Abstract
We study the origin of antisymmetric perturbation of the fiber in are-induced long-period gratings that couple the core mode into the antisymmetric cladding modes. We demonstrate that this perturbation is caused by a temperature gradient in the fiber, which is induced, in turn, by a temperature gradient in the arc discharge.

Abstract
By measuring intensity distributions of cladding modes and using an optimization technique we show that the perturbation which forms arc-induced gratings in standard fibers is antisymmetric, while the perturbation in boron-germanium codoped fibers is symmetric. © 2006 Optical Society of America.

Abstract
A phase-shifted long-period fiber grating sensor fabricated by electric arc technique is used to measure bending curvature and temperature. © 2006 Optical Society of America.

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
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
The measurement of micro-displacement or bending using a long-period fibre grating (LPG) in a self-referenced fibre optic intensity sensor is presented. The sensing head is based on a LPG whose attenuation peak changes as a function of its micro-displacement or bending and the fibre optic intensity sensor is referenced in frequency. Two other LPGs were used as rejection filters. located at the output of the optical source to shorten its spectral width. The implemented experimental set-up is described and, the results are presented being considered the measurement range and the intrinsic resolution.