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Optical metasurface can provide control over wavefront, polarization and spectrum of light fields while having just nanoscale thickness, making them promising candidates for flat optical components. Most metasurfaces studied so far consist of two-dimensional subwavelength arrays of designed metallic or dielectric scatterers. Deviations from a periodic, ordered arrangement are usually associated with a deterioration of the optical properties. However, the introduction of controlled disorder also provides interesting opportunities to engineer the optical response of metasurfaces. For example, the introduction of disorder can decrease unwanted anisotropy in the optical response [1], it suppresses scattering into discrete diffraction orders, and it can enhance the metasurfaces’ channel capacity [2].
Here we investigate different types of disordered metasurfaces. We demonstrate that the introduction of rotational disorder at the unit-cell level enables the realization of chiral plasmonic metasurfaces supporting pure circular dichroism and circular birefringence. We show experimentally that the polarization eigenstates of these metasurfaces, which coincide with the fundamental right- and left-handed circular polarizations, do not depend on the wavelength over the spectral range of the metasurface resonances. Thereby, our metasurfaces mimic the behaviour of natural chiral media, while providing a stronger chiral response. Furthermore, we systematically investigate how the introduction of different types of positional disorder influences the complex transmittance spectra of Mie-resonant silicon metasurfaces, showing that disorder provides an independent degree of freedom for engineering their spatial and spectral dispersion.
[1] S. S. Kruk et al., Phys. Rev. B 88, 201404(R) (2013).
[2] D. Veksler et al., ACS Photonics 2, 661 (2015).
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