Controlling light with geometric symmetries

Light is an electromagnetic wave defined by several degrees of freedom (DoF), including frequency, momentum, amplitude, phase, and polarization. Controlling these properties is a key need in a wide array of technologies. Nanophotonic devices called “metasurfaces” fill this need by structuring common materials (such as silicon, glass, and metals) at subwavelength scales (micrometer and smaller). Recently, “nonlocal metasurfaces” with strong light-matter interactions have emerged as a platform for customizing scattering from a thin film using both local responses (isolated to single nanostructures) and nonlocal responses (collective effects from many adjacent nanostructures). Such interactions can be customized at will—a sandbox for invention in a platform that is readily manufacturable.

Our research aims to both (1) invent, design and develop new devices using novel and emerging physical phenomena and (2) apply these new tools to exciting applications. Starting from an array of uniform subwavelength structures, we introduce small geometric perturbations that break specific symmetries, imparting remarkable control to light point-by-point across the device—in some cases, “complete” control over the physically relevant DoF. The complex geometries of these devices are “written down” by equations rooted in group theory and perturbation theory, minimizing or eliminating the need for computationally expensive optimization. Applications include new methods for optical combiners in augmented reality systems, custom couplers in integrated photonics for communications systems, and controlling the directionality and polarization of thermal emission in surprising ways.