Fringe visibility enhanced Fabry-Perot interferometer and its application as gas refractometer

In this paper, we propose a gas refractometer based on a fringe visibility enhanced optical fiber Fabry-Perot interferometer. The Fabry-Perot cavity is fabricated by cascading single mode fiber and capillary tubes with different inner diameters. Gas can enter and leave the cavity freely through the hole of the capillary tube. A graded index fiber based collimator is inserted in between the single mode fiber and capillary tube to compensate the light loss and improve the fringe visibility. The numerical simulation and experiment results of Fringe visibility enhancement are presented. Gas refractive index measurement using the proposed interferometer is also demonstrated.