Russian Physicists Determine Indices Enabling Prediction of Laser Behaviour
Russian scientists, including researchers at HSE University, examined the features of fibre laser generation and identified universal critical indices for calculating their characteristics and operating regimes. The study findings will help predict and optimise laser parameters for high-speed communication systems, spectroscopy, and other areas of optical technology. The paper has been published in Optics & Laser Technology.
Erbium fibre lasers are devices that generate light within a fibre doped with ions of the rare-earth element erbium. These lasers operate at a wavelength of approximately 1.5 micrometres, making them ideal for long-distance data transmission with minimal loss. Radiation at other wavelengths requires amplification every 20-30 kilometres when passing through optical fibre, whereas radiation from erbium lasers needs 2-3 times fewer amplifiers, significantly reducing equipment and operational costs. Moreover, erbium lasers can produce radiation with a narrow spectral linewidth (less than 1 kHz), which is used in high-precision optical sensors and transducers.
As demands for data transmission speed and capacity increase, there is a growing need to miniaturise lasers and shorten cavities without compromising their efficiency. A cavity is a component of a laser that consists of two mirrors and is responsible for amplifying light as it passes repeatedly through an active medium.
Depending on the cavity length and the concentration of erbium ions, the laser can operate in different regimes — either pulsed or continuous-wave (CW). The primary challenge is that reducing the size of the cavity requires an increase in the concentration of erbium ions. This causes the laser to operate in pulsed mode, which can result in data transmission instability, power limitations, and increased noise levels.
A group of Russian scientists, including physicists at HSE University, prepared two types of active fibres for seven lasers and compared the effects of erbium ion concentrations (ranging from 0.03% to 0.3%) on the laser parameters. As a result, they determined the parameters of the active medium and pump power that allow for a short cavity length and CW operation simultaneously, as well as the conditions under which the switching from CW to pulsed mode occurs.
'The transition from continuous-wave to pulsed operation regime is somewhat analogous to a classical phase transition, which follows mathematical laws and characterises processes in other systems, such as liquids and solids. Lasers with a high concentration of erbium ions exhibit two thresholds: the first is associated with the onset of pulsed mode operation, while the second marks the transition to continuous-wave mode. These laws resemble power-law dependencies and describe how the laser parameters change near the generation threshold,' explains Oleg Butov, co-author of the paper, Deputy Director and Head of the Laboratory of Fiber Optic Technologies at Kotelnikov Institute of Radioengineering and Electronics of RAS.
For the first time, researchers experimentally determined the critical indices for erbium lasers—specifically, the slopes of the logarithmic relationships between the frequency, duration, and amplitude of laser pulses and the laser radiation power.
'We have established that the calculated dependencies are universal for erbium lasers, regardless of significant variations in the core composition of the active fibre, cavity length, and Q-factor (a ratio of stored energy to energy consumed in one period). The results will enable predictions of the erbium fibre lasers radiation parameters and facilitate the optimisation of their operation for various applications,' according to Alexander Smirnov, co-author of the paper and Professor at the ‘Nanoelectronics and Photonics’ Joint Department with Kotelnikov Institute of Radioengineering and Electronics (RAS) of the HSE Faculty of Physics.
The study was supported by a grant from the Russian Science Foundation (No. 20-72-10057).
See also:
HSE Researchers Uncover Causes of Gender Pay Gap among Recent University Graduates in Russia
A study conducted at HSE University shows that despite having the same education and similar starting conditions, the pay gap between male and female recent graduates can be as high as 22%. This is partly because female students often choose less lucrative fields and also because they tend to seek jobs in sectors that offer lower pay but are perceived to have more stable and safer working conditions.
Scientists at HSE University Devise More Accurate Method for Predicting the Electrical Conductivity of Electrolyte Solutions
Researchers at HSE MIEM have developed a model for calculating the electrical conductivity of aqueous electrolyte solutions; for the first time, it considers the spatial distribution of ion charges instead of assuming their localisation at a single point. The model remains effective even at high electrolyte concentrations and across a wide temperature range. This breakthrough will contribute to the development of more efficient batteries and enable the calculation of electrical conductivity without the need for experimental testing. The study has been published in the Journal of Chemical Physics.
