Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Ok, so, my simplified understanding of fiber optics is that light is sent down the cable and it rebounds off the sides to end up at its destination. Which got me thinking, if it has to bounce more times (and having a shorter travel between each bounce), does the light (data) take longer to get to the other end of the cable? Like this:

A part of me is saying no, because it's still the same distance to travel and bouncing doesn't take up any time, but another part of me is saying yes because the light will have further to travel the more times it bounces, and thus will take longer to get to its destination. I'm swaying towards it taking more time.


share|cite|improve this question
The polarization certainly changes, but the time of travel does not. You have to think in terms of fields and not billiard balls bouncing around. Changing the length of the fiber will certainly change the time of arrival/detection. – Antillar Maximus Feb 23 '12 at 19:47

That picture is only really true for lightguide type large plastic fibres. For single mode fibre used in communication the wave is essentially directly down the centre

share|cite|improve this answer
This distinction (between light guides and single mode fibers) is lost in pop-sci discussions of how fiber optics work, but is worth understanding if you are going to do serious work with fiber. – dmckee Jul 26 '12 at 14:42

One of the main reasons fiber optics is a great engineering tool to distribute light is because virtually all of the light is internally reflected. Meaning there is very little light lost from transmission out of the cylinder. The main reason for this is because firber optics cables are small.

Larger optical fibers cause more losses to transmission because the incident angle is closer to the normal of the surface. We all know optical fibers are essentially completely transparent (unlike standard glass), so this also means that if the strand is considered infinitely long in relation to it's radius, the only light that won't be lost will be considered parallel to the cylinder axis.

So because optical fibers have a small radius and are "infinitely long", the light traveling inside is considered parallel to the cylinder axis. And since bending a strand doesn't change the strand's length, there is no effect on the time.

If, however, the radius of the strand isn't negligible in relation to it's length, all hypothesis fail and the light travel time may vary. However, in such a case, bending the strand isn't a trivial matter. I believe the strand would likely break before light travel distance varies enough to even consider taking it into account.

share|cite|improve this answer
A great answer, is there a way we can calculate the minimum length of a fibre that would be affected? – jwbensley Nov 18 '12 at 21:33

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.