Ericsson Builds a Terabit
That's an important difference, because it means Ericsson can match today's reaches -- up to 3,200 km, according to Antonio Tartaglia, the photonics expert who's explaining the technology at Ericsson's OFC/NFOEC booth.
Ericsson didn't bring a demo to the show and isn't presenting a paper about it at OFC/NFOEC, but the company did have an explanatory video with the lab guys explaining the technology. (See Ericsson Demos Terabit.)
As in other 1Tbit/s demos, such as the one shown by Ciena Corp. (NYSE: CIEN) last fall, electronics are the key to Ericsson's setup. (See Ciena Goes Terabit.)
The difference is that Ericsson also uses dual-polarization quadrature phase-shift keying (DP-QPSK) modulation rather than quadrature amplitude modulation (QAM).
Both send multiple bits per symbol, but DP-QPSK is suitable for long-haul reaches -- it's what's being used for 100Gbit/s coherent transmission. QAM -- which has shown up in 400Gbit/s demos at the show -- can't travel as far. (See Ciena Pushes Ahead to 400G, AlcaLu Can Do 400G Too and Huawei Strives for Optical Respect.)
Infinera Corp. (Nasdaq: INFN) also used QPSK in its 1Tbit/s demo described at last year's OFC/NFOEC. That setup used 10 channels of 100Gbit/s each, while Ericsson uses seven channels of ... whatever a terabit divided by seven is. (See OFC/NFOEC 2011: Infinera Talks Terabit.)
Ericsson fits a 1Tbit/s wavelength in a 200GHz space on the ITU grid -- which is what other demos have shown. Ericsson uses seven subcarriers inside that superchannel, as opposed to the five carriers shown by Ciena.
That's more that the five carriers that other 1Tbit/s superchannel demos have used, but Ericsson's use of those carriers might be a little different. Ericsson lets them overlap substantially, literally blurring them together.
"If you look at the signal coming out of the fiber, it's messed up. You have no idea what's happening," Tartaglia says.
Ericsson cleans this up on the receiving end with digital signal processors (DSPs). That part is hardly unique, as DSP signal cleanup is part of coherent transmission and is likely to be used in speeds beyond 100Gbit/s in general.
Keep up with all our OFC/NFOEC coverage at http://www.lightreading.com/ofc-nfoec.
— Craig Matsumoto, Managing Editor, Light Reading