CAREER: Epsilon-Near-Zero Conducting Oxide Metasurface Perfect Absorbers, Color Filters, and Beam Steering Devices with Gate-tunability

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Conventional optical components from lenses to filters are playing a critical role in modern imaging and display technologies, such as an optical camera's image sensor, the smartphone's display, and precise optical-imaging microscopy. However, there is an ongoing pressure to shrink the size of optical systems. Metasurfaces, which are ultrathin surfaces patterned with nanostructures, provide a new method to control the phase and amplitude of transmitted, reflected, and scattered light. Because of the virtually flat nature of metasurfaces (typical thickness 100 nm), they can enable novel ultrathin optical components such as flat lenses, waveplates, and holography surfaces over a broad range of the electromagnetic spectrum. However, the optical properties for most metasurfaces are fixed upon their nanofabrication, restricting many real-world applications. Therefore, there is a need to develop a tunable version of an ultrathin metasurface. The first goal of this project is to establish electronically-tunable conducting oxide metasurfaces that could be used for a variety of next-generation imaging and display technologies (e.g. tunable perfect absorber, color filter, beam steering device, etc.). The second goal of this project is to utilize our nanophotonic research and infrastructure to provide two-year technical college students, university undergraduate students, and graduate students with the nanophotonic skills and knowledge necessary for future academic and industrial careers. Furthermore, the project's events with area schools and a local science museum will provide exciting opportunities to introduce nanophotonic concepts to students and the general public in a fun and informative way. Technical description: Optical metasurfaces are single- or few-layer structures with subwavelength thickness which produce abrupt changes in the phase, amplitude, or polarization of light. They show promise for extraordinary light manipulation and could enable novel ultrathin optical elements such as flat lenses, holograms, and optical vortex generation/detection devices. While metasurfaces hold considerable promise for future fundamental advances and novel optical applications, the lack of efficient optical tunability and low optical efficiency are key limiting issues for their use in a wide range of optical applications. The long range goal of this project is to develop an integrated program of research and education focused on developing efficient nanoscale metasurface components and their applications in meta-devices. The objective of this CAREER research is to establish an efficient and broadband electrical management of the absorptivity, optical phase, and spectral response of conducting oxide metasurfaces under an Epsilon-Near-Zero (ENZ) regime. To achieve this objective, the PI will identify approaches which yield efficient control of the carrier concentration of conducting oxide materials and the ENZ frequency with field-effect tunable metasurface resonance and gradient-index ENZ multilayer via atomic layer deposition. Establishing techniques to efficiently exploit the voltage-tuned ENZ resonance in metasurfaces to manipulate optical responses will enable development of tunable metasurface beam steering devices, color filters, and perfect absorbers, opening the path to revolutionary nano-optical imaging, display, and communication applications. Examples of novel devices that would utilize the technology include high-resolution beam steering devices for next generation visible LIDAR technology, perfect absorbers/spectrum splitting elements for photo/thermal-voltaic applications, tunable color filters/lenses for CMOS optical imaging and cutting-edge smartphone microscopies/spectroscopies, and ultrafast spatial light modulators with nanoscale pixels. The educational objective is to integrate research and classroom activities based on advanced nanophotonic technology for training two-year technical college students, university undergraduate students, and graduate students with the nanophotonic skills and knowledge necessary for future academic and industrial careers.