Characterization of a K-type side-hole polarization-maintaining fiber for simultaneous distributed pressure and temperature sensing

This work presents a polarization-maintaining K-type side-hole fiber (SHF) optimized for simultaneous distributed measurements of hydrostatic pressure and temperature using optical frequency-domain reflectometry (OFDR) based on Rayleigh backscattering. The specific orientation of the elliptical core relative to the pair of side holes ensures record-high differential pressure sensitivity between the two orthogonal polarization modes (-1.9 GHz/MPa and 0.7 GHz/MPa), while maintaining nearly identical temperature responses. The fiber's design prevents pressure-induced birefringence compensation, thus preserving stable polarization separation over the entire pressure range. A two-channel polynomial model was applied to decouple the effects of temperature and pressure on the spectral shift. Simultaneous measurements of both parameters were demonstrated for the first time in a distributed Rayleigh-based configuration, achieving an accuracy close to 0.1 ° and 0.1 MPa. The proposed sensing concept combines high-pressure sensitivity, thermal stability, and strong polarization selectivity, enabling reliable operation under varying thermo-mechanical conditions. These findings pave the way for advanced multiparameter distributed fiber-optic sensors applicable in energy-storage systems, pulsating heat pipes, oil and gas exploration, and structural health monitoring of pressure-critical components.