Tapered optical couplers with grating: Beyond the weak-guidance limit

Abstract

We describe the operation of a grating-assisted optical coupler consiting of two different curved slab wave guides. A version of vectorial, nonorthogonal coupled-mode theory based on local modes is applied. The coupled-mode equations contain mode overlap terms and coupling terms, which vary with distance. These equations are solved numerically for even-transverse magnetic modes propagating in the non-weakly guided slabs. We show output light powers as a function of the input wavelength assuming a condition of contradirectional coupling. For comparison we also show the result in the limit of weak guidance and a result from the vectorial theory without mode overlaps.