AlcaLu Pushes the Optical Envelope
In one post-deadline paper released today, AlcaLu announced that it transmitted 25.6 Tbit/s of optical data over a single fiber strand using 160 Wavelength Division Multiplexing (WDM) channels. The transmission went through three 80km spans, using WDM in both the C and L wavelength bands.
Researchers used polarization multiplexing in each wavelength to double capacity, and Raman amplification was used to increase the optical signal-to-noise ratio.
AlcaLu also sought to exploit spectral efficiency, which it did by using an advanced signaling format called RZ-DQPSK (return to zero differential quadrature phase-shift keyed). This allowed it to realize 3.2 bits/second/Hertz (b/s/Hz) of spectral efficiency, compared with commercial systems that generally operate at spectral efficiencies between 0.2 and 0.4 b/s/Hz.
Alcatel-Lucent took advantage of research expertise from both sides of the organization, as researchers from Alcatel's Research and Innovation center in France paired up with a team from Lucent's U.S.-based Bell Labs to work on the project.
The previous record -- a 14-Tbit/s transmission -- was set in September 2006 by NTT Group (NYSE: NTT). (See NTT Demos 14 Tbit/s and NTT Plans 10-Tbit/s Network.)
In addition to its record-breaking optical transmission news, the company touted other work aimed at pushing the limits of existing optical networks.
For example, Bell Labs demonstrated the ability to upgrade 40-Gbit/s long-haul networks to 100 Gbit/s. Using WDM channels typical of 40-Gbit/s networks, researchers transmitted 10 100-Gbit/s WDM data channels over a 1,200km optical transmission distance, achieving spectral capacity of 1 b/s/Hz and effectively doubling throughput.
Martin Zirngibl, director of Bell Labs Data/Optical Networks Research Department, said his team used DQPSK to achieve this. DQPSK, he says, "has much lower bandwidth requirements… about the same as 40 Gbit/s," which could ultimately allow carriers to reuse existing 40-Gbit/s components for 100-Gbit/s applications.
Zirngibl believes interest in 100-Gbit/s will be driven by increased adoption of video on demand (VOD) services. "If you look at VOD -- if it takes off, carriers will need to upgrade their networks. In a few years, 90 percent of traffic will be VOD, and bandwidth demand will go up by a factor of 10."
Heavy Reading analyst Sterling Perrin agrees, saying that there's heavy carrier interest in the technology. "In a survey of 72 operators published in February, 45 percent of operators surveyed said that 100-Gbit/s is 'under investigation' right now and only 13 percent expressed 'no interest' in the technology," Perrin says.
— Ryan Lawler, Reporter, Light Reading