[Ronja] What about using a polarizer?

[Gyurkó Martin]

Hi!

Actually I already thought about that a year ago and also made some 
experiments. See the archive.
The 100MBit/s are actually 125MBit/s.
The MLT3 coding on the ethernet cable makes a maximal modulating 
frequency of 31.25MHz. What is more important: 8ns Rise and fall time 
for the LED. So the transmitter could be easy, directly modulating the 
voltage of the ethernet cable onto the light.

I did not have time to create a reasonable receiver.
The only thing i was measuring the sent signal was a photodiode serially 
connected to a small ohm resistor.
Maybe it is more complicated than we think.

Also with LED and polarizer you are wasting lots of energy.
Would be more efficient to use Laser Diodes. But those are hazardous.

I actually tried LD-s. Watching the perfectly collimated red beam of a 
DVD reader pickup in a distance of 900m was very interesting. It got 
around 30cm wide, with starting beam of 0.4cm.
The light was very bright, although it was only 0.5mW of power (estimated).
BUT!. The air made it speckle a lot. Speckle interferences would destroy 
the whole transmission to a crap.
So I stopped the experiments with lasers,  and never got time for LED 
transission.

hmmm. When using polarized laser ligt, you could use 1 tube to send AND 
receive. No more aligning problems.

bye,
Martin



Kilian Kiekenap írta:
> Hello,
> 
> I often thought about how to make Ronja 100mbit. I think the main problem is 
> to get the nrz-code over the optical link. So I thought it would perhaps be 
> possible to use two transmitters with different polarization and two 
> receivers which can receive them independently. So you could get four 
> different symbols.
> 
> Just a thought...
> 
> Kilian
>