Faraday Rotators

The polarisation state of a linearly polarised millimetre wave signal propagating through a magnetised ferrite tile is rotated. This polarisation rotation is non-reciprocal and is called Faraday rotation. Quasi-optical isolators and circulators use Faraday rotation to separate transmitted and received signals. The diagram below shows how a linearly polarised signal propagating from the left has its polarisation rotated as it passes through the ferrite due to the strong interaction between one of its constituent circular polarisation states and the precessing electrons within the ferrite material. If the rotated signal on the right of the diagram were to be propagated back through the ferrite, its polarisation state would be rotated by a further angle, theta, with respect to the original signal.