Improvement of Measuring Range in Fiber Interferometric Liquid Level Sensor by Employing Digital Filter for Mode Selectivity

A liquid level sensor system based on dual tapers all‐fiber Mach‐Zehnder interferometer incorporating digital filtering is proposed for extended measurement range. Digital filtering technique is employed to selectively isolate beating of a particular dominant cladding mode, resulting a more consistent response in terms of spectra quality and wavelength shift. Sensing characteristics of cladding modes also are studied theoretically and experimentally. From experiment, continuous measurement of water level is demonstrated over 1016‐mm range with sensitivity of −0.0021 nm/mm and R2 of 0.9972. To our knowledge, this is the highest measurement range and linearity for liquid level sensor based on interferometric sensing system has been reported. The proposed technique can be very useful to enhance sensing performance for various fiber interferometric sensor applications.