In this work, the experimental analysis of the sensitivity characteristics to the surrounding refractive index in nanoscale coated long period gratings is presented. Polymeric coatings of refractive index higher compared to the cladding one have been considered with thickness values ranging in hundreds of nanometers. The presence of the high refractive index coating induces the cladding to overlay mode transition depending on the overlay features (thickness and index) and the surrounding refractive index. The immediate consequence is a drastic modification of the sensitivity characteristics from the sub-linear monotone behavior to a resonant like shape. Here, for the first time, the sensitivity characteristics of coated long period gratings have been investigated to outline their dependence on the overlay thickness and order mode. Finally, it was proved how by using low cost technologies to coat these devices, significant sensitivity improvements can be obtained for specific applications.
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