Subwavelength Holes Research Articles

Quantum transport of a single photon through a subwavelength hole by a single atom

The localization and transport of a photon through a subwavelength hole with the help of a neutral atom are studied. A method proposed and realized in the study is based on the absorption of a photon by a neutral atom directly in front of a subwavelength hole, the flight of the atom through the hole, and photon emission on the other side of the screen. The influence of the interaction of the excited atom flying through the subwavelength channel with the screen material is estimated. The estimate showed that the atomic excitation can be quenched in holes with diameters smaller than 200 nm, which affects the photon transport efficiency.

Extraordinary light transmission through a metal film perforated by a subwavelength hole array

It is shown that, depending on the incident wave frequency and the system geometry, the extraordinary transmission of light through a metal film perforated by an array of subwavelength holes can be described by one of the three mechanisms: the “transparency window” in the metal, excitation of the Fabry–Perot resonance of a collective mode produced by the hybridization of evanescence modes of the holes and surface plasmons, and excitation of a plasmon on the rear boundary of the film. The excitation of a plasmon resonance on the front boundary of the metal film does not make any substantial contribution to the transmission coefficient, although introduces a contribution to the reflection coefficient.

Extraordinary optical transmission of periodic array of subwavelength holes within titanium nitride thin film

We focused on the optical properties of square array of subwavelength holes created within a titanium nitride (TiN) thin film. The TiN layer was placed on top of the dielectric layer as a surface plasmonic system originated from an intermetallic–dielectric arrangement. The finite-difference time-domain method was used via an Optiwave package to simulate periodic array of square and circular holes within the TiN layer. The effect of geometrical and material parameters such as periodic constant (a), size (S), shape of the holes, and the electric permittivity of the dielectric substrate has been investigated. An extraordinary optical transmission was observed in comparison with the nonhole system. It was shown that the wavelength of plasmonic modes, as a characteristic feature of the system, was affected by changing the periodic constant and electric permittivity. Meanwhile, changing the size as well as the shape of the holes did not affect the position of the peaks. These results are in agreement with the characteristic equation for plasmonic structure, which relates the surface plasmon wavelength (λsp) to the geometrical and material parameters of the system. The intensity of excited peaks was explained by distribution of the z-component of the electric field obtained from simulation, which illustrated the role of the surface plasmon polariton, localized surface plasmon resonance, and waveguide mode in tuning the optical behavior of the system. The results showed that TiN is a promising candidate for replacing metals in a plasmonic application with particular chemical and mechanical features.

Modulating and tuning relative permittivity of dielectric composites at metamaterial unit cell level for microwave applications

Dielectric materials with desirable relative permittivity (εr) may not be readily available in nature and are usually difficult to be tailored precisely. We hereby predict and experimentally achieve the flexible tuning of εr for dielectric materials at the unit cell level in microwave range, as inspired by the recent developments in metamaterials. A series of composite dielectric stock sheets with εr in the range of 3–7 and low loss tangent (tanδ<0.01) were successfully fabricated by dispersing different volume fractions of TiO2 nanoparticles into polypropylene polymer matrix. To further enable the flexible tuning of εr, sub-wavelength holes with different diameters were drilled on the composite dielectric sheets based on 5×5×5mm3 metamaterial unit cells. The resultant effective εr of the metamaterials conformed well to the simulation results by CST STUDIO SUITE® software. By utilizing the drilled-hole PP/TiO2 composite metamaterials, a potential scheme to implement a dielectric gradient index lens with discretized shells of varying εr is presented. This drilling-hole approach to modulate and tune the effective εr at the metamaterial unit cell level can be generalized to produce a variety of desirable permittivity values with great flexibility. The applications of these materials can be easily extended to other microwave or optical devices including cloaks, lenses, and beam shifters.

