Gav "The Mechatronics Guy" explains circular polarised light and demonstrates his physical laser cut models to help understand this concept in his quest to make a pixel mapped polarised light camera.
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And I'm here. We gave the mechatronics guy you've seen gave before and he's going to show us what he's been working on. My obsession recently has been polarized Light and I've been often on this one for a couple of years. So I've been play around with polarized light and I really really love it and it's a really interesting kind of polarized light is all around us and we can't see it and that frustrates me.

I think it's rude. So this is a modification I made of something made by David Ferrucci when the Hackaday Prize a couple years ago for the Dole Pie polarization camera and it's using some LCD shutters that I've modified and put extra layers on. These are LCDs from shutter glasses like 3d one pixel and and what. You can kind of model them as a voltage-controlled wave plate.

we'll get to that later, but if we I don't if we can shoot through here and look at the tables. So this is just an ordinary scene with some tables and if we put this in front they're pulsating and it's not, we're not looking at particular mirrors Reince this is just sheen on just plastic table or grass that's a little bit damp for these tiles or and it's totally changing. the polarization and having done that bounce from the sky to us and in the same way. Everything we look at is is is slightly not quite perfectly polarized so we get information there that we just totally can't see normally.

And our second example for that is if we look through the the circular one so the circular one's not really doing much. No, you can see a little bit of flesh there. That might be more to my mind device being a little bit imperfect about the rotations around a sphere it's doing. But if we go and look at the table, so if we look at the stuff on the table, we can see one of the lenses flashing.

It wasn't flashing before when I was looking through, There we go. Oh, there we go because you're alternating. Me: that's it. Right, right hand, circular, left hand, circular, right, left, right, left, right, left.

And that's how the 3d cinema works is No. I it's got to do that. You know? Yep, like 40 times a second or whatever. There's different ways.

Like people know, they like to be polarized, but there's actually really different ways that it can be polarized. So if you consider light stuff to electromagnetic, let's say the electric field, and if it's coming in, it could grab a charged particle, It kind of move it up and down. And if it's moving up and down, we'll call that vertically polarized. And if it's left right, call it horizontally polarized.

but you could just as easily have it diagonal so 45 degrees or my anti-diagonal minus 45 degrees. But it's also possible if you've got something that's got a horizontal and vertical component, they're a little bit out of phase that you'll have something that produces circular polarization. So right in circular polarization. Left-hand circular polarization.

If you sort of think about all the ways these can come together, There's a there's a model called the Poincare sphere from Mr.. Poincare A and he's a tangible version. I'm built of it. This is to get it straight in my head that you know what's gonna, what's going on, and and what do optical components do to this.
So for example, you can have light that's perfectly horizontally polarized and that would be this point on the sphere. Or it could be perfectly vertically polarized and that'd be that point on the sphere. And what a lot of complex optical things do. like wave plates and linear filters and sugar rotators and faraday rotators and things like that do.

It's actually just a rotation on this sphere. So as an example, if I get a wave plate and I drop it on there. What that actually does. This can convert horizontal light into circular light.

So if I start off horizontal and I put my wave plate at 45 degrees, then that would turn horizontal light into right-hand circular polarized light and it would turn vertical light into left-hand circularly polarized light. And this, this might seem a little bit weird Why I'd want to do this because it's pretty straightforward if you're just looking at one element of a filter. but when you're looking at a whole bunch of filters or a whole complex optical system, suddenly, it gets very complex quickly and I wanted something to just tangibly show me what was going on. And so that's a wave plate, so that's one come up common optical component.

Another thing you can have is if you put sugar and you shoot light through a sugar water solution, it's actually going to do a rotation around this axis and ordinary biological sugar that we sort of used to is all right handed sugar. So it actually does a right-handed rotation which is doing that around the city. So horizontal light through a sufficient thickness of sugar water would become diagonal lines, so you just have to dissolve it of water. And that's that's yeah.

And you could tell the difference between lab synthesize sugar and biological sugar. Because the lab synthesize one is going to have an equal mix of left and right-handed and on average it's going to do nothing. no rotation. But here's the interesting thing.

