New Focus, New Laser
Devices like these appear to have a multibillion-dollar future. They promise to be a vital ingredient in next-generation networks, being reconfigurable on the fly to provide wavelengths wherever and whenever they’re needed. And ultimately, if they become cheap enough, they could replace standard transmitters, simplifying spare parts and inventory lists.
New Focus is already known as a vendor of tunable lasers for test and measurement applications. These use a design called an external cavity laser (ECL), which contains a tiny laser chip that sends light round a closed loop made of mirrors and gratings. The laser is tuned by mechanically moving a mirror.
New Focus's telecom laser is an ECL, it says. This means it has taken a radically different approach from most other tunable laser makers, who either use MEMS (micro-electro-mechanical systems) or souped-up DBR (distributed Bragg reflector) designs for tuning (see Tune In!). It's the external cavity design that makes it possible to achieve such high powers -- about five times what any other vendor is offering so far (see Agility Launches First Product for example).
The main gripe about ECLs is that they are big -- typically the size of a shoe box -- but New Focus has overcome this. In fact, it's taken the ECL and modified it out of all recognition. The telecom-grade tunable laser -- called PowerTune -- sits in a module measuring 55x100x12.5 millimeters. That space includes a built-in wavelength locker, power control, and control electronics, unlike other vendors' tunable devices, which often require extra chips around them, according to Paul Smith, VP of the telecom division at New Focus.
"We had to do a lot of things to make sure this was a telecom-class product," he says. "The cavity configuration is radically different from anything we've ever done before."
The resulting device still contains a moving part, but this won't be a problem, says Smith. "The technology is almost identical to what's in a [mechanical] VOA [variable optical attenuator]." That's a proven technology, he adds.
"In any case, we went to our potential customers and asked them what their comfort level was with [mechanical parts]. And they came back and said, as long as it passes the [Telcordia] standard, they don't care what's inside." So far, the tunable laser is on track to meet Telcordia 468. Smith sees no problem in getting tests finished before the end of 2001, the time at which it should start shipping to customers.
Startup Iolon Inc. is also known to be making an ECL-based tunable laser, but it's pursuing a more tricky design, Smith reckons. "Based on the slides they show, it looks like Iolon is using the cavity configuration that we use in our test and measurement lasers. We abandoned that for telecom lasers ages ago."
He adds that the reason New Focus abandoned the design was because it was continuously tunable, which is hard to do reliably at high powers. PowerTune snaps to any wavelength on the ITU grid and has filters to stabilize it there, he says.
Iolon has yet to announce details of its tunable laser but confirms that it is continuously tunable. "We have technology that allows that to be done in a reliable and stable way," says Hal Jerman, Iolon's founder and director of micromachining technology.
Iolon points out that its continuously tunable laser can be tuned to a finer granularity than New Focus's PowerTune - an issue that's likely to become increasingly important as channel spacings in DWDM systems are reduced.
— Pauline Rigby, senior editor, Light Reading http://www.lightreading.com