Dual broadband near-infrared perfect absorber based on a hybrid plasmonic-photonic microstructure

Ultra-narrow-band metamaterial perfect absorber based on surface lattice resonance in a WS2 nanodisk array

Metamaterial perfect absorbers (MPAs) are attractive platforms for the unique manipulation of electromagnetic waves from near-field to far-field. Narrow-band MPAs are particularly intriguing for their potential applications as thermal emitters or biosensors. In this work, we proposed ultra-narrow-band MPAs based on surface lattice resonance (SLR) modes of WS₂ nanodisk arrays on gold films. The SLR modes stem from the coupling between the magnetic dipole modes of individual nanodisks and the Rayleigh anomaly of the array giving rise to high quality-factor resonances. With proper design of the nanodisk array, an ultra-narrow-band of 15 nm is achieved in the near infrared wavelength range. The underneath gold film provides the loss channel converting the incident light within the narrow band into heat in the gold film, effectively creating a perfect absorber. Systematic numerical simulations were performed to investigate the effects of the geometrical parameters on their optical properties, demonstrating the great tunability of this type of MPAs as well as their potential for engineering light-matter interactions.

Black paints covered with multidielectrics: light absorbers

Black paints are commonly used to provide broadband light absorbers in high-precision optics. We show how multidielectric coatings improve the performances of these absorbers. The coated rough paints still exhibit a quasi-lambertian diffuse reflection, but this scattering pattern can be reduced by several orders of magnitude, which strongly enhances absorption. Predictions are based on an exact electromagnetic theory of light scattering from arbitrary rough multilayers. Results are also compared to useful approximate theories.

Plasmonic sensors with an ultra-high figure of merit

We propose and numerically demonstrate a high-quality hybridized resonant platform, composed of a one-dimensional metal grating and a dielectric cavity. Under a moderate oblique illumination, an ultra-high spectral quality (Q) factor of 1375 is achieved, which shows orders of magnitude larger than that of the system under normal excitation. The high-Q mode results from the strong coupling effect between the surface plasmon polariton of the metal grating and the photonic mode of the dielectric cavity. Based on this hybridized plasmonic resonator, a high-performance sensing scheme with the spectral sensitivity (S) up to 800 nm/RIU (refractive index unit, RIU) is further introduced. Moreover, the figure of merit reaches 1337, indicating a new record for both the localized or propagating surface plasmons based sensors. These features could find applications in sensing and detecting devices, plasmonic switches, and light flow modulators.

Active controllable dual broadband terahertz absorber based on hybrid metamaterials with vanadium dioxide

In this paper, we present an active controllable terahertz absorber with dual broadband characteristics, comprised by two diagonal identical patterns of vanadium dioxide in the top layer of the classical three-layer structure of metamaterial perfect absorbers. Simulation results show that two bandwidths of 80% absorption are 0.88 THz and 0.77 THz from 0.56 to 1.44 THz and 2.88 to 3.65 THz, respectively. By using thermal control to change the conductivity of the vanadium dioxide, absorptance can be continuously adjusted from 20% to 90%. The impedance matching theory is introduced to analyze and elucidate the physical mechanism of the perfect absorption. Field analyses are further investigated to get more insight into the physical origin of the dual broadband absorption. In addition, incident polarization insensitivity and wide-angle absorption are also demonstrated. The proposed absorber promises diverse applications in terahertz regime, such as imaging, modulating, sensing and cloaking.

Polarization-insensitive, ultra-broadband, and compact metamaterial-inspired optical absorber via wide-angle and highly efficient performances

Because of exhibiting extraordinary features, metamaterial absorbers have captured considerable attention in recent years, especially at visible frequencies. In this paper, a new design of a metamaterial-inspired perfect visible absorber (MIPVA) is investigated, which exhibits ultra-broadband, polarization-independent, and wide-angle performances. The proposed MIPVA provides a flat and near unity absorbance (>99%) in an ultra-broad range of radiation wavelengths from λ=500 to 625 nm, while retaining its convincing absorptivity over the entire visible wavelengths. A comprehensive parametric study is accomplished to demonstrate the effects of structural parameters on the absorptivity of the designed MIPVA. To clarify the physical mechanism of absorption, the electric field and surface current distributions of MIPVA are also monitored and elaborately discussed throughout the paper. The results show that the proposed MIPVA exhibits a polarization-insensitive absorption behavior in a wide range of incident wave angles. The interference theory is also utilized to verify the results. In addition, our MIPVA has a compact and low-profile design, while its ability to absorb solar radiation is significantly improved with respect to preceding studies in terms of both the frequency bandwidth and absorptivity; thereby, it is a worthy candidate to play an essential role in different visible-range applications.

