Rigorous theory of grating-assisted couplers

This is the authors' abstract. We don't add key points for this paper.

We examine the operation of grating-assisted couplers by describing the fields inside the periodic coupling region in terms of a rigorous modal formulation. This approach reveals that the wave coupling process takes the form of a mode conversion mechanism. We then evaluate the effectiveness of a coupler to transfer power incident at the input waveguide to another waveguide at the output. Our results show that, in general, the optimal conditions for this power transfer may be different from those predicted by conventional coupled-mode methods. We also find that the efficiency of a coupler can be adversely affected by boundary discontinuities at the terminals of the grating region, and we suggest ways to avoid their negative impact on the desired power transfer.