All-fiber MZI sensor based on seven-core fiber and fiber ball symmetrical structure

An all-fiber and compact Mach-Zehnder interferometric (MZI) sensor is proposed and experimentally demonstrated. The sensor with symmetrical structure is fabricated by splicing a segment 7 mm length of seven-core fiber (SCF) and two single-mode fiber (SMF) ball. The mode field of the fiber ball used in our experiments close to the region of hexagonally distributed fiber cores of the SCF, which is helpful to obtain a high coupling efficiency. Such an MZI could be used to realize the measurement of temperature and curvature. The temperature sensitivities is 76.38pm/degrees C with the linearity 0.9855 in the range of 50-130 degrees C, and the curvature sensitivities 19.60 dB/m(-1) via the intensity modulation of interference fringes, with a linearity 0.9911 at the range of 0.5-1 m(-1). That is, the MZI-based sensor overcomes the cross-sensitivity problem between curvature and temperature by means of different demodulation methods. Moreover, the proposed MZI sensor exhibits the advantages of more compact structure (only about 8 mm), simple manufacturing process and high reliability.