We use the finite-element method for simulating light transmission through a 2D-periodic array of rectangular apertures in a film of highly conductive material. We report results with a relative error of the transmissivity lower than 0.01%. This is an improvement of about one order of magnitude compared to previously reported results. Further, the influence of corner and edge roundings on light transmission through the subwavelength apertures is investigated.
Light transmission through circular subwavelength apertures in metallic films with surrounding nanostructures is investigated numerically. Numerical results are obtained with a frequency-domain finite-element method. Convergence of the obtained observables to very low levels of numerical error is demonstrated. Very good agreement to experimental results from the literature is reached, and the utility of the method is demonstrated in the investigation of the influence of geometrical parameters on enhanced transmission through the apertures.
Extraordinary transmission through subwavelength metallic apertures has been extensively studied and demonstrated. At resonance, the coupling between surface plasmons on both surfaces of the metallic film tunnels the photon from the one side to the other through the subwavelength aperture with small transmission efficiency based on the metals dielectric parameters and aperture geometrical dimensions. Here, we report a completely different form of extraordinary transmission, where the two subwavelength complementary apertures when coupled with an optical cavity induce about 100% extraordinary t…
Transmission through sub-wavelength apertures in perfect metals is expected to be strongly suppressed. However, by structural engineering of the apertures, we numerically demonstrate that the transmission of transverse electric waves through periodic arrays of subwavelength apertures in a thin metallic film can be significantly enhanced. Based on equivalent circuit theory analysis, periodic arrays of square structured subwavelength apertures are obtained with a 1900-fold transmission enhancement factor when the side length $a$ of the apertures is 10 times smaller than the wavelength ($a/λ=0.1$…
We report subwavelength-thick, polarization insensitive micro-lenses operating at telecom wavelength with focal spots as small as 0.57 wavelengths and measured focusing efficiency up to 82%. The lens design is based on high contrast transmitarrays that enable control of optical phase fronts with subwavelength spatial resolution. A rigorous method for ultra-thin lens design, and the trade-off between high efficiency and small spot size (or large numerical aperture) are discussed. The transmitarrays, composed of silicon nano-posts on glass, could be fabricated by high-throughput photo or nanoimp…
Spatial effects of interference and interaction of light modes in the subwavelength part of the near-field optical microscopy probe have been theoretically studied. It was found that the mode interference can lead to higher spatial compression of light (lambda = 500 nm in free space) within the transverse size of 25 nm inside the probe output aperture of 100 nm in diameter. The results principally demonstrate the possibility of increasing spatial resolution of the near-field optical microscopy technique.
We report the enhanced transmission of electromagnetic waves through a single subwavelength aperture by making use of the resonance behavior of a split ring resonator (SRR) at microwave frequencies. By placing a single SRR at the near-field of the aperture, strongly localized electromagnetic fields are effectively coupled to the aperture with a radius that is twenty times smaller than the resonance wavelength. We obtained 740-fold transmission enhancement by exciting the electric resonance of SRR. A different coupling mechanism, through the magnetic resonance of SRR, is also verified to yield …
We study, and illustrate with numerical calculations, transmission enhancement by subwavelength 2D slits due to the dominant role played by the excitation of the eigenmodes of plasmonic cylinders when they are placed at the aperture entrance; and also due to reinforced and highly localized energy in the slit as a consequence of the formation of a nanojet. We show that, providing the illumination is chosen such that an aperture transmitting eigenmode is generated, the phenomenon is independent of whether or not the slit alone produces extraordinary transmission; although in the former case this…
