High-mesa waveguides have been fabricated for a compact infrared sensing system, as they have a benefit of having optical evanescent field outside of their solid waveguides and thus this contributes to the sensing of gas or liquid in a compact area. Fabricated semiconductor on insulator (SOI)-based Si/SiO2 high-mesa waveguides, by using neutral loop discharge (NLD) plasma etching technique, showed extremely low propagation loss compared to those fabricated by using conventional reactive ion etching (RIE) technique. Moreover, we also demonstrate actual sensing for liquid methanol. By using 6 mm SOI-based Si/SiO2 high-mesa waveguide with waveguide width of 0.7 micro-meters, we could successfully obtain sufficient infrared absorption for the first time, therefore, this proved that the proposed waveguide had an optical field outside of the waveguide.
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