Four fiber based distributed strain sensor

This paper presents a novel four fibers based optical fiber sensor for distributed strain measurement. The sensor is composed of two active and two passive fibers. Localized strain makes light couple from the active fiber to the passive fiber. The output of active fiber is used for strain value sensing whereas the outputs of the passive fibers are used to calculate the position of strain. Distributed sensing is realized based on the attenuation of the passive fiber, which has a greater attenuation coefficient than the active fiber. The theoretical model and limit parameter analysis, including the maximum length and the spatial resolution are proposed.