Sensing nitrous oxide with QCL-coupled silicon-on-sapphire ring resonators

We report the initial evaluation of a mid-infrared QCL-coupled silicon-on-sapphire ring resonator gas sensor. The device probes the N2O 2241.79 cm(-1) optical transition (R23 line) in the nu(3) vibrational band. N2O concentration is deduced using a non-linear least squares fit, based on coupled-mode theory, of the change in ring resonator Q due to gas absorption losses in the evanescent portion of the waveguide optical mode. These early experiments demonstrated response to 5000 ppmv N2O. (C) 2015 Optical Society of America