High Sensitivity Fiber-Optic Strain Sensor Based on Modified Microfiber-Assisted Open-Cavity Mach-Zehnder Interferometer

In this paper, a modified microfiber-assisted open- cavity (MMA-OC) structure is proposed by introducing two pieces of multimode fiber and a novel sub-millimeter in-line Mach-Zehnder interferometer is theoretically and experimentally completed. The cavity-length dependence of MMA-OC on axial strain sensing is characterized and the comprehensive strain tests are conducted under an optimal waist diameter. The experimental results show that the selective intensity-/wavelength- modulated strain response can be achieved by varying the cavity length. For a shorter cavity length, MMA-OC presents more than 20-dB intensity variation and near-zero wavelength drift. But an apparent and flat red-shift of fringes occurs in the structure with >1000-μm cavity length. Moreover, due to inverse feature of temperature response, the calculated cross-sensitivity is merely 0.106 μϵ/°C. And the detection resolution up to ~0.2 μϵ is gained when the cavity length is equal to 503 μm, with the measurement error of ±0.021 μϵ. Our sensor with the merits of compactness, low-cost and ease of fabrication is very promising for high-precision engineering monitoring and sensing.