Unlocking laser emission exceeding 2.1 µm with an only thulium-doped fiber laser

A new scientific milestone was recently reached by researchers at French-German Research Institute of Saint-Louis (ISL) with the demonstration of laser emission beyond 2.1 µm using only a thulium (Tm)-doped fiber—without co-doping or complex architectures. This breakthrough, enabled by Exail’s advanced fiber technology, marks a key step for the development of high-power continuous-wave (CW) lasers in the 2 µm spectral range, with major implications for defense, medical, and sensing applications.

In the field of high-power fiber lasers, Tm-doped fibers are gaining strong interest for their ability to generate emission in the 2 µm wavelength range—a spectral window that offers unique advantages for applications in defense, medicine, and environmental sensing. Fiber lasers in this range benefit from eye-safety, efficient atmospheric transmission, and compatibility with nonlinear frequency conversion schemes, making them a valuable tool for next-generation photonic systems.

Microscope image of the thulium-doped fiber developed by Exail.

However, pushing laser emission beyond 2.1 µm using solely Tm-doped fibers has remained a major challenge for the scientific community. Until now, reaching this spectral boundary typically required complex co-doping schemes or alternative gain media, often at the cost of reduced efficiency or increased system complexity.

In a recent publication*, researchers at French-German Research Institute of Saint-Louis demonstrated a high power continuous-wave laser operation beyond 2.1 µm using only a Tm-doped fiber, marking a significant breakthrough laser development. The experimental setup, built around a linear cavity incorporating Exail's highly engineered Tm-doped fiber, successfully achieved laser emission at 2.12 µm with more than 130 W. These results open the door to simpler and more efficient laser architectures for applications requiring longer wavelengths such as optical parametric oscillators (OPOs) direct pumping.

"We are proud to see Exail's thulium-doped fiber technology enabling this breakthrough." comments Mohamed Omar Sahni, active fiber product manager at Exail. "With a portfolio that also includes Ho-doped and Tm/Ho co-doped fibers, we offer tailored solutions across the 2 µm range."

In collaboration with partners like ISL and ONERA, Exail remains at the forefront of high-power laser innovation.

* C. Louot and al, Emission Wavelength Limits of a Continuous-Wave Thulium-Doped Fiber Laser Source Operating at 1.94 µm, 2.09 µm or 2.12 µm, Photonics 2024, 11(3), 246; https://doi.org/10.3390/photonics1103024