Tech Notes » Polarization Tutorial

Light, as the electromagnetic wave, is characterized by its power, wavelength (frequency), phase and polarization state. The vectors (Ē and H) of the electric and magnetic fields of the Tranverse Electro-Magnetic (TEM) wave are perpendicular to one another and orthogonal to the direction of light energy propagation (Pointing Vector P).

Polarization

Polarization characterizes the direction of the Electric field vector of light. Any arbitrary polarized beam may be resolved into two orthogonal components along the reciprocally perpendicular Basis Vectors laid in the ĒH plane defined by the asymmetry of the media (or geometry of propagation).

Two important cases of the Basis Vectors definition are:

1. Propagation through the anistropic medium. One of the Basic Vectors (seen below as "e" – extraordinary) is along the projection of the medium's optical axis on the ĒH plane. Another (see below: "o" – ordinary) is perpendicular to the first one in the same plane.

2. Reflection (or refraction) on the titled surface separating two different optical media. One of the Basis Vectors (seen below as "P component") is parallel to the plane of incidence (the plane defined by the incident and reflected or refracted rays). Another called "S component" is perpendicular to the plane of incidence.

In the case of medium isotropy (or isotropy of the geometry of propagation), the Basis Vectors can be arbitrarily chosen in the EH plane, yet they must be reciprocally perpendicular.

At any point, the state of polarization of light is defined by the reciprocal amplitude and phase between two orthogonal components. For arbitrary amplitudes and phase shifts, the state of polarization is usually elliptic (the electric field vector draws an ellipse with the same frequency of rotation as the frequency of light). In certain cases, the ellipse is transformed into a plane (note: plane polarized light exists when the phase shift is 0° or 180° or one of the components is absent) or circle (note: circular polarized light exists when the phase shift is ± 90° and the amplitudes of the components are equal. The plane polarized light may be P-Polarized if the direction of polarization is parallel to the plane of incidence; S-polarized if perpendicular.

The transmittance (T) and reflectance (R) of multilayer, dielectric coatings depend strongly upon the state of polarization of light incident upon them.

polarization-equation

The polarization state of light can be either S. P, or random. Any polarized light an be resolved into S- and P- Polarization components using polarizers. There are several types of polarizing optics available, but RMI deals only with Coated Prism Cubes and Thin Film Plate Polarizers because they have properties such as high efficiency, low absorption, large beam aperture, and high power handling capabilities which are required for sophisticated, high-tech devices.