Spectral characteristics in long-period fiber gratings with nonuniform symmetrically ring shaped coatings

In this work, the spectral characteristics of nonuniform symmetrically ring shaped coatings deposited on long-period fiber gratings have been theoretically and experimentally investigated. Electrostatic self-assembling technique was used to deposit with fine control uniform azimuthally symmetric coatings at nanoscale level. UV laser micromachining operating at 193 nm was applied to selectively remove the coating with high spatial resolution on ring shaped geometry. Phase shift effects and multiple interference fringes have been observed for all the attenuation bands, strongly depending on the length of the uncoated region and the coating features (thickness and optical properties). The ability of the proposed structure to exhibit wavelength selective operation, combined with the effects of high refractive index coatings on the cladding modes distribution, provides a valid technological platform for the development of advanced photonic devices for sensing and telecommunication applications.