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Thread: film or thin plate to switch between polarization states?

  1. #1
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    Default film or thin plate to switch between polarization states?

    Basically I have to combine two separate broadband (445nm-650nm) beams of light, then separate them again. When separated they have to be the same polarization.
    I think the easiest solution is linearly polariing one of the beams, using a reflective wire polarizer to combine the beams, then on the other end another reflective wire grid polarizer to separate the beams but have a half wave plate for one to make both beams the same polarization.
    Will a half waveplate switch the polarization state of a linearly polarized broadband beam of light?
    And if yes, do such half waveplates come in very thin or film forms?

    Longer description:
    I want two video projections to go through the same lens, then be split apart again on the other side of the lens. Since both are in the same wavelength range only way I see them sharing the same lens is having a different polarization. On the other side I'd want both of them to be the same polarization after being split again. If I have them different polarization when going into the lens on the other side I can't easily get both the same polarization anymore as using a simple absorbtive polarization filter will filter one out completly. Only solution I see is having one image polarized, the other unpolarized and using that to split the two after the lens with a reflecive polarizer and then waveplate for one of the beams.

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    I partially understand what your plan is. I would recommend a rotator plate instead of a half waveplate. The size might be an issue as they are 10 till 15mm in size. To combine and split you can do a rotator in 1 of the beams to combine with a pbs pass the lens setup and after that a second pbs. The second should split the beam again but i could be wrong. Can someone comment on this?


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  3. #3
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    These guys:

    meadowlark.com

    Can tell you the possibly do-able.
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    I'm sending you there for an education.
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    "Achromatic Retarder" which are also going to make Edison's day, as some of their better grade plastic retarders work great at 15 watts of large frame Ion.
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    In Polarization optics you only get what you pay for...

    Steve
    Last edited by mixedgas; 08-06-2018 at 06:38.
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    If you combine and then separate with cubes the input and output should be the same. In a fashion they undo each other. So if you don't care if they are out of polarization in the middle of the process, your good. Hence if you start polarized the end should also be polarized. (A+B)=A+B*=(A+B) were brackets are pbs cube operation. {Eab( A|B>);|Epbs(1|AB*>);Eab(A|B>)} little bra|ket> for you. IF you want a headache look up Jones vectors and Jones calculus.



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    Kecked, each of the two beams can be any polarization going into the lens, I just want to be able to have both of them going to the same lens (be combined) and separate them after the lens and have them the same (to each other, not necessarily to what they used to be) polarization.

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    Sounds like you got a plan then. Two cubes. One combine. One uncombine. In=Out

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    You mean have one beam s and the other p polarization before the first cube? This means after the second cube the beams won't be the same polarization from each other, right? What would you use to convert one of them? I'd need something which works in the visible spectrum and has a thickness of <=0.1mm.

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    Quote Originally Posted by joec View Post
    You mean have one beam s and the other p polarization before the first cube? This means after the second cube the beams won't be the same polarization from each other, right? What would you use to convert one of them? I'd need something which works in the visible spectrum and has a thickness of <=0.1mm.

    They must go in unpolarized to combine and so same on way out. The use waveplate to polarize the output. 0.1mm not sure but certainly less that 1mm. All glass has some depth.

    Other way to do it is turn the beam 90 degrees. This sounds like 3d projection? Hard to help build a black box.

  9. #9
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    I,m not sure a rotator or waveplate will work as its not for example 2 beams of 445nm he wants to combine and split again. He wants 2 beams of 400-700nm so the retarder seems the better solution but i don,t entirely understand how they work. It seems a broadband rotator or waveplate to me but i,m not sure.


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  10. #10
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    Quote Originally Posted by kecked View Post
    They must go in unpolarized to combine and so same on way out. The use waveplate to polarize the output. 0.1mm not sure but certainly less that 1mm. All glass has some depth.

    Other way to do it is turn the beam 90 degrees. This sounds like 3d projection? Hard to help build a black box.
    I don't understand then, how can they properly combine and be separated again if they are unpolarized?

    I'm just trying to stack two projections next to each other horizontally with a bit of seam, but not having it distance dependent. With two lenses next to each other extra lenses will be needed and also more distance between the two pair of lenses, and if you move the screen closer or farther the seam will either turn into an overlap or large gap respectively. This way its similar to knife edge combining, but video projections. Hope it makes sense. If not, I can make a raw diagram. I think a similar trick can be used to horizontally or vertically stack laser projections as well.

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