You could make right hand sugar in a lab, but you'd have to have something that was already right-handed or or of one particular handedness as a catalyst. You couldn't start from nothing and get an asymmetry in the amount of handedness there. You'd have to use some catalyst which is already or some runaway reaction and you get and there'd be a 50/50 crapshoot of which which had a district got just out. Okay, be right-handed right-handed right back.

right-handed Sucrose is levo sucrose. Lead extra. Sorry. Dextrose.

Dexterous. That's why it's called dextrose. It's it's Dexter It's It's dexterous. Yes, and artificial would be believed.

Oh yeah, leave it extra L dexterous. Whatever. The chemist is probably gonna call me out on that, but that's because and in the same way as sugar does a rotation, you can make a Faraday rotator which is being present now. Made this with olive oil and a solenoid and you can change the direction of the applied field same axis and it'll do the same rotation.
but that one you can. because you can flip the magnetic field, you can actually make it go in the other direction. So these are three models. What three common things you might find in a lab due to the polarization of light.

I Made another model of this conserved quantity because the amount of horizontal in this squared plus the amount of diagonal squared plus the amount of right hand in the squared equals one. which is why it's a sphere, which is why it's this conserved quantity. So unless you have a filter that throws away amplitude, you're not actually going to do anything to the the aperture. There, it's It's going to be conserved.

as a mathematicians call this set of things. So3 special orthogonal groups Three, but every filter is going to have a ten, You Asian, a teeny little bit of a ten. Okay, so that doesn't matter too much. Okay, well in this all, a wave plate, a fairly rotator and sugar rotator You can also sign kind of close to ideal versions of those that don't throw any amplitude away.

Something like a polarizing field from the other hand will throw away 50% of the light and that's kind of just going smooch to one side of the sphere is it throws away 50% Is that an inherit an inherent nature of everything that comes out is I Think it's the likelihood that it'll get through is the cosine squared of the angle? That is something like that. Yeah, now this is the pointer. A sphere which is for polarizations of light and I made a similar model called the Bloch sphere here and this is another structure which is so3. It's A it's a conserved quantity under rotation and this is a qubit.

So this is a qubit with a 0 state, a 1 state, and because probability amplitudes of complex numbers I won't get into that. but they're a complex thing. You can have a plus, a minus, a plus I and a minus I as the for combinations there and these are actually kind of equivalent to each other under under certain circumstances. and it actually makes a lot of sense if you're thinking about doing quantum computing with photons because the photon is often called a flying cubed.

so that's it. That's the Bloch sphere. And that was that was a background of sort of thinking about these quantities and and working with them. But what? The wave plate does is really cool because it it's doing this rotation.

and there's a device called a polarization controller that looks like this. So it's three wave plates, one after the other. Oh, should I explain about what a wave plate is? Yes, Yeah, yeah. I should something What a wave plate is.
So if you get like a mineral like calcite, it's a what do you call it anisotropic? It's it's it's different. It it has a preferred direction of like the crystal structure is aligned in one direction, which means that it kind of has some more dense going this way than this way. It has a slightly different speed of light going this for like going polarized this way versus like polarized this way. And if you were to cut a calcite crystal to a certain thickness, then the light that's coming in say it was diagonally polarized.

That's got a little bit of a component in the horizontal, in the vertical and a little bit of a component in the horizontal. So those two things go through the crystal. One of them, they're split into two two different ways to traverse. They're on two travel leaders and one travelator is going faster than the other.

So by the time the crowd recombines, there's a phase shift between those two waves and your horizontal and vertical are out of phase and your diagonally polarized light is now doing a circular. So you can use a wave plate. Usually a quarter wave plate is the most common one and that will convert linear light in a circular light. and and this is actually what frustrating is because if you say to love physicists like what does the wave plate do and they go, a wave plate converts linear light to circular light.

it's like no it doesn't it really doesn't it he can. But if we jump back to the jump back to the Bloch sphere at the point where a sphere. So this this is most definitely converting say vertical light into right hand circular polarized light if we do that right. But what if I put in light that was diagonally polarized.

it's not going to do squat because it's axis is lined up with the axis of the wave plate. and so there's actually always going to be two points where it does absolutely nothing and it'll convert and it does kind of less a conversion. So if you had a little bit diagonally polarized and a little bit mostly diagonally, a little bit vertically polarized and you do rotation, it'll be still mostly diagonal. but it'll just be the little bit right hand circular polarizer.

so be elliptical. But and so it's like that I really wanted to something to visualize what's actually going on with this because if you jump back to them, that polarization controller. actually these these things are really cool. The actual implementation of this.

