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 scattering process in optical fibers. The SBS process has long been known to limit the maximum power that can be transmitted in low-loss optical fibers. In this paper we show that recently observed large optical fluctuations resulting from SBS degrade the signal-to-noise ratio and consequently 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 providing 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 threshold. Measurements with a 1.5-mum externally modulated laser at 2.5 Gb / s indicate that this dither in no way degrades the performance in the presence of chromatic dispersion.