Pioneering tunable laser startup Coretek may have been closed down after its acquisition by Nortel Networks Corp. (NYSE/Toronto: NT), but that doesn't mean other vendors have given up on the idea of developing tunable Vertical Cavity Surface Emitting Lasers (VCSELs) (see Coretek Is Closed).

Indeed, a new startup -- BeamExpress Inc. -- has recently sprung up in Europe. It is featured in a new report on tunable lasers, published today on Light Reading: Tunable Lasers Revisited.

BeamExpress was founded in late July 2001 by Professor Eli Kapon at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland (see Swiss Launch Light Emitter Startup). In October last year, it revealed its intention to manufacture tunable lasers and fixed-wavelength laser arrays (see BeamExpress Intros VCSEL, CEO).

It takes on established startup Bandwidth9 Inc., which appears to be the only vendor offering a tunable VCSEL for sale today.

Both companies want to capture the market for metro transmitters. "There isn't much choice in the metro," says BeamExpress's CEO Jean-Claude Charlier. "You either use long-haul technology, which is expensive, or you use inexpensive plastic enterprise transceivers, which don't do the job properly." Tunable VCSELs could find the middle ground, offering a combination of medium cost and solid performance.

The technological challenges faced by these two startups are not to be sniffed at. Making a VCSEL that operates in the DWDM band around 1550 nm is not trivial, because indium-phosphide -- a material that generates light at 1550 nm -- is difficult to design with (see Laser Blazers). Adding tunability presents an extra challenge.

The two companies have contrasting approaches to the same goal. Bandwidth9 uses a technique called "pseudomorphic growth," which is a way of depositing one material on top of a dissimilar material in a single epitaxial process (see Bandwidth9 Claims Laser Breakthrough). It uses this technique to combine an indium phosphide gain (light-producing) region, with a gallium-arsenide-based Bragg mirror.

BeamExpress, on the other hand, uses wafer bonding, which is a high-temperature way of fusing two materials together. The materials are first produced in separate processes.

Not everyone believes that the wafer bonding approach is a viable technique for mass production. According to Markus Ortsiefer, CTO of German VCSEL startup VertiLas GmbH, says it's difficult to bond whole wafers uniformly, so the technique is generally only used for small pieces of semiconductor. "Wafer-bonding has no future," he says. "It's too complicated, trust me." VertiLas has an alternative method of making 1550 nm VCSELs, but only plans to make fixed-wavelength, not tunable devices.

But BeamExpress stands by its technology. "We have a partnership with a company developing wafer bonding kit, so we can produce very high-quality fused interfaces," claims the startup's CEO Jean-Claude Charlier.

The resulting laser has an output power in the region of 1 mW, typical for a VCSEL but insufficient for metro and long-haul applications. To overcome this drawback, BeamExpress plans to pump the laser optically, using a second laser. In this respect, its technology resembles that of Coretek, which also used optical pumping.

However, BeamExpress says that its laser will be better than Coretek's in a couple of ways. Coretek boosted the output power of its laser by integrating an amplifier into its package, in addition to using optical pumping, whereas BeamExpress claims to achieve high output powers without an amplifier. "The amplifier is the most expensive part by far, and we don't need one of those," says Charlier.

Bandwidth9, on the other hand, chooses to boost the transmission distance of its laser by integrating a modulator from CyOptics Inc. (see Bandwidth9 Picks CyOptics Modulator). This kind of amplifier delivers some gain and has what's called "negative chirp," which increases the resistance of the signal to dispersion, allowing it to go farther with lower power.

The other area in which BeamExpress claims an advantage is in the design of the MEMS (micro-electro-mechanical system) cantilever and mirror, which are used to tune the device. "We have achieved a record low control voltage of just 4 volts," Charlier boasts. Coretek and Bandwidth9 need much higher control voltages than this, he contends -- up to 40 V.

Bandwidth9 acknowledges that the tuning voltage is 40 V. But, says the company's VP of marketing Jake Weise, this is with almost no current. Additionally, he notes that the latest product, MetroFlex G2, takes +/- 5 V user-supplied inputs and generates 40 V internally. (It was difficult to verify Coretek's tuning voltage, since the company no longer exists.)

Of course, it should be pointed out that Bandwidth9 has been around a lot longer than BeamExpress and has notched up design wins with some top tier customers, such as Nortel (see Bandwidth9 Scores a Coup). It is now on its third-generation product and has had time to get further with reliability testing -- a process that cannot be speeded up. BeamExpress will have its work cut out to compete successfully.

— Pauline Rigby, Senior Editor, Light Reading