1) In a "step-index" fiber, the wave number B in the resultant wave
E(r)=f(r)exp(i(Bz-wt)) is constrained to:
(n2)k = k2<= B<=k1=(n1)k, where
k is the vacuum wave number, n2 is the clad index and n1 is the core index.
Thus the fiber phase velocity always "lies" between the bulk phase
velocities v1 and v2 (n1 and n2 typically vary by less than a few percent).
2) In a typical graded index fiber, where n(r) goes, via a power law in
(r), from a value n1(at r=0) to a final (cladding) value n2, B => n2.
3) In both cases, the product of the phase and group velocities = c^2.
Bob Sciamanda
Physics, Edinboro Univ of PA (Em) http://www.winbeam.com/~trebor/
trebor@winbeam.com
----- Original Message -----
From: "Edmiston, Mike" <edmiston@BLUFFTON.EDU>
To: <PHYS-L@LISTS.NAU.EDU>
Sent: Monday, February 14, 2005 9:59 AM
Subject: Re: Travel distance in a waveguide.
| . . .
| 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)?
| . . .|
| Michael D. Edmiston, Ph.D.
| Professor of Chemistry and Physics
| Bluffton University
| Bluffton, OH 45817
| (419)-358-3270
| edmiston@bluffton.edu
|
|