We report on the use of a fiber Bragg grating (FBG) based sensor written in a photonic crystal fiber (PCF) to monitor the cure cycle of composite materials. The PCF under study has been specifically designed to feature a high phase modal birefringence sensitivity to transverse strain and a very low sensitivity to temperature. We exploit these particular properties to measure strain inside a composite material in the out-of-plane direction. The embedded FBG sensor has been calibrated for transverse and axial strain as well as for temperature changes. These FBGs have then been used as embedded sensors during the manufacturing of a composite material in order to monitor how strain develops inside the composite during the cure cycle. We show that our sensors allow gaining insight in the composite cure cycle in a way that would be very difficult to achieve with any other sensor technology.
Microstructured optical fibers are increasingly used in optical fiber sensing applications such as for example optical fiber
based structural health monitoring. In such an application the fiber may experience substantial mechanical loads and has
to remain functional during the entire lifetime of the structure to be monitored. The resistance to different types of
mechanical loads has therefore to be characterized in order to assess the maximum stress and strain that a fiber can
sustain. In this paper we therefore report on the extensive set of tensile tests and bending experiments that we have
conducted both on microstructured optical fibers with an hexagonal air hole lattice and on standard optical fibers. We use
Weibull statistics to model the strength distribution of the fibers and we follow a fracture mechanics approach in
conjunction with microscopic observations of the fractured end faces to study crack initiation and propagation in both
types of fibers. We show that the failure strain of microstructured fibers is about 4.3% as obtained with tensile tests,
compared to 6.7% for reference fibers. Although the mechanical strength of microstructured optical fibers is lower than
that of the standard fibers it is still adequate for these fibers to be used in many applications.
We discuss on-going reliability studies of micro-optical components and assemblies as conducted in the EU FP6 Network of Excellence on Micro-Optics "NEMO". We focus on three case studies including first biaxial fatigue testing of micro-optical components, second reliability testing and quality control of MEMS and third micro-interferometric tomography for measuring optical fibre refractive index changes. For each of these case studies we discuss the dedicated measurement and characterization methods as well as first results and the perspectives for future research.