Robust Design of Slow-Light Tapers in Periodic Waveguides

We consider the design of tapers for coupling power between uniform and slowlight periodic waveguides. We describe new optimization methods for designing robust tapers, which not only perform well under nominal conditions, but also over a given set of parameter variations. When the set of parameter variations models the inevitable variations typical in the manufacture or operation of the coupler, a robust design is one that will have a high yield, despite these parameter variations. We introduce the ideas of successive refinement, and robust optimization based on multi-scenario optimization with iterative sampling of uncertain parameters, using a fast method for approximately evaluating the reflection coefficient. We compare our robust design results to a linear taper, and to optimized tapers that do not take parameter variation into account. Finally, we verify the robust performance of our designs using an accurate, but much more expensive, method for evaluating the reflection coefficient.