Research on Cascade Inner Microcavity-Based Fiber Sensor

A multimode interference-based fiber cavity sensor was proposed. It was a single-mode–multimode–single-mode cascaded structure with an inner air cavity. The sensitivities of microcavity-based fiber sensor were theoretically analyzed. The sensitivities of temperature and axial strain were formula derived. A microcavity model was established with COMSOL software to study the sensitivities affecting factors. The transmission modes in cavity wall were analyzed, and the effective refractive indexes of them were simulated. With these simulation results, a conclusion could be obtained that the effective refractive indexes were depended on the mode order and the cavity diameter. The temperature and axial strain sensitivities were decided by the effective refractive indexes, and the size of the cavity was the key factor. The larger the size of the microcavity and the higher of the transmission modes, the higher the sensitivity of the sensor could be obtained. It can be a theoretical guidance to design and fabricate fiber cavity sensors.