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Re: Asymmetrical Newton's Cradle



The purpose of the graded-index fiber, according to
Hecht (Optics, 3rd edition, page 202) is to reduce the
intermodal dispersion (from about 20 ns/km, for the
stepped-grade multimode fiber, to about 2 ns/km).
Fibers are most often used at single wavelengths,
for example, 1.3 microns. The intermodal dispersion
limits the speed at which pulses (zeros and ones in
the case of computers) can be transferred. It occurs
because light traveling along the near axis paths arrives
before the light traveling along the more zig-zag paths.

Single mode fibers (diameter around 10 wavelengths)
"esentially eliminate intramodal dispersion" writes
Hecht. What is then responsible for the upper limit of
the transmission speed in single mode fibers?
Ludwik Kowalski

On Saturday, Nov 8, 2003, at 08:17 US/Pacific, Brian Whatcott wrote:

At 12:50 PM 11/8/2003, Ludwik, you wrote:
On Saturday, Nov 8, 2003, Brian Whatcott wrote:

One next remembers that there is an alternative to a
quarter wave length of transmission line. This is a
device of specific length and impedance intermediate
between two line sections to be joined of greatly
different characteristic impedances.

One can instead, intersperse a length of gradually
changing impedance, which matches the preceding
and succeeding sections exactly. This has the great
advantage of being broad band, so that one is not
limited to a frequency where a quarter wave has a
fixed length.

Has this kind of approach been used to make a
"broad band" antireflection coating on a lens?

I am not familiar with examples of graded index
anti reflection coatings.
The graded index fiber light guide is ubiquitous.