US Patent 8379188 Optical system

The disclosure provides an optical system having an optical axis, where the optical system includes a polarization manipulator which includes first and second subelements. The first subelement has a non-planar, optically effective surface. For light passing through the first subelement, the first subelement causes a change in the polarization state. A maximum effective retardation introduced by the first subelement along the optical axis is less than a quarter of the working wavelength of the optical system. The first subelement and the second subelement have mutually facing surfaces which are mutually complementary. The optical system also includes a position manipulator to manipulate the relative position of the first and second subelements.