Set a photon: new optical chips will speed up the work of data centers

Russian scientists have proposed a way to create optical devices that retain their properties even in the presence of accidental defects. They have developed a metamaterial that can be used in optical computing and data transmission systems. For example, it can be used in chips where the light wave should propagate only in one direction, and communication lines in which defects should not weaken the signal. Today, photonic chips are used in large data centers, and the introduction of new technology can increase data processing speed and reduce power consumption. However, so far the development is only a step towards the creation of new devices, scientists told Izvestia.

Defect-insensitive material for microelectronics

Photonic chips can become more reliable and cheaper to manufacture thanks to the development of scientists at the New ITMO Physics and Technology Institute. They have created a metamaterial that works as a one-sided lens for microwaves and is practically insensitive to internal defects: the wave passes through it without scattering on irregularities.

In practice, such a metamaterial can be used in the production of photonic integrated circuits, a promising alternative to conventional microcircuits that are approaching the limit of miniaturization. In such circuits, photons are used instead of electrons, which allows for faster operation and lower power consumption. However, in the manufacture of devices, defects often occur that worsen their characteristics. The developed structure is a step towards solving this problem.

Photonic elements are already used in some data centers.: huge amounts of data pass through such equipment, which must be transmitted at high speed, experts explained to Izvestia.

Scientists Dmitry Vagin and Maxim Gorlach have developed a structure that not only reduces the impact of defects, but also focuses light in an unusual way. In conventional optics, the path of the light rays is reversible: the collecting lens focuses the light regardless of which side the stream is directed at it. This symmetry is broken in the new structure: it works as a collecting or scattering lens depending on the direction of light incident. This effect is achieved due to the magnetic field and the special symmetry of the lattice of the metamaterial.

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Domestic technologies will be linked to guaranteed demand and mass production.

The designed surface is designed to work with microwaves. They are easier to control than visible light due to their longer wavelength: in microwaves, it is centimeters, so the elements of the structures that control them can be relatively large — millimeters. To work with visible light, elements of hundreds of nanometers in size would be required — about 1 thousand. times thinner than a human hair. It is much more difficult to manufacture such parts.

A metamaterial is an artificial structure made up of many elements. Externally, the developed structure looks like an opaque dark plate, but microwave radiation passes freely through it.

— To control the wave in the calculations, we used yttrium garnet, a material that reacts to a magnetic field. The cylinders are made of it. When a wave hits them from one side, it passes through the structure with one delay, and when it hits them from the other side, it passes through the structure with another delay. If you change the magnetic field, for example by moving magnets closer or further away, the effect will increase or decrease. This is how you can change the focal length of a non—interchangeable lens, which focuses light only on one side and scatters it on the other," explained Dmitry Vagin, the first author of the article, a graduate student at the New ITMO Physics and Technology Institute.

Prospects of new photonic chips on the market

Using numerical calculations, the scientists tested how the material behaves when a wave falls from different directions. Calculations also showed that defects inside the structure have almost no effect on the passage of the wave. The signals, which were reflected randomly from deformed and shifted cylinders and wires, extinguished each other due to the magnetic field and the asymmetry of the structure.

— In recent years, scientists have worked hard to reduce the effect of defects on the optical properties of micro- and nanostructures. Our work demonstrates a new way to solve this problem. So far, we have proposed an implementation in the microwave range, but it is possible that it will be possible to transfer it to photonic chips," said Maxim Gorlach, head of the frontier laboratory, a leading researcher at the New ITMO Physics and Technology Institute.

The main value of the work is that the authors offer protection from defects in the entire volume of the material, explained Evgeny Vishnevsky, NTI expert on new materials and technologies, to Izvestia. Topological insulators, the main tool for this task today, protect the wave only at the boundary of the structure.

— In optics, the most anticipated application would be built-in insulators that protect the laser from the reflected signal. Today, this is one of the most difficult photonic chip elements to integrate. There is another interesting effect for data centers and domestic microelectronics in general. If the structure does not respond well to manufacturing errors, then the requirements for manufacturing accuracy can be mitigated. Then it will be possible to produce workable photonic microcircuits with a higher proportion of usable products and on less precision equipment," the specialist explained.

At the same time, in the near future, the technology may find application in microwave communication devices, antenna and radar systems, since the developed model is designed specifically to work with microwaves, said Ruslan Permyakov, Deputy director of the NTI Competence Center "Technologies of Trusted Interaction" based on TUSUR.

"This is still a prospect for photonic chips: researchers have performed numerical calculations, and transferring the technology to the optical range will require nanoscale elements and a new way to implement magnetic control," the specialist said.

The work was carried out with the support of the Priority 2030 program and the Russian Science Foundation. The results of the study are published in the journal Physical Review Letters.