Soliton Switching in Semiconductor Directional Couplers

Abstract

There is an urgent need in all-optical signal processing to implement fast switching devices with high switching contrast. Nonlinear directional couplers (NLDC) have attracted a great deal of interest as basic all-optical elements because the output may be routed between the two channels as a function of the input power launched into one channel. The stationary response of that device has been discussed in detail for numerous situations (for a summary, see e.g. the review paper¹ and the references therein). That approach holds also in the nonstationary regime provided that the pulses are sufficiently long and/or the waveguides are short. In that case the dispersion of the group velocity (GVD) may be neglected. The time in the reference frame of the pulse enters the coupled mode equations merely as a parameter. This has the consequence that the coupling behavior (efficiency and coupling length) depends on the instantaneous intensity of the pulse at a certain time leading to the detrimental pulse break up² and thus to an incomplete switching between both channels. This phenomenon limits considerably the opportunity of cascading different switching elements.