Single Subwavelength Aperture Research Articles

Enhanced Optical Transmission through a Hybrid Bull's Eye Structure Integrated with a Silicon Hemisphere.

In this work, we demonstrate a novel structure that can generate extraordinary optical transmission with a silicon hemisphere placed on a conventional bull's eye structure. There is a single subwavelength aperture surrounded by concentric periodic grooves on a substrate. The extraordinary optical transmission in this work is realized by the coupling of the surface plasmon polaritons in the periodic grooves and the localized electromagnetic field generated by the Mie resonance in the silicon hemisphere. The maximum normalized-to-area transmission peak can reach up to 662 with a decreasing device area and size. The electromagnetic field distribution at different geometry parameters is analyzed to clarify the mechanisms of the work in this paper. Additionally, the use of dielectric material in the aperture can avoid ohmic losses of metal material compared with the conventional one, which may suggest that a wider range of bull's-eye-structure applications is possible.

Wavelength scale terahertz spectrometer based on extraordinary transmission

Subwavelength-slotted parallel plate waveguides exhibit a localized electromagnetic resonance bound to the slits at a frequency slightly below the transverse electric cutoff [R. Merlin, Phys. Rev. X 2, 031015 (2012)]. The resonance is long-lived and, as opposed to the vanishingly small transmission shown by a single sub-wavelength aperture, it gives perfect transmission for perfectly conducting plates. We show that the aperture-supported resonances of a pair of slotted copper plates have long lifetimes at Terahertz (THz) frequencies. Finite element method calculations show that these bound resonances can have quality factors greater than 100. The effects of the plate dimensions and imperfect parallel alignment are also discussed. Using THz time domain spectroscopy, we measured the transmission of a broadband pulse through a test structure for several plate separations and demonstrated, as a proof-of-principle, the function of the slotted waveguide as a highly compact THz spectrometer.

A Scattering Nanopore for Single Nanoentity Sensing

Optical nanopore methods are widely believed to be practical approaches to address the flicker noise and the throughput limitations of nanopore detection. However, most optical nanopore methods in the literature are based on fluorescent labeling, which perplexes the detection operation and limits their applications. In this paper, we demonstrate a brand new optical nanopore technique named “scattering nanopore method”. This method achieves single nanopore readouts without the introduction of dyes by detecting scattering light through a single subwavelength aperture on Au film. The single particle induced optical fluctuations could be detected simultaneously with the nanopore ionic current readouts. The method we demonstrated here opens a new direction for nanopore sensing of single particles, even single molecules in the near future.

Magnetically tunable dual-band transmission through a single subwavelength aperture

By placing two pairs of dielectric cubes and ferrite cuboids symmetrically on both sides of a single subwavelength aperture, we realize a magnetically tunable dual-band transmission. One transmission peak is induced by the Mie resonance of dielectric cubes, and the other one is induced by the ferromagnetic resonance of ferrite cuboids. The enhancement transmission controlled by the ferromagnetic resonance can be tuned by adjusting the applied magnetic field, which is confirmed by the experimental and simulated results. This work provides a way to realize tunable enhanced transmission through a single subwavelength aperture, which has greater potential for the tunable filters.

Mie-resonance-coupled total broadband transmission through a single subwavelength aperture

Using strongly localized electromagnetic fields and efficiently coupled Mie resonances of two high-permittivity low-loss ceramic particles located at either side of a metallic aperture, we demonstrate total broadband transmission of microwaves, requiring no specific polarization, through a single subwavelength aperture. With radius 17 times smaller than the resonance wavelength, coupling efficiency is enhanced 12- and 300-fold over that attained for resonator-aperture and aperture-only couplings. The proposed approach can be tuned from microwave to optical bands to realize total transmissions.

Beaming Visible Light with a Plasmonic Aperture Antenna.

