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Homework Help: Fibre Optic cable vs Copper wire

  1. Feb 12, 2010 #1
    Is the fibre optic cable cheaper than copper wire for transmission? I believe there is still loses in a fibre optic cable. As the critical angle of glass is 42 degrees, thus about 50% of the signal would be lost. Is that true?
     
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  3. Feb 12, 2010 #2

    berkeman

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    Not sure about the relative costs per meter, but your loss number is not right. Read about single-mode fiber. The losses are much lower.
     
  4. Feb 12, 2010 #3

    PhanthomJay

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    I can't directly answer your question, but miles and miles and miles of fiber optic cable have been or are being installed by telephone, cable tv, electric, and internet provider companies, etc, using light pulse signals, . I don't see any copper (using electric current) being installed. On a material cost basis, fiber probably costs more, but does a lot more. So its more than material cost, it's greater realized income. Mind you, this response is from a non expert in the communications field.
     
  5. Feb 12, 2010 #4
    Generally, yes? Although, it depends on the data rate and distance involved. Short distance and lower data rates are more conveniently handled and probably cheaper with a copper solution.

    Note that USB cables on computers are copper based because the distance is short; however, trans-atlantic telecommunications is done with fiber because the net cost is much much cheaper.

    There are losses in optical fiber, of course, but the loss is much less than copper.

    Note that the critical angle depends on the fiber type. There can be issues of coupling light into optical fiber due to the acceptance angle. However, this is generally not a big issue. This is because lasers and LEDs are available with high optical power, coupling methods achieve 50 % to 90 % coupling efficiency, and once the light is coupled into the fiber, it transmits with very much lower loss than copper.

    The exact value of the loss depends on the wavelength of light used and the type of fiber used. The most common fiber type is made from silica glass. For these, typical communications wavelengths are 800 nm, 1300 nm and 1550 nm, all in the infrared range. The low loss window is 1550 nm with a loss of about 0.2 dB/km. Note that this equates to loss of half the light after 15 km. There is another transmission at 1300 nm with a local minimum loss of about 0.4 dB/km. The loss at 800 nm is significantly higher, but still quite good.
     
  6. Feb 12, 2010 #5
    Is trans Atlantic cable done with fibre optics? Trans Atlantic cable was laid before the age of fibre optics. Why change it? The actual manufacturer price of the fibre optic and copper cable per metre. Which is cheaper?
     
  7. Feb 12, 2010 #6
    Fibre optics is cheaper and yes the trans-altantic cable has been laid several times and currently fibre optics are used.
     
  8. Feb 12, 2010 #7

    mheslep

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    No, the cost comparison depends on the length of the cable, the bandwidth required, and the environmental conditions. High temperature FO transceivers, for example, are expensive.
     
  9. Feb 12, 2010 #8

    berkeman

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    Links guys. My gut says fiber is more cost effective for BW/cost, but I haven't looked for supporting links...
     
  10. Feb 12, 2010 #9
    What is up with you? The OP asked the question is fibre optics cheaper, in the case of the transatlantic or any distance at which laying cables is needed. Fibre optics is preferable.
     
  11. Feb 12, 2010 #10

    berkeman

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    I'm only guessing, but for short distances and lower BW, UTP is cheaper overall. I agree that that's probably not the OP's question however.
     
  12. Feb 13, 2010 #11

    mgb_phys

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    Fibre can carry vastly more data.
    The early copper cables could carry telegrams at a few bits/second, modern fibre can carry several billion bits/second.
    The fibre cable is much smaller and cheaper to make and lay, especially if you are trying to lay 1000s of km of the stuff. It's also extremely low loss so fewer amplifiers and much less power is needed.

    This long, but utterly fascinating, account explains all about the wonderful world of international telecoms fibre http://www.wired.com/wired/archive/4.12/ffglass_pr.html
     
  13. Feb 13, 2010 #12
    I believe that was the primary driving force behind the decision to lay new cables with the additional pressure that more data would be needed to transferred in the future.
     
  14. Feb 13, 2010 #13

    mheslep

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    The OP didn't specify a distance at all, nor bandwidth, nor environmental conditions. You assumed 'transatlantic' or 'laying' cable distances and gave a blanket answer. Cables have to be terminated in connectors, and driven by a transceiver. IF the cable is relatively short, such as in network LAN, then the connector & transceiver cost make up a significant portion of the cost. Even the cheapest FO ST connectors are more expensive installed than a comparable Ethernet RJ-45 jack. If the BW is high enough, say greater than 5-Gbit, so that copper has to move from twister pair to coax, then the balance tips back in favor of FO again. Include the cost of the transceiver and FO looks much worse than even 1Gbit-Ethernet, again for short distances.
     
  15. Feb 13, 2010 #14

    mheslep

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    Agreed.
     
  16. Feb 13, 2010 #15

    mheslep

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    Cables to Go Ethernet 100Base-TX cable - RJ-45 - M - Stranded wire 5 ft: $2
    http://www.cablesondemand.com/category/LC-LC9/product/FO-LCX2SIMP00/URvars/Items/Library/InfoManage/FO-LCX2SIMP00.htm" [Broken]: $13.73
     
    Last edited by a moderator: May 4, 2017
  17. Feb 13, 2010 #16
    mheslep & OP:

    From http://www.thefoa.org/tech/fo-or-cu.htm

    by the Fibre Optic Association a international non-profit educational organization.
     
