[Phys-L] Re: Travel distance in a waveguide.

[Bernard Cleyet <anngeorg@PACBELL.NET>]

I would think so.

Again I use the easier to visualize X band example.  The group speed in
a std. evacuated X band wave guide will have a particular value (for a
given "free space" wave length).  Fill the guide w/ wax and the group
speed will be further reduced.  A fun? experiment would be to determine
the N of the wax (most accurate would, I guess, be to use an
interferometer *) and predict the resultant wave guide wax combo.

* Strong's Optics text shows how to do this, if I remember correctly.

bc

p.s. I have worried about how accurate a cavity measurement of N is,
because I think it might be like a wave guide.  Similarly I was about to
check the gross accuracy of an absorption wave meter using a slotted
wave guide and then I realized tit wouldn't do directly.

Edmiston, Mike wrote:

> Let's see how the following two points sound... plus another question at
> 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
cut

> 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