We calculate, by means of fluctuational electrodynamics, the thermal emission of an aperture filled by vacuum or a material at temperature T. We show that thermal emission is very different whether the aperture size is large or small compared to the thermal wavelength. Subwavelength apertures filled with vacuum (subwavelength blackbody) have their thermal emission strongly decreased compared to classical blackbodies. A simple expression of their emissivity can be calculated and their total emittance scales as T 8 instead of T 4 for large apertures. Thermal emission of disk of materials with a …
Resonant transmission of light is a surface-wave assisted phenomenon that enables funneling light through subwavelength apertures milled in otherwise opaque metallic screens. In this work, we introduce a deep learning approach to efficiently compute and design the optical response of a single subwavelength slit perforated in a metallic screen and surrounded by periodic arrangements of indentations. First, we show that a semi-analytical framework based on a coupled-mode theory formalism is a robust and efficient method to generate the large training datasets required in the proposed approach. S…
We present a novel theoretical approach for modeling the resonant properties of transmission through subwavelength apertures penetrating metal films. We show that cavity mode theory applies to an effective resonant cavity whose dimensions are determined by the aperture's geometry and the evanescent decay lengths of the associated diffracted waves. This method suggests a concrete physical mechanism for the enhanced transmission observed in periodic aperture arrays, namely it is the evanescently scattered light, localized in the near field of metal surface, which couples into the apertures. Furt…
This contribution reviews the studies on subwavelength aperture antennas in the optical regime, paying attention to both the fundamental investigations and the applications. Section 2 reports on the enhancement of light-matter interaction using three main types of aperture antennas: single subwavelength aperture, single aperture surrounded by shallow surface corrugations, and subwavelength aperture arrays. A large fraction of nanoaperture applications is devoted to the field of biophotonics to improve molecular sensing, which are reviewed in Section 3. Lastly, the applications towards nano-opt…
For a narrow slit structure backed by a conducting strip which is taken as a representative example of an aperture-body resonance (ABR) problem, the transmission resonance condition (i.e., condition for maximum power transmission) and the transmission width (i.e., normalized maximum transmitted power through the slit) are found to be the same as those for narrow slit coupling problem in a thick conducting screen, which is designated as a transmission-cavity resonance (TCR) problem. From a viewpoint of equivalent circuit representation for the transmission resonance condition and the funneling …
In this work, we study the heat dissipated at metal surfaces by the electromagnetic field scattered by isolated subwavelength apertures in metal screens. In contrast to our common belief that the intensity of waves created by local sources should decrease with the distance from the sources, we reveal that the dissipated heat at the surface remains constant over a broad spatial interval of a few tens of wavelengths. This behavior which occurs for noble metals at near infrared wavelengths is observed with nonintrusive thermoreflectance measurements and is analyzed with an analytical model which …
y coating a cover layer with metallization of cut wire array, the transmission of transverse electric waves (TE; the electric field is parallel to the slits) through subwavelength slits in a thin metallic film is significantly enhanced. An 800-fold enhanced transmission is obtained compared to the case without the cut wires. It is demonstrated that a TE incident wave is highly confined by the cut wires due to the excitation of the electric dipole-like resonance, and then effectively squeezed into and through the subwavelength slits.
We present plasmonic Bragg reflectors for increasing the extraordinary optical transmission through periodic arrays of subwavelength apertures in a metal film. The increase in transmission arises by preventing loss at the edges of the array. The plasmonic Bragg reflectors have periodicity of half the usual array's periodicity. Nano-hole arrays flanked thus by reflectors exchibited double the transmission as compared to the arrays without reflectors. These structures may also be used to isolate devices in plasmonic integrated circuits.
