Design Presents Cheaper Alternative for 2-μm Fiber Lasers

A new fiber laser design eliminates a costly component that had been necessary to generate beams around 2 μm, a band useful for surgery, materials processing and atmospheric study.

Typical 2-μm lasers are based on an optical fiber ring containing a gain region, with an isolator forcing the light to circulate in a single direction. Now researchers at the Swiss Federal Institute of Technology in Lausanne (EPFL) have shown how to generate 2-μm beams without an isolator.

"We plug a kind of deviation that redirects the light heading in the wrong direction, putting it back on track," said professor Camille Brès.

Camille Brès and Svyatoslav Kharitonov developed a cost-effective way to generate 2-μm laser beams using thulium-doped optical fibers instead of isolators. Courtesy of Alban Kakulya/EPFL.

"We replaced the traffic cop with a detour," said doctoral assistant Svyatoslav Kharitonov.

Not only is the system less expensive, it also generates a higher-quality beam than traditional systems, the researchers said. It provides output power <1 W with a linewidth of 0.2 nm and a tuning range of 1900 to 2050 nm.

The researchers attributed their system's performance to its design, which incorporates thulium-doped fiber and a theta cavity, which is a ring resonator with S-shaped feedback.

"While the association of amplifying fibers and high power usually weakens traditional lasers' performance, it actually improves the quality of this laser, thanks to our specific architecture," Kharitonov said.

In recent years, 2-μm lasers have been of growing interest among researchers. In the areas of surgery and molecule detection, for example, they offer significant advantages over traditional, shorter-wavelength lasers.

Laser light around 2 μm is easily absorbed by water molecules, which are the main constituents of human tissue. In the realm of precision surgery, they can be used to target water molecules during an operation and make incisions in very small areas of tissue, simultaneously cauterizing the wound, and without penetrating deeply.

The wavelength range is also useful for gathering key meteorological data over long distances through the air, as well as for processing various industrial materials.

The research was published in Light: Science & Applications (doi: 10.1038/lsa.2015.113 [open access]).