Broadband Faraday Isolator
  Driving on an analogy with the technique of composite pulses in quantum physics, we propose a broadband Faraday rotator and thus a broadband optical isolator, which is composed of sequences of ordinary Faraday rotators and achromatic quarter-wave plates rotated at the predetermined angles. 
Michal Berent, Andon A. Rangelov and Nikolay V. Vitanov
physics.optics