title: Reliability analysis and comparison of demodulation methods for dual-beam wavelength-modulation spectroscopy water vapor detection.
abstract: Subtraction, division, and balanced ratiometric detection (BRD) are three extensively used demodulation methods for dual-beam wavelength-modulation trace gas detection. However, reliability comparisons among these methods under changing environmental conditions were rarely researched. In this paper, the influences of ambient temperature and bend loss of fibers are analyzed in detail, and the reliabilities of the subtraction, division, and BRD methods are quantitatively compared for the first time to our knowledge. When the ambient temperature is increased by 1°C, the deviation of the division method is only 0.29%, which obviously outperforms the subtraction method (2.90%) and the BRD method (0.55%). Furthermore, a concept, "power fluctuation rejection ratio," is introduced to compare the suppression effects of the subtraction, division, and BRD methods on the laser light source power fluctuation. The study results demonstrate that the division method provides better reliability when the ambient temperature or bending loss is varied. The validity and reliability are fully verified by the fact that the experimental results give good agreement with the theoretical simulation.
authors.affiliation: School of Information Science and Engineering and Shandong Provincial Key Laboratory of Laser Technology and Application, Shandong University, Jinan, China.
authors.forename: Cunguang
authors.initials: C
authors.lastname: Zhu
authors.forename: Jun
authors.initials: J
authors.lastname: Chang
authors.forename: Pengpeng
authors.initials: P
authors.lastname: Wang
authors.forename: Weijie
authors.initials: W
authors.lastname: Wang
authors.forename: Qiang
authors.initials: Q
authors.lastname: Wang
authors.forename: Yongning
authors.initials: Y
authors.lastname: Liu
authors.forename: Guangping
authors.initials: G
authors.lastname: Lv
authors.forename: Xiangzhi
authors.initials: X
authors.lastname: Liu
authors.forename: Wei
authors.initials: W
authors.lastname: Wei
authors.forename: Fupeng
authors.initials: F
authors.lastname: Wang
authors.forename: SaSa
authors.initials: S
authors.lastname: Zhang