Fiber Fabry–Pérot Interferometers Based on Air-Bubbles/Liquid in Hollow Core Fibers

This letter develops a miniature and highly sensitive fiber Fabry-Pérot interferometer (FFPI) that is based on an air-bubble and liquid in a hollow core fiber (HCF). The endface of the proposed FFPI is sealed off by an optical fiber plug to ensure the optical/chemical stability of the used liquids. The fiber plug is fabricated with a single-mode fiber taper to close the end of the liquid core fiber. The proposed technique ensures that the filled liquid neither effuses nor becomes contaminated. Experimental results show that the presence of both an air-bubble and liquid in the FFPI enables the highly sensitive measurement of temperature (T), the sensitivity of which can be controlled by changing the ratio of the volume of air to that of liquid in the HCF.