Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!

 


Forgot your password?
Close
typodupeerror
×
The Internet Technology Hardware

Bent Fibers Put Networks At Risk 207

Posted by timothy from the kinks-in-the-nu-all-perfect-future dept.
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.'"
This discussion has been archived. No new comments can be posted.

Bent Fibers Put Networks At Risk More

Bent Fibers Put Networks At Risk

Comments Filter:

  • Bends (Score:5, Funny)

    by mopslik ( 688435 ) on Wednesday August 06, 2003 @12:39PM (#6626529)

    ...tight bends can prove catastrophic for optical fibers.



    Similarly, the bends can prove catastrophic for nautical divers.

  • Don't bend your fiber. I could of swore not bending optial equipment was a given.....

    • Re:For everyone too lazy to read.... (Score:5, Informative)

      by Nintendork ( 411169 ) on Wednesday August 06, 2003 @12:48PM (#6626624) Homepage
      No doubt. You don't even want to bend solid CAT5 cable [cabling-design.com] too much when you use it to wire a building. Typical rule is a 1" radius. Optical cables are much more sensitive [netoptics.com] to bending with a 2" radius limit.

      -Lucas

      • I was recently called in to investigate network trouble at an office. The network laser printer frequently went offline and lost jobs, and no one could figure out why. I traced the cable and found that it went through a door hinge before plugging into the ether switch. The door couldn't close completely due to the cat-5 cable, and there was about 6" of "bite marks" along the cable where it had been pinched between the door and the frame. Changing the cable and rerouting away from any doors (the office h
        • The door couldn't close completely due to the cat-5 cable, and there was about 6" of "bite marks" along the cable where it had been pinched between the door and the frame.

          It doesn't even have to be that obvious.

          A large building will "move" based on wind input. It need not be a high-rise skyscraper - just a steel structure with enough surface area to catch a significant amount of wind energy (buildings by a freeway or major road will also be susceptible to movement due to the subsequent shaking of the ea

    • Re:For everyone too lazy to read.... (Score:5, Funny)

      by L. VeGas ( 580015 ) on Wednesday August 06, 2003 @12:59PM (#6626730) Homepage Journal
      Don't bend your fiber!
      Don't polish your helmet!

      I'm sick of these technical articles making moral judgements on my hobbies.
    • Don't bend your fiber.

      Actually, if you read closer, you'll find:

      catastrophic for optical fibers

      So... if you have fibers and they are made out of optical, then you can't bend them. It doesn't say anything about fiber optics so I assume that it is safe to bend it.

      Seriously.
    • Don't bend your fiber. I could of swore not bending optial equipment was a given.....

      Obviously you have to allow for some amount of bending, or it would be a useless technology. The issue here is that radii originally thought to be "safe", might not be if you pump a strong enough signal through. So the current standards are fine as long as you keep your power at a certain level. If you do need to increase signal strength, then things may start failing.

  • In related news... (Score:5, Insightful)

    by djh101010 ( 656795 ) on Wednesday August 06, 2003 @12:40PM (#6626545) Homepage Journal
    ...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.

    • Re:In related news... (Score:4, Informative)

      by Anonymous Coward on Wednesday August 06, 2003 @01:03PM (#6626762)
      I agree this is nothing new and should be common sense but it isn't. Bending a wire of any kind will subject one side to compression and the other side to tension, and what kind of failure occurs depends on the material properties involved (i.e. some materials fair better under compression, and others better under tension).

      A fairly small percentage of the power is absorbed but as it is absorbed it changes the structure of the coating causing some more absorption until there is a run away effect," said Sikora. "Depending on the input power the temperature can easily go up to 1000C or more."

      Thermal run away can have catastrophic consequences. Take copper wiring in a aircraft for example. Place plastic coated copper wire with a excessively small bend radius and over time the plastic will start to crack on the outside of the bend.

      If the wire is located in a non pressurized area of the plane, the wire can be subject to extreme levels of condensation. This condensation will come in contact with the exposed wire creating a carbon residue on the outside of the wire. Over time this residue builds and as electricity is run through the residue it is heated, melting more of the plastic cover and exposing more wire. If this occurs on/inside a wire bundle which can contain dozens and dozens of wires you can get anything from a system short(s) to the entire bundle starting on fire.

      AC

    • Re:In related news... (Score:4, Funny)

      by swordboy ( 472941 ) on Wednesday August 06, 2003 @01:19PM (#6626852) Journal
      minimum bend radius for fiber is nothing that hasn't been obvious to anyone working with the stuff

      I've been supplementing my diet with fiber every day now and it has certainly increased the minimum bend radius in my sigmoid colon!
    • I'm having a hard time saying this is surprising.

