1. Limited time only! Sign up for a free 30min personal 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!

Collimating light from Optical fibre problem

  1. Apr 11, 2012 #1
    1. The problem statement, all variables and given/known data

    A thin lens of focal length f is used to collimate the light emerging from two different optical fibres.
    When used with a first fibre of small core diameter and numerical aperture NA it acheives a diffraction limited divergence of θ1 for the collumated beam. Find the separation u between the lens and the fibre that provides the best collimation. Find θ1 and the diameter D of the collumated beam immediately behind the lens.

    When used with a second fibre of a large core diameter d but the same numerical aperture, the beam diverges much faster than it did using the first fibre. Calculate this larger divergence angle 2 as a function of f and d


    2. Relevant equations

    NA = sin(θ1)

    1/u+1/v=1/f

    3. The attempt at a solution

    I am not entirely sure how to approach this problem as it is not a point source. I would like to say that:

    for best collimation u = f -- from lens equation
    and then

    D=f tan(θ1) ≈ fθ1 ≈ f NA -- from trigonometry

    however I am not sure if this is correct. Any hints on how to approach this question would be greatly appreciated. Many thanks
     
  2. jcsd
  3. Apr 11, 2012 #2
    wow, so difficult to me!!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Collimating light from Optical fibre problem
  1. Optics and light (Replies: 6)

  2. Optics Problems (Replies: 2)

  3. Optics Problems (Replies: 1)

Loading...