High fringe visibility fiber sensor based on MMF-FCF-MMF structure for dual-parameter detection

•A novel optical fiber sensor based on MMF-FCF-MMF structure is proposed.•The maximum fringe visibility of the interference resonance dips exceeds 26.3 dB.•The MMFs are used to improve the light coupling efficiency between the input SMF and the FCF.•The sensor has advantages of simple fabrication process, good stability, repeatability and high fringe visibility. In this paper, a novel optical fiber sensor based on multimode fiber (MMF) - four-core fiber (FCF)-MMF structure is proposed and experimentally demonstrated. The device consists of a segment of FCF sandwiched between two MMFs. The MMFs are used to improve the light coupling efficiency between the input single mode fiber (SMF) and the FCF, and the FCF is used as sensing arm. Due to the multipath interference configuration embedded in one fiber, higher phase sensitivity can be obtained in our scheme. The maximum fringe visibility of the interference resonance dips exceeds 26.3 dB. The interference fringe of the sensor would shift with the variation of liquid level and temperature. So it is possible to measure dual-parameter simultaneously by simply monitoring the different wavelength shift. For 10 pm wavelength resolution, the resolution of the sensor is 0.14 cm and 2.08 °C in liquid level and temperature, respectively. Moreover, the proposed sensor has the advantages of simple fabrication process, good stability, repeatability and high fringe visibility, which mean it has a broad application prospect in liquid level measurement.