      I agree. It may not be so intuitive for copper, but c'mon, fiber is glass. Of course if you bend it too much there will be problems. When I used to install fiber cabling, we always used a larger bend radius than the standards required -- it just made sense. Not to mention the fact that if you include a service loop in the walls, every time you pull some more of the extra fiber out of the wall, you decrease the bend radius of the service loop.

      • Sure it's glass, but the problem is with the heat buildup (hence the reference to different effects) in the bends.

        • The heat may be the problem being presented here, but the issue could be completely avoided if people spec out their cable installations properly to begin with, and use a little common sense. I don't care how much heat is generated, at 13mm, there's a good chance that the cable will shatter eventually anyway.

          • Yeah, that's pretty much so. My understanding is that a bent fiber, no matter how slight the bend, eventually snaps. You can delay the inevitable by making the bend less acute though. By the time you get to a bend radius measured in 10s of cm the lifetime is probably in the multiple decades.

  • Huh? (Score:3, Insightful)

    by stratjakt ( 596332 ) on Wednesday August 06, 2003 @12:41PM (#6626554) Journal
    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.

    • Re:Huh? (Score:5, Informative)

      by 680x0 ( 467210 ) <vicky @ s t e e d s . c om> on Wednesday August 06, 2003 @12:57PM (#6626716) Journal
      You cant bend fibres, or light will just come shooting out.
      Actually, you can bend fibers to a certain minimum radius. The light is reflected off the inside wall of the fiber. Long-haul connections use something called "single-mode" fibers, which I believe is made from glass fibers. Shorter connections use a plastic fiber, called "multi-mode", which can bend more.

      But, I guess what the article is saying is that the minimum radius (i.e. how "sharp" the bend is) is larger for higher power signals, and as carriers increase the power (for more bandwidth) they may discover some of the existing bends in their fiber infrastructure suddenly become too sharp.

      To understand the radius/diameter of a bend, imagine the fiber following the outside of a circle with the given radius or diameter. If you need a 90-degree turn, you follow around 1/4 of the circumference of the circle.

      • Multimode vs. single-mode (Score:5, Informative)

        by Andy Dodd ( 701 ) <atd7NO@SPAMcornell.edu> on Wednesday August 06, 2003 @01:24PM (#6626885) Homepage
        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.
        • 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
          I believe that chromatic dispersion occurs independantly of the path through the fibre the different modes take. Depending on the free spectral range and fibre length, this dispersion may or may not be significant.
        • Just one more note as to why glass fibres are usually single mode, and plastic multimode: Glass fibres, while extremely low loss (especially in the infrared (1.55 and 1.3 microns)), also tend to be brittle. Thus the standard single mode fibre with these only has about 8 micron core diameter, while a multimode fibre has a core diameter of about 50 microns - half the width of a hair. Plastic optical fibre (POF), tends to be cheaper and much more flexible, allowing for tighter bends and thicker fibres (~1mm

      • Re:Huh? (Score:4, Interesting)

        by pclminion ( 145572 ) on Wednesday August 06, 2003 @01:33PM (#6626945)
        But, I guess what the article is saying is that the minimum radius (i.e. how "sharp" the bend is) is larger for higher power signals

        Nah. The maximum radius doesn't depend whatsoever on the intensity of light passing through the fiber. If the radius is too tight, light will leak out, regardless of how weak. Light is already leaking out of these over-bent fibers. The problem is when the power gets too high, and the amount of leaked light becomes so great that it actually starts heating up the cladding.

        BTW, the maximum curvature radius you can use depends on both the material the fiber itself is made of, and the material the cladding is made of. You want the two materials to have dissimilar indices of refraction -- the more dissimilar, the tighter you can bend the fiber without light leaking out of it. To some degree it also depends on the frequency of light you are using. But it does not depend on the intensity of the light.

        • Obviously I meant the minimum radius of curvature, not the maximum.

        • Re:Huh? (Score:2, Insightful)

          by Shane-24 ( 695974 )
          Uhm - I do beg to differ. There is going to be loss at ANY bend, however the minimum bend radius gives to the limit of the acceptable loss.

          Now if the light becomes too intense (and 500mW to 1W is a LOT of light in a single mode fibre), the fraction lost in the bend although in itself acceptable, becomes great enough to actually damage the structure of the fibre.

