Fiberpaedia
Rayleigh scattering
Reflection of some of the light back along the fiber from the glass itself. This is a linear elastic scattering process, caused by the presence of sub-microscopic variations in the density and composition of the glass, leading to localized index variations which encourage some of the light to propagate backwards. This scattering decreases according to a fourth-power law as wavelength increases (i.e. 1/l4).