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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.'"
Similarly, the bends can prove catastrophic for nautical divers.
...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.
I always thought this was a given?
Whats new here that everyone whos so much as read a magazine article about fibre optic tech doesnt know?
You cant bend fibres, or light will just come shooting out.
I don't need no instructions to know how to rock!!!!
The zero's can turn corners easily enough, but those ones get hung up in the corners.
You would not believe how many mice cords this effects yearly.
Life moves pretty fast; if you don't stop and look around once in a while, you could miss it. -FB
I don't know how the average fibre installer works today, but I know the few times I played with it, we always installed with corners were gentle enough that a full loop would be about 30 cm. This included ensuring no significant load on the fibre at the attachment points, so no 90 degree bends at the switch or server.
I'm only talking about the last few feet, not the 'last mile' of course, but if I upped the power and had a fibre failure, I'd be saying very rude things to the rep of the company that did the installation (if they survived the .bomb, of course).
Scientists today showed that electrical conducting wires can fail when run through a bathtub and that your car won't run after going over a cliff.
The researchers were said to be "disappointed".
42 - So long and thanks for all the fish.
They should put some Pantene Pro-V on them fibers.
/me pulls fire alarm.
It works for me!
No, wait . . . ok, well, at least that stuff isn't flammable.
No, wait . . . shit.
According to the article the cause of failure is an increase in temperature in the fibers when bent.
"the damage is caused by an increase in temperature that occurs when the power leaks out of the fiber at a bend and is absorbed by its coating. This either causes the fiber coating to burn off leaving the silica beneath exposed or if the temperature is high enough (around 1100C) the fiber itself deforms giving rise to a large permanent optical loss."
It would seem that research needs to be done in the optical fiber coatings and their heat transfer properties as the fibers can handle the increased temperature, but the coatings can't. Either that or we are seeing the limits of fiber systems and the amount of load they can carry. Anyone know what the current coatings are made of, or any alternatives to these coatings that would alleviate these problems?
Perhaps this is a good stock tip... When you hear of a company that has created a new fiber optic coating that increases the amount of heat trasnferred away from fibers, jump on their stock.
MMORPG fan-boy? Prove your worth
Folks, a 5mm bend is darned tight. 5mm is almost 1/5th of an inch. Even a 15mm bend is pretty tight - just over half an inch.
I'd take this "study" with a large block of saly, personally. I never bent myheliax abtebba cable this tight, and I doubt that any sane technician would try to bend glass optical cable this tight, either.
Lemon curry?
-Lucas
At the car parts store is ugly tubing in a closed "C" profile called wire loom. It is somewhat inflexible. It works. But that gets too much important stuff accomplished without enough consultancy firms and PHB's employed. Sheesh. The next thing you know people will be selling bottled water and canned air! (Shaking head.)
"I bent my Wookie."
When I was a student worker I was "volunteered" to pull cable. We were running fiber from the Science Center to the Health Professions building. At the time I had no idea what fiber was even made of, I just knew to take it from point A to point B. It was a pretty fun day though, I still remember swinging on the fiber like it was vine. Good times.
"The Internet is a fad." - WB
A clever person solves a problem. A wise person avoids it. -- Einstein
... the "new" thing being reported is the microbends fail by going opaque when higher optical powers are being transmitted in the fibers. For modern systems in most inter-city networks, the number of channels (40, 80, ...) is going up, as is the power per channel. This is a combination not seen earlier in installations where most fibers (bent or not) carried fairly low power signals.
Interestingly enough, microscopic dust particles are equally hazardous to the system's health at these high power levels. Dust particles caught in unclean connectors has been known to scatter enough power to fuse/weld (its those friggin laser beams) together the connector parts together.
yawn.
yes, 42.
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.
Don't bend your fiber!
Don't polish your helmet!
I'm sick of these technical articles making moral judgements on my hobbies.
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Optical fibres can be used as couplers between two lasers (the second laser amplifies the signal from the first). We use such a system in our lab, where average powers of 40-100W can be sent down a single fibre (multimode in our case). If the surface of the end of the fibre gets scratched, or if dust lands on it, the tip can explode. With each pulse (it's a 25kHz pulsed laser) another piece of fibre is destoyed, and it acts like a fuse. If you don't turn the laser off quickly you can soon lose kilometres of fibre. All that's left is a ringing in your ears and a few bits of scorched plastic.
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.
I think you just need a handy black hole or two
to bend the light by gravity. Could play hell with the equipment and personnel losses, though.
Is it still has tedious to put the connectors on the ends?
When I was doing it, IIRC, the process ran something like this:
In grad student (chemistry) days I ran an apparatus for stimulated, mass-selective Raman spectroscopy of molecular clusters. The Raman pump beam was two colors, generally tuned for power (a watt or two each, depending on tuning). The molecular clusters were formed in a vacuum chamber and we had a quartz window to let the laser light in. If there was a speck of dust on the window at the point the beam entered, the absorption was sufficient to start drilling a hole in the window. The noise was our cue to cut the laser beam before the window was breached (there were dedicated electronic circuits to protect the vacuum chamber's diffusion pumps, but we didn't want to take the risk of failure).
Of course, we spent a lot of time cleaning that window, and for that matter all the optics.
The clearance system sounds logical. It is not. It is completely arbitrary. -- John Bolton
It's perfectly possible for multimode fiber to be glass and single-mode to be plastic. The difference is the diameter of the waveguide itself. Single-mode fibers (At least the waveguide portion, the total fiber is usually similar in thickness for structural reasons) are much thinner than multi-mode fibers, only allowing one waveguide "mode" to exist. (Hence single-mode). Each mode in a waveguide travels at slightly different velocities (Actually, in reality the light travels in the same speed, but certain modes travel longer distances due to the way they bounce within the waveguide), so multimode fiber suffers from pulse spreading since not all of the light travels the same distance.
Glass vs. plastic - Glass is always more transparent. As a result, singlemode fibers ARE usually made from glass since there's not much point in reducing pulse spreading if your attenuation is not reduced.
retrorocket.o not found, launch anyway?
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
if you do fiber right, you have nothing to worry about.
So does this mean I'm going to have to stop making fiber animals with my patch cables? Damn!
And I'm not kidding. Using dBm = 10 log10[ P / 1 mW], you get 27 dBm.
Most lasers in the telecommunications world run between -10 dBm and 5 dBm. Over a good fiber link, you can reach over 100km with a couple dBm.
EDFAs and Raman amplifiers may be up in the 20 or 30 dBm range, but they are not widely used, nor will they ever be. You only need that much power for very long runs - like between remote cities in the mid-West US.
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