Subwavelength Hole Arrays Research Articles

Enhanced lens byεandμnear-zero metamaterial boosted by extraordinary optical transmission

In this paper we report directivity enhancement by a short-focal-length plano-concave lens engineered by stacked subwavelength hole arrays (fishnet-like stack) with an effective negative index of refraction close to zero, $n$ \ensuremath{\rightarrow} 0, that arises from \ensuremath{\varepsilon} and \ensuremath{\mu} near-zero extreme values. The plano-concave lens frequency response shows two enhancement peaks, one at the wavelength corresponding to $n$ $=$ \ensuremath{-}1 and, prominent in this configuration, another unexpected peak when $n$ \ensuremath{\rightarrow} 0 that comes as a result of the similar low values of \ensuremath{\varepsilon} and \ensuremath{\mu}. The frequency-dependent negative refractive index and beam-forming properties of the lens are supported by finite-integration-frequency- and time-domain simulations and experimental results. This near-zero metamaterial lens can find applications in terahertz and even optics since the building block, stacked extraordinary optical transmission layers, has already been reported for those regimes under the name of fishnet structure.

Polarization independent visible color filter comprising an aluminum film with surface-plasmon enhanced transmission through a subwavelength array of holes

The enhanced transmission through periodic arrays of sub-wavelength holes in optically-thick metallic films has many potential applications, such as in wavelength filters, light extraction from light emission diodes, and subwavelength photolithography. A color filter comprising arrays of subwavelength holes in an aluminum film has been fabricated. In addition to the simplicity of the process, the aluminum film enables the excitation of visible-range surface plasmons due to its high plasma frequency. Periodic nanostructures in the aluminum film open the way for new visible color filters.

Plasmonic antiresonance through subwavelength hole arrays

It has been shown both experimentally and numerically that the phenomenon of extraordinary transmission through subwavelength hole arrays is generally associated with a drop in transmission located very close to it. Paradoxically, this antiresonant drop occurs at the wavelength that, at first glance, should provoke a resonant excitation of a surface plasmon propagating along the metallic surface of the screen. The present paper gives a theoretical demonstration of this phenomenon, which dispels the paradox. Our theory is supported by numerical calculations.

Controlling Extraordinary Optical Transmission by Subwavelength Hole Arrays -Bragg gratings structure

We demonstrate a controlling of extraordinary optical transmission by using a novel structure composed of metal film with subwavelength hole arrays and Bragg structure. Extraordinary optical transmission through periodic arrays of subwavelength holes usually presents two obvious speaks. By controlling parameters of Bragg structure such as refractive indices or thickness, we can realize the switching of one of the peaks of extraordinary optical transmission. This structure might be used as tunable filters in future integrated optical circuit.

Extraordinary terahertz transmission in superconducting subwavelength hole array

We report the extraordinary terahertz (THz) transmission through subwavelength hole array in superconducting NbN film. As the temperature drops below the superconducting transition temperature, the transmission spectra experience distinct changes. The extraordinary transmission is greatly enhanced in superconducting state due to the enhancement of surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs). We have also observed temperature-dependent resonance frequency shift, which mainly depends on the coupling between SPPs and LSPs.

Mechanism of enhancement in absorbance of vibrational bands of adsorbates at a metal mesh with subwavelength hole arrays

We have investigated the mechanism of enhanced absorption intensities of vibrational bands of adsorbates on copper meshes with subwavelength holes by measuring and simulating temporal profiles of infrared pulses transmitted through the meshes. As reported previously [Williams et al., J. Phys. Chem. B, 2003, 107, 11871], the absorption intensities of CH stretching bands of alkanethiolate adsorbed on the mesh increase substantially with decreasing hole size. The enhancements of absorption intensities are associated with temporal delays of infrared pulses transmitted through the mesh. Finite difference time domain calculations reproduce the observed pulse delays as a function of hole size. These facts indicate that the delays of transmitted pulses are not caused by coupling of infrared radiation to surface plasmon polaritons propagating on the front and rear surfaces of the mesh, but they are caused by the reduction in group velocity owing to coupling to waveguide modes of mesh holes. Consequently, the strong enhancements of the absorption intensities are attributed to adsorbates inside the holes rather than to those on the mesh surfaces that have been proposed previously.

Terahertz superconducting plasmonic crystals

We present a thermal active control over terahertz (THz) extraordinary transmission induced by a plasmon in a periodic subwavelength holes array and a patch array. Both arrays consist of high transition temperature YBCO superconductors using THz time domain spectroscopy (THz-TDS). In the periodic subwavelength YBCO holes array, we observe a transition between a virtual excitation type surface plasmon polaritons (SPP) mode and a real SPP mode accompanied with transmission amplitude modulation. This can be attributed to the c-axis Josephson plasma frequency. On the other hand, since dipole localized surface plasmon can be excited by direct optical illuminations without phase-matching techniques, we observe a transmission amplitude modulation induced by combining the normal state carriers and the superconducting carriers in the periodic subwavelength YBCO patch array. These THz superconducting plasmonic crystals hold great potential in application for extreme low-loss, large dynamic amplitude modulation, surface plasmon-based function devices.

