Refractive index and strain sensing using inline Mach–Zehnder interferometer comprising perfluorinated graded-index plastic optical fiber

•Novel fabrication of an inline Mach–Zehnder interferometer (MZI) via tapering of perfluorinated graded-index plastic optical fiber (POF).•This MZI shows interference fringes that are sufficiently sharp for usage as refractive index (RI) and strain sensors.•These interference fringes are observed to linearly shift in proportion to the RI of the surrounding medium with a proportionality constant of 3.44nm/RI unit.•The measured strain sensitivity of 0.2pm/μɛ indicates that the MZI is potentially applicable to strain sensing.•POF-based inline MZI sensor retains the key advantage of high flexibility, simplicity and lower cost. This paper details the fabrication and performance evaluation of an inline Mach–Zehnder interferometer (MZI) consisting of a perfluorinated graded-index plastic optical fiber fabricated via a heat-and-pull tapering technique. This MZI exhibits interference fringes that are sufficiently sharp for usage as refractive-index (RI) and strain sensors. These interference fringes shift linearly with the RI of the surrounding medium, with a proportionality constant of 3.44nm/RI unit. The measured strain sensitivity of 0.2pm/μɛ suggests that the MZI may be viable for strain-sensing applications.