Someone, I think it may have been Richard, once mentioned a form of
distortion that was due, I think, to the modulation itself.

tom
K0TAR

On Fri, 23 Feb 2007 22:55:09 -0600, Tom Ring
wrote:


Someone, I think it may have been Richard, once mentioned a form of
distortion that was due, I think, to the modulation itself.

Hi Tom,

There are several, some that are way out in the decimals but separable
(Raman scattering). Others like Solitons (a rather old observation)
are used to increase bandwidth in commercial links.

I hesitate to ask what the question is, because all of these effects
require some strain to achieve with very high power densities, often
in the megawatts to gigawatts. If you can find a suitably fast pulse
source, you might do it on a kitchen table. The hardest part of
getting a lot of optical power into a small fiber is overcoming
Numerical Aperture mismatch (sound familiar once you discard the NA?).
Some sources take this in stride (notably semiconductor lasers), while
others (like the sun) are stunningly inefficient.

I had a buddy who built a CO2 UV laser from a Scientific American
Amateur Scientist column. It packed quite a punch for all of five to
ten nanoseconds (capacitor arc discharge from a cap of several hundred
picofarads charged to twenty thousand volts using a very low
inductance lead design). He chose to be careful by aiming it out the
window into the sky. He fired the laser and cracked the window. The
thermal expansion of the glass was sufficiently slow enough to
accumulate enough stress (due to the attenuation) to create a
fracture. Classic thermal runaway.

The design comes from the June, 1974 issue (available from Wes'
introduction of Dr. Shawn here some months ago). The lead paragraph
says it all:
"A RECENTLY DEVELOPED LASER that operates on a six-volt dry
battery emits 10 pulses of ultraviolet radiation per minute, each
pulse about the size and shape of a broomstick. The pulses range
in power from 50 to 100 kilowatts."
....
"The ultraviolet laser can readily be scaled to higher powers. A
discharge path one meter long can develop an output pulse of
almost a million watts, although there is a trick to it."

I will leave the details of that trick to subscribers of Dr. Shawn to
investigate further - if push comes to shove, email me for a copy of
the details.

One thought occurred, this device (augmented to one meter length)
could suitably test the illusion of the anti-glare coating hypothesis.
Free suntan lotion will be supplied to those who rely on faith and
half baked mathematics to prove all reflections are canceled. :-O

Hi Wes,

Thanx again for introducing Dr. Shawn here. I had been looking for a
complete collection of Scientific American construction articles for a
very long time.

73's
Richard Clark, KB7QHC

Richard Clark wrote:

On Fri, 23 Feb 2007 22:55:09 -0600, Tom Ring
wrote:


Someone, I think it may have been Richard, once mentioned a form of
distortion that was due, I think, to the modulation itself.


Hi Tom,

There are several, some that are way out in the decimals but separable
(Raman scattering). Others like Solitons (a rather old observation)
are used to increase bandwidth in commercial links.

I hesitate to ask what the question is, because all of these effects
require some strain to achieve with very high power densities, often
in the megawatts to gigawatts. If you can find a suitably fast pulse
source, you might do it on a kitchen table. The hardest part of
getting a lot of optical power into a small fiber is overcoming
Numerical Aperture mismatch (sound familiar once you discard the NA?).
Some sources take this in stride (notably semiconductor lasers), while
others (like the sun) are stunningly inefficient.
snip

73's
Richard Clark, KB7QHC

This came up last night while we were putting racks together for a new
data center. Someone mentioned that it was theoretically possible to
put an infinite amount of information through a fiber because you could
have an infinite number of carriers even though the total available
frequency response was finite. I declined to argue with him, because he
is always right, even when he's not. That reminded me of something I
thought you mentioned months ago. You either named the effect, or gave
a link to an article about it.

And NA mismatch doesn't ring any bells.

thanks,
tom
K0TAR

On Sat, 24 Feb 2007 10:04:15 -0600, Tom Ring
wrote:

This came up last night while we were putting racks together for a new
data center. Someone mentioned that it was theoretically possible to
put an infinite amount of information through a fiber because you could
have an infinite number of carriers even though the total available
frequency response was finite.

