Abstract
In the present paper, the influence of the fiber Bragg grating (FBG) length and its coating on embedded FBGs in polymers is evaluated. Different FBG lengths and coatings, uncoated and acrylate-recoated, are used. The evolution of their spectra is also followed during laminate curing on a hot-plate press. The Bragg gratings are used as optical fiber sensors, and their sensitivity and reliability are analyzed. The resulting sensor signal characteristics and the strain answers to different loading modes, i.e. tensile, flexural and through-thickness compression, are also studied.

Abstract
An optical fibre sensor for determination of acetic acid is presented. The sensing probe is based on a fibre Bragg grating (FBG) Fabry-Perot cavity, coated with a thin film of sol-gel-PVP (polyvinylpyrrolidone) composite material. The polymeric thin film renders the interferometric output sensitive to the presence of carboxylic acid species. Results show that the wavelength of the interferometric peaks changes with acetic acid concentration, enabling its quantification. Coupling the fibre probe with a serrodyne modulated readout interferometer enables pseudo-heterodyne interrogation and the detection of acetic acid with a sensitivity of 92.6 deg/% L/L and a resolution of 0.2% L/L. The results demonstrate the potential of the proposed scheme to operate as a sensitive chemical sensor platform.

Abstract
In this work, a laser sensor that uses the multipath interference produced inside a ring cavity to measure the power loss induced by a moving taper intensity sensor is described. The laser is created due to the virtual distributed mirror formed by the Rayleigh scattering produced in a dispersion compensating fibre when pumped by a Raman laser. Two laser peaks were formed, one of them is obtained by the Raman gain (1555 nm) inside the ring and the second is created by the combination of the Raman gain and the Rayleigh scattering (1565 nm). A taper sensor is used as displacement sensor and with the increases of losses the second laser peak amplitude is reduced. In the process the first peak is maintained constant and can be used as reference level.

Abstract
The strain and temperature sensing characteristics of a modal interferometer based on two Bragg fibers have been investigated. The special nature of this sensor is that the two Bragg fibers used present a different external cladding shape. It appears that the sensitivity to the sensing parameters are different for the two Bragg fibers, which makes it possible to fabricate several sensing configurations based on the combination of these two Bragg fibers for strain and temperature discrimination.

Abstract
A highly birefringent photonic bandgap Bragg fiber loop mirror configuration for simultaneous measurement of strain and temperature is proposed. The group birefringence and the sharp loss peaks are observable in the spectral response. Because the sensing head presents different sensitivities for strain and temperature measurands, these physical parameters can be discriminated by using the matrix method. It should be noted that this Bragg fiber presents high sensitivity to temperature, of similar to 5.75 nm/degrees C, due to the group birefringence variation. The rms deviations obtained are +/- 19.32 mu e and +/- 0.5 degrees C, for strain and temperature measurements, respectively. (C) 2011 Optical Society of America

Abstract
In this work, a laser sensor is described that uses the multipath interference produced inside a ring cavity to measure the power loss induced by a moving taper intensity sensor. The laser is created due to the virtual distributed mirror formed by the Rayleigh scattering produced in a dispersion compensating fiber when pumped by a Raman laser. Two laser peaks were formed, one of them is obtained by the Raman gain (1555 nm) inside the ring and the second is created by the combination of the Raman gain and the Rayleigh scattering (1565 nm). A taper sensor is used as displacement sensor and when the losses is applied in the taper the second laser peak is reduced and the first peak is maintained constant and can be used as reference level.