Scientists from ITMO, Zhejiang University and the A.F.Ioffe Institute of Physics and Technology of the Russian Academy of Sciences have created a meta-surface that allows almost 100% accuracy in separating the directions of swirling polarized light waves. The artificial coating reflects the light swirled to the left and passes the light swirled to the right. The thickness of the structure is several hundred nanometers, so it can be used even in the most high—tech electronic devices. The development will speed up the process of conducting medical tests, simplify the task of detecting "spiral" molecules, according to the type of DNA, and also open up new opportunities for experimental physicists. The results of the study were published in the journal Laser & Photonics Reviews.
Light is electromagnetic waves. In other words, fluctuations in electric and magnetic fields, each of which has its own direction. How this direction changes is determined by polarization, a physical property that determines the orientation vector of the light wave in space. If we compare light with waves of water, then polarization in this case will be an indicator of the direction of change in its level.
There are two main "types" of polarization: linear and circular. With linear polarization, the direction of the electric field changes along the line. Such polarization is widely used, for example, in glasses for drivers or skiers. Circular polarization is characterized by the swirling of the electric field in a spiral — clockwise or counterclockwise. It plays a key role in the processes of interaction of light with other matter. For example, DNA molecules, sugar, and drugs such as levomycetin or ibuprofen. They also resemble a spiral in shape, so they actively interact with light of circular polarization. To recognize such molecules using light waves with circular polarization, metasurfaces are usually used, the elements of which repeat the "trajectory" of the swirling light.
Although such structures have existed for a long time, their creation remains a difficult technological task. However, ITMO physicists managed to find a solution to this problem. They have developed a nanostructure that separates right-handed and left-handed circular polarization with almost 100% accuracy. Another advantage of the development is the affordable manufacturing technology.
The design is based on silicon nanoparticles in the shape of ellipses located on a plate of glass. Each particle maintains resonances, that is, it can delay light. The location of the nanoparticles on the plate determines how they interact with light. The particles also enhance each other's resonant effect. Ideally, they form a perfect resonator in which the so-called bound states in the continuum arise. In this special state, particles can hold the energy of light inside the structure indefinitely.
"Nanoparticles support two types of resonances: electric and magnetic dipole. They correspond to fluctuations in the electric and magnetic fields of light. With proper placement of nanoparticles, we can make these resonances correlate with left- or right-handed circular polarization of light. However, using only one of the resonances does not allow achieving 100% selectivity with different polarizations. We were able to combine two types of resonances using reflection from the glass on which the nanoparticles are located. As a result, both types of resonances reinforce each other, and the structure becomes an ideal mirror for one circular polarization and ideally transparent for the second. In other words, one of the polarizations lingers on the metasurface, and the other is reflected from it," notes one of the developers of the project, Doctor of Physico—Mathematical Sciences, professor at the ITMO Faculty of Physics Mikhail Rybin.
The ability of the metasurface to retain light from one of the circular polarizations also makes it possible to accelerate the processes of its interaction with nearby "spiral-shaped" molecules. And changes in the intensity of light reflection in the nanostructure will signal the presence of these particles in the substance under study. Therefore, the design can become the most accurate detector for recognizing certain substances. For example, the same sugar molecules, DNA or levomycetin.
The development of scientists can be used to increase the speed of obtaining the results of chemical and biological analyses and improve the quality of telecommunications. It also opens up new possibilities for conducting experiments when working with swirling particles such as electrons.
The study was conducted within the framework of the RNF grant No. 24-72-10038.
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