At the Electronex trade show last week I bumped into Dave Jone from EEVBLOG. We got chatting about the polarization stuff I was working on, and after a few minutes Dave turned to me and said “Wait, why aren’t we filming this?”. So I toodled off to my car and grabbed a bunch of bits and pieces and we did an impromptu filming session outside:

Apologies to anyone I confused, everything was totally off the cuff and improvised, and I didn’t have a chance to print out supporting diagrams which might have made it clearer.

I should also mention that I’m just following in the footsteps of David Prutchi, and if you want to get into polarized imaging please read his excellent whitepaper on the subject.

http://www.diyphysics.com/wp-content/uploads/2015/10/DOLPi_Polarimetric_Camera_D_Prutchi_2015_v5.pdf

and and check out the page for his Dolpi Imager.

The relevant blog posts for the bits I was playing with are here:

• Better Poincare Sphere
• Clockwork Waveplates – Polarization Calculations With Gears
• Desktop Qubit Model – Poincare and Bloch spheres

A couple of minor things to correct in what I said:

• Single mode fibres aren’t narrower than the wavelength of light they carry, just close-ish to it. (As opposed to multi-mode fibre that might be a hundred times larger) E.g. an IR laser might have a wavelength of 1.5um, a single mode fibre for it might be 8um, and a multi-mode fibre for it might be 100um.
• Glucose is the sugar I was talking about, in right handed (dextrose or D-glucose) and left handed (L-glucose) and which is capable of optical rotation. Sucrose is more complicated.

And a couple of questions people asked me after:

• Why not use sugar to do the optical rotation and determine the difference between left and right handedness?
  • Good question. A sugar rotator’s axis is through the R/L points on the sphere, so it won’t move things of the equator. To do that you need something like a waveplate (the green arrow in my model)
• Why the hell didn’t you clean the window on your LCD device. It’s dirty!
  • That’s not dirt, that science! Or, rather I was avoiding the need for an expensive professional waveplate by using adhesive cellophane which has been stretched and oriented at an exact angle to the LCDs optical axes. It’s not super pretty, but the device would have gone from costing maybe $20 to more than $100 if I hadn’t used it. When I’ve finished my next round of testing I’ll publish a full set of design files and plans for people to make their own.
• So what about your ipad screen?
  • Yeah, OK, that dirt is actual dirt.