Ultra-wide range and wavelength fixed trace gas detection technology based on single chamber multiplexing

• Published in: Optics and lasers in engineering Vol. 158; p. 107170
• Main Authors: Zhu, Guoan, Bai, Yunrui, Yang, Yingying, Yu, Haijuan, Nan, Zongliang, Zhang, Xu, He, Chaojian, Lin, Xuechun
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2022
• Subjects: Fiber optics sensor; Laser spectroscopy; Mach-Zehnder interferometer; Phase modulation; Photo-thermal; Photonic crystal fiber; Photonic crystal fiber; Mach-Zehnder interferometer; Photo-thermal; Phase modulation; Fiber optics sensor; Laser spectroscopy
• ISSN: 0143-8166; 1873-0302
• DOI: 10.1016/j.optlaseng.2022.107170

•An all-fiber PTI system with pump intensity external modulation is proposed in this paper. The system is a wavelength-fixed system, which is not limited by the gas absorption line and has a high SNR.•The factors affecting the dynamic range of the system were deduced theoretically and experimentally, and the lower limit of detection can be increased by increasing pump light power and gas injection pressure. The upper detection limit can be extended by the red and blue shift of the pump light wavelength.•A C2H2 gas trace system was demonstrated by red-shifting the pump wavelength to 1530.41 nm. The detection limit of 9.24 ppm and an extensive dynamic detection range of five orders of magnitude can be obtained. The all-fiber photo-thermal interference (PTI) system based on hollow-core photonic crystal fiber (HC-PCF) has the advantages of wide dynamic range, ultra-sensitivity, and small volume, which is of great significance in gas trace analysis. Most of the previous PTI systems obtain the relationship between gas concentration and phase modulation by wavelength scanning and extracting the second harmonic signal absorbed by the gas. However, the residual modulation caused by the asynchronism between wavelength and modulation signal seriously affects the signal-to-noise ratio (SNR) and dynamic detection range of the system. In addition, wavelength scanning has limitations for detecting gas with irregular absorption lines. This paper proposes an all-fiber photo-thermal interference system with pump intensity external modulation. The system is not limited by the gas absorption line and has a high SNR. The factors affecting the dynamic range of the system are analyzed theoretically and experimentally. It is verified that increasing the injection gas pressure can significantly increase the detection limit of the system compared with increasing the pump light power. The redshift of the pump light can dramatically increase the detection limit of the system. A C2H2 gas trace system with the pump wavelength redshifted to 1530.41 nm was demonstrated. The detection lower limit of 9.24 ppm and an extensive dynamic detection range of five orders of magnitude were obtained.