Giant optical chirality has been realized at visible wavelengths in planar engineered surfaces. Strong optical chirality is desired for various applications. Metamaterials are promising for realizing this, but three-dimensional ones are difficult to make, while planar ones impart low chirality. Now, Alexander Zhu of Harvard University and co-workers have made metasurfaces consisting of an array of miniature gammadion-cross-shaped dielectric structures that gave a circular dichroism in transmission of 80% for green light, while numerical simulations suggested that 95% should be possible. Furthermore, 600-namometer-thick surfaces can provide a circular birefringence as large 60 degrees of polarization rotation, equivalent to 100,000 degrees per millimeter thickness — much larger than that measured in other media, whether natural or engineered. The metasurfaces could lead to high-performance flat devices for controlling the polarization of light beams in applications such as telecommunications.
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