Polarizers

A polarizer is an optical device that transmits light with a preferred polarization while attenuating components with orthogonal polarization. In general, it reduces the intensity of light polarized perpendicular to its transmission axis. For linearly polarized light, the transmitted intensity Iout follows Malus’s law: Iout = Iin cos^2 theta, where theta is the angle between the incident polarization and the polarizer’s axis.

Types of polarizers include linear polarizers, which transmit a single linear polarization, and circular polarizers, which combine a linear polarizer with a quarter-wave plate. Circular polarizers suppress reflections from non-metallic surfaces while remaining compatible with most camera systems, because the exiting light is effectively circularly polarized. Other polarizers include dichroic film polarizers, liquid-crystal tunable polarizers, and wire-grid (often used for infrared) devices.

Materials and construction vary. Linear polarizers are commonly made from dichroic polymers (such as iodine-doped polyvinyl alcohol films) or from crystalline materials. Inorganic polarizers may use birefringent crystals like calcite or quartz. Polarizers are characterized by parameters such as transmission, extinction ratio (the ratio of transmitted to blocked light for the undesired polarization), spectral range, and angular dependence.

Applications span science and industry. They are used in photography and cinematography to reduce glare and increase contrast; in sunglasses and safety eyewear; in liquid-crystal displays and other optical instrumentation; in spectroscopy, microscopy, and fiber-optic communications to control and analyze polarization states.

Limitations include reduced light throughput, sensitivity to wavelength and temperature, and potential color shifts in some configurations. Proper alignment and matching to the light source’s spectrum are important for optimal performance.