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Sorry for the long delay between postings...._______________________________________________
John S. Denker wrote:
On 02/26/05 02:56, James McLean wrote:Well, in that sense a hall of mirrors could be called a waveguide. I
How can it be that a fiber optic cable "works like a wave guide"?It's a waveguide in the sense that it guides the wave.
suppose that it is etymologically true, but at some point it stops being
a useful physical model. (Here I am referring to the "solve Maxwell's
Eq. with boundary conditions" model, as opposed to the "light ricochet"
Oh yeah, of course. Actually, I realized this about 48 hours after myThe apparatus that we have has a single-fiber cable, the fiber beingThat's core+cladding+protective jacket. The physically-
maybe 0.75mm in diameter (I don't have it handy to measure exactly).
relevant dimension is the core diameter, which is a
whooole lot smaller.
posting. Sadly, the equipment and manual for the apparatus provide no
information at all about these dimensions; not a very promising
reflection on the product...
Huh? Perhaps we have different ideas of what is "easily-observable"?I'm sure that the light source is probably not visible but it probablyAssuming what you've got is communication fiber, it's
is in the IR. So if the wavelength is 1 micron, we're in mode 1500 of
the waveguide? That doesn't sound very "scrunched" to me!
probably 1.06 micron light in a 50-micron core. OK,
that's not _very_ scrunched, but even for the 0,0 mode
there would be an easily-observable effect on the speed
of propagation (which is where this thread started).
According to Bernard Cleyet's equation, which you seem to have condoned,
v_g = c*sqrt[1- (free space wavelength/2*waveguide dimension)^2],
I get v_g = 0.999944c. For the fiber, I suppose that this would have to
be divided by the core material refractive index.
I suppose this difference could be measured by some techniques, it being
only 1 order of magnitude less important that the difference between
vacuum and air. But it is a level of accuracy well beyond the apparatus
Dr. James McLean phone: (585) 245-5897
Dept. of Physics and Astronomy FAX: (585) 245-5288
SUNY Geneseo email: email@example.com
1 College Circle web: http://www.geneseo.edu/~mclean
Geneseo, NY 14454-1401