Stimulated Raman scattering in a multimode optical fiber: evolution of modes in Stokes waves

Stimulated Raman scattering in a 50-μm multimode graded-index optical fiber was studied with a pulsed dye laser as the pump source. With 30 m of the fiber, the scattered waves (the Stokes waves) in the fiber could be made to propagate predominantly in one of the low-order modes of the fiber by careful adjustment of the light-launching conditions. The observed phenomenon is believed to be the result of nonuniform excitation of the modes by the pump. The experimental results are presented and discussed.