Ultra-broadband Tunable Resonant Light Trapping in a Two-dimensional Randomly Microstructured Plasmonic-photonic Absorber

Recently, techniques involving random patterns have made it possible to control the light trapping of microstructures over broad spectral and angular ranges, which provides a powerful approach for photon management in energy efficiency technologies. Here, we demonstrate a simple method to create a wideband near-unity light absorber by introducing a dense and random pattern of metal-capped monodispersed dielectric microspheres onto an opaque metal film; the absorber works due to the excitation of multiple optical and plasmonic resonant modes. To further expand the absorption bandwidth, two different-sized metal-capped dielectric microspheres were integrated into a densely packed monolayer on a metal back-reflector. This proposed ultra-broadband plasmonic-photonic super absorber demonstrates desirable optical trapping in dielectric region and slight dispersion over a large incident angle range. Without any effort to strictly control the spatial arrangement of the resonant elements, our absorber, which is based on a simple self-assembly process, has the critical merits of high reproducibility and scalability and represents a viable strategy for efficient energy technologies.

When plasmonics meets membrane technology

In this review, we present the applications of thermoplasmonics in membrane processes. We discuss the influence of the heat capacity of the solvent, the amount of plasmonic nanoparticles in the membrane, the intensity of the light source and the transmembrane flow rate on the increase of permeability. Remarkably, thermoplasmonic effects do not involve any noticeable loss of membrane rejection. Herein, we consider application feasibilities, including application fields, requirements of feed, alternatives of light sources, promising thermoplasmonic nanoparticles and scaling up issues.

Highly efficient metallic optical incouplers for quantum well infrared photodetectors

Herein, we propose a highly efficient metallic optical incoupler for a quantum well infrared photodetector (QWIP) operating in the spectrum range of 14~16 μm, which consists of an array of metal micropatches and a periodically corrugated metallic back plate sandwiching a semiconductor active layer. By exploiting the excitations of microcavity modes and hybrid spoof surface plasmons (SSPs) modes, this optical incoupler can convert infrared radiation efficiently into the quantum wells (QWs) layer of semiconductor region with large electrical field component (E_z) normal to the plane of QWs. Our further numerical simulations for optimization indicate that by tuning microcavity mode to overlap with hybrid SSPs mode in spectrum, a coupled mode is formed, which leads to 33-fold enhanced light absorption for QWs centered at wavelength of 14.5 μm compared with isotropic absorption of QWs without any metallic microstructures, as well as a large value of coupling efficiency (η) of |E_z|² ~ 6. This coupled mode shows a slight dispersion over ~40° and weak polarization dependence, which is quite beneficial to the high performance infrared photodetectors.

2D-ordered dielectric sub-micron bowls on a metal surface: a useful hybrid plasmonic-photonic structure

Recently, it has been demonstrated that the combination of periodic dielectric structures with metallic structures provides an efficient means to yield a synergetic optical response or functionality in the resultant hybrid plasmonic-photonic systems. In this work, a new hybrid plasmonic-photonic structure of 2D-ordered dielectric sub-micron bowls on a flat gold surface was proposed, prepared, and theoretically and experimentally characterized. This hybrid structure supports two types of modes: surface plasmon polaritons bound at the metallic surface and waveguided mode of light confined in the cavity of bowls. Optical responses of this hybrid structure as well as the spatial electric field distribution of each mode are found to be strongly dependent on the structural parameters of this system, and thus could be widely modified on demand. Importantly, compared to the widely studied hybrid systems, namely the flat metallic surface coated with a monolayer array of latex spheres, the waveguided mode with strong field enhancement appearing in the cavities of bowls is more facilely accessible and thus suitable for practical use. For demonstration, a 2D-ordered silica sub-micron bowl array deposited on a flat gold surface was fabricated and used as a regenerable platform for fluorescence enhancement by simply accommodating emitters in bowls. All the simulation and experiment results indicate that the 2D-ordered dielectric sub-micron bowls on a metal surface should be a useful hybrid plasmonic-photonic system with great potential for applications such as sensors or tunable emitting devices if appropriate periods and materials are employed.

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.

Tunable light trapping and absorption enhancement with graphene ring arrays

Graphene ring arrays are proposed to introduce tunable light trapping and enhance the absorption in the surrounding light-absorbing materials.

Automatically acquired broadband plasmonic-metamaterial black absorber during the metallic film-formation

Broadband electromagnetic wave absorbers are highly desirable in numerous applications such as solar-energy harvesting, thermo-photovoltaics, and photon detection. The aim to efficiently achieve ultrathin broadband absorbers with high-yield and low-cost fabrication process has long been pursued. Here, we theoretically propose and experimentally demonstrate a unique broadband plasmonic-metamaterial absorber by utilizing a sub-10 nm meta-surface film structure to replace the precisely designed metamaterial crystal in the common metal-dielectric-metal absorbers. The unique ultrathin meta-surface can be automatically obtained during the metal film formation process. Spectral bandwidth with absorbance above 80% is up to 396 nm, where the full absorption width at half-maximum is about 92%. The average value of absorbance across the whole spectral range of 370-880 nm reaches 83%. These super absorption properties can be attributed to the particle plasmon resonances and plasmon near-field coupling by the automatically formed metallic nanoparticles as well as the plasmon polaritons of the metal film with the induced plasmonic magnetic resonances occurring between the top meta-surface and the bottom metal mirror. This method is quite simple, cost-effective for large-area fabrication, and compatible with current industrial methods for microelectro-mechanical systems, which makes it an outstanding candidate for advanced high-efficiency absorber materials.