Optics 101

Polarizer - Basic Definition and Types of Polarizers

A polarizer is a device that converts a beam of electromagnetic waves such as light which is unpolarized or mixed-polarization into a beam with a single polarization state - either linear, circular or elliptic. The applications of polarizers include many optical techniques and instruments. Polarizing filters are found in applications such as photography, liquid crystal display technology, and polarizing sunglasses.

Polarizers can be categorized into two groups:

  • Absorptive Polarizers
  • Beam-Splitting Polarizers

Polarizers only allow light to pass if it has a particular angle of polarization. Image credit: Wikimedia Commons.

Absorptive Polarizers

Wire-grid polarizer is the simplest polarizer in concept. Wire-grid polarizer is composed of a regular array of fine metallic wires that is parallel to one another. It is then placed in a plane at 90 degrees to the incident beam that is unpolarized.

If the waves in the unpolarized beam that are at 90 degrees to the fine metallic wire, the unpolarized beam is able to travel through the grid with very little energy being reflected or lost. However if the waves in the unpolarized beam is parallel to the wires, then it will be absorbed or reflected. In simple terms, it is only when light travels in a certain direction will pass through the polarizer, and the rest of the light beam will be absorbed or reflected.

The distance separating the wires must be less than the radiation wavelength for any practical uses of the wire-grid polarizer. Wire-grid polarizers are generally applied only for microwaves and for infrared light in the far- and mid-range.

Beam-Splitting Polarizers

The incident beam is divided into two differing polarization beams in beam-splitting polarizers. Only one of the two differing polarization beam is fully polarized for many common beam-splitting polarizers.

Since beam splitting polarizers does not absorb or reflect the energy of the rejected polarization state, beam-splitting polarizers are more suited for applications such as laser light. True polarizing beamsplitters are also practical where the two polarization components are to be studied or simultaneously used.

Working Principle

Polarizers operate on the principle of dichroism. Dichroic materials are those which exhibit different absorptions for perpendicular incident planes. The intensity of the transmitted light that is incident at angles other than 90° is given by Law of Malus.

Source: AZoOptics

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