Achromatic polarization retarder realized with slowly varying linear and circular birefringence.

Using the phenomena of linear and circular birefringence, we propose a device that can alter general elliptical polarization of a beam by a predetermined amount, thereby allowing conversion between linearly polarized light and circularly polarized light or changes to the handedness of the polarization. Based on an analogy with two-state adiabatic following of quantum optics, the proposed device is insensitive to the frequency of the light-it serves as an achromatic polarization retarder.