Abstract
It is reported a new optical sensing system, based on long period fiber gratings (LPFGs) coated with cuprous oxide (Cu2O), for the quantification of ethanol concentration in ethanol-gasoline mixtures. The detection principle is based on the spectral features dependence of the Cu2O coated LPFGs on the refractive index of the surrounding medium. The chemical constitution of the ethanol-gasoline samples was obtained by gas chromatography mass spectrometry (GC) and GC thermal conductivity detection. Two different modes of operation are presented, wavelength shift and optical power shift mode of operation, with good linear relations between ethanol concentration and the corresponding spectral features of the LPFGs, R-2 = 0.999 and 0.996, respectively. In the range of ethanol concentration up to 30% v/v, the sensitivities were 0.76 +/- 0.01 nm/% v/v and 0.125 +/- 0.003 dB/% v/v with resolutions of 0.21% v/v and 0.73% v/v and limits of detection of 1.63% v/v and 2.10% v/v, for the for the same operation modes, respectively.

Abstract

Abstract
Long period fiber gratings (LPFGs) were coated with iron (Fe) and exposed to oxidation in air and in water having different concentrations of sodium chloride (NaCl) to detect the formation of iron oxides and hydroxides. The process was monitored in real time by measuring the characteristics of the LPFGs attenuation bands. Thin films of Fe were deposited on top of silica (SiO2) substrates, annealed in air, and exposed to water with NaCl. The composition of the oxide and hydroxide layers was analyzed by SEM/EDS and X-ray diffraction. It observed the formation of oxide phases, Fe3O4 (magnetite), and Fe2O3 (hematite) when annealing in air, and Fe-2(OH)(3) Cl (hibbingite) and FeO(OH) (lepidocrocite) when exposed to water with NaCl. Results shows that Fe-coated LPFGs can be used as sensors for real-time monitoring of corrosion in offshore and in coastal projects where metal structures made of iron alloys are in contact with sea or brackish water. In addition, LPFGs coated with hematite were characterized for sensing, leading to the conclusion that the sensitivity to the refractive index of the surrounding medium can be tuned by proper choice of hematite thickness.

Abstract
Pressure fiber sensors play an important role in downhole high pressure measurements to withstand long term operation. The purpose of this paper is to present an application of hollow core photonic crystal fiber (HC-PCF) as a high pressure sensor head for downhole application based on dispersion variation. We used a high pressure stainless steel unit to exert pressure on the sensor. The experimental results show that different wavelengths based on sagnac loop interferometer have additive sensitivities from 5 x 10(-5) nm/psi at 1480 nm to 1.3 x 10(-3) nm/psi at 1680 nm. We developed a simulation to understand the reason for difference in sensitivity of wavelengths and also the relationship between deformation of HC-PCF and dispersion variation under pressure. For this purpose, by using the finite element method, we investigated the effect of structural variation of HC-PCF on spectral transformation of two linear polarizations under 1000 psi pressure. The simulation and experimental results show exponential decay behavior of dispersion variation from -3.4 x 10(-6) 1/psi to -1.3 x 10(- 6) 1/psi and from -5 x 10(-6) 1/psi to -1.8 x 10(-6) 1/psi, respectively, which were in a good accordance with each other. (C) 2014 AIP Publishing LLC.

Abstract
The combustion of coal wastes resulting from mining is of particular environmental concern, and the importance of proper management involving real-time assessment of their status and identification of probable evolution scenarios is recognized. Continuous monitoring of the combustion temperature and emission levels of certain gases allows for the possibility of planning corrective actions to minimize their negative impact on the surroundings. Optical fiber technology is well suited to this purpose and here we describe the main attributes and results obtained from a fiber optic sensing system projected to gather data on distributed temperature and gas emissions in these harsh environments.

Abstract
In this paper, we analyze numerically and experimentally a remote optical sensor system based on Raman Amplification, composed by one long period grating operating as a sensor head separated by 50 km from the optical source and the interrogation unit composed by two fiber Bragg gratings. Since the active components of the system and the sensor head are separated over such a large distance, it is necessary to consider optical amplification to strengthen the optical signal. The use of Raman amplification allows reaching the desirable gain bandwidth by changing the pump lasers parameters such as the power, number of pumps and spectral position. We present the obtained measurement results of the environmental temperature for two different setups that was analyzed a priori by the numerical model. We show that the power ratio between the two central wavelengths of the FBG has a linear relation with the change of LPG resonance with temperature.