Analytical study of optical dielectric interfaces for sensing applications

Dynamic optical sensors, as those based on the reflectivity of isotropic dielectrical interfaces, can be useful for measuring small changes in the refractive index of fluid media. Exact and approximated explicit formulas for their sensitivity are developed. These expressions clarify the influence of each of the constructive parameters of the device, both in partial and in total reflection. It is analytically found that sensitivities are always greater when the angle of incidence approaches the angle of total reflection. It is also demonstrated that close to the critical angle for both types of reflection, the sensitivity of the p mode is greater than that of the s mode.