On 17 Apr 2007 08:30:41 -0700, K7ITM wrote:
On Apr 17, 12:33 am, Richard Clark wrote:
On 16 Apr 2007 17:50:10 -0700, "K7ITM" wrote:
...
I still
don't have a reference that a fiber optic cable is a TEM transmission
line, though I have others that say that it's not.
That example of the non-TEM fiber optic would be rare species indeed.
I've seen them, but that hardly constitutes the sole species of the
breed.
So give me a reference already. I find lots of references, including
ones that explain the propagation, that talk about TM, TE, hybrid, and
even quasi-TEM mode propagation in a fiber. What boundary conditions
are there in an optical fiber that give TEM mode?
Hi Tom,
This is curious request indeed. Can you name any example of light
that is not TEM? Let's see, wikipedia's entry for TEM includes Fiber
Optics as example (along with the sources and illustrations for many
modes). TEM00 is the principle mode of the ubiquitous "single mode"
fiber optic that is laid in the millions of miles every year.
One vendor of Fiber modeling software
http://www.zemax.com
specifically at
http://www.zemax.com/kb/articles/154...MAX/Page1.html
offers:
"ZDC thanks Steve Dods of OptiWave Corporation for supplying the
SMF-28 fiber simulation data used in this article.
"In the article How to Model Coupling Between Single-Mode Fibers
SMF-28 single mode fiber is modeled using data from the
manufacturer's datasheet. The only data provided on the optical
radiation produced at 1.31 is the mode field diameter, which is
stated to be 9.2 ± 0.4 µm.
"As a result, the fiber mode of both launch and receiver fibers
was entered as a Gaussian (TEM0,0) mode of waist 4.6µ. The
resulting fiber coupling calculation agrees well with experimental
measurement."
Corning SMF-28 has been in production for nearly 20 years.
I still don't have
information on whether a soliton wave can propagate in a linear
medium, though I have references that say it is a non-linear
phenomenon that occurs in non-linear media.
Of course it can propagate in a linear medium. Solitons were first
reported in linear media - water - something like one hundred seventy
years ago.
Solitons can induce non-linearity in otherwise linear
media. Solitons also interact in collision with a phase shift
afterwards. Solitons have been applied to data transmission in fiber
optics for a dozen years or more.
Your references are pretty sparse.
Yours seem non-existent. Mine at least did a good job explaining the
phenomena.
To which there is scant difference as nearly every point you recite
has already been anticipated in my earlier post (shown above). Your
rebuttal that water is non-linear is already answered in this same
quote. If this is basenote drift, we are now into the treble clef.
If you can convince me
that a wavefront coming to a Magic T doesn't see it as an impedance
discontinuity, we could perhaps post more about that--or not.
Consult Terman. He is quite compelling when it comes to describing
microwave plumbing. This hardly constitutes more than 4 pages total
reading, if you choose to move on beyond the first page of discussion.
I find nothing in the index of my "Radio Engineers' Handbook" by
Terman under either "Magic" or "Hybrid". Sorry. The three different
coaxial "Magic T" hybrid designs I DID find all do show an impedance
discontinuity: the junction of more than two lines of equal impedance
and/or impedance steps in through-lines. Sorry.
Time to move on.
For others that are not moving on, but interested in the use and
issues of reflection to the source driving a Magic T, I quote work
from Q MEASUREMENTS FOR HIGH-Q CAVITIES
R. A. RAPUANO and J. HALPERN, MIT (1946):
"The heart of this equipment is the "magic T". This is an
eight-terminal network (Fig. 3) in waveguide or coax having
symmetry properties analogous to those of a "hybrid coil".
In the case of an ideal T, power entering the E aria is divided
equally between S1 and S2, both parts being out of phase; none
goes directly to H. Power entering the H arm is divided equally
between S1 and S2, with both parts now in phase; no power goes
directly to E. Power reflected from the loads on S1 and S2,
however, can be coupled from H to E, depending upon the magnitude
and phase of the terminal impedances on S1 and S In the case of
two short circuits the power going from H to E can be caused to
vary from zero to the full amount depending on their position
along the line. If a short circuit is placed on S1 and a resonant
cavity is placed on S2, then the power going from H to E is a
function of frequency. The power reflected back from H is the
difference between the input and the loss due to transmission
through E and absorption in the resonator."
Figure 3 (use fixed font):
S1
||
||
||
H ======== ======== E
||
||
||
S2
where the interior blank space represents the plumbing too difficult
to render here.
I would further offer that Walt is working on a fairly similar
treatment employing the "Rat Race" (alluded to as a Hybrid Coil in the
monograph extract above). The discussion above is germane in that
sense and would be beneficial to those who eventually see his
rebuttals to arguments pressed against him.
73's
Richard Clark, KB7QHC