Fiber-Optic Laser Sensor Based on All-Fiber Multipath Mach–Zehnder Interferometer

A novel fiber-optic sensor using fiber ring cavity laser based on multipath Mach–Zehnder interferometer (m-MZI) is proposed and experimentally demonstrated. The m-MZI consists of a segment of four-core fiber (FCF) spliced between two single-mode fibers. The m-MZI is inserted in the fiber ring laser cavity, which acts as a bandpass filter and the sensing component simultaneously. Compared with previously reported MZI, higher phase sensitivity can be obtained in the proposed m-MZI due to the multipath interference configuration embedded in one fiber. The interference fringe of the FCF would shift with the variation of monitoring parameters and then caused the lasing wavelength changes. So it is available to measure these parameters by simply monitoring the variation of lasing wavelength. Experimental results show that the sensitivities of the sensor in strain, RI, and curvature are 2.21 pm/ $\mu \varepsilon $ , 113.27 nm/RIU, and 2.55 nm/ $\text{m}^{-1}$ , respectively. Thus, the proposed sensor is easy to conduct and monitor, in addition, it also has the advantages of high resolution and high signal-to-noise ratio.