1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Fibre Optics - Dispersion

  1. Jan 15, 2008 #1
    I'm confused as to sources of dispersion in a fibre. Any clarification would be appreciated.

    Modal (Intermodal) dispersion: pulse spreading due to different group velocities of different modes in the fibre. Each mode has a slightly different n-effective hence the different Vg for each mode. Not present in single mode fibres, as there's only one mode. Can also be though of as different ray paths - light travelling down the centre of the fibre will reach the end before light which is TIR'ing its way along.

    Intramodal covers the following;

    Material Dispersion: Spectral width; each spectral component will in general travel with a different group velocity -> difference wavelengths travel at different speeds. Sources of spectral width: LED greater width than a laser, and sidebands caused by modulation.

    Waveguide dispersion: ?? changes in the distribution of light between core and cladding? Dependant on core diameter?


    So with Dispersion Shifted Fibres :- single mode fibre, therefore no modal dispersion. Waveguide dispersion is negative and material dispersion is positive -> therefore at a particular wavelength they cancel -> 0 dispersion. Wave guide dispersion can be shifted so that the 0 occurs at a different wavelength (1550nm)
     
    Last edited: Jan 15, 2008
  2. jcsd
  3. Jan 15, 2008 #2

    dlgoff

    User Avatar
    Science Advisor
    Gold Member

    www.cmste.uncc.edu/new/papers/Attenuation%20in%20Fiber%20Optics.doc
     
  4. Jan 15, 2008 #3

    berkeman

    User Avatar

    Staff: Mentor

    That's cool stuff. What part is confusing? What learning resources do you have available, and what have you read so far on the web?
     
  5. Jan 15, 2008 #4

    berkeman

    User Avatar

    Staff: Mentor

    Doh! dlgoff is quick today!
     
  6. Jan 15, 2008 #5
    dlgoff - Thanks, that link, along with going through the maths, has helped clarify waveguide dispersion.

    A great book on the subject is Ghatak, Ajoy and K., Thyagarajan. (2000). Introduction to Fibre Optics. Cambridge, UK : Cambridge University Press.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?