Metal Hole Arrays Research Articles

Interplay of surface plasmon and Fabry-Perot resonances in metallic hole arrays on dielectric layers

Interplay of surface plasmon and Fabry-Perot resonances in metallic hole arrays on dielectric layers

Enhanced Sugar Sensing via a Fano Resonance Terahertz Metasurface With a Metallic Cross-Shaped Hole Array

Enhanced Sugar Sensing via a Fano Resonance Terahertz Metasurface With a Metallic Cross-Shaped Hole Array

A Highly Efficient Plasmonic Polarization Conversion Metasurface Supporting a Large Angle of Incidence

The angle of incidence of the compact polarization conversion device is crucial for practical use in integrated miniaturized optical systems. However, this index is often ignored in the design of quarter-wave plate based on metasurface. Herein, it is shown that a thick metallic cross-shaped hole array supports extraordinary optical transmission peaks controlled by a Fabry–Pérot (FP) resonator mode. The positions of these peaks have been proven to be independent over a large range of incidence angles. We numerically design a miniatured quarter-wave plate (QWP) with an 80 nm bandwidth (840~920 nm) and approximately 80% average efficiency capable of effectively functioning as a linear-to-circular (LTC) polarization converter at an incidence inclination angle of less than 30°. This angle-insensitive compact polarization conversion device may be significant in a new generation of integrated metasurface-based photonics devices.

Surface plasmon-cavity hybrid state and its graphene modulation at THz frequencies

Abstract Fabry–Pérot (F–P) cavity and metal hole array are classic photonic devices. Integrating F–P cavity with holey metal typically enhances interfacial reflection and dampens wave transmission. In this work, a hybrid bound surface state is found within rectangular metal holes on a silicon substrate by merging an extraordinary optical transmission (EOT) mode and a high-order F–P cavity mode both spatially and spectrally. Transmission, Q-factor, and bandwidth can be enhanced significantly with respect to the classical EOT and F–P interference by simply sweeping the cavity length. This state can provide EOT properties and ten times broader EOT bandwidth well below the effective plasma frequency of the periodic metal holes, where the metal holes typically show evanescent properties and do not support EOT in theory. Furthermore, a large modulation range of 25 % and 39 % is demonstrated with various graphene patterns for the transmittance of this hybrid state at 500 and 582 GHz, respectively.

Near-Perfect Infrared Transmission Based on Metallic Hole and Disk Coupling Array for Mid-Infrared Refractive Index Sensing

Nanostructured color filters, particularly those generated by the extraordinary optical transmission (EOT) resonance of metal–dielectric nanostructures, have been intensively studied over the past few decades. In this work, we propose a hybrid array composed of a hole array and a disk array with the same working period within the 3–14 μm mid-infrared band. Through numerical simulations, near-perfect transmission (more than 99%) and a narrower linewidth at some resonance wavelengths were achieved, which is vital for highly sensitive sensing applications. This superior performance is attributed to the surface plasmon coupling resonance between the hole and disk arrays. A high tunability of the near-perfect transmission peak with varying structural parameters, characteristics of sensitivity to the background refractive index, and angle independence were observed. We expect that this metallic hole and disk coupling array is promising for use in various applications, such as in plasmon biosensors for the high-sensitivity detection of biochemical substances.

Origin of plasmonic Fano resonance in metal-hole/split-ring-resonator metamaterials disclosed by temporal coupled-mode theory.

In plasmonic Fano resonance, the interaction between a discrete plasmonic mode and a continuum of plasmonic mode gives rise to an asymmetric line shape in the scattering or absorption spectrum, enabling a wide range of applications such as sensing, switching, and slow light devices. Here, we establish a theoretical solution in the framework of temporal coupled-mode theory (TCMT) to study the three-dimensional (3D) and two-dimensional (2D) Fano resonances induced by strong coupling between metal hole (MH) and split ring resonator (SRR) array. We first separately analyze the transmission spectra of the MH array and SRR array under different polarized light excitation. We further investigate the electromagnetic field and charge density distribution corresponding to the resonant modes at the peak or valley wavelength of the transmission spectrum and figure out the electric/magnetic dipole feature of these resonance modes. We then establish a theoretical solution by TCMT for Fano resonances arising from the coupling of these modes. The calculated transmission spectrum is closely matching with the numerically simulated transmission spectrum for these Fano resonances in the MH-SRR array, which effectively elucidates that the asymmetry of the Fano resonances is caused by the coupling between bright and dark plasmonic modes involved in the two structures. Our results can help to understand the profound physics in such coupled plasmonic systems.

Terahertz asymmetric metallic hole arrays with polarization-independent quasi-bound states in the continuum for membrane sensing.

