Dual-Function Composite Optical Fiber Fabry–Pérot Sensor and Its Demodulation System for Simultaneous High-Precision Measurement of Pressure and Temperature

The composite cavity Fabry–Pérot (FP) sensor provides a promising solution for multiparameter measurements, enhancing the stability of FP sensors and enabling parameter compensation. For example, it can be applied to measurements of temperature and pressure under extreme conditions (with temperature ranges from $0~^{\circ }$ C to $500~^{\circ }$ C, pressure ranges up to 4 MPa, small volume). However, the dual-cavity structure introduces complex coupled reflection spectra, and effective decoupling is crucial for optimizing the performance of composite cavity FP pressure sensors. To address this challenge, we propose a rapid decoupling method based on spectrometer hardware design and spectral partitioning, which allows for the quick decoupling of the dual cavities. In addition, we conducted experiments to test the spectral signals under various temperatures and pressures, leading to the establishment of a calibration database encompassing temperature, pressure, and composite FP cavity length information. The sensing results show that across the entire measurement range, the temperature cavity exhibited an accuracy of 0.35% full scale (FS). With the implementation of a temperature compensation model, the accuracy of the pressure sensor improved to 0.52%FS. The proposed sensor effectively measures temperatures from $0~^{\circ }$ C to $500~^{\circ }$ C and pressures from 0 to 4 MPa, successfully enabling the simultaneous measurement of both temperature and pressure. This method offers a universal solution for spectral decoupling in multiparameter measurement systems with composite cavities, showing great potential for sensor demodulation and information decoupling in highly complex environments.