Lasers?
So if you shot your laser pistol into the lense of the Magesight cable it will come out the other end and still be focused enough to do damage?
Might blind the mage but I'm not so sure it would be powerful enough to do any real damage.
Of course, blinding is the point so I'm down with it.
Who the hell carries a laser gun around though?
Thinking too big! (But cool IF you pack a laser weapon

)
Laser projection site

That little red dotty thing? shine it right down the fiber optic cable... and right into the eyeball of the mage! Now he is not casting any spells for a few minutes to hours! (or, if you have a Redline pistol, EVER!
Signal degradation in FO is tiny. I mean so little it is only possible to tell with math! (our current photo sensors can not tell a difference in the beam strength over 500km! Considering signal strength drop in copper wire can be measured after a single meter, FO is a much better medium for process control and signal transmission then any other medium we currently have, after you factor in all other considerations.)
But, currently it's options for use are limited as FO can not transmit power (electricity). So it's great when you need to feed or send a signal between two powered points... but if you are "daisy chaining" the system so that both power and signal are carried by the same line, then Multiple Paired Copper wire is the best.
Cost is an other factor. Currently the costs of FO are pretty high, but Copper is high as well... If copper goes up an other $1 or so, then, maybe engineers will start using FO more.
Some things to consider:
FO is not as flexible as copper. It can shatter if lateral (twisting) stress is put on it. Does not handle rapid, sudden, extreme temperature changes. Conducts heat extremely well. Is (industrially speaking) fragile and must be supported and protected.