Raman Risks Emerge

ANAHEIM, Calif. -- OFC2001 -- A potential drawback of Raman amplification, a technology that’s widely used in ultra-long-haul transport equipment, appears to have gotten swept under the carpet here at the Optical Fiber Communications conference.

The need to avoid this drawback –- that distributed Raman pumping might actually damage fiber and create safety hazards in some circumstances –- explains why WorldCom Inc. (Nasdaq: WCOM) has conducted lab trials of equipment from OptiMight Communications Inc., which aims to support ultra-long-haul transmission without using Raman technology (see OptiMight Details Long-Haul Box).

Here’s the score. Distributed Raman works by pumping lots of light into the outer cladding of optical fiber in a way that boosts the strength of the signal running through the core.

Worldcom has found that things can go wrong when fibers carrying this extra load of light are disconnected from patch panels (the boards used to link one fiber to another), as they're likely to be when engineers implement network changes.

“If the connector has some dirt on it, you can damage it. If you’re not careful, the tip can melt,” says David Chen, advisory engineer in the optical and data network division of WorldCom Inc. (Nasdaq: WCOM). “We see a potential maintenance issue with Raman amplification,” he says.

”It’s not only a technical issue. It’s a safety problem as well,” notes Philippe A. Perrier, director of photonic subsystems engineering at Xtera Communications Inc. Such powerful light could injure the engineers working on patch panels, he warns.

Perrier doubts whether light would be powerful enough to melt the fiber but says that it can carbonize the tip if the connector is dirty. The tip would then require regrinding and polishing.

Xtera, by the way, uses “discrete” rather than distributed Raman amplification to boost signals in its ultra-long-haul S-band amplifiers (see Xtera's $110M Surprise). This means that pumping occurs at intervals, over limited lengths of fiber, well away from patch panels.

Nortel Networks Corp. (NYSE/Toronto: NT), which makes distributed Raman equipment, acknowledges that fiber could be damaged if couplers are dirty. However, it plays down the potential safety hazard. Nortel incorporates technology that automatically shuts down lasers in the event of problems, a spokesperson says.


These concerns led Worldcom into conducting trials of Optimight equipment, which supports ultra-long-haul transmission without using a Raman approach. In the trial, Worldcom and Optimight successfully transmitted 400 Gbit/s (40 channels at 10 Gbit/s a channel) for distances of up to 6,800 kilometers.

Here’s where the OFC connection comes in. Chen and a bunch of engineers from Optimight submitted a report on their trial for inclusion in the OFC’s prestigious “post deadline papers,” to be presented at the conference tomorrow (Thursday). Getting a post deadline paper accepted is considered a big deal by engineers. It equates to recognition of world-class research.

To cut a long story short, Chen’s paper was one of the many papers that didn’t get picked for tomorrow's session. Something like 900 submissions were made and only 39 made it through the OFC’s selection process, according to Chen. His paper is posted on http://www.optimight.com/news/03202001.html

One reason why Chen’s paper may not have made it is that it describes the trial without mentioning the real reason for conducting it in the first place -- to examine ways of avoiding potentially significant maintenance problems.

Light Reading has been told unofficially that Chen’s paper wasn’t accepted because Worldcom’s trial isn’t a record. Even longer distance transmissions without Raman amplification have been reported in the past.

This is disputed by Optimight, which says that Worldcom wouldn’t have gone ahead with the trial if the technology already existed. The implication is that the folk selecting the OFC’s post deadline papers wanted to avoid the whole issue, possibly because of vested interests. Chen has declined to comment, saying he doesn’t want to get involved in vendor politics.

-- Peter Heywood, international editor, Light Reading http://www.lightreading.com
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fanfare 12/4/2012 | 8:41:56 PM
re: Raman Risks Emerge Is that the best they could come up with? OptiMight's pitch against competing tech for ULH is limited to potential damage to fiber tips? I should hope they will be giving their sales teams a bit more of a 'needs/benefit' approach when trying to outsell companies using Raman tech.

I could just see their salesmen making their pitch: "and .. we don't know this for sure .. but .. it is possible that your technicians might get injured when they have to pull fiber out of a switch."

