[hansc]

This is the case in Multimode fiber, which is used for short distances (meters). For anything longer, single mode fiber is used and the core of the fiber guides the light. See https://garyherlache.wikispaces.com/Digital+Communications+F...

[amazon_not]

Single mode fiber isn't immune to dispersion or other impairments, it just does better than multimode.

[gsnedders]

That looks like single mode fiber never refracts… Surely it can't go round any bend, then, though? (And I'm probably missing something obvious. It's been a while since I've done optics of any sort.)

[amazon_not]

> That looks like single mode fiber never refracts…

No, it does.

> Surely it can't go round any bend, then, though?

No, if you bend the fiber too much the light leaks out into the cladding.

[rocqua]

I believe the fiber acts as a waveguide, essentially keeping the wavefront perpendicular to the fiber at all times.