Sensitivity-Improved Curvature Sensor Based on Microwave-Photonic Fiber Ring Resonator

This work reports the development of an optical fiber curvature based on the integration of a miniature sensor head with a microwave-photonic fiber ring resonator (MWP-FRR) system with enhanced sensitivity. The sensor head is a well-known heterogeneous device, constructed by the combination of a section of hollow core fiber (HCF) and two sections of single-mode fibers (SMFs), forming the SMF-HCF-SMF (SHS) configuration. In contrast to the conventional approach of directly quantifying optical transmission alterations in response to bending within the SHS device, our study innovatively harnesses the transformation of these transmission losses into pronounced fluctuations in the frequency response profile of the MWP-FRR system. It is revealed that the magnitude variations observed in the frequency response, under bending conditions and interrogated by the MWP technique, are amplified compared to those derived from direct optical transmission measurements utilizing an optical spectrum analyzer. Additionally, a strategy for further sensitivity improvement is proposed and experimentally verified. The possibility of using the sensor system for dynamic sensing is also explored. This work reveals that the integration of an intensity-modulation-based optical fiber sensor head with the MWP-FRR system offers a versatile and effective platform for developing high-performance optical fiber sensors.