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Polarizer is a kind of optical filter where the light transmission depends strongly on the polarization state usually linear polarization or sometimes circular polarization with aid of quarter waveplates.
The performance of a polarizer is characterized by various specifications:
Polarizer made of birefringent crystal such as Calcite, alpha-BBO, YVO4, MgF2 and Quartz has high extinction ratio(ER 1:106) and can be operated under high power laser for wavelength range from 200 nm (a-BBO) to 4500 nm (YVO4).
There are different kinds of birefringent polarizers either use the principles of 1) total internal reflection occurs for one polarization state, but not for the other such as
- Nicol prism
- Glan–Thompson prism
- Glan–Taylor prism
- Glan–Foucault prism
2) or exploit somewhat different refraction angles due to birefringence, such as
- Wollaston prism
- Nomarski prism
- Rochon prism
- Sénarmont prism
The reason for the use of many different designs of birefringent polarizer is that different applications can have quite different requirements on the polarizers, and no design can meet all requirements.
Thin film polarizer consist of a dielectric coating on one side of glass window/prism
1) either at Brewster's angle, so that no anti-reflection coating is required on the other side,
2) or operated at 45 deg. so as to made Cube polarizing beamsplitter which has polarizing coating applied on one 45deg. prism and anther 45deg prism cement to the coating.
An advantage of thin-film polarizer is that they can be made with rather large dimension, convenient cube shape and low cost, which are more difficult with crystalline (birefringent) polarizers.
Wire grid polarizers are made by fabricating very narrow (sub-wavelength) metal stripes on a glass substrate (using a lithographic technique) or in a free-standing arrangement (for longer wavelengths). A polarization direction along the chains is strongly reflected (or absorbed), whereas the absorption is weak for light with a polarization direction perpendicular to these. Such devices reflect or absorb s-polarized light, while p-polarized light is transmitted.
Polarized glass (silver or copper nanoparticles embedded) and Polaroid filters or polarizing sheets made of stretched polymer use the same principles.
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