Hybrid AG-FFPI/RLPFG for Simultaneously Sensing Refractive Index and Temperature

This work presents a novel, simple, and sensitive device for simultaneously sensing refractive index (RI) and temperature (T) of its surrounding environment. The sensing elements are based on a hybrid air-gap fiber Fabry-Pérot interferometer (AG-FFPI) with a reflective long-period fiber grating (RLPFG). An air gap of around 10 μm is formed in an Sn-overlaying process on the fiber endface to make a fiber Fabry-Pérot interferometer whose interferometric cavity is formed between the fiber endface and the surface of the Sn metal. The proposed devices are characterized by the simple fabrication and high sensitivity to both T and RI, which can be simultaneously measured. Additionally, the proposed device can readily recognized the response from ambient variations in T or the RI.