'Our Research Is Primarily Focused on Developing Lasers as Carriers of Information'

© HSE University–St Petersburg

The International Laboratory of Quantum Optoelectronics at HSE University–St Petersburg develops semiconductor microlasers. The components and systems created by the laboratory also enable high-speed data transmission and processing. Natalia Kryzhanovskaya, Head of the Laboratory and Doctor of Sciences in Physics and Mathematics, spoke with the HSE News Service about the laboratory’s research areas and future prospects.

— What are the laboratory's main areas of focus?

— The laboratory was established in January 2020 as part of the HSE University–St Petersburg School of Physics, Mathematics, and Computer Science. Our key research priorities include studying the properties of innovative semiconductor materials used in optoelectronic devices, as well as systems and devices based on these materials.

Natalia Kryzhanovskaya

© HSE University–St Petersburg

— What does that involve?

— It involves studying the fundamental interactions between electromagnetic radiation (light) and various semiconductor structures and developing new optoelectronic devices. These include:

 coherent light sources—microlasers capable of generating monochromatic, highly directional radiation.

 photodetectors, which measure the intensity and energy of photons.

 radiation modulators, which alter parameters of radiation such as frequency and amplitude, and more.

The main focus of our laboratory is the study of direct band gap semiconductors. In our research, we actively use direct band gap semiconductors composed of elements from groups III–V of the Mendeleev periodic table, such as gallium, indium, aluminium, and others. These semiconductors are synthesised using advanced molecular beam epitaxy and metal-organic vapor-phase epitaxy techniques, which enable the fabrication of multilayer semiconductor structures with precisely controlled properties at the atomic level.

— Nanotechnology was once widely discussed, but what does it mean from a scientist’s perspective?

— In science, nanotechnology is regarded as an interdisciplinary field focused on the development and control of materials and devices at the atomic and molecular levels, with dimensions on the order of nanometres (1 nm ≈ 10⁻⁹ m). In our laboratory, this specifically involves designing complex, multilevel devices with atomic precision. The model of a future structure takes into account the distribution of components and the thickness of layers down to a single atomic layer. This approach enables precise control over material properties at the nanoscale and allows us to tailor the composition of each successive nanolayer.

Next, technologists synthesise the semiconductor heterostructure using advanced epitaxial techniques. Once the synthesis stage is successfully completed, the resulting heterostructure undergoes comprehensive analysis using optical methods and state-of-the-art equipment available in our laboratory. The spectral properties of the grown heterostructure are examined using steady-state photoluminescence spectroscopy and time-resolved photoluminescence spectroscopy, as well as measurements of light absorption and transmission spectra. These experiments help determine whether the structure exhibits the intended properties and whether its characteristics match the design specifications. In addition to developing technological methods for synthesising materials with tailored properties, this stage also addresses fundamental problems in semiconductor physics. For example, studies investigate the excitation and relaxation rates of charge carriers, their lifetimes, and changes in carrier concentration within the material. Understanding these aspects provides a foundation for the subsequent design and fabrication of optoelectronic devices, such as semiconductor lasers, that offer high efficiency and stable performance.

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— Assuming a semiconductor with the desired parameters has been created, what comes next?

— The next stage involves developing highly efficient miniature light-emitting devices that cover a broad spectral range, from ultraviolet (UV) to near-infrared (IR) radiation. To create lasers, special optical resonators are used, which can sustain stable resonant states—known as closed modes. The operation of any laser is based on amplifying light within an active medium using a resonator, which provides feedback and selects specific wavelengths that define the characteristics of the emitted radiation.

The compactness of the devices we create is achieved through the use of a special type of microresonator—resonators that support whispering gallery modes.

— What does this term mean?

— The term refers to a special type of resonant vibration in a laser resonator known as whispering gallery modes. The name comes from a physical phenomenon observed in St Paul’s Cathedral in London by the English scientist John William Strutt, also known as Lord Rayleigh. In this acoustic effect, sound waves travel along the inner surface of a circular structure—in this case, the whispering gallery of the cathedral dome—in a way that allows sound to be transmitted over long distances with minimal loss, so that even a whisper can be heard clearly on the opposite side of the gallery. Similarly, in the optical range, short electromagnetic waves travel along the walls of an annular or disk-shaped resonator, maintaining stable vibrations.

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— Why do we need such tiny lasers that are invisible to the human eye?

— Microlasers are versatile sources of coherent optical radiation with unique properties, making them highly valuable across many fields of science and technology. They are used for data transmission and processing, as well as for highly sensitive environmental detection. Compact microlaser-based sensors, for example, can be used to develop devices capable of detecting even the smallest changes in body biomechanics, such as joint bending.

However, our research is primarily focused on developing microlasers for information reception, transmission, and processing, as well as on integrating optical components with optoelectronic circuits.

