Gassing up potential for silicon microring resonators

Silicon microring resonators are becoming indispensable to gas sensing applications, such as the detection of explosive materials, volatile organic compounds, and toxicity and viruses. But these extremely tiny and compact devices have plenty of room for improvement. Their waveguide design, intended to counter light scattering caused by etching-induced device sidewall roughness, can hinder light-gas interaction and make balancing a high-quality factor with a significant evanescent field in the air difficult.

In a proof-of-concept demonstration, Guo et al. used a suspended nanomembrane silicon (SNS) waveguide configuration to break through this longstanding limitation and achieve sensitive gas sensing on a chip.

“We proposed an SNS waveguide that enables light guiding around the surface of the ultra-thin silicon waveguide,” said author Zhenzhou Cheng.

The researchers showed that their design of a wide subwavelength-cladding waveguide avoids the large overlap between optical modes and waveguide sidewalls. At the same time, the deep subwavelength thickness squeezes the light field to the waveguide’s surface and bottom, where the smoothness is easily controllable at the sub-nanoscale.

“This clever design not only achieves sub-million-level intrinsic quality factor of a silicon micro-ring but also guarantees giant interaction between light and gases,” said Cheng. “It brings us the possibility of ultra-sensitive gas sensing on a chip.”

Additionally, the team used the new design to explore a carbon dioxide gas sensing application at mid-infrared wavelengths by harnessing different light resonances through engineered waveguide modes for boosting sensing sensitivity.

“In the future, we plan to make our efforts to achieve simultaneous sensing of multiple gases with ultra-high sensitivity for biochemical sensing, food science, and environmental science,” said Cheng.

Source: “High-Q silicon microring resonator with ultrathin sub-wavelength thicknesses for sensitive gas sensing,” by Rongxiang Guo, Qi He, Zunyue Zhang, Yingqi Xu, Shujiao Zhang, Qiyue Lang, Shuqi Xiao, Peize Han, Jiaqi Wang, Tianben Ding, Tiegen Liu, Hon Ki Tsang, Keisuke Goda, and Zhenzhou Cheng, Applied Physics Reviews (2024). The article can be accessed at http://doi.org/10.1063/5.0189343 .