The Faraday rotator works because one polarization of the input light is in ferromagneticresonance with the material which causes its phase velocity to be higher than the other. Specifically, given two rays of circularly polarized light, one with left-hand and the other with right-hand polarization, the phase velocity of the one with the polarization in the same sense as the precessing magnetization is greater.
In other words, the plane of linearly polarized light is rotated when a magnetic field is applied parallel to the propagation direction. The empirical angle of rotation is given by:
Where β is the angle of rotation (in minutes of arc). B is the magnetic flux density in the direction of propagation (in gauss). d is the length of the path (in cm) where the light and magnetic field interact. Then is the Verdet constant for the material. This empirical proportionality constant (in units of minutes of arc per gauss per cm of path, or in SI units, radians per tesla per metre) varies with wavelength and temperature and is tabulated for various materials.
Faraday rotators are used in Faraday isolators to prevent undesired back propagation of light from disrupting or damaging an optical system.
This linearly polarizedlight enters a Faradayrotation element 6 and is derived out as signal light through an analyzer 7 optically coupled to the exit of the element 6.
In this arrangement, the positioning of the polarizer 5 and the analyzer 7 at the opposite ends of the Faradayrotation element 6 is indispensable.
The exit light from the upstream polarization-maintaining optical fiber 103 enters a Faradayrotation element 106 in the form of a YIG device in the illustrated embodiment.
In physics, the Faraday effect or Faradayrotation is a magneto-optical phenomenon, or an interaction between light and a magnetic field.
The rotation of the plane of polarization is proportional to the intensity of the component of the magnetic field in the direction of the beam of light.
Faradayrotation is an important tool in astronomy for the measurement of magnetic fields, which can be estimated from rotation measures given a knowledge of the electron number density.
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