Abstract
In this work a wavelength multiplexing concept was demonstrated for frequency based self-referenced fibre optic intensity sensors relying on the utilisation of Bragg gratings and WDM couplers. The experimental results obtained showed a fairly good agreement with those predicted from the theory. It turned out that the system had negligible crosstalk between the two sensors. The resolution obtained for the sensors was found to be ˜0.05 dBvHz. It should be emphasised, that the sensing concept described in this work is particularly favourable in terms of the minimisation of system noise. This happens because what is monitored is the amplitude of two sinewaves, i.e., the detection bandwidth can be made as narrow as practically feasible, with the consequent decrease of the system noise level. The power budget of the sensing network can be improved if shorter lengths of delay fibre are used, with the penalty, however, of working with higher frequencies. On the other hand, if the reflectivity of the FBGs is optimised, the power received by the detectors will increase correspondingly. Finally, a proper choice of the coupling coefficient of the couplers in the reflective ladder topology will have a strong impact on the optical power levels reaching the detector unit. © 2002 IEEE.

Abstract
Theoretical and experimental results were presented which validated a new dual interferometric configuration with serrodyne processing for the remote sensing of electrical current. Linearity and waveform reproduction at 50 Hz were observed and a current resolution (˜22.4 ArmsHz- 1/2) was obtained. The utilization of the proposed interferometric concept to simultaneously perform metering and relaying current measurements was also addressed. © 2002 IEEE.

Abstract
An optical fiber current sensor based on a permanent magnet fixed on the center of a micromachined Si membrane has been presented. The transducing operation principle is magneto-mechanical and has a linear response. A great improvement of the sensitivity of the microcavities was achieved by the use of a planar coil. Interrogation of the transducer has been carried out using a Fabry-Perot interferometer with an all-fiber detection system to avoid the influence of electromagnetic noise. The effectiveness of a fiber scheme based on the utilization of two fibre Bragg gratings to generate two quadrature phase-shifted interferometric signals has also been reported. © 2002 IEEE.

Abstract
We present what we believe to be a novel miniaturized sensor configuration based on fiber Bragg gratings for simultaneous measurement of curvature and temperature in smart structures and composite materials. Because of the particular geometry of the sensing head, it is possible not only to measure the radius of curvature but also to determine the plane of curvature. We arrange three Bragg gratings in the vertices of the smallest equilateral triangle that can be defined by the cross sections of the fibers. The set is then inserted into a glue-filled capillary stainless-steel tube to provide both suitable protection for the Bragg sensors and rotational symmetry to the sensing head. This tube also ensures isolation from axial strain, allowing for the additional determination of temperature. The proposed sensing head is particularly well suited for applications in smart structures because it can be embedded along any layer of a composite material (including the neutral line) without special concern for the relative orientation of the Bragg gratings and the composite layers. We can also use this sensing configuration to implement more-sophisticated sensors dedicated, for example, to the measurement of multiaxial acceleration or flow and temperature. (C) 2002 Optical Society of America.

Abstract
An amplitude-phase-conversion self-referencing technique for intensity-modulated photonic sensors that uses two different-wavelength fiber Bragg gratings is presented. With this technique, the system response has been demonstrated to be almost unafffected by network power variations as high as 90%, of the total power launched by the source. We prove the multiplexing capability of this type of self-referenced fiber sensor by wavelength-division multiplexing two of them in a star network. A tunable fused biconical wavelength-division multiplexer is used for sensor addressing at the detection block, providing both good isolation and low cross-talk values. (C) 2002 Optical Society of America.

Abstract
We present a novel method to study the behaviour of the optical propel-ties of photopolymer materials with temperature. The photopolymer is deposited on the tip of optical fibres by dip coating to fabricate low-finesse Fabry-Perot microcavities. The signal processing technique utilized to interrogate the cavity is based on the generation of two quadrature phase-shifted interferometric signals using two Bragg fibre gratings. This technique enables the determination of the values of the thermo-optical coefficient and the linear coefficient of thermal expansion of the photopolymer. The effectiveness of the processing technique is also exploited in the study of the dependence of the temperature sensitivity on the cavity thickness.