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Science Forum Index » Optics Forum » circular polarization selective beam splitter
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| jesey |
 Posted: Mon Feb 18, 2008 5:52 pm |
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As I know, there are many polarization beam splitter, which transmit p-
polarization, and reflect s-polarization.
But is there any beam splitter whichi transmit right circular-
polarization, and reflect left circular-polarization?
If there is, how does it work?
And how much does it cost compared to the general PBS? |
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| Salmon Egg |
| Posted: Tue Feb 19, 2008 2:49 am |
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In article
<bdd1e473-15c3-4986-aa9a-fc3900f705bf@s12g2000prg.googlegroups.com>,
jesey <jesey68@gmail.com> wrote:
Quote: As I know, there are many polarization beam splitter, which transmit p-
polarization, and reflect s-polarization.
But is there any beam splitter whichi transmit right circular-
polarization, and reflect left circular-polarization?
If there is, how does it work?
And how much does it cost compared to the general PBS?
Without giving it great thought, it should be possible. You may have to
combine splitters with waveplates and feflectors.
In principle, it should be possible to get that result from the magnetic
Faraday effect. If one rotation is absorbed strongly enough, that
rotation is also going to be reflected.
At this time, I am not interested in doing the heavy brain work required
to work out the details. I am willing to have someone else file for
patents.
Bill |
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| Timo A. Nieminen |
| Posted: Tue Feb 19, 2008 4:15 am |
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| Guest |
| Posted: Tue Feb 19, 2008 10:18 am |
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On Feb 19, 3:15 am, "Timo A. Nieminen" <t...@physics.uq.edu.au> wrote:
Quote: On Mon, 18 Feb 2008, jesey wrote:
As I know, there are many polarization beam splitter, which transmit p-
polarization, and reflect s-polarization.
But is there any beam splitter whichi transmit right circular-
polarization, and reflect left circular-polarization?
If there is, how does it work?
And how much does it cost compared to the general PBS?
A quarter-wave plate + a standard polarising beam splitting gives you a
circular polarisation beam splitter. If you actually want circularly
polarised outputs, you'll need another 2 quarter-wave plates.
--
Timo Nieminen - Home page:http://www.physics.uq.edu.au/people/nieminen/
E-prints:http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits:http://www.users.bigpond.com/timo_nieminen/spirits.html
One additional hint --
for this method to work, you'll naturally want the fast axis of the
quarter plate to be oriented 45 degrees away from the two axes
defining the s and p polarizations of the polarizing beamsplitter cube
(PBSC). Then all the power in one handedness of circular polarization
will emerge from one face of the PBSC, and all the power in the other
handedness of circular polarization will emerge from the other face of
the PBSC. If you want to know which output gives the power in Left
circular polarization, and which one give Right circ. pol., then
you'll have to do a lot more work -- including understand ing what L
and R cic. pols. mean, and which is the fast (as opposed to the slow)
axis of your quarter-wave plate.
Regards,
D. Van Baak |
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| Phil Hobbs |
| Posted: Tue Feb 19, 2008 8:41 pm |
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jesey wrote:
Quote: As I know, there are many polarization beam splitter, which transmit p-
polarization, and reflect s-polarization.
But is there any beam splitter whichi transmit right circular-
polarization, and reflect left circular-polarization?
If there is, how does it work?
And how much does it cost compared to the general PBS?
You could do this by adapting any of the ordinary crystal polarizer
designs, replacing linear birefringence by circular
birefringence(usually called _optical activity_).
For instance, you could make a circular polarizer analogue of a
Wollaston by using two triangular glass cells, one containing a solution
of normal (levorotatory) sucrose and one containing dextrorotatory
sucrose. If you used mixed-isomer (racemic) sucrose for one of the
cells, you'd make the circular-polarizer equivalent of a Rochon prism.
There are two problems with this sort of idea in real life. Firstly,
optical activity is generally very weak compared with linear
birefringence, which means you could get only very small angular
separation between the beams. Secondly, optical activity is highly
dispersive, often varying by a factor of 2:1 or more over the optical
region. This means that prisms relying on optical activity would work
as designed only in a narrow wavelength region.
A third problem is that most optically active solids are also
birefringent, so that it's quite difficult to get a pure circular
birefringence. The circular birefringence of quartz is on the order of
1% as strong as its linear birefringence, for example.
You're generally much better off using waveplates to convert to linear
polarization, use a normal polarizing beamsplitter, and then convert
back to circular.
Cheers,
Phil Hobbs |
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