High-Sensitive Vector Curvature Sensor With Tri-Core Fiber-Based Hybrid Interferometer

This paper proposes and demonstrates a hybrid interferometer based on tri-core fiber (TCF) and capillary fiber (CF) that adopts a CF-TCF-CF (CTC) sandwich structure for simultaneous measurement of curvature magnitude and direction. The fabricated CTC structure with short length of 5.6 mm exhibits two pronounced resonant dips (dip1 and dip2) together with a resonant peak in the transmission spectrum Within the curvature range of 0.098-0.98 m⁻¹, the sensor exhibits significant differences in sensitivity in different directions, with highly linear response characteristics. The maximum curvature sensitivity could be up to –30.84 nm/m⁻¹. Benefiting from the interaction between cladding modes and surrounding medium, the sensor exhibits high sensitivity exceeding 1.5 × 10⁴ nm/RIU in high refractive index range of 1.4526–1.4552 RIU. Within the temperature range of 30-80 °C, the sensor exhibits negligible wavelength shift with a low sensitivity of –0.002 nm/°C. Notably, the curvature sensitivity remains nearly invariant with temperature, resulting in an ultralow temperature cross-sensitivity of ~ 0.0019 m⁻¹/°C. The proposed sensor supports simultaneous measurement of curvature and temperature through dual-parameter demodulation, achieving curvature and temperature resolutions of 9.85 × 10⁻⁴ m⁻¹ and 0.145 °C, respectively, illustrating that it effectively suppresses temperature cross-sensitivity during curvature measurement, guaranteeing high accuracy and long-term reliability for curvature-sensing applications. This high-performance hybrid interferometer, as a versatile, temperature-robust and high-resolution sensing platform, exhibits great application potential in structural health and environmental monitoring.