Microfiber-Enabled In-line Fabry–Pérot Interferometer for High-Sensitive Force and Refractive Index Sensing

A microfiber-enabled Fabry-Perot interferometer (FPI) constructed by splicing a section of microfiber between two cleaved standard single-mode fibers (SMFs) with unique relative fiber cross section relationship has been proposed and experimentally demonstrated. The opening air cavity between the two SMF ends connected by the microfiber serves as an FP cavity and also a direct sensing head. The sensing characteristics of the FPIs with different cavity lengths and microfiber diameters have been studied. A force sensitivity as high as 167.41 nm/N (~200 pm/μe) and a high refractive index (RI) sensitivity of 1330.8 nm/RIU (around a RI of 1.33) have been achieved by using the microfiber-based FPI with ~21 μm cavity length and ~44 μm microfiber diameter. Such a device has several merits such as simple configuration, compactness and reliability in operation owing to the extremely low thermal cross-sensitivities.