Ultracompact gas sensor with metal-organic-framework-based differential fiber-optic Fabry-Perot nanocavities

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 mu m(2) and the sensor showed an enhanced sensitivity of 48.5 mV/CO(2)Vol%, a dynamic range of 0-100 CO(2)Vol%, and a resolution of 0.019 CO(2)Vol% 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. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement