Deep inside Laser Zentrum Hannover's laboratory in Germany, researchers have just cracked a problem that has stalled the medical and manufacturing worlds for years: how to build reliable, powerful lasers that operate at the 2-micrometer wavelength. Their breakthrough comes at exactly the moment when surgeons need scalpels that cut with infrared precision, farmers need tools that work in light conditions where conventional lasers fail, and plastics manufacturers need heat sources they can control with unprecedented finesse.
For decades, thulium-doped fiber lasers—the workhorses of the 2-micrometer range—have promised much but delivered inconsistently. These lasers excel where ordinary light sources struggle, but the commercially available versions have always forced an impossible choice: pick two of three. You could have high beam quality. You could have sufficient power. Or you could have reliability in quasi-continuous operation at around 1 kilowatt. Never all three. The missing piece, it turned out, was buried in the fiber itself.
The LZH team, working with partners Futonics Laser GmbH and South Korean firms COSET, inc. and the Korean Photonics Technology Institute, turned to an unconventional material: triple-clad fibers. These specialty fibers contain multiple layers of glass cladding, each serving a different optical purpose. But making them work required inventing an entirely new way to connect components together. The researchers developed a patented CO₂ laser-based processing technology that surgically removes small sections of the outermost glass cladding, creating lateral access points. This lets them splice pump diode fibers directly to the inner pump light cladding—delivering the energy that makes the laser fire without the losses that plagued previous designs.
The numbers tell the story. At input powers up to 475 watts, the signal-pump couplers achieved an average coupling efficiency of 90.1 percent—the same efficiency as couplers made from conventional fibers, a benchmark the industry has chased for years. For triple-clad fibers, this represents a significant new development. What makes it more remarkable is what the researchers left on the table: they still had headroom. The available pump power was the limiting factor in their tests, not the design itself. This suggests the components can operate reliably at significantly higher powers, potentially reaching the targeted 1-kilowatt class.
The team also engineered cladding mode strippers—components that remove unabsorbed pump light from the fiber system using the same CO₂ laser structuring technique. These achieved an outcoupling efficiency of more than 20 decibels, handling derived optical power of 250 watts. Together, these innovations make triple-clad fiber designs practical for the first time, opening pathways not just to higher power but to higher integration, better beam quality, and systems that can scale to meet the most demanding applications.
The implications ripple outward from Hannover. Surgeons will soon have more precise tools for delicate procedures. Agricultural laser systems will work in conditions that currently force shutdowns. Plastic manufacturers will gain new capabilities for welding, cutting, and marking. What began as a materials problem becomes, through careful engineering and unconventional thinking, a gateway to new possibilities across three entirely different industries.