Polarization Aspects of Localized Optical Spots Obtained Using Plasmonic Nano-Antennas
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Polarization Aspects of Localized Optical Spots Obtained Using Plasmonic Nano-Antennas Erdem Ogut1 and Kursat Sendur1 Sabanci University, Faculty of Engineering and Natural Sciences, Istanbul, 34956, Turkey.
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ABSTRACT Electromagnetic radiation beyond the diffraction limit with a particular polarization emerges as a need for plasmonic applications. One of these applications is all-optical magnetic recording, which requires circularly-polarized electromagnetic radiation. In this study, a plasmonic cross-dipole nano-antenna is illuminated with diffraction-limited linearly polarized radiation. An optimal configuration for the nano-antenna and the polarization angle of the incident light is identified to obtain linearly, circularly, and elliptically polarized optical spots beyond the diffraction limit. The Poincaré sphere representation is utilized to visually present calculated Stokes parameters for optical spots with linear, circular, and elliptical polarizations from specific antenna geometries.
INTRODUCTION Polarized electromagnetic radiation has led to interesting technical applications and significant advancements at both optical [1, 2, 3, 4, 5] and microwave frequencies [6]. With advances in nanotechnology, electromagnetic radiation beyond the diffraction limit with a particular polarization is an emerging need for plasmonic nano-applications. Among these applications, all-optical magnetic recording [7, 8] is an application which requires circular polarization. In the literature, it has been demonstrated that the magnetization can be reversed in a reproducible manner using a circularly polarized optical beam without an externally applied magnetic field [7, 8]. To advance the areal density of hard disk drives beyond 1 Tbit/in.2 using such a scheme, a sub-100 nm circularly polarized optical spot beyond the diffraction limit is required. In this study, a plasmonic cross-dipole nano-antenna is illuminated with diffractionlimited linearly polarized radiation. Plasmonic resonances of longitudinal and transverse components of the nano-antenna, and angle of incident polarization are adjusted to obtain optical spots at the nanoscale with linear, circular, and elliptical polarizations. Amplitude ratios and phase differences between the field components are presented for optical spots beyond the diffraction limit with various polarizations. Right-hand and left-hand circularly and elliptically polarized optical spots at the nanoscale are achieved. The Poincaré sphere representation is utilized to visually present the calculated Stokes parameters for optical spots with linear, circular, and elliptical polarizations. Amplitudes and phase differences between the field components of the achieved polarizations are used to calculate the particular Stokes parameters. Antenna geometry and incident polarization angle are identified to obtain various polarization states on the Poincaré sphere.
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