High-Sensitivity Fiber Curvature and Temperature Sensor Fabricated by Femtosecond Laser for Dual Waveguides

We propose a in-line Mach-Zehnder interferometer (MZI) structure based on femtosecond laser-inscribed dual waveguides in a no-core fiber (NCF). The in-line MZI comprises two waveguides with refractive index differences in NCF. Through systematic simulation studies, critical parameters including coupler length, waveguide length, and inter-waveguide spacing were optimized to achieve optimal sensor performance. Experimental results demonstrate that the proposed sensor exhibits superior sensitivity to both temperature and curvature, with a distinct directional selectivity observed in curvature detection. Within the curvature range of 1-1.5 m^-1, the sensor achieves a maximum curvature sensitivity of 34.727 nm/m^-1. Over a temperature range of 45 to 75 °C, the sensor exhibits a temperature sensitivity of 109.57 pm/°C. Furthermore, by constructing a sensitivity matrix, parameters of curvature and temperature can be measured simultaneously. With high sensitivity, a compact design, and robustness, the proposed sensor is appropriate for construction, bridge engineering, and aerospace applications.