Variable geometric-phase polarization rotators for the visible

We present the principles of Variable pure polarization rotators based on t he accumulation of a geometric phase that is obtained by coiling a beam of light via discrete reflections. They consist of two pseudo rotators in seri es. By changing the angle between the pseudo rotators the geometric phase a cquired by die light is varied. We describe in detail two important example s: the variable-angle Porro rotator, which uses four linear-polarization pr eserving reflectors to work at a predetermined wavelength range, and the va riable compensating phase-shift rotator, which uses eight reflections to co mpensate the overall s- and p-polarization phase shifts, and thus is achrom atic. (C) 1999 Published by Elsevier Science B.V. All rights reserved.