Corvis Eliminates EDFAs
The products aim to carry up to 800 Gbit/s per fiber on cables with no intermediate amplifiers for distances of up to 350 kilometers. The CorWave XL supports terrestrial connections and the CorWave XF supports point-to-point and festoon subsea connections. Festoon refers to applications where subsea cables are looped along a coastline, linking multiple landing points.
Corvis says that it will ship these products in the second quarter of this year, and that they mark a real breakthrough. Its press release quotes Andrew McCormick, a senior analyst with Aberdeen Group Inc., saying that Corvis is “first to commercialize Raman amplification.”
It’s “disruptive technology,” according to a quote attributed to David Huber, Corvis’s president and CEO, in the press release. It will enable Corvis to target new markets and new potential customers, it says.
At first glance, all of this may seem a little confusing from two points of view. First, Corvis’s existing products have already been used in trials demonstrating that optical signals can be carried over much longer distances -- up to 4,000 kilometers -- without needing regeneration (see Corvis Drives 4,000 Kilometers...).
Second, established vendors of submarine cable systems say the use of Raman amplification on unrepeatered subsea cables isn’t new. It was first demonstrated six years ago, when STC Submarine Cables -- now part of Alcatel SA (NYSE: ALA; Paris: CGEP:PA) –- showed a system driving 16 channels of 2.5 Gbit/s over a distance of 426km at the European Conference on Optical Communications (ECOC) in 1995. The demo was repeated over a distance of 511km at the Optical Fiber Conference (OFC) in the same year.
Alcatel has now installed a commercial system of this sort in Canada, according to Eric Brandon, manager of Alcatel’s unrepeatered system design team. In lab experiments, Alcatel has already demonstrated a system carrying 32 channels at 40 Gbit/s over 250km and plans to unveil a system carrying one terabit a second over 350km at OFC next month.
Other submarine cable system vendors have also developed Raman amplication products. NEC Corp. (Nasdaq: NIPNY), for instance, says that it can already do 640 Gbit/s over 350km.
However, Corvis’s claims stand up to scrutiny on closer inspection.
Here’s the score. Nowadays, most of the fiber that's installed on long-haul routes incorporates EDFAs (erbium doped fiber amplifiers). The EDFAs are sections of special fiber that are spliced into the normal fiber every 60 to 80 kilometers. The outer cladding of the fiber is pumped with light from a local laser, and this boosts the power of the actual signal passing through the core.
Raman amplification works on a similar principle, but in this case, there’s no need for special fiber.
The distance records of thousands of kilometers that Corvis (and other vendors) have achieved are over fiber fitted with EDFAs. The new products unveiled by Corvis achieve a maximum distance of 350 kilometers without EDFAs. That's the key point.
Likewise, the records claimed by Alcatel for Raman pumping over unrepeatered subsea systems are for fiber that incorporates “at least one EDFA” according to Marc Fullenbaum, an Alcatel product marketing manager. The “unrepeatered” term refers to the absence of electrical regeneration of the signal, not the absence of EDFAs.
The lab experiment that Alcatel will report at next month’s OFC carried 100 channels of 10 Gbit/s over 350 kilometers of fiber incorporating one EDFA. Corvis says that its new products will support 320 channels of 2.5 Gbit/s or 80 channels of 10 Gbit/s over the same distance, with no EDFAs. Right now, this is a claim. It’s yet to be proved in trials.
So, is eliminating a single EDFA such a big deal? It probably is, in that EDFAs involve putting power down the cable to power the lasers that drive them. “It’s not cheap,” admits Fullenbaum. Having lasers at the bottom of the sea also raises questions about reliability.
-- Peter Heywood, international editor, Light Reading http://www.lightreading.com