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Impact of Surface Roughness in Nanogap Plasmonic Systems
摘要： Recent results have shown unprecedented control over separation distances between two metallic elements hundreds of nanometers in size, underlying the effects of free-electron nonlocal response also at mid-infrared wavelengths. Most of metallic systems however, still suffer from some degree of inhomogeneity due to fabrication-induced surface roughness. Nanoscale roughness in such systems might hinder the understanding of the role of microscopic interactions. Here we investigate the effect of surface roughness in coaxial nanoapertures resonating at mid-infrared frequencies. We show that although random roughness shifts the resonances in an unpredictable way, the impact of nonlocal effects can still be clearly observed. Roughness-induced perturbation on the peak resonance of the system shows a strong correlation with the effective gap size of the individual samples. Fluctuations due to fabrication imperfections then can be suppressed by performing measurements on structure ensembles in which averaging over a large number of samples provides a precise measure of the ideal system’s optical properties.
关键词： hydrodynamic model,nonlocal response,coaxial aperture,plasmonics,epsilon-near-zero mode,surface roughness
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting - Atlanta, GA, USA (2019.7.7-2019.7.12)] 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting - Slow light at the nanoscale based on active epsilon-near-zero plasmonic waveguides
摘要： Plasmonic waveguides exhibit an effective epsilon-near-zero (ENZ) response at their cut-off frequency. In this work, we demonstrate the formation of an exceptional point (EP) in a nanoscale open and lossy (non-Hermitian) nanophotonic system consisting of an array of periodic nanowaveguides loaded with a very low gain coefficient material. We theoretically analyze the obtained EP, as well as its topological properties, by using a transmission-line model adapted to the plasmonic properties of the proposed device. The dispersion of the active ENZ mode and the group velocity are thoroughly investigated. Reflectionless transmission (perfect loss compensation) and ultraslow group velocity values at the nanoscale are realized at the EP, which coincides with the ENZ cut-off frequency of the proposed plasmonic system. This special spectral degeneracy (EP) is a unique feature of the presented nanoscale symmetric plasmonic ENZ configuration, different from most of the previous works that were mainly focused on asymmetric bulky micron-scale active photonic configurations.
关键词： Plasmonic waveguides,epsilon-near-zero (ENZ),non-Hermitian,exceptional point (EP),group velocity,nanophotonic system
更新于2025-09-16 10:30:52
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Ultracompact and Unidirectional On-Chip Light Source Based on Epsilon-Near-Zero Materials in an Optical Communication Range
摘要： An on-chip light source is one of the essential components for integrated photonic circuits and quantum-information processing chips. To date, it has been a great challenge to construct an on-chip light source with high directionality, high collection efficiency, and ultrasmall feature size simultaneously in the optical communication range. Here, an on-chip light source, consisting of a circular paraboloid etched in an aluminum-doped zinc-oxide film, which is an epsilon-near-zero material, is experimentally realized at 1550 nm. Photons emitted from the a PbS quantum-dot cluster placed near the focal point of this paraboloid are reflected into a directional parallel beam due to the large impedance mismatch between aluminum-doped zinc oxide and ambient medium. An ultrasmall emission divergence angle of only ±3°, and an ultrahigh directional emission contrast ratio of 44 dB are achieved from the ultracompact device with a feature size of only 1.5 μm. Also, an ultrahigh collection efficiency of up to 92% is predicted by simulation. This work not only opens an alternative way for the realization of integrated photonic devices based on epsilon-near-zero materials, but also provides another method for the precise assembling of composite functional nanostructures.
关键词： nanomanipulation,on-chip light source,optical communication,epsilon-near-zero materials,quantum dots
更新于2025-09-12 10:27:22
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[IEEE 2018 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium) - Boston, MA (2018.7.8-2018.7.13)] 2018 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium) - Robust Multi-Layer Graphene-Based Plasmonic Cloaking
摘要： In this paper, a plasmonic cloak is designed at 1.55 μm in an epsilon-near-zero (ENZ) comprised of alternating layers of a graphene-silica stack. Because the inclusion is covered by Au and moreover, the ENZ’s boundaries are sealed by this material with optimized thicknesses, such a cloak can only work for TM incidence. This cloak is robust against the inclusion shape which is capable of working in an exceedingly large bandwidth.
关键词： TM incidence,graphene-silica stack,epsilon-near-zero,plasmonic cloak,robust,large bandwidth
更新于2025-09-11 14:15:04
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Edge-plasmon assisted electro-optical modulator
摘要： An efficient electro-optical modulation has been demonstrated here by using an edge-plasmon mode specific for the hybrid plasmonic waveguide. Our approach addresses a major obstacle of the integrated microwave photonics caused by the polarization constraints of both active and passive components. In addition to subwavelength confinement, typical for surface plasmon polaritons, the edge-plasmon modes enable exact matching of the polarization requirements for silicon based input/output grating couplers, waveguides, and electro-optical modulators. A concept of the hybrid waveguide, implemented in a sandwichlike structure, implies a coupling of propagating plasmon modes with a waveguide mode. The vertically arranged sandwich includes a thin layer of epsilon-near-zero material (indium tin oxide) providing an efficient modulation at small length scales. Employed edge plasmons possess a mixed polarization state and can be excited with horizontally polarized waveguide modes. It allows the resulting modulator to work directly with efficient grating couplers and avoid using bulky and lossy polarization converters. A 3D optical model based on Maxwell equations combined with drift-diffusion semiconductor equations is developed. Numerically heavy computations involving the optimization of materials and geometry have been performed. Effective modes, stationary state field distribution, an extinction coefficient, optical losses, and charge transport properties are computed and analyzed. In addition to the polarization matching, the advantages of the proposed model include the compact planar geometry of the silicon waveguide, reduced active electric resistance R and a relatively simple design, attractive for experimental realization.
关键词： polarization constraints,hybrid plasmonic waveguide,drift-diffusion semiconductor equations,electro-optical modulation,edge-plasmon mode,indium tin oxide,epsilon-near-zero material,Maxwell equations
更新于2025-09-11 14:15:04
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On the planewave scattering from a circular cylinder with core or coating made of ENZ and DNZ mediums
摘要： The phase profiles of the field components and the scattering widths of a circular cylinder with coating or core made of epsilon-near-zero (ENZ) and double-near-zero (DNZ) mediums for normally incident planewave are investigated. It was found that the axial components generally had a uniform phase inside a bare ENZ or DNZ cylinder for both the TE and TM polarization states in the cylinders with small as well large radii. The azimuthal components could have a slowly varying phase only for large cylinders. When the ENZ or DNZ mediums were used as cores or coatings, the uniformity of the phases decreased. Generally, DNZ mediums have more slowly varying phases than the ENZ mediums, and the TE polarization has a more uniform phase than the TM polarization. The scattering widths were found to be the smallest for DNZ-coated dielectric cylinder and the largest for dielectric-coated ENZ or DNZ cylinder. This study can provide a guideline for the thickness of the near-zero index medium in device design since different thicknesses are needed for achieving uniform phase inside the ENZ or DNZ medium for a particular component of the electric and magnetic fields in the three configurations studied in this paper.
关键词： Zero index medium,Epsilon-near-zero,Double-near-zero
更新于2025-09-09 09:28:46