DEGRADATIONS DUE TO STIMULATED BRILLOUIN-SCATTERING IN MULTIGIGABIT INTENSITY-MODULATED FIBEROPTIC SYSTEMS

Severe degradations in the bit-error-rate performance in multigigabit fiber-optic systems may result from the stimulated Brillouin scatterin g process in optical fibers. The SBS process has long been known to li mit the maximum power that can be transmitted in low-loss optical fibe rs. In this paper we show that recently observed large optical fluctua tions resulting from SBS degrade the signal-to-noise ratio and consequ ently the system bit error rate. Since SBS has potentially the lowest power threshold of all fiber nonlinearities, it is critical that it be addressed. It is shown that the SBS threshold can be increased by pro viding a low-frequency sine-wave dither to the laser pre-bias current. We find that a modulation index as low as 2% can quadruple the SBS th reshold. Measurements with a 1.5-mum externally modulated laser at 2.5 Gb / s indicate that this dither in no way degrades the performance i n the presence of chromatic dispersion.