Gain-flattening of fiber Raman amplifiers using non-linear pump spectral broadening

Abstract

We demonstrate experimentally that gain flattening of single-pump fiber Raman amplifiers is possible by use of non-linear broadening of the pump spectrum. In our experiments, pump broadening of a continuous-wave Raman fiber laser tuned at 1455 nm is achieved by propagation in a non-zero dispersion-shifted fiber with small anomalous dispersion at the pump wavelength. The broadened pump spectrum can reach a full width at half maximum of as much as 28 nm. Our results demonstrate that an acceptable flatness of the Raman gain spectrum can be obtained in the 1560–1640 nm region while avoiding pump-to pump non-linear interactions. On the dark side, our measurements show that this configuration introduces more noise than the conventional, non-broadened pump configuration since a non-negligible fraction of the broadened pump power falls within the band of amplification. However, we believe that further work and optimization should demonstrate that gain-flattened fiber Raman amplifiers using a single pump can be achieved over the C (1525–1565 nm) and L (1565–1625 nm) bands.