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Fiber Lasers Power Up

August 01, 2003

By: Neil Savage

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OE Magazine, August 2003

With the output power of fiber lasers growing all the time, manufacturers are hoping they'll be powerful enough to edge out the lasers already ensconced in industrial settings. "The results are going up almost on a monthly basis," says Bryce Samson, director of business development at Nufern (East Granby, CT), which sells specialty fibers to laser makers. Nufern was one of the companies that talked about the potential of fiber lasers at Photonics West in January, an event Samson predicts will come to be seen as the turning point in fiber lasers. "The industrial laser people sat up and took notice," says Samson.

At Photonics West, Southampton Photonics Inc. (SPI; Los Gatos, CA) reported a fiber laser with a single-mode, continuous wave output of 270 W at 1080 nm. By May, IPG Photonics (Oxford, MA) announced they had achieved 300 W of single-mode output at that wavelength. By June, Samson had heard of laboratory results as high as 700 W. He expects researchers will be able to output a kilowatt by the end of the year.

"I think all of us have been pretty amazed at how rapidly we have been able to make progress," says Don Spalinger, senior vice president at SPI.

Increasing Power
In fiber lasers, the optical fiber itself acts as the resonator cavity. The devices typically consist of a single-mode fiber core doped with erbium, ytterbium, or a combination thereof; other dopants such as thulium can be used, but the development effort is less advanced. Energy from a solid-state source is coupled into the fiber's cladding, from which it moves into the core and pumps the dopant. Output tends to be around 1080 or 1550 nm.

To increase output power, manufacturers enlarge the beam's mode field by increasing the size of the fiber core. "The limiting factor now is how to get the pump power in," says Samson. Laser makers, for instance, can apply various beam-shaping technologies to the output from the diode bars typically used for pump sources.

Although typically continuous wave, fiber lasers can provide pulsed output. Combining several fibers produces higher end power; IPG, for instance, has shipped a 6 kW fiber laser in which the beams from multiple diode lasers are delivered through separate fibers then combined to pump the fiber laser. The U.S. Defense Advanced Research Projects Agency is funding research that looks at ways to coherently combine the beams from multiple fibers.

The Battle Ahead
Fiber lasers could appeal to the military, Samson says, as makers study ways to combine the output of many fiber lasers to produce hundreds of kilowatts, which could be used to destroy missiles. The Airborne Laser program is funding such research, because the lightweight, compact nature of fiber is appealing for operation in aircraft.

With the higher outputs, and the advantages glass fiber has for thermal management and potentially more compact devices, makers of the lasers predict the systems can move from their current use in marking, based on 25- to 50-W devices, to other applications now dominated by carbon dioxide and neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers.

The automotive industry, for example, is very excited about fiber lasers for welding, says David Belforte, the editor of Industrial Laser Solutions magazine. Right now they use Nd:YAG lasers and, because of the need to save floor space in auto plants, deliver the beam through a fiber. "But if the fiber is the laser, isn't that much more attractive?" says Belforte.

In applications in which established lasers already offer reliability, eye safety, and superior beam quality, fiber laser manufacturers face more of a challenge. The question they now have to answer, says Belforte, is "What's wrong with the lasers that are out there now?"