Abstract: A mode control device for operation at a selected wavelength in cooperation with first and second waveguides, integrates first and second adjacent layers for passing electromagnetic energy from the first waveguide to the second waveguide through the layers in series. In a first embodiment, the first and second layers are composed of materials having a distinct indices of refraction and are spaced apart a distance other than one-quarter of said selected wavelength. In a second embodiment, the layers are disks having distinct circular diameters.

Abstract: A method for designing an aperiodic grating structure for mode conversion and control which is based upon an inverse scattering optimization procedure. In accordance with this method, no predetermined shape or material variation of the grating structure is assumed. A constrained domain of all surfaces and material variations is searched to find an optimum aperiodic conversion surface profile for maximum conversion efficiency into the required output mode(s) or optimum control. Accordingly, the present method results in the design of rough surfaces or non-homogeneous structures for mode conversion and control. Because this method relies on scattering produced by short, forceful field perturbations, it is possible to achieve very small conversion lengths which are much less than one grating period.