High optical resonance sensitivity to its environment of a fibered bowtie nano-aperture antenna

In this paper, we present a numerical study based on 3D FDTD (finite-difference time-domain) simulations that demonstrate the high sensitivity of the optical response of a bowtie nano-aperture antenna (BNA), engraved at the apex of a metal-coated tip, to the distance variation between it and a given substrate. This study mainly discussed the case of the collection mode regime of the BNA and considered the case of two different substrates (high and low refractive index). The coupling between the substrate and the BNA may greatly affect the properties of the optical resonance of the nano-antenna. A blueshift of the resonance wavelength, as large as Δλλ=0.3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\frac{\varDelta \lambda }{\lambda }=0.3$$\end{document}, is obtained when the tip moves away over only 10 nm from the substrate (InP) interface. These results open the way to the design of stand-alone optical near-field probes that allow faithful interaction control with a given sample as a function of the distance between them.