Polarisators

Polarisators, or polarizers, are optical devices that transmit light with a selected polarization while attenuating other polarizations. They are essential components in many optical systems, enabling control of polarization state, improving contrast, and reducing glare. Polarisators can be broadly classified as linear, which transmit a single plane of polarization, and circular, which convert light to circular polarization and then pass or reject it depending on handedness. Some devices use anisotropic materials or nanostructures to achieve polarization selection.

Linear polarizers include absorption polarizers, such as polymer-based films containing aligned dichroic molecules, and crystal polarizers based on birefringent materials like calcite or quartz. Wire-grid polarizers use subwavelength metal lines to transmit a chosen orientation of the electric field, particularly at infrared wavelengths. Circular polarizers typically combine a linear polarizer with a quarter-wave plate to produce circular polarization; in photography this arrangement allows reflections from nonmetallic surfaces to be reduced while preserving color saturation.

Materials and performance: an ideal polarizer transmits one polarization with unit transmittance and blocks others, described by the extinction ratio. Real devices have wavelength dependence, finite transmittance, and angular sensitivity. Common specifications include transmission, extinction ratio, and operating wavelength range.

Applications span photography and cinematography (glare control), liquid-crystal displays, microscopy, spectroscopy, polarimetry, and optical communication. The concept dates to early 20th century work by Edwin H. Land on polymer-based polarizing films.