Control of optical mode properties in cross-slot waveguides

A cross-slot waveguide geometry provides high confinement of the mode field of both fundamental quasi-TE and quasi-TM modes in geometrically perpendicular slots. A unique possibility to tailor optical mode characteristics such as effective index and confinement factor quite independently for the two polarizations with geometric and material parameters is shown. Nonbirefringent cross-slot geometries are presented. Fabrication related tolerances of the cross-slot geometry for low birefringence operation are studied. Means to externally tune the birefringence by a thermo-optic effect is also analyzed. Fabrication of a cross-slot waveguide test structure is demonstrated.