Integration of the next generation of photonic structures with electronic and optical on-chip components requires the development of effective methods for confining and controlling light in subwavelength volumes. Several techniques enabling light coupling to sub-wavelength objects have recently been proposed, including grating-, and composite-based solutions. However, experi-mental realization of these couplers involves complex fabrication with \sim 10nm resolution in three dimensions. One promising alternative to complex coupling structures involves materials with vanishingly small dielectric…
Light transmission through bilayered thin metal films perforated with subwavelength hole arrays are numerically studied based on a full-vector finite-difference time-domain approach. A variety of transmission peaks originating from different physical mechanisms are observed. In addition to the direct tunnelling and Fabry-Pèrot resonances, generally possessed by idealized bilayered dielectric slabs, the near-field localized plasmon polaritons also play important roles. They not only influence the direct tunnelling in a destructive or constructive way, the interactions between these localized pl…
Using a holographic approach, we experimentally study the near-field intensity distribution of light squeezed through an isolated subwavelength plasmonic hole in a thin metallic film. Our experiments revealed an in-plane electric dipole moment excited near the isolated hole. By analyzing the fringe patterns formed between the in-plane dipole and plane wave illumination, both the transmission coefficient and phase shift of the dipole can be retrieved. We also observed opposite phases of the excited dipoles from the subwavelength dent and protrusion in the metallic film, in good agreement with t…
We demonstrate experimentally and numerically that in fiber tips as they are used in NSOMs azimuthally polarized electrical fields (|E$_{\text{azi}}$|$^2$/|E$_{\text{tot}}$|$^2$ $\approx$ 55% $\pm $ 5% for 1.4μm tip aperture diameter and λ$_0$ = 1550nm), respectively subwavelength confined (FWHM $\approx$ 450nm $\approx$ λ$_0$/3.5) magnetic fields, are generated for a certain tip aperture diameter (d = 1.4μm). We attribute the generation of this field distribution in metal-coated fiber tips to symmetry breaking in the bend and subsequent plasmonic mode filtering in the truncated conical taper.
Using transmission electron microscopy (TEM) to analyse the physical-chemical surface properties of subwavlength structured silver films and finite-difference time-domain (FDTD) numerical simulations of the optical response of these structures to plane-wave excitation, we report on the origin and nature of the persistent surface waves generated by a single slit-groove motif and recently measured by far-field optical interferometry. The surface analysis shows that the silver films are free of detectable oxide or sulfide contaminants, and the numerical simulations show very good agreement with t…
Subwavelength aperture arrays in thin metal films can enable enhanced transmission of light and matter (atom) waves. The phenomenon relies on resonant excitation and interference of the plasmon or matter waves on the metal surface. We show a new mechanism that could provide a great resonant and nonresonant transmission enhancement of the light or de Broglie particle waves passed through the apertures not by the surface waves, but by the constructive interference of diffracted waves (beams generated by the apertures) at the detector placed in the far-field zone. In contrast to other models, the…
Measurement of the transmitted intensity from a coherent monomode light source through a series of subwavelength slit arrays in Ag films, with varying array pitch and number of slits, demonstrate enhancement (suppression) by as much as a factor of 6 (9) when normalized to that of an isolated slit. Pronounced minima in the transmitted intensity were observed at array pitches corresponding to lambda_SPP, 2lambda_SPP, and 3lambda_SPP where lambda_SPP is the wavelength of the surface plasmon polariton (SPP). Increasing the number of slits to more than four does not increase appreciably the per-sli…
This commentary aims to expose the fallacy of claiming that a plasmonic silver film superlens is capable to image real subwavelength objects. This lens was proposed by the Berkeley's group who, in their misleading experiment, inappropriately regarded subwavelength apertures as the objects to be imaged whereas the main function of these apertures was to transform free space laser light into an evanescent field necessary for exciting the surface plasmon resonance phenomenon in silver. In addition, the apertures also determined the constrained effective area on the silver film where the phenomeno…
Enhanced transmissions through a gold film with arrays of subwavelength holes are theoretically studied, employing the rigid full vectorial three dimensional finite difference time domain method. Influence of air-holes shape to the transmission is firstly studied, which confirms two different resonances attributing to the enhanced transmission: the localized waveguide resonance and periodic surface plasmon resonances. For the film coated with dielectric layers, calculated results show that in the wavelength region of interest the localized waveguide resonant mode attributes to sensing rather t…
Recently, we have showed a mechanism that could provide a great transmission enhancement of the light waves passed through subwavelength aperture arrays in thin metal films not by the plasmon-polariton waves, but by the constructive interference of diffracted waves (beams generated by the apertures) at the detector placed in the far-field zone. We now present a quantum reformulation of the model. The Hamiltonian describing the interference-induced enhancement of the intensity and energy of a multimode quantum optical field is derived. Such a field can be produced, for instance, by a subwavelen…
This work confirms that not only surface plasmons but many other kinds of electromagnetic eigenmodes should be considered in explaining the values of the transmittivity through a slab bearing a two-dimensional periodic corrugation. Specifically, the role of Brewster-Zennek modes appearing in metallic films exhibiting regions of weak positive dielectric constant. It is proposed that these modes play a significant role in the light transmission in a thin chromium film perforated with normal cylindrical holes, for appropriate lattice parameters.
