High-performance meta-devices based on multilayer meta-atoms:interplay between the number of layers and phase coverage

Transmissive metasurfaces have provided an efficient platform to manipulate electromagnetic(EM)waves, but previously adopted multilayer meta-atoms are too thick and/or the design approach fully relies on brute-force simulations without physical understandings. Here, based on coupled-mode theory(CMT) analyses on multilayer meta-atoms of distinct types, it is found that meta-atoms of a specific type only allows the phase coverage over a particular range, thus suitable for polarization-control applications.However, combinations of meta-atoms with distinct types are necessary for building ultra-thin wavefront-control meta-devices requiring 360° phase coverage. Based on these physical understandings,high-efficiency meta-atoms are designed/fabricated, and used to construct three typical meta-devices,including quarter-and half-wave plates and a beam deflector. Our results elucidate the physics underlying the interplay between thicknesses and performances of transmissive metasurfaces, which can guide the realizations of miniaturized transmissive meta-devices in different frequency domains.

Tailoring the lineshapes of coupled plasmonic systems based on a theory derived from first principles

Coupled photonic systems exhibit intriguing optical responses attracting intensive attention,but available theoretical tools either cannot reveal the underlying physics or are empirical in nature.Here,we derive a rigorous theoretical framework from first principles(i.e.,Maxwell’s equations),with all parameters directly computable via wave function integrations,to study coupled photonic systems containing multiple resonators.Benchmark calculations against Mie theory reveal the physical meanings of the parameters defined in our theory and their mutual relations.After testing our theory numerically and experimentally on a realistic plasmonic system,we show how to utilize it to freely tailor the lineshape of a coupled system,involving two plasmonic resonators exhibiting arbitrary radiative losses,particularly how to create a completely“dark”mode with vanishing radiative loss(e.g.,a bound state in continuum).All theoretical predictions are quantitatively verified by our experiments at near-infrared frequencies.Our results not only help understand the profound physics in such coupled photonic systems,but also offer a powerful tool for fast designing functional devices to meet diversified application requests.