Optical gain spectrum of GeO2-SiO2 Raman fibre amplifiers

The spectral dependence of the stimulated Raman gain coefficient for the GeO2-SiO2 glass system is deduced by measurement of the spontaneous Raman scattered light from optical fibre preforms doped with up to 65 mol% germania. For Raman shifts in the range 100–600 cm−1 the Raman cross-section is found to depend linearly on the germania concentration. This data enables the computation of the Raman gain spectra for a given core germania concentration, and as examples the gain properties in the 1.5–1.6 μm low-loss optical telecommunications window of silica-based Raman fibre amplifiers doped with 3 and 22 mol% germania are discussed.