Gas Refractometer Based on Optical Fiber Extrinsic Fabry—Perot Interferometer With Open Cavity

In this letter, we proposed a gas refractometer based on optical fiber Fabry-Perot interferometer with an open cavity. The Fabry-Perot cavity is a short section capillary tube spliced between a single-mode fiber and a side-hole fiber (SHF). The unique cladding of the SHF enables gas entering or leaving the Fabry-Perot cavity freely. The measurement of pressure-induced refractive index change of nitrogen gas has been demonstrated by monitoring the wavelength shift of the interference pattern. The robust and microsize architecture make the interferometer a good candidate for gas sensing applications.