Performance of strain-free stimulated Brillouin scattering suppression fiber

We have investigated experimentally the performance of an SBS suppression fiber with a nonuniform dopant concentration along its length fabricated by the VAD method. We have achieved an SBS threshold of 15 dBm against a continuous wave at 1.55 /spl mu/m. This is 7 dB larger than that of conventional fiber. We have confirmed experimentally that the increase in the SBS threshold can be estimated from the ratio of the Brillouin frequency shift change over the effective interaction length to the intrinsic Brillouin gain bandwidth. Moreover, we have confirmed that there is no BER degradation after a transmission of 138 km through a 2.5 Gb/s intensity modulation direct detection system when the SBS suppression fiber is used with an input power of 16 dBm.