Abstract

We propose a strategy to improve sensing performance of sub-wavelength-grating (SWG) waveguide-based sensors by introducing a substrate-overetch (SOE) geometry. The proposed SOE-SWG waveguide shows enhanced analyte interaction and a reduced group index, which improves the sensitivity of resonator-based sensors. The $ {{\rm SiO}_2} $ overetch process was realized in $ {\rm Ar}/{{\rm C}_4}{{\rm F}_8}/{{\rm O}_2} $ plasma for 40 sec with a $ {{\rm SiO}_2}/{\rm Si} $ selectivity of 10:1, obtaining a 285-nm anisotropic overetch in the $ {{\rm SiO}_2} $ layer. Sensor performance of the SOE-SWG architecture is characterized by using isopropyl alcohol solutions, indicating an enhanced bulk sensitivity up to 575 nm/RIU (479 nm/RIU before the SOE), and a maximum waveguide mode sensitivity larger than one.

© 2019 Optical Society of America

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