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Homework Help: Fibre Optic questions

  1. Jun 7, 2014 #1
    Hi, I have some fibre optics questions that I can't seem to get my head around.

    How does providing a cladding of a refractive index slightly lower than the core increase the critical angle? I can do the mathematics to see that it does however is there a logical explanation.

    Why is increasing the critical angle a good thing? Doesn't that mean that less light will undergo TIR and will be refracted instead?

    If for example the critical angle was 20 deg then surely the incoming light could hit at a smaller angle and still undergo TIR, if the critical angle is higher then there is a smaller window for TIR?
  2. jcsd
  3. Jun 7, 2014 #2


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    Homework Helper

    For the critical angle between the glass core and the cladding material, sinθc=N(cladding)/N(glass). The sine function is monotonously increasing between 0 and π/2, so the cladding increases the critical angle with respect to no-cladding, when the sine of the critical angle would be 1/N(glass).
    The advantages of cladding are shown here http://www.schoolphysics.co.uk/age16-19/Optics/Refraction/text/Fibre_optics/index.html

  4. Jun 7, 2014 #3
    Math is logic. If you can do the math than you do understand the logic.
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