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Let's see how the following two points sound... plus another question atcut
the end.
(1) If I measure the group delay of a light pulse through a fiber optic
cable, I can divide the cable length by the group delay to find the
However, in a step-index cable there is a single refractive index, so we
could have a hunk of that material for which we could determine the
refractive index by other means.
How would the group refractive index measured for a step-index fiber
optic cable compare to the refractive index measured for the bulk
material using a prism in a spectrometer or using a flat hunk of the
material in an Abbe refractometer (critical-angle technique)?
Bob Sciamanda implied that we can think of the refractive index measured
in a hunk of the material as a group refractive index because even in
the hunk of material we should think of the velocity as a group
velocity. But it seems to me this group refractive index will be
different than the group refractive measured for the same material in a
fiber optic cable because the geometry is different. (The group
velocity in a wave guide depends on the dimensions of the wave guide.)
Is this correct reasoning that the bulk refractive index and the fiber
optic group refractive index would be different?
Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu