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Homework Help: Velocity in fiber optics cable

  1. Aug 23, 2011 #1
    1. The problem statement, all variables and given/known data
    I'm taking an introduction course in optics and I came across this exercise which I can't find how to solve:
    "Two light pulses with different wave lengths 500 and 600 nm is sent in to a 1 km long fiber.
    n(610 nm) = 1.399, n(600 nm) = 1.400, n(510 nm) = 1.448, n(500) = 1.45.
    When will the two pulses come out of the fiber relative to each other?"
    (Hopefully the translation is OK..)

    2. Relevant equations
    I suspect that I might need to use group velocity (http://en.wikipedia.org/wiki/Group_velocity), but this has not been taught in the class so far, so perhaps there is an easier way to tackle the problem??

    3. The attempt at a solution
    Nothing that has ended up embarrassingly wrong... :/

    Thanks in advance!

  2. jcsd
  3. Aug 23, 2011 #2


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    Staff Emeritus
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    Gold Member

    Welcome to Physics Forums, mmanu.

    So you have been given the refractive index of the fibre optic cable for a range of frequencies. How is the refractive index defined?
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