Seven-core fiber based in-fiber Mach–Zehnder interferometer for temperature-immune curvature sensing

An in-fiber Mach–Zehnder interferometer (MZI) based on a brief coreless fiber (CLF) and a section of seven-core fiber (SCF) sandwiched in single mode fiber (SMF) is proposed and demonstrated. A supermode interference is created in the SCF that forms interference spectrum to perceive external curvature changes. A linear enhanced sensitivity of -26.5517 dB/m−1 for temperature-immune curvature measurement within the curvature range of 0.527–1.395 m−1 is experimentally achieved. Moreover, the strain response of the MZI is experimentally investigated. This MZI exhibits accurate and high sensitivity for curvature detection by economic intensity detection, which indicates its potential applications in the engineering field.