Degradations due to stimulated Brillouin scattering in multigigabit intensity-modulated fiber-optic systems

The stimulated Brillouin scattering (SBS) process limits the maximum power that can be transmitted in low-loss optical fibers in multigigabit fiber optic systems. It is shown 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. It is found that a modulation index as low as 2% can quadruple the SBS threshold. Measurements with a 1.5-μm externally modulated laser at 2.5 Gb/s indicate that this dither in no way degrades the performance in the presence of chromatic dispersion