Laser Diodes Look for Long Life

Paula M. Powell

How long is long enough for a laser diode to last? The answer essentially depends on the application. According to engineers at Newport Inc. in Irvine, Calif., telecom applications in the metro space will often work fine with lower-cost, lower-life laser diodes. Submarine applications, however, are a different matter altogether.

Available lifetime is a key factor in the project’s cost equation. JDS Uniphase, for example, has traditionally offered products rated for more than 100,000 hours, but Toby Strite, business development manager for the company’s active components business unit in Hagendorn, Switzerland, reported that many applications are content with 10,000 hours or less. He noted that it is relatively straightforward to re-rate lasers — such as AlInGaAs broad-area pump lasers. “Trading off higher output power for lower MTBF [mean time between failures] allows us to serve more price-sensitive markets, such as medical and graphics/imaging, at a lower dollar-per-watt price point.”

Laser diodes are gaining prominence in manufacturing, both as pump lasers and in direct application. This roof welding application at Volkswagen uses a fiber-fed solid-state laser.

Not all laser diode technology can reach even the 10,000-hour mark yet. Consider ongoing research sponsored by the US Department of Defense — specifically the Defense Advanced Research Project Agency — into semiconductor-based UV light sources for both biosensor and nonline-of-sight communications applications. Lt. Col. John Carrano, program manager for semiconductor UV optical sources, said that deep-UV sources, specifically those in the wavelength range of 280 nm or less, offer unique opportunities here. In the biosensor field, for example, tryptophan, a common constituent of biological organisms, has a peak absorbance at this wavelength. In communications applications, a wavelength of 280 nm or less translates to operation in the solar-blind region where “terrestrial solar flux is essentially nil,” he added.

Carrano reported that, although the defense agency’s UV source program has already reached some critical milestones, one important problem still to be resolved is device lifetime. The project benchmark is reliable UV optical sources at 10,000 hours or more.

The following articles discuss several key developments in the area of lifetime test of laser diodes and LEDs. Topics range from enhanced lifetimes for specific categories of devices to the need for international testing standards. For more on Carrano’s project, visit www.darpa.mil/mto/suvos.