Fig. 1. HITRAN-based CH₄ absorption line and the curve of laser current versus emission wavelength number at 36 ℃

Fig. 2. Structure block diagram of hardware reconfigurable wavelength modulated CH₄ sensor，and a photo of the electrical part based on FPGA

Fig. 3. FPGA internal logic structure diagram of the sensor

Fig. 4. Test waveform under continuous and intermittent working modes

Fig. 5. According to Modelsim software，simulated gas absorption waveform，laser driving signal waveforms and second harmonic waveform

Fig. 6. Sine signal verification experiment and result analysis

Fig. 7. Stability analysis of sine signal amplitude acquisition

Fig. 8. CH₄ detection experiment and result analysis

Fig. 9. Dynamic response time test of the sensor

Fig. 10. Stability analysis of the sensor system

Fig. 11. Field detection results of CH₄ leakage test