Abstract
In this work an all optical hot-wire flowmeter based on a silver coated fibre incorporating a long period grating and a Bragg grating is demonstrated. Optical energy at 1480 nm propagating down the fibre is coupled by the long period grating into the fibre cladding and absorbed by the metallic coating deposited on the fibre surface over the Bragg grating position. This absorption acts like a hot-wire raising locally the fibre temperature, which is effectively detected by the FBG resonance shift. The temperature raise depends on the flow speed of the surrounding air that has the effect to cool the fibre. In this way, the FBG Bragg wavelength shift can be related with the flow speed. Results obtained demonstrate the working principle and a flow speed resolution of 0.08 m/s is demonstrated.

Abstract
We propose and theoretically study a novel surface-plasmon-resonance sensor based on an H-shaped, elliptical-core optical fibre. The two grooves of the H-fibre are coated with a thin, uniform metal layer that in turn is covered with a high-index dielectric layer to allow broad spectral tunability. The sensor maintains linear polarization and facilitates effortless splicing. Electromagnetic mode analysis indicates a sensitivity of 1800 nm/RIU (refractive-index unit) for aqueous analytes.

Abstract
In this work, the authors present an alternative Sagnac interferometer based on a suspended twin-core fibre. Using the suspended twin-core fibre, the pattern fringe is due to the different optical paths of the light in the two cores. In this case, the value of the refractive index difference between the two cores is 10(-3), which indicates an advantage of this approach, namely the possibility to use a small length of the suspended twin-core fibre. The sensing configuration was characterized for strain, temperature, curvature and torsion, respectively.

Abstract
In this work, we propose to take advantage of properties of a Bragg fibre for optical sensing. The Bragg fibre exhibits three concentric high refractive index layers embedded in pure silica and surrounding a 35 mu m diameter core. A short (0.3 m long) piece of Bragg fibre slightly multimode, is used to elaborate an intermodal interferometer, the spectral response of which exhibits a fringe pattern that depends on the operating wavelength, which can therefore be used as a sensor. The two modes considered were found to be the fundamental LP(01) and the high-order mode LP(02). The sensor has been characterized in strain and temperature and presents a sensitivity of - 1.09 pm/mu epsilon and 14.1 pm/degrees C respectively. The sensor demonstrated insensitivity to curvature thanks to well known Bragg fibre properties.

Abstract
In this work, we demonstrate the possibility of fabricating short LPGs and rocking filters in highly birefringent Photonic Crystal Fiber using CO(2) laser. In our experiments both kinds of gratings were made in the same Boron doped highly birefringent PCF using similar exposure parameters. We also present the sensing capabilities of both fabricated gratings to temperature, strain and hydrostatic pressure by interrogation of the wavelength shifts at the different resonances.

Abstract
A concept of long-period-based optical fiber sensors, with broadband light illumination generated just after the sensing structure, is presented in this work. This new approach allows the interrogation in transmission of the sensing head while integrated in a reflective configuration, which means the long-period grating (LPG) sensor is seen in transmission by the optical source but in reflection by the measurement system. Also, it is shown that with this illumination layout the optical power balance is more favorable when compared with the standard configurations, allowing better sensor performances, particularly when the sensing head is located far away from the photodetection and processing unit. This is demonstrated for the case of the LPG structure applied to measure strain and using ratiometric interrogation based on the readout of the optical power reflected by two fiber Bragg gratings spectrally located in each side of the LPG resonance.