High-Sensitivity Optic Fiber Pressure Sensor Based on Balloon-Like Single-Mode Fiber

A high-sensitivity optic fiber pressure sensor based on balloon-like single-mode fiber (SMF) is proposed and thoroughly investigated. Under pressure, the balloon-like SMF and the substrate collaborate, resulting in changes in the stress state of the core and cladding of the fiber in the sensor, which leads to changes in the difference between the effective refractive index (RI) of the core and cladding of the fiber and shifts the spectra, so as to achieve pressure measurements. First, the mechanical model of the proposed sensor is established, explaining the relationship between the varying of RI of the sensing unit involving fiber and substrate, and the pressure. Then, the effects of the substrate stiffness and fiber bending diameter on the sensor sensitivity are analyzed, so as to optimize the sensor’s structural and relevant parameters. It reveals that, under pressure, the substrate stiffness has a significant effect on the sensor sensitivity. A series of experimental tests were carried out based on the fabricated substrate using iron, caoutchouc, and polydimethylsiloxane (PDMS) as substrates and applying different bending diameters for the SMF, it shows that when the substrate is caoutchouc and the bending diameter of the fiber is 3.8 mm, the sensitivity of the optimized balloon-like SMF optic pressure sensors can reach up to 90.3 nm/N in the range of 0–1 N. The experimental results effectively verify the feasibility of the optimized design method of the balloon-like SMF optic pressure sensors as well as the achievability of the high-sensitivity pressure detection.