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
A fiber optic sensor for high sensitivity refractive index and temperature measurement able to withstand temperature up to 450 degrees C is reported. Two identical LPG gratings were fabricated, whereas one was coated with a high refractive index (similar to 1.78) sol-gel thin film in order to increase its sensitivity to the external refractive index. The two sensors were characterized and compared in refractive index and temperature. Sensitivities of 1063 nm/RIU (1.338 - 1.348) and 260 pm/degrees C were achieved for refractive index and temperature, respectively.

Abstract
One of the major issues in the modeling of subwavelength optical materials resides in how to compute the effective properties of such media. An efficient technique must be able to describe appropriately the electromagnetic response of the overall structure. Within this context, this work is focused on the calculation of effective parameters of metallic silver nanowires embedded in alumina background. An algorithm based on modal propagation is considered in order to estimate the refractive index at the visible spectrum. The resonances obtained in the computing model are compared to the predictions of analytical Bruggeman and Maxell-Garnett theories and analyzed by regarding excitation of surface modes at the metal-dielectric interface.

Abstract
This Letter reports on the assembly on the tip of an optical fibre of a metamaterial film fabricated by a self-assembly bottom-up method, composed of silver nanowires embedded in an alumina matrix. By illuminating the film through the fibre in a reflection configuration, we observe experimentally the optical response of the metamaterial in agreement with theoretical predictions and interpreted as the excitation of surface plasmon-polaritons in the cylindrical surface of the nanowires. These results pave the way for low-cost optical fibre devices that incorporate metamaterial films. (c) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Abstract
An optical fiber probe sensor based on a tapered-fiber Bragg grating (FBG) coated with 150-nm-thick Pd film is proposed for hydrogen detection. The FBG was written in a 50-mu m-diameter tapered fiber by deep ultraviolet femtosecond laser technology. A second FBG was inscribed in the 125 mu m-fiber section for temperature compensation. The sensing head was able to detect H-2 concentration in the range 0%-1% (v/v) H-2 at room temperature; a maximum sensitivity of 81.8 pm/%(v/v) H-2 was attained with temperature compensation. The influence of the Pd coating over temperature sensitivity of standard and tapered-FBGs is also presented.

Abstract
An intensity curvature sensor using a Photonic Crystal Fiber (PCF) with three coupled cores is proposed. The three cores were aligned and there was an air hole between each two consecutive cores. The fiber had a low air filling fraction, which means that the cores remain coupled in the wavelength region studied. Due to this coupling, interference is obtained in the fiber output even if just a single core is illuminated. A configuration using reflection interrogation, which used a section fiber with 0.13 m as the sensing head, was characterized for curvature sensing. When the fiber is bended along the plane of the cores, one of the lateral cores will be stretched and the other compressed. This changes the coupling coefficient between the three cores, changing the output optical power intensity. The sensitivity of the sensing head was strongly dependent on the direction of bending, having its maximum when the bending direction was along the plane of the cores. A maximum curvature sensitivity of 2.0 dB/m(-1) was demonstrated between 0 m and 2.8 m.