Noise squeezing due to Kerr effect nonlinearities in optical fibres with negative dispersion

Kerr effect nonlinearities in optical fibres have been the subject of extensive studies [1 – 3]. Four wave-mixing (FWM) between the signal and the amplified spontaneous emission (ASE) noise was found to be an important source for system performance degradation, especially in systems using in-line optical amplifiers. With positive fibre dispersion, this effect is known as modulation instability (MI). Although most published works have dealt with a change of optical spectrum caused by MI, in intensity modulated systems with direct detection (IM-DD), performance degradation due to MI is caused by a nonlinear increase of the relative intensity noise (RIN) within the signal baseband [4, 5]. We demonstrate that the amplitude of RIN can be reduced by this FWM, in systems with negative fibre dispersion.