two questions about fiber cables

thedramathedrama Senior MemberMember Posts: 291
1) why can multi mode fibers travel less distance compared to single mode?
(the answer is not the core size)

2) how to identify which fiber is multi mode or single mode by looking at it? (if there are no letters MM or SM) on the cable?
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  • it_consultantit_consultant Senior Member Member Posts: 1,903
    There is a technical difference between the way that multi-mode and single mode transmit. In essence, multi-mode fiber is more resistant to bends (OM3 can be almost kinked and still work) but it sacrifices distance. Single mode is more fragile and needs to be quite straight, but it can transmit long wave signal, which gives it the ability to go long distance at high bandwidth. I have 2 10GB 10KM optics that require single mode to work.

    From what I have seen, orange is multi-mode and yellow is single mode. You can have a fiber guy come and look, they have tools which can tell you both the mode and the resistance; which is critical when you are buying your optics.
  • DevilWAHDevilWAH The Bringer of Light Member Posts: 2,997 ■■■■■■■■□□
    You can tell the difference by looking at the end of the fibre (Assuming there is no light passing down it, dont want to damage your eyes). it is easy to see the different size cores.

    Also the standard Single ode fibre is yellow, and multimode is grey, blue or orange. But this is not definitive.

    you also have 65.5 or 50nm core for multi mode and you can't tell between them by site. (edit the standard is orange 65.5 and aqua 50, but again you can order any colour you want this is what you will get if you don't specific from most retailers)

    As for the differences look it up on wiki or other places, people have mentioned about the modal despersion and refraction angles. Long story short single mode travels more like a straight line done the core while mulitmode bounces. But that is so over simplified people will lynch me! how light travels down a fibre is a PHD subject in its self, but single mode interacts less with the fibre and so retains more energy and definition so can transmilt longer distance and higher speed
    • If you can't explain it simply, you don't understand it well enough. Albert Einstein
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  • lurker53lurker53 Junior Member Member Posts: 7 ■□□□□□□□□□
    thedrama wrote: »
    1) why can multi mode fibers travel less distance compared to single mode?
    (the answer is not the core size)

    As I understand it, it's based on how the signal inside the cable travels. Let's say we use this image for the explanation :

    Basically, while traveling the signal in multimode cabling attenuates due to modal dispersion, which limits its practical distance. Similar to how fast ethernet over copper isn't optimal once you exceed 100 meters in length.

    Single mode doesn't suffer the same fate as it only carries a single ray of light (mode)

    Source: Wikipedia/Google
  • gc8dc95gc8dc95 Senior Member Member Posts: 206 ■■□□□□□□□□
    I'm on my phone, so no long post. The differences are in refraction, angles, walvelength, frequency, modal dispersion, chromatic dispersion, etc

    Use the google machine for some of that info.
  • RouteMyPacketRouteMyPacket Senior Member Member Posts: 1,104
    Pretty much what you will see today is like said above, two separate colors for MM and SM fiber

    Orange = Multi Mode and think of it as used "internally"

    Yellow = Single Mode Fiber, used externally by provider coming into the building

    That's how I learned a long time ago.
    Modularity and Design Simplicity:

    Think of the 2:00 a.m. test—if you were awakened in the
    middle of the night because of a network problem and had to figure out the
    traffic flows in your network while you were half asleep, could you do it?
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