Meta-atoms and Metasurfaces for Nonreciprocal Conversion between Free-space Propagating Waves and Guided Waves

Description

Lorentz reciprocity is a fundamental theorem in classical electromagnetism that implies a symmetric response of the systems under the interchange of source and detector. Breaking the Lorentz reciprocity can open numerous possibilities for exploring new physics and realizing novel optical properties. Optical nonreciprocity can be realized by several mechanisms, including nonlinearity, external field biasing, and time modulation. It has been applied to manipulate various properties of light, leading to many essential optical devices and applications such as optical isolators, optical circulators, invisible sensing, and full-duplex communications.Conventional research mainly focused on the nonreciprocal manipulation of free-space propagating waves (FPWs) or guided waves (GWs) separately. In this proposed project, we plan to conduct theoretical and experimental study on the nonreciprocal conversion between FPWs and GWs. We aim to realize the unidirectional conversion between the two types of waves, i.e., allowing the conversion from one type to the other butsuppressing the reversed conversion. We will design meta-atoms (i.e., artificial resonating unit) breaking the local time-reversal symmetry and enabling nonreciprocal conversion between FPWs and GWs. We will then apply the meta-atoms to design metasurfaces to achieve efficient nonreciprocal conversion between FPWs and GWs. In addition, we will engineer the metasurfaces to control the directionality of the converted GWs to realize wave steering and focusing.The project is grounded on the PI’s expertise in nanophotonics and metasurfaces and is expected to generate rich outputs. It will offer new mechanisms for achieving efficient one-way conversion between FPWs and GWs, facilitating the development of photonic integrated circuits and light energy harvesting technologies. It will generate metasurfaces with new functionalities for designing ultra-thin optical devices in the era of flat optics. The results will contribute to a comprehensive understanding of Lorentz reciprocity in optical systems and will also benefit the research of non-Hermitian physics and topological photonics where nonreciprocal hopping plays an essential role.