Robust evanescent fused tapered couplers

Abstract

In the ubiquitous fused tapered coupler the two processes of fusing and tapering are achieved in a single processing step. This leads to a longitudinal variation in the coupler cross-section, from a figure-of eight at the extremities to anything between this figure-of-eight and a full circle at the middle of the taper waist. Through separation of the fusing and tapering processes, a new coupler type is reported. This coupler has a predominantly evanescent mode of coupling being shorter and fatter (more robust) than its conventional tapered counterpart.