SBS THRESHOLD OF A FIBER WITH A BRILLOUIN FREQUENCY-SHIFT DISTRIBUTION

The SBS threshold of a fiber with Brillouin frequency shift distributi on along its length is investigated theoretically and experimentally. We obtain a simple equation for estimating the SBS threshold from the effective gain coefficient, which is calculated by using the Brillouin frequency distribution along its length. The dopant concentration dep endence of the Brillouin frequency shift are measured for fibers with an F and GeO2 codoped silica core. The evaluated frequency shift per u nit of dopant concentration is 277 MHz/wt% and 45 MHz/wt% for F and Ge O2, respectively, at 1.55 mu m. The SBS threshold of a fiber with a no nuniform Brillouin frequency shift distribution prepared by the VAD me thod is investigated experimentally, The fiber exhibits 7 dB improveme nt in its SBS threshold. This value is in good agreement with one esti mated by calculating the effective gain coefficient. This simple equat ion will be useful for estimating the SBS threshold of various fibers.