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'[OT]: About smart dust and more'
2002\07\06@154221 by Peter L. Peres

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Another link I found today (must read):

http://zapport.eecs.berkeley.edu/~salt./mfv/publications/salt_12feb00.pdf

Notice the date.

Peter

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2002\07\06@195132 by Jinx

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Pretty nifty

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2002\07\08@192525 by Brendan Moran

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The whole MAV thing combined with this, though it seems to be for
applications like weather stations, makes me paranoid.  I fear for the well
being of privacy.  They noted that 1Mbps is plenty for transferring
real-time video with modest compression that can be done in hardware.

It looks to me like James Bond's newest surveillance toy.

Aside from that, très cool.  Check out fsona for something similar, though a
different applicaion and higher data rates.

http://www.fsona.com/

They're designing golden mile comm applications

golden mile for those who don't know is the last mile distance between the
fibre-optic backbone of a network and the businesses wanting connections.
Typically, this is the most expensive portion of the entire connection (if
you have to rip up a street to put in your fibre connection, you know that
you'll be paying through the nose for it)

Fsona's tech is based on laser comm similar but much more powerful than that
depicted in the article listed by Peter (though as I said before, it is for
a different purpose) and it provides quite reliable (can be interrupted by
the occasional bird for a few ms) connections.

I think it's a great idea.  Cheap installation (in $/Gbps terms).  Cheap
maitainance compared to other techs of similar BW.  Looks good to me.

{Original Message removed}

2002\07\09@140219 by Peter L. Peres

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Of course the golden mile is important, especially if you can DIY and if
you can skip the backbone altogether ;-). Look for a DIY point to point
10MBps optical link from Czechia called metropolis. URL:

http://atrey.karlin.mff.cuni.cz/~clock/twibright/ronja/

Peter

PS: I'd like to hear of places where students/techies/geeks formed
point-to-point networks like this, not unlike UUCP nets used to be. Know
any ?

On Mon, 8 Jul 2002, Brendan Moran wrote:

{Quote hidden}

>{Original Message removed}

2002\07\09@142327 by Brendan Moran

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> Of course the golden mile is important, especially if you can DIY and if
> you can skip the backbone altogether ;-). Look for a DIY point to point
> 10MBps optical link from Czechia called metropolis. URL:
>

err... I had thought that several GBps was in a little bit of a different
class.  Anyways, anyone know how high a datarate you can get out of the LED
in a laser pointer?

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2002\07\09@151736 by Peter L. Peres

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On Tue, 9 Jul 2002, Brendan Moran wrote:

>> Of course the golden mile is important, especially if you can DIY and if
>> you can skip the backbone altogether ;-). Look for a DIY point to point
>> 10MBps optical link from Czechia called metropolis. URL:
>>
>
>err... I had thought that several GBps was in a little bit of a different
>class.  Anyways, anyone know how high a datarate you can get out of the LED
>in a laser pointer?

In theory, about c/(2*lambda) Hz (== Bauds in this case). In practice, as
much as you can drive the device to. Diodes for high data rates have
special design (like controlled impedance feeds and such). I once had a
book that showed how to interface a laser diode to a ham RF transmitter
for 432MHz. It consisted of an impedance matching network and a fast diode
or two, plus a very simple bias network that used a D cell I think. The Tx
ran 10-20W into the air cooled diode.

Peter

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2002\07\09@154243 by Peter L. Peres

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On Tue, 9 Jul 2002, Peter L. Peres wrote:

>
>In theory, about c/(2*lambda) Hz (== Bauds in this case). In practice, as
>much as you can drive the device to. Diodes for high data rates have
>special design (like controlled impedance feeds and such). I once had a
>book that showed how to interface a laser diode to a ham RF transmitter
>for 432MHz. It consisted of an impedance matching network and a fast diode
>or two, plus a very simple bias network that used a D cell I think. The Tx
>ran 10-20W into the air cooled diode.

The actual limit is lower than I implied, the modulation is deteriorated
by the decay time of the intermediary laser levels (the non-lasing
transitions). However frequency-modulated lasers apparently do not have
this limit ?

Peter

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2002\07\09@201215 by Dave Tweed

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On Tue, 9 Jul 2002, Peter L. Peres wrote:
> In theory, about c/(2*lambda) Hz (== Bauds in this case). In practice, as
> much as you can drive the device to. Diodes for high data rates have
> special design (like controlled impedance feeds and such). I once had a
> book that showed how to interface a laser diode to a ham RF transmitter
> for 432MHz. It consisted of an impedance matching network and a fast diode
> or two, plus a very simple bias network that used a D cell I think. The Tx
> ran 10-20W into the air cooled diode.

and later added:
> The actual limit is lower than I implied, the modulation is deteriorated
> by the decay time of the intermediary laser levels (the non-lasing
> transitions). However frequency-modulated lasers apparently do not have
> this limit ?

I thought really high data rates used external (electro-acoustic?)
modulators.

-- Dave Tweed

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2002\07\10@025520 by Michael Rigby-Jones

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{Quote hidden}

They do mostly.  You can achive 10Gbps through a direct modulated laser, but
chirp really limits your link length due to dispersion.  For lower
dispersion, EA (Electro-Absorbtion) and MZ (Mach-Zender) modulators are used
with a CW laser source.  At 40Gbps it's pretty much mandatory have have an
external modulator.  Interestingly both of these external modulators can be
configured to give negative chirp, so that performance over a long length of
fibre can actualy be better than a short length.

Frequency modulated lasers have been under a good deal of research.  There
are several benefits, but one big negative which is the increased complexity
of the receiver.

Regards

Mike

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