Optical confinement in the nanocoax: coupling to the fundamental TEM-like mode.

The nanoscale coaxial cable (nanocoax) has demonstrated optical confinement in the visible and the near infrared. We report on a novel nanofabrication process which yields optically addressable, sub-µm diameter, and high aspect ratio metal-insulator-metal nanocoaxes made by atomic layer deposition of Pt and Al2O3. We observe sub-diffraction-limited optical transmission via the fundamental, TEM-like mode by excitation with a radially polarized optical vortex beam. Our experimental results are based on interrogation with a polarimetric imager. Finite element method numerical simulations support these results, and their uniaxial symmetry was exploited to model taper geometries with both an electrically large volume, (15λ)3, and a nanoscopic exit aperture, (λ/200)2.

Wireless communication system via nanoscale plasmonic antennas.

Present on-chip optical communication technology uses near-infrared light, but visible wavelengths would allow system miniaturization and higher energy confinement. Towards this end, we report a nanoscale wireless communication system that operates at visible wavelengths via in-plane information transmission. Here, plasmonic antenna radiation mediates a three-step conversion process (surface plasmon → photon → surface plasmon) with in-plane efficiency (plasmon → plasmon) of 38% for antenna separation 4λ0 (with λ0 the free-space excitation wavelength). Information transmission is demonstrated at bandwidths in the Hz and MHz ranges. This work opens the possibility of optical conveyance of information using plasmonic antennas for on-chip communication technology.

Aluminum Nanowire Arrays via Directed Assembly.

Freestanding and vertically-oriented metal nanowire arrays have potential utility in a number of applications, but presently lack a route to fabrication. Template-based techniques, such as electrodeposition into lithographically defined nanopore arrays, have produced well-ordered nanowire arrays with a maximum pitch of about 2 µm; such nanowires, however, tend to cluster due to local attractive forces. Here, we modify this template fabrication method to produce well-ordered, vertically-oriented, freestanding Al nanowire arrays, etched from an underlying Al substrate, with highly tunable pitch. In addition, optical measurements demonstrated that the nanowires support the propagation of surface plasmon polaritons.

Nanocoaxes for optical and electronic devices.

The evolution of micro/nanoelectronics technology, including the shrinking of devices and integrated circuit components, has included the miniaturization of linear and coaxial structures to micro/nanoscale dimensions. This reduction in the size of coaxial structures may offer advantages to existing technologies and benefit the exploration and development of new technologies. The reduction in the size of coaxial structures has been realized with various permutations between metals, semiconductors and dielectrics for the core, shield, and annulus. This review will focus on fabrication schemes of arrays of metal - nonmetal - metal nanocoax structures using non-template and template methods, followed by possible applications. The performance and scientific advantages associated with nanocoax-based optical devices including waveguides, negative refractive index materials, light emitting diodes, and photovoltaics are presented. In addition, benefits and challenges that accrue from the application of novel nanocoax structures in energy storage, electronic and sensing devices are summarized.

Leakage radiation microscope for observation of non-transparent samples.

We describe a leakage radiation microscope technique that can be used to extend the leakage radiation microscopy to optically non-transparent samples. In particular, two experiments are presented, first to demonstrate that acquired images with our configuration correspond to the leakage radiation phenomenon and second, to show possible applications by directly imaging a plasmonic structure that previously could only be imaged with a near-field scanning optical microscope. It is shown that the measured surface plasmon wavelength and propagation length agree with theoretically-calculated values. This configuration opens the possibility to study important effects where samples are optically non-transparent, as in plasmonic cavities and single hole plasmonic excitation, without the use of time-consuming near-field scanning optical microscopy.

Near-field observation of light propagation in nanocoax waveguides.

We report the observation of propagating modes of visible and near infrared light in nanoscale coaxial (metal-dielectric-metal) structures, using near-field scanning optical microscopy. Together with numerical calculations, we show that the propagated modes have different nature depending on the excitation wavelength, i.e., plasmonic TE11 and TE21 modes in the near infrared and photonic TE31, TE41 and TM11 modes in the visible. Far field transmission out of the nanocoaxes is dominated by the superposition of Fabry-Perot cavity modes resonating in the structures, consistent with theory. Such coaxial optical waveguides may be useful for future nanoscale photonic systems.