Acoustically tunable optical transmission through a subwavelength hole with a bubble

Efficient manipulation of light with sound in subwavelength-sized volumes is important for applications in photonics, phononics and biophysics, but remains elusive. We theoretically demonstrate the control of light with MHz-range ultrasound in a subwavelength, 300 nm wide water-filled hole with a 100 nm radius air bubble. Ultrasound-driven pulsations of the bubble modulate the effective refractive index of the hole aperture, which gives rise to spectral tuning of light transmission through the hole. This control mechanism opens up novel opportunities for tuneable acousto-optic and optomechanical metamaterials, and all-optical ultrasound transduction.

Study of a nano optical antenna for intersatellite communications

Nowadays, communications are moving to the optical frequencies, due to the extended bandwidth available, and the saturation of the RF spectrum. The dimensions of the antennas decrease with the operating wavelength. Therefore, in the optical domain, building an antenna may imply the design of a device with dimensions of several nanometers. The development of nanotechnology has enabled the development of these new devices, known as nanoantennas or optical antennas. New phenomenology has appeared with these new devices. In 2006 it was discovered that the transmission of light through arrays of subwavelength holes in a metal, gives rise to the phenomenon of extraordinary optical transmission, or in other words the amount of optical energy appearing on the other side of the metal is much greater than was expected by theoretical studies. The applications of these new antennas are fascinating, and are present in a very broad range of areas from biophotonics to quantum communication, data processing or optical wireless communications. This paper aims at studying and characterizing, in a classical perspective, an optical antenna formed by an array of subwavelength holes in a metal sheet that could be integrated in the transmitter or receiver ends of an intersatellite optical communication system.

Low-loss polarization-maintaining THz photonic crystal fiber with a triple-hole core.

In this paper, we report a novel low-loss and polarization-maintaining terahertz (THz) photonic crystal fiber with a triple-hole unit inside the core. The properties of birefringence, effective material loss, confinement loss, bending loss, power fraction, dispersion, and single-mode condition are analyzed in detail by using the finite element methods. Simulation results show that high birefringence at a level of 10-2 can be achieved by simply reducing the diameter of one air hole of the triple-hole core. And low effective material loss down to 30% of its bulk material loss can be achieved in our interested band around 3 THz, due to the high core porosity of the designed triple-hole core. Moreover, this design dramatically facilitates the fabrication process, because of the typical hexagonal structure with all circular air holes and avoiding the troublesome multiple sub-wavelength air holes in the core area. The results reveal that this proposal has potential for efficient THz transmission and other functional applications.

Evolutionary Design and Prototyping of Single Crystalline Titanium Nitride Lattice Optics

This paper describes the design and prototyping of single-crystalline TiN plasmonic metasurfaces based on subwavelength hole arrays. An evolutionary algorithm with a multiobjective fitness function was developed to produce a variety of three-dimensional (3D) light profiles with balanced intensities at the light spots. We also demonstrated a simple, efficient technique to prototype these lattice designs in large-area TiN films by combining focused ion beam milling and wet chemical etching. Multilevel phase control was achieved by tuning nanohole size, and multipoint focusing with arbitrary light spot patterns was realized. Using anisotropic nanohole shapes, the TiN lattice lenses could exhibit dynamic tuning of the focal profiles by changing the polarization of incident light.

Coherent Terahertz Radiation from Multiple Electron Beams Excitation within a Plasmonic Crystal-like structure

Coherent terahertz radiation from multiple electron beams excitation within a plasmonic crystal-like structure (a three-dimensional holes array) which is composed of multiple stacked layers with 3 × 3 subwavelength holes array has been proposed in this paper. It has been found that in the structure the electromagnetic fields in each hole can be coupled with one another to construct a composite mode with strong field intensity. Therefore, the multiple electron beams injection can excite and efficiently interact with such mode. Meanwhile, the coupling among the electron beams is taken place during the interaction so that a very strong coherent terahertz radiation with high electron conversion efficiency can be generated. Furthermore, due to the coupling, the starting current density of this mechanism is much lower than that of traditional electron beam-driven terahertz sources. This multi-beam radiation system may provide a favorable way to combine photonics structure with electronics excitation to generate middle, high power terahertz radiation.

