Abstract
Monitoring the quality of high refractive index edible oils is of great importance for the human health. Uncooked edible oils in general are healthy foodstuff, olive oil in particular, however, they are frequently used for baking and cooking. High quality edible oils are made from seeds, nuts or fruits by mechanical processes. Nevertheless, once the mechanical extraction is complete, up to 15% of the oil remains in oil pomace and in the mill wastewater, which can be extracted using organic solvents, often hexane. Optical fiber sensors based on long period fiber gratings (LPFG) have very low wavelength sensitivity when the surround refractive index is higher than the refractive index of the cladding. Titanium dioxide (TiO2) coated LPFG could lead to the realization of high sensitivity chemical sensor for the food industry. In this work LPFG coated with a TiO2 thin film were successfully used for to detect small levels of hexane diluted in edible oils and for real time monitoring the thermal deterioration of edible oils. For a TiO2 coating of 30 nm a wavelength sensitivity of 1361.7 nm/RIU (or 0.97 nm /% V/V) in the 1.4610-1.4670 refractive index range was achieved, corresponding to 0 to 12 % V/V of hexane in olive oil. A sensitivity higher than 638 nm/RIU at 225 degrees C was calculated, in the 1.4670-1.4735 refractive index range with a detection limit of thermal deterioration of about 1 minute.

Abstract
Optical fiber optrodes are attractive sensing devices due to their ability to perform point measurement in remote locations. Mostly, they are oriented to biochemical sensing, quite often relying on fluorescent and spectroscopic techniques, but with the refractometric approach being also considered when the objective is high measurement performance, particularly when focusing on measurand resolution. In this work, we address this subject proposing and theoretically analyzing the characteristics of a fiber optic optrode relying on plasmonic interaction. The optrode structure is a fiber optic tapered tip layout incorporating a lateral bimetallic layer (silver + gold) and operating in reflection.

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

Abstract
It is proposed the multiplexing of optical fiber-based surface plasmon resonance (SPR) sensors deployed in a ladder topology, addressed in wavelength by combining each sensor with specific fiber Bragg gratings (FBGs) and considering intensity interrogation. In each branch of the fiber layout, the FBGs are located after the sensor and the peak optical power reflected by the FBGs is a function of the relative spectral position between the SPR sensor and the FBG resonances, with the former dependent on the refractive index of the surrounding medium. The concept is tested for the multiplexing of two SPR sensors fabricated in an etched region of a single-mode fiber showing intrinsic refractive index sensitivity up to 5000 nm/RIU, which translates into a sensitivity of similar to 829 dB/RIU from the interrogation approach considered. The obtained refractive index resolution is in the order of 10(-4) RIU, and the crosstalk level between the sensors was found negligible.

Abstract
In this paper real time monitoring of oxidation of transition metals using long period fiber gratings (LPFG) is performed for nickel, copper, titanium, chromium and zinc. A thin layer is deposited over the LPFG with physical process deposition and is annealed up to 700 degrees C in air with a small oven. The whole oxidation process can be monitored by tracking the LPFG features of the attenuation band which results in an abrupt change when the oxidation occurs depending on the metal sample. A preliminary study to optimize optical fiber sensors sensitivity allowing choosing the correct oxide layer in a specific application is presented.

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.