          I also wonder how the heating effects the refractive index of the core/cladding itself, and if this might lead to a feedback loss/heating effect.

      • Re:Huh? (Score:3, Interesting)

        by SuiteSisterMary ( 123932 )

        I believe what they're saying is 'although we always knew that bending your fibre would result in less efficient connections, we're now finding out that it will ALSO actually damage the fibre itself over time.'

        Much like, kink a CAT-5 enough, and it won't pass traffic at full speed, but it's not going eventually burn the cable.

  • It's the ones... (Score:5, Funny)

    by Xandar01 ( 612884 ) on Wednesday August 06, 2003 @12:42PM (#6626565) Journal
    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.
  • Being a network engineer I deal with fibers in a 19" rack. You simply have to bend the fibers in order to keep a clean tidy rack which does not look like a spaghetti. But as long as it's just a simple patchcable which is broken and not a fiber burried somewhere deep, It's just a simple case of shit happens. Just make sure you have your cabletester nearby :)

    • Re:As long as its just a patchcable.. (Score:5, Insightful)

      by Lumpy ( 12016 ) on Wednesday August 06, 2003 @12:57PM (#6626710) Homepage
      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.
      • 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!

      • It's the schmucks and management that are cutting corners that are going to get bitten. -- What this world needs is some geeks with the backbone to stand up for what they believe in.

        If this is a sig it's great, but particularly appropriate for this post. In every data centre I've been in, there have been giant cable infrastructure nightmares - everyone knows about the monsters under those raised floors, but have you ever seen a rats nest of cables so large that it has to be supported or the weight will
        • Excellent post.

          One thing we've done to combat this is to make it an action item on every project (via a child change-record) to clean up the cable mess your project leaves behind.

          Yeah, we still have some legacy cable issues from before this was implemented, but everything since then has gone extremely well.

          I monitor what goes on (and under) my raised floor pretty religiously now, and I have to say things are looking really good!
  • Light still can't travel around corners.

  • If the installation was done by the book... (Score:4, Interesting)

    by Baron_Yam ( 643147 ) on Wednesday August 06, 2003 @12:43PM (#6626572)

    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).

  • In other news... (Score:5, Funny)

    by jhines0042 ( 184217 ) on Wednesday August 06, 2003 @12:44PM (#6626576) Journal
    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".

  • The cause of the failure (Score:5, Informative)

    by groove10 ( 266295 ) on Wednesday August 06, 2003 @12:46PM (#6626601) Homepage
    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.

    • Re:The cause of the failure (Score:5, Informative)

      by pclminion ( 145572 ) on Wednesday August 06, 2003 @12:54PM (#6626689)
      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.

      The problem actually is, when you bend a fiber beyond a certain point, the pulses end up striking the outside wall at an angle steeper than the critical angle. Total internal reflection no longer occurs, and some of the pulse energy escapes the fiber and heats up the coating. The problem isn't that the coating needs to be tougher -- the problem is, the fiber shouldn't be bent that much.

      Now, it seems counterintuitive, but the narrower a fiber is, the more sharply you can bend it without a loss of TIR. This is because a narrower fiber causes the pulse to reflect more rapidly as it goes around the corner, so the total bending angle is distributed over more reflections. This keeps the light in the fiber.

      I see four ways to solve this: 1) replace the fibers with narrower fibers, 2) replace the cladding with cladding that can take the heat dissipation, 3) use a lower transmission power, 4) have someone go out and assess each place where the fiber bends, and make it bend at a shallower angle if necessary.

      Option 3 is pretty much impossible, since you need higher power to get a higher data rate (this is, after all, why the powers keep increasing). I think option 4 is pretty much the best shot.

      Looks like some people forgot basic optics when they were laying the fiber...

    • According to the article the cause of failure is an increase in temperature in the fibers when bent.

      What they failed to mention was that the light source was sharks with fricken laser beams on their heads.

  • "Slight" bends?! Yeah right! (Score:3, Informative)

    by MsWillow ( 17812 ) on Wednesday August 06, 2003 @12:47PM (#6626613) Homepage Journal
    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.

    • No crap, 5mm or 15mm, you're basically creasing the fiber. Imagine a 90 degree bend, with light coming in. Duh, it's going to hit that corner a lot. Duh it'll heat up. Duh, insulation goes bad from heat.

      Slashdot should have an "obvious" topic or tag... or are they catering to the complete idoits who have been showing up more and more?

