Diffraction-limited near-spherical focal spot with controllable arbitrary polarization using single objective lens

We report a time-reversal method based on the Richards-Wolf vectorial diffraction theory to generate a diffraction-limited near-spherical focal spot with arbitrary three-dimensional state of polarization using single objective lens. Three orthogonal dipole antennae are positioned above a flat mirror at a prescribed distance and an aplanatic objective lens is utilized to collect all the radiation fields emitted by the dipole antennae. The optical field in the pupil plane is calculated in a time-reversal manner and the vectorial Debye integral is used to verify the spatial intensity and polarization distributions in the focal region. The ability to confine the optical power within a subwavelength near-spherical volume with controllable three-dimensional polarization with single objective lens may be exploited in high-resolution imaging, high-density data storage, laser direct writing, lithography, spin-directional coupling, anisotropic particle trapping and manipulation.