# Is there an optical filter which exclusively passes right or left circularly polarized light?

Is there a circular analog to the linear polarizer filter, which can be configured to pass only right (left) and block left (right) circularly polarized light?

• What would this filter do with linearly-polarized light? Reject it, or pass 50% intensity? What about light that's just about circularly polarized, but has slight (say, 1%) imperfections in the ellipticity? That is, are you looking for a linear filter, or something that will only pass perfectly polarized light. The latter is essentially impossible; the former is most commonly realized in 3D cinema lenses. Commented Mar 14, 2016 at 1:03
• I believe I had a anti-glare screen for a monitor that worked on that principle once. It accepted the same handedness both ways, but of course reflected light swaps handedness. Can't find a reference. Commented Mar 14, 2016 at 1:06
• A linear polarizer sandwiched between two quarter wave plates (aligned correctly). Commented Mar 14, 2016 at 1:26
• Thanks @ThePhoton, that's what I'm looking for. It seems to be called a homogenous circular polarizer (en.wikipedia.org/wiki/Polarizer#Homogeneous_circular_polarizer). Commented Mar 16, 2016 at 4:16

## 1 Answer

You have just described the 3D glasses handed out in movie theatres.

So, the answer is "yes." :-) . To be more helpful, here's a quote from the Wikipedia page

As shown in the figure, the analyzing filters are constructed of a quarter-wave plate (QWP) and a linearly polarized filter (LPF). The QWP always transforms circularly polarized light into linearly polarized light. However, the angle of polarization of the linearly polarized light produced by a QWP depends on the handedness of the circularly polarized light entering the QWP. In the illustration, the left-handed circularly polarized light entering the analyzing filter is transformed by the QWP into linearly polarized light which has its direction of polarization along the transmission axis of the LPF. Therefore, in this case the light passes through the LPF. In contrast, right-handed circularly polarized light would have been transformed into linearly polarized light that had its direction of polarization along the absorbing axis of the LPF, which is at right angles to the transmission axis, and it would have therefore been blocked.