Abstract
In this research programme, methodologies for structural health monitoring (SHM) of composite over-wrapped pressure vessels (COPV) were addressed. So, this work is part of the development of a COPV laboratorial prototype incorporated with non-destructive sensing technologies. The aim is to detect and identify critical aspects that can happen during operation, in order to reduce possible safety problems. Fibre Bragg grating (FBG) optical sensors and polyvinylidene fluoride (PVDF) polymeric piezoelectric were the selected sensing technologies. These sensors were embedded in the liner-composite interface during its manufacturing and monitored the prototype while tested under cyclic internal pressure loading. The measurements collected from the sensors were compiled with the analysis of test data and are presented in this paper. Also, the suitability of the two sensing technologies, issues related to sensor embedding and the monitoring strategy are discussed.

Abstract
A low-coherence technique in a Michelson interferometer for measuring polarization mode dispersion (PMD) was tested. The measured PMD mean value for one reel, in a period of several days, was 0.0405 +/-. 0.0008 ps/km(1/2) and for the other reel, it was 0.0463 +/- 0.0004 ps/km(1/2). Stochastic and random PMD behavior was observed. (C) 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2310-2312, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25428

Abstract
In this work, it is presented a Sagnac interferometric configuration based on a suspended twin-core fibre for sensing applications. Using the suspended twin-core fibre, the fringe pattern is due to the differential optical path of the light in the two cores associated with a refractive index difference of similar to 10(-3), which indicates an advantage of this approach compared with those based on Hi-Bi fibres, namely the possibility to use a small length of suspended twin-core fibre. The sensing configuration was characterized for torsion, temperature and strain. Using the Fast Fourier Transform technique it is possible to obtain the measurand induced amplitude variations of the fringe pattern. The results obtained indicate the viability of a temperature and strain independent torsion sensor.

Abstract
In this paper, it is presented a brief review of the sensing applications using photonic crystal fibres. Since the first publication, several authors have studied their properties and possible applications in engineering. Due to their geometry, the great potential in optical sensing is in bio and gas sensing. Recently, with the possibility of inscribing Bragg grating structures on these fibres, it is possible to use them for other applications. Finally, this paper reviews the recent works with different types of photonic crystal fibres for interferometry.

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.