[Laser] ~OT: High-power polarized light?

[Glenn Thomas]

James -

An interesting idea, though I'm not sure of exactly what it is you are 
suggesting. Is it something along the lines of BPSK? (with P == 
Polarity) At least you would have to deal with polarity noise while 
limiting out amplitude distortion. Is polarity distortion easier to deal 
with than amplitude distortions?

Interesting idea. I have no idea if atmospheric refractive cells would 
distort the polarity. Or, perhaps smog provides some polarization 
distortion on urban paths due to optical isomeres in the air? 
Interesting thought. Perhaps this is a way we can all quantitatively 
measure the hydrocarbon content of the atmosphere. More polarity 
distortion of a linearly polarized signal means more hydrocarbons along 
the path. I'm not sure if that distortion would take the form of 
polarization shift or polarization dispersion. Perhaps there is room for 
research here.

Or... are there are two different channels in spatial polarity (not 
phase) quadrature, each independently modulated, presumably with some 
form of amplitude modulation? I'm not sure how this is better than 
simply using two different wavelength emitters on the same path. I'm 
guessing that wavelength distortion is far less significant than 
polarity distortion on terrestrial paths. Of course, dual - or even 'n' 
- channels can easily be done with just one emitter and a TDM modulating 
signal of some sort.

Still, optical angle modulation (polarity, not phase) sounds like an 
interesting concept.

73 de Glenn wb6w

On 3/8/2011 3:39 PM, n5gui at cox.net wrote:
> I do not know if it has been done.  Perhaps there are others on the list that have heard of such.
>
> Years ago, I put up a post suggesting that it could be done.  I do not know of any benefit, just that it is a way to impress information on a light beam.
>
> A very simple system would be to shift polarization by 90 degrees at the transmitter.  On receive, split the beam into two paths, each going through a polarizing filter so that one peaks on each of the transmitted segments.  Assuming there are no path related polarization effects, the beam would appear a non-polarized sensor to have the same intensity regardless of the information transmitted.  The intensity might fluxuate due to other effects.  Perhaps this could be used to compensate for "twinkle", or at a minimum mark un-reliable signals.  Said another way, the two polarization paths should compliment each other.  Where they have the same state, then the data is corrupt.
>
> Another way to use two differing polarized paths is to sent two data streams:  different data, compressed data, or redundancy.
>
> Might be interesting to tinker with.
>
> James
>   n5gui