Figure 1
Multimode fibre Raman laser scheme: three CW multimode laser diodes (MM LD) pigtailed by SIF with 100-µm core are combined by a pump combiner and pump a 1-km GIF with 100-µm core, where a resonator is formed by an UV-inscribed highly-reflective (R ~ 90%) fibre Bragg grating (HR FBG) and a fs-inscribed output coupler (R ~ 4%) (OC FBG), playing the role of a 10-dB filter for the fundamental mode, due to localization near the GIF axis (the OC FBG microscopic image is shown at the top, while OC and HR FBGs reflection spectra are shown at the bottom). The laser output is collimated by a lens, and characterized by a power meter (P), beam profiler (M2) and optical spectrum analyzer (OSA), with the use of corresponding interference filters for selection of either the pump (940 nm) or the Stokes (976 nm) beam. Beam spectrum and cross-sections for the multimode LD pump radiation measured before and after pump combiner in SIF and GIF, respectively, and after OC FBG, are shown together with the generated Stokes beam shape and spectrum at the output.
