FPI-FBG Cascaded High-Temperature Pressure Sensor up to 700 °C Based on Vernier Effect Utilizing Femtosecond Laser

A fiber optic high-temperature pressure dual parametric sensor utilizing femtosecond laser technology based on the Vernier effect is proposed, demonstrated, and experimentally validated for gas pressure and temperature monitoring in high-temperature environments. The sensor features two parallel Fabry-Pérot interferometers (FPIs) and a fiber Bragg grating (FBG). Each FPI is fabricated using femtosecond laser-induced water breakdown and arc discharge techniques, serving as the sensing FPI and the reference FPI, respectively. These FPIs have closely matched free spectral ranges (FSRs), producing the traditional Vernier effect to enhance pressure sensitivity. Additionally, an FBG prepared with femtosecond laser technology is cascaded in front of the sensing FPI to measure gas temperature and compensate for pressure variations. The sensor was validated by a two-parameter experiment at $700~^{\circ }$ C and 5 MPa. At room temperature ( $24.7~^{\circ }$ C), the gas pressure sensitivity of this sensor is approximately 18.66 nm/MPa, which is about 4.7 times greater than that of a single sensing FPI. At a high temperature of $700~^{\circ }$ C, the gas pressure sensitivity is approximately 6.09 nm/MPa. The temperature sensitivity of the FBG for temperature measurement is 12.4 pm/°C. The sensor exhibits a maximum full-scale pressure error of 5.68% across the entire temperature range, utilizing the FBG to measure gas temperature and compensate for pressure sensitivity. This sensor demonstrates high-temperature resistance and high-pressure sensitivity, making it suitable for gas temperature-pressure dual parameter monitoring in high-temperature environments. Additionally, it is easy to fabricate and exhibit robustness, sensitivity, and reliability.