in physics, the faraday effect or faraday rotation is a magneto-optical phenomenon, that is, an interaction between light and a magnetic field in a medium. the faraday effect causes a rotation of the plane of polarization which is linearly proportional to the component of the magnetic field in the direction of propagation. formally, it is a special case of gyroelectromagnetism obtained when the dielectric permittivity tensor is diagonal. discovered by michael faraday in 1845, the faraday effect was the first experimental evidence that light and electromagnetism are related. the theoretical basis of electromagnetic radiation (which includes visible light) was completed by james clerk maxwell in the 1860s and 1870s. this effect occurs in most optically transparent dielectric materials (including liquids) under the influence of magnetic fields. the faraday effect is caused by left and right circularly polarized waves propagating at slightly different speeds, a property known as circular birefringence. since a linear polarization can be decomposed into the superposition of two equal-amplitude circularly polarized components of opposite handedness and different phase, the effect of a relative phase shift, induced by the faraday effect, is to rotate the orientation of a wave's linear polarization. the faraday effect has a few applications in measuring instruments. for instance, the faraday effect has been used to measure optical rotatory power and for remote sensing of magnetic fields. the faraday effect is used in spintronics research to study the polarization of electron spins in semiconductors. faraday rotators can be used for amplitude modulation of light, and are the basis of optical isolators and optical circulators; such components are required in optical telecommunications and other laser applications.see http://www.rp-photonics.com/regenerative_amplifiers.html ==history==  by 1845, it was known through the work of fresnel, malus, and others that different materials are able to modify the direction of polarization of light when appropriately oriented, making polarized light
Magnetism Michael_Faraday Optics Polarization_(waves)