ST. PETERSBURG, Russia, Sept. 8, 2025 — Device miniaturization, an established trend in smartphones and cameras, now includes technologies for integrating microlasers into chips, miniature sensors, and quantum platforms. However, shrinking a laser while preserving its optical properties, efficiency, and reliability is a challenge requiring complex calculations and precise fabrication techniques.

This challenge was met by researchers at HSE University-St. Petersburg (the National Research University Higher School of Economics), who discovered a way to create effective microlasers with diameters as small as a red blood cell. The team's disk-shaped microlasers operate at room temperature, without requirements for cooling, and can be integrated into microchips to provide an on-chip light source. They could potentially be used to make photonic, optoelectronic, and quantum devices smaller, cheaper, and better integrated, the developing researchers said.

The microlasers are built using a crystal structure composed of indium, gallium, nitrogen, and aluminum compounds (InGaN/GaN/AlGaN) grown on a silicon substrate. InGaN/GaN quantum well lasers are typically grown on expensive GaN substrates or on sapphire/silicon carbide (SiC). The silicon substrates provide a cost-effective platform for the microlasers, in addition to providing high crystalline quality and size benefits.

The more compact the laser, the harder it is to trap the light so that it can be reflected and amplified continually without losing energy, which is essential for stable operation. To trap light in such a tiny laser, the team implemented the whispering gallery effect, which enabled light to be repeatedly reflected inside the disk-shaped microlaser, minimizing energy loss. However, despite the use of whispering gallery mode, it was still possible for light waves to partially escape into the silicon substrate and become lost.

To prevent light leakage into the substrate and reduce mechanical stress, the researchers added a stepped buffer layer to the microlaser design. This buffer layer compensates for mechanical stresses between the silicon and nitride layers and decreases radiation leakage, enabling the laser to operate in a stable manner, even at micron sizes.

Disk and ring resonators, which support high-quality whispering gallery modes, enable compact lasers with low lasing thresholds and diameters of just a few microns. These microlasers can efficiently couple light into waveguides, which is useful for integrating optical devices. The buffer in the microdisk laser acts as the bottom cladding of the waveguide and ensures good field localization in the active region.

The researchers demonstrated laser light generation at room temperature in microlasers with diameters of 5-8?µm, operating under pulsed optical pumping in whispering gallery modes. They observed a wavelength shift from 406 nm to 425?nm, which they attributed to a reduction in optical losses as the laser diameter increased within the gain bandwidth of the InGaN/GaN quantum well active region.

The microlasers could potentially be embedded into microchips to provide compact, efficient, on-chip light sources. Their small size and stable operation could make them suitable light sources for quantum technology platforms for sensing and communications. The microlasers could also be used in miniaturized sensors.

“Our microlasers operate stably at room temperature without the need for cooling systems, making them convenient for real-world applications,” professor Natalia Kryzhanovskaya said. “In the future, such devices will enable the creation of more compact and energy-efficient optoelectronic technologies.”

The research was published in Letters to the Journal of Technical Physics (https://journals.ioffe.ru/articles/60487).

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