High performance refractive index sensor with stacked two-layer resonant waveguide gratings

A refractive index (RI) sensor which contains a dielectric cavity composed of two parallel planar waveguide gratings (WGGs) is proposed. Reflection and transmittance through stacked gratings are studied after converting the diffraction problem into the two coupled resonances. The method of analysis is applied to estimate the performance when used as a biosensor. The sensor achieves its high-sensitive detection by tracking a narrow resonant reflection peak via a tunable wavelength light source, and the desired RI can be determined from the resonant wavelength shift. It will be shown that, in comparison with conventional single grating guided mode resonance (GMR) sensor with equal available area, extremely narrow resonance linewidth can be obtained by using stacked gratings. The sensitivity of the sensor can reach to 497.83 nm/RIU, and the value of the figure of merit (FOM) can reach up to 551. Because of its advantages such as high-sensitivity, label-free, small size and non-destructive, the sensor has an extremely broad application prospect in the field of biomedicine detection. Keywords: Guided-mode resonance, Refractive index sensor, Resonant gratin