Modeling of symmetric 2 × 2 fused-fiber couplers.

A complete analysis of symmetric 2 × 2 fused-fiber couplers in terms of supermode beating is made. The tranverse and longitudinal geometry of the couplers has been carefully modeled to take into account the fabrication parameters. The first two scalar supermodes and their polarization corrections have then been calculated for each degree of fusion and taper ratio, resulting in powerful tools for the design of particular couplers. The good agreement between the observed and the predicted responses for slightly and strongly fused couplers confirms the validity of each step of this analysis.