Numerical Study on an Efficient Coupler of Metal-dielectric Nano-grating

A subwavelength metal grating with single layer and double layer structure are proposed and analyzed. The two gratings are evaluated and compared in terms of the reflectance spectra and the coupling efficiency. Numerically simulation shows that the absorption peak wavelength shows some red-shift when duty cycle of the grating increases for the single layer grating. The height modulated reflectance spectra of the double layer grating is discussed too, the shift of coupling efficiency is deeply affected by the Fabry-Perot cavity modes and LSPR modes. The formation mechanism of low reflection band is discussed by modulating stripe thickness of the grating. It has significant applications in optical communication, biomedical sensors, plasmonic circuitry, and so on.