You usually achieve this in a lab. David And if you can do like a Google image search and throw a photo on top of this right is if you look at a polarization controller, it's just you feed in a single mode optical fiber through coils and because you're coiling it up and it's just stressing it a little bit. It's affecting the polarization so all you do. it's just a fiber going through a loop and then another loop and another loop.
And it's stressing the fiber a little bit and affecting the polarization the same way that the crystal does. And so what you do is you rotate the paddles around. It's just three paddles and you just go Swivel swivel swivel and you can turn any polarization state into any other polarization state I've seen. Then you can actually buy them and they physic, rotate their they physically move.

It's just ordinary five single-mode optical fiber, right? Any single mode fiber and it's any single mode fiber that you that you stress I believe will do that. I Don't think it has to be a polarization maintaining five or anything I think it can't be followers ation. Return five. Do you know the magic about what single mode fiber is? So if this this if I go over here.

Is that all right? Yeah, so this these these tiles over here if this was a canal and we had waves coming along through there because this canal is like really really, wide, it could support waves going this way, but it's wide enough that it could slightly support waves going that way. so you could have any pulse that came through here would kind of be reflected more than once and there are multiple possible ways for the amplitude coming in to get to the amplitude coming out. But if you make the channel narrow enough like this grating frame here so that it's much smaller than the wavelength of light, it's not just hard, it's impossible for light waves to exist at that dimension. There are no modes that support oscillation, so the only way that it possible this grating could possibly oscillate would be straight down the ball.

I mean that single policy and single pulse out and you get the minimum amount of broadening that you can possibly get compared to something much, much wider going on. And the advantage of multimode though is that you can send is that you can make use of those different. You can do that with single mode as well. You can do that with single mode as well.

You can send multiple wavelengths down there. The difference is how much each pulse each perfectly a narrow pulse will be smeared out. Reminder: Talk about some bragg gratings and fiber couplers and how they make them. and it's basically just doing terrible things to a fiber until the signal meter goes flip and it just just likes feeding the fiber up until to two layers.

a kind of kind of cross coupling and there's like yep, done that all right. Call that one done. Next one, put the next one in the rig. Yeah, back to the fiber controller.

So that the fiber controller is really cool because with three quarter wave plates, three things that are doing in a 90 degree rotation on this sphere, you can turn any input polarization state into any other polarization state. So if you wanted to turn diagonal into sixty seven point two degrees polarize that, you could do that quite easily just by manipulating those three paddles. I Wanted a tangible model of that. So actually first of all, this is what I made for the half wave plate.
So half wave plate is doing a 180 rotation on the sphere and that's really useful because the right hand circular would convert to left hand circular polarization. So what this is is our input coordinate frame and you can see you've got vertical, horizontal, anti diagonal, diagonal, right hand circular and this is the output one and you can see that right hand is always turned into the left hand and depending on which acts at what angle you put the fast axis of your wave plate, you can just do whatever you like with the polarization. So this is a tangible model of an actual like half wave plate you could get in a lab and that's really cool. But I wanted to go a little bit beyond that and do any any to any mapping and see if I could get something tangible that you could play with.

There is a point to this in the end of what you're actually doing this all for. so let's just say that you can I don't know if you want to later on I'll show you the shutter thing and you could start with that and then yeah. so this is three quarter wave plates joined together in a physical model and basically I just choose what I want my my task to be what I want to convert between this coordinate system say I want to go I want anti-diagonal to go to vertical and I can just kind of turn it until that happens and actually I've switched right and left elevation so I'd have to play around a little bit more until what can I do with that this just playing around you can make anything happen and so this is. This is a model of using those three plates to do anything to anything.

and I've actually any other physical models like this like educational models. This is precisely why I made it I wanted to make something that you could play with because it's like because otherwise you're just doing. you're just moving three paddles around and it's totally unintuitive as to what's actually happening. Whereas this is maybe it's not the easiest to work with, but it's actual very tangible and you can see what it physically means at each stage of the process.

