Theoretical study on the generation of a low-noise plasmonic hotspot by means of a trench-assisted circular nano-slit

Abstract

We propose a novel trench-assisted circular metal nano-slit (CMNS) structure implementable on a fiber platform for the generation of a low-noise cylindrical surface plasmon (CSP) hotspot. We design trench structures based on a multi-pole cancellation method in order that a converging surface plasmon signal is well separated from co-propagating non-confined diffracted light (NCDL) at the hotspot location. In fact, the secondary radiation by the quasi-pole oscillation at the edge of the trench cancels the primary NCDL, thereby enhancing the signal-to-noise ratio (SNR) of the CSP hotspot. In particular, we investigate two types of trench structures: a rectangular-trench (RT) structure and an asymmetric-parabolic-trench (APT) structure, which are considered for the sake of the simplicity of fabrication and of the maximal enhancement of the SNR, respectively. In comparison with a conventional CMNS having no trenches, we highlight that the mean SNR of the CSP hotspot is enhanced by 6.97 and 11.89 dB in case of the optimized RT and APT CMNSs, respectively. The proposed schemes are expected to be useful for increasing the SNR of plasmonic devices that are interfered by NCDL, such as various types of nano-slits for generating high-resolution plasmonic signals, for example.

Numerical and Experimental Study on Multi-Focal Metallic Fresnel Zone Plates Designed by the Phase Selection Rule via Virtual Point Sources

“…They can be used not only as a replacement for conventional focusing lenses, but also as optical elements with exquisite properties by implementing various novel patterns onto the metallic annular slit structure, such as multi-focal, multi-chromatic, and super-oscillatory lenses [6][7][8][9][10]. Among them, studies of MFZPs for multi-focal applications have recently received considerable attention.…”

Plasmonics on Optical Fiber Platforms

“…To date, various configurations have been suggested for plasmonic focusing, such as nanoparticles [14], circular nanoslits [15], bowtie structures [16], metal tips [17], etc. Among them, circular metallic nanoslits (CMNSs) engraved on a thin metal film are of great interest because of their capability of generating focused cylindrical SPPs (C-SPPs), that is, plasmonic hotspots, via modest fabrication procedures [8]. While various structures and schemes were extensively investigated to intensify the plasmonic hotspots, the effect of nonconfined diffracted light (NCDL) that accompanies C-SPPs has not been investigated rigorously [18].…”

“…A full-vectorial simulation of a CMNS constructed on top of an optical fiber facet is considered in the following, which was initially proposed and analyzed in [8]. It was assumed that the optical fiber had a step-index core with a diameter of 8 μm and a numerical aperture (NA) of 0.1, and that the metal was made of gold, the material parameters of which, that is, the refractive index and extinction coefficient, were given by n = 0.16918 and k = 3.8816, respectively.…”

“…First of all, a simple CMNS without having any trench structure was numerically analyzed [8]. The C-SPP (graded red/yellow) and NCDL (graded blue) field intensity patterns are illustrated in Figure 2.…”

“…Among them, the author focuses on the optical fiber facet structures in that they inherently provide an easy and efficient access to light that the core of the optical fiber guides. Thus, in this chapter, the author investigates and discusses various optical fiber facet structures for an efficient platform for plasmonics research and applications: First, the author investigates trench-assisted circular metallic nanoslits on flat-cleaved optical fiber facets for the generation of axially symmetric SPP hotspots with significantly enhanced noise characteristics [8]. Second, the author investigates fiberized plasmonic Fresnel zone plates for super-variable focusing with incident wavelength and for selective focusing with incident polarization [9].…”