Future belongs to 980-nm pumps
The market for pump-laser modules is by all accounts abysmally slow, but innovation continues nonetheless. The quality of the laser chips improves by 50% each year in terms of power at constant reliability, contends Toby Strite, marketing director of the Optical Pumps Business Unit at JDS Uniphase (San Jose, CA). "That's opening up new doors. We've gone from a world where 980-nm power was very dear and never quite enough to the point where there's an abundance of 980-nm power," he explains.
Pump lasers at 980- and 1480-nm are used to boost power levels in erbium-doped fiber amplifiers (EDFAs), while their 14xx counterparts are used in Raman amplifiers. The Raman market has stalled and the 980- and 1480-nm market doesn't look much better, prompting several big-name vendors, including Nortel Networks, Agere Systems, and ADC, to sell off or abandon their product lines.
According to Tom Hausken, director of optical communications components at Strategies Unlimited (Mountain View, CA), this thinning of the ranks is a positive turn of events. The market simply cannot support as many players as before, he says, adding that Bookham Technology, Furukawa, and JDS Uniphase are the front-runners in today's pump-laser market. "While there's always room for some smaller players," he concedes, "the battle is really among those three."
That said, none of these players can afford to abandon their research and development efforts, despite sluggish sales. "If these guys just sit back, they're going to have a medium-power laser while somebody else is going to come out with a high-power laser, and they're not going to get the contracts," says Hausken. "It's a nasty business, because right now there's no money coming in, but you still have to work on the next projects."
The trend for pump lasers is almost always toward higher power, asserts Jay Titus, president and CEO of PowerNetix (San Jose). Before the downturn, most of the applications for 980-nm lasers required about 100 mW per pump. Today, most applications specify 250-300 mW per pump, driven by the increased complexity of amplifier designs. More channels, for example, require higher pump powers.
Manufacturers are now beginning to develop 980-nm lasers that can produce 500 mW of light, which is "starting to creep into 1480-nm country," says Strite. "We see a pretty clear trend in upcoming designs where 1480-nm pumps are being designed-out in favor of 980-nm pumps."
"Instead of using two medium-power pumps in next-generation amplifier designs, the idea is why not use one?" continues Hausken. "Or maybe instead of four medium-power pumps, for example, why not use two? Or even one? It used to be that these pumps were 100 mW, so you can imagine that you needed a whole bunch of them. Now they have 500-mW pumps, so if you need a lot of power, you only need one or two of them now."
There's a strong economic argument for higher-power pumps—assuming that you can do it at all, adds Hausken. "They are pretty hard to make," he admits. "There's probably only going to be a couple of companies that can even do it, so that's why it's an exciting area."
The recent development of uncooled 980-nm pump lasers has enabled vendors to create higher-power amplifiers. The uncooled laser operates over a wide temperature range without a thermoelectric cooler (TEC), which is the "big power hog," says Strite. The cooler can consume as much as 80-90% of the total power in worst-case conditions. An uncooled laser consumes less power, dissipates less power, and can be housed in a smaller package.
The smaller size is the result of removing the cooler, which has been the bulkiest component in the traditional butterfly package. Last March, Alcatel Optronics, JDS Uniphase, and Nortel announced a multisource agreement establishing form, fit, function, and performance parameters for 980-nm pump lasers in what is known as a mini-DIL package. It has become the de facto standard, says Strite. "The mini-DIL will fit on your pinky finger, whereas the butterfly package would take up the top half of your thumb," he explains. The mini-DIL platform has about 10-20% less volume than the butterfly.
Traditionally, an EDFA might have a 980-nm pump and 1480-nm pump. "The next-generation EDFA," says Strite, "will probably have an uncooled pump in the front half that would consume about 3 W less than its cooled predecessor, and then we would go with a cooled, high-power 980-nm pump in the booster stage, on the backside, which would save you something like 4 or 5 W versus a high-end 1480-nm pump."
The 1480-nm pumps cannot be packaged in an uncooled platform, given their sensitivity at higher temperatures. Their efficiency and performance levels degrade significantly without the TEC.
The 980-nm uncooled pumps haven't quite made the grade yet, however. "The real operating-temperature range most customers would like is -40° to +85°C," says Titus. "Today, state-of-the-art for uncooled pumps is basically -5° to +75°C."
Even today's less-than-optimal higher-power lasers are being purchased for developmental projects, leading Hausken to wonder if the medium-power pumps will ever sell. "Is it a matter of too much inventory that needs to be worked off before they sell or are they just doomed? Will they just go to the junkyard?" he muses, then adds, "Very likely, they'll go to the junkyard."