Abstract
Metasurfaces are generally designed by placing scatterers in periodic or pseudo-periodic grids. We propose and discuss design rules for functional metasurfaces with randomly placed anisotropic elements that randomly sample a well-defined phase function. By analyzing the focusing performance of random metasurface lenses as a function of their density and the density of the phase-maps used to design them, we find that the performance of 1D metasurfaces is mostly governed by their density while 2D metasurfaces strongly depend on both the density and the near-field coupling configuration of the surface. The proposed approach is used to design all-polarization random metalenses at near infrared frequencies. Challenges, as well as opportunities of random metasurfaces compared to periodic ones are discussed. Our results pave the way to new approaches in the design of nanophotonic structures and devices from lenses to solar energy concentrators.
Highlights
Recent advances on the control of light in complex media[36] have motivated the study of random or disordered metasurfaces for specific applications such as decreasing the radar cross-section[37,38,39,40], improving SERS enhancement[41], reducing laser coherence[42], designing wide band-gaps[43], or increasing light-matter interaction and the absorption of solar cells[44,45]
The circular symmetry of the elements is statistically restored by the randomness[55], which enables the design of polarization independent metalenses with anisotropic elements
We demonstrated successful focusing by 1D and 2D random metasurfaces
Summary
Recent advances on the control of light in complex media[36] have motivated the study of random or disordered metasurfaces for specific applications such as decreasing the radar cross-section[37,38,39,40], improving SERS enhancement[41], reducing laser coherence[42], designing wide band-gaps[43], or increasing light-matter interaction and the absorption of solar cells[44,45]. To establish general rules and guidelines for such designs, the resonators are first considered in a periodic framework to numerically obtain their phase maps φ(l), i.e. the phase-shift provided by the element as a function of a geometrical parameter—the length in our case—for different periods of the array. These periods, corresponding to a density of the phase-map, are used as references from which a resonator can be chosen.
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