Numerical and analytical evaluations of the sensing sensitivity of waveguide mode in one-dimensional metallic gratings

We study numerically and analytically the refractive index sensing sensitivities of surface plasmon (S SP) and waveguide (S WG) modes arising from one-dimensional Au gratings. By using rigorous coupled wave analysis, we find that while S SP is mainly controlled by the periodicity of the grating, the shape of the groove governs S WG. As a result, it is possible to increase S WG to 1000nm/RIU and figure of merit to 24 by tailoring the height and width of the groove. Finally, a simple analytical expression is derived to describe S WG and it agrees well with the numerical data. This easy-to-use expression not only reveals the origin of waveguide mode sensitivity, but also provides useful guidance for the theoretical design and experimental realization of high-sensitivity metallic-gratings-based biosensors.