Photonics Handbook
Vexlum to Develop a Yellow Guide Star Laser for the European Space Agency
TAMPERE, Finland, Dec. 3, 2025 — Vexlum, a semiconductor laser manufacturer, has entered into a contract with the European Space Agency that aims to establish a framework for more telescopes around the world to use vertical external-cavity surface-emitting laser (VECSEL) technology in high-bandwidth optical communications. Per the contract, the Finland-based company will develop a high-power VECSEL, operating in the yellow wavelengths of the visible spectrum, that will make it possible for telescopes to communicate large datasets in real time.
Broadly, the initiative will develop high-power VECSEL-based optical sources for use with ground-based adaptive optics systems for optical communications between the Earth and orbiting satellites
At present, the benefits of adaptive optical correction are only seen by large telescopes with the space and budget to operate current systems that enable corrections to focusing issues caused by atmospheric air currents. The yet-to-be-developed compact system will use yellow VECSELs to make it possible for a larger number of telescopes to communicate large datasets, such as hyperspectral images, in near real-time.
Vexlum’s technology helps solve the common challenges of space-to-ground optical links, including turbulent air currents, by eliminating the need for the massive, costly yellow lasers used in extremely large telescopes.
“[The project] is opening up this capability to more telescopes and smaller telescopes that aren't just very large scientific observatories,” said Philip Makotyn, physicist and president of Vexlum US. In addition to miniaturization, the use of VECSELs also promises reductions in cost.
VECSELs can be manufactured to any wavelength between 350 nm – 2.1 µm, which allows them to be customized for this specific application. The optically-pumped VECSELs allow the laser power to be scaled up easily by increasing the pump spot size, which helps to produce a bright enough guide star in the upper atmosphere. The VECSEL architecture also features single-mode output, low-frequency noise, and excellent beam quality for precise excitation of sodium.
“VECSELs are an ideal technology that provides the most flexible platform for special applications at nearly any spectral color that benefits from a smaller, cost-effective format than existing solutions,” said Jussi-Pekka Penttinen, CEO and co-founder of Vexlum. “Delivering a compact high-power yellow laser tuned to the sodium line is exactly what VECSEL excels at. We’re excited to provide this capability to more telescopes to correct atmospheric aberrations, leading to clearer observation of celestial objects.”
The project will produce two yellow wavelengths: 589.157 nm and a 589.179 nm sideband, an offset of 1.7 GHz, to excite the sodium D2 line. Exciting sodium in the atmosphere creates a "guide star" which can be imaged to correct for atmospheric turbulence and improve imaging precision.
The project technology will enable high-speed data such as hyperspectral imaging for monitoring wildfires, floods, and ecosystems, as well as more space situational awareness precise tracking of satellites and space debris to enable trajectory corrections and collision avoidance. The first step of the work, according to Vexlum, will be to develop and prototype a laser system that can generate an artificial guide star in the atmosphere. This will allow telescopes to measure and correct atmospheric distortions, ensuring that high-speed laser links remain stable and efficient, regardless of atmospheric conditions or time of day.
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