Infinera: in it for the ultra-long haul

At NXTcomm next week, Infinera plans to launch ILS2 — an optical system that will scale to 8 Tbit/s of capacity on a single fibre, and extend to 2,500 km without the need for signal regeneration, potentially setting new records for capacity and scalability.

ILS2 consists of a new set of modules that are compatible with the vendor's original DTN digital ROADM (reconfigurable optical add-drop multiplexer) chassis and network management software. The new units include 160-channel wavelength multiplexing modules, as well as Raman and EDFA optical amplifier modules.

Infinera is also introducing an "optical express" capability that allows traffic to stay all-optical as it passes through a node on the network.

These developments seem to indicate that Infinera's well-defined digital view of the world has gone a bit fuzzy around the edges. The company started out with the ambition to build networks that didn't require dispersion compensation or optical amplification — and now it's putting some of these functions back into the network.

Will this re-introduce some of the complicated optical functions that Infinera went to such lengths to eliminate? The honest answer is yes, says the company's director of marketing Geoff Bennett.

The more important message, however, is about flexibility. "You've heard the phrase 'To a man with a hammer every problem is a nail.' I'm sure in the past plenty of people felt Infinera was like that — we were preaching virtues of the digital optical network," says Bennett. "The new features give us the ability to be flexible to a customer's needs, but not to have to be religious about being digital."

Some of the new customer applications that the ILS2 system will address include submarine festoon networks, "hut-skipping" (increasing the distance between amplifiers to eliminate alternate amplifier huts), ultra-long haul, and collector/express lanes for long-distance traffic across regional networks.

The optical express capability, for instance, allows customers to stay all-optical if that's what they want to do. Bennett believes that Infinera's existing customers will probably say they won't use it because they like the digital nature of the network, but new customers, like the tier one accounts that the vendor wants to break into, are a completely different story.

"When we devised the PICs [photonic integrated circuits], they made OEO [optical-electronic-optical] conversions more cost-effective — more cost effective, but not free," he says. "Many of our customers look at the price of an all-optical ROADM and they see that its cheaper. We're only talking 10-15%, but the kind of customer accounts we're trying to get into [the tier ones] are driven by the procurement departments."

Adding some all-optical features to Infinera's digital ROADM system could lower the initial capital outlay required for a carrier to deploy Infinera gear, helping to build a more compelling case for that carrier to bump an incumbent supplier from its network.

Cranking up capacity
The ILS2 modules will also allow Infinera to achieve a breakthrough level of capacity on a single fibre — although the headline figure of 8 Tbit/s will only be achieved by fully-populating the system with 100 Gbit/s wavelengths, which aren't likely to be available for a couple of years.

"What's key is that we're actually doubling the channel count in the C-band," says Bennett. "Other companies have talked about 160 channels systems in the past, but typically those systems would have been C- plus L-band systems. This is a pure C-band system."

Infinera doubled the number of channels by squeezing them closer together. The plan is that 10 and 40 Gbit/s will operate with 25 GHz channel spacings, while the vendor expects to move to 50 GHz spacings when it introduces 100 Gbit/s wavelengths.

Long-haul systems from competing vendors, such as Alcatel-Lucent's 1625 LambdXtreme transport system or Huawei's SuperWDM ULH system, deploy 50 GHz channel spacing for 10 Gbit/s wavelengths.

Bennett says there are several reasons why network equipment manufacturers have been reluctant to adopt 25 GHz channel spacings. For starters, high-precision filters cost more. Infinera overcomes this problem with integration — eliminating expensive fibre couplings offsets the higher cost of the narrow filters.

Next is the practical issue of dealing with 160 transponder cards, which need linking to the wavelength multiplexer cards with fibre patch cables. "Everyone else is using transponder cards. All you need to do is step back from the rack those systems live in, and you see spaghetti everywhere," Bennett explains.

Infinera cuts this problem down by a factor of 10 because its active PIC replaces 10 transponder cards. "We don't have this explosion of transponder boards or fibre couplings because everything is done internally either across our chip or across our backplane. We're not afraid of large numbers of wavelengths."

The third reason is that ROADM-based systems, whether they are 2D MEMS or wavelength-selective switch (WSS) type, are typically built with channelized gain-flattening devices that prevent cross channel interference. Optical components vendors aren't seeing significant demand for 25 GHz components — for the two reasons we've just described — and so these components haven't become available.

Infinera sidesteps this issue because it manufactures both the components and the system. What's more, the company's passive PICs do continuous rather than channelized gain flattening, which means that both 25 and 50 GHz spaced channels can run over the same hardware.

The ILS2 system will be generally available this summer.