Pulse propagation through a nonlinear optical amplifier

We report an investigation of pulse propagation through a recently proposed nonlinear amplifier composed of asymmetrical twin-core fibre. While the pulse is amplified and the associated noise is suppressed, we find that the pulse is strongly chirped. While the chirp in the centre of the pulse can be easily eliminated by inserting a short piece of dispersive fibre right after the amplifier, the chirp in the wings may remain and lead to the eventual destruction of the pulse. This residual chirp can be removed through a damped and radiative oscillation by judicious adjustment of the parameters of the amplifier and the dispersive fibre. Finally, we consider the effect of noise in the pulse. We discovered a threshold of the noise amplitude below which the noise is suppressed (which must be a characteristic asset of the nonlinear amplifier). Above the threshold, the noise tends to shift the centre of the pulse.