  • I've always been taught to never coil or bend fibre cables tighter than about 45 degrees over a 2 inch span.
    And don't pull hard on fibre cables, that tends to pull the heads away from the rubber coating, making the cables even more exposed to damage. Or to cause a kink that violates the bending contraints.

    While this isn't a life or death situation, even in a production environment ( which should have redundant paths and whatnot built in ), it's probably a big pain in the ass for long runs.
    Having said

  • Obvious solution (Score:3, Informative)

    by finallyHasANickname ( 559395 ) on Wednesday August 06, 2003 @12:51PM (#6626657) Journal
    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.)
  • Improper handeling and installation of fiber can effect performance and even the operation of the fiber? The hell you say?

    That must be in the book right after "An end-user that constantly runs over their cat5 cable with an office chair might eventually experience connectivity issues." and "Why does my server spontainiously re-boot when it's plugged in a power strip with five HP5000 laser printers?"

    This brought to you by the Ministry for the Preservation of Stating the Obvious.

  • Ralph Wiggam says... (Score:5, Funny)

    by Tumbleweed ( 3706 ) on Wednesday August 06, 2003 @12:54PM (#6626686)
    "I bent my Wookie."
    • Hehe, I love that line. I have a t-shirt with that scene on it. I like Ralph because some part of me wants to be Ralph, dumb but happy rather than smart but sad. Nothing gets Ralph down because he simply doesn't understand it.
      • > I like Ralph because some part of me wants to be Ralph, dumb but happy rather than smart but sad.

        He's also a little scary, though, what with the Leprechaun who tells him to "burn things." *yikes*

        My other fav Ralph line is when the dam bursts, and Ralph is left in his bed in the middle of the street, "I think I wet my bed."
  • ...when I'll hopefully be building my own house in a few years. Better allow enough space for optical cabling, adding it afterwards would be a pain if bend radius has to be that big.
    • Yeah, cause 15 millimeters is, like, huge. Wait, no, I measured it, and the word "huge" on my screen is only 13 millimeters.
    • ...adding it afterwards would be a pain if bend radius has to be that big

      But it's not that big. You can do a 45degree angle within a couple inches of arc length... just don't kink the damn things.

      I just ran Cat5e throughout my house to drops and such... plenty of room for optical cabling to run in its place... just handle it carefully.
    • Is 802.11(a,b,g) not fast enough for you? Wherever you put the wire/fiber/whatever, it'll be in the wrong place and obsolete in 5 years. If your feed isn't faster than, say, 11Mb/second, why bother with anything other than wireless?

  • Yes! (Score:5, Funny)

    by vgaphil ( 449000 ) on Wednesday August 06, 2003 @12:56PM (#6626701)
    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
    • Yeah- I remember when I was working in my college's AV room my Boss told me about a job posting. They wanted some students to wire the Compsci building with fiber, and they wanted to pay some ridiculously small amount (6, 7 bucks an hour?) such that she said "if I was the kid doing that job and getting paid squat like that, I'd show up High every day."

      Granted- she used to hang with John Waters, so maybe thats not an odd response.

  • its the high power (Score:5, Interesting)

    by wheatking ( 608436 ) on Wednesday August 06, 2003 @12:56PM (#6626706)
    ... 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.
    • ... the "new" thing being reported is the microbends fail by going opaque when higher optical powers are being transmitted in the fibers
      The funny thing to me is that this may become a self-regulating condition.
      When carriers first started moving from SONET->CWDM->DWDM, everyone was concerned that packing so much data into a fiber would cause a huge glut of unlit (dark) fiber.
      Now, as more and more power gets shoved down the line, they toast the fibers that used to be functional, forcing them to

  • The fun starts at really high powers (Score:5, Interesting)

    by NCFlipper ( 69861 ) on Wednesday August 06, 2003 @01:00PM (#6626738)
    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.

    • Or even not-so-high powers (Score:5, Interesting)

      by Mark of THE CITY ( 97325 ) on Wednesday August 06, 2003 @01:23PM (#6626883) Journal
      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.

      • Re:Or even not-so-high powers (Score:2, Funny)

        by Anonymous Coward
        What two colors of Raman did you use? Personally, I like the pink (shrimp) and yellow (chicken) together.

        Because there weren't enough raman jokes attached to this story yet, that's why.
  • '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.'

    I'm not saying a meteor is going to hit Earth tomorrow, but I just want you to be aware that it MIGHT happen in the future under certian circumstances.

