Faraday Rotator

A Farady rotator is made from a non-linear material with an electric current passing either across the light path or along the light path in the crystal. They are used in Ring Lasers and in Faraday Isolators.

A Faraday Rotator rotates light using the Faraday Effect. The degree of rotation is controled by an induced magnetic field. The two main uses for a Faraday Rotator are putting a polarizer in front so that back scatter is rotated and blocked by the polarizer and using them with wave plates to make a ring laser.

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 radians).
• B is the magnetic flux density in the direction of propagation (in teslas).
• d is the length of the path (in metres) where the light and magnetic field interact.
• Then V is the Verdet constant for the material. This empirical proportionality constant (in units of radians per tesla per metre, rad/(T·m)) varies with wavelength and temperature and is tabulated for various materials.