Oscillator interrogated time-of-flight optical fiber interferometer for global strain measurements

In this paper, we demonstrate an oscillator interrogated time-of-flight optical fiber interferometer that provides global strain information for large-scale structures. The sensing resolution of the interferometer is sufficient for many structural applications, while the system is relatively inexpensive and durable as compared to previous methods. The measurable displacement range is determined by the oscillator frequency and can therefore be designed to be significantly larger than that of current systems. An optical length change resolution of 9.5 mm and range of 1.39 m are demonstrated experimentally. To easily embed the interferometer in structures and effectively increase the fiber sensing length, a commercially available prefabricated fiber ribbon is used. Results from static loading tests of a FRP strengthened reinforced concrete beam with embedded fiber ribbons show the feasibility of this technique for monitoring infrastructure systems.