Spontaneous light scattering in pulsed excitation of fiber-optic waveguides

A theoretical analysis is made of some features of the evolution, in fiber-optic waveguides (FOWs), of spontaneous Brillouin, Raman, and Rayleigh light scattering excited by single optical pulses and developing in the forward and backward directions (relative to the radiation incident at the entry end of a FOW). It is shown that regardless of the widely varying duration of the incident radiation pulses the intensity of the spontaneous forward scattering passes through a maximum at a point in the FOW whose coordinates are governed by the waveguide losses. A variant of the familiar backscattering method is proposed. It is shown experimentally and theoretically that when studying stimulated Raman scattering, the sections of decaying intensity observed at the beginning of the backscattering oscillograms are the result of the growth of spontaneous Raman backscattering.