[Laser] Polarization Subtraction

[Tim Toast]

Hi All,
Here's an article in Laser Focus World about a simple 
polarisation "trick" that brings out hidden detail in images.

http://www.laserfocusworld.com/articles/print/volume-48/issue-10/world-news/novel-cameras-polarization-difference-imaging-camera-reveals-unseen-features.html
or
http://tinyurl.com/9ga4n4j

In the example image on the website, you can see how well 
it cuts through fog to show the mountains in the distance. 

In a play on dual receivers or diversity reception, I think 
this might have some application for optical comms with their 
"single pixel" cameras. The idea apparently is to simultaneously 
capture two images of the same scene each having a different 
polarization (orthigonal or 90 degrees apart) and then subtract 
one from the other. This can be done either with two optics with 
two separate detectors or by splitting the image from a single 
optic into two images, each with its own polarization filter and 
detector. Either way, two detectors would be needed. Then with an 
op-amp, or other arangement, subtract one signal from the other. 

It is interesting to note that when two orthogonal polarizing 
filters are placed on top of each other, almost no light passes 
through.

Several people over the years have thought of doing this but 
without polarisation filters, just for noise reduction. Having 
two detectors usually means more noise as well. The dual detector 
idea is used in microphone techniques to cancel noise but this 
is usually done when there is plenty of signal and not at the very 
weak signal levels in optical front ends.

At any rate, i thought i'd bring this up to the groups in case 
there is something useful here that hasn't been tried before.

Cheers!
-toast