Fiber Lasers Mark Their Territory

Compact, efficient, and air-cooled, they’re displacing Nd:YAGs in industrial applications, and they may make their way into telecom.

Lasers that use optical fiber for a resonator cavity are making inroads into industry, replacing bigger, bulkier devices. «It’s a very interesting technology and something that really could be a disruptive technology in the laser business,» says Robert Steele, director of optoelectronic services at Strategies Unlimited (Mountain View, CA).

In a typical fiber laser, a single-mode fiber core is doped with erbium or erbium-ytterbium. An array of laser diodes, often fiber- pigtailed, pumps the core, which re-emits the desired wavelength. Many of the fiber lasers being developed for industrial use are based on double-clad pumping, in which the energy is pumped into an inner cladding layer (surrounded by its own cladding) and transferred into the core.

The advantage of such a setup, says Paul Rivett, CEO of Resonance Photonics (Markham, Ontario, Canada), is that it can put more power into the fiber. Resonance Photonics does not make the fiber lasers themselves but rather a power concentrator designed to increase the lasers’ energy output. «We have customers talking to us about 100 W of original pump power,» he says, which he estimates would translate to about 50 W of output power.

Most of the fiber lasers on the market today have outputs that range from 1 W to 25 W; higher outputs should be possible. The main area of application is in materials processing, specifically marking. About 60% of the industrial fiber lasers produced by the non-telecom end of JDS Uniphase (San Jose, CA) are for marking, says Ruediger Hack, product-line manager for fiber lasers.

From printing to soldering

Double-clad fiber lasers were originally developed by Polaroid Corp. (Cambridge, MA) in 1992 for use in the company’s printers, Hack says. SDL purchased the technology from Polaroid in 1998, and JDS Uniphase inherited the technology when it bought SDL.

Hack says the fiber lasers are becoming popular for such applications as flexographic printing, in which the laser etches away a layer on print media. In comparison to diode lasers, which can only generate about 0.5 W, the fiber laser can go up to 25 W. Higher power means higher throughput—and bigger profits. For marking, the fiber laser is much more compact than the neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers currently used in that application. It also does not require the complex optics of the YAG, and it is air-cooled. «When we talk about materials processing, the reason people go to the fiber laser is because of the compactness, low energy consumption, and ease of integration,» Hack says. Steele adds that the lasers are highly efficient in terms of light conversion and power consumption.

Fiber lasers also show promise for such processes as microsoldering, microwelding, and microbending, which are in increasing demand as the number of portable electronics devices such as cell phones and disk drives grows. One downside, Hack says, is that fiber lasers cannot be Q-switched, locking them out of applications such as engraving metal and plastic. They can be mode locked, however.

Openings in telecom

Potential for fiber lasers also exists in the telecom market. Spectra-Physics Lasers (Mountain View, CA), for instance, makes a fiber laser with 5 W of output for accelerated life testing of the components in optical communications systems. The laser has the advantage that its output can be coupled directly from its SMF-28 fiber core into the component; whereas light from the titanium-doped sapphire lasers typically used for such testing has to be injected into the fiber, with the associated complexities.

Fiber lasers are also being developed as pump sources for Raman amplifiers for boosting telecom signals. So far, says Bill Holtkamp, Spectra-Physics director of sales for active telecom products, that application hasn’t been very successful because the gain profile of such devices isn’t flat enough for telecom uses. Spectra-Physics and Lucent Technologies (Murray Hill, NJ) are working on fiber lasers with three wavelengths, which may solve that problem.

(By Nell Savage, OEMagazine, 2001, August)

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