And I've actually done that. Took a random task of turning polarization into another polarization on my website and manually manipulated until I got it lined up as I wanted, then noted the angles to the wave plates, did the Muller calculus on that which is like 4x4 matrix operations, multiplying three of them together, then putting a full vector in as the input, and then looking at the output and I got the right answer. I got like within a few percent of the right answer. So I'm super happy with that.

As a for laser cut wood and like hastily assembled not quite a 90-degree you know been aluminium, that's not not too bad. This is how they would have done it before computers came along. This is how you. This is how you did algebra.
like algebra. like you draw you didn't just before you had digital computer, you just didn't just pack up and go home. it's you. had to do it.

Yeah, you built or drew something to model it. This is totally different than my original idea. I originally had it as a link thing that was more like a pen until you know and I realized that I had the I had the arrangement backwards. so it's like 10 o'clock at night and I'm like stuff it? yeah, just just do simple stuff.

and so I like laser cut really simple ones as examples and then just like hot glued them together and did enough of them that I was satisfied that this relationship with the gears should work and then started and like because at the 10:30 at night, I'm not really thinking on cylinders and it's like alright, what? how can I trade off effort for thinking and let's just laser cut it and hot glue it together until I'm sure that I'm not fooling myself what the result is, so that's yeah. So so the end goal of all of these things that I've been playing around with is following on from from David's work with the polarization cameras: I Really want to make a camera that will take a full picture of an image and for every pixel in that image, give a steer breakdown of where it is because every pixel has a different story to tell about its polarizations and it's maybe it reflected off the table. or maybe it's off the sky and it's and the sky polarized is light subtly differently and it is it strongly polarized. in which case it's right on the edge of the sphere, is it weakly polarized in which case is much close to the origin and the rotations are really affected that much.

So there's all this information there, which is kind of hidden in our just everyday view of things. and I really really? You want to get a camera that can just capture that? and so I can actually start seeing that and you think you can do it on an individual pixel level? Yes, absolutely absolutely. by having moveable filters and things like that and taking multiple images and then calculating two to get back to the original. States As part of this, I built an optical table that can rotate filters around and characterize materials and I'm trying to bootstrap up from from the ground up.

How much can I kind of get without any known lab grade stuff and I'm slowly getting it. But an interesting thing has been I Can I can figure out what what vertical polarization is and what horizontal polarization is based on how light reflects off the surface of water or some some known surface. But the difference between right-hand circular and left-hand circular is actually really, really hard because I need a wave plate. At a known wave plate that I know which axis is the fast axis, in which axis is a slow axis.

Otherwise, it's like if I if I have this on the sphere, it's what this does is completely different. If the X is line up that way, then if the axis is lined up that way it's it's it's right and left is going to be completely symmetrical. If I don't know which way it is I can tell the difference, but I don't know which one is truly right-handed in an absolute sense. III So these things are according to the real 3d website and places.
The left lens is left circularly polarized and the right lens is right circularly polarized. That tells me everything right? No, Because there's two conventions that are about equally popular: whether light is coming from the source off to what's the observer as to whether it's the the left and right according to that. So I still don't know. So I'm slowly building some stuff to figure that out and get in my quest for left from right happening and that's going to rely on having I've made some stuff out of I made my own ROM Frizzles ROM Which is how Mr.

Frenzel originally trained all brenell, originally converted it. The trouble is I've laser cut the acrylic and I've got it polished. but I've introduced so much heat stress from the laser cutting it's now completely birefringence and overwhelming. So I'm now trying to anneal the acrylic back to of being optically perfect and that's that's an ongoing project.

No, yeah, wouldn't you start the process again? No, no no I I wouldn't I wouldn't staff from scratch because if I want to shape the if I want to shape the acrylic with a laser I'm gonna introduce stress or if I use a sore I'm going to introduce some stresses as well and heating up and so what I need to do is is make it the shape that I want and then anneal it back to being completely unstressed. And I've done some experiments and and like hated it up to ninety degrees which is just on the glass transition temperature. He'll live for several hours and brought it back down at no more than ten degrees per hour. and I've massively reducing my stress, but it's still not zero yet.

