The authors present a system performance analysis of an optical single sideband system (OSSB) when biasing drifts occur in the modulating signal driving the dual arm Mach-Zehnder modulator (MZM). The performance is evaluated in terms of the optical sideband suppression, received subcarrier power variation and BER. Experiments were carried out and a mathematical model of the OSSB system, incorporating the biasing drift was developed. Both the theoretical and experimental results show that OSSB system is optimized to combat the chromatic dispersion when the biasing ratio, ε is ranged from 0.48 to 0.52.