Refractive-index (RI)-based sensing is a major optical sensing modality that can be implemented in various spectral ranges. While it has been widely used for sensing of biochemical liquids, RI-based gas sensing, particularly small-molecule gases, is challenging due to the extremely small RI change induced by gas concentration variations. We propose a RI-based ultracompact fiber-optic differential gas sensor that employs metal-organic-framework (MOF)-based dual Fabry-Perot (FP) nanocavities. A MOF is used as the FP cavity material to enhance the sensitivity as well as the selectivity to particular gas molecules. The differential sensing scheme leverages the opposite change in the cavity-length-dependent reflection of the two FP cavities, which further enhances the sensitivity compared with single FP cavity based sensing. For proof-of-concept, a fiber-optic CO₂ sensor with ZIF-8-based dual FP nanocavities was fabricated. The effective footprint of the sensor was as small as 157 µm² and the sensor showed an enhanced sensitivity of 48.5 mV/CO₂Vol%, a dynamic range of 0-100 CO₂Vol%, and a resolution of 0.019 CO₂Vol% with 1 Hz low-pass filtering. Although the current sensor was only demonstrated for CO₂ sensing, the proposed sensor concept can be used for sensing of a variety of gases when different kinds of MOFs are utilized.

中文翻译：

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具有基于金属有机框架的差分光纤Fabry-Perot纳米腔的超紧凑型气体传感器

基于折射率（RI）的传感是一种主要的光学传感方式，可以在各种光谱范围内实现。尽管它已被广泛用于生化液体的传感，但由于气体浓度变化引起的RI变化极小，因此基于RI的气体传感（尤其是小分子气体）具有挑战性。我们提出了一种基于RI的超紧凑型光纤差分气体传感器，该传感器采用了基于金属有机框架（MOF）的双Fabry-Perot（FP）纳米腔。MOF用作FP腔材料，以增强对特定气体分子的灵敏度以及选择性。差分传感方案利用了两个FP腔的腔长相关反射的相反变化，与基于单个FP腔的传感相比，这进一步提高了灵敏度。对于概念验证，_制作了具有基于ZIF-8的双FP纳米腔的₂传感器。传感器的有效占地面积小至157 µm ²，并且传感器显示出增强的灵敏度48.5 mV / CO ₂ Vol％，动态范围0-100 CO ₂ Vol％和分辨率0.019 CO ₂ Vol％具有1 Hz低通滤波。尽管仅演示了电流传感器用于CO ₂感测，但是当使用不同种类的MOF时，建议的传感器概念可用于感测多种气体。