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
In this letter, we present a new structure composed by a long-period grating (LPG) and a microsphere in series, which works as a modal interferometer besides allowing the mode coupled to the cladding to be coupled back to the core. The LPG was written by the electric arc technique and the microsphere was fabricated using a splicing machine. It is possible to use this new structure for simultaneous measurement of strain and temperature. It also allows one to obtain a temperature compensated strain sensor by using a proper data processing algorithm, which utilizes two distinct wavelengths for strain and temperature. Then, a strain sensitivity of 0.86 pm/mu epsilon and a reduced temperature sensitivity of 0.7 pm/degrees C were achieved.

Abstract
Optical fiber tweezers have been gaining prominence in several applications in Biology and Medicine. Due to their outstanding focusing abilities, they are able to trap and manipulate microparticles, including cells, needing any physical contact and with a low degree of invasiveness to the trapped cell. Recently, we proposed a fiber tweezer configuration based on a polymeric micro-lens on the top of a single mode fiber, obtained by a self-guided photopolymerization process. This configuration is able to both trap and identify the target through the analysis of short-term portions of the back-scattered signal. In this paper, we propose a variant of this fabrication method, capable of producing more robust fiber tips, which produce stronger trapping effects on targets by as much as two to ten fold. These novel lenses maintain the capability of distinguish the different classes of trapped particles based on the back-scattered signal. This novel fabrication method consists in the introduction of a multi mode fiber section on the tip of a single mode (SM) fiber. A detailed description of how relevant fabrication parameters such as the length of the multi mode section and the photopolymerization laser power can be tuned for different purposes (e.g., microparticles trapping only, simultaneous trapping and sensing) is also provided, based on both experimental and theoretical evidences.

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
In this work, a relative humidity (RH) sensor based on a structure with multimode interference is proposed and experimentally demonstrated. The multimode sensor is fabricated by fusion splicing a coreless fiber section to a single mode fiber. A hydrophilic agarose gel is coated on the coreless fiber, using the dip coating technique. By changing the surrounding RH, the refractive index of the coated agarose gel will change, causing a wavelength shift of the peak in the reflection spectra. For RH variations in the range between 60.0%RH and 98.5%RH, the sensor presents a maximum sensitivity of 44.2 pm/%RH, and taking in consideration the interrogation system, a resolution of 0.5%RH is acquired. This sensor has a great potential in real time RH monitoring and can be of interest for applications where a control of high levels of relative humidity is required.

Abstract
There is a set of important selection criteria in the design of fiber optic sensors that determine the compromise between design complexity and performance. Optical fiber sensors not only withstand high temperatures, but they can also operate in different chemical and aqueous media allowing measurements in areas not otherwise accessible. A Fabry-Perot cavity based on an air bubble created in a multimode fiber section is proposed. The air bubble is formed using only cleaving and fusion splicing techniques. The parameters used to produce the microcavities were found empirically. Two different configurations are explored: an inline cavity formed between two sections of MMF, and a fiber tip sensor. In the last, after the air bubble is created, a cleave is made near the cavity, after which the sensor is subjected to several electrical arcs to reshape the cavity and obtain a thin diaphragm. The inline sensor, with a length of similar to 297 mu m, was used to measure strain and presented a sensitivity of 6.48 pm/mu epsilon. Regarding the fiber tip sensor, it was subjected to glycerin/water mixture variations, by immerging the sensing head in several solutions with different concentrations of water in glycerin. In this case, the sensor had a length of similar to 167 mu m and a diaphragm thickness of similar to 20 mu m. As expected, with the increase of the external medium refractive index, the sensor visibility decreased. Furthermore, a wavelength shift towards red was observed, with a sensitivity of 7.81 pm/%wt. Both devices exhibited low dependence to temperature (<1.8 pm/degrees C).