Abstract
An optoelectronic system for detection and monitoring of methane has been developed and implemented. The signal processing technique used in the proposed system is based on Wavelength Modulation Spectroscopy (WMS). When associated with the revolutionary microstructured fibres, this scheme revealed an effective way to measure gas concentration. Aiming the optimization of the sensing head design, the methane diffusion time inside a hollow-core fibre was evaluated. An error of 2.8% between experimental and theoretical values was obtained, thus validating the adopted model. These results were very encouraging towards the implementation of a practical unit for remote gas monitoring applications. © 2008 IEEE.

Abstract
An investigation on the application of fiber Bragg gratings for the interrogation of interferometric low-finesse Fabry-Perot cavities is reported. The proposed scheme is based on the generation of two quadrature phase-shifted signals that allows the recovering of the change in the cavity length. Besides being totally passive, this technique offers a high degree of flexibility and has the potential to be used in the interrogation of very short cavities.

Abstract
A new fiber Bragg grating sensor configuration is presented for simultaneous measurement of strain and temperature. The sensor utilizes the effect of boron codoping on the temperature dependence of the refractive index in germanosilicate fibers. By writing gratings with close wavelengths in undoped and boron doped fibers, different temperature sensitivities are obtained while strain sensitivities remain the same. These gratings are then spliced to obtain a simple sensor head suitable for applications in smart structures and composite materials.

Abstract
A signal processing scheme for fiber Bragg grating sensors based on the utilization of adjacent modes of a multimode laser diode light source is demonstrated which allows high sensitivity to be obtained over a large measurement range, For strain measurements, a range of 4800 mu epsilon is achieved with a resolution of 0.08 mu epsilon/root Hz, yielding a dynamic range of 95 dB.

Abstract
A pseudoheterodyne, open-loop demodulation technique? for detecting wavelength shifts in wavelength encoded fiber Bragg grating sensors is presented, The scheme uses a processing Bragg grating that is identical to one used as a sensor, When the processing fiber grating is stretched periodically, the system of two gratings produces a carrier at this frequency with its phase modulated by the measurand signal applied to the sensing grating, The demodulation technique is intrinsically immune to fluctuation of optical power in the system and is independent of the source spectral profile characteristics. A resolution of approximate to 1 mu epsilon/root Hz for static axial strain was achieved.

Abstract
An optical sensor capable of simultaneously measuring displacement and temperature is presented. It incorporates a fiber Bragg grating temperature sensor and a low-finesse extrinsic Fabry-Perot cavity. A white light tandem interferometric technique is used to recover signal from the low finesse cavity. Signals obtained from the interferometer and the Bragg grating provide required information to simultaneously determine temperature and displacement. Experimental results are presented which demonstrate the feasibility of this sensor topology in practical applications.