Resonances with both high-quality factor and polarization-independent characteristics are highly desirable for terahertz (THz) sensing. Here, THz sensors based on asymmetric metallic hole arrays (AMHAs) are experimentally demonstrated. Such sensors consisting of four-hole arrays support polarization-independent quasi-bound states in the continuum (BICs). The induced quasi-BIC presents a quality factor exceeding 2000, which enables enhanced sensing for thin membranes. Results show that the frequency shift is 97.5 GHz for the 25-µm thick polyimide (PI), corresponding to a sensitivity of 147.7 GHz/RIU. The sensing performance strongly relates to the enhanced field originating from sharp quasi-BICs. A maximum field enhancement of 15.88 in contrast to the incident field is achieved. When the PI thickness is large than the decay length of enhanced fields, the interaction strength of field-PI becomes weak, resulting in a saturation effect for the shift of quasi-BICs. The proposed sensor possessing polarization-independent quasi-BICs has great potential for practical sensing applications in real-time chemical and biomolecular.

A study of structural effect on the spectral property of metallic cross-hole array in mid-infrared wavelengths

Based on the earlier success in developing multichannel detection in long (8–14 μm) infrared wavelengths, this paper reports our recent progress for spectral filters in the mid-infrared band of 4–10 μm by introducing a new design with metallic cross annular hole array. The effects of structural dimensions on filtering performance were investigated by numerical simulations with the finite-difference time-domain method and experimentally verified by optical characterizations of fabricated filters made by electron beam lithography. The transmission peaks were optimized with the maximum transmittance of 62%. The existing problem of low spectral resolution of transmittances was tackled by using a thick Au film for the filter, which remains a big challenge for conventional electron beam lithography. By modeling ice lithography in amorphous solid water for constructing the filter, it was found that ice lithography certainly possesses significant advantage in replicating nanoscale features with high aspect ratio. The proposed ice lithography in this work provides an effective solution for the nanofabrication of high performance filters with dense elements in an array in the mid-infrared wavelengths.

Directional amplified spontaneous emissions from Ag nanohole array with high diffraction orders.

Surface plasmon excitations in metallic hole arrays have been extensively studied in the context of light-matter interaction, since the generated Bloch surface plasmon polariton (Bloch-SPP) exhibits unique properties of nanoscale light confinement, near-field enhancements, and long-range metal surface propagation. In this work, we experimentally demonstrate a plasmonic device that exhibits highly directional emission in visible light; using Ag film with a thickness of 100 nm deposited on a subwavelength porous alumina array as a plasmonic cavity, four-level rhodamine 6G (R6G) is selected as the gain material. It is suggested that a Bloch-SPP with high diffraction orders on a Ag nanohole array can generate a strong local electric field and a high Purcell factor at a nanohole edge. Moreover, directional five-fold enhanced amplified spontaneous emission (ASE) with polarization dependence is observed under a low threshold of 199.9 W/cm2 in the visible light region, which comes from the optical feedback provided by the 2D periodic nanohole array. This work opens up a wide range of applications for real-time tunable wavelength, controlled multimode laser, fluorescence detection, etc.

Independent control method for plasmonic skin depth based on transformation from spoof surface plasmon polaritons to bound states in the continuum

A metal plate array (MPA) is the complementary structure of a metal hole array and forms spoof surface plasmon polaritons (SSPPs) supported by parallel plate modes in a unit cell. A ring dipole array, which is a periodic structure designed by providing an aperture in the conductive part of the unit cell of an MPA, has the potential to produce bound states in the continuum (BICs). In this paper, the transformation from SSPPs to BICs is confirmed using these two structures by broadening the aperture in the unit cell. Making use of this phenomenon, control of the skin depth of surface modes is numerically demonstrated while retaining the resonant frequency, and the fitting values of the plasmonic skin depth are in good agreement with theoretical values.

Design of Plasmonic Coupler with Germanium Spacer Layer for Quantum Well Infrared Photodetectors

A design of a plasmonic coupler, composed of metal hole arrays and a germanium spacer layer, integrated with a quantum well infrared photodetector structure is presented. Insertion of a germanium spacer layer in this hybrid structure enhances absorption and the z-component of an electric field in the quantum well absorption region under both substrate-side and air-side illumination configurations. By changing thickness of the germanium spacer layer, the plasmonic resonance wavelengths can be adjusted with peak quantum well response. This plasmonic coupler is believed to be promising to improve performance of quantum well infrared photodetectors.

