Tailoring surface structure and diameter of etched fiber Bragg grating for high strain sensing

Sensitivity and mechanical properties are the key factors that affect the performance of strain-sensitive etched fiber Bragg grating (EFBG) sensors. Typically, EFBG sensors are fabricated via solvent etching. The manipulation of etching temperature and hydrofluoric acid (HF) concentration during the solvent etching process is particularly crucial to control the surface and mechanical properties of the sensors. In this study, the effects of these two etching conditions on the surface and mechanical properties of the etched fiber surface were investigated. It is found that higher etching temperature and higher HF concentration can cause rougher fiber surface with lower Young’s modulus, fracture stress and strain. EFBG produced at 20 °C temperature and 30% HF concentration exhibits smooth surface and high mechanical properties. Under these optimized etching conditions, the sensitivity of EFBGs was improved by reducing the fiber diameter. The results show that EFBGs with smaller diameters demonstrate higher strain sensing performance due to lower fiber stiffness. EFBG with a diameter of 15 μm has Young modulus of 7.21 GPa and achieves the highest strain sensitivity of 52.74 pm/με. To conclude, EFBG with excellent strain sensing performance can be obtained by tailoring the surface structures and fiber’s diameter during the etching process.