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Study of strain measurement by fiber optic sensors with a sensitive fiber loop ringdown spectrometer

A sensitive fiber loop ringdown (FLRD) spectrometer without any additional optical component was utilized to obtain strain measurement on a single mode fiber optic sensor. The strain data were obtained by employing the theory of bending loss in single mode fibers. The best sensitivity of the sensors was obtained as 5.99 με with an 80.0 cm long sensor head when the sensor heads were stretched at the midpoint. The spectrometer system had a baseline-stability of 0.22%. Stretching the sensor head from off-midpoint positions resulted faster decays with higher optical losses. Comparison of the slopes relative to the stress positions showed that it may be utilized to obtain strain location without using any high-cost equipment. This portable, basic, and simpler FLRD spectrometer system offers high sensitivity with great baseline stability without utilization of any additional optical components and/or creating air-gap/air-cavity and encapsulation on the sensor head region. With its very attractive features of such as easy setup, low cost, and simple design, sensitive FLRD sensors may have a high potential for early detection in several applications such as structural health monitoring, biomedical sensing, mining, transportation and rail applications for continuous monitoring in real-time.