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
Recent trends on microbiology point out the urge to develop optical micro-tools with multifunctionalities such as simultaneous manipulation and sensing. Considering that miniaturization has been recognized as one of the most important paradigms of emerging sensing biotechnologies, optical fiber tools, including Optical Fiber Tweezers (OFTs), are suitable candidates for developing multifunctional small sensors for Medicine and Biology. OFTs are flexible and versatile optotools based on fibers with one extremity patterned to form a micro-lens. These are able to focus laser beams and exert forces onto microparticles strong enough (piconewtons) to trap and manipulate them. In this paper, through an exploratory analysis of a 45 features set, including time and frequency-domain parameters of the back-scattered signal of particles trapped by a polymeric lens, we created a novel single feature able to differentiate synthetic particles (PMMA and Polystyrene) from living yeasts cells. This single statistical feature can be useful for the development of label-free hybrid optical fiber sensors with applications in infectious diseases detection or cells sorting. It can also contribute, by revealing the most significant information that can be extracted from the scattered signal, to the development of a simpler method for particles characterization (in terms of composition, heterogeneity degree) than existent technologies.

Abstract
We present a new method for coupling light to high-Q silica whispering gallery mode resonators (WGMs) that is based on long period fiber gratings (LPGs) written in silica fibers. An LPG allows selective excitation of high-order azimuthally symmetric cladding modes in a fiber. Coupling of these cladding modes to WGMs in silica resonators is possible when partial tapering of the fiber is also implemented in order to reduce the optical field size and increase its external evanescent portion. Importantly, the taper size is about one order of magnitude larger than that of a standard fiber taper coupler. The suggested approach is therefore much more robust and useful especially for practical applications. We demonstrate coupling to high-Q silica microspheres and microbubbles detecting the transmission dip at the fiber output when crossing a resonance. An additional feature of this approach is that by cascading LPGs with different periods, a wavelength selective addressing of different resonators along the same fiber is also possible. (C) 2014 Optical Society of America

Abstract
A refractive index sensor based on a bent in-line Mach-Zehnder interferometer is investigated via numerical analysis through the beam propagation method. Comparative results are presented for the conventional not bent sensor and for the cases in which this sensor is bent at certain radii of curvature. The results showed poor sensitivity for the not bent sensor presenting a wavelength shift similar to 75 nm/RIU within the refractive index range of 1.33 to 1.41 and 55 nm/RIU near the refractive index value of 1.41. In contrast, when the sensor was bent its sensitivity was greatly increased presenting the best response at a radius of curvature of 12 mm achieving similar to 1025 nm/RIU for values of refractive index from 1.33 to 1.41 and similar to 2000 nm/RIU near the refractive index value of 1.41.

Abstract
This work presents numerical results related to an in-line Mach-Zehnder interferometer used as a refractive index sensor. The in-line Mach-Zehnder is based on abrupt tapers in standard single mode optical fiber. Numerical simulations were carried out using commercial software based on Beam Propagation Method in order to analyze the sensitivity response in terms of wavelength shift when this sensor is bent at certain radii of curvature. We realized that application of bending in the In-line Mach-Zehnder interferometer enhanced considerably the sensitivity of this sensor to the external refractive index. The best result was achieved for a radius of curvature of 10 mm (similar to 500 nm/RIU for the refractive index range of 1.33 to 1.41) improving the sensitivity about eight times in comparison with the case with no bent.

Abstract
This letter presents experimental results of a refractive index sensor using a bent optical fiber taper. The approach of this sensor is based on an in-line Michelson interferometer implemented with a single mode tapered fiber with a cleaved tip end and changing tilt angle, enabling to tune its refractive index sensitivity. Several radii of curvature are tested and their refractive index sensitivities are analyzed for a refractive index range between 1.333 and 1.405. A clear enhancement of the sensor response is achieved at specific taper bending radii. A substantial improvement in the refractive index sensitivity, at values very close to distilled water, is obtained with a radius of curvature of 11 mm. A significant enhancement of the sensor response is also achieved for a refractive index close to 1.40 with a radius of curvature of 16.5 mm. (c) 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:921-924, 2015