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Buyer's Guide

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Definition: the phenomenon of double refraction, or the polarization dependence of the refractive index in a medium

German: Doppelbrechung

Category: general optics

How to cite the article; suggest additional literature

In the literature, the term birefringence occurs with two different meanings. In classical optics, it is normally considered to have the same meaning as double refraction, as explained below. In nonlinear optics and laser technology, however, birefringence is usually meant to be the property of some non-isotropic transparent material that the refractive index depends on the polarization direction (direction of the electric field). The latter property makes this material (then called birefringent) capable of exhibiting double refraction, when being hit by an unpolarized light beam.

Consequences of a Polarization-dependent Refractive Index

The polarization dependence of the refractive index can have a variety of effects:

Examples of Birefringence

In laser technology and nonlinear optics, the phenomenon of birefringence occurs mainly in the context of non-isotropic crystals:

Even in a naturally isotropic medium, birefringence can be induced e.g. by inhomogeneous mechanical stress. This can be observed e.g. by placing a piece of acrylic between two crossed polarizers: when stress is applied to the acrylic, one observes colored patterns resulting from the wavelength-dependent effect of stress-induced birefringence. Similar effects occur in bent optical fibers, and also due to thermal effects in laser crystals, which can lead to depolarization loss.

Straight optical fibers usually exhibit only a small degree of random birefringence, which can however scramble the polarization state of guided light over some propagation distance, e.g. 1 m. There are polarization-maintaining fibers, where a strong artificial birefringence can be used for suppressing such effects.

Quantifying Birefringence

The magnitude of birefringence can be specified in different ways:


[1]R. Ulrich et al., “Bending-induced birefringence in single-mode fibers”, Opt. Lett. 5 (6), 273 (1980)
[2]S. J. Garth, “Birefringence in bent single-mode fibers”, J. Lightwave Technol. 6, 445 (1988)

(Suggest additional literature!)

See also: refraction, polarization beat length, birefringent tuners, birefringent phase matching, polarization-maintaining fibers, polarization of laser emission, spatial walk-off, fiber polarization controllers, Lyot filters, Spotlight article 2007-05-26

In the RP Photonics Buyer's Guide, 29 suppliers for birefringent materials are listed.

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