Spontaneous Nonlinear Scattering Processes in Silica Optical Fibers

When light travels in a optical fiber, a fraction of its total power is always scattered to other wavelengths (or polarization) due to material non linearity. Whether that scattering is weak or strong, desirable or not, depends on the situation. One distinguishes (i) scattering stimulated by the presence of a seed wave (at another wavelength or polarization), (ii) spontaneous scattering, and (iii) amplified spontaneous scattering. Stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS) and four-wavemixing (FWM) are examples of stimulated scatterings. Those have been thoroughly studied in the past thirty years and are well summarized in classic nonlinear fiber optics textbooks, e.g. (Agrawal, 2007). Several chapters of this book also deal with specific aspects and applications of stimulated scattering. The present chapter focuses on spontaneous scattering processes, cases (ii) and (iii). The chapter also concentrates on nonlinear scattering in silica fibers because nowadays those are the most common and widely used types of fibers. Gas-filled hollow core fibers (Benabid et al., 2005) and ion doped fibers (Digonnet, 2001) are not considered here, and it is assumed that the fiber has not been subjected to poling (Bonfrate et al., 1999; Huy et al., 2007; Kazansky et al., 1997), so that the main non linearity is of third order. In this context the most important spontaneous nonlinear scattering processes are