NUST MISIS scientists, together with colleagues from MIET, Moscow State University of Economics, NPC Technological Center, HSE and the Russian Quantum Center, have identified the most promising materials for manufacturing photonic chips that are controlled by light directly on a microcircuit and can be used to create photonic memory, fully optical neuromorphic networks and other devices for transmitting and processing information.
The scope of application of photonic chips is extensive. They can be used in optical processors to accelerate matrix multiplications, which underlie the learning and operation of neural networks; rapid diagnosis of diseases using spectral analysis of light; data transmission at ultra-high speeds through fiber; in compact solid-state lidars for scanning the space around unmanned vehicles; generation and distribution of quantum keys in secure quantum communication systems; high-precision optical sensors for industry, ecology and agriculture.
"To control light on a chip, we investigated special phase-shifting materials that can change their state under the influence of short laser pulses. In different states, the material has either an ordered (crystalline) or disordered (amorphous) structure with a very different refractive index. After exposure to a laser, the sample retains a certain state and can be used to store information," said Grigory Goltsman, one of the authors of the study, chief researcher at the NTI Quantum Communications Competence Center at NUST MISIS, Doctor of Physico—Mathematical Sciences.
The scientists compared five compounds based on various semiconductor compounds of germanium, antimony and tellurium and selected the most promising ones. All materials were applied to identical silicon nitride waveguides, through which light propagates inside the chip. This made it possible to compare the properties of materials without changing the design of the device itself. It was important to understand how much the material changes the passage of light, and how quickly this change occurs. The best combination of contrast and switching speed showed the compositions Ge₁Sb₂Te₄ and Ge₁Sb₄Te₇. According to the researchers, they may replace the widely used GE₂sb₂te₅ today.
"The result may change when using waveguides made of other materials, such as silicon on an insulator, or laser pulses with different wave parameters, so additional tuning is required for each material. The results show that the composition of the material directly affects how well it is suitable for controlling light on a chip. At the same time, it is impossible to select a material based on only one indicator — it is important to take into account at the same time the magnitude of the signal change, the switching speed, and the cell size of the material on the silicon nitride waveguide," said Alexey Prokhodtsov, research engineer at the Laboratory of Photonic gas sensors at NUST MISIS.
According to the researchers, the results obtained can become the basis for further development of photonic devices with non—volatile memory - that is, those that preserve the recorded state without constant power supply.
"In the future, such technologies can be used in photonic computing and devices capable of storing and processing information using light. For the practical application of the selected materials, it is still necessary to check their durability, stability of operation and preservation of the recorded state," added Alexey Nevzorov, Candidate of Physico—Mathematical Sciences, researcher at the Center for Quantum Communications of NTI NUST MISIS.
The research was carried out within the framework of a grant from the Russian Science Foundation and with the financial support of the Ministry of Education and Science of the Russian Federation under the program "Priority 2030" of the national project "Youth and Children".
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