US Patent 10261294 Rotational varifocal planar lens

A varifocal lens includes a first phase plate and a second phase plate which are rotatable relative to each other about an optical axis. The first phase plate includes a plurality of first phase conversion elements, the second phase plate includes a plurality of second phase conversion elements, and the plurality of first phase conversion elements and the plurality of second phase conversion elements are arranged so that light transmitted through the first phase plate and the second phase plate is focused on different positions on the optical axis depending on a relative rotational displacement between the first phase plate and the second phase plate.