Qusion Touts Wideband Modulator
Modulators are key components that control lasers by turning the optical signals on and off to transmit digital data. "Wideband" indicates that the device operates over a large 40 nanometer wavelength range, enough to cover the entire C band. This makes the modulator "a perfect fit" with widely tunable lasers, says Qusion's CEO Philip Wallace.
According to Wallace, the product represents a significant improvement over existing electro-absorption modulators (EAMs), which only work over a limited wavelength range, typically 5 to 15nm. He claims that a range of 40nm is an industry first.
But competitor Agility disputes the claim.
"The thing about that is, we've got one too," said James Regan, Agility Communications Inc.'s managing director for Europe, upon hearing Qusion's claim. Agility developed a widely tunable EAM some time ago, which it has integrated on-chip with its tunable laser (see Agility Packs Three Into One).
Regan concedes that Qusion may indeed be first with a standalone EAM with wideband properties. But, to put it rather bluntly, he can't see the point of a standalone product. In his view, most of the advantages of an EAM result from integrating it with other components.
A second factor is polarization sensitivity. If both laser and modulator are on chip, it simplifies things -- the polarization state is known, so it can be accounted for in the design.
If, on the other hand, the signal has to pass through an ordinary fiber pigtail between laser and modulator, the polarization becomes scrambled because of stress-induced birefringence (caused by bends, vibrations, and so on). The result is high polarization-dependent loss (PDL) at the modulator output.
Some of these drawbacks can be mitigated by adopting a slightly different approach -- co-packaging. This means the laser and modulator are still separate items but are placed inside the same package, along with microlenses to couple light from one to the other. Since there is no fiber pigtail, the PDL problem goes away. Although it is expensive to align the elements inside the package, it's still cheaper than packaging separately.
Qusion declined to provide a technical expert to comment on the details of its approach or whether this might get around the potential drawbacks pointed out by Agility.
Marconi PLC (Nasdaq/London: MONI) and Nortel Networks Corp. (NYSE/Toronto: NT) both make co-packaged laser products. The fact that Qusion plans to sell its modulator in die form suggests that it's planning to partner with other vendors and do a spot of co-packaging. The startup says samples will be available from February 2002.
But in this application, too, Qusion will still have to convince other vendors that indium phosphide EAMs are a better prospect than lithium niobate, and that's not going to be straighforward. While EAMs do have certain advantages in size and low-voltage operation, they still have some catching up to in terms of performance (see CyOptics Claims Modulator Milestone).
Qusion says it's not planning to integrate its modulator with a laser anytime soon. "This isn't our entrée into the tunable lasers; it's not even our next step," says Wallace. "We expect that in a few years, we will have products with lasers in."
— Pauline Rigby, Senior Editor, Light Reading