Multiplex, Vitesse Transponding
Yesterday, both companies announced new 10-Gbit/s transponders conforming to the 300-pin SFF multisource agreement (MSA). Even with the rise of new MSAs such as Xenpak, the 300-pin MSA still rules the market, prompting components makers to find ways to cut costs or expand the possible uses of the modules.
Note that none of this is directly related to Vitesse's pending acquisition of 10-gig specialist Multilink (see Vitesse to Buy Multilink). Multiplex is approaching the question from the optics side, replacing the usual 1550nm laser with a 1310nm version (see Multiplex Goes 40km With 1310nm). The resulting module, targeted at 40km distances, costs about the same as its 1550nm counterpart but should be easier to use for some OEMs, says David Chen, director of transponder product management.
"On the client side, the enterprise side, people like to use 1310nm because most fiber between buildings was optimized on 1310nm," Chen says. "The other reason is there's very little dispersion penalty on the fibers," meaning there's less of a loss penalty with 1310nm and less need to provide an extra margin of output power.
Transmissions of 40 km normally call for a 1550nm lasers, which exhibit lower loss than 1310nm varieties. Multiplex got around this with home-grown products on both the transmitter and receiver sides. For transmission, Multiplex replaced the typical Distributed Feedback (DFB) Lasers with its 1310nm electro-absorption modulated laser (EML), because EMLs provide a cleaner signal "eye," allowing them to transmit across longer distances. (They're very proud of that EML -- see Multiplex Touts Novel Laser.)
On the receiver side, Multiplex officials say they've developed an avalanche photodiode (APD) with high enough sensitivity to interpret the signal cleanly. The company considers this to be another of its specialties.
Vitesse, by contrast, continues using 1550nm lasers for long distances but is hammering away at the electronics side of the transponder, hoping to lower costs (see Vitesse Goes Cheap With 10-Gig). The VIT 5020, 5040, and 5080 transponders cover 20-, 40- and 80-km distances, respectively (clever, eh?).
The key to the new modules is the VSC8473, an electronic transceiver chip that consumes about 1W of power. The compactness of that chip gives Vitesse more room for more electronics, which can be used for fancy signal conditioning, says John Stewart, director of product marketing.
In other words, Vitesse gets to add features such as adaptive equalization, which helps map the signal eye to the proper levels so the zeroes and ones can be read properly. With tricks like that, electronics can compensate for less than optimal optics -- meaning you can get away with cheaper optics.
"The object is to make the 10-gig so [economically] attractive that everybody drops the 2.5-Gbit/s and goes straight to 10-gig," Stewart says.
Vitesse plans to add a couple more transponders to the line next month -- one for distances less than 2 km, and a 10km part for 10-Gigabit Ethernet.
Vitesse's transponders range in price from $2,000 to $5,000. All three are sampling now, with volume production due in August.
— Craig Matsumoto, Senior Editor, Light Reading