[Laser] Re: fundmentals

[Art]

I'm not sure polarization is useful in free space, especially at 
medium and long ranges. I think the atmosphere destroys the 
polarization and shifts it wildly at random rates.

Perhaps it's more usable at shorter distances.

Maybe someone has tried this recently. There was a discussion on this 
list many years ago about polarization filters, but I don't have the 
full archive here.

Regards,

Art



At 02:37 AM 2/14/2007, you wrote:
>hi James and Glenn
>i just wanted to point out there IS another modulation
>other than AM or OOK for light beam carriers. Polarization.
>You can shift or rotate the polarization of any light beam,
>be it coherent or not. It would use the principle of the
>"polarizer-analyzer" setup:
>
>http://plc.cwru.edu/tutorial/enhanced/files/lc/light/light.htm
>
>One way you could do it would be:
>At the transmitter you shine the light beam through a
>polarizing filter. The filter is mounted so that it can be
>mechanically rotated to change the polarization of the beam
>through 360 degrees - actually spun via a motor at
>different rates to encode the message say.. Similar to the
>motor driven chopper modulations mentioned in here before.
>
>Then at the receiver, in front of the photodetector, you
>have a second polarizing filter that is stationary (the
>analyzer) to 'decode' the beam. In the end, the beam is
>converted into AM by the analyzer...(a nice smooth
>sinewave)
>at the frequency of the spinning filter of the transmitter.
>
>Maybe polarization modulation has an advantage over AM in
>some cases?? Good quality polarizers can nearly 100% the
>beam, although some light is lost and absorbed by the
>filter. Some filters are more efficient than others. While
>searching through my list archive I noticed James proposed
>some experiments with polarized light to see what effects
>it had on a channel a couple years ago. (see march 2005)
>
>There are also electronic ways to shift or rotate the
>polarization of a beam that could work at much faster
>speeds.
>
>
>
>
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