Guolan Fu

Tunable Plasmon-Induced Transparency of Double Continuous Metal Films Sandwiched with a Plasmonic Array

Making a continuous metal film with near-unity transparency has received more and more attention in recent years because of its potential applications for various optoelectronic devices. Here, we theoretically show that a high tunable plasmon-induced transparency metal film structure can be performed by double continuous metal films inserted with a two-dimensional hexagonal lattice array of plasmonic nanopariticles. The proposed structure shows near-unity anti-reflection and intensively enhanced transmission via the cooperative effects of strong resonant near-field light input and output coupling by the plasmonic array and the excitation of surface electromagnetic waves of the metal films. The optical response can be efficiently mediated by varying the sizes of nanoparticles and the separated distance between the metal array and the metal films. With the merits of high transparency, sub-wavelength sizes and wholly retained metal characteristics including high conductivity via using the pure metallic materials, the structure proposed here suggests various potential applications in optoelectronic integrated circuits.

Multi-band light perfect absorption by a metal layer-coupled dielectric metamaterial

Multispectral light perfect absorption is desired for many applications. Herein, we propose and demonstrate a novel multi-band light perfect absorber (MLPA) scheme based on a triple-layer dielectric meta-material structure coupled with a metal substrate. Four absorption bands with the maximal absorbance up to 98.9% and the narrow bandwidth down to 2 nm are achieved in the visible range. Optical cavity resonances and the plasmon-like dipolar resonance of the high-index dielectric resonators and their hybridization effects contribute to the observed absorption behaviors. Moreover, the obtained MLPA is with high scalability in the frequency range by tuning the structural parameters. These features pave a new and feasible way for multispectral light absorption and hold applications in the optoelectronic detection, filtering and imaging.

Monochromatic filter with multiple manipulation approaches by the layered all-dielectric patch array.

Monochromatic filtering with ultra-narrowband and high spectral contrast is desirable for wide applications in display, image, and other optoelectronics. However, owing to the inherent omhic losses in the metallic materials, a broadband spectrum with a low Q-factor down to 10 inevitably limits the device performance. Herein, we for the first time theoretically propose and demonstrate an ultra-narrowband color-filtering platform based on the layered all-dielectric meta-material (LADM), which consists of a triple-layer high/low/high-index dielectrics cavity structure. Owing to the lossless dielectric materials used, sharp resonances with the bandwidth down to sub-10 nm are observed in the sub-wavelength LADM-based filters. A spectral Q-factor of 361.6 is achieved, which is orders of magnitude larger than that of the plasmonic resonators. Moreover, for the other significant factor for evaluation of filtering performance, the spectral contrast reaches 94.5%. These optical properties are the main results of the excitation of the resonant modes in the LADMs. Furthermore, polarization-manipulated light filtering is realized in this LADM. The classical Malus law is also confirmed in the reflective spectrum by tuning the polarization state. More interestingly and importantly, the filtering phenomenon shows novel features of the wavelength-independent and tunable resonant intensity for the reflective spectrum when the LADM-based filter is illuminated under an oblique state. High scalability of the sharp reflective spectrum is obtained by tuning the structural parameters. A single-wavelength reflective filtering window is also achieved in the visible frequencies. These features hold promise for the LADM-based filter with wide applications in color engineering, displaying, imaging, etc.

Semiconductor meta-surface based perfect light absorber

We numerically proposed and demonstrated a semiconductor meta-surface light absorber, which consists of a silicon patches array on a silicon thin-film and an opaque silver substrate. The Mie resonances of the silicon patches and the fundamental cavity mode of the ultra-thin silicon film couple strongly to the incident optical field, leading to a multi-band perfect absorption. The maximal absorption is above 99.5% and the absorption is polarization-independent. Moreover, the absorption behavior is scalable in the frequency region via tuning the structural parameters. These features hold the absorber platform with wide applications in optoelectronics such as hot-electron excitation and photo-detection.

Tunable Extraordinary Optical Transmission in a Metal Film Perforated with Two-Level Subwavelength Cylindrical Holes

We propose a novel plasmonic metal structure composed of a silver film perforated with a two-dimensional square array of two-level cylindrical holes on a silica substrate. The transmission properties of this structure are theoretically calculated by the finite-difference time-domain (FDTD) method. Double-enhanced transmission peaks are achieved in the visible and infrared regions, which mainly originate from the excitation of localized surface plasmon resonances (LSPRs), the hybridization of plasmon modes, and the optical cavity mode formed in the holes. The enhanced transmission behaviors can be effectively tailored by changing the geometrical parameters and dielectric materials filled in the holes. These findings indicate that our proposed structure has potential applications in highly integrated optoelectronic devices.

Partially hollowed ultra-thin dielectric meta-surface for transmission manipulation

Impressive optical properties are numerically demonstrated in the partially hollowed dielectric meta-surface (p-HDMS), which consists of an air cavity array intercalated in an ultra-thin (~λ/6) high-index dielectric film. Multispectral transmission band-stop response with near-perfect spectral modulation depth is achieved. The spectral slop is up to 80%/nm, indicating the sharp and narrowband transmission behavior. Classical Malus law is confirmed by this sub-wavelength platform. Moreover, the multispectral light propagation manipulation can be perfectly reproduced by using the actual dielectric with absorption loss. In this all-dielectric meta-surface, conduction loss is avoided compared to its metallic plasmonic counterpart. Such configurations can therefore serve as excellent alternatives for plasmonic meta-surfaces and constitute an important step in nanophotonics.

Improved Multispectral Antireflection and Sensing of Plasmonic Slits by Silver Mirror

We propose and demonstrate an improved multiband antireflection from plasmonic slits array using an opaque metal mirror. The introduced mirror could enhance the optical field coupling and confinement, and therefore produce intensified plasmonic resonances in comparison with those of the open slit built by the dielectric substrate. The sharp triple-band nearunity antireflection is with a high scalability at optical frequencies via tuning the structural parameters. High-performance sensing measurements with a remarkably improved sensitivity (S ~ 1.5 λ nm/refractive index unit) and a high signal-to-noise ratio of the spectral intensity difference (AR > 57%) and with a large slope of 18.6%/nm are achieved based on this subdiffraction-limit (λ/5) structure. This proposed scheme and findings hold potential applications, including high-efficiency subtractive polychromatic filtering and ultracompact biosensing.

Effects of Compound Rectangular Subwavelength Hole Arrays on Enhancing Optical Transmission

The optical transmission properties of the metallic film with an array of compound rectangular nanoholes are numerically investigated by the finite-difference time-domain (FDTD) method. The compound rectangular nanohole (unit cell) in such a structure consists of a large square hole with two small rectangular holes symmetrically distributed at its both sides. Extraordinary optical transmission (EOT) of more than 85% is obtained in this structure, which is larger than that found in the metal film perforated only with the large hole array (55%) or the small hole array (18%). The EOT in the optical regime mainly results from the excitation and coupling of localized surface plasmon resonances and surface plasmon polaritons. The EOT properties can be efficiently tailored in both wavelength and transmission intensity by varying the size and shape of nanoholes. Our structure also shows the sensitivity to environmental dielectric constant. These results indicate that our structure has potential applications in plasmonic filters and sensors.

Robust Optical Transparency of a Continuous Metal Film Sandwiched by Plasmonic Crystals

Light opacity is a natural phenomenon of a continuous metal film. In various applications, such as transparent electrodes in solar cells or touching screens in ultrathin displayers, low transmittance is a major issue. Here, we present a new concept that enhances the transmission of light through a continuous metal film to reach the transmittance of glass. In order to cancel the potential electron scattering when electrons propagate in the metal film, it is sandwiched between two photonic crystal (PC) layers made of nontouching metallic particles. This geometry shows a robust, near-unity, optical transparency behavior that could be highly tuned by changing the geometrical parameters of the structure. These findings suggest potential applications in ultraintegrated optoelectronics based still benefiting from both electric and mechanical properties metals offer while still achieving optical transparency through plasmon coupling effects.

Near-field plasmon effects in extraordinary optical transmission through periodic triangular hole arrays

Abstract. We present a theoretical investigation of the transmission properties of light through a metallic film perforated with different arrays of compound triangular holes. The extraordinary optical transmission (EOT) in the optical region is obtained by employing the finite-difference time-domain method. The excitation of localized surface plasmon resonances (LSPRs) at the top corners and surface plasmon polaritons (SPPs) on the metal surface, plasmon coupling effects between adjacent apertures, and the waveguide modes for delivering light mainly contribute to the EOT in such structures. The optical characteristics can be effectively tailored by changing the arrangement of triangular holes and the structural parameters. This study may be helpful for plasmonic nanostrucutres based on EOT, and has potential applications in optoelectronic devices.