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Tailor-made surface swaps light polarization

A new approach to designing surfaces patterned at subwavelength scales may lead to novel optical applications.

Manipulating the properties of light—amplitude, phase, and polarization, for instance—typically involves using an array of lenses, polarizers, and other elements on an optical table. Two-dimensional metamaterials called metasurfaces offer a compact alternative based on the engineering of subwavelength structural features to achieve specific electromagnetic properties. For example, Anthony Grbic and his colleagues at the University of Michigan have designed and fabricated a new type of asymmetric circular polarizer. As illustrated here, their 400-nm-thick device consists of three patterned gold surfaces separated by dielectric substrates. When right-handed circularly polarized (RHCP) light is incident on one side of the metasurface, it emerges from the other side as left-handed circularly polarized (LHCP) light. At the operating wavelength of 1.5 μm, the transmittance for RHCP to LHCP is 50% whereas for other combinations — LHCP to RHCP, LHCP to LHCP, and RHCP to RHCP — the transmittances are below 2.5%. Those results mean that the metasurface works as a filter that selectively passes circularly polarized light. What’s more, the device is asymmetric: It reflects RHCP light incident on the other side while converting LHCP light to RHCP light. The tiny circular polarizer could be useful in applications like optical polarimetry, where it could be combined with a detector to make a single integrated device. What is maybe more important, the researchers believe the basic geometry of cascading patterned metallic sheets can provide the basis for cleverly designing and fabricating a broad range of optical devices, including symmetric circular polarizers, polarization rotators, and asymmetric linear polarizers. (C. Pfeiffer et al., Phys. Rev. Lett., in press.)


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