Faraday rotator
![Polarization mechanism due to the Faraday effect. The field lines are usually closed through a permanent magnet around the rotator.](/Images/godic/202501/12/Faraday-effect.svg0141.png")
A Faraday rotator is an optical device that rotates the polarization of light due to the Faraday effect, which in turn is based on a magneto-optic effect.
The Faraday rotator works because one polarization of the input light is in ferromagnetic resonance with the material which causes its phase velocity to be higher than the other.