  • Cladding to prevent this? (Score:3, Interesting)

    by Mannerism ( 188292 ) <keith-slashdotNO@SPAMspotsoftware.com> on Wednesday August 06, 2003 @01:04PM (#6626773)
    Does anyone know of supplemental cladding (preferably something more sophisticated than a thick layer of duct tape) that can be added to the cable at critical points to prevent excessive bending while still allowing a reasonable degree of flexibility?
    • Typically, proper cable chases, conduits and fibre looms limit the abillity to bend the fibre excessively although, they do not prevent excessive lateral force wich results in stretched or broken fibre. I've never tried the duct tape but, it seems like that would work well too. Chalk up another great use for duct tape.

      Remember, if the women don't find you handsome, they should at least find you handy. -- Red Green

  • Worker Sabotage... (Score:5, Insightful)

    by stefanlasiewski ( 63134 ) * <(moc.ocnafets) (ta) (todhsals)> on Wednesday August 06, 2003 @01:08PM (#6626795) Homepage Journal
    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.

    • Re:Worker Sabotage... (Score:3, Interesting)

      by stienman ( 51024 )
      Fortunately for them, there are tools that not only tell you how much signal loss you're experiencing in a given cable (so you can replace a lossy cable) but also tell you where a significant problem exists along the cable. Very useful for underwater and other long links - you have a good idea, to within a few cm, where the problem is. Go to it and splice - but, of course, only if the splice is going to be significantly less lossy than the problem itself.

      -Adam
    • We repulled all our fiber when we moved our data center. The old fiber was lame plastic jacketed single strands.

      The new stuff has 8 strands and is inside what I can only describe as being like Liquidtight Metallic Conduit -- a heavy plastic jacket over a coiled metal jacket. Where it's pulled and "publicly" accessable (common closets), it'd be impossible to bend it without a hacksaw.

  • huh? (Score:2, Funny)

    by Lowen Na ( 648807 )
    "Bent Fiber Put Networks at Risk"

    No shit?

    In other new, magnet endanger floppy disk and metal shrapnel is bad for your eyes

  • the 'new' thing (Score:5, Insightful)

    by theMightyE ( 579317 ) on Wednesday August 06, 2003 @01:17PM (#6626840)
    There's been a lot of posts to the effect of 'everyone knows you don't bend a fiber - duh!', but I think they might be missing the point of the article. The article was trying to point out that as laser powers get higher, the bend radius becomes larger since phenomena that don't matter at low power come into effect when you try to cram more optical power into the same fiber.

    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.

    • It's the same problem, really, as people touching circuitry and not wearing a static strap. The damage doesn't show immediately, so by the time it does, it's attributed to something other than the real cause.

      No different than someone kinking a cable, trying it, finding it's OK, and forgetting about it for a few months/years. Eventually, someone will get bit by the mistake of years ago.

      As with so many things in the IT field, a mistake now may take a long time to show up, but it will bite you. Be it a se

  • Fiber and connectors (Score:5, Informative)

    by RevMike ( 632002 ) <revMikeNO@SPAMgmail.com> on Wednesday August 06, 2003 @01:19PM (#6626857) Journal
    I helped do a job installing fiber in a Manhattan office tower almost fifteen years ago. It was being used to interconnect the datacom closets on each floor with a central datacom room. I haven't had reason to use it since.

    Is it still has tedious to put the connectors on the ends?

    When I was doing it, IIRC, the process ran something like this:

    1. Strip the sheath form the fiber.
    2. Epoxy the fiber into a connector, with plenty sticking out from the "business end".
    3. Use a special knife to score the fiber flush with the connector.
    4. Break off the excess fiber.
    5. Attach the connector to a flat round disk which would hold it perfectly perpendicular to a flat surface.
    6. Using increasingly fine grits of "sand paper", polish the end if the fiber perfectly smooth and flush to the connector by rubbing it (and the disk) in a figure-8 pattern.
    7. Inspect the termination with a microscope.
    • 8. Place cut strand upright in co workers chair

      -Adam

    • Re:Fiber and connectors (Score:3, Informative)

      by Anonymous Coward
      yep, still done the same way.

      there is now a 'cold' method that does away with the epoxy, the fiber is cleaned and placed in a special connector then placed in a mechanical device that's sorta like a spring loaded hammer.

      cock the device and press the lever and a die squishes the connector tightly to the glass without crushing it.

      still have to polish and all that.
  • Judging by some of the content of the Internet, I'd say all the fibers are seriously bent.