Miniaturised entangled photon sources are highly demanded for the development of integrated quantum photonics. Since the invention of subwavelength optical metasurfaces and their successes at replacing bulky optical components, the possibility of implementing entangled photon sources on such devices is actively investigated. Here, as a first step towards the development of quantum optical metasurfaces (QOM), we demonstrate photon pair generation via spontaneous parametric down-conversion (SPDC) from subwavelength films. We achieved photon pair generation with a high coincidence-to-accidental r…
Near-field imaging with terahertz (THz) waves is emerging as a powerful technique for fundamental research in photonics and across physical and life sciences. Spatial resolution beyond the diffraction limit can be achieved by collecting THz waves from an object through a small aperture placed in the near-field. However, light transmission through a sub-wavelength size aperture is fundamentally limited by the wave nature of light. Here, we conceive a novel architecture that exploits inherently strong evanescent THz field arising within the aperture to mitigate the problem of vanishing transmiss…
We investigate the transmission of focused beams through single subwavelength holes in a silver film. We use radially and azimuthally polarized light, respectively, to excite higher order waveguide modes as well as to match the radial symmetry of the aperture geometry. Remarkably, the transmission properties can be described by a classical waveguide model even for thicknesses of the silver film as thin as a quarter of a wavelength.
One-dimensional light harvesting structures illuminated by a conventional lens are studied in this paper. Our theoretical study shows that high transmission efficiencies are obtained when the structure is placed near the focal plane of the lens. The considered structure is a finite slit-groove array (SGA) with a given number of grooves that are symmetrically distributed with respect to a central slit. The SGA is nano-patterned on an opaque metallic film. It is found that a total transmittance of 80% is achieved even for a single slit when (i) Fabry-Perot like modes are excited inside the slit …
We present a theorical investigation of the optical transmission of a dielectric grating carved in a tungsten layer. For appropriate wavelengths tungsten shows indeed a dielectric behaviour. Our numerical simulations leads to theoretical results similar to those found with metallic systems studied in earlier works. The interpretation of our results rests on the idea that the transmission is correlated with the resonant response of eigenmodes coupled to evanescent diffraction orders.
We apply the technique of far-field interferometry to measure the properties of surface waves generated by two-dimensional (2D) single subwavelength slit-groove structures on gold films. The effective surface index of refraction measured for the surface wave propagating over a distance of more than 12 microns is determined to be 1.016 with a measurement uncertainty of 0.004, to within experimental uncertainty of the expected bound surface plasmon-polariton (SPP) value for a Au/Air interface of 1.018. We compare these measurements to finite-difference-time-domain (FDTD) numerical simulations of…
We analyze, by means of numerical simulations, transmission enhancements through sub- wavelength slits due to the presence of sets of plasmonic nanocylinders, placed near the exit of these apertures. Further, we extend this study to photonic crystals of dipolar plasmonic particles in front of an array of extraordinarily transmitting slits practiced in a metallic slab.
