High sensitivity gas refractometer based on all-fiber open-cavity Fabry–Perot interferometer formed by large lateral offset splicing

A compact, all-fiber, open-cavity Fabry–Perot interferometer gas refractometer formed by fusion splicing a short section of single-mode fiber (SMF) between two sections of SMFs with a large lateral offset is proposed. Only simple fabrication steps including cleaving and fusion splicing are involved, so the fabrication is easy, safe, and cost effective. Such fabricated sensors have been successfully demonstrated as gas refractometers having a refractive index response of high sensitivity (∼1540nm/RIU), good linearity, and high repeatability. Temperature evaluations also show that this kind of interferometer has a very low thermal sensitivity.