Researchers at Georgia Institute of Technology (Atlanta, GA) have demonstrated an optical metamaterial whose chiral properties in the nonlinear optical regime produce a spectral shift with power levels in the milliwatt range. They showed properties of their chiral metamaterial in which they spectrally modified two absorptive resonances by incrementally exposing the material to power intensities beyond its linear optical regime. With a 15 mW change, they measured a 10 nm spectral shift in the material's transmission resonances and a 14° polarization rotation. The metamaterial itself was less than λ/7 thick. The researchers believe that may be the strongest nonlinear optical rotation ever reported for a chiral metamaterial, and is about 100,000X larger than the current record measurement.
The material is made by nanopatterning layers of silver approximately 33 nm thick onto glass substrates. Between the layers is a 45 nm layer of dielectric material. An elliptical pattern is created using electron-beam lithography, and then encapsulated within a dielectric material to prevent oxidation. The material operates in the visible to near-IR spectrum (740 to 1000 nm). The optical rotation and circular dichroism measurements were taken with the beam entering the material at a normal-incidence angle. This modulation of chiral optical responses from metamaterials by manipulating input power has potential in all-optical switching and light modulation. Reference: S. P. Rodrigues et al., Nature Commun. (2017); http://dx.doi.org/10.1038/ncomms14602.