A more tolerant design of 3-dB adiabatic couplers

A more tolerant design of 3-dB adiabatic couplers is proposed. In this design a central region is added to the structure of the conventional cross-coupler. The waveguides of the central region are linearly tapered in both width and separation. Numerical computations of the proposed design show the possibility of five-fold increase in the fabrication tolerance compared to the conventional design.