Power modulation based fiber-optic loop-sensor having a dual measurement range

A fiber-optic sensor is investigated in this work for potential applications in structural health monitoring. The sensor, called fiber-loop-sensor, is based on bending an optical fiber beyond a critical radius to obtain intensity losses and calibrating the losses with respect to the applied force or displacement. Additionally, in the present case, the use of single-mode optical fibers allows the appearance of several resonance peaks in the transmitted power-displacement graph. The intensity of one of these resonances can be tracked in a narrow range to obtain high sensitivity. Experimental results show that the resolution of 10(-4) N for force and 10(-5) m for displacement can be obtained in these sensors. The sensors are calibrated for various loop radii and for various loading rates. They are also tested under loading-unloading conditions for over 10(4) cycles to observe their fatigue behavior. The sensors show very repeatable response and no degradation in performance under these test conditions. Simple construction and instrumentation, high sensitivity, and low cost are the advantages of these sensors.