Intensity-Modulated Fiber-Optic Strain Sensor Using Multimode Fiber and Microfiber Joint-Assisted Micro-Cavity Interferometer

In this paper, a novel micro-cavity based Mach-Zehnder interferometer is proposed by joint-assistance of microfiber and multimode fiber (MMF). The light field distribution is comprehensively investigated, and the quantitative beam expansion range and the length of MMF are obtained. Under the optimized fabrication parameters, a joint-assisted micro-cavity structure is experimentally completed and the axial strain tests are performed. The experimental results show that obvious intensity responses of fringes are exhibited in the range from 0 to $300~ {\mu \varepsilon }$ , but with gradually reduced wavelength sensitivities. It is found that a near-zero wavelength drift exists in the fringe of 1589.83 nm with the intensity sensitivity of ~0.02 dB/ ${\mu \varepsilon }$ . Besides, the corresponding temperature response is −81 pm/°C with a slight fluctuation of ~0.003 dB/°C. Such high discrimination between axial strain and temperature brings $\sim 0.5~ {\mu \varepsilon }$ detection resolution and ultra-low temperature crosstalk ( $\sim 0.15~ {\mu \varepsilon }/^{ {\circ }}\text{C}$ ), simultaneously. With the merits of high sensitivity and practicality, our sensor is very promising and potential in high-precision axial-strain related engineering monitoring and sensing.