A laser emitter must meet several strict requirements: it must achieve high efficiency in converting electrical energy into optical energy, maintain stable performance at elevated operating temperatures, exhibit low noise, and operate precisely within a specified spectral range according to the intended application.

Another important requirement is the laser’s speed—its rapid response time, which enables the transmission of large amounts of information with minimal delay. This is achieved through careful study of every stage of the technological process, from material synthesis to the design and testing of specific laser structures.

— Why does a laser need to be high-speed?

— High-speed lasers are essential for efficient transmission of large volumes of information—gigabytes and terabytes of data. They enable rapid data processing and transfer, ensuring consistently high communication speeds. The development of high-speed devices is a critical and in-demand task. Currently, this challenge is partly addressed through the use of specialised modulators that allow the intensity of laser radiation to be varied at high speeds. However, increasingly stringent requirements for stability and reliability will necessitate new solutions, including the creation of compact, highly efficient laser sources—an area in which our laboratory is actively engaged.

— So, the goal is to speed up information processing?

— Exactly. The primary objective of our laboratory is to develop lasers that can efficiently and rapidly process optical signals as information carriers. We aim to integrate these devices directly into photonic integrated circuits, ensuring high stability and reliability in signal processing. Our team specialises in developing innovative light sources compatible with modern integrated circuits. Unlike vertically emitting lasers, our technology delivers laser output directly on the circuit board, eliminating the need for mirrors or complex adapters. This enhances integration efficiency and reduces the risk of mechanical failure. This approach also paves the way for new technologies in high-speed optical information processing, such as the development of optical computers and sensors capable of detecting environmental changes by monitoring the properties of laser radiation.

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— What are the distinctive features of microlasers?

— Microlasers have a unique ability to alter their spectral output when interacting with biological molecules adsorbed on their surface. This property enables the creation of highly sensitive biosensors capable of detecting even minute concentrations of target substances, as the selective binding of molecules induces measurable changes in the characteristics of the emitted radiation. In addition, microlasers are highly sensitive to external conditions such as temperature, pressure, and the chemical composition of their surroundings. This property is particularly important for developing devices that detect low concentrations of biomolecules, as it ensures high measurement accuracy even at minimal signal levels.

— How do basic science and applied research come together in your work?

— Our approach combines theoretical analysis with experimental research, all aimed at developing innovative technologies. One of the main goals of our laboratory is to establish a world-class scientific school dedicated to studying semiconductor spectroscopy and developing highly efficient laser devices. One could say that in essence, our work aims to build a solid scientific foundation that enables the creation of next-generation devices that are both highly efficient and competitive.

— Is it possible to explain the goals of the laboratory to someone whose knowledge of physics is limited to a basic school course?

— The main goal of the laboratory is to develop miniature light sources and laser devices that can efficiently convert electrical energy into intense, directed optical radiation. We focus on creating reliable and durable light sources capable of operating even under extreme environmental conditions.

— Another fascinating topic seems to be encoding information using lasers.

— Encoding information with laser radiation is particularly interesting due to the unique properties of optical signals. Using laser beams opens new possibilities for information transmission by controlling parameters such as intensity, frequency (wavelength), and polarisation, among others. These properties allow for a far greater number of encoding methods compared to traditional approaches based on electrical signals. Another important advantage of optical signals is that intersecting light beams do not interfere with each other, ensuring the integrity of information when multiple data channels operate simultaneously. This property enables the creation of compact, efficient communication networks with higher channel density and greater data transmission bandwidth.

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— How is international scientific cooperation developing at present? How actively do you and your team participate in conferences abroad?

— International scientific cooperation is undergoing a certain period of transformation in the current context. Despite existing limitations, our laboratory continues to actively participate in international conferences and events held in Russia. Today, our laboratory's international collaborations are increasingly shifting to Asia, particularly China, where we engage in conferences, events, and joint projects with local research groups.

— How are the results of your laboratory’s work applied in the educational process?

— The achievements and scientific results of our laboratory are extensively integrated into the educational process. Our staff actively participate in teaching, incorporating the latest scientific knowledge into both core courses and specialised subjects. This allows students to engage directly with current trends in scientific development during lectures and practical seminars, stimulating their professional growth and enhancing the quality of their training.

— How actively do students, including doctoral students, participate in the laboratory's work?

— We always welcome students who wish to join us in conducting research. Students, including doctoral students, play a vital role in our laboratory, actively contributing to ongoing research projects and grants. Early-career researchers have a unique opportunity to immerse themselves in the academic environment, gain essential theoretical knowledge, and acquire valuable practical skills while working with state-of-the-art equipment. Although integrating early-career researchers into projects requires time and effort, this experience forms a crucial foundation for their professional development and future career growth.