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Bent Fibers Put Networks At Risk
opticsorg writes "The combination of moderate optical powers and tight bends can prove catastrophic for optical fibers, according to research carried out by BT Exact in the UK. Although the effect is unlikely to cause problems in current networks, it means that designers may need to think carefully before scaling up the power in their systems or deploying Raman amplifiers with pump powers of several hundred milliwatts or more. In the July 10th issue of Electronics Letters, Ed Sikora and his colleagues report that powers as low as 500 mW can induce permanent damage in singlemode fiber that is bent (13 mm bend diameter or less). 'These bends could be found in exchange racks or splice trays, for example, especially if a fiber is tugged or pulled,' Sikora told Optics.org. The BT researchers carried out tests on four types of fiber subjected to a range of bend diameters (5 to 15 mm) and optical powers of up to a few watts. In all cases the fibers fail within 53 hours. 'What was unexpected was that the catastrophic failure can occur in 90 bends at fairly low powers of less than 1 W or so,' said Sikora. 'It's important to understand that we're not saying that networks are going to fall over tomorrow, but as powers go up you have to aware this effect could occur under certain circumstances.'"
...if you abuse copper conductors, they'll fail too.
I'm having a hard time saying this is surprising; minimum bend radius for fiber is nothing that hasn't been obvious to anyone working with the stuff. As long as you're treating it well, you'll be fine. If you or your upstream is stupid about how to handle it, well, it's like any other poor infrastructure, it's gonna bite you. No surprises there.
You simply have to bend the fibers in order to keep a clean tidy rack which does not look like a spaghetti.
Bull!
if you buy the correct trays and storage equipment for your fiber rack you can easily stay within the minimum bend radius. It boggles my mind how many times I see network engineersthat are now having to deal with fiber treating it like cat-5 or coax. you have to treat fiber like fiber. Correct sotrage boxes, splice trays with the proper loops for that fiber count and yes downspouts and radius curves for the raceways.
your fiber needs to droop down and then come back laying on the radius shelf entrance.
if you do fiber right, you have nothing to worry about.
It's the schmucks and management that are cutting corners that are going to get bitten.
Do not look at laser with remaining good eye.
This is a good reason to keep your optical fiber cables hidden when it is outside the server room.
I've been to more then one place where a major fiber is laying there in the open. I could easily see a disgruntled worker bending the cable a little bit. The fiber in these installations is usually for some mission-critical app, a bend fiber can cause a big financial loss.
With cut copper cable, it's easy to spot the two broken strands of cable. With fiber, it's harder to spot. Someone could easily bend the cable, and then straighten it out. All that's left is a minor kink in the wire and the plastic sheathing that is discolored from being stretched.
"Can of worms? The can is open... the worms are everywhere."
I design and build fiber-coupled semiconductor lasers as a day job, and some of the stuff in our R&D lab has a significantly higher power than what is currently used in most systems out there. A fiber bend radius that leaks/absobs x% of the power at 10mW with no difficulty becomes dangerous when you put a 5W laser in the system - the amount of leaked power becomes enough to fry fiber claddings (especially if the fiber was metalized for soldering to a package) and make a crunchy black line where a perfectly good bit of cable had been moments before.
The take-home message of all of this is that as optical powers go up to increase bandwidth, some existing fiber installation methods may need to be re-thought. That said, I'd doubt that this will have much of an impact on many systems outside of long-haul lines since local systems don't need to have powers of this type to get the bits across town or around an office building.
Aside from the obvious, DUH!, the biggest problem I've found is right at the equipment where the plug is. Most equipment have the plug hole perpendicular to the front face (insert sexual pun here). Consequently, the LEDs and labels and everything else is on the face as well, so most engineers/technicians try to keep it clean. Keeping it clean is why the bending happens. I've only seen a few equipment vendors make plug holes that were at an offset angle more lateral to the face. Smart design. More equipment vendors need to follow.
Cisco are you listening? Ya dumb clod.
"Last one in is a rotten goblin!" - Kepp