Optical systems need to have the means to control the propagation of light through the system. Most optical system components propagate light bidirectionally.  However, some optical systems, such as lasers, are directed energy systems that require components to act as a one-way street for light; any back reflected light may interfere with the system’s operation or in the extreme case can cause catastrophic damage.

A Faraday rotator when combined with appropriately aligned polarizers forms an optical isolator, which only allow light propagation in one direction.  A Faraday rotator is a magneto-optical component that is capable of rotating in a particular direction linearly polarized light that happens to propagate through the Faraday medium.  The degree of rotation is associated with the strength of a magnetic field applied to the medium. An optical isolator based on Faraday rotator not only protects the source from back reflections and other unwanted signals from propagating towards the source, but also can be used for polarization switching as well as depolarization correction.

With high average power laser systems, there is understandably a need for optical components that can withstand the demanding operating conditions.  Of relevance is thermal load; if not properly addressed, heat-induced optical aberrations are introduced, which leads to a decline in the overall performance of the system.