Guided Mode Resonance Sensor With Enhanced Surface Sensitivity Using Coupled Cross-Stacked Gratings

Cross-stacked gratings are introduced for refractive index sensing based on guided mode resonance (GMR) effect. Reflection from and transmission through cross-stacked gratings is computed after converting the diffraction problem into an equivalent transmission line formulation. This formulation, which lends itself for the analysis of a biperiodic dielectric structure, can be used to calculate diffraction characteristics of the cross-stacked gratings with a high degree of accuracy. With the help of this analysis, it is shown that the cross-stacked gratings possess two mutually coupled GMRs. The method of analysis is then applied to various cross-stacked gratings to estimate their performance when used as a biosensor. It will be shown that, in comparison with conventional single grating GMR sensor with equal available area, a roughly two-fold surface sensitivity, equal bulk sensitivity, and extremely narrow resonance linewidth can be obtained by using cross-stacked gratings. Consequently, this structure improves detection ability of the GMR biosensor particularly for small analyte detection.