This paper presents a method for gas concentration determination based on the measurement of the refractive index dispersion of a gas near the gas resonance in the near-infrared region (NIR). The gas refractive index dispersion line shape is reconstructed from the variation in the spectral interference fringes’ periods, which are generated by a low-finesse Fabry-Perot interferometer during the DFB diode’s linear-over-time optical frequency sweep around the gas resonance frequency. The entire sensing system was modeled and then verified experimentally, for an example of a low concentration methane-air mixture. We demonstrate experimentally a refractive index dispersion measurement resolution of 2 × 10^–9 refractive index units (RIU), which corresponds to a change in methane concentration in air of 0.04 vol% at the resonant frequency of 181.285 THz (1653.7 nm). The experimental and modeling results show an excellent agreement. The presented system utilizes a very simple optical design and has good potential for the realization of cost-efficient gas sensors that can be operated remotely through standard telecom optical fibers.

中文翻译：

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一种用于测量NIR折射率色散的光纤气体传感器和方法。

本文提出了一种基于气体在近红外区域（NIR）内气体共振附近的折射率分散度测定方法来确定气体浓度的方法。气体折射率色散线的形状是根据光谱干涉条纹周期的变化而重建的，该光谱干涉条纹周期的变化是由低精良的Fabry-Perot干涉仪在DFB二极管围绕气体共振频率进行线性随时间的光学频率扫描时产生的。对整个传感系统进行建模，然后进行实验验证，例如低浓度的甲烷-空气混合物。我们通过实验证明了折射率色散的测量分辨率为2×10 ^–9折射率单位（RIU），它对应于在181.285 THz（1653.7 nm）的共振频率下空气中甲烷浓度的变化为0.04 vol％。实验和建模结果显示出极好的一致性。提出的系统利用非常简单的光学设计，并具有实现可通过标准电信光纤远程操作的高性价比气体传感器的良好潜力。