Analysis of the long-term reliability of fiber optic cantilever beams with application to optical sensors

Among others, the structure based on a simple optical fiber in a cantilever beam configuration has been proposed as the sensing element in several optical sensors for vibration monitoring. The imposed vibration pattern can be measured by means of the displacement of the fiber end; in this case, the fiber beam acts as a spring-mass mechanical system, and it is capable of measuring low frequency accelerations. In this case, a fatigue-induced degradation of the optical fiber material is expected due to the continuous vibration with alternate cycles of tension and compression. Therefore, the possibility of a short lifetime due to a fracture of the fiber beam is a major concern with this structure. Up to now, the mechanical reliability of the optical fiber has been extensively analyzed for axial stress in optical cables for telecommunications applications or in static bending experiments. However, it would be desirable to analyze the fatigue process induced by the stress using the same cantilever configuration. We report an experimental analysis of the long-term reliability of this structure, with application to a wide range of sensors for mechanical magnitudes.