Hi Tom,

His argument fails on the face of it. If something is finite, that
about ends the discussion. Your workmate is confusing his sense of
being unable to encompass a large number with the sense of infinity.

Given there are an infinite number of infinities, you could argue that
perhaps he is talking about one of the smaller, less significant ones.

That reminded me of something I
thought you mentioned months ago. You either named the effect, or gave
a link to an article about it.

It seems that google has changed their search engine and dumbed it
down significantly. I don't recall the discussion except in the most
general terms and searching for it was frustrating. Maybe the thought
will emerge later.

All I can offer that brings us back to 'tronics (and peripherally to
'tennas) is that to fit enough bits into the information content, they
need to be have a certain rise time (very small of course). Rise time
and bandwidth are inextricably related by a factor of about 3. An
infinite amount of information would thus require 3X infinite
bandwidth (see what I mean about infinities?). We encounter the same
limitation in listening to code. When CW is sent at a certain rate,
it defines the receive bandwidth necessary to recover the information.
And NA mismatch doesn't ring any bells.

As it shouldn't, it is a side topic but relatable to fiber
transmission. I struggled for years trying to get 5 joules of light
energy into a 1mm fiber. I was probably 5% efficient at best and
researching the topic didn't offer the prospects of my expecting much
better. That is why I find impedance matching debates here so amusing
when so much of was just armchair experience.

73's
Richard Clark, KB7QHC

Tom Ring wrote in news:45e06207$0$17199$39cecf19
@news.twtelecom.net:

....
This came up last night while we were putting racks together for a new
data center. Someone mentioned that it was theoretically possible to
put an infinite amount of information through a fiber because you could
have an infinite number of carriers even though the total available
frequency response was finite. I declined to argue with him, because
he
is always right, even when he's not. That reminded me of something I
....

Tom,

Perhaps you could explain to him that since he makes the assumption that
the width of a carrier (a single frequency) is zero and that therefore an
infinite number could fit within a finite bandwidth, he has overlooked
the use of more common media (eg phone lines) to carry an "infinite
amount of information" by this magical technique.

Don't disabuse him of his concept that a signal of zero bandwidth can
carry information at any rate above zero. He might even seek to patent
the method!

Such misconceptions are not unusual amongs IT experts who's education
started and ended with MS certification.

Owen

On Fri, 23 Feb 2007 22:55:09 -0600, Tom Ring
wrote:


Someone, I think it may have been Richard, once mentioned a form of
distortion that was due, I think, to the modulation itself.

Hi Tom,

In unrelated research for a forum I am doing for the Foreign Policy
Association's Global Decisions, I ran across an article that may bear
on your workmate's discussion.

Reference: "The Ultimate White Light," Robert R. Alfano, Scientific
American, Dec. 2006.

The piece is about "supercontinuum light" that exhibits self-phase
modulation when the fiber is forced into nonlinear behavior with
sufficiently high power densities (hence my sidebar discussion in
another posting). The boon here is that this laser replaces 100
parallel lasers (of differing wavelengths) while maintaining coherence
across its spectrum. This increases the data capacity to transmission
rates of petabits. Even compared to today's gigabits, this is still a
very long way from infinite, however.

73's
Richard Clark, KB7QHC

I had a buddy who built a CO2 UV laser from a Scientific American
Amateur Scientist column. It packed quite a punch for all of five to
ten nanoseconds (capacitor arc discharge from a cap of several hundred
picofarads charged to twenty thousand volts using a very low
inductance lead design). He chose to be careful by aiming it out the
window into the sky.

by carfull you mean he made sure no planes or satalites birdies etc
were in his 'aimed' path??




He fired the laser and cracked the window. The
thermal expansion of the glass was sufficiently slow enough to
accumulate enough stress (due to the attenuation) to create a
fracture. Classic thermal runaway.