Recents works deal with the optical transmission on arrays of subwavelength holes in a metallic layer deposited on a dielectric substrate. Making the system as realistic as possible, we perform simulations to enlighten the experimental data. This paper proposes an investigation of the optical properties related to the transmission of such devices. Numerical simulations give theoretical results in good agreement with experiment and we observe that the transmission and reflection behaviour correspond to Fano's profile correlated with resonant response of the eigen modes coupled with nonhomogeneo…
For several years, periodical arrays of subwavelength cylindrical holes in thin metallic layers have taken a crucial importance in the context of the results reported by Ebbesen et al, on particularly attractive optical transmission experiments. It had been underlined that the zeroth order transmission pattern does not depend on the polarization of the incident light at normal incidence. In the present paper, we show that it is not the case for rectangular holes, by contrast to the case of circular holes. In this context, we suggest a new kind of polarizer that present the advantages brought b…
Using simulations and theoretical arguments we investigate the specular reflection of a perforated gold film deposited on a glass substrate. A square lattice of cylindrical holes is assumed to produce the periodic lateral corrugation needed to hybridize the surface plasmons with radiative states. It is shown that, contrasting transmission approaches, a knowledge of the reflection on either side of the film provides separate information on the gold-vacuum surface plasmons and on the gold-glass interface plasmons. Recent experimental data on a specific implementation of this system are reexamine…
We experimentally demonstrate single beam directional perfect absorption (to within experimental accuracy) of p-polarized light in the near-infrared using unpatterned, deep subwavelength films of indium tin oxide (ITO) on Ag. The experimental perfect absorption occurs slightly above the epsilon-near-zero (ENZ) frequency of ITO where the permittivity is less than one. Remarkably, we obtain perfect absorption for films whose thickness is as low as ~1/50th of the operating free-space wavelength and whose single pass attenuation is only ~ 5%. We further derive simple analytical conditions for perf…
The extra energy, negative energy and annihilation of energy by the subwavelength conservative systems that have a wave nature of light or matter (quantum) objects are predicted. The creating and destroying of energy break the energy conservation law in any subwavelength physical system. The paradoxical phenomenon is demonstrated in the context of extraordinary transmission of light and matter through subwavelength apertures [T.W. Ebbesen et al., Nature (London) 391, 667 (1998) and E. Moreno et al., Phys. Rev. Lett. 95, 170406 (2005)].
Here I report on comparisons between two different techniques in fabricating arrays of subwavelength cross-shaped apertures in metallic screens. The aim was to determine the most appropriate fabrication technique to be used considering the cost, ease of fabrication and accuracy in which the apertures were created. Some interesting physical effects are observed.
We introduce the first conceptual design of a free-space thin-sheet isolator with unlimited aperture and the possibility of a broadband omnidirectional rejection of the backward propagating light. The proposed design involves a multilayered resonant cavity incorporating subwavelength magnetic layers, dichroic nanolayers, and an optional metallic nanolayer. The cavity resonance enhances the Faraday rotation produced by the subwavelength magnetic layers, while providing nearly total absorption of the backward-propagating light by the dichroic nanolayers. The latter is a necessary and the most ch…
Diffraction is a fundamental property of light propagation. Owing to this phenomenon,light diffracts out in all directions when it passes through a subwavelength slit.This imposes a fundamental limit on the transverse size of a light beam at a given distance from the aperture. We show that a subwavelength-sized beam propagating without diffractive broadening can be produced in free space by the constructive interference of multiple beams of a Fresnel source of the respective high-refraction-index waveguide. Moreover, it is shown that such a source can be constructed not only for continuous wav…
Subwavelength Coherent Scaling of High-Order Nonlinear Light Generation in Bulk Monolayer MoS2 Thin Films
University of California, Los Angeles（加州大学洛杉矶分校）；University of California, San Diego（加州大学圣地亚哥分校）；University of California, Irvine（加州大学尔湾分校）；California NanoSystems Institute（加州纳米系统研究所）
The technologies of heating, photovoltaics, water photocatalysis and artificial photosynthesis depend on the absorption of light and novel approaches such as coherent absorption from a standing wave promise total dissipation of energy. Extending the control of absorption down to very low light levels and eventually to the single photon regime is of great interest yet remains largely unexplored. Here we demonstrate the coherent absorption of single photons in a deeply sub-wavelength 50% absorber. We show that while absorption of photons from a travelling wave is probabilistic, standing wave abs…
