ABSTRACT
Until this point we have described nonlinear pulse propagation, more specifically, an envelope function multiplied on a carrier frequency. This has been done using a quasi monochromatic wave in Chapter 9. In Chapters 7 and 8 we have discussed mutual interactions among two frequencies in Raman and Brillouin scattering. In this chapter we focus on mutual interaction among three or four frequencies, in centrosymmetric materials, i.e. materials where χ(2) equals zero. This is often referred to as four-wave mixing or degenerate four-wave mixing when two out of the four frequencies are identical. More specifically we turn our attention toward nonlinear interactions that occur because of the intensity dependent refractive index. When the effects of Raman and Brillouin scattering together with intrinsic loss are ignored in this nonlinear interaction, the material in which the nonlinear interaction happens, only plays a passive role in the sense that no energy is transferred to or from the material. Consequently, the nonlinear interaction that we discuss in this Chapter is referred to as a parametric process.
