Abstract
A closed loop technique for measuring Bragg wavelength shifts based on active wavelength tuning of a WDM coupler is presented. By stretching the coupling region of a fused biconical WDM, the 3 dB point is set by the feedback loop to always match the reflected Bragg wavelength. With this scheme, sensitivities usually associated with highly selective WDM can be obtained without compromising the measurement range.

Abstract
A technique for the demodulation of fiber Bragg grating (FBG) sensors based on the use of a second wavelength-matched FBG receiver to track wavelength shifts from the FBG sensor is analyzed, particularly regarding its sensitivity as determined by primary noise sources. Numerical and experimental results show that there is an optimum Bragg wavelength difference between the two FBG's that maximizes the sensitivity for this demodulation technique. (C) 1997 Optical Society of America

Abstract
A passive self-referencing all-fibre technique for Bragg wavelength detection using a biconical fibre filter is described. This filter, basically a tapered depressed-cladding fibre, exhibits a periodic spectral power dependence which permits direct tracking of wavelength shifts in a 20nm unambiguous range. Dynamic strain resolution of 1.5 mu strain/root Hz has been achieved.

Abstract
Progressive ladder topology is studied by consideration of its properties of power budget and coupler tailoring. Optimization criteria are addressed for lossless and real systems, and their basic characteristics are compared with other topologies. Numerical results are presented, and an experiment is described for the case in which the network supports interferometric and intensity (with referentiation) fiber-optic-based sensors.

Abstract
A simulation characterization with FEM was made, showing that the HiBi fibre was sensitive to different applied load angles. As such, the experimental data for transversal strain was assessed and the obtained sensibility values were in accordance with the simulation results. The collected data enable the complete characterization of the HiBi FBG, showing its capability to be used as a multiparameter sensor.

Abstract
A chirped fibre Bragg grating was written in an Erbium doped fibre. It was found that the slope of the reflected spectral power could be tuned by changing the pump power. The gratings fabricated were demonstrated to be useful in the development of a technique for optical interrogation of FBGs sensing heads with tunable sensitivity. © 2003 OSA/BGPP.