Ultra-broadband Perfect Absorption Research Articles

Switchable dual ultra-broadband perfect absorber based on graphene and vanadium dioxide hybrid metamaterials

The phase transition property of vanadium dioxide (VO2) makes it an attractive field in temperature-controlled chips. In this paper, a microstructure based on a graphene disk and a ring-shaped VO2 hybrid metamaterial is proposed to achieve switchable dual ultra-broadband perfect absorption in the terahertz region, which is analyzed by the phase transition property of VO2 and the dynamic electrical regulation of graphene. When the graphene disk is not present, the absorption intensity can reach up to 97.07%. When the graphene disk is present and respectively interacts with the VO2 metallic and insulated phases, the results exhibit an ultra-broadband perfect absorption (>90%) from 1.620 THz to 4.533 THz and from 1.506 THz to 3.576 THz, respectively, where the bandwidths are as high as 2.913 THz and 2.070 THz, respectively. Adjusting the Fermi level of graphene and the VO2 conductivity allows the absorption intensity and bandwidth to be effectively controlled, where the fractional bandwidth from 81.46% to 94.69% and a high modulation depth of 95.09% can be achieved. These results suggest that dual ultra-broad perfect absorption can be dynamically switched within a single absorber and has various modulation means, which are expected to be developed in applying multifunctional modulators.

Ultra-broadband solar absorber based on TiN metamaterial from visible light to mid-infrared

We study and design an ultra-broadband absorber based on TiN metamaterial. The proposed structure consists of a rectangle pillar, two rectangle rings, an Al2O3 substrate, and a TiN substrate. The average absorption in the range of 300–4962 nm is 97.02%. The physical mechanism is illustrated by electric-field and magnetic-field distributions, including the dielectric lossy property of TiN itself in shorter wavelengths, Fabry–Perot resonance, and local surface plasmon resonance in longer wavelengths. The result indicates that the energy absorption spectrum can be well matched with the standard solar spectrum under AM 1.5 over the full range of 300–5000 nm, and then we compare the solar absorption spectrum of different structures. In the end, the influence of different materials and geometrical parameters on absorption is investigated. The absorber can achieve ultra-broadband perfect absorption, and has a simple structure that is easy to manufacture. The result of this work can be applied in many potential fields, for example, thermal photovoltaic power generation, infrared imaging, solar cells, and other optoelectronic devices.

Numerical simulation of efficient solar absorbers and thermal emitters based on multilayer nanodisk arrays

In this work, we design a solar absorber and thermal emitter with ultra-broadband perfect absorption and high thermal radiation efficiency. The solar absorber has a high absorption efficiency of 91.5 % in the full wavelength range (280–4000 nm), and the weighted average absorption efficiency (AM1.5) is as high as 99 % by the finite difference time domain method (FDTD) simulation calculation. And the absorption bandwidth with absorption efficiency greater than 90 % reaches 2929 nm (280–3209 nm), and the average absorption efficiency in this band is as high as 97.4 %. Such strong absorption is due to the plasmon resonance and near-field coupling of the multilayer nanodisks. In addition to being used in solar absorbers, the structure also has potential applications in thermal emitters. The novelty of this work is to explore the application of the structure in the field of thermal radiation, and the optimal working temperature of the structure for thermal radiation is obtained. Through calculation, we approximately consider that the optimal working temperature of the structure as a thermal emitter is 2000 K, and the thermal radiation efficiency at this temperature is 94.8 %. The structure proposed by us is polarization-independent, insensitive to incident angle changes, the absorption spectra of transverse electric (TE) mode and transverse magnetic (TM) mode are the same, and the absorption efficiency remains 80 % even when the incident angle is increased to 60°. The excellent performance makes the structure widely used in the fields of solar energy absorption and emission.

An ultra-broadband solar absorber based on α-GST/Fe metamaterials from visible light to mid-infrared.

