Wow! This stuff is REALLY cool. Thanks for posting!

Going to try this out. Always wanted to experiment with light modulation.
Even easier and safer with some fiber optic cable.

On Tuesday, 27 December 2011, RussellMc <apptechnz@gmail.com> wrote:
> Tidy format & related comments here
>
>
http://electronics.stackexchange.com/questions/24214/using-a-led-to-transmi=
t-data/24225#24225
>
> ___________________
>
> Untidy gist:
>
>
> >From Mark Rages Ronja reference
>
> [Through air optical coms page](http://www.modulatedlight.org/)
>
> It says:
>
>  - This page deals with long-distance atmospheric (through-the-air)
> optical ("lightbeam") communications of various types using coherent
> and noncoherent light sources, methods of mitigating atmospheric
> effects on such communications, as well as various technologies
> involved in transmitting and receiving such communications.  The
> majority of the content on these pages is produced by self-funded
> hobbyists that have taken on the challenge of furthering the state of
> the art in this somewhat arcane field.)
>
> [More on same](
http://www.modulatedlight.org/optical_comms/optical_index.html)
> same people
>
> [Ronja](http://ronja.twibright.com/)
>
> They say:
>
>  - Ronja is a free technology project for reliable optical data links
> with a current range of 1.4km and a communication speed of 10Mbps full
> duplex.
>
>  Applications of this wireless networking device include backbone of
> free, public, and community networks, individual and corporate
> Internet connectivity, and also home and building security. High
> reliability and availability linking is possible in combination with
> WiFi devices. The Twibright Ronja datalink can network neighbouring
> houses with cross-street ethernet access, solve the last mile problem
> for ISP=92s, or provide a link layer for fast neighbourhood mesh
> networks.
>
> _______________________
>
> Well worth a look:
>
> [This August 2009 "letter" shows how fast you can push a slow white LED
!!!]
>
>              (
http://northumbria.openrepository.com/northumbria/bitstream/10145/119149/2/=
Le%2520Minh%2520et%2520al%2520-%2520100-Mbs%2520NRZ%2520visible%2520light%2=
520communications%2520using%2520a%2520postequalized%2520white%2520LED%2520-=
%2520article.pdf
).
>
>  They use a white LED with phosphor response in the few MHz range,
> filter out the slow yellow component and  equalise, to get 50 MHz
> modulation bandwidth, which allows on/off NRZ at 100 Mb/s.
>
>  They note that the achieved 50 Mb/s is 25x the unequalised unfiltered
> bandwidth.
>
> I'd wonder, why not use a blue LED without phosphor?
>
>
> ________________
>
> [This abstract]
>
>            (
http://ieeexplore.ieee.org/Xplore/login.jsp?url=3Dhttp%3A%2F%2Fieeexplore.i=
eee.org%2Fiel5%2F3%2F23011%2F01070555.pdf%3Farnumber%3D1070555&authDecision=
=3D-203
)
>
> notes that InGaAsP LEDS are good for 300 Mbps at full power if you
> talk to them nicely (reverse bias off pulsing to sweep charge out
> faster) and 200 Mbps if you drive with non reverse bias.
>
>  They say:
>
>  - The application of reverse bias pulses at on-off transitions
> increased the maximum bit rate of full power operation of long
> wavelength InGaAsP LED's from 200 to 300 Mbits/s by reduction of the
> stored charge fall time.
>
>  Although designed primarily for nonreturn to zero (NRZ) DS-4
> experiments, the circuitry operates from 50 to 300 Mbits/s for the
> return to zero (RZ) or NRZ format with fixed or pseudo-random word
> patterns.
>
> ______________
>
> Here is
> [a useful but compact answer to "How fast is an LED"]
>
>           (http://www.eng.yale.edu/posters150/pdf/woodall2.pdf) and
> it is worth noting that they say 'about 2 GHz modulation bandwidth or
> about 1 Gb/s' compared to the  300 Mb/s above. Note that for
> engineering purposes 300 ~~~=3D 1000 :-)
>
>
> __________________
>
>
>  [1]: http://i.stack.imgur.com/ZPCTC.jpg
>
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