Breath sensing is an effective tool for health monitoring. Previously, high-mesa waveguide structures have been proposed by our group for realizing a compact breath-sensing photonic circuit. By using the doped SiO2 as the waveguide core, 50% concentration CO2 has been detected. One issue of preventing parts per million (ppm)-order detection is the low portion of evanescent light (Gamma(air) = 2.2%) in the doped SiO2 waveguides. In order to realize low propagation loss a and high simultaneously, thin silicon (Si) waveguides with a Gamma(air) as high as 37.6% have been proposed and fabricated in this work. A thermal oxidation technique was applied to further reduce a, so that a was decreased from 1.45 to 0.84 and 0.29 to 0.2 dB/cm for the 0.5 and 3-mu m-wide waveguide, respectively. According to our analysis, the significantly decreased alpha is attributed to recovering the damaged Si core and smoothing the waveguide sidewalls. The high Gamma(air) air and effective loss reduction show a promising potential of applying Si high-mesa waveguides to realize ppm-order sensing. (C) 2020 Optical Society of America
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