Rayleigh Scattering and the Impulse Response of Optical Fibers

The term "Rayleigh scattering" describes light scattering from refractive index inhomogeneities whose linear dimensions are much shorter than the wavelength of light. Most of the scattered light escapes from the core region of the fiber and enters the cladding or the space outside of the fiber. Some of the scattered power goes into other guided modes. Rayleigh scattering thus contributes to the losses in the fiber and also influences the impulse response through mode coupling. Since mode coupling tends to improve the impulse response of optical fibers, 1,2 the question may be asked: How beneficial is Rayleigh scattering for light transmission in multimode fibers because of its mode-coupling ability? To answer this question we investigate the loss penalty that is incurred if Rayleigh scattering is assumed as the only mode-coupling mechanism. For simplicity, our study is limited to a slab waveguide model (see Fig. 1) assuming that there is no variation of the refractive index or the light field in the y direction. Ignoring coupling between guided 705