Abstract
We propose and investigate an ultra-wideband leaky-wave antenna that operates at optical frequencies for the purpose of efficient energy coupling between localized nanoscale optical circuits and the far-field. The antenna consists of an optically narrow aluminum slot on a silicon substrate. We analyze its far-field radiation pattern in the spectral region centered around 1550 nm with a 50% bandwidth ranging from 2000 nm to 1200 nm. This plasmonic leaky-wave slot produces a maximum far-field radiation angle at 32° and a 3 dB beamwidth of 24° at its center wavelength. The radiation pattern is preserved within the 50% bandwidth suffering only insignificant changes in both the radiation angle and the beamwidth. This wide-band performance is quite unique when compared to other optical antenna designs. Furthermore, the antenna effective length for radiating 90% and 99.9% of the input power is only 0.5λ(0) and 1.5λ(0) respectively at 1550 nm. The versatility and simplicity of the proposed design along with its small footprint makes it extremely attractive for integration with nano-optical components using existing technologies.
Highlights
The emerging field of nano-photonics has been gaining significant attention in recent years
The theory of this work is inspired by the analysis for an infinite perfect-electric-conductor (PEC) slot placed between two homogeneous dielectrics, similar to the one shown in Fig. 1 [17, 18]
The interesting feature of this leaky-wave antenna is that the radiation angle is almost frequency invariant, because the phase constant β is primarily determined by the relative electric permittivity of the two dielectric media as described in Eq (3)
Summary
The emerging field of nano-photonics has been gaining significant attention in recent years. Some resonant structures have been introduced in order to reduce the coupling length but are essentially narrowband [6] Another area that demands the effective coupling of free-space with nano-optical elements is the emission enhancement of nano-scale emitters. The emitter size is on the order of only a few tens of nanometers Such a scale mismatch is challenging for the energy conversion because small circuit elements lead to inefficient coupling with free-space due to their impedance mismatch [7]. An elementary dipole and a quantum dot are both extremely poor radiators at RF and optical frequencies respectively This problem can be alleviated by coupling the nanoscale localized energy through an optical antenna because it provides better matching to free-space. Fabrication tolerances on this size scale can pose serious impediments for achieving a desired functionality through the use of highly resonant structures
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