An In-Fiber Dual Air-Cavity Fabry–Perot Interferometer for Simultaneous Measurement of Strain and Directional Bend

摘要

A simultaneous strain and directional bend sensor based on an in-fiber dual air-cavity Fabry–Perot interferometer (FPI) is presented and demonstrated. The hybrid structure is composed of a fraction of dual side-hole fiber fusion spliced in between a seven-core fiber and a multimode fiber. The bending sensitivities of the two air-cavity FPIs at two opposite most sensitive directions are 120.5 pm/ text{m}^{-1} and −122 pm/ text{m}^{-1} , 110.4 pm/ text{m}^{-1} , and −121.1 pm/ text{m}^{-1} , respectively. The strain sensitivities of the two FPIs are 1.59 pm/ mu varepsilon and 1.52 pm/ mu varepsilon , respectively. By using the method of difference between the two mutually independent air-cavity FPIs, the highest bending sensitivities can be improved to be 242.5 pm/ text{m}^{-1} and −231.5 pm/ text{m}^{-1} , respectively, and the axial strain effect can be eliminated simultaneously.