  18. Feb 13, 2010 #17
    Referencing a commercial website and comparing two dissimilar products is pathetic. Has it not crossed your mind that they can charge whatever they want for a fibre optic cable because they KNOW people will believe it is superior and are therefore likely to buy it, so why not take a huge profit on that item. Basic business.
     
    Last edited by a moderator: May 4, 2017
  19. Feb 13, 2010 #18

    mheslep

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    The all fiber LAN article has some interesting points, but its hype laden:

    :rolleyes:
    Yes, they're all simple rubes who don't know any better, waiting for enlightenment from the FOA.
     
  20. Feb 13, 2010 #19
    This may be true for computers, but for telecoms, using fibre optics is substantially more cheaper than using copper.
     
  21. Feb 13, 2010 #20

    mheslep

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    No, but wild assertions are.

    I for one don't believe its superior for all needs, and I buy FO cable by the km from the lowest bid when I need it. You're stacking assertion on top of assertion.
     
  22. Feb 13, 2010 #21

    What I am saying is that your referencing, to put it bluntly, is rubbish. Take consideration when using websites to provide evidence for your arguments. Think critically.
     
  23. Feb 13, 2010 #22
    All modern trans-ocean telecommunications is done with fiber optics. The old copper cable is essentially obsolete. The change was made because the bandwidth of fiber is so great. Each fiber has teraHertz of bandwidth and the fiber is 0.25 mm in diameter, hence allowing many separate fibers to be included in one cable.

    When talking about ocean cables you need to understand that the cable itself is an engineering marvel. It includes steel strength members, protective outer coatings, copper power conductors, in addition to the fibers themselves. It must be able to withstand great depths, shark bites (no kidding!), temperature extremes and the stresses of laying the cable.

    Given the above, you can see that the cost of the fiber itself (of the order of $.1 per meter) is a small part of the cable's material cost, manufacturing cost and installation cost. In addition, the number of repeaters required with copper is prohibitive in terms of their number, required electrical power and cost. Nowadays, simple and inexpensive optical amplifiers can be used (with fiber) to directly amplify the light at 1550 nm wavelength. This again reduces cost and complexity of a repeater and allows very long spacing between repeaters (many tens of km, even 100 km).

    When talking about trans-ocean telecommunications, making a comparison between copper and fiber is like comparing cell phones to the old telegraphs. And, that is no exaggeration. :smile:
     
    Last edited: Feb 13, 2010
  24. Feb 15, 2010 #23

    mheslep

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    No, again the answer depends on distance and required BW. Certainly for long distances and high capacity, fiber is cheaper. For short distances, copper UTP is usually cheaper. Add to the reasons I have detailed above (terminations and transceiver costs): power requirements at the end of subscriber loops.
     
  25. Feb 15, 2010 #24

    FAC

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    There are more variables still. Scale-economics play into this in a big way.

    In large enterprises, for example, due to the distance constraint of copper cables (100 meters) sometimes two or three LAN rooms are required on every floor of a building.

    In a skyscraper, supporting copper could lead to using hundreds of LAN Rooms that are equal in complexity toTier II type data centers (the number of LAN rooms on campuses becomes geometrically more numerous depending on how many buildings a campus contains), where each room comes complete with dual air conditioners, UPS, humidification and fire controls, raised flooring and air returns, automated access constrols, etc. ete.

    Fiber, on the other hand, has no such distance limitation, hence can be centrally located in only one or two rooms.
     
  26. Feb 15, 2010 #25

    mheslep

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    I've seen this claim from all-fiber-LAN advocates before, but at least this 'fiber needs no closets' part of it doesn't bare out in practice, at least not from what I've seen in drawing up lab installation plans in existing office bldgs. In my largish office building for instance, all of the building wiring, power and LAN, is in drop ceilings. That seems to be the today's standard practice in generic office buildings. The LAN rooms are broom closet size containing one router, a switch or two, and some punch down blocks. The high capacity trunk lines floor-to-floor are fiber-optic. There is no additional environmental control beyond what's available for offices and desktops, nor is it necessary since if the offices lose power the LAN closets serve no purpose. Data centers are another story of course, often using raised floors and specialized environmental gear, but their bldg scope is much more limited.

    Second, I've not yet seen a building network design that eliminates LAN closets with all-fiber, though I'll grant it could reduce the closet count. The idea of running all the fiber lines from a basement center to each office desktop on higher floors, just because fiber can make the hop distance, is still untenable for cable routing reasons. Break out points are unavoidable, in the same way that large skyscrapers require intermediate elevator stops between the ground and top floor: the entire core of the bldg would consumed by elevator shafts. Building cabling also traditionally has the requirement of allowing cheap floor-by-floor modification and additions (e.g. a new office) without requiring entirely new cable pulls over the length of the entire building.
     
    Last edited: Feb 16, 2010
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