Ultrashort Near-Infrared Fiber-Optic Sensors for Carbon Dioxide Detection

In this paper, we report a fiber-optic carbon dioxide (CO₂) near-infrared (IR) absorption sensor with only 8-cm sensing length that is coated with nanoporous metalorganic framework material Cu-BTC (BTC = benzene-1,3, 5-tricarboxylate). The multimode optical fiber was etched by hydrofluoric acid to remove the cladding and part of the core, resulting in larger evanescent field to sense the near-IR absorption induced by the adsorbed CO₂. The Cu-BTC thin film with 100 nm thickness was then grown onto the ethced core through a stepwise layer-by-layer method. Our real-time measurement results show that the CO₂ detection limit is better than 500 ppm and the overall response time is 40 s for absorption and 75 s for desorption. To the best of our knowledge, this is the shortest near-IR fiber-optic sensor for CO2 detection at 1.57-μm wavelength.