Sensitivity characteristics in nanosized coated long period gratings

This work presents an experimental analysis of the sensitivity characteristics to the surrounding refractive index (SRI) in long period gratings coated with polymeric overlay with high refractive index and thickness values ranging in hundreds of nanometers. The presence of the coating induces the cladding to overlay mode transition depending on the overlay features and the SRI. The immediate consequence is a drastic modification of the sensitivity characteristics from the sublinear monotone behavior to a resonantlike shape. Here, the sensitivity characteristics of coated long period gratings have been investigated to outline their dependence on the overlay thickness and order mode.