CAREER: Photonic Integrated Guided-Wave-Driven Metasurfaces

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Wiring light on a chip like electronic circuits, integrated photonics provides a promising long-term solution for increasing demands for data transmission bandwidth and energy efficiency of computing and communication systems. A photonic integrated circuit (PIC) combining many light-controlling components into a single chip, similar to complementary metal oxide semiconductor (CMOS) chips that have revolutionized the electronics industry, offers great advantages in terms of speed, bandwidth, reliability, scalability, power consumption, and etc. In order to fully exploit the benefits of PICs in free-space applications, it is crucial to have an interface that can flexibly control light when it converts between guided and free-space modes. However, conventional coupling techniques such as edge couplers and surface gratings have limited functionalities and lack of the capability to complete control over light. Although arrays of gratings can achieve more advanced functions, such as off-chip beam steering, focusing, and holographic image construction, they have large footprints and suffer from loss due to the existence of high-order diffractions. Therefore, there is a strong demand for a unified approach to achieve complex free-space optical functions on PICs. The major goal of the proposed program is to develop a hybrid architecture where metasurfaces – ultrathin artificial surfaces which manipulate light by locally imposing abrupt changes to optical properties through engineered sub-wavelength structures also known as meta-atoms – are directly driven by guided waves to realize complex free-space functions. The proposed program will include closely integrated educational activities (such as developing a new course on nanophotonics) designed to stimulate undergraduate and graduate students to pursue engineering career by exposing them to the exciting development of nanophotonic devices solving important societal problems in optical computing, communication, and networking. Besides, nanophotonic cloud computing tools will be developed that are free-to-run in web browsers without the need for powerful workstations that will be especially beneficial for economically disadvantaged research communities worldwide. Furthermore, outreach activities, such as organizing fun exhibitions of optics effects, will also be provided to promote the interests and participations of K-12 teachers and students in local schools and public libraries.The overarching goal of this research program is to combine two powerful, complimentary technologies – the integrated photonics and the metasurface – together to develop a new architecture where metasurfaces are directly driven by the guided waves in PICs for realizing complex optical functions. The meta-atom building blocks with sizes much smaller than the optical wavelength will be placed on top of photonic integrated components. Through the metasurfaces consisting of such meta-atoms, the guided light can be molded to any desired complex light fields in free space or in PICs. The proposed research will establish a theory, design, material synthesis, and device nanofabrication platform and provide a complete photonic integrated route for complete light control. Tremendous benefits will be offered by the proposed hybrid architecture: (1) metasurfaces that are driven directly by guided waves in PICs; (2) light can be routed to different metasurfaces performing multiple complex functions on a single waveguide; and (3) PICs are now empowered with the ability to control light at the subwavelength scale. The technology will pave new exciting ways for building multifunctional photonic integrated devices with flexible access to free space and lead to a large spectrum of novel applications particularly where the grand challenges of the system size, weight, and power, performance are concerned.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.