Influence of field shape change in nonlinear fibre couplers

In the usual analysis of optical waveguide couplers for all-optic switching the nonlinear influence on the fundamental mode field shape is neglected. Using an accurate approximation method, the nonlinear modal field effect in these couplers is investigated. It is found that the nonlinear mode field effect can be significant and that it should be considered in the analysis and design of nonlinear waveguide couplers.