We investigate experimentally the parameter space defining, in the visible range, the far-field diffraction properties of a single circular subwavelength aperture surrounded by periodic circular grooves milled on a metallic film. Diffraction patterns emerging from such an antenna are recorded under parallel- and perpendicular-polarized illumination at a given illumination wavelength. By monitoring the directivity and the gain of the antenna with respect to a single aperture, we point out the role played by the near-field surface plasmon excitations. The results can be analyzed through a Huygens–Fresnel model, accounting for the coherent interaction between the field radiated by the hole and the plasmonic field, propagating along the antenna surface and diffracted away in free space.

Nanophotonics using a subwavelength aperture in a metal film

AbstractThis review focuses on the optical theory and applications of a single subwavelength aperture in a metal film. We begin with Bethe’s aperture theory for the optical transmission through a subwavelength aperture in a perfect electric conductor film and extend the discussion to apertures in real metals of finite thickness and to apertures with different shapes. Extraordinary optical transmission (EOT) is reviewed, particularly for an aperture in a transverse waveguide screen and for waveguide EOT with applications to aperture near-field probes. We overview applications of single subwavelength nanoapertures to refractive index sensing, single molecule fluorescence detection, Raman spectroscopy and optical trapping of dielectric nanoparticles, including biological matter. Finally, we discuss the potential of combining these many different capabilities to create greater functionality with a single aperture.

Reconfigurable plasmonic devices using liquid metals

We experimentally demonstrate an approach to create reconfigurable plasmonic devices in which the geometry of the device can be changed dramatically. The specific embodiment we present utilizes eutectic gallium indium (EGaIn), a metal that is liquid at room temperature, which is injected into or withdrawn from channels encapsulated by a polydimethylsiloxane (PDMS) bullseye mold fabricated on a gold coated substrate. Using terahertz (THz) time-domain spectroscopy, we measure the enhanced transmission properties of a single subwavelength aperture surrounded by differing numbers of concentric annular EGaIn rings. The results obtained from different device geometries, with either a single or multiple rings, are performed using a single device, demonstrating true reconfigurability. We explain the properties of the observed temporal waveforms using a simple time-domain model. This represents, we believe, a first step in developing more complex reconfigurable plasmonic devices.

Single sub-wavelength aperture with greatly enhanced transmission

High transmission efficiency at terahertz (THz) frequency is reported for a single aperture with sub-wavelength dimensions having a Siemens-star shape, microfabricated in the metal film and surrounded by periodic surface corrugations. Compared to theoretical predictions for a simple circular hole of equivalent area, up to ∼106 transmission enhancements were observed experimentally. Such a pointed-shape aperture was also used to obtain the detailed profile of the electric field distribution in the focal plane of a linearly polarized focused THz beam. Applications could be extended to other regions of the electromagnetic spectrum by appropriate scaling of aperture microstructure.

All-optical ultrafast control of beaming through a single sub-wavelength aperture in a metal film

We propose an ultrafast all-optical technique to control and beam the light emerging from a sub-wavelength slit in a planar gold film by exciting a transient grating in the area around the slit. A FDTD model is used to show how excitation of surface plasmon polaritons by the grating governs the beaming process. Both the grating and the beaming effect are shown to decay on a picosecond time-scale. An on-off contrast of 5 dB is obtained for the beaming, with a divergence angle of only 2.4 degrees.

Near-Field Enhancement Through a Single Subwavelength Aperture with Gaps Inside

Structured subwavelength apertures have been studied widely to enhance the transmission or obtain super resolution, such as bull’s eye hole, H-shaped aperture, and bowtie aperture. In this letter, we present another structured aperture with two gaps inside, which can also lead to near-field enhancement. And the resonance wavelength can be tuned by the geometric parameters of the gaps. The enhancement of this gap-aperture depends strongly on the polarization of the incident wave. Only the polarization perpendicular to the connecting line of the two gaps can realize the enhancement. We attribute the near-field enhancement of this structured aperture to the resonance excitation of the localized surface plasmon. We combine the tooth-aperture and our gap-aperture together and this special aperture can achieve stronger enhancement and super resolution simultaneously.

