Directional couplers realized on silicon-on-insulator

An asymmetrical rib configuration of directional couplers was demonstrated numerically and experimentally. With this geometry structure, the effective coupling lengths were shortened to half of the conventional ones. These new 3-dB and cross couplers were fabricated on silicon-on-insulator wafers, with the measured insertion loss 2.3 dB, nonuniformity 0.2 dB. The full vector H~ field finite edge element method was applied to the design and analysis.