Disorder-enabled pure circular dichroism in bilayer plasmonic metasurfaces

In optical metasurfaces, disorder, e.g. in the arrangement or shape of its building blocks, is usually associated with a deterioration of the optical properties due to an increase of incoherent scattering. However, more recently, researchers have started recognizing the introduction of controlled disorder as a strategy to diversify engineering options of metasurfaces. For example, the introduction of disorder can be used to decrease unwanted anisotropy in their optical response [1] and enhance the information density encoded in wavefront shaping metasurfaces [2].Financial support by the Thuringian State Government within its ProExcellence initiative (ACP2020) and by the German Research Foundation (STA 1426/1-1 and PE 1524/10-1) are gratefully acknowledge

Disorder-Enabled Pure Chirality in Bilayer Plasmonic Metasurfaces

We experimentally study the effect of rotational disorder at the unit-cell level on the optical response of chiral bilayer plasmonic metasurfaces consisting of asymmetric dimers of gold nanoantennas. The structures are fabricated based on a two-step electron-beam lithography process in combination with a precision alignment procedure. For a comprehensive characterization of the chiral optical response of the fabricated bilayer metasurfaces, we combine two different measurement strategies, namely, direct measurement of the circular transmission using circularly polarized incident light and measurement of the Jones matrix using interferometric spectroscopy with linearly polarized incident light. This allows us both to do a comprehensive analysis of the polarization dependent properties and to retrieve the effective polarization eigenstates of the metasurface in the ordered and disordered regime directly from experimental data. Our results demonstrate that rotational disorder provides a route toward chiral plasmonic metasurfaces with orthogonal, purely circular eigenstates, leading to circular dichroism and optical activity without linear birefringence. Our experimental findings are additionally complemented and verified by numerical simulations for the ordered case.Financial support by the Thuringian State Government within its ProExcellence initiative (ACP2020) and by the German Research Foundation through the Priority Program SPP 1839 “Tailored Disorder” (STA 1426/1-1 and PE 1524/10-1) is gratefully acknowledge

Tailored structural disorder in optical metasurfaces

We experimentally realize various optical metasurfaces with tailored rotational and positional disorder, and demonstrate their ability to support pure circular dichroism and to tune the intensity of the transmitted light almost independently from its phase