In this paper, we proposed an ultra-broadband and high absorption rate absorber based on Fe materials. The proposed absorber consists of a rectangle pillar, two rings, a SiO2 film, a Ge2Sb2Te5(GST) planar cavity, an Fe mirror, and a SiO2 substrate. The average absorption reaches 98.45% in the range of 400-4597 nm. We investigate and analyze the electric field distributions. The analysis of the physical mechanism behind the broadband absorption effect reveals that it is driven by excited surface plasmons. Furthermore, the absorber can maintain high absorption efficiency under a large incident angle. The geometrical symmetric structure possesses polarization insensitivity properties. The proposed structure allows for certain manufacturing errors, which improves the feasibility of the actual manufacture. Then, we investigate the effect of different materials on absorption. Finally, we study the matching degree between the energy absorption spectrum and the standard solar spectrum under AM 1.5. The results reveal that the energy absorption spectrum matches well with the standard solar spectrum under AM 1.5 over the full range of 400 to 6000 nm. In contrast, energy loss can be negligible. The absorber possesses ultra-broadband perfect absorption, a high absorption rate, and a simple structure which is easy to manufacture. It has tremendous application potential in many areas, such as solar energy capture, thermal photovoltaics, terminal imaging, and other optoelectronic devices.

Optically switchable ultra-broadband terahertz perfect absorption in doped superlattice photonic-crystal silicon

We propose an optically switchable ultra-broadband terahertz (THz) perfect absorber based on doped superlattice photonic-crystal silicon. The structure consists of a superlattice photonic crystal silicon slab capped by a SU-8 layer with no metal reflector. It achieves ultra-broadband perfect absorption due to the coupled cavity modes of superposed lattices with two different cavity radii and the enhanced diffraction assisted by the top SU-8 layer. Switchable absorption is realized by changing the carrier concentration of doped silicon controlled by pump beam. Simulation shows that proposed structure exhibits polarization-insensitive and wide-angle absorption with efficiency larger than 90% within 1.03 to 5 THz ultra-broadband, with modulation depth larger than 60% within bandwidth more than 1 THz. The all-dielectric structure uncommonly integrates optical switching, ultra-broadband absorption, polarization, and incident angle insensitivity, which may find potential applications in dynamic THz devices.

Ultra-broadband absorber based on cascaded nanodisk arrays

An ultra-broadband perfect absorber consisting of cascaded nanodisk arrays is demonstrated by placing insulator–metal–insulator–metal nanodisks on insulator–metal film stacks. The absorber shows over 90% absorption in a wavelength range between 600 nm and 4000 nm under transverse magnetic (TM) polarization, with an average absorptivity of 91.5% and a relative absorption bandwidth of 147.8%. The analysis of the electric field and magnetic field show that the synergy of localized surface plasmons, propagating surface plasmons, and plasmonic resonant cavity modes leads to the ultra-broadband perfect absorption, which accords well with the results of impedance-matched analysis. The influences of structural parameters and different metal materials on absorption performance are discussed. Furthermore, the absorber is polarization-independent, and the absorption remains more than 90% at a wide incident angle up to 40° under TE polarization and TM polarization. The designed ultra-broadband absorber has promising prospects in photoelectric detection and imaging.

Ultra-broadband perfect absorber based on nanoarray of titanium nitride truncated pyramids for solar energy harvesting

A metamaterial perfect absorber working in the ultraviolet to near-infrared band is proposed based on a triple-layer structure composed of titanium nitride (TiN) periodic nanoarray, dielectric film, and TiN bottom layer. Each unit cell of the nanoarray is a truncated pyramid structure with its width tapered linearly from the bottom to the top. The physical mechanism of the absorber was explained by analyzing the electric field distributions at different wavelengths, and the absorption performance was simulated as a function of its geometric parameters and the angle and polarization of incident light as well. Optimal geometric parameters are presented. The absorber implemented using the optimal parameters would display an excellent performance with almost perfect absorption (above 99%) over the entire spectral region from 300 to 2500 nm. The ultra-broadband perfect absorption behavior is attributed to the localized surface plasmon resonance effect of the TiN pyramid, the intrinsic loss of the TiN material and the coupling of resonance modes between two adjacent pyramids. Besides, the absorber also exhibits a polarization-independent feature at normal incidence and good angular acceptance capability of incident light. The reported ultra-broadband metamaterial absorber shows great application prospects in the solar energy harvesting industry and solar thermophotovoltaic systems.

