07 Jul Fiberoptics for 2 µm kilowatt lasers
Laser systems operating at wavelengths around 2 µm offer a wide range of opportunities in medical technology, agriculture, and plastics processing. One laser source for this wavelength range is the thulium-doped fiber laser. Until now, however, commercially available laser sources combining high beam quality, sufficient output power, and the reliability required for quasi-continuous-wave (QCW) operation at power levels of around 1 kW have been unavailable.
In a recent project, researchers at the Laser Zentrum Hannover (LZH) developed novel fiber-optic components based on triple-clad fibers that are designed to enable a reliable, low-maintenance laser architecture. According to LZH, the institute collaborated with Futonics Laser as well as the South Korean partners Coset and the Korean Photonics Technology Institute to develop the final laser system.
Cladding-Coupled Pumping
The LZH researchers used a CO₂ laser-based processing technique to selectively remove small sections of the outer glass cladding of the triple-clad fibers, providing lateral access to the pump cladding. This approach allows pump fibers to be fused laterally onto the inner pump-light cladding, enabling efficient delivery of the pump energy required for the laser process. In addition, the team developed cladding mode strippers by structuring the triple-clad fibers with a CO₂ laser, allowing unabsorbed pump light to be efficiently removed from the fiber system.
Pump‑light coupler for operation at a 2 µm wavelength. Image: LZH
The signal-pump combiners developed in the project achieved an average coupling efficiency of 90.1 ± 2.5 % at input powers of up to 475 W, with the available pump power representing the limiting factor, according to the researchers. This corresponds to the state of the art for combiners based on conventional fibers. For triple-clad fibers, however, the researchers describe this as a significant advancement. The low optical losses also indicate that the components could operate reliably at substantially higher power levels, potentially enabling the targeted 1-kW performance class.
Funding
The project ‘Development of high-power QCW 2 µm fiber lasers for medical and agricultural applications (Decomp)’ was funded through the Eurostars program under grant numbers E!234 and 01QE2206B.
Source and image: www.lzh.de
Caption: Pump fibers can be fused onto triple-clad fibers to increase coupling efficiency.