Long period grating coated with high refractive index layer

In this work, we theoretically and experimentally investigated the cladding modes re-organization in high refractive index coated long period gratings (LPGs), focusing the attention on the influence on the refractive index sensitivity. When azimuthally symmetric nano-scale HRI coatings are deposited along LPGs devices, a significant modification of the cladding modes distribution occurs, depending on the layer features (refractive index and thickness) and on the surrounding refractive index. In particular, if these parameters are properly chosen, the transition between cladding modes and overlay modes occurs. Here, numerical and experimental results on the effect of the modes transition surrounding refractive index (SRI) sensitivity are presented.