We show that a device consisting of an optical rotator placed between two identically oriented quarter-wave plates always acts as a halfwave retarder for some pair of orthogonal elliptically polarized states that can be selected by linear adjustment of the optical rotation and orientation of the quarter-wave plates.
© 1997 Optical Society of America
Rajendra Bhandari, "Halfwave retarder for all polarization states," Appl. Opt. 36, 2799-2801 (1997)