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 TEM-mode for illumination with radially polarized light inside the si…
Phase transition materials are promising for realization of switchable optics. In this work, we show reflectance resonances in the near-infrared and long-wave infrared wavelengths in highly subwavelength partially oxidized Vanadium thin films. These partially oxidized films consist of a multilayer of Vanadium dioxide and Vanadium as shown using Raman spectroscopy and four-probe measurements. As Vanadium dioxide is a phase transition material that shows insulator to metal phase transition at 68 C, the observed infra-red resonances can be switched with temperature into a high-reflectance state. …
We present an intuitive analytical model for extraordinary optical transmission (EOT) through corrugated metallic films. In the framework of this model, EOT emerges from standing wave resonances of the different diffraction orders, and is an inherent property of periodic structures, which does not require specific polarization dependent properties such as surface plasmons. The model correctly predicts the conditions for the EOT resonances in various geometrical configurations, in both TE and TM polarizations,and in the subwavelength and non-subwavelength spectral regimes, using the same underl…
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 optomechanic…
Interaction between metal surface waves and periodic geometry of subwavelength structures is at the core of the recent but crucial renewal of interest in plasmonics. One of the most intriguing points is the observation of abnormal strong transmission through these periodic structures, which can exceed by orders of magnitude the classical transmission given by the filling factor of the plate. The actual paradigm is that this abnormal transmission arises from the periodicity, and then that such high transmission should disappear in random geometries. Here, we show that extra energy can be couple…
Transmission spectra of metallic films or membranes perforated by arrays of subwavelength slits or holes have been widely interpreted as resonance absorption by surface plasmon polaritons (SPPs). Alternative interpretations involving evanescent waves diffracted on the surface have also been proposed. These two approaches lead to divergent predictions for some surface wave properties. Using far-field interferometry, we have carried out a series of measurements on elementary one-dimensional (1-D) subwavelength structures with the aim of testing key properties of the surface waves and comparing t…
We have investigated the spontaneous decay rate of an excited molecule placed near a circular aperture in a metal film of finite thickness and finite conductivity. We have considered the metal film both suspended freely in vacuum and lying on a substrate. A significant effect of molecule the position and the presence of the substrate on the rate of spontaneous emission of the molecule is shown. The asymptotes which can be used to describe this process are found. Total, radiative, and non-radiative spontaneous decay rates of the excited molecule are extracted and compared. The results may be us…
The absorption to mass ratio of the infrared arrays is enhanced to approximately 1.33 to 7.33 times larger than the previously reported structures by incorporating two design characteristics: first, the coupling of evanescent fields in the air gaps around pixels to create effectively larger pixel sizes, and, second, the use of guided mode resonance (GMR) within the subwavelength metal-dielectric gratings. The bilayer Ti-Si3N4 gratings achieve broadband long-wave infrared (LWIR, 8 to 12 um) absorption by the combined effects of free carrier absorption by the thin Ti films and vibrational phonon…
Spectral cameras with integrated thin-film Fabry-Pérot filters have become increasingly important in many applications. These applications often require the detection of spectral features at specific wavelengths or to quantify small variations in the spectrum. This can be challenging since thin-film filters are sensitive to the angle of incidence of the light. In prior work we modeled and corrected for the distribution of incident angles for an ideal finite aperture. Many real lenses however experience vignetting. Therefore in this article we generalize our model to the more common case of a v…
In this letter, we study the scattering of light by a single subwavelength slit in a metal screen. In contrast to previous theoretical works, we provide a microscopic description of the scattering process by emphasizing the generation of surface plasmons at the slit apertures. The analysis is supported by a rigorous formalism based on a normal-mode-decomposition technique and by a semi-analytical model which provides accurate formulae for the plasmonic generation strengths. The generation is shown to be fairly efficient for metals with a low conductivity, like gold in the visible regime. Verif…
