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In article , (Stewart
Pinkerton) writes:

Um, you might care to note that nothing in what Steve correctly stated
suggests that over a typical 1 metre cable, there will be *any*
difference in whatever linkage is used.

I would agree that, at 1m, the difference between any medium would be slight
(if even measurable). I do agree that, if a bitstream arrives with no errors,
it certainly doesn't matter HOW it got there!

Oh, BTW, Steve is wrong in one respect. The light source has nothing
to do with the fibre. Monomode fibre (not 'single' mode) is just as
useful with visible light as with any other, and in actual fact glass
fibres are more commonly used with infrared emitters, which are of
*lower* frequency than visible light.

Not sure why you deny me "single mode" when this is all it is ever called here
in the US. Is this a Transatlantic thing? In the Belden fiber section of the
catalog it is all single mode and multimode. I have never seen "monomode"
although the stuff is the same, regardless of what you call it. And the
difference between "monomode" and multimode (and toslink beyond that) is
"numerical aperture", the size of the opening through which the light will
pass. Small aperture allows more coherent (aligned) waves. That is why "mono"
goes so much farther than "multi" and "multi" goes so much farther than
"toslink".

Single (mono) mode: 8 microns

Multimode: 50 microns / 62.5 microns

Toslink: 900 microns.

Sure, visible light will go through all of them, but the glass fibers have
wavelength (frequency) windows (850nm/1300nm for multimode, 1310nm/1550nm for
single/mono). I think you have me on the actual "wavelength". Yes, these
wavelengths (in nm = nanometers) are all infrared.

ultraviolet light is rapidly absorbed by glass. Quartz fibres are much
better for the higher UV frequencies, although such light sources are
seldom used in practice.

Unaware there even is UV fiber! Learn something every day!

In conclusion...

Is there a difference between glass fiber and plastic fiber? Sure.

Could it be mesaured? Sure.

Is it big enough to make a difference in a bitstream. Probably not at 1m, but
certainly at longer distances, 10m, 20m, I would bet money you could see the
difference in an eye pattern or BERT (bit error rate tester).

Fair enough?

Steve Lampen
Belden Electronics Division