Broadband extraordinary transmission in a single sub-wavelength aperture

Coordinate transformation is applied to design an all-dielectric device for Extraordinary Transmission (ET) in a single sub-wavelength slit. The proposed device has a broadband feature and can be applied from microwave to visible frequency bands. Finite-Difference Time-Domain (FDTD) simulations are used to verify the device's performance. The results show that significantly increased transmission is achieved through the sub-wavelength aperture from 4 GHz to 8 GHz when the device is applied. In contrast with previously reported systems, the frequency sensitivity of the new device is very low.

Extraordinary transmission through a single coaxial aperture in a thin metal film

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 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.

Geometrical effects of split-ring resonators onthe transmission of a single subwavelength aperture

Geometrical effects of split-ring resonators onthe transmission of a single subwavelength aperture

Light trapping cavity enhanced light transmission through a single sub-wavelength aperture in a metal film

We demonstrate that optical transmission of a normally incident, monochromatic plane wave through a single sub-wavelength aperture in an opaque metal film can be substantially enhanced by a thin, semitransparent metal film placed parallel to the opaque metal film in front of the aperture. When the semi-transparent and the opaque metal film are separated by a proper distance, a light trapping cavity is formed and the sub-wavelength aperture exhibits a transmission maximum. An enhancement factor of approximately 40 is demonstrated for a cylindrical 100 nm diameter hole in a silver film.

Enhanced transmission through a subwavelength aperture using metamaterials

We report an enhanced transmission through a single circular subwavelength aperture that is incorporated with a split ring resonator (SRR) at the microwave regime. Transmission enhancement factors as high as 530 were observed in the experiments when the SRR was located in front of the aperture in order to efficiently couple the electric field component of the incident electromagnetic wave at SRR’s electrical resonance frequency. The experimental results were supported by numerical analyses. The physical origin of the transmission enhancement phenomenon was discussed by examining the induced surface currents on the structures.

Split-Ring-Resonator-Coupled Enhanced Transmission through a Single Subwavelength Aperture

We report the enhanced transmission of electromagnetic waves through a single subwavelength aperture by using 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 20 times smaller than the resonance wavelength (r/lambda=0.05). 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 lead to enhanced transmission.

Enhanced transmission and directivity from metallic subwavelength apertures with nonuniform and nonperiodic grooves

Nonuniform and nonperiodic grooves are used to enhance the transmission and directivity of emissions from a single metallic subwavelength aperture. By using nonuniform and nonperiodic grooves, the amplitude and phase of the diffracted power flow from each groove can be adjusted properly. As a result, the transmission and emission directivity can be further improved when compared to apertures with uniform and periodic grooves. Our experimental results are in good agreement with the finite difference time domain simulation results.

Enhanced and confined light transmission through a funnel-type aperture with a sub-wavelength outlet

Enhanced transmission through sub-wavelength hole arrays and a single sub-wavelength aperture with periodic corrugations surrounded have been investigated extensively. We report the similar phenomenon through a funnel-type aperture with a sub-wavelength outlet in a thick silver film, which was obtained numerically by using finite-difference time-domain method. Properties of the transmission spectrum can be modulated by geometric parameters of the funnel-type aperture. With periodic grooves or dielectric gratings on the output surface of the structure, beaming light emission can be obtained.

Optical transmission through single subwavelength apertures using prism coupled input of laser light of annular intensity profile

Light transmission through a single subwavelength aperture in a silver film is examined with a novel input configuration comprising an annular laser beam of variable diameter that is prism-coupled to the back face of the silver. Transmission peaks driven by excitation of the back-face surface plasmon mode or by the aperture resonance itself are separately observed. For both cases, comparison of films with and without a front-face, circular, grating implies significantly more efficient coupling from the aperture fields to the front-face surface plasmon than directly to free radiation.