Super-Absorbers by Randomly Distributed Titanium Spheres

Electromagnetic wave absorbers have been widely investigated in these years. Nevertheless, the structural models were mainly based on the metal-insulator-metal metamaterials. In this work, we show a study on the achievement of ultra-broadband perfect absorption via a randomly distributed titanium spheres in the hydrogel layer. In the visible and near-infrared range ( $0.38-2.0\,\,\mu \text{m}$ ), the spectral average absorption reaches 93.6%. Taking the absorption efficiency above 90% into account, the bandwidth of the spectral window is 1386 nm. Moreover, the maximal absorption is even up to 98.9% in this open structure since there is no metal reflector back. In particular, these impressive absorption properties can be well maintained under complex electromagnetic surroundings, indicating the insensitive response to the polarization and incident angles. The particle plasmons and the near-field coupling effects for the adjacent spheres in-plane and out-of-plane are the main contributions for the ultra-broadband absorption. The absorption properties together with the simple structural characteristics including the flexible hydrogel layer will hold wide applications in the solar energy related technologies such as the solar thermal steam generation, desalination, macula-removing, and biological sterilization.

Refractory Ti/TiN resonators based meta-surface for perfect light absorption

Refractory materials have wide applications due to their high thermal and chemical stability. In this work, we numerically design the plasmonic structure for perfect light absorption using the resonant behaviours for these materials. The results of the simulation are presented using the three-dimensional finite-difference time-domain method. The maximum absorption reaches 99.9% and the near-unity absorption window spans a bandwidth of 1182 nm from 413 nm in the visible to 1595 nm in the near-infrared range. Strong plasmonic near-field coupling between the adjacent parts in the split circular Ti resonator and their coupling to the plasmon resonances of the TiN layer are the main reasons for the ultra-broadband perfect absorption. Moreover, the absorption is observed to be incident angle insensitive and polarization independent. Absorption properties can be manipulated via tuning the structural parameters. These impressive absorption features and the high thermal stability can have wide applications in the high-intensity or extreme condition operation such as laser pumping and nonlinear optics, and solar related technologies including thermal steam generation and desalination of seawater.

Ultra-broad band perfect absorption realized by phonon–photon resonance in periodic polar dielectric material based pyramid structure

In this research, a mid-infrared wide-angle ultra-broadband perfect absorber which composed of pyramid grating structure has been comprehensively studied. The structure was operated in the reststrahlen band of SiC and with the presence of surface phonon resonance(SPhR), the perfect absorption was observed in the region between 10.25 and 10.85 μm. We explain the mechanism of this structure with the help of PLC circuit model due to the independence of magnetic polaritons. Besides, by studying the resonance behavior of different wavelength, we bridged the continuous perfect absorption band and the discrete peak in 11.05 μm (emerge two close absorption band together) by modification of the geometry. The absorption band has been sufficiently broadened. More over, both 1-D and 2-D periodic structure has been considered and the response of different incident angles and polarized angles has been studied and a omnidirectional and polarization insensitive structure can be realized which may be a candidate of several sensor applications in meteorology. The simulation was conducted by the Rigorous Coupled Wave Method(RCWA).

Ultra-Broadband Absorber Based on Metal-Insulator-Metal Four-Headed Arrow Nanostructure

We propose an ultra-broadband metamaterial absorber composed of a four-headed arrow-shaped top layer and titanium-bottom film spaced by a dielectric layer. The absorber attains an average absorption of 95.21% ranging from 300 to 2000 nm, and the peak absorptivity reaches up to 99.9%. The synergy of surface plasmon resonances, cavity modes, and lightning-rod effects lead to the ultra-broadband perfect absorption. We also demonstrate the proposed absorber is insensitive for both transverse electric and transverse magnetic polarization and can retain 90% absorption at a larger incident angle. The proposed ultra-broadband absorber holds promising potential in solar cells, optical imaging, polarization detectors, and other large-area applications.

Simultaneously achieved narrowband and ultra-broadband perfect absorption via plasmonic refractory-colloid crystals

We propose and demonstrate a novel perfect absorber platform by combining the colloidal crystal and refractory metal layer. Dual-band absorption with the efficiency up to 99.8% (0.336μm) and 99.1% (1.382μm) is achieved. Moreover, the absorption bandwidths are 81 nm and 1237 nm for the two bands in the UV and near-infrared ranges, suggesting the simultaneous achievement of narrowband and ultra-broadband absorption. Furthermore, the resonant wavelengths in the two bands are with the geometric multiples up to 3∼6, indicating the large differential frequency responses. In addition, the absorption properties can be artificially adjusted via the structural parameters. These features can hold potential applications in the nonlinear optics such as frequency multiplication, difference and mixing, and the selective spectral filtering and manipulation, etc.

