Optical components

Photonic Integration Starts Slowly at 100G

Photonic integration is going to be a necessity for some designs, according to a recent Heavy Reading report, but that trend hasn't manifested itself in 100Gbit/s yet.

It's certainly needed at the client-side module level, but for the most part, systems makers probably won't have to make any grand photonic-integration moves until the 400Gbit/s generation.

"It's not like every company needs to do a large-scale, parallel-integration chip like Infinera Corp. (Nasdaq: INFN) just to succeed at 100Gbit/s," says Sterling Perrin, Heavy Reading's optical analyst.

There's some photonic integration involved in the Optical Internetworking Forum (OIF) definitions for systems, but it's low-level serial integration -- that is, the merging of neighboring functions.

Still, photonic integration is poised to become a necessary fact of optical design, according to the recent report, "Photonic Integration, Super Channels & the March to Terabit Networks." Perrin wrote the report along with Gazettabyte editor Roy Rubenstein.

It's a follow-up to Perrin's 2008 report on the topic, and Perrin admits he thought photonic integration -- the combining of multiple components and functions into a single device -- would be closer to ubiquity by now.

Coherent detection has been one factor. "The industry is using sophisticated electronic processing to enable 100Gbit/s transport using less sophisticated optics (specifically, optics built to handle 25Gbit/s data rates," Perrin and Rubenstein write in the report.

Photonics are also different from semiconductors. Chip integration tends to be a no-brainer, because it almost always brings benefits in size, power consumption and cost. But for optical components, a photonic integrated circuit (PIC) doesn't always bring those power savings. Even the cost savings of photonic integration are sometimes not that great, because of the R&D costs that have to come first.

None of this means photonic integration should be dismissed. For one thing, there's the size factor.

The CFP optical module, a client-side standard for 100Gbit/s, is due for a shrink, and the smaller CFP2 and CFP4 modules are almost certain to take advantage of photonic integration.

"They've got these form-factor requirements that are very strict. You really do need to combine a lot of components to reduce the size of what's fitting into the module," Perrin tells Light Reading. "For CFP4, everybody we've talked to says you need photonic integration."

Photonic integration will get its starring role in optical transport as systems strive for interface speeds of 400Gbit/s and 1Tbit/s. It's looking like those interfaces will be built of superchannels, multiple wavelengths of light that are combined to carry one traffic stream. A superchannel requires multiple lasers, so parallel integration becomes a pretty obvious way to go.

That's certainly been the case so far. Every 1Tbit/s demo has used superchannels, and the 400Gbit/s designs shown off earlier this year used two 200Gbit/s channels. (See Ciena Pushes Ahead to 400G, AlcaLu Can Do 400G Too and Huawei Strives for Optical Respect.)

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— Craig Matsumoto, Managing Editor, Light Reading

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