A topological insulator is a material with non-trivial topological order that behaves as an insulator in its interior but whose surface is current-conducting. The thin conducting surface topologically protects electrons from external disturbances and material`s imperfections due to impurities and defects.

ITMO University researchers developed a similar material, which protects electromagnetic waves instead of electrons. The researchers suggested that the wave has to affect a zigzag-shaped particles` array. Due to resonance effect particles become resonant; electric fields around them are perpendicular to each other. Thanks to their interaction waves center around edges of the structure. Changes of wave polarization give an opportunity to manage spatial distribution of the field i.e. “activate” edges by turns or simultaneously.

“The modern technological trend is to downsize new devices. The smaller structures are developed the more attention one should pay to quality of their edges. Optical calculations are said to be cutting-edge technology. To use them in the future we should provide the high-grade communication,” noted Alexander Poddubniy, one of the authors of the article, researcher at Chair of Nanophotonics and Metamaterials. “For example, we have a chip equipped with two sources of electromagnetic waves. If a distance between them is shorter than a wave length they will disturb each other. So one cannot develop smaller and smaller structures. The technology of topologically protected states can solve this problem.”

Previously the scientists presented a theoretical research of this field. The paper was published in 2014 by ACS Photonics and was put on the cover of the February issue. Then they proved it in practice by providing microwave and optical experiments.

The paper contains the pioneering results. Russian researchers were the first who analyzed subwave edge states that were smaller than a light wave length. The researchers used a way of scanning near field optical microscopy. According to Anton Samusev, researcher of Chair of Nanophotonics and Metamaterials, it caused the difficulty with visible light experiment. The size of resonance particles is 250 nanometers; so it was very difficult to take measurements without affecting electromagnetic properties of the structure.

“Carrying out the experiment with microwaves we had no problems with measurements because it didn`t affect the experiment; analyzing probe was smaller than the structure. However while researching nano objects we faced the following challenge: a needle probe had the same size as the structure. We managed to register the effect, which verified topologically protected states,” said Ivan Sinev, researcher of Chair of Nanophotonics and Metamaterials.

According to Alexander Slobozhanyuk, the scientists decided to offer Optics & Photonics News to publish the article in August 2015. Finally it was considered as one of the best papers of 2015.

“Optics & Photonics News ranked our research among the top-20 articles of 2015. This recognition is very important for us because the last year was titled as the International Year of Light and Light-based Technologies,” said Mr. Slobozhanyuk.

The development made by Russian researchers can be practically implemented in optical chips, network lines and quantum computers.