Higher-Order Wave and Charge Confinement Effects in Semiconductor Double-Doped Optical Fibers: Quasi-Soliton Propagation and Bistability

Abstract

Wave and charge confinement are usually employed to enhance the efficiency of many nonlinear optical processes. The purpose is to increase the interaction length or the optical nonlinearity, respectively. These two effects can be implemented simultaneously by use of quantum confined structures (for example — semiconductor-doped glasses) in waveguide geometry. In this contribution we consider the effect of wave and charge confinement on fifth-order nonlinearities in semiconductor-doped optical fibers and briefly discuss some resulting physical phenomena such as quasi-soliton pulse propagation and bistability. If we consider a nonlinearity [1] of saturation type and the electron and hole motions are completely decoupled, then the ls-ls transition is isolated enough and each crystallite behaves as an ideal two-level system that may be bleached at the same frequency “ that is resonant with the transition frequency ” _1s , and thus contribute to the degenerate nonlinear optical susceptibility χ⁽⁵⁾(ω, — ω,ω,- ω,ω). Recently a way was proposed [2] for increasing essentially the contribution of the fifth-order nonlinearity in semiconductor doped fibers: doping the fiber with two appropriate materials, both having a saturable nonlinearity. The refractive index change law of both dopands is assumed to be of Kerr type with saturation intensities I _s1 » I _S2 and nearly the same values for the nonlinear refractive index coefficients. Then, in a regime far from saturation, the refractive index of the fiber takes the form {fy(1)|311-1}