Highly Sensitive Air-Gap Fiber Fabry–Pérot Interferometers Based on Polymer-Filled Hollow Core Fibers

This letter, for the first time, investigates a novel, and ultracompact air-gap fiber Fabry-Pérot interferometer (AG-FFPI), which is based on a polymer-filled hollow core fiber (HCF) endface. The proposed polymer-filled AG-FFPI has advantages of easy fabrication, high temperature sensitivity, low cost, and arbitrary length of air-gap. The variation of the Fabry-Pérot cavity length can be greatly enhanced from exploiting the high thermal expansion coefficient of the elastic polymer-filled in the HCF. The proposed device exhibits a wavelength shift of the interference fringes that corresponds to temperature sensitivity of , which is equivalent to sensitivity to a change in cavity length of .