Controlled coupling of planar waveguides using a negative-refractive-index medium

We demonstrate that a negative-refractive-index material can provide efficient controllable coupling between planar waveguides in a noninvasive fashion. An index matched negative layer acts like optical antimatter to the adjacent cladding layers, leading to significantly reduced effective separation between the guiding layers. This results in nearly mode-independent coupling between the waveguides where the thickness of the negative layer provides the necessary control. When the optical density of the negative coupling layer is different (higher or lower) from the adjacent cladding layers, the negative layer itself can support guided modes. Significant control over coupling can be achieved by engineering the mode structure of the negative waveguide with respect to the modes of the positive waveguides. Furthermore, we demonstrate the possibility of identifying a specific mode and tailoring the waveguide characteristics to achieve any desired level of coupling.