Continuously tunable middle-IR bandpass filters based on gradient metal-hole arrays for multispectral sensing and thermography

Continuously tunable middle-infrared bandpass filters have been developed based on gradient metal-hole arrays with two distinct geometries. The rotation filter relies on an array of metal holes with gradually changing periods and hole sizes in the azimuthal direction, while the translation filter exploits a metal-hole array with a linear gradient. The filters are fabricated in a Ti film on a ZnSe substrate using electron-beam nanolithography. They are characterized experimentally using Fourier-transform infrared spectroscopy, and the observed results are compared with numerical predictions of the finite element method. The developed filters offer wide spectral tunability when operating with a focused beam. Particularly, the central wavelength of the transmission band is tunable in the [Formula: see text] range, for the rotation filter, and in the [Formula: see text] range for the translation one, as a linear function of the filter angular or linear displacement. The filters feature relatively broad bandwidths of [Formula: see text], while their spectral contrast and energy efficiency depend on the gradient type. The filter spectral response function shape and the extent of its spectra tunability can be further optimized by judicious design of the hole geometry and the metal-hole array gradient, respectively. The developed filters hold strong potential in the infrared multispectral sensing and imaging, thanks to their conceptual simplicity. Considering the linearity of Maxwell’s equations and availability of appropriate technologies for the fabrication of gradient arrays of sub-wavelength metal holes, the developed concept can be translated to other spectral ranges.

Enhanced broadband extraordinary terahertz transmission through plasmon coupling between metal hemisphere and hole arrays

Enhanced extraordinary optical transmission (EOT) is generated by a gold hole array with a concentric hemisphere in the terahertz (THz) region. By introducing hemispherical particles and using the plasmon coupling effects of surface plasmon polaritons and localized surface plasmon resonances, it can be found that not only the transmission intensity is greatly enhanced to 0.97 and the bandwidth is nine times wider than that of a non-particle in a hole, but also the size of the structure can be significantly reduced. Additionally, optical characteristics of the hemisphere-in-hole structure are thoroughly analyzed by the schematic diagram, transmission spectra, and optical field distribution. In addition, with the diameter of the hemisphere increasing, the transmission peak maintains at a high value and the peak position redshifts correspondingly. Finally, we alter the shapes and sizes of the central particles to verify the influence on the enhanced THz EOT. Our results provide a reference for theoretical understanding and expand the application prospects for many THz plasmonic devices.

Optimization study of metallic hole arrays as the multi-channel spectral filters in long-infrared wavelengths.

The development of miniaturized multi-channel infrared filters based on plasmonic metasurfaces is attracting growing attention, driven by its potential applications in infrared imaging, photodetectors, and spectroscopy. However, the advance of such filters in long-infrared wavelengths has rarely been reported. This paper reports our recent progress on developing multi-channel spectral filters based on micrometer metallic hole arrays in the long-infrared band of 10-15 µm. The effects of structural parameters and the shapes of metallic hole arrays on filtering performance are investigated by numerical simulations with the finite-difference time-domain method and then experimentally verified by optical characterizations of fabricated filters using electron beam lithography. The transmission peaks of the filter on a zinc selenide substrate were optimized with a maximum transmittance of 63%. A comparison of the hole shapes shows that elliptical holes give rise to sharper transmission peak quality than round ones by 28%. The progress achieved in this work should be a promising step in the development of metallic hole-based spectral filters with miniaturized dimensions.

Modulating extraordinary terahertz transmissions in multilayer plasmonic metasurfaces

Manipulations of light–matter interaction via sub-wavelength plasmonic structures have opened up many new research opportunities in photonics from microwave to the visible spectrum, including the relatively underdeveloped but technologically important terahertz regime. Here, we have studied manipulation of terahertz transmission through a bilayer metasurface consisting of a metallic hole array and a complimentary patch array separated by an ultra-thin dielectric spacer. The terahertz transmission spectra through our studied metasurfaces exhibit characteristic resonances due to the surface plasmon induced extraordinary transmission peak. Our study reveals a counterintuitive blue shift of the transmission peak with increasing spacer thickness, which is explained by reduced Coulomb interaction between two plasmonic layers. The measured quality factor exhibits a strong dependence on the spacer thickness, and the maximum quality factor is observed for a spacer thickness of around λ/30, indicating strong electric-field confinement inside the dielectric spacer. These bilayer plasmonic structures will aid in realizing next-generation terahertz plasmonic devices such as ultrasensitive thin-film sensors, modulators, narrow-band filters, and other nonlinear components.

Optimization of an extremely high Q-factor terahertz perfect absorber for environmental refractive index sensing using quasi-analytical solutions

Terahertz (THz) radiation can be used to monitor the environment by sensing its variation of refractive index. Previous studies have shown that a THz perfect absorber with several hundred Q-factors can function as sensitive THz refractive-index sensors (THz-RISs). However, the electromagnetic field simulation of THz-RIS is currently based on the numerical methods, which are inefficient when THz-RIS has extremely high Q-factors in several orders of magnitude. In this study, we present the quasi-analytical solutions of THz-RIS made by a 2D metallic hole array coated by polymer thin-film (2D-HACP) for the efficient optimization of extremely sensitive THz-RIS. It is found that the optimized 2D-HACP shows the absorption peak about 96.7% at the resonant frequency close to 1 THz. The absorption peak has full width at half-maximum about 39.1 MHz, yielding the Q-factor equal to 25,555. It is shown that the figure of merit associated with the variations of the real part and imaginary part of environment’s complex refractive index are equal to 2.56 × 10 4 1/RIU and 4.12 × 10 8 1/(RIU·THz), respectively. Therefore, the optimized 2D-HACP may work as an extremely sensitive environmental sensor by monitoring the tiny variation of the environment’s complex refractive index.

