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Fiber loop ringdown gas flow sensors

Fiber loop ringdown (FLRD) is a versatile sensing technique, which has been increasingly used for the development of high sensitivity, fast response FLRD chemical, physical, and biomedical sensors. In this paper, we report the first fiber loop ringdown gas flow sensor. The FLRD gas flow sensor is based on a micro-bending sensing mechanism, in which optical loss is induced when a gas flows through the sensor head and creates a physical deformation. The sensor was employed to determine airflow at various rates. Two different sensor head configurations were investigated. The results show that the sensor has a high upper measuring range of 5–22.5 standard liters per minute (slpm). Given the known airflow cross sections used, the corresponding airflow speeds measured in this work are within the range of 5.7–311.0 m s−1. A theoretical detection resolution limit (minimum detectable change) for the sensor is estimated to be 0.1 slpm using the best fiber loop ringdown baseline stability of 0.2%, while the experimentally measured resolution limit is 2.5 slpm (or 2.9 m s−1). The sensor demonstrated a fast response (<1 s) and excellent reproducibility and reversibility. Compared with other types of airflow fiber optic sensors, this new FLRD airflow sensor, besides its simplicity and low cost, offers the additional capability of measuring higher gas flow rates and a high potential for the fiber optic gas flow sensor network.