# The Naked Scientists Forum

### Author Topic: What is circular polarisation?  (Read 1231 times)

#### thedoc

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##### What is circular polarisation?
« on: 15/08/2012 12:30:01 »
Colin Strand asked the Naked Scientists:

Circular Polarisation.

I can understand the idea of polarisation in a particular plane as light has wave properties as well as particle properties, but I cannot get my head around the idea of circular polarisation. Please help.

PS. If you can explain ordinary and circular polarisation without using your hands, I will give you a bonus point!

Many thanks - I always listen to the shows x4 or 5

What do you think?
« Last Edit: 15/08/2012 12:30:01 by _system »

#### evan_au

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##### Re: What is circular polarisation?
« Reply #1 on: 15/08/2012 12:55:39 »
For animations instead of hand-waving, see: http://en.wikipedia.org/wiki/Circular_polarisation

Some examples of the use of circular polarisation:
• Some 3D glasses in cinemas use circular polarisation. This is better than linear polarisation, because you can tilt your head without seeing some of the left image in your right eye (and vice-versa). http://en.wikipedia.org/wiki/Polarized_3D_system#Circularly_polarized_glasses
• Some early satellite antennas used circularly polarised signals, so the uplink could be polarised (say) clockwise, and the downlink anticlockwise, with minimal interference between them. The antennas look like a pair of cylindrical spirals, the wire spiralling in opposite directions.

#### JP

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##### Re: What is circular polarisation?
« Reply #2 on: 15/08/2012 13:07:24 »
Interestingly, circular polarization is a more fundamental state of light, since it's related to the fact that light has spin of +/- 1.  You can construct linear polarization by adding up two photons in opposite states of circular polarization.  If you look at the wiki link that evan_au posted, you can imagine that if you add two of those together with opposite rotation, the left/rightness of the arrows could be made to cancel out, so they only move up/down.

This is something that always confused me in school, and it only made sense after thinking about it a lot and figuring out how you could add sinusoids pointing in different directions so that you formed a helix (as in circular polarization) or how you could add two helices to get a linear sinusoid (as in linear polarization).

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##### Re: What is circular polarisation?
« Reply #2 on: 15/08/2012 13:07:24 »