Experimental and theoretical investigations of an air-slot coupler between dielectric and plasmonic waveguides.

In this paper, we experimentally show an effective method of coupling light between dielectric waveguides and metal-dielectric-metal plasmonic waveguides using an air-slot waveguide that extends into both types of waveguides. Our experimental results validate the theoretical calculation results of the proposed coupler. In addition, we investigated the sensitivity of our design to different fabrication challenges that may result in changing the width and length of the targeted optimum values in our design. Numerical simulation results show that the cut-off wavelength can be shifted by either changing the width of the dielectric or slot waveguide. The shift occurs because, as the waveguide's width changes, the mode size changes and consequently the impedance mismatch between the dielectric and slot waveguide changes. We also found that changing the position of the air-slot waveguide with respect to the center of the dielectric waveguide resulted in a reduction in the coupling efficiency due to the reduction in the overlapped area between the mode supported by the slot waveguide and that of the dielectric waveguide.