Fano resonance and tunability of optical response in double-sided dielectric gratings

A tunable resonant doubled-sided dielectric grating (DSDG) structure has been designed for operating in the near-infrared (NIR) wavelength range under transverse electric (TE) polarization. The rigorous coupled-wave analysis (RCWA) is applied to determine the optical characteristics, and the reflection resonance of the grating structure is analyzed by varying their geometrical parameters. The excited sharp Fano resonance (FR) is demonstrated numerically that does not occur in single layer grating. The maximal magnitude of electric field in the spacing layer sandwiched by the gratings is 35 times enhanced compared with incident filed, that dues to the waveguide resonance, which can be excited by a normally incident plane wave in the proposed design. The relationship between structure parameters of DSG and the reflectance spectrum in order to guarantee the appearance of FR in the designed structure is fully investigated. An optical refractive index (RI) sensor with a potential sensitivity of 602.15 nm/RIU is designed based on the proposed structure. The method demonstrated may lead to potential applications for the design of tunable filter or modulator with narrow-band with a wide range of potential applications including telecommunications, optical information processing, and optical sensors.