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.


LLNL researchers have developed a high average power Faraday rotator that is gas-cooled and uniquely designed to dissipate heat uniformly so that it does not build up in the optical component and affect its performance.  The Faraday rotator material is sliced into smaller disks like a loaf of bread so that high speed helium gas can flow between the slices.  With this highly efficient cooling design, each slice maintains a uniform thermal profile, mitigating adverse effects such as optical aberrations induced by temperature gradients.  This novel Faraday rotator when combined with other optical components would form an improved optical isolator suitable for laser systems that deliver high optical average powers.

  • Enables optical isolation (one way transmission of light), polarization switching and depolarization correction for high average power laser systems
  • Simplifies kW-class industrial laser system design architectures
Potential Applications
  • Optical isolator component for kW-class laser systems
  • Can be used to isolate high power optical amplifier stages from harmful back-reflections
  • Can be used to eliminate damaging back-reflections from the workpiece at the output of a laser peening, welding or cutting system
  • Other applications include high average power laser drivers for inertial fusion energy, laser accelerator systems, defense applications and additive manufacture.
Development Status

Current stage of technology development:  TRL 4

LLNL has filed for patent protection on this invention.


U.S. Patent Application No. 2020/0218100 GAS COOLED FARADAY ROTATOR AND METHOD published 07/09/2020

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