I've been reading the "waveguide" thread with interest but confusion. We
also have the "Speed of light in a fiber" apparatus described in the
original post. I'm pretty waveguide-ignorant, so maybe I'm about to
"put my foot in it," but...
How can it be that a fiber optic cable "works like a wave guide"? My
impression was that a defining characteristic of waveguides is that
their transverse dimensions are comparable to the wavelength. The web
page reference given by Bob S. at microwaves101.com seems to confirm
this for microwaves. John D.'s statement that "A wave ... is slowed by
the fact that the wavefunction is scrunched in the lateral directions"
encourages me that maybe I understand this correctly.
The apparatus that we have has a single-fiber cable, the fiber being
maybe 0.75mm in diameter (I don't have it handy to measure exactly).
I'm sure that the light source is probably not visible but it probably
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!
I'm also a bit confused by the fact that microwave waveguides are made
of conducting materials. I gather that the wall conductivity is what
determines the transmission power loss. Fiber optics obviously don't
involve conductors. Of course, both involve solutions of Maxwell's
equations under zero-field boundary conditions. But is the difference
in the reason for those boundary conditions really totally unimportant?
--
Dr. James McLean phone: (585) 245-5897
Dept. of Physics and Astronomy FAX: (585) 245-5288
SUNY Geneseo email: mclean@geneseo.edu
1 College Circle web: http://www.geneseo.edu/~mclean
Geneseo, NY 14454-1401