12 Jan. Easily tunable IR laser without moving parts
Ateam of researchers from the Vienna University of Technology (TU Wien) and Harvard University has developed a new semiconductor laser that generates infrared radiation with a variable wavelength. It has no moving parts, can be integrated onto a chip, and is suitable for a broad spectral range. Infrared laser radiation is indispensable for science and technology – for example, for medical spectroscopy in tissue analysis, for industrial detection of gases in pipelines, as well as for testing procedures in safety engineering. Tunable infrared lasers also play a central role in optical communication.
Three ring lasers from a single array cover an optical bandwidth of more than 1 THz; each ring is tuned based on its bias current. Image: Optica Publishing Group
Ring architecture supports precise emission
The new concept uses ring-shaped semiconductor resonators. Each ring is of a defined size and therefore possesses a specific resonance frequency. Electrical control can be used to determine which ring is active and which wavelength will be emitted. The researchers combine several such rings to achieve greater spectral coverage. If several resonators are controlled simultaneously, the output power is amplified while the emission remains limited to a specific line.
Professor Benedikt Schwarz, head of the Optoelectronic Devices research group at TU Wien, explains: “Tunable lasers, i.e., lasers whose light wavelength can be changed and controlled, have become indispensable in many technologies, from high-speed telecommunications through medical diagnostics to safety checks on gas pipelines.” Continuing, he explains: “However, laser technology usually requires compromises: if you want a laser that can be tuned to many different wavelengths across a broad spectrum, the precision of the respective wavelengths is lower. Lasers that can be precisely tuned to many colors have required moving parts until now, which has made them complex and expensive.”
The special design of the new beam source solves a well-known problem with tunable lasers: previously, a compromise between spectral precision and flexibility was necessary. Systems with mechanical tuning elements achieved high accuracy but were complex and susceptible to failure. Other designs covered a wider range but lost stability.
Single ring laser element consisting of four straight sections of length d, connected by four quarter circles of radius r (here: d=50 µm, r=260 bis 220 µm). Image: Optica Publishing Group
Robust operation in harsh environments
Another advantage is its stability against optical coupling. In conventional lasers, reflected light can destabilize the source. The ring-shaped structure reduces this risk and allows for reliable operation even under difficult environmental conditions.
Co-author Theodore Letsou, a doctoral student at the Massachusetts Institute of Technology and a member of Professor Federico Capasso’s laboratory at the Harvard John A. Paulson School of Engineering and Applied Sciences, explains: “By adjusting the ring size, we can effectively target any desired line and any desired laser frequency.” Capasso adds: “The versatility of this new platform means that similar lasers can be manufactured at various commercially relevant wavelengths, for example for telecommunications applications, medical diagnostics, or any laser that emits in the visible light spectrum.”
Simple manufacturing scheme requires very little space
The beam source was manufactured in the clean rooms of the Center for Micro- and Nanostructures at TU Wien. Johannes Fuchsberger, a doctoral student at TU Wien, emphasizes: “The beauty of our laser is its simple manufacturing process. We have no mechanically moving parts and a simple manufacturing scheme that requires very little space.”
The collaboration between TU Wien and Harvard University has already produced several developments in semiconductor laser research. The current project shows how the combination of European and US research is creating new solutions for photonic applications.
Original publication
[J. Fuchsberger et al.: Continuously
and widely tunable semiconductor
ring lasers, Optica 12, 7, 985 (2025),
DOI 10.1364/OPTICA.559884]
Source: www.tuwien.at
Image: Joshua Mornhinweg (jmornhinweg.com)