Wide-gamut plasmonic color filters using a complementary design method

Plasmonic color filters (PCFs) can acquire primary colors from non-polarized incident light through a two-dimensional arrangement of subwavelength holes. However, owing to the geometry of the 2D array, unintended secondary transmitted peaks derived from the higher-order modes of the surface plasmon resonance (SPR) lead to color cross-talk with the primary peaks. Herein, we propose a complementary design method for generating high-purity red, green, and blue (R/G/B) by combining the G/B filters of hole-arrays with the R filters of dot-arrays. Metallic dot-array filters, wherein the wavelength band under 575 nm was effectively blocked by the induction of peak broadening, operated as optical high-pass filters exhibiting pure red, and consequently widen the color gamut of PCFs by 30% without loss of luminance and color tunability. This harmonious combination promises to yield competitiveness for a next-generation color filter by enhancing the color reproducibility of plasmonic nanostructures.

Single photon transport by a moving atom

The results of investigation of photon transport through the subwavelength hole in the opaque screen by using single neutral atom are represented. The basis of the proposed and implemented method is the absorption of a photon by a neutral atom immediately before the subwavelength aperture, traveling of the atoms through the hole and emission of a photon on the other side of the screen. Realized method is the alternative approach to existing for photon transport through a subwavelength aperture: 1) self-sustained transmittance of a photon through the aperture according to the Bethe’s model; 2) extra ordinary transmission because of surface-plasmon excitation.

Magneto-optical Studies of Noble Metal-Magnetic Dielectric Systems

The extraordinary optical transmission and Faraday effects of the bilayer heterostructure consisting of a metallic film perforated with subwavelength hole arrays and a uniform dielectric film magnetized perpendicular to its plane were systematically studied by three-dimensional finite-difference time-domain method. Results of the calculation found that for the magneto-plasmonic crystals under polarized incident light with transverse magnetic mode, the resonant transmittance reached 36.9%, the Faraday rotation acquired 1.216°, and the ellipticity got a positive value of 0.840. The value of Faraday rotation and ellipticity is respectively 15.2 and 93.3 times enhancement of the 0.08° and −0.009 of the bare BIG film at the wavelength. In the transverse electric mode, the Faraday effects of the systems also had a large enhancement in contrast to the bare magnetic film. The magneto-optical effects of the systems could be manipulated by polarization mode of incident light, geometry of perforated subwavelength hole arrays, and thickness of metallic and magnetic films. Evolution of the magneto-optical properties on the structural parameters was also analyzed. Possible mechanisms underlying the extraordinary phenomena were profoundly discussed. All these results indicated that the systems could find potential applications in magneto-optical devices such as data storages, sensors, and telecommunications.

Single photon transport by a moving atom through sub-wavelength hole

The results of investigation of photon transport through the subwavelength hole in the opaque screen by using single neutral atom are represented. The basis of the proposed and implemented method is the absorption of a photon by a neutral atom immediately before the subwavelength aperture, traveling of the atoms through the hole and emission of a photon on the other side of the screen. Realized method is the alternative approach to existing for photon transport through a subwavelength aperture: 1) self-sustained transmittance of a photon through the aperture according to the Bethe’s model; 2) extra ordinary transmission because of surface-plasmon excitation.

Resonantly induced transparency for metals with low angular dependence

Thin (sub skin-depth) metal layers are known to almost completely reflect radiation at microwave frequencies. It has previously been shown that this can be overcome at resonance via the addition of closely spaced periodic structures on either side of the film. In this work, we have extended the original one-dimensional impedance mechanism to the use of two-dimensional periodic structures both experimentally and analytically using an equivalent circuit approach. The resulting device shows experimentally a low (&amp;lt;5% relative frequency shift) dependence in both angle of incidence and polarisation. We also show that the same principle can be used to transmit through a thicker (∼μm) perfectly conducting film perforated with a non-diffracting (short pitch) array of subwavelength holes with the cut-off frequency above 900 GHz showing resonant transmissivities in the 20–30 GHz range above 40%.

