PULSE-PROPAGATION THROUGH A NONLINEAR-OPTICAL AMPLIFIER

We report an investigation of pulse propagation through a recently pro posed nonlinear amplifier composed of asymmetrical twin-core fibre. Wh ile 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 d ispersive fibre right after the amplifier. the chirp in the wings may remain and lead to the eventual destruction of the pulse. This residua l chirp can be removed through a damped and radiative oscillation by j udicious adjustment of the parameters of the amplifier and the dispers ive fibre. Finally, we consider the effect of noise in the pulse. We d iscovered a threshold of the noise amplitude below which the noise is suppressed (which must be a characteristic asset of the nonlinear ampl ifier). Above the threshold, the noise tends to shift the centre of th e pulse. (C) 1997 Elsevier Science B.V.