Cross-modulation distortion in subcarrier multiplexed optical systems

Abstract

Shown to be significant in a multi-carrier optical system is a cross-modulation distortion (CMD) coming from the inherent non-linearity of a semiconductor laser diode. It is not always valid to assume that CMD may be ignored compared to inter-modulation distortion (IMD). The CMD and IMD are also shown to be different for the two end channels, the dis-symmetry being due to the fact that the laser diode is not memoryless. Particularly for frequencies less than the relaxation frequency of the laser diode, the CMD and IMD are not always seen to be the worst, although the centre channel has the largest number of distortion products.