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A novel and in-line fiber low-frequency vibration sensor based on Butterfly-Shape Mach-Zehnder Interferometer (BSMZI) is proposed and demonstrated experimentally. The sensing element is a tapered hollow-core fiber (HCF) sandwiched between two single-mode fibers (SMFs). The frequency measured by the Butterfly-Shape vibration sensor can well match with the applied frequency, and the presence of the higher harmonics can verify that the sensor does not distort the measured vibration signal. The maximum relative error of vibration frequency is 0.27%. The intensity of vibration signal (of the fiber sensor) is linearly proportional to the driving power of vibration platform. The vibration measurement sensitivity is 13.575 dB/w in the range of 0.1 w to 0.5 w under a constant vibration frequency of 50 Hz, and the linear fitting coefficient is 0.9556. The proposed sensor has a negligible temperature sensitivity in the range of 30.3 °C–69.5 °C. Because of its compact structure, easy preparation, low production cost, high frequency measurement accuracy of low-frequency vibration, and good linearity of vibration sensing, the proposed BSMZI sensor has potential application prospect in low-frequency vibration sensing field. [ABSTRACT FROM AUTHOR]

Mach–Zehnder interferometers have attracted attention due to their flexible structures and extensive applications. In this study, a simple and highly sensitive curvature sensor based on an asymmetrical Mach–Zehnder interferometer comprising an up-taper and a peanut-like section was theoretically and experimentally characterized. A simulation was conducted to investigate the influence of structural parameters on the interference spectrum. Experimental measurements show that a high curvature sensitivity of −35.3 nm/m−1from 1.35 to 2.20 m−1was obtained and high mechanical strength was demonstrated. The temperature–curvature cross-sensitivity of 4.44 × 10−4 m−1/°C was lower than the curvature resolution. The high curvature sensitivity and low temperature cross-sensitivity make this sensor a candidate for practical applications. [ABSTRACT FROM PUBLISHER]

All-fiber Mach-Zehnder interferometers (MZIs) working as curvature sensors have been attracting increasing attention. However, previously reported MZI-based curvature sensors with offset or abrupt-taper structures suffer from weak mechanical strength and low curvature sensitivity. In this letter, a robust and highly-sensitive MZI-based curvature sensor formed by cascading two up-tapers in a single mode fiber (SMF) is proposed and experimentally demonstrated. By optimizing structural parameters of the MZI both in simulation and in experiment, a high quality interference spectrum with a maximum extinction ratio (ER) of around 20 dB is obtained, which is crucial in curvature sensing with spectrum intensity variation and interference dip identifiability being considered. Experimental results show that a high curvature sensitivity of −35.41 nm/m −1 is obtained in the range of 0.6846 m −1 – 1.0606 m −1 , which is 2.4 times higher than that of the interferometer with single-mode-multimode-single-mode (SMS) structure. The two up-tapers, featured by great mechanical strength, are fabricated by only fusion pushing together a whole SMF without cleaving procedure, contributing to excellent repeatability and consistency in the sensor fabrication process. Such an all-fiber sensor exhibits advantages of simple configuration, ease of fabrication, excellent mechanical strength, low cost, and high curvature sensitivity. [ABSTRACT FROM AUTHOR]