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 145 nm 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 similar to 7162 nm/RIU was achieved in the RI range from 1.440 to 1.456 and more than 12,000 nm/RIU at 1.440 RI. Using a ZnO film thickness of 116 nm and in the RI region between 1.320 and 1.360 the average sensitivity of similar to 806 nm/RIU was measured for a 145 nm thick film. Working as an intensity sensing device, the 87 nm coated LPFG shows a linear sensitivity of 216.4 dB/RIU in a wide range of RI from 1.340 to 1.420.

Abstract
A long-period grating (LPG) written on a standard single mode fiber is investigated as a curvature and vibration sensor. It is demonstrated a high sensitivity to applied curvature and the possibility to monitor vibration in a wide range of frequencies from 30 Hz to 2000 Hz. The system was tested using an intensity based interrogation scheme with the LPG sensor operating in the curvature regime. Results have shown a reproducible frequency discrimination in the 30 Hz to 2000 Hz, with resolutions between 11 mHz and 913 mHz. Frequency retrieval could be perfouned independent of temperature up to 86 degrees C.

Abstract
Sensors based on long-period fiber gratings (LPFGs) over coated with metal oxide were fabricated and characterized for refractive index (RI) sensing. Oxidation of Ni, Ti, Al, and Cr was monitored in real time by following the features of the LPFG attenuation band. Themetals were deposited simultaneously on top of Si substrates for further chemical and morphological analysis. Wavelength sensitivities (nm/RIU) of about 10 437 at 1.432, 1150 at 1.400, 20 125 at 1.448, and 875 at 1.420 were achieved for LPFGs coated, with 68 nm of Ni, 60 nm of TiO2, 50 nm of Al2O3, and 62 nm of Cr2O3, respectively. For surrounding RI higher than the cladding RI, the wavelength sensitivities are 1937, 6801, 5762, and 3051 nm/RIU at 1.457 for the Ni, Ti, Al, and Cr oxides, respectively. Working as intensity sensing devices sensitivities up to 167 dB/RIU were measured. Metal oxide coated LPFGs leads to wavelength sensitivity enhancement comparing to bare LPFGs and may be used in systems with RI higher than the fiber cladding, a region where bare LPFGs are insensitive.

Abstract
This work reports the theoretical investigation of optical fiber surface plasmon resonance sensors incorporating an internal metallic layer of silver covered with an oxide layer. This research is supported by the application of an effective analytical model combining geometrical optics with the transfer matrix theory for stratified optical media. Different oxide materials like titanium dioxide, silicon dioxide, and aluminum oxide are considered aiming to achieve increased/enhanced sensitivity to refractive index variations of the external medium, particularly when addressing phase interrogation. It is shown that the combination of a 50-nm thickness silver inner layer with a dielectric titanium oxide layer of a specific thickness enables high-performance phase sensitivity reading and is compatible with tailoring the sensor working region to the third telecommunication wavelength window around 1550 nm.

Abstract
In this work, a Fabry-Perot cavity based on a new silica tube design is proposed. The tube presents a cladding with a thickness of similar to 14 mu m and a hollow core. The presence of four small rods, of similar to 20 mu m diameter each, placed in diametrically opposite positions ensure the mechanical stability of the tube. The cavity, formed by splicing a section of the silica tube between two sections of single mode fiber, is characterized in strain and temperature (from room temperature to 900 degrees C). When the sensor is exposed to high temperatures, there is a change in the response to strain. The influence of the thermal annealing is investigated in order to improve the sensing head performance. (C)2015 Optical Society of America

Abstract
A study of a sensor for hydrogen (H-2) detection based on fiber Bragg gratings coated with palladium (Pd) with self-temperature compensation is presented. The cladding around the gratings was reduced down to 50 mu m diameter by a chemical etching process. One of the gratings was left uncoated, and the other was coated with 150 nm of Pd. It was observed that palladium hydride has unstable behavior in environments with high humidity level. A simple solution to overcome this problem based on a Teflon tape is presented. The sensing device studied was able to respond to H-2 concentrations in the range 0%-1% v/v at room temperature and atmospheric pressure, achieving sensitivities larger than 20 pm/% v/v. Considering H-2 concentrations in nitrogen up to 1%, the performance of the sensing head was characterized for different thicknesses of Pd coating ranging from 50 to 200 nm. (C) 2015 Optical Society of America