Simulation of Hollow-Core Photonic Crystal Fibre-Based Photothermal Spectral C2H2 Gas Sensor

Fault characteristic gas analysis is one of the important methods for monitoring the operating status of power equipment. This study presents the construction of a simulation model for a hollow-core photonic crystal fibre (HC-PCF)-based photothermal spectroscopy gas detection system. The relationship between the phase change of the probe beam and the acetylene concentration, pump power, ambient temperature and the modulation frequency is examined. It is achieved by simulating the wavelength modulation of the pump beam and the phase change of the probe beam. The findings demonstrate that there is a linear positive correlation between the pump power and the amplitude of the phase change of the probe beam and the acetylene concentration. For example, acetylene concentration grew from 1 to 10,000 ppm, whereas phase change amplitude increased from 4.71 × 10⁻⁴ to 3.70 rad. The pump power grew from 7 to 2000 mW, whereas phase change amplitude increased from 3.73 × 10⁻⁴ to 1.01 × 10⁻¹ rad. The phase change of the probe beam is non-linearly and negatively correlated with the ambient temperature. The ambient temperature decreases from 373.15 to 173.15 K, and phase change amplitude increases from 5.05 × 10⁻³ to 2.15 × 10⁻² rad, an enhancement of 4.26 times. The modulation frequency is needed to balance the thermal conduction process in the HC-PCF. In the 1–100 Hz range, the amplitude of the phase change is stable and almost independent of the modulation frequency. In the 100–40,000 Hz range, the amplitude of the phase change decreases rapidly with the increase of the modulation frequency. The results of the paper provide a reference for constructing the HC-PCF-based photothermal spectroscopy gas detection system.