New Nanoscale Structure can Provide Full and Unprecedented Control over Light Localization

A recent research work on three-dimensional topological insulators was recognized as one of the most promising developments in photonics in 2017 by Optics & Photonics News. These structures can control light with no losses due to material defects and absorption, making them a potential candidate for applications in communication networks, optical computers, lasers and antennas.

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Topological insulators are unique structures that conduct electric current along the surface alone but they remain insulating on the inside. An unusual protected state is created at the surface where electrons in the current remain unaffected by all external influences or material defects. Thus, the current runs through the material in a single direction without any reflection or loss.

Although electronic topological insulators have been studied by scientists for several decades, no such structures were developed for electromagnetic waves until 2015. Physicists from the ITMO University and the Australian National University were first able to create a nanoscale structure capable of providing full and exceptional control over light localization. The development on electromagnetic topological insulators holds potential for major technological developments in the near future.

The research started with a one-dimensional structure, which was essentially a chain of subwavelength-sized nanodisks. The topologically protected states existing at the edges of this structure enables the spatial distribution of the electromagnetic field to be controlled at the nanoscale, thus paving the way for transferring an optical signal without any reflection and defect-induced scattering in two-dimensions. Professor Alexander Khanikaev from the City University of New York proposed how it could be performed theoretically. Using his idea, a team headed by Alexey Slobozhanyuk, a PhD student of ITMO University and the Australian National University carried out an experiment.

Even though, the experimental structure was initially based on metallic metamaterials, it was only an initial success.

Although the signal propagated linearly avoiding reflection at acute angles, metals could not be used for optics due to strong absorption. Later we performed our first successful experiment with dielectric metamaterials. However, two-dimensional systems didn't provide a full control over light propagation in any direction. Now we know that this is possible even in three dimensions.

Alexey Slobozhanyuk, PhD Student, ITMO University

Further research established the existence of three-dimensional photonic topological insulators with a significant practical potential. This finding was reported in the Nature Photonics journal early this year. These three-dimensional photonic topological insulators may find use in stable optical communication lines wherein the signal is allowed to propagate linearly as well as in other ways, preventing reflection and energy loss.

Not only can this make Internet connection faster but also serve as a basis for high-power lasers and optical computers.

We've generalized the formalism of solid-state physics and now use it in electromagnetic systems. Using three-dimensional insulators based on dielectric metamaterials we can make light waves behave in ways previously considered impossible.

Professor Alexander Khanikaev, City University of New York

The international team is already conducting research work on three-dimensional insulators. Prof. Yuri Kivshar, who is working at the ITMO University and at the Australian National University being a world-renowned leader in nonlinear optics and metamaterials, supervises the study.

"It is much more difficult to conduct experiments with a three-dimensional structure, but Alexey Slobozhanyuk with his young colleagues is working hard on this," says Yuri Kivshar. "This is the second time research involving Alexey is recognized by Optics & Photonics News. Special December issues of this journal traditionally highlight about 30 of the best works published in the field of optics and photonics during the year, selected by a specially appointed editorial team. This year the editors stressed the importance of these results placing an image of a three-dimensional topological insulator on the magazine cover."

"Optics and Photonic News is a members' magazine of the Optical Society of America, and it is very prestigious among scientists,” adds Alexey Slobozhanyuk. “When your work is recognized in such a way, you know how important and useful your efforts are."

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