Hetero-core fiber SPR sensor with ionic liquid gel coating for CO2 detection

We proposed a CO
₂
sensor based on a hetero-core structured fiber optic SPR sensor with ionic liquid (IL) gel coating. As an IL, we used 1-Ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF
₄
]) which is known to have a good CO
₂
adsorption property. In this study, we investigated whether the CO
₂
concentration in the surrounding environment could be measured by detecting the change in transmitted light loss using a hetero-core structured optical fiber SPR sensor. The results showed that the relationship between the light loss and the CO
₂
concentration was linear in the range of 25-100% of the CO
₂
concentration, and the sensitivity was 0.002 dB/%. The response time for 100% CO
₂
was approximately 2 min. It indicates that the proposed sensor has a potential to measure CO
₂
concentration in the surrounding environment with a cost-effective sensing system that uses an LED with a wavelength of 850 nm and an optical power meter.