THE DESIGN OF MODE EVOLUTION COUPLERS

The design of an optical switch based on a directional coupler with ta pered velocity and tapered coupling is investigated. The physical prin ciple is based on power transfer by the evolution of a single normal m ode. We consider cases where the coupling coefficient and guide mismat ch variation are determined by optimized shape functions related to re ctangle, raised cosine, Hamming, and Blackman window functions. Follow ing simplified analysis by coupled mode theory, the physical parameter s of the device are determined and the predicted performance is verifi ed by the method of lines. Significant improvement in sidelobe levels and coupling length can be obtained by careful design.