Wave-Bending Cloaks Conquer Corners & Bumps

Optical cloaks that can bend electromagnetic waves could pave the way for the development of next generation photonic and plasmonic devices.

AsianScientist (Jun. 15, 2015) – Researchers have shown how to build cloaks capable of controlling the paths of surface electromagnetic waves over a wide range of wavelengths, preserving their properties while bending them sharply around obstacles.

The research, led by Dr. Zhang Baile from Nanyang Technological University in collaboration with Zhejiang University and the Massachusetts Institute of Technology, was published in the Proceedings of the National Academy of Sciences.

Over the past few decades, substantial efforts have been devoted to develop photonic circuits, which could potentially power optical chips and computers, in order to replace the traditional electronic circuits.

Since a photonic circuit would manipulate pulses of electromagnetic waves instead of electrons, it could potentially be lighter and faster than an equivalent electronic circuit while using less energy and emitting less waste heat. However, any photonic circuit will have to overcome a seemingly simple challenge: corners.

“Although a 90-degree sharp bend is routine in electronic circuits, it’s still fundamentally difficult to bend optical surface waves, as their energy would be scattered in the process,” explains Zhang. “However, in our study we demonstrated, using a few newly designed ‘cloaks’ that can effectively hide the corner, that this is not only possible, but also can be extremely broadband.”

“Our main technique is known as transformation optics, which uses metamaterials to effectively warp the optical space in much the same way that gravity curves space in general relativity. As they pass by the metamaterials, the surface waves thus will be cheated into propagating as if they were still traveling along a flat surface, even when they are actually crossing a sharp corner.”

The researchers demonstrated this by building two separate cloaking devices, using a metamaterial made from alternating layers of ceramic and polymer foam. The first was a ‘corner cloak’, which allowed surface waves to bend around a sharp corner without scattering, while the second was a ‘carpet cloak’ and allowed surface waves to travel over a bump without scattering. In either case, the waves could not propagate past the obstacle when the cloak was absent and lost all their energy to scattering.

However, with each cloak in place, the waves traveled past with nearly no energy loss. These devices also worked over a wide range of microwave frequencies, from the lowest frequency of almost zero to the highest frequency of 6 GHz. Furthermore, the waves also had their phases preserved, as well as their amplitude, making it seem as if the obstacle had not appeared in their path at all.

“This is the first demonstration of surface wave guidance around very sharp obstacles in a wide band of frequencies,” Zhang commented, “which opens the way for a range of possible applications.”

“For example, it could allow for the next generation of photonic and plasmonic devices to be designed more flexibly, probably even in a multi-layer structure without any worries about bends or sharp corners in the design of circuitry. Also, these cloaks could contribute to the development of super resonators which can pick out and amplify certain frequencies with very precise selectivity.”

As such, these new cloaks add further promise to the already-exciting field of photonics.

The article can be found at: Xu et al. (2015) Broadband Surface-Wave Transformation Cloak.


Copyright: Asian Scientist Magazine; Photo: Zhang Baile/Nanyang Technological University.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Shern Ren is studying towards a PhD degree in physics at the National University of Singapore. When he isn't working on the statistical mechanics of nanomachines and single-molecule systems, you may find him scratching his head over politics, education and the mathematics of Threes.

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