Characteristics of stimulated Raman light scattering in SiO2+GeO2 glass-fiber optical waveguides

An investigation was made of stimulated Raman scattering (STRS) of light in SiO₂+GeO₂ multimode fiber-optical waveguides having a complex refractive index profile. By investigating STRS using a neodymium-doped garnet laser, it was possible to distinguish three waveguide structures in the multimode waveguide (two few-mode and one multimode structure) and by selectively exciting each of these, it was possible to obtain STRS in a few-mode waveguide without exciting directly guided modes in this waveguide. Qualitative information was obtained on the refractive index profile. Saturation of the pump power and of the Stokes STRS components was observed and it was found that this was related to broadening of the STRS spectral lines. When a multimode fiber-optical waveguide was pumped by 1.064 µ radiation, nonlinear effects gave rise to high-intensity radiation with a continuous spectrum in the 0.4–1.8 µ range which was observed at the waveguide exit. This wide-band source of nanosceond pulsed radiation is potentially useful both for investigations of fiber-optical waveguides and for various spectroscopic investigations.