Fiber-based gain-assisted incoherent broadband cavity enhanced spectroscopy is a novel technique used to enhance spectroscopic measurement sensitivity. This technique overcome the drawbacks of the conventional cavity enhanced techniques, in the need for optical alignment and high reflectivity mirror as they are based on free-space Fabry-Perot cavity. However, to assess the value of this technique, the sensitivity enhancement factor over the direct path absorption spectroscopy should be calculated. In this work, an analytical, and experimental study for the sensitivity of the fiber-based incoherent gain-assisted ring enhanced spectroscopy techniques are demonstrated. Two fiber-based configurations are studied for different system parameters. The first configuration is a dual-coupler ring with the source outside the resonator and the gain medium inside the resonator. The broadband source is the amplified spontaneous emission (ASE) of a semiconductor optical amplifier (SOA). While the second configuration is single-coupler resonator with the gain medium acting as the broadband source. The optical absorption of acetylene (C2H2) gas around 1540 nm wavelength has been measured. The output spectrum has been measured using an optical spectrum analyzer (OSA) of 70 pm resolution. The sensitivity is enhanced by a factor of 942 in the case of the single-coupler configuration, compared to the direct absorption of the gas cell. The study elaborates that intracavity (single-coupler) configuration provides SNR enhancement in thermal noise limited system. In contrast to conventional incoherent broadband techniques that don’t provide any enhancement in case of thermal noise limited system.

中文翻译：

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增益辅助腔增强光谱的灵敏度增强因子

基于光纤的增益辅助非相干宽带腔增强光谱是一种用于提高光谱测量灵敏度的新技术。该技术克服了传统腔增强技术的缺点，需要光学对准和高反射率反射镜，因为它们基于自由空间法布里-珀罗腔。然而，为了评估这种技术的价值，应该计算直接路径吸收光谱的灵敏度增强因子。在这项工作中，对基于光纤的非相干增益辅助环增强光谱技术的灵敏度进行了分析和实验研究。针对不同的系统参数研究了两种基于光纤的配置。第一种配置是双耦合器环，源位于谐振器外部，增益介质位于谐振器内部。宽带源是半导体光放大器 (SOA) 的放大自发辐射 (ASE)。而第二种配置是单耦合器谐振器，增益介质作为宽带源。已测量乙炔 (C2H2) 气体在 1540 nm 波长附近的光吸收。使用分辨率为 70 pm 的光谱分析仪 (OSA) 测量了输出光谱。与气室的直接吸收相比，在单耦合器配置的情况下，灵敏度提高了 942 倍。该研究阐述了腔内（单耦合器）配置在热噪声受限系统中提供 SNR 增强。