The world’s first single-frequency radiation-balanced fiber amplifier is unveiled

Recent advancements in laser technology have spurred the demand for high-power, superior beam quality, and ultra-low noise. However, conventional cooling methods fall short of meeting these requirements, as they introduce bulky, cost-ineffective, and vibration-prone solutions. Countering these issues, anti-Stokes fluorescence (ASF) has proven its effectiveness for decades, but it was only in 2020 that it was demonstrated for the first time in standard silica Yb-doped fibers.

Back in 2020 Prof. Digonnet’s research group at Stanford University demonstrated the first self-cooling in Yb-doped optical fiber hosted in silica. This innovation allowed lasers to operate without external cooling systems by preventing heat generation. This breakthrough opened possibilities for more stable, high-quality lasers radiation and today the second generation of radiation-balanced (athermal) fiber lasers and fiber amplifiers are real possibilities.

In a recent publication the world’s first single-frequency radiation-balanced fiber amplifier is unveiled. In the research Dr. Enkeleda Balliu, currently Senior Laser Engineer and Product Manager at HÜBNER Photonics, has joined forces with fellow researchers from Stanford University, Clemson University, University of Illinois, and Universite’ Laval (Canada) to elevate the output power of a fiber laser to hundreds of mW and demonstrate the world’s first single-frequency radiation-balanced fiber amplifier.

These devices utilize a single-mode silica fiber heavily doped with Yb³⁺ and co-doped with Al to enhance cooling efficiency. With optimized parameters, the continuous-wave fiber laser achieves an impressive 192 mW output power, marking a significant improvement over previous fiber lasers.

The significance of the breakthrough

This breakthrough is noteworthy due to the utilization of a small-core Yb-doped silica fiber, which presents cooling challenges. By leveraging anti-Stokes fluorescence and advancements in material fabrication, substantial gain and energy extraction have been achieved while maintaining high efficiency and stability. When asked about the impact of these finding Dr. Balliu said:

The rapid progress in this domain underscores the pivotal role of interdisciplinary collaborations. What lies ahead? We aspire to a trajectory marked by groundbreaking advancements in materials for optical fibers, culminating in the realization of Watts-level anti-Stokes cooled fiber lasers and fiber amplifiers. This heralds a future characterized by quieter lasers and enhanced performance capabilities.

The development of these radiation-balanced fiber lasers and amplifiers represents a major advancement in zero-net heat laser technology. With their enhanced performance and efficiency, they hold promise for applications requiring stable, high-power laser systems in quantum technologies and beyond.

This work was partially funded by Vinnova. The Clemson authors acknowledge the J. E. Sirrine Foundation for financial support. The authors from Université Laval acknowledge the Natural Sciences and Engineering Research Council of Canada. We at Cobolt, a part of Hubner Photonics, are delighted to have been part of this collaboration.