Fig. 1. Absorption intensity of common gas in near-infrared band near 1653 nm. (a) Absorption peak of CH₄; (b) absorption intensity of interference gas

Fig. 2. Structural diagram of near-infrared methane detection system

Fig. 3. Experimental result of temperature controlled stability of laser

Fig. 4. Testing results of output spectra of laser (driving current is 50 mA and change range of driving temperature is 39-44 ℃). (a) Spectra; (b) central wavelength

Fig. 5. Repeatability test result of laser's output spectrum

Fig. 6. Test results of signal extraction performance of orthogonal phase-locked amplifier. (a) Waveform of differential signals; (b) second harmonic signal

Fig. 7. Results of optical chamber performance test based on hollow-core photonic crystal fiber. (a) Simulated mode distribution of HC-PCF; (b) response speed test

Fig. 8. Concentration calibration and fitting result

Fig. 9. Stability test result

Fig. 10. Allan deviation curve of detection system