Polarization-Dependent Quasi-Far-Field Superfocusing Strategy of Nanoring-Based Plasmonic Lenses

• Main Authors: Hao Sun, Yechuan Zhu, Bo Gao, Ping Wang, Yiting Yu
• Format: Article
• Language: English
• Published: SpringerOpen 2017-06-01
• Series: Nanoscale Research Letters
• Subjects: Polarization; Nanoring-based plasmonic lenses; Subwavelength structures; Superfocusing; Geometric optics
• Online Access: http://link.springer.com/article/10.1186/s11671-017-2154-1
• ISSN: 1931-7573; 1556-276X

Abstract The two-dimensional superfocusing of nanoring-based plasmonic lenses (NRPLs) beyond the diffraction limit in the far-field region remains a great challenge at optical wavelengths. In this paper, in addition to the modulation of structural parameters, we investigated the polarization-dependent focusing performance of a NRPL employing the finite-difference time-domain (FDTD) method. By utilizing the state of polarization (SOP) of incident light, we successfully realize the elliptical-, donut-, and circular-shape foci. The minimum full widths at half maximum (FWHMs) of these foci are ~0.32, ~0.34, and ~0.42 λ 0 in the total electric field, respectively, and the depth of focus (DOF) lies in 1.41~1.77 λ 0. These sub-diffraction-limit foci are well controlled in the quasi-far-field region. The underlying physical mechanism on the focal shift and an effective way to control the focusing position are proposed. Furthermore, in the case of a high numerical aperture, the longitudinal component, which occupies over 80% of the electric-field energy, decides the focusing patterns of the foci. The achieved sub-diffraction-limit focusing can be widely used for many engineering applications, including the super-resolution imaging, particle acceleration, quantum optical information processing, and optical data storage.