AT&T says it managed to send 400Gbit/s signals across 12,000 km on a 100GHz-spaced grid. The company's own previous record, using a 50GHz grid, was more like 3,000 km, using a 50GHz grid.

The release doesn't give full details, because they'd like you to attend the paper presentation at 3 p.m. Tuesday, March 19, in Anaheim, Calif. But it does mention that the 400Gbit/s signals were built from subcarriers and that AT&T's technique involves tuning the modulation to match the available spectrum and/or to trade off spectral efficiency for reach.

Tunable modulation has been a persistent theme as the 100Gbit/s generation has matured. It's probably going to be commonplace in 400Gbit/s deployments.

AT&T's was one of three research papers that OFC/NFOEC personnel highlighted in a preview release issued Tuesday morning. The others were an IBM Corp. breakthrough in sending "massive amounts of data" at low power, and a splicing technique from AFL Telecommunications that could make multicore fiber more practical to use.

Why this matters
Starting around mid-2010, 1Tbit/s optical transmission was getting a lot of attention. But the industry has taken the smaller and probably more pragmatic step of making 400Gbit/s the next standard speed, both in optical networking and for Ethernet.

OFC/NFOEC research papers often come years ahead of practical products, but it still might be interesting to peek at what AT&T has done. Don't fret if you can't make it, though. Plenty of other 400Gbit/s papers will probably be presented.

For more

• OIF Takes an Early Look at 400G
• Japanese Firms Tackle 400G
• Why a 400G Standard Might Draw Complaints
• Alcalu Claims 400G Is Hot
• Ciena Pushes Ahead to 400G

— Craig Matsumoto, Managing Editor, Light Reading