Raman-gain estimates for high-gain optical fibers

The amplification of light signals by the mechanism of stimulated Raman scattering is discussed, with specific reference to certain heavy-metal germanate and arsenate glasses with Raman-gain-coefficients G of up to 20 times that of fused silica. Calculations are presented of the intrinsic scattering losses from Rayleigh, Brillouin, and spontaneous Raman sources for these compositions which, when combined with the measured G values, determine the potential signal-amplification capabilities as a function of pump power and fiber length L. Direct comparisons are made with an equivalent calculation for an ideally pure germania fiber. The results hinge sensitively upon the degree to which concentration fluctuations (leading to concentration-scattering Rayleigh loss) are intrinsic in the multicomponent high-G glass compositions. In spite of this, some compositions are located which can outperform pure germania fibers even in the presence of signficant concentration-scattering loss. This is particularly so for high pump powers and short fiber lengths L<2 km.