AlcaLu Climbs to 16.4 Tbit/s
In a post-deadline paper presented here yesterday, AlcaLu described how it sent a 16.4-Tbit/s transmission over 2,550 kilometers of fiber in the lab. It was one of four post-deadline papers the company published. (See AlcaLu Claims Optical Records.)
An OFC/NFOEC post-deadline paper is a big deal. The technical sessions here are filled with new experimental results, but companies sometimes save their niftiest work for the post-deadline papers, which traditionally get published and presented on the conference's penultimate day.
Last year's post-deadline crop included an experiment involving 10 wavelengths of 111 Gbit/s apiece, sent down 2,400 km of fiber. That one was presented by CoreOptics Inc. , the Eindhoven University of Technology , and Siemens AG (NYSE: SI; Frankfurt: SIE). (See CoreOptics Demos 100G.)
AlcaLu's 16.4-Tbit/s result is a kind of sequel to that paper. Both experiments used a modulation scheme called (deep breath) polarization division multiplexed quadrature phase-shift keying (PDM-QPSK). But AlcaLu took the idea further by packing many more wavelengths, using up the entire C and L bands.
PDM-QPSK is designed to be robust to polarization mode dispersion (PMD), one of the optical effects that causes high-speed signals to degrade as they traverse long distances. Companies often cite PMD as one of the bugaboos that arises with serial 100-Gbit/s transmission.
Post-deadline papers don't represent products that are coming out any time soon. But AlcaLu's results -- and CoreOptics's a year ago -- show that it's feasible to send 100 Gbit/s signals down the infrastructure that was built for 10 Gbit/s. That's considered a critical factor in developing 100-Gbit/s Ethernet.
One of the biggest questions around serial 100-Gbit/s transmission is the modulation scheme. Most companies prefer some kind of "quad" format, where data gets sent four bits at a time. That would turn the 100 Gbit/s problem into an easier 25 Gbit/s one.
Differential quadrature phase shift keying (DQPSK) is the modulation scheme most talked about as a 100 Gbit/s candidate.
— Craig Matsumoto, West Coast Editor, Light Reading