Design of planar waveguide directional couplers with arbitrary modal electric field

The purpose of this work is to present a method for designing planar waveguide couplers of arbitrary modal electric field distributions. The idea here is to create couplers with unusual electric fields, which confine in one planar waveguide. This is possible if a planar waveguide profile supporting two pre-selected mode fields is designed. Their interference will have to transfer the optical power from one region (bottom layer) to another region (top layer) completely. The inverse transmission-line technique and the desired electric field are applied, based on which the refractive index profile of the couplers exhibiting excellent crosstalk is reconstructed. By choosing this technique, it is feasible to design planar components in sensing applications, such as high power, temperature or pressure sensors and numerous other possibilities, using unusual electric field distributions.