  • Where to bend (Score:5, Insightful)

    by mobileskimo ( 461008 ) on Wednesday August 06, 2003 @01:37PM (#6626980) Journal
    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.
  • Simply save all your viagra spam and transmit it down the bent cable, that'll straighten it out!

  • Fear (Score:2)

    by Cyno ( 85911 )
    Are you affraid of what might put your network at risk? Then let me help you be affraid:

    If you know nothing about networks your network could be at risk of:

    bent fiber
    bent copper
    bent pins
    unseated memory
    old equipment
    unlocked network closets
    lazy admins
    stupid users
    uneducated management
    sun spots
    anything
    everything

    Get the point?

  • 500 mW it A LOT of power (Score:3, Informative)

    by mrand ( 147739 ) * on Wednesday August 06, 2003 @02:05PM (#6627209)
    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.

  • "Depending on the input power the temperature can easily go up to 1000C or more."

    Network failure is bad, but isn't the fire risk an even greater danger?

  • Not applicable in the enterprise at this point (Score:3, Interesting)

    by petrilli ( 568256 ) on Wednesday August 06, 2003 @02:28PM (#6627356) Homepage
    Today, normal enterprise/campus networks don't work with any amount of power, quite honestly. Horizontal building cable is almost exclusively copper or multi-mode fiber, and riser/inter-building cable is single-mode, but relatively cheap stuff. Where this kind of thing comes into play is in the long-haul networks of companies like AT&T, Level 3, Sprint, etc., where you have 100Km+ between OA (Optical Amplifier) sites.

    Many people are working to extend the OA interval to 600Km through doped and Raman amplifiers, which are giving you launch powers in the 30db+ range, and are starting to approach the powers that can do this. However, as someone pointed out, none of this happens with normal correct fiber installation. I know my company, which runs a large (tens of thousands of miles) network has reams of paper describing exact splice tray designs, stress on cables, bend angles. It goes down to how you support things going in and out of a OA, etc., and addresses the radius, which I believe we try and keep around 15-20cm minimum.

    If you follow smart rules, these don't matter. If you don't, well, it probably won't affect anyone who is working outside the large telco space. The cost of an EDFA (Erbium doped fiber amplifier) is tens of thousands of dollars.

    No story, move along. :-)

  • This is ridiculous! (Score:2, Informative)

    by Anonymous Coward
    Having worked at JDS Uniphase (world's biggest fiber component manufacturer) for several years, the minimum bend radius is not a suggestion, it is a requirement, especially when you crank the laser power. READ THE LABELS AND FOLLOW THEM!!!

    But, when you try make something idiot-proof, the world will make a better idiot.

    Long-term, I think the only solution is change the plastic cladding, so that it can't be bent beyond the minimum radius of the fiber.

    (and no, I don't work at JDS anymore. But it was fun and
  • When we did our first (thickwire) Ethernet installation, we were impressed with all the warnings about the importance of maintaining, IIRC, a six inch bend radius. Just for fun, we took a scrap piece with the idea of bending it too sharply just to see what would happen. What we found was that the cable was very, very hard to bend. It seemed that you'd need tools--or a very muscular person trying very deliberately to bend it--to violate the spec.

    So, what's the situation with optical fiber? A 13 mm bend diam
    • Um, have you payed with optical fibre at all? It's entirely unlike thicknet (coax) cable.

      It's quite possible to bend optical cable to that small of a diameter. On the other hand, they warn you about it endlessly. Only the chronically stupid should have to worry about this.

  • What types?? (Score:3, Interesting)

    by Servo ( 9177 ) <dstringf@noSPam.tutanota.com> on Wednesday August 06, 2003 @03:31PM (#6627830) Journal
    The article states that 4 different types of fiber were tested, but doesn't state what those types are, or related too. There are different materials fiber optic cabling can be made out of, as well as different diameters. Were they talking about different diameters, or the materials?

    This was obviously written for a somewhat technical audience, given the subject matter and source that published it. By omitting the facts of which 4 types they tested, it really doesn't do justice to the subject. For all we know, they tested low end cabling made from plastics.

  • VERY OLD NEWS (Score:2, Informative)

    by Donelurking ( 695819 )
    I spent many years working in fiber optics. Bending-induced failure modes have been well known for decades.
  • Manufacturers should build them stiffer or add a structure that doesnt allow the fibers to be bent that much. It will be really hard for network admins to lay their cables *very carefully* only to trip on it and break it.

Slashdot Top Deals

Wishing without work is like fishing without bait. -- Frank Tyger

Close