Noise characteristics of four-wave mixing between short pulses in semiconductor optical amplifiers

The noise characteristics of four-wave mixing between short optical pulses in semiconductor optical amplifiers are investigated, with the effects of f ast gain saturation taken into account. An approximate simplified expressio n for the power spectral density of the amplified spontaneous emission nois e under the injection of a sequence of short optical pulses is derived, in which the spatial dependence of the inversion factor is included. The depen dence of the signal-to-noise ratio of the output four-wave mixing signal on the input pump and signal powers is also investigated. (C) 1999 Optical So ciety of America [S0740-3224(99)02111-6].