A SLOW LIGHT FISHNET-LIKE ABSORBER IN THE MILLIMETER-WAVE RANGE

A novel route to achieve a narrowband free-space electromagnetic absorber in any range of the spectrum based on stacked subwavelength hole arrays is proposed. The absorption is obtained by means of a slow light mode inside a flshnet-like engineered structure and exploiting the unavoidable misalignments and bucklings of the free-standing stack. An incoming pulse becomes permanently trapped in the structure due to the near zero group velocity which causes an enhancement of the radiation-structure interaction that leads to a huge increment of losses arising from the flnite conductivity of the metal as well as arrangement tolerances. This approach is studied not only by simulation but also experimentally under normal incidence at millimeter wavelengths. Moreover, a basic grasp about the angular dependence of the structure is given by analyzing the 2D dispersion diagram. It shows that this scheme may also display high absorption under oblique incidence for s-polarization (or TE-polarization), whereas p-polarization (TM-polarization) would degrade its performance.

Extreme Scattering Effect: Light scattering analysis via the Discrete Sources Method

The effect of the Extraordinary Optical Transmission (Ebbesen et al. Nature 1998; 391, 667) through subwavelength holes array in noble metal screen is used for multiple practical applications in nanooptics and biophotonics. In this paper the Extreme Transmission Effect (Eremina et al. Opt. Comm. 2008; 281, 3581) in the noble metal film deposited on a glass prism in the evanescent wave’s area is in focus. The Discrete Sources Method (DSM) has been adjusted to calculate the polarized light scattering by an axially symmetric inclusion located in a film deposited on a glass prism. We extended the DSM for the evaluation of the Scattering Cross-Section in the prism domain. It has been shown that the maximum value of the Reflection Cross-Section appears at the same incident angle as for the Transmission Cross-Section. It has been demonstrated that the Reflection Cross-Section can exceed the Transmission Cross-Section under certain circumstances. Analysis of the correlation between the Plasmon Resonance in the gold film and the Extreme Scattering Effect demonstrates that the Plasmon Resonance plays an important but not the exclusive role in the appearance of the Extreme Scattering Effect.

Modifying infrared scattering effects of single yeast cells with plasmonic metal mesh

The scattering effects in the infrared (IR) spectra of single, isolated bread yeast cells (Saccharomyces cerevisiae) on a ZnSe substrate and in metal microchannels have been probed by Fourier transform infrared imaging microspectroscopy. Absolute extinction [(3.4±0.6)×10(-7) cm(2) at 3178 cm(-1)], scattering, and absorption cross sections for a single yeast cell and a vibrational absorption spectrum have been determined by comparing it to the scattering properties of single, isolated, latex microspheres (polystyrene, 5.0 μm in diameter) on ZnSe, which are well modeled by the Mie scattering theory. Single yeast cells were then placed into the holes of the IR plasmonic mesh, i.e., metal films with arrays of subwavelength holes, yielding "scatter-free" IR absorption spectra, which have undistorted vibrational lineshapes and a rising generic IR absorption baseline. Absolute extinction, scattering, and absorption spectral profiles were determined for a single, ellipsoidal yeast cell to characterize the interplay of these effects.

Sound transmission through perforated plates with subwavelength hole arrays: A rigid-solid model

We present, a model to calculate sound transmission through plates perforated with periodically distributed subwavelength holes. Measurements performed using aluminium-perforated plates immersed in water are compared to predictions obtained with the calculation model. The calculated results agree well with experimental ones. It is also showed, both experimentally and numerically, that the number of the transmission peaks, related to the Fabry-Pérot resonances, depends on the plate thickness. Finally the existence of a transmission dip, when the water wavelength is equal to the array period, is a manifestation of the Wood anomaly.

Enhancement of extraction efficiency by metallic photonic crystal embedding in light-emitting diode

The bandgap effect of photonic crystals (PCs) and the effect of grating diffraction can be used to improve the extraction efficiency of light from the light-emitting diode (LED). The transmission of light at certain wavelength through periodic sub-wavelength hole arrays in metal films is extraordinary, surface plasmon (SP) effects effectively. In this letter, silver metallic photonic crystals with square lattice of cylinder unit cells are fabricated in GaN layer of GaN-based blue LED. We use the finite-difference time-domain (FDTD) method to investigate the optical transmission, the results show that the light extraction efficiency is enhanced by more than four times. Then we use the surface plasmon dispersion relation to analyze the mechanism of antireflection.

Superconducting plasmonics and extraordinary transmission

Negative dielectric constant and dominant kinetic resistance make superconductors intriguing plasmonic media. Here we report on the first study of one of the most important and disputed manifestations of plasmonics, the effect of extraordinary transmission through an array of subwavelength holes, using a perforated film of high-temperature superconductor. We show that in the millimetric wave part of the spectrum exceptionally strong extraordinary transmission exists in the ideal conductor state, improves in the plasmonic regime of a superconductor, and diminishes in a highly lossy metal.

