Abstract
Nanoantennas are efficient devices exhibiting large confined electric field enhancements. So far, they have been extensively researched mainly in the receiving mode, which means that the illuminating field is essentially a plane wave. In this article, we consider the problem of designing an efficient and highly directive transmitting nanoantenna where the system is energized by a nonplane wave field, a subwavelength laser excitation. The main objective of this article is to establish through an accurate computational model a basic understanding of how a dipole-type radiator can be made to resonate with such complex nonplane-wave type of near-field illumination. Including short-wavelength components allowed us to achieve a 200-nm spot radius, which is a quarter of its incident wavelength (800 nm). Near- and far-field antenna quantities are introduced and calculated using an efficient full-wave finite-element method-based multiphysics solver. A nanoscale optical antenna is then presented with optimized dimensions and material settings. Various design data and insights are also discussed in connection with issues such as how to define efficiency and determine whether the system is radiating properly.
Highlights
R ESEARCH on nano-antennas for visible and infrared radiation is an emerging field with novel applications in many areas such as biomedical imaging, near-field nanooptics, quantum communications, and optical signal processing [1]
The importance of nanoantennas comes from their ability to provide a substrate for observables and potential useful interactions between light and structures that are much smaller than the diffraction limit
The nanoantenna allows light localization at a subwavelength scale by establishing light-matter interactions involving objects whose size is below the diffraction limit [3]
Summary
R ESEARCH on nano-antennas for visible and infrared radiation is an emerging field with novel applications in many areas such as biomedical imaging, near-field nanooptics, quantum communications, and optical signal processing [1]. Focused lasers can be deployed for excitation because they are able to concentrate the EM field within a domain smaller than the diffraction limit. This allows the laser field to illuminate parts of the nanoantenna even if the wavelength of the laser is in the optical regime. We consider a different method to excite a transmitting nanoantenna, which is via illumination by a subwavelength laser. Subwavelength laser is a method to generate coherent optical fields at the nano-scale (beyond diffraction limit) [16], [17]. A detailed and full investigation of how to model and design transmitting nanoantenna using a subwavelength laser excitation method is provided.
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