Translation Please: Dense-Wave-Division What?


Amid the blur of announcements coinciding with last month'sWestern Show was a flurry of news about advancements in a terrific example of thetechno-gibberish name game: dense-wave-division multiplexing, or DWDM.

We all just have to accept the fact that lightwavetechnology almost always comes with a daunting moniker. History supports the premise: Afew years ago, it was 'erbium-doped fiber amplifiers,' because whoever named thetechnology thought that it was important to include the name of the rare earth ion thatworked to send light signals further.

Then, there was that pesky 'polarization modal dispersion'problem, which basically meant that the actual piece of fiber was a bit more oval than itwas round, which created problems.

This is my long way of saying: Fear not. Despite itsintimidating name, DWDM is not all that hard to grasp.

In short form (and, as always, with apologies to thepurists), DWDM is a way to send more signals much further over the same single strand offiber.

It's not a new concept, either. Long-distance carriers havebeen using WDM gear for years to send phone signals over their optical networks; two yearsago, BellSouth Corp. bought WDM equipment from Pirelli so that it could jam some 130,000simultaneous voice channels onto a strand of fiber and send it about 310 miles.

The more recent news is from Scientific-Atlanta Inc. andSynchronous Communications, both of which trotted out new DWDM gear last month.

From a technology standpoint, Synchronous' news was perhapsthe most startling, because it crams signals into 32 wavelengths (loose translation: 32different colors of light) that travel on the same, 1550-nanometer strand of fiber.

S-A's solution crams signals into eight wavelengths (oreight different colors of light), which can go a distance of about 100 milesona single piece of 1550-nm fiber.

At the moment, these DWDM moves mostly apply to theregional backbone, and they will be particularly useful in cases where operators are shorton fiber, but where they had the foresight a few years ago to put in at least one strandof 1550-nm fiber.

The vendors are saying that generally speaking, DWDM usagecan shave about 50 percent off the cost of the alternative, which is to install multiplefibers to carry signals.

But despite its clunky name (S-A's press materialsrecommend the use of yttrium/erbium-doped fiber amplifiers with its DWDM gear: Yikes!),this looks like one of those technologies that is finally coming down the cost curveenough to be of real benefit -- especially for headend elimination and regionalinterconnects.