Proof of concept for continuously-tunable terahertz bandpass filter based on a gradient metal-hole array.

A continuously-tunable terahertz (THz) bandpass filter based on the resonant electromagnetic-wave transmission through a metal-hole array featuring a gradually changing period was developed and fabricated on a silicon substrate using optical lithography. A gradient geometry of the metal-hole array yields a wide tunability of the filter transmission, when operating with a focussed THz beam. The filter was studied numerically, using the finite element method, and experimentally, using the THz pulsed spectroscopy. We find that the central wavelength of the filter transmission band can be tuned in the wide range of λc = 400-800 μm with the relative bandwidth of Δλ/λc ≃ ~0.4. Finally, Kapton-based anti-reflection coating was applied to the filter flat side, in order to suppress an interference pattern in the filter transmission spectrum. We believe that the developed filter holds strong potential for multispectral THz imaging and sensing due to its conceptual simplicity and case of operation. Moreover, the presented filter concept can be translated to other spectral ranges, where appropriate technologies are available for the fabrication of gradient sub-wavelength metal-hole arrays.

Enhanced circular dichroism of TDBC in a metallic hole array structure**Project supported by the Fundamental Research Funds for the Central Universities and the National Key R&D Program of China (Grant No. 2016YFA0301300).

We investigate the enhanced chirality of chiral molecular J-aggregates (TDBC) by the propagating surface plasmons (PSPs) in the metallic hole array structure filled with TDBC. The two ends of the hole in the metal film form a low quality factor Fabry–Perot (FP) cavity, and this cavity confines PSPs. The resonant wavelength of the metallic hole array is tuned by the lattice constant and the size of the hole. Both the resonant wavelength of Ag hole array and the volume ratio of TDBC in the hybridized structure influence on the enhancement of the circular dichroism (CD) spectrum. The curve of CD spectrum shows Fano-like line-shape, due to the interaction between the non-radiative field in the FP cavity and the radiative field in chiral TDBC. The maximum of the CD spectrum of the hybridized structure is 0.025 times as the one of the extinction spectrum in a certain structure, while the maximum of the CD spectrum of TDBC is 1/3000 times as the one of the extinction spectrum. The enhanced factor is about 75. The resonant wavelength of the metallic hole array can be tuned in a large wavelength regime, and the chirality of a series of molecular J-aggregates with different resonant wavelengths can be enhanced. Our structure provides a new method to amplify the chirality of molecular J-aggregates in experiments.

Quantum teleportation mediated by surface plasmon polariton

Surface plasmon polaritons (SPPs) are collective excitations of free electrons propagating along a metal-dielectric interface. Although some basic quantum properties of SPPs, such as the preservation of entanglement, the wave-particle duality of a single plasmon, the quantum interference of two plasmons, and the verification of entanglement generation, have been shown, more advanced quantum information protocols have yet to be demonstrated with SPPs. Here, we experimentally realize quantum state teleportation between single photons and SPPs. To achieve this, we use polarization-entangled photon pairs, coherent photon–plasmon–photon conversion on a metallic subwavelength hole array, complete Bell-state measurements and an active feed-forward technique. The results of both quantum state and quantum process tomography confirm the quantum nature of the SPP mediated teleportation. An average state fidelity of 0.889pm 0.004 and a process fidelity of 0.820pm 0.005, which are well above the classical limit, are achieved. Our work shows that SPPs may be useful for realizing complex quantum protocols in a photonic-plasmonic hybrid quantum network.

Analysis and observation of the breakdown of Babinet\u2019s principle in complementary spoof surface plasmon polariton structures

A metal plate array (MPA) which is a structure complimentary to a metal hole array (MHA), supports spoof surface plasmon polaritons (SSPP) as well as an MHA does. Babinet’s principle attributes the phenomenon of duality to transmission characteristics of the complimentary impedance surfaces because of the symmetry of the behaviors of electric and magnetic fields. However, it is also a fact that the complimentary structures do not follow this principle if they have wavelength-size thickness, because electromagnetic waves do not treat such thick structures as a boundary surface but as propagation spaces with the specific boundaries such as a waveguide which shows SSPP modes. If the thickness is so small that it is negligible, Babinet’s principle is still valid, while it has been uncertain how the layer thickness works to break the principle as it is increased. The unconfirmed transformation is revealed analytically and experimentally with the use of MPAs and MHAs of varying thicknesses.