# Polarization Beamsplitter Cubes

1. Feb 7, 2012

### Niles

Hi

Say I have a laser beam, which is linearly polarized. Now I let it pass through a polarization beamsplitter cube (PBS). If I orient the PBS such that the polarization of light is "parallel" to the coating/cement (nicely illustrated here: http://www.thorlabs.com/images/TabImages/BS_PolarizedCube2.gif), I get 100% reflection (the red beam).

Say my beam is elliptically polarized instead with the long axis parallel to the cement. Is it correct that the reflected beam is merely the projection of the ellipse onto the axis parallel to the cement?

Help is greatly appreciated. I have thought about this for some time, and I can't figure it out. Hecht's "Optics" doesn't explain it either.

Best wishes,
Niles.

2. Feb 7, 2012

### xts

Yes.
You may treat elliptically polarized beam as a linear combination of vertical and horizontal waves, shifted in phase by $90^\circ$. The vertical part will be reflected in one direction, the horizontal one in another in your cube.