Dual-Channel D-Shaped Ge-Doped PCF–SPR Sensor for Simultaneous Methane Concentration and Temperature Sensing

A novel dual-channel D-shaped germanium-doped photonic crystal fiber (PCF) sensor leveraging the surface plasmon resonance (SPR) effect is proposed for the high-precision simultaneous detection of methane concentration and temperature. The sensor architecture incorporates a dual-layer air hole configuration, where the inner layer, consisting of four asymmetrical air holes, is strategically arranged around the core to optimize mode coupling, while an eight-hole outer layer ensures stable light confinement. By employing a bilateral polishing process, two independent sensing channels are integrated onto the D-shaped surfaces, functionalized with methane-sensitive Cryptophane-A and thermo-optic PDMS thin films, respectively. Simulation results reveal that the sensor achieves the peak methane sensitivity of 72 nm/% within the 0-3.5% concentration range and the maximum temperature sensitivity of 39 nm/°C within the range of 18-100 °C. Notably, the design demonstrates remarkable decoupling capabilities with negligible cross-sensitivity. The proposed matrix-based demodulation was validated using simultaneous variation test cases, achieving mean absolute errors (MAEs) of 0.102% for methane concentration and 1.064 °C for temperature, with the corresponding maximum errors of 0.223% and 1.461 °C, respectively. Due to its electromagnetic immunity, intrinsic safety, and robust dual-parameter demodulation, the proposed sensor offers a promising solution for multi-analyte monitoring in hazardous environments, such as underground coal mines and natural gas infrastructure.