Experiments on optical amplifiers for two channel transmission

Experiments are reported in which two channels are simultaneously amplified by an optical amplifier. The crosstalk is investigated. The experiments reveal nonlinear distortions in the amplification. The generated crosstalk may become a serious problem in multichannel transmission links. Semiconductor laser amplifiers are expected to play an important role in future communications. Recently several experiments on amplifiers with reduced facet reflectivity were reported. This amplifier type exhibits a smooth gain spectrum with a superimposed 'ripple' caused by the residual Fabry-Perot resonator. Its gain characteristic is strongly affected by the optical input signal, especially near saturation. For instance, an increase of the optical input signal reduces the carrier density in the active region by stimulated emission, and thus changes the complex refractive index. This affects the gain and shifts the residual Fabry-Perot modes towards longer wavelengths.