Highly Sensitive Microdisplacement Sensor Based on Sidewall Resonance Effect of Optical Fiber Liquid Cladding

Optical fiber displacement sensors are extensively used in pre-warning of landslide and earthquake. Here, we propose a highly sensitive micro-displacement sensor based on side-wall (SR) resonance effect of optical fiber liquid cladding. The sensor structure has two single-mode fibers (SMF) fused at both ends of a no-core fiber (NCF), placed in a glass capillary filled with cedar oil. The effective refractive index (RI) of the cedar oil can be matched with the RI of optical fiber, which is conducive to the SR effect. The micro-displacement of the monitored object will cause the bending of the sensing structure, resulting in a change in the thickness of the liquid cladding and the shifting of the SR dips in output spectrum. Besides, we introduce a piece of tapered no-core fiber (TNCF) into the original structure. Experimental results demonstrate that the displacement sensitivity of improved structure is increased from 5.02 nm/μm to 9.02 nm/μm, compared to the sensor with NCF, while the compensated temperature sensitivity is increased from –3.69 nm/°C to –13.76 nm/°C. Due to the excellent performance of the micro-displacement sensing structure based on SR effect of optical fiber liquid cladding, it offers broad prospects for applications such as monitoring earthquake waves and building frame.