Sort of like the vacuum cleaner guy telling my wife that OUR vacuum just wasn't pulling ALL the dirt out of our carpeting ... "and this could be a potentially serious health concern to you and your family".

Well .. yeah .. I guess it could be .. but I'm sure there is a better solution than scraping our $300 Phantom and buying his $2000 Kirby.

C'mon guys ... even if this were as gigantic of a problem as you'd have us believe ... how long before CORV or NT find a solution to this potential maintainence problem? When was the last time you saw implementation of leading edge tech that did not need/get improved upon over time.

I may just install central vac.
hagisorcine 12/4/2012 | 8:41:55 PM
re: Raman Risks Emerge Here is the web site for FDA laser safety requirements. Anyone building equipment for sale that use lasers have to meet these requirements.

ownstock 12/4/2012 | 8:41:55 PM
re: Raman Risks Emerge Would have been a lot safer if it was one of those 100KVolt power lines that gets hung, buried, handled, switched and terminated every day...

Gee, in this era of increasing competition, if the option is twice (or more) the install cost with lumped amps, I guess thats a better answer, huh?

LR is way over the top on this one...

areyousure 12/4/2012 | 8:41:55 PM
re: Raman Risks Emerge I hear there is a warning that is going to be put on the pumps:

"WARNING: When disconnecting the fiber optic cable from this pump, there is a possibility that you might get hit by a flying manhole cover"

The ever popular warning on the laser itself:

"Do not look into laser with remaining eye"

And finally:

"Do not look directly into the sun as you might become blind"

You have been warned.
optical illusion 12/4/2012 | 8:41:54 PM
re: Raman Risks Emerge
guaranteed NPR will run this story tomorrow.
rafaelg 12/4/2012 | 8:41:53 PM
re: Raman Risks Emerge We all know how conditions in the field are. Raman amps will phase out as more improvements are made in Tx. No one is going to take a chance of wiping out a fiber by an inexperienced engineer or an unclean connection. I've seen new cable under a microscope that looks like it came from a sandstorm in Saudi. And this was from the manufacturer!!!!!Yeah, you can put all sorts of warnings and stickers everywhere, but how many of us (engineers) read the instructions on a manual?
We will see more free expressive tattoos in Optical soon...
lmtis 12/4/2012 | 8:41:53 PM
re: Raman Risks Emerge Stick to vacuum cleaners.

The potential problems with high optical power in fibers has been well documented, if not well read. The potential problems extend beyond the connectors to the fiber itself. When mating or de-mating a connector on a live circuit with >20dBm in the core of the fiber it is possible to initiate a fuse condition in which the core of the fiber will be destroyed all of the way back to the source. Just a bit more than a maintenance problem then eh?
ubwdm 12/4/2012 | 8:41:53 PM
re: Raman Risks Emerge "Would have been a lot safer if it was one of those 100KVolt power lines that gets hung, buried, handled, switched and terminated every day..."

If carriers can afford to retrain their people
and put class III label all over places like power industry has to... Not much luck with
Worldcom, it seems.
Else just do what Williams did, splice everywhere.

boson3 12/4/2012 | 8:41:52 PM
re: Raman Risks Emerge
A lit fiber without Raman can blind you or melt a connector. That's why Verizon uses chimps in the field.

optical_guy 12/4/2012 | 8:41:51 PM
re: Raman Risks Emerge I would expect a completely one-sided argument from a vendor...after all, self interest and competition is all that motivates corporations. But I would expect LR to have balanced this article better.

First, there is not a system out there without seperate and redundant eye safety shut down sub-systems. The previously referenced FDA requirements as well as industry standard expectations demand it. When you read eye safety, read shut down in case of any break in the external light path. This hoooey about all the poor burned and blind techs that Raman will yeild is hysterical journalism below even the National Enquirer.

With respect to connectors burning out, this is not a Raman unique issue but is related to power density. Pitting, scoring, dirt can all lead to connector failure. I have never ever heard of a connector failure for such causes leading to the burning out of the 45-60 km of fiber to which it is attached. I would love to hear of a real world instance of this.

Aside from Raman systems currently being deployed and operated with connectors in the light path as a refutation of the dooms day tenor of this article, there are also new higher power capacity connectors coming to market. Raman or not, I expect power density to increase over time and development of technology, not declined.
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