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B Why can't we use opaque object in optical fibres?

  1. Jun 11, 2017 #1
    in an optical fibre the cladding used is ussually of a lesser refractive index so that total internal reflection occurs inside core. instead of using such a combination why cant we use a mirror like surface? will the use of opaque material partially absorb some amount of light?
  2. jcsd
  3. Jun 11, 2017 #2


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    Staff: Mentor

    I think so. Total internal reflection reflects nearly 100% (99.9+%) of the incident light, while most mirrors reflect perhaps 85-99%.
  4. Jun 11, 2017 #3
    Light is refracted in optic fibers due to the fact that the refractive index of the material (i think silica) is closer to that of vacuum and total internal refraction is observed. An opaque object will absorb all incoming light and will only give out luminosity. Thus opaque objects will not show total internal refraction (in fact no refraction at all).
    P.S. I might be wrong.
  5. Jun 11, 2017 #4


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    Staff: Mentor

    It's total internal reflection, not refraction. :smile:

    The OP is asking about reflection off of the reflective surface of an opaque object.
  6. Jun 11, 2017 #5
    Ahhhh. Sorry.
  7. Jun 11, 2017 #6


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    Gold Member

    I thought that a metal waveguide worked perfectly well in the way described, with mirror walls.
  8. Jun 11, 2017 #7
    It may also have to do with the fact that different materials become more or less reflective at various wavelengths.
  9. Jun 11, 2017 #8
    In addition to the efficiency arguments presented, I would think creating a mirror-like surface would also be more expensive.
  10. Jun 13, 2017 #9


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    Waveguide walls do not work on TIR. They reflect the waves like a mirror, due to induced currents in a good conductor. A different mechanism, which is far from 100% reflective. You cannot use 100s of meters of waveguide without appreciable loss.
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