Temperature-insensitive curvature sensor based on twin-hole fiber cascaded graded-index multimode fiber structure

A novel temperature-insensitive fiber-optic curvature sensor based on the asymmetric splicing structure is proposed. The sensor is constructed by asymmetrically splicing the twin-hole fiber (THF) to the graded-index multimode fiber (GI-MMF). Utilizing core-diameter mismatch to excite cladding modes that interfere with fundamental modes, the Mach-Zehnder interferometer is formed with the sensing unit length of 1.53 cm. The sensor exhibits the maximum sensitivity of –19.300 nm/m -1 within the curvature range of 0.4261-4.9625 m -1 , while maintaining the low temperature crosstalk coefficient of 6.58×10 -5 m -1 /°C. By embedding the sensor into an elastic waistband, real-time monitoring of human respiratory patterns is successfully demonstrated. Combining high sensitivity, miniaturized structure, simple fabrication, and superior temperature stability, this sensor provides a practical solution for structural health monitoring and medical respiratory detection.