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Optical dispersion (was tor[sion])



Brian wrote:

Dispersion has been a problem in long range communication
with laser excited optical fibers. The Fourier analysis shows
why a narrow pulse has a stretched line width - to steal a
concept from another thread on the list.

One wishes to provide a high data rate, and a light pulse
washes out before too long unless measures are taken to
reduce dispersion. One way has been the graded fiber which
refracts peripheral rays towards the axis in a time locked fashion.

But I find the distributed optical amplifiers exciting, in that
the need for extraordinary measures to reduce dispersion
can be avoided by regenerating the pulse train.

This evokes vivid memories of the relay repeaters provided
for early telegraphs - of which so many were needed ...

It also evokes achromatic lenses in which inventivness was
used to overcome limitations imposed by optical dispersion.
Two dispersions nearly cancelling each other.