Optical characterization of retarding devices

An apparatus for optically characterizing the retardation and eigenpolarization of an unknown retarding device, comprising:

• a) an optical source for generating an optical probe beam with a pre-determined polarization;
• b) a beam splitter for splitting the probe beam into two components, with constant dynamic phase difference between the components, the retarding device being arranged to receive from opposite directions each of the two probe beam components so that the polarization of each probe beam component is retarded by an equal degree;
• d) a polarizing analyzer arranged to receive both the retarded probe beam components, the analyzer having a pre-determined polarization axis to resolve the polarization of each of the retarded probe beam components along said axis;
• e) an optical detector arranged to receive the polarisation resolved beams so that said beams maintain the same dynamic phase and interfere coherently depending on a different geometric phase between the two polarization resolved beams, and to measure therefrom said interference;
• f) means for rotating the angle of the polarization axis of the analyzer to resolve the polarization of each beam along said rotating axis and to vary the geometric phase between the two polarization resolved beams;
• wherein the apparatus includes means for rotating the angle of the polarization axis of the analyzer to resolve the polarization of each of the polarization resolved beams along said rotating axis, in order to vary the geometric phase and hence the measured interference from the detector, the measured varying interference being used by a processor to calculate the retardation and elgenpolarisation of the unknown retarding device.