摘要：The generation of subwavelength spots smaller than the Abbe diffraction limit has attracted great interest due to the various applications in many fields, such as high-density optical data storage and particle manipulation. Planar optics that can miniaturize conventional refractive optics have become increasingly attractive. In this work, we first formed a subwavelength bright spot and a three-dimensional optical trap under the illumination of an azimuthally polarized (AP) beam by only a single planar element, a spiral zone plate (SZP). Initially, the SZP was proposed as a computer-generated hologram to generate optical phase singularities. However, the SZP in this work was used to focus and modulate the incident AP beam with a vortex phase simultaneously. Therefore, no additional vortex phase modulating element was introduced in our method. The SZP has an ultra-long focal length of 250λ for a numerical aperture (NA) of 0.95 and an incident wavelength of 632.8 nm. The generated spot is purely transversely polarized with a lateral full width at half maximum (FWHM) of 0.43λ beyond the diffraction limit of 0.54λ. The generated focal field formed a stable optical trap for a Rayleigh dielectric particle in three dimensions.
