ANALYSIS OF GRATING-ASSISTED DIRECTIONAL-COUPLERS USING THE FLOQUET-BLOCH THEORY

The Floquet-Bloch theory is used to develop a theory for grating-assis ted directional couplers which predicts the coupled power and coupling lengths and is applicable to lossy waveguides, This theory views grat ing-assisted directional couplers as conceptually similar to conventio nal synchronous (nongrating) couplers. In the Floquet-Bloch analysis o f the directional coupler, it is necessary to include both proper and improper space harmonics, The determination of which space harmonics a re improper is critical to the understanding of the coupler performanc e, The choice of the improper space harmonics used for the analysis of the coupler is different from that used in contemporary papers.