Collaborative Research: Thin-Film Chalcogenide Glass Materials for High-Quality Integrated Photonics

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Nontechnical Description: The main objectives of this collaborative research project between MIT and Washington University are (1) to develop critical understandings of the optical loss mechanisms in thin-film chalcogenide glass materials through spectroscopic studies, (2) to exploit innovative processing science to synthesize ultra-low-loss chalcogenide glass materials in the thin-film form and (3) to fabricate optical devices with novel functionalities. Based on these fundamental findings, the research aims to demonstrate chalcogenide glass resonant cavity devices with high quality factors as building blocks for photonic sensors, light emitters and nonlinear optical signal processing systems. The research is expected to have significant impacts on many areas including materials science, nanotechnology, nonlinear optics and integrated photonics. The participating undergraduate and graduate researchers benefit from the cross-disciplinary collaboration between the two research groups at MIT and Washington University. Results obtained from the research are incorporated into new undergraduate courses on glass materials at MIT. The project also expands K-12 initiatives on both campuses through lab open houses and summer internship programs.Technical Description: Chalcogenide glasses (ChGs) are recognized as an emerging material platform for integrated photonics given their unique properties, such as substrate-blind integration capacity, extreme processing versatility, widely tunable optical and thermal characteristics via composition alloying, large Kerr nonlinearity, and broadband optical transparency. Unlike silica glass, multi-component chalcogenide glasses contain a far more diverse group of nanoscale glass network moieties. These properties result in complicated structural transformations and optical losses that are highly sensitive to processing history and cannot be described using the classical Rayleigh scattering formalism. As a consequence, traditional loss reduction methods cannot be simply transferred to chalcogenide materials without an in-depth understanding of the kinetics of micro-structural evolution and loss mechanisms in chalcogenide films. The challenge of differentiating optical loss contributions in chalcogenide films is further compounded by the small interaction volume in thin films, which severely limits the sensitivity of most traditional optical characterization methods. In this project, new waveguide- and resonator-based spectroscopic characterization methods are developed to extract critical material information such as nanoscale phase composition, intrinsic absorption, and different scattering processes. The project advances our understanding of the nanoscale structural transformation mechanisms associated with material's optical characteristics as well as the structure-processing-property relationship in ChG materials. By combining kinetic modeling and experimental validation of novel surface-tension-assisted processing techniques, the project also aims to develop ultra-high-quality planar ChG structures with performance exceeding the current state-of-the-art.