Novel Aspects of Topological Photonics in Open Optical Systems: Non-Hermiticity and Fano-Resonances

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Nontechnical description: Our ability to control light scattering and propagation is at the core of modern technologies, from lenses in smartphone cameras to optical fiber networks in datacenters. Many advancements in functionality of today's optical components are attained by using new or improved materials. The concept of metamaterials further enables this approach by offering artificially structured materials with properties absent in any natural materials system. One such unique engineered property, known as robustness, is found in specially designed structures referred to as topological metamaterials. Topological metamaterials allow guiding light with unprecedented insensitivity to obstacles and defects, inevitably present in any material or device, thus upending common notions of propagation and scattering of light. Most importantly, topological metamaterials offer a new platform for optical materials and devices exhibiting significantly higher tolerance to fabrication errors. In this project, we aim to design and test such optical devices, whose functionality is tolerant to both fabrication imperfections and environmental factors. This project is interdisciplinary in nature, bridging areas of fundamental and applied sciences. Significant outreach efforts towards high school and undergraduate minority students are planned. Activities for high school students from local schools include summer research conducted in the PI's laboratory through CCNY Summer Science Program.Technical description: Topological photonics offers a fundamentally new vision on optical scattering, which may be exploited to manipulate the phase and amplitude of light in locally non-uniform ways. This suggests that open topological metamaterials with their topological modes leaking into a surrounding medium, such as two-dimensional metasurfaces patterned on the nanoscale, may offer new mechanisms of controlling scattering of light and thus enabling new approaches to generate desirable scattering patterns. On the other hand, the open character of the system, which renders photonic systems non-Hermitian, may itself affect topological properties of metamaterials in a nontrivial way. The goal of this project is to understand aspects of the interplay between topology and non-Hermiticity, and to explore the limits of topological robustness in open systems. Our research reveals the role of leakage of topological modes into free-space, and of their interaction with incident light. Understanding these properties enables a new class of topological optical devices endowed with topological protection. Within this project we aim to design and test topological gratings, metasurfaces, flat-lenses, and vortex phase plates. The proposed research plan bridges areas of fundamental and applied science, optics, photonics, and condensed matter physics. The project presents opportunities for students from high-school to the graduate level to get involved in all stages of research, and to obtain hands-on experience in photonic materials and devices. By opening opportunities in research on topological metamaterials to students, this project further attracts emerging generations to pursue careers in physics and engineering.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.