Highly efficient broadband conversion of light polarization by composite   retarders
  Driving on an analogy with the technique of composite pulses in quantum physics, we propose highly efficient broadband polarization converters composed of sequences of ordinary retarders rotated at specific angles with respect to their fast-polarization axes. 
S. S. Ivanov, A. A. Rangelov, N. V. Vitanov, T. Peters, and T.   Halfmann
quant-ph