OP: Super-Coupling Nanoplasmonics with Silicon Photonics for Mid-Infrared Biosensing

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Nontechnical: This project aims to develop a miniaturized and integrated optical sensor system to detect biomedical molecules with the potential for point-of-care applications. The sensor measures the molecule's unique optical absorption features of infrared light, with high sensitivity and the capability of identifying them. Moreover, the project will realize a novel structure consisting of metallic optical nanostructures and silicon waveguide, which are efficiently coupled together. The new architecture may also lead to efficient optoelectronic devices for high-speed optical communications that will play an important role in future data centers and 5G wireless network. For education, the project will provide graduate and undergraduate students with experience in nanotechnology and instrumentation. For K-12 outreach, the PIs will build an interactive Activity Station at the Science Museum of Minnesota every year and enhance the public awareness of the benefits of nanotechnology to our society. More women and underrepresented minorities will be given opportunities to experience nanotechnology. Finally, the PIs will continue support for REU and local recruit high school students for summer research experience.Technical: Nanoplasmonics and silicon photonics are two categories of photonic systems with unique features and advantages in the manipulation and detection of light. Integrating the two distinctive systems in a synergistic way can potentially combine their merits and circumvent their weakness, to enable applications ranging from chemical and biological sensing to optoelectronics and optical communications. The realization of such a hybrid integration approach with both efficiency and sensitivity, however, is hindered by the large phase mismatching between the different types of optical modes in the two systems, which leads to low coupling efficiency between them. This program aims to solve the problem and achieve a hybrid platform that efficiently integrates nanoplasmonic resonators and silicon photonic waveguides with an emphasis on operation in the technologically important mid-infrared (mid-IR) band. The phase mismatching challenge is resolved innovatively by utilizing the super-coupling effect brought by the epsilon-near-zero (ENZ) phenomenon in ring-shaped plasmonic coaxial resonators to achieve waveguide-plasmonics coupling efficiency greater than 90%. The hybrid system enables surface-enhanced infrared absorption (SEIRA) sensing, which will be demonstrated with model systems such as lipid bilayer membranes and proteins. There are three-fold intellectual merits of the program. First, the novel physics of super-coupling enabled by the epsilon-near-zero (ENZ) phenomenon is explored and utilized to efficiently couple nanoplasmonic resonators with silicon waveguides. The second intellectual merit lies in the research emphasis in the mid-IR band, which is currently experiencing very fast development and is exceedingly powerful for spectroscopic chemical and biological sensing. The third intellectual merit of the program is to achieve SEIRA biosensing. A new reflection mode detection scheme is investigated that avoids the passage of IR light through the solution and thus largely circumvents water absorption. The anticipated significant improvement in the signal-to-noise ratio would directly lead to enhanced detection sensitivity in SEIRA.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.