

Photophone - SteveGregory
http://en.wikipedia.org/wiki/Photophone

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sambeau
When I was a kid I had a a kit for doing this.

This also the principal behind spying on someone in a room by watching the
wobble of reflected light on a window.

~~~
fit2rule
I also had this as a kit when I was a kid - it was one of the experiments one
could perform with the home-built laser I constructed. I built the receiver,
gave it to my little sister, and off she went over the dunes .. we confirmed
the experiment, and she subsequently lost the receiver in the dunes. Always
wished I'd been the one to go out that day ..

There was another experiment where you could shine the laser on a window, and
pick up its reflection and using that, listen in on the room. It required a
more complicated circuit to be built, so I never did it, but its fascinating
that such technologies were, in the 70's and 80's, available to inquiring
teenage minds.

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quinndupont
Great example in the long, varied history of communication devices going back
to the ancients, but really picking up speed in the Renaissance. For more
example of interesting optical communication devices I recommend Deep Time of
the Media by Zielinski (it includes lots of pictures
too!):[http://mitpress.mit.edu/books/deep-time-
media](http://mitpress.mit.edu/books/deep-time-media)

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eeZi
A few groups of HAM Radio operators have been experimenting with what they
call terahertz communication for quite some time now.

The transceivers got pretty sophisticated, with very complex optics. There are
reports of successful conversations over distances of >150km.

Apparently, many of them are in Germany so quite a few of the sources are in
German.

[http://modulatedlight.org/optical_comms/optical_index.html](http://modulatedlight.org/optical_comms/optical_index.html)

[http://www.db6nt.de/laser.html](http://www.db6nt.de/laser.html)

[http://modulatedlight.org/optical_comms/SDIM8379h.jpg](http://modulatedlight.org/optical_comms/SDIM8379h.jpg)

[http://www.dd1wks.de/laser.html](http://www.dd1wks.de/laser.html)

[http://www.dl2dr.de/6.html](http://www.dl2dr.de/6.html)

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pmcjones
In 1972, Gary Starkweather (inventor of the laser printer) rigged up a laser-
based data link with 35 megapixels/second bandwidth because Xerox Parc was
split across two buildings: one with the controller and one with the marking
engine for his printer. See page 42 of
[http://www.computerhistory.org/collections/catalog/102702465](http://www.computerhistory.org/collections/catalog/102702465)
.

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kylebrown
Bell invented this too?! Was this before or after the telephone?