Russian Scientists Integrate Microdisk Laser and Waveguide on a Single Substrate
A group of Russian scientists led by Professor Natalia Kryzhanovskaya at HSE Campus in St Petersburg has been researching microdisk lasers with an active region based on arsenide quantum dots. For the first time, researchers have successfully developed a microdisk laser coupled with an optical waveguide and a photodetector on a single substrate. This design enables the implementation of a basic photonic circuit on the same substrate as the radiation source (microlaser). In the future, this will help speed up data transfer and reduce equipment weight without compromising quality. The study results have been published in Semiconductors.
Scientists Disprove Bunkbed Conjecture
Mathematicians from Russia, including two HSE graduates, have disproven a well-known mathematical conjecture that, despite lacking solid proof, had been considered valid for 40 years. The ‘Bunkbed Conjecture’ belongs to percolation theory—a branch of mathematics that studies the formation of connected structures in independent environments.
Men Behind the Wheel: Three Times More Violations and Accidents than Women
Men are three times more likely than women to commit traffic violations while driving and to be involved in accidents. Moreover, they are more likely to create situations on the road that are highly dangerous to others. Men are also twice as likely to drive under the influence and nearly one-third more likely to receive a prison sentence for reckless driving. Perhaps it comes down to cultural norms and the different attitudes men and women have toward driving. These are the conclusions reached by Anton Kazun, Assistant Professor at the HSE Faculty of Economic Sciences, and Research Assistant Mikhail Belov.
HSE Scientists Discover How to Predict Charitable Behaviour Through Physiological Reactions
Researchers at the HSE Institute for Cognitive Neuroscience have investigated how the emotional impact of advertising affects the amount people willing to donate to support animal welfare. To accomplish this, the researchers measured physiological responses such as heart rate, electrodermal activity, and facial expressions in individuals viewing various photos of dogs. The findings indicate that willingness to donate is most accurately predicted by heart rate and facial muscle activation. The study has been published in Social Psychology.
'We Are Creating the Medicine of the Future'
Dr Gerwin Schalk is a professor at Fudan University in Shanghai and a partner of the HSE Centre for Language and Brain within the framework of the strategic project 'Human Brain Resilience.' Dr Schalk is known as the creator of BCI2000, a non-commercial general-purpose brain-computer interface system. In this interview, he discusses modern neural interfaces, methods for post-stroke rehabilitation, a novel approach to neurosurgery, and shares his vision for the future of neurotechnology.
First Successful Attempt in 55 years: Physicists in Russia and Germany Confirm 1969 Experiment Results
A team of researchers, with the participation of physicists from HSE University, replicated the 1969 experiment on superconductivity and its properties. The scientists induced superconductivity by deliberately deteriorating the interfaces between the layers of superconductors and ferromagnets in the system, resulting in better performance of spin valves compared to the classical version, where the interfaces between the layers are ideal. This approach could lead to the development of more efficient devices for data storage and computing. The study findings have been published in the Beilstein Journal of Nanotechnology.
Healthy Nutrition Saves Public Funds: Strategies to Reduce Healthcare Costs in Russia
In Russia, the annual cost of treating type 2 diabetes alone exceeds 500 billion roubles. Promoting healthy nutrition programmes can ease the burden on the healthcare system and increase life expectancy. This was the conclusion reached by economists at HSE University after analysing global experiences with government involvement in promoting a healthy lifestyle.
Conscientious Individuals Live Longer
Personality traits such as conscientiousness, emotional stability, and an internal locus of control significantly influence one's lifestyle and longevity. Not only can personality traits influence health through beneficial and harmful habits but can also have a direct effect on mortality. Higher conscientiousness reduces the risk of premature death by 20 percentage points, while higher neuroticism increases it by 12 percentage points. These are the findings from a new study by Ksenia Rozhkova, Junior Research Fellow at the Laboratory for Labour Market Studies of the HSE Faculty of Economic Sciences.