion of its amplitude noise into phase noise. To overcome this, we propose and demonstrate a scheme in which the products of four-wave mixing are instead synthesised using spectral shaping of multicast replicas of the signal, rather than naturally through four-wave mixing itself. This allows us to emulate the advancement of four-wave mixing without incurring unwanted amplitude noise to phase noise conversion. A final stage of four-wave mixing is used to bring about amplitude squeezing, with little impact on the phase noise of the signal. Using this technique, we are able to demonstrate phase preserving amplitude squeezing of a 10 GBd QPSK signal using as a medium, a highly nonlinear fibre in which the traditional, single pump approach fails.