Intensity-asymmetric wavefront shaping in nonlocal meta-lens
Jin Yao, Zhihui Wang, Yubin Fan, Ke Zhang, Rong Lin, Jiajun Wu, Chang Peng, Shumin Xiao, Din Ping Tsai
Abstract
Asymmetric wavefront shaping can unlock essential functionalities for next-generation photonic systems, such as unidirectional transmission, nonlinear signal routing, and nonreciprocal light control. However, achieving these functionalities in passive nonlinear metasurfaces remains challenging due to the required trade-offs among nonlinear efficiency, phase modulation, and directional asymmetry, particularly on low-index substrates with weak intrinsic asymmetry. Here, we propose a meta-lens that effectively integrates local Mie-type resonances with nonlocal quasi-bound states in the continuum, tailoring their interaction. Without any additional layers, this hybrid design produces a strong directional response originating from asymmetries induced by the silica substrate, while preserving high nonlinear efficiency and robust phase modulation. Experimentally, directional focusing is achieved across the fundamental wavelength and its second and third harmonics, with a maximum forward-to-backward power ratio exceeding 10 dB. This work opens new opportunities for nonreciprocal LIDAR and optical computing applications. Passive metasurfaces suffer from a complex balancing of their nonlinear efficiency, phase modulation capabilities and directionality. Here, authors propose a nonlocal meta-lens integrating Mie-type resonances with quasi-bound states in the continuum. Driven by the asymmetry of a low-index silica substrate, they realize directional response with a forward-to-backward ratio of up to 10 dB.