Plasmonics [Scanning the issue

Surface plasmon photonics (“plasmonics”) is an expanding field at the frontiers of optical science and engineering, concerned with the interaction of light with metallic structures. Surface plasmons are coupled electromagnetic/charge-density waves propagating along metal-dielectric interfaces or localized at metal nanostructures. Light suitable for exciting surface plasmons is typically within or near the visible but may extend into the infrared and ultraviolet regions. Metallic structures that support surface plasmons are highly varied, including planar arrangements of metal films, stripes or grooves, metal gratings, and metal nanoparticles such as islands, spheres, rods, or antenna-inspired structures. Surface plasmons can be localized at subwavelength scales, and, for example, are involved in optical transmission through one or several subwavelength holes in a metal film, in what is now referred to as “extraordinary optical transmission.” Surface plasmons are intimately involved in the response of “metamaterials” and “metasurfaces” constructed from deep subwavelength metallic features, producing esoteric macroscopic properties such as a negative refractive index, or a permittivity/permeability near zero.

Extraordinary optical transmission inside a waveguide: spatial mode dependence.

We study the influence of the input spatial mode on the extraordinary optical transmission (EOT) effect. By placing a metal screen with a 1D array of subwavelength holes inside a terahertz (THz) parallel-plate waveguide (PPWG), we can directly compare the transmission spectra with different input waveguide modes. We observe that the transmitted spectrum depends strongly on the input mode. A conventional description of EOT based on the excitation of surface plasmons is not predictive in all cases. Instead, we utilize a formalism based on impedance matching, which accurately predicts the spectral resonances for both TEM and non-TEM input modes.

Coupled-cavity-based slow light metamaterials with antireflection structures

A slow light metamaterial based on a coupled Fabry-Pérot cavity is proposed and numerically studied using finite-difference time-domain simulations. The coupled cavity-based slow light metamaterial is composed of a periodic array of partial mirrors with low transmittance, i.e., thin metal films perforated with a subwavelength hole array. The tight-binding model is employed to investigate the transmission properties of the coupled-cavity-based metamaterial. It is shown that the group velocities of the slowly propagating modes can be controlled by adjusting the radius of holes in the mirrors. We also show that undesirable reflections at the boundaries of the finite-size metamaterial can be minimized by introducing optimized antireflection structures.

Dynamics of Strong Coupling between CdSe Quantum Dots and Surface Plasmon Polaritons in Subwavelength Hole Array.

We have investigated the strong coupling interaction between excitons of CdSe quantum dots (QDs) and surface plasmon polaritons (SPPs) of gold nanohole array by steady-state spectroscopic method and transient absorption measurements. Numerical and experimental steady-state measurements demonstrate that the SPP-QD system can indeed undergo strong coupling, characterized by a Rabi splitting up to 220 meV. In particular, it is found that in the transient absorption spectra, under resonant excitation, the 1S transition bleaching band from uncoupled CdSe QDs is completely separated into two distinctive bleaching bands, remarkably fingerprinting the hybrid SPP-QD state. It was also found that the lifetime of these hybrid bands is just slightly shorter than the lifetime of bare CdSe QDs, possibly caused by the phonon bottleneck effect due to the large Rabi splitting. These results could open a new avenue toward the development of novel nanoplasmon devices with strong SPP-QD interaction.

Strong Coupling: Dynamics of Strong Coupling between J‐Aggregates and Surface Plasmon Polaritons in Subwavelength Hole Arrays (Adv. Funct. Mater. 34/2016)

Strong Coupling: Dynamics of Strong Coupling between J‐Aggregates and Surface Plasmon Polaritons in Subwavelength Hole Arrays (Adv. Funct. Mater. 34/2016)

A study of angle dependent surface plasmon polaritons in nano-hole array structures

We report that the light-matter interaction in metallic nano-hole array structures possess a subwavelength hole radius and periodicity. The transmission coefficient for nano-hole array structures was measured for different angles of incidence of light. Each measured transmission spectrum had several peaks due to surface plasmon polaritons. A theory of the transmission coefficient was developed based on the quantum density matrix method. It was found that the location of the surface plasmon polariton and the heights of the spectral peaks were dependent on the angle of incidence of light. Good agreement was observed between the experimental and theoretical results. This property of these structures has opened up new possibilities for sensing applications.