Big all-optical switches are coming back

Despite the failure of a wave of all-optical switches near the turn of the century, a new market for large all-optical switches is opening up this year, according to one trusted source.

By the end of the year, at least three vendors will likely introduce an all-optical composite-fiber switch with a port count of 128 by 128 or higher, said Glenn Wellbrock, director of backbone and network technologies for Verizon Business. “Our objective is to do a trial this year, and we hope to deploy in mid-2009 (assuming the switches work as advertised, of course).”

Verizon plans to use these switches to further automate its network and to aid in asset management, remote testing and overall efficiency. They coincide with the company’s current efforts to automate the management of fiber patch-panel interconnections in central offices.

Among the methods Verizon is evaluating for automating patch panels is a free-space optics approach that uses tiny mirrors to redirect light paths. But such an approach is limited in scale, Wellbrock said. “You’re never going to build a very large switch out of free-space devices.”

However, Verizon may be able to scale the approach by building all-optical versions of the three-stage Clos switch fabrics that the carrier has been building with electronic switches for years. Tying together three edge switches with a centralized switch fabric increases loss and cost, Wellbrock said, but it allows enough scale to work with the imminent large all-optical switches mentioned above.

“Ten thousand by ten thousand [ports] could easily be achieved in a Clos-type fabric,” he said. “That’s probably the method we’ll use to scale these. I say probably because maybe someone out there has an idea on how to do it in single stage.”

Large all-optical switches were hyped and famously self-destructed amid the telecom bubble. But they’ve slowly begun to resurface in industry conversations lately, as network traffic volumes explode and all-optical equipment such as reconfigurable optical add/drop multiplexers (ROADMs) grow more prevalent in carrier networks, driving more wavelengths to manage. During a panel discussion at last year’s NXTcomm trade show, Emanuel Nachum, vice president of Americas marketing for equipment vendor ECI Telecom, predicted the need for a new breed of all-optical crossconnects to manage the growing number of multi-degree ROADMs in carrier networks. As carriers deploy ROADMs with double-digit degrees, Nachum said, “At some point it will make sense to have a different type of network element, call it a next-gen optical crossconnect. We’re not there yet; these devices are still expensive. I know several companies tried to develop them back in 2000. They probably had bad timing back then.”

That unfortunate past could make it harder for vendors to rekindle interest in all-optical switches. For that and other reasons, this new breed of gear won’t threaten electronic optical switches anytime soon, said Shin Umeda, vice president at research firm Dell’Oro.

“All-optical switches should not have a substantial affect on the OEO switch market for the near term,” Umeda said. “The applications and network architectures are different, so I don't see all-optical as a like-for-like replacement of OEO. In particular, OEO switches can do sub-wavelength grooming, something not possible on all-optical.”

In addition, he added, “All-optical switches are unproven, both from a technology and a large-scale deployment standpoint.”