ROADMs Get Ready to Go Off-Grid
Next-Generation ROADM News Analysis Craig Matsumoto, Editor-in-Chief, Light Reading 9/8/2010
A technology name that's concise and even kind of catchy. We're stunned.
The idea behind Flexgrid is to let carriers define wavelengths that don't fit the ITU grid. This might come in handy for reconfigurable optical add-drop multiplexers (ROADMs) as 400-Gbit/s or 1-Tbit/s transmission starts to emerge.
Equipment vendors say carriers want to hedge against the possibility that these future technologies might generate wavelengths that don't fit comfortably in ITU grid boundaries. These wavelengths might need to occupy a wider amount of spectrum, or they might need to be separated by unusually thick guard bands of unused spectrum. (See OFC/NFOEC: For ROADMs, Less Is More.)
The most vocal proponent is Verizon Communications Inc. (NYSE: VZ), which has added the feature to its future ROADM checklist, in addition to wanting the subsystems to be colorless, directionless, and contentionless. (See Verizon: Give Us More Flexible ROADMs for 100G.)
Flexgrid is a byproduct of Finisar's WSS being software-programmable, able to flip between 50GHz and 100GHz spacing on command. With Flexgrid, Finisar is now saying it can vary the channel bandwidth in increments of 12.5GHz. (See Finisar Flexes WSS Muscle.)
The "12.5" figure is arbitrary, according to Craig Cameron, a Finisar product line manager. In an email to Light Reading, he notes that Finisar has taken the same technology (liquid crystal on silicon) to 1GHz granularity, available in a line of optical processors called WaveShaper.
CoAdna Photonics Inc. , Nistica , and Oclaro Inc. (Nasdaq: OCLR) are similarly claiming gridless capabilities for their WSSs, at the requests of carriers.
It's not certain that the feature will become necessary, though. In fact, vendors aren't sure of all the network implications of gridlessness.
"When we ask our customers how they're going to use it, no one can give us an answer," says Jack Jian Xiu, CoAdna's vice president of sales and marketing. "The reasonable answer is that it's a future-proof feature. No one knows how to provide the actual architectures behind this requirement."
For example, management systems would have to adapt to these nonstandard wavelengths, accounting for WSSs that are carrying standard-grid wavelengths alongside them. New transponders would be necessary, too, although they'd obviously be available if 400-Gbit/s or 1-Tbit/s wavelengths do need to be so exotic.
— Craig Matsumoto, West Coast Editor, Light Reading