Metasurface composed of arrays of subwavelength scale optical antennas emerges as a new paradigm for light field manipulation and unpins various flat optical diffractive devices. Based on their phase modulation mechanisms, the reported metasurfaces can be classified into three categories: resonance phase, propagation phase and geometric phase. In this talk, we propose a new metasurface design allowing to fully control the phase, amplitude, polarization and frequency of visible light simultaneously. This is achieved through a generalized geometric phase mechanism which combines the detour phase and the Pancharatnam–Berry phase. Utilizing a diatomic design strategy, the in-plane displacements and orientations of two identical meta-atom in each unit meta-molecules are fully exploited enabling light field manipulation at multi-dimensions. Leveraging this appealing feature, we experimentally demonstrated the broadband vectorial holographic images with spatially-varying polarization states, dual-way polarization switching functionalities, and full-color complex-amplitude vectorial holograms. Our work may suggest a new route to achromatic diffractive elements, polarization optics and ultra-secure anti-counterfeiting.
Non-Hermitian, Topological, and Lorentz non-reciprocal photonic resonators have attracted intense attention due to their complexities which are strongly dependent on their spatial and temporal structures. Strongly dispersive materials such as plasmonic and gyromagnetic materials lead to additional difficulties in defining topological bands. In this talk, I will introduce recent progress in my group and discuss the bands and edge modes in these low-symmetry photonic systems. Arrays of plasmonic nanoparticles and gyromagnetic resonators will be used as examples to illustrate the topological and Lorentz non-reciprocal effects.