Light scattering in optical waveguides

The coupling of scattered radiation from Raman-active core and cladding regions to the waveguide normal modes is analyzed by treating the scattered light as a classical incoherent effective source. Numerical results are presented for the limiting cases of single-mode or highly multimode excitation of the fiber. The effect of a finite frequency shift between the exciting and scattered fields is also considered. It is found that radiation produced by scattering of the evanescent field in the cladding is coupled to the guided modes with a peak efficiency of about one-fifth that of light scattered in the core. The implications of these effects for optical devices utilizing fibers are briefly discussed.