Fig. 1. Schematic of the tight focusing of the CPBB, where the insets denote the amplitude and the polarization profiles of the input beam, the green and blue markers denote the radial (e_ρ) and azimuthal (e_φ) polarizations, and θ denotes the angle between the focused ray and the z-axis.

Fig. 2. Optical needle is generated by the tightly focused CPBB. (a)–(c) The intensity distributions of the longitudinally and radially polarized components and the total field in yz-plane, with the transverse focal spots within 5λ squared areas inserted. (d) The intensity profile of the optical needle along the z-axis. (e) The total field, radially, and longitudinally polarized components in the focal plane.

Fig. 3. The focusing properties of the optical needle in the focal plane versus β. (a) The FWHM and ratio of I_zmax/I_rmax. (b) The DOF and energy proportion (η).

Fig. 4. Optical needle with longitudinal oscillating profiles. (a) The profiles of the input CPBBs with different β, where the abscissa has reached the upper limit. (b)–(e) The normalized intensity distribution and intensity profile of the total field in yz-plane when β = 2158, 2180, 2206, and 2238 with an NA = 0.95, respectively.

Fig. 5. Optical dark channel is generated by the tightly focused CPBB. (a) The intensity distribution of the total field in the yz-plane, with the transverse focal spots inserted. (b) The transverse intensity distribution of the azimuthally, radially, and longitudinally polarized components at the focal plane. (c) The DOF and the FWHM of the focal plane versus β.