Single‐Spot Focusing with Plasmonic Phase Manipulation

• Published in: Annalen der Physik Vol. 530; no. 11
• Main Authors: Darak, Mayur S., Mote, Rakesh G., Shukla, Shobha
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.11.2018
• Subjects: Focusing; Lenses; Light diffraction; Linear polarization; nanoscale; Nanotechnology; near‐field optics; optical components; phase manipulation; plasmonics; Polaritons; Polarized light; Ring structures; Rings (mathematics); Symmetry; Telecommunications industry
• ISSN: 0003-3804; 1521-3889
• DOI: 10.1002/andp.201800193

The ring structure has an inherent symmetry that can be used to focus light to a single in‐plane spot for near‐field plasmonic applications. However, when excited with a linearly polarized light, it yields split focal spot at the center due to destructive interference of surface plasmon polaritons (SPPs). Here, twin configurations of a slit‐based plasmonic lens for in‐plane focusing of a linearly polarized light are proposed. Lenses are designed based on the ring geometry in order to exploit symmetric nature of the ring structure. Either a metallic or a dielectric semicircular protrusion is introduced in the symmetric ring structure for compensating the phase mismatch between SPPs counter‐propagating from two sides of the ring. The focusing properties of the lenses are analyzed using finite‐difference time‐domain simulations. A single focal spot with full width at half maxima of 0.27λ0 and 0.28λ0 is obtained for plasmonic lenses with metallic and dielectric protrusions, respectively. Thus the diffraction limit is beaten by focusing the light to a subwavelength region of approximately quarter its wavelength. The lenses have potential applications in nanosensing, nanoimaging, and nanolithography, wherein closely populated focused spots are desired using linearly polarized excitation. Twin configurations of a slit‐based plasmonic lens are proposed for in‐plane focusing of a linearly polarized light to a single spot. To analyze the focusing properties of lenses, finite‐difference time‐domain simulations are performed. The proposed lenses beat the diffraction limit by focusing light to a subwavelength region of approximately quarter its wavelength. These lenses have potential applications in nanosensing, nanoimaging, and nanolithography.