Miniature refractometer based on Mach–Zehnder interferometer with waist-enlarged fusion bitaper

Abstract

A miniature refractometer by using a Mach–Zehnder interferometer (MZI) in a standard single mode fiber (SMF) with two waist-enlarged fusion bitapers is proposed and experimentally demonstrated. Such an all-fiber SMF-MZI incorporates an intermodal interference between the core mode and cladding modes. Because the cladding modes are sensitive to the external environment, the SMF-MZI is exploited for refractive index measurement. Experimentally, high sensitivity of 266.5 nm/RIU and resolution of 3.75×10^−5 RIU are achieved within a range from 1.346 to 1.4412. The temperature effect of the proposed refractometer is also analyzed.