Exhaled breath optical fiber sensor based on LMRs for respiration monitoring

In this work, the fabrication and characterization of a small and portable exhaled breath sensor based on Lossy Mode Resonances (LMR) is presented. Tin oxide (SnO₂) coatings fabricated onto optical fibers are used as LMR supporting coatings. The principle of operation is based on the measurement of refractive index changes by the LMR device (with an average sensitivity of 8355 nm/RIU) originated by the condensation of micro water droplets in the surroundings of the SnO₂ coating during the breath natural process. The sensor shows a repetitive response with less than 100 ms of response time and a wavelength shift of 150 nm from inhalation to exhalation.