Extraordinary optical transmission with coaxial apertures

Physical Review B, 2006

We simulate the optical fields and optical transmission through nanoarrays of silica rings embedded in thin gold films using the finite-difference-time-domain method. By examining the optical transmission spectra for varying ring geometries we uncover large enhancements in the transmission at wavelengths much longer than the usual cutoffs for cylindrical apertures or where the usual planar surface plasmons or other periodic effects from the array could play a role. We attribute these enhancements to closely coupled cylindrical surface plasmons on the inner and outer surfaces of the rings, and this coupling is more efficient as the inner and outer ring radii approach each other. We confirm this hypothesis by comparing the transmission peaks of the simulation with cylindrical surface plasmon ͑CSP͒ dispersion curves calculated for the geometries of interest. One important result is that a transmission peak appears in the simulations close to the frequency where the longitudinal wave number k z in the ring satisfies k z = m / L, where m is an integer and L the length of the aperture, for a normal CSP TE 1 or TM 1 mode. The behavior of the CSP dispersion is such that propagating modes can be sent through the rings for ever longer wavelengths as the ring radii approach, whereas the transmission decreases only in proportion to the ring area.

Applied Physics Letters, 2006

Utilizing normal mode analysis of Maxwell's equations and finite-difference-time-domain simulations we find extraordinary optical transmission in nanoarrays of insulating coaxial cylindrical rings embedded in metal films. As the rings become narrower we find transmission peaks at longer wavelengths, with the peak wavelength increasing indefinitely as the rings narrow. This behavior results from the excitation of cylindrical surface plasmon resonant modes on the cylindrical insulator-metal interfaces of the rings. These findings indicate that the excitation of cylindrical surface plasmons in these structures can produce propagating modes and enhanced transmission at wavelengths longer than those predicted previously.

2009

abstract It has been theoretically predicted and experimentally shown that circular coaxial aperture arrays have higher transmissivities with respect to simple circular ones. This observation is mainly attributed to the propagating waveguide modes supported by the circular coaxial unit cell. In this letter, we investigate extraordinary light transmission in simple rectangular and coaxial rectangular aperture arrays through decaying TE waveguide modes at mid-infrared wavelengths.

Nanophotonics

Recent development in nanofabrication technology has enabled the fabrication of plasmonic nanoapertures that can provide strong field concentrations beyond the diffraction limit. Further utilization of plasmonic nanoaperture requires the broadband tuning of the operating wavelength and precise control of aperture geometry. Here, we present a novel plasmonic coaxial aperture that can support resonant extraordinary optical transmission (EOT) with a peak transmittance of ~10% and a wide tuning range over a few hundred nanometers. Because of the shadow deposition process, we could precisely control the gap size of the coaxial aperture down to the sub–10-nm scale. The plasmonic resonance of the SiNx/Au disk at the center of the coaxial aperture efficiently funnels the incident light into the sub–10-nm gap and allows strong electric field confinement for efficient second harmonic generation (SHG), as well as EOT. In addition to the experiment, we theoretically investigated the modal prope...

Optics Letters, 2008

Here we experimentally and computationally demonstrate high transmission through arrays of coaxial apertures with different geometries and arrangements in silver films. By studying both periodic and random arrangements of apertures, we are able to isolate transmission enhancement phenomena due to surface plasmon effects from those due to the excitation of cylindrical surface plasmons within the apertures themselves.

Optics Express, 2010

We investigate experimentally the transmission properties of single sub-wavelength coaxial apertures in thin metal films (t = 110 nm). Enhanced transmission through a single sub-wavelength coaxial aperture illuminated with a strongly focused radially polarized light beam is reported. In our experiments we achieved up to four times enhanced transmission through a single coaxial aperture as compared to a (hollow) circular aperture with the same outer diameter. We attribute this enhancement of transmission to the excitation of a T EM-mode for illumination with radially polarized light inside the single coaxial aperture. A strong polarization contrast is observed between the transmission for radially and azimuthally polarized illumination. Furthermore, the observed transmission through a single coaxial aperture can be strongly reduced if surface plasmons are excited. The experimental results are in good agreement with finite difference time domain (FDTD) simulations.

2005

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Microelectronic Engineering, 2010

In a recent paper Ebbesen et al. ͓Nature 391, 667 ͑1998͔͒ reported on extraordinary optical transmission through hole arrays in metallic films. They suggested an enhancement of the transmission by surface plasmons. Using the Chandezon method, we have performed numerical calculations for the transmission through silver gratings with very small slits. Our results agree qualitatively with Ebbesen's measurements. By evaluating the near field in the media above and below the metal we can verify that the astonishingly high transmission maxima indeed correspond to the excitation of surface plasmons on either side of the metal.

Optics Express, 2007

Extra ordinary transmission through arrays of subwavelength apertures has been investigated using near-field scanning optical microscopy. For such studies arrays were fabricated to give maximum resonance enhancement of light transmission at the wavelength of illumination that was used (532 nm). To define this enhancement a design was employed that allowed in one field of view of a near-field image the investigation of single apertures of dimension that was similar to what was incorporated into the sub-wavelength hole array. Significant asymmetry in the transmission and the propagation of the light along the aperture array was detected. This non-uniformity could be explained by polarization of the incident light, edge effects and the geometry of the array. The results support a hypothesis of both enhanced transmission due to surface plasmons and a non-diffracting beaming as a function of distance effect in the propagation of the light from the array.

Optics Express - OPT EXPRESS, 2005

An analysis of several types of one-dimensional transmission gratings structures with different metal contact geometries is used to study the role of horizontally oriented surface plasmons, cavity modes and other optical modes in enhanced transmission. Several competing theories of enhanced transmission are presented and the analysis of the structures in this work clearly establishes that horizontal surface plasmons can enhance or inhibit transmission depending on whether the HSPs establish vortices of energy that circulate in a direction that enhances or inhibits the flow of energy through the center of the grooves. Also, we show that enhanced transmission can be achieved using a different mechanism than previously reported in the literature. This new mechanism is a Fabry-Perot resonance produced by small notches in the top metal surface, which concentrates the energy from the incident beam and steers it through the slit openings and into the substrate. Finally, applications of the...