Novel Fibre Optic Based Structures for Sensing Applications

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Orlando Frazão
Francisco Araújo
Paulo Caldas
Gaspar Rego
José Luís Santos
Luís Alberto Ferreira
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Optical sensing based on optical fibres can be boosted to new performance levels by combining the fibre waveguide with other fibre structures, such as Bragg gratings, long period gratings, tapers, couplers, multimode interference devices and even microspheres. Along this path, it will be shown the feasibility to have new fibre optic interferometers highly sensitive to environmental parameters, particularly to the refractive index of the surrounding medium, to curvature, to flow and others. Also, it will be presented results that show the possibility to tune the intrinsic strain sensitivity of a fibre Bragg grating when this device and a fused taper are properly integrated. Finally, it will be described a fibre optic structure for simultaneous measurement of strain and temperature, which relies on the utilization of two cascaded fibre loop mirrors, containing one of them an Hi-Bi photonic crystal fibre, while the second one includes a length of internal elliptical cladding fibre