Engineers have developed a conformal metasurface coating that can simultaneously control diverse optical properties of dielectric waveguides, including mode confinement, polarization, scattering signature and crosstalk. The two-layer coating can shrink the diameter of waveguides, enabling more flexible control of waveguide characteristics.

Existing methods for controlling waveguides using 3D structures can provide efficient paths for obtaining highly confined modes, optical activity, or a low-scattering signature; but typically these efficiencies come at the expense of increased propagation loss.

A conformal, metasurface-enabled approach developed by a Pennsylvania State University research team has demonstrated simultaneous manipulation of the mode confinement, polarization and scattering signature of a dielectric waveguide, while avoiding the increased volume, weight and loss associated with 3D-based approaches.

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Rod shaped waveguide with two quasi-2D conformal coatings that shield the waveguide from crosstalk and blocking and allow the waveguide to be smaller. Courtesy of Werner Lab, Penn State.

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Researchers developed and tested two quasi-2D conformal coatings — one for guiding the signal and one for cloaking the waveguide. The coatings were applied to a rod-shaped, Teflon waveguide, with the inner, guiding layer touching the Teflon and the cloaking layer on the outside.

The inner and outer layers together were found to enable a highly confined sub-wavelength dielectric waveguide, with a low-visibility and broadband optical activity.

Researchers further demonstrated that the effectiveness of the artificial coating could be well maintained for waveguide bends by properly matching the dispersion properties of the metasurface unit cells. Although the coating can be applied to a bend in the waveguide, the waveguide cannot be bent after the coating has been applied.

The novel flexible coating could enable simultaneous control over the propagation, polarization and scattering of electromagnetic waves. By allowing the waveguides to be smaller and alleviating crosstalk, use of the coating could lead to increased miniaturization. 

It is possible that the concept and associated design strategy could be applied to the development of waveguiding components and other novel electromagnetic devices with multiple functionalities at terahertz frequencies and possibly even in the IR regime.

“In terms of applications these would include millimeter-wave/terahertz/infrared systems for sensing, communications, and imaging that need to manipulate polarization, squeeze signals through waveguides with a smaller cross-section, and/or require dense deployment of interconnected components,” said professor Zhi Hao Jiang.

The research was published in Nature Communications (doi:10.1038/s41467-017-00391-0).

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