High-performance sub-wavelength grating-based resonator sensors with substrate overetch.

Area of Science:

• Photonics and Sensing Technology
• Materials Science and Engineering

Background:

• Sub-wavelength-grating (SWG) waveguides are crucial for advanced sensor designs.
• Improving the sensitivity and analyte interaction of SWG waveguide sensors remains a key challenge.

Purpose of the Study:

• To propose and validate a novel substrate-overetch (SOE) geometry for enhancing SWG waveguide sensor performance.
• To investigate the impact of SOE on analyte interaction and group index for improved sensitivity.

Main Methods:

• Fabrication of the SOE-SWG waveguide using Ar/C4F8/O2 plasma etching.
• Achieving a 285-nm anisotropic overetch in the SiO2 layer with high SiO2/Si selectivity (10:1).
• Characterization of sensor performance using isopropyl alcohol solutions.

Main Results:

• The SOE-SWG waveguide demonstrated enhanced analyte interaction and a reduced group index.
• Bulk sensitivity was significantly improved, reaching up to 575 nm/RIU (compared to 479 nm/RIU previously).
• A maximum waveguide mode sensitivity exceeding one was achieved.

Conclusions:

• The proposed SOE geometry offers a viable strategy for enhancing the sensing capabilities of SWG waveguide-based devices.
• This advancement holds promise for developing more sensitive and efficient optical sensors.
• The optimized etching process provides a pathway for fabricating high-performance SOE-SWG structures.