Polarizer

A linear polarizer transmits one linear polarization and suppresses the orthogonal one. Two ideal crossed polarizers block light unless an intervening medium changes its polarization of an electromagnetic wave. A twisted nematic field effect uses this selection to convert field-driven reorientation into brightness modulation.

A prism polarizer associated with William Nicol. Its birefringent crystal arrangement selects one transmitted polarization; two such prisms can serve as the polarizer and analyser in a polariscope.

A polarizing element used to examine the polarization of incident light. Rotation converts that polarization information into an intensity variation, described by Malus's law for an incident linearly polarized beam and an ideal linear analyser.

A reciprocal optical circular polarizer can be assembled from a linear polarizer followed by a quarter-wave plate whose axes make $45^{\circ }$ to the transmitted linear state. Forward passage converts unpolarized light into circular light of half the ideal incident intensity. Reverse passage encounters the retarder first; it leaves unpolarized light unpolarized until the linear polarizer transmits half as linear light. Thus the one-pass intensity can be equal in both directions even though the outgoing polarization differs. Use a coherency matrix, not a single Jones vector, for unpolarized input.