Abstract

Abstract

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 Letter, a hybrid interferometer for simultaneous measurement of the partial pressures of O-2 and CO2 mixtures is reported. The sensing head consists in the combination of two interferometric structures, one a Fabry-Perrot cavity and the other a modal interferometer. The intrinsic Fabry-Perot was formed by splicing a single mode fiber with a graded index fiber length that was then subjected to chemical etching creating an air cavity. The second interferometer is based on a splice of a pure silica tube in series with the Fabry-Perot. It was observed for a particular gas that its refractive index changes with pressure variation in a specific way, a characteristic that permitted the simultaneous measurement of partial pressures of CO2 and O-2 with rms deviations of similar to +/- 48.7 kPa and similar to +/- 20.1 kPa, respectively. (C) 2012 Optical Society of America

Abstract
It is reported a LPG dynamic interrogation technique based on the modulation of fibre Bragg gratings located in the readout unit that permits to attenuate the effect of the 1/f noise of the electronics in the resolution of the LPG-based sensing head. The concept is tested to detect variations of the external refractive index and a resolution of 2.0x10 (4) NIR was achieved without system optimization. Additionally, the effect in the sensor resolution when introducing Erbium and Raman optical amplification is experimentally investigated.

Abstract
A high birefringent D-type fibre loop mirror used as refractometer is reported. A chemical etching was applied to the D-type fibre and presented high sensitivity for the surrounding medium refractive index. The refractometer was tested with different refractive indices in liquids and characterized in temperature, showing a linear and independent response to both parameters. With these results the refractometer can perform simultaneous measurement of refractive index and temperature.