Optical Polarizers

Optical polarizers are optical devices that can transform unpolarized or natural light into polarized light, usually by the selective transmission of polarized rays. They are used in infrared (IR), visible light, and ultraviolet (UV) applications. IR polarizers are designed for use in the 750 nm to 2500 nm wavelength range. Optical polarizers for visible light are designed for use in the 380 nm to 750 nm wavelength range. UV polarizers used in the 4 nm to 380 nm wavelength range. For each type of optical polarizer, performance specifications include clear aperture, extinction ratio, transmittance, beam deviation, and operating temperature. 

There are many different types of optical polarizers. Calcite polarizers are crystals that separate unpolarized light into two separate-plane polarized beams. Circular polarizers block all photons rotating in one direction, while allowing those rotating in the opposite direction to pass. These optical polarizers are assemblies that consist of a linear polarizer and a wave retarder, usually a quarter or a half waveplate. Depolarizers obliterate the polarization of a polarized beam by reflecting the beam in all directions at right angles to its axis. Linear polarizers transmit light waves along one axis and absorb them along the other. The transmitting and absorbing axes of linear polarization are oriented at 90 degrees to each other. 

Optical polarizers include polarization rotators and waveplates or retardation plates. Polarization rotators maneuver incident linearly-polarized light about an optical axis. Waveplates, which are sometimes known as retardation plates, are optical elements with two principal axes (one slow and one fast) that resolve an incident polarized beam into two mutually perpendicular polarized beams. The emerging beam recombines to form a particular single polarized beam. Other unlisted, specialized, and optical polarizers are also available. 

Surface quality and surface flatness are important specifications to consider when selecting optical polarizers. There are to components to surface quality: scratch and dig. A scratch is a defect on a polished optical surface whose length is many times its width. A dig is a defect on a polished optical surface that is nearly equal in terms of its length and width. For optical polarizers with a surface quality of 10 / 5, the average length of a scratch is .10 mm and the average diameter of the digs is .05 mm. Others scratch/dig surface qualities are 20 / 10, 40/ 20, 60 / 40, and 80 / 50.

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