So I'm getting there. That's my question for left from right via annealing acrylic. And yeah, that's great because I don't I don't have any lab grade stuff that I can just look up the calibration sheet and go oh, that's the fast axis and that's the slow axis syrup. Yeah, you can you can salute Lee Canada But at this point it was like a challenge of how much can I? How can I do from First Principles: Are there any animals out there that are sensitive to polarized light? Have they evolved it? What's is there any advantage to that? And so the the mantis shrimp I believe can see in circular, circularly polarized light.

There's a bunch of other underwater ones. a cuttlefish I think can also do it. A lot of beetles have carrot paces on the back of the beetle that are preferentially right, circularly polarized instead of left and they think it's like a signal to the same species to not so. Mike If my my playing around with the acrylic and the Raman stuff didn't work, my backup plan was to go to the museum with the glasses and look at beetles and figure out whether the beetle this brighter in this sigh or in this side.
So the beetles as an ISO standard calibration objectives. Yeah, the ISO beetle. Alright, thank you very much. Jeff That's hugely fascinating.

Good luck with the project. Maybe we can do a follow up. Yeah, I'll show you the optical table at some page because that'll be open-source and CNC controlled filter rotators. And yeah, you.


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By YTB

25 thoughts on “Eevblog #1120 – how to understand polarised light”
  1. Avataaar/Circle Created with python_avatars EnigmaticMF says:

    This is the most confusing thing I have ever heard in my entire life.

  2. Avataaar/Circle Created with python_avatars AES says:

    This is way over my head

  3. Avataaar/Circle Created with python_avatars needforsuv says:

    the thingy could use a clean and a protective outer layer put in

  4. Avataaar/Circle Created with python_avatars NC Dave says:

    If you have 3D glasses just put them on and stand in front of a mirror. Mirror reverses light polarization, so light can't go trough same eyeglass twice. It's very fun first time you try it ๐Ÿ™‚

  5. Avataaar/Circle Created with python_avatars Markiss Boi says:

    GAV NEAR THE END > My ๐Ÿง  brains not working on all cylinders trust me whos isnt 24/7 hypsynopsiss said 90% the time humans walk around in a hypnotic trance we wander off in dreamworld alot listen ? huh gav wot did yah u say again lol ๐Ÿ™€๐Ÿ’ฌ

  6. Avataaar/Circle Created with python_avatars Markiss Boi says:

    NOTE: THE HARDEST THING IN LIFE is to Listen ๐Ÿ“ฃ๐Ÿ’ฌAnd for scientist to mock it down abit to a simple demo so alot us can get a jist of it or % of the idea – I open these blogs without 1 hair razoo about anything and just try to absorb what i can & let my brain cells chugg away & try 2 work out WTF is going on- if gav didnt demonstrate like i do alot with objects i would've just skipped thru this video like eeeh fook it so so & another science bit jargon that means nothing to me BUT I DIDNT >POLARISED as in GLASSES SPACE ? VR ? im working it out
    HOW MY brain;s trys to absorb & explain here > is beyond me ๐Ÿ™‚ But without knowledge of any degree in this type field doesn't stop me trying to learn Some Days months years latter 2 ide's collide and make a bang ๐Ÿ’ฅin your head and low & behold a pic appears > idea ๐Ÿ™‹โ€โ™€๏ธ cup coffee time > โ˜• here alot wont try & rather watch tv or – i also experiment in different time waves i say a quote at 21 & keep reminding me of that quote so i wont forget an import message to future me at 21 yr old this thought pops in my head DRUGS EITHER Pharmacy OR backyard are dangerous & will cause problems to your brain or body functions and 2nd was never stop thinking about free energy motors or alike a vision popped in my head & the day after a guy from europe same age comes to out house & tells me he built an engine from a train motor & with a bit elect tech made it work all alone after a boot start from a battery – that was like to me so weird i still think of it every year ๐Ÿ™‚ & look now days in youtube to see whos doing what a bit interest in science nature films and a lot good know how bench work keep me going WHY cause it stops the evil Mr boredom from eating my soul adventure away ๐Ÿ“ฃ๐Ÿ’ฌ๐Ÿ™€ ( in alot things) is the key to a good open mind – if my words seem cluttered im tired late so ? eeh shell do for now bye ANYWAY GOT WATCH THE END OF GAV;S POLARIZED THEORY THINGY ME BOOB IDEA HAS ME INTRIGUED ๐ŸŒ๐Ÿ“ฃ ๐Ÿ’ฌWOT?

