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Chiroptical Adjustment

A metal cone section showing red light in the circle of the top

Laser light shows the nanopatterned structure of a chiral meta­material developed by researchers in the Georgia Tech School of Electrical and Computer Engineering.

By John Toon

Researchers have demonstrated an optical metamaterial whose chiroptical properties in the nonlinear regime produce a significant spectral shift with milliwatt power levels.

The researchers recently demonstrated the properties of their metamaterial, in which they spectrally modified two absorptive resonances by incrementally exposing the material to power intensities beyond its linear optical regime. With just a 15-­milli­watt change in excitation power, they measured a 10-nanometer spectral shift in the material’s transmission resonances and a 14-degree polarization rotation.

“Nanoscale chiral structures offer an approach to modulating optical signals with relatively small variations in input power,” said Sean Rodrigues, a Ph.D. candidate who led the research in the laboratory of Associate Professor Wenshan Cai in Georgia Tech’s School of Electrical and Computer Engineering. “To see this kind of change in such a thin material makes chiroptical metamaterials an interesting new platform for optical signal modulation.”

Modulating metamaterial responses through the manipulation of input power offers the potential for new types of active optics useful in all-optical switching.

Chiral materials exhibit optical properties that differ depending on the right or left circular polarization incident on them. The differences between these responses, which are created by the nanoscale patterning of absorptive materials, can be utilized to create large chiroptical resonances.

The materials are made by nanopatterning layers of silver onto glass substrates and include a dielectric material between them. The research, supported by the National Science Foundation and the Air Force Research Laboratory, was reported in the journal Nature Communications.

Related: Chiral Metamaterial Produces Record Optical Shift Under Incremental Power Modulation, March 1, 2017

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