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Thermally Controllable High-Efficiency Unidirectional Coupling in a Double-Slit Structure Filled with Phase Change Material

We present the realization of a high-efficiency, compact, and thermally tunable unidirectional launcher of surface plasmon polaritons (SPPs) in a double-slit structure filled with phase change materials (PCMs). PCMs such as VO2 provide a feasible way for tailoring optical properties, particularly refractive index as a function of heat. By introducing a narrow hybrid dielectric layer beneath the slits, SPPs couple efficiently into waveguide mode and propagate within the slot waveguide with considerably high intensity. Our simulation results revealed up to 80% coupling efficiency into the slot waveguide with extinction ratio of 1:800 between the left and the right slots can be achieved at telecommunication wavelength for normally incident P-polarized light. By heating the coupler above the VO2 phase transition temperature, the coupling and consequently the crosstalk approaches zero. Propagation length and other properties of the structure are characterized to confirm the feasibility of the coupler. This approach of unidirectional coupling into slot waveguides may lead to the development of integrated plasmonic circuits and on-chip applications.