[FoRK] Electronically varying polarization of light

Stephen D. Williams sdw at lig.net
Tue May 14 00:02:25 PDT 2013

A while back I was trying to find this while trying to completely explain how .  No one could identify how this was done.  I did 
find the Rapatronic camera shutter, but here are all three main types of effect related to electronically controlling variable 
polarization of light.

> Pockels cells are used in a variety of scientific and technical applications:
>   * A Pockels cell, combined with a polarizer, can be used for a variety of applications. Switching between no optical rotation
>     and 90° rotation creates a fast shutter capable of "opening" and "closing" in nanoseconds
>     <https://en.wikipedia.org/wiki/Nanosecond>. The same technique can be used to impress information on the beam by modulating
>     the rotation between 0° and 90°; the exiting beam's intensity <https://en.wikipedia.org/wiki/Intensity_%28physics%29>, when
>     viewed through the polarizer, contains an amplitude-modulated <https://en.wikipedia.org/wiki/Amplitude_modulation> signal.
> # Pockels cells can be used for quantum key distribution <https://en.wikipedia.org/wiki/Quantum_key_distribution> by polarizing 
> <https://en.wikipedia.org/wiki/Photon_polarization> photons <https://en.wikipedia.org/wiki/Photon>.
> # Pockels cells in conjunction with other EO elements can be combined to form electro-optic probes.
> # A Pockels Cell was used by MCA Disco-Vision (DiscoVision <https://en.wikipedia.org/wiki/DiscoVision>) engineers in the optical 
> videodisc mastering system. Light from an Argon-Ion laser was passed through the Pockels Cell to create pulse modulations 
> corresponding to the original FM video and audio signals to be recorded on the master videodisc. MCA used the Pockels Cell in 
> videodisc mastering until the sale to Pioneer Electronics. To increase the quality of the recordings, MCA patented a Pockels Cell 
> stabilizer that reduced the 2nd Harmonic Distortion that could be created by the Pockels Cell during mastering. MCA used either a 
> DRAW (Direct Read After Write) mastering system or a Photoresist system. The DRAW system was originally preferred, since it didn't 
> require clean room conditions during disc recording, and allowed instant quality checking during mastering. The original 
> single-sided test pressings from 1976/77 were mastered with the DRAW system as were the "educational", non-feature titles at the 
> formats release in December 1978.
> Post <http://www.mtbs3d.com/phpbb/viewtopic.php?p=102157&sid=001fea202d10fcbdf059f46aefe709ca#p102157> Re: HOWTO: Use old active 
> shutter on regular LCD monitors! <http://www.mtbs3d.com/phpbb/viewtopic.php?f=26&t=16456#p102157>
> The basic element of a retarderfilm is a quarterwave retarder. It's used to change linear polarization into circular and vice 
> versa. A halfwaveretarder is two quarterwaveretarders stacked onto each other.
> The basic element of a polarizer is a linear polarizer. When combinated with a qw-retarder and proper orientation you will have a 
> circular polarizer.
> All lcd tv's/monitors in their original shape emitts linear polarized light. The orientation varies and can be 0 or 45°. In order 
> to make these into interleaved 3d-monitors the manufacturer applies a u-pol retarderfilm with the alternating pattern that suits 
> the monitor. The result for passive 3d-monitors will then be circularly polarized and is the reason why probably all passive 
> 3d-monitors/tv-sets are circular polarized.
> This trick with a retarderfilm works well because the linear polarized light from the lcd is transformed into circular before 
> reaching the first polarizer of the shutterglasses. To be entirely correct a halfwave retarder should be used but is in my 
> experience totally unnecessary. Circular polarized light goes easily through a linear polarizer.

Based on this perhaps they don't use anything active, but use a projection LCD or two with alternately circularly polarized filters.

Anyway, good to know the options.


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