  7. Avataaar/Circle Created with python_avatars Jason says:

    Truly amazing stuff! Can't wait to see the images from your camera… Your models are astonishing too – as a chemist working with optical molecules I never fully understood these relationships – would have loved to have these as tools! Good explanation regarding sugars too – it's worth noting that we're referencing a dextrose, or glucose, monosaccaride when referring to dextro and levorotatory properties. Sugar, a sucrose fructose disaccaride, or indeed any polysaccaride, will of course also display rotation characteristics as a function of their combined monosaccarides.

  8. Avataaar/Circle Created with python_avatars David Hoff says:

    great video. I'd also like to add that I appreciate the couple extra seconds at the end of each video, so I can pause it to like or comment before my playlist continues. I wish more people did that.

  9. Avataaar/Circle Created with python_avatars D Stanoev says:

    I didn't get that. Can you, please, repeat, just slowly? Thank you!

  10. Avataaar/Circle Created with python_avatars pepe6666 says:

    Man that was awesome.

  11. Avataaar/Circle Created with python_avatars Dave B says:

    I could listen to this guy all day, what a brilliant mind.

  12. Avataaar/Circle Created with python_avatars Robert Gaines says:

    Help! My poor brain! I must be stupid! He did make some cool models using a computer controlled, laser cutter though. Curse my American high school education!

  13. Avataaar/Circle Created with python_avatars MIKIVELES369 says:

    This guy is…….. just WOW!

  14. Avataaar/Circle Created with python_avatars HamburgerExplosion says:

    Video was a lot easier to watch once i pretended he was a 1600's scientist who'd been bathing in mercury for too long.

    Couldn't understand anything, dude's wacked. "the light, it's in a certain way that can't be seen! the alignment of the light, it's going to rotate! for example, sugar rotates to the right. it's much denser horizontally" ???

  15. Avataaar/Circle Created with python_avatars Gordon Freeman says:

    Yup, I still don't understand how this works :D, it's all magic to me lol.

  16. Avataaar/Circle Created with python_avatars Macro Cosmos Microscopy says:

    Polarised light is also extremely useful in the fields of photography and microscopy, which are both interests of mine.

  17. Avataaar/Circle Created with python_avatars Jeff Grant says:

    This is very cool… reminds me of the "slide rule" days where specific formulas were made into physical slide rule calculators… Man was put on the moon with slide rules, after all. This seems like a natural evolution of that simple yet powerful technology, as this is a 3d slide rule for polarized light. Awesome video… thanks for sharing it!

  18. Avataaar/Circle Created with python_avatars Richard KB Formally FireballXL5 says:

    Why can he not water jet cut the acrylic? instead of laser cut.

  19. Avataaar/Circle Created with python_avatars Josh Mapstone says:

    Try water jet cutting your acrylic, this should reduce the heat when cutting. We do this when cutting lenses for our cameras. Which require being optically clear

  20. Avataaar/Circle Created with python_avatars MedSou says:

    Awesome ๐Ÿ‘๐Ÿ‘๐Ÿ‘๐Ÿ‘

  21. Avataaar/Circle Created with python_avatars Jedi Buddhist says:

    Very Nice guy.. but I cant transpose the demo to usefully visualise it in my own mind.
    So as @Rob s said yeah still no idea.

  22. Avataaar/Circle Created with python_avatars Lori says:

    This guy is very nifty!

  23. Avataaar/Circle Created with python_avatars FindLiberty says:

    APPROVED

  24. Avataaar/Circle Created with python_avatars Skyfox says:

    Tell Gav to use a water jet cutter to cut the acrylic pieces he needs so he doesn't introduce any heat stress into them.

  25. Avataaar/Circle Created with python_avatars rinserofwinds says:

    Great interview partner!

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