I see, perhaps we are at cross purposes then. Of course individual photons will go different routes.Originally Posted by MartinT
But although the fibre may be carrying millions of bits per second, nevertheless each bit - each optical "high" state - comprises billions of photons, for which the average paths have been the same.
It's a bit like the old two slit diffraction experiment where you turn the laser intensity down to single photons at a time. You can never be sure where any individual photon will go, but you know what the aggregate picture will look like, averaged over billions of photons. You will always get the same pattern.
Same thing in the toslink example. Each "bit" of information coming down the fibre will be identical in terms of the smearing that has occurred. Each will be compromised of billions of photons that have all gone different routes, but on average the make up of each bit is the same.
That is why you don't get any jitter in the fibre per se.
However, to a certain extent, I am arguing over semantics. The smearing of the waveform *does* cause the receiver to induce jitter because for each packet it has to do it's best to work out when exactly the transition from 1 to 0 or 0 to 1 is supposed to have occurred... and the cheap Toslink receivers (they only cost a few cents each) do a pretty bad job of it.
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