Abstract
A fiber-optic refractive index (RI) sensor based on a long period fiber grating (LPFG) coated with a zinc oxide (ZnO) thin film was fabricated and characterized. A method to overcoat the LPFG's with a homogeneous ZnO thin films was developed.Characterization of ZnO thin films, deposited simultaneously on silicon (Si) planar substrates, was performed using Scanning Electron Microscope, Energy Dispersive X-ray Spectroscopy and X-ray Photoelectron Spectroscopy. The LPFGs with ZnO coatings from 29 to 145nm of thickness were characterized and compared in terms of the wavelength shift and the intensity of the attenuation bands changing the surrounding refractive index (SRI) from 1.300 to 1.600. An average wavelength sensitivity of ∼7162nm/RIU was achieved in the RI range from 1.440 to 1.456 and more than 12,000nm/RIU at 1.440 RI. Using a ZnO film thickness of 116nm and in the RI region between 1.320 and 1.360 the average sensitivity of ∼806nm/RIU was measured for a 145nm thick film. Working as an intensity sensing device, the 87nm coated LPFG shows a linear sensitivity of 216.4dB/RIU in a wide range of RI from 1.340 to 1.420.
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