Acoustic transmission resonance and suppression through double-layer subwavelength holearrays

We present a theoretical study of acoustic waves passing through double-layersubwavelength hole arrays. The acoustic transmission resonance and suppression areobserved. There are three mechanisms responsible for the transmission resonance: theexcitation of geometrically induced acoustic surface waves, the Fabry–Perot resonance in ahole cavity (I-FP resonance) and the Fabry–Perot resonance between two plates (II-FPresonance). We can differentiate these mechanisms via the dispersion relation of acousticmodes supported by the double-layer structure. It is confirmed that the couplingbetween two single-layer perforated plates, associated with longitudinal intervaland lateral displacement, plays a crucial role in modulating the transmissionproperties. The strong coupling between two plates can induce the splitting of thetransmission peak, while the decoupling between plates leads to the appearance oftransmission suppression. By analyzing the criterion derived for transmissionsuppression, we conclude that it is the destructive interference between the diffractedwaves and the direct transmission waves assisted by the I-FP resonance of thefirst plate that leads to the decoupling between plates and then the transmissionsuppression.

Lumped elements circuit of terahertz fishnet-like arrays with composite dispersion

We have analyzed and characterized a terahertz stacked holes array over a broad transmission bandwidth. In this context, we identify the key contributions of the surface plasmon modes related to the periodicity of array, and of the subcut off transmission through the holes responsible of a ground left-handed dispersion branch. The experimental verification of a multimode electromagnetic behavior is performed by time domain spectroscopy, with a complementary assessment by full-wave analysis. A circuitlike approach appears suitable for the understanding of a zero-gap transition between the left- and right-handed characteristics, opening the way of nonvanishing group velocity in a near-zero index propagation medium. Such a balanced composite operation, pointed out over the past in the dual element transmission line approaches, is thus generalized for a stacked subwavelength holes array, whose operation can be compared to the one of the so-called fishnet structures.

Polarization-selective window-mirror effect in inductive gold grids

A thin gold film perforated with an array of subwavelength holes is known to exhibit extraordinary transmission at normal incidence, irrespective of the state of polarization of illumination [T. W. Ebbesen et al., Nature (London) 391, 667 (1998)]. We report that, at slightly non-normal incidence $(\ensuremath{\sim}8\ifmmode^\circ\else\textdegree\fi{})$, a properly designed inductive metal nanogrid may act as a window (with enhanced transmittance of 70%) or a mirror (with zero transmittance and enhanced reflectance) at a given wavelength, depending on the state of polarization of incident light. Experimental and numerical investigations reveal the role of surface plasmons as the underlying physical mechanism of this effect.

Optical transmission through double-layer, laterally shifted metallic subwavelength hole arrays

We measure the transmission of IR radiation through double-layer metal films with periodic arrays of subwavelength holes. When the two metal films are placed in sufficiently close proximity, two types of transmission resonances emerge. For the surface plasmon mode, the electromagnetic field is concentrated on the outer surface of the entire metallic layer stack. In contrast, for the guided mode, the field is confined to the gap between the two metal layers. Our measurements indicate that, as the two layers are laterally shifted from perfect alignment, the peak transmission frequency of the guided mode decreases significantly, while that of the surface plasmon mode remains largely unchanged, in agreement with numerical calculations.

High transmission and low color cross-talk plasmonic color filters using triangular-lattice hole arrays in aluminum films

Three primary color (red, green and blue) filters consisting of subwavelength triangular-lattice hole arrays in an aluminum film on glass were simulated and fabricated. A silicon dioxide cap layer, deposited on the patterned aluminum film, was found to almost double the transmission efficiency for all the filters. The measured peak transmittance for each color filter was above 30%, exhibiting a wavelength spectrum with a full-width at half-maximum of approximately 100 nm. Simulation results of various structures with different cap layers revealed the enhanced coupling between surface plasmon resonances at both sides of the metal film in a symmetrical configuration. It was found that gratings with as few as three periods were sufficient to demonstrate filtering. The effect of metal thickness and hole size was investigated in detail.

Cavity resonant mode in a metal film perforated with two-dimensional triangular lattice hole arrays

The transmission property of metallic films with two-dimensional hole arrays is studied experimentally and numerically. For a triangular lattice subwavelength hole array in a 150 nm thick Ag film, both cavity resonance and planar surface modes are identified as the sources of enhanced optical transmissions. Semi-analytical models are developed for calculating the dispersion relation of the cavity resonant mode. They agree well with the experimental results and full-wave numerical calculations. Strong interaction between the cavity resonant mode and surface modes is also observed.

Increased photocurrent in quantum dot infrared photodetector by subwavelength hole array in metal thin film

Photocurrent enhancement in quantum dot (QD) infrared photodetector (QDIP) with an optical grating of subwavelength hole array in a thin metal film has been studied by calculating the transmission and diffraction of the infrared optical field through the grating and the light-matter interaction between the transmitted optical field and electrons confined in the QD. It is shown that due to the small aspect ratio of realistic QDs in QDIPs, the light diffraction due to the surface plasmon effect at the metal-semiconductor surface and the photonic subwavelength hole array structure is dominant in increasing the photocurrent.