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
In this work, we analyze a remote optical sensor system based on Raman amplification, composed by one Long Period Grating (LPG) as a sensor head, separated by 50 km from the optical source, and the interrogation unit composed by two Fiber Bragg Gratings (FBGs) modulated by two Piezoelectrics Transductors (PZTs). Optical fiber sensor systems are typically limited to operate at distances of only few kilometers due to the attenuation effects and noise present in the optical fiber that adversely affects the performance of the sensor interrogation process. We present experimental and simulated results obtained in the context of the analysis of remote optical fiber sensors. The simulation models compute the Raman interaction between the pumps and the sensor signals and allow speeding up the analyses regarding the setup to be experimentally implemented in order to measure/monitor environmental temperature. Experimental results obtained in the implemented setup show that under Raman amplification the power ratio between the two central wavelengths of the FBGs has a linear relation with the change of the LPG resonance induced by environmental temperature.

Abstract
In this work. the LPG-assisted fibre Michelson modal interferometer is studied as a sensing structure to environmental refractive index, temperature and liquid level when coherence addressing and heterodyne interrogation are considered. The effects on measurand sensitivity of the order of the cladding mode excited by the LPG, of the degree c etching of the sensing fibre and of the fibre type used are investigated.

Abstract
Birefringence monitoring of a Hi-Bi fibre under chemical etching is conducted. The Hi-Bi fibre (a bow-tie type) was inserted in a fibre loop mirror and the optical spectral response was measured while chemical etching of the Hi-Bi fibre was taking place. The birefringence of the bow-tie fibre has decreased due to the etching and the wavelength spacing of the fringe minima of the fibre loop mirror has increased.