Estimation of BER performance and cascadability of wavelength converters based on cross-gain modulation in semiconductor optical amplifiers

The transmission of the input intensity noise for wavelength converters based on cross-gain modulation in semiconductor optical amplifiers is investigated theoretically. It is shown how the noise statistics change due to the nonlinear transmission function and how bit error rates can be estimated. The power penalty strongly depends on the wavelength shift and can be 5.2 dB at 2.5 Gbit/s when the wavelength is up-shifted by 20 nm. When the extinction ratio is enhanced by the converter, even negative penalties are obtainable. In agreement with computer simulations, the input dynamic range is determined to be at least 13 dB. Furthermore, it is demonstrated that at 2.5 Gbit/s, 62 wavelength converters can be cascaded when each converter is operated so that the extinction ratio is preserved. However, when the wavelength is alternatively down-and up-shifted by 15 nm, less than eight stages are cascadable.