EFFECTIVE NONLINEAR COEFFICIENTS OF OPTICAL WAVE-GUIDES

Using the weakly guiding approximation, and with the assumption that t he nonlinearities are sufficiently weak so as not to change the transv erse mode profile, perturbation theory is used to derive simple expres sions for evaluating the modal, or effective, non-linear coefficients of optical waveguide structures based on the non-linear coefficients o f the constituent materials. In particular, the third-order and fifth- order optical non-linearities of refraction and absorption are discuss ed. The expressions are used to estimate the effective modal non-linea r refraction coefficients for various types of slab waveguides, focusi ng primarily on femtosecond refractive non-linearities in semiconducto r amplifiers, including quantum-well structures. The results are of pa rticular relevance to the design of all-optical switches based on thes e effects.