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- Polarization Conversion Systems for Digital Projectors
Polarization Conversion Systems for Digital Projectors
- By Michael Pate
- Published 21 April 2006
- User Articles , Digital Projection Optics
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System Integration

Because the PCS is mounted at the field array, the small lateral offset introduced does not matter, as the condensor lens produces a uniform illumination on the LCD or LCoS panel:

We can see a layout of the fly’s eye array with the PCS array on the back surface of the second array and then a single element condenser lens above. The function of the condenser lens is to overlap all of the individual channels, in the fly’s eye array of channels, on top of each other. This chopping up of the non-uniform illumination from the lamp assembly and overlapping each channel on top of each other is what enable the fly’s eye array to provide uniform illumination at the spatial light modulator panels, plus convert all the unwanted polarization into the desired polarization.
4 Responses to "Polarization Conversion Systems for Digital Projectors" 
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said this on 12 May 2006 6:50:16 AM PDT
The halfwave plate only rotates the polarisation state correctly at one wavelength so you don't get a completely lineaerly polarised system if you have a polychromatic source
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said this on 17 May 2006 4:22:25 PM PDT
PCS doubles the etendue (are/solid angle product) of the optical system by doubling the area where the PCS is performed. If the projection lens can handle a doubling of etendue, couldn't you just as easily double the collection efficiency from the source and not bother with polarization issues? In that case you would have twice as much light, and throw half away in polarization. In the other case you have half the light, use both states of polarization, but end up with the same etendue in both cases. Just wondering...
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said this on 19 May 2006 4:23:46 PM PDT
Reply to Comment #1
Hi Philip, you are correct about the model shown has a monochromatic half wave plate and would not give completely linearly polarized light for most mercury and xenon lamps in digital projectors. There are achromatic wave plates and system engineering choices in digital projects such as clean up polarizers before LCD and LCOS modulator panels. These are projector design details and beyond what I was trying to demonstate the capability to model a PCS with Zemax.
If you are interested in more details please check out my ebook on Digital Projector Techology
http://www.oscintl.com/dpt_ebook.htm
or my DVD
http://www.oscintl.com/prod01.htm
or Applied Digital Projector Design w/ Zemax Course
http://www.oscintl.com/dpdwz.htm
Thanks, Michael
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said this on 03 Mar 2008 4:20:09 PM PDT
Thanks for the rare articles.
Could you please clarify one thing? How can the surface between two adjacent rhombs both pass through and reflect all light of a given polarization?
In fig 6, right side, a horizontal and a vertical beam combine into a single horizontal beam, which breaks etendue conservation...
Wouldn't this PCS system require only half the rhombs illuminated in order to work properly, effectively halving source etendue, as some other reader suggested?
Reply from Michael: Good question. “Wouldn't this PCS system require only half the rhombs illuminated in order to work properly “. No, it requires a blocking aperture (not shown) so light dosen’t get into every rhomb. Light (unpolarized) should only enter every other rhomb and it then gets split at the polarization beam splitter surface and P light plunges through (the arrow) and S light skips off (the white dot) and exits the face of alternate rhombs. This IHMO does not double the etendue. I think there is some misunderstanding in the industry around the original prism type PCS and doubling the etendue because it doubled the exit area and these rhomb type PCS’s.
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