Significant Propagation Loss Reduction on Silicon High-Mesa Waveguides Using Thermal Oxidation Technique

摘要

Breath sensing is an effective tool for health-monitoring, because some contents present in the breath directly correlate to specific diseases. Previously, for breathing sensing at the telecom band, a SiO_2 high-mesa waveguide has been proposed by our group. For the first time in the world, we have used the high-mesa SiO_2 waveguide-based cavity ring-down spectroscopy to detect 50% concentration CO_2. In order to detect ppm-order breath content, a high portion of the guided light out of the waveguide (Γ_(air)) is required, however Γ_(air) of the high-mesa SiO_2 waveguide is only 2.2%. For this reason, we have proposed an optimized design of 100 nm thick Si high-mesa waveguide to achieve a much higher Γ_(air) in this work; however, the propagation loss is too high for the ppm-order detection purpose. Therefore, we have exploited Si thermal oxidation technique to reduce the propagation loss. Significant propagation loss reduction from 1.45 to 0.84 dB/cm and 0.29 to 0.2 dB/cm at a waveguide width of 0.5 and 3.0μm has been achieved successfully.