Design and Optimization of High-Pressure Sensitivity Irregular Side-hole Fiber Based on Fiber Bragg Grating Sensors

The pressure sensor based on Side-hole Fiber Bragg Grating (SH-FBG) can effectively reduce the crosstalk between pressure and temperature in operation, making it particularly suitable for high-temperature and high-pressure environments in oil wells. However, the relatively low sensitivity of SHF pressure sensors limits their further application in oil wells. In this paper, the key to improving the sensitivity of SHF pressure sensors is theoretically derived to be the increase in the unevenness of stress generated at the core in the $\mathbf{X}$ and $\mathbf{Y}$ directions. Finite element analysis is then employed to investigate the influence of SHF cladding shape on pressure sensing characteristics. By optimizing the waveguide structure of SHF and proposing an Irregular Side-hole Fiber (ISHF) with a cladding shape of negative curvature arc, the pressure sensitivity is increased to $33.37 \mathrm{pm} / \mathrm{MPa}$. This effectively enhances the pressure sensitivity of SHF, holding significant implications for high-pressure monitoring in oil wells.