Colloid templated semiconductor meta-surface for ultra-broadband solar energy absorber

In this work, a thin semiconductor void resonators meta-surface is theoretically proposed and numerically demonstrated as a novel platform for perfect solar absorber. The absorber exhibits an ultra-broadband perfect absorption in the visible and infrared range. In comparison with the noble metals coupled absorbers, it is observed that the introduced titanium substrate produces a strong enhancement (90%) of the spectral absorption for the Ge resonators in a wide spectral window from 1.283 μm to 2.830 μm. As for the actual solar light absorption measurement, the spectrally weighted solar energy absorption efficiency is up to 88% for this semiconductor material based plasmonic absorber in the whole sun irradiation range (280–4000 nm). The absorption behaviors can be artificially manipulated via tuning the structural parameters. Photonic resonant modes in the semiconductor resonators and the plasmonic resonances of the titanium material are the main contributions for the excellent absorption response. In sharp contrast to the metal-insulator absorber, the herein absorber platform can hold three main advantages on the optoelectronic responses by the active semiconductor resonators, the broadband or full-spectrum solar perfect absorption in the semiconductor/titanium composite system, and the stronger thermal stability by the refractory titanium metal.

Multi-scale micro-nano structures prepared by laser cleaning assisted laser ablation for broadband ultralow reflectivity silicon surfaces in ambient air

To meet the ultra-broadband perfect absorption of visible-infrared light on silicon surfaces, a green, efficient and economical method for fabricating multi-scale micro-nano composite structures in ambient air is proposed. We experimentally demonstrate laser cleaning assisted femtosecond laser ablation for fabricating anti-reflection structures. Laser cleaning technology not only effectively eliminates oxide deposition on the laser textured surfaces, but also manufactures the small scale fine-microstructures and nanostructures. A focused ellipse laser spot is innovatively applied to realize large area and energy decays continuously multiple laser cleaning of laser-treated surfaces, and solve the problem that new oxide deposition is generated in the cleaning process. The processing efficiency is also increased by 4.8 times. The average reflectance of 2.06% is reached from 300 to 2500 nm. Great enhancement of infrared light absorption of silicon from 2.5 to 16 μm is realized experimentally. The average reflectance is reduced to 4.98% with a broadband reflectance below 6.6%. Especially, a reflectance below 5.0% from 2.5 to 10 μm and an average reflectance of 4.3% is achieved, which is the least reported to date by laser processing techniques as far as we know. This strategy for anti-reflection structures is excellent candidate for future optoelectronic devices.

Metamaterials and Metasurfaces

Since the proposal of metamaterials by Rodger Walser in 1999, the recent twenty years have witnessed the rapid development of various metamaterials and 2D metasurfaces in a wide range of frequency bands covering the microwave, terahertz, infrared, visible and ultraviolet. Metamaterials exhibit unusual electromagnetic properties not occurring in natural materials, such as negative refraction and hyperbolic dispersion, enabling numerous completely novel applications, including perfect imaging, invisibility cloaking, quantum effects enhancement and even the mimic of celestial mechanics. Although 3D metamaterials have experienced thriving advancement in the microwave and infrared region, the realization of low-loss optical metamaterials has been scarce. As a result of the easiness of large scale fabrication, 2D metasurfaces have attracted considerable attention in the latest 10 years. Through the generalization of Snell's law to ultra-broadband perfect absorption of light, metasurfaces have shown their great potentials in the manipulation of all the properties of electromagnetic waves. Currently, most of the commercial meta-devices are operating in the microwave regime, in the form of some kinds of metasurfaces.1 It is also believed that the first generation of practical optical meta-devices will utilize metasurface implementations.2, 3 It is a great dream of physical scientists and engineers to convert theoretical breakthroughs to revolutionary technologies and products. However, there are still some gaps between the theories and mass production for both the metamaterials and metasurfaces in the optical bands. For example, the operating bandwidth and efficiency of traditional resonant meta-devices are limited as a consequence of the strong resonance and damping of energy. In addition, the metalenses are suffering from chromatic dispersion, which limits their applications in broadband white light imaging. Besides these theoretical challenges, the large-scale fabrication of subwavelength structures with low cost and high precision is urgently required. Although it is relatively easy for the microwave community, the difficulty increases dramatically when the minimal structure dimensions scale down to tens of nanometers. In the past few years, many efforts have been devoted to solving the above problems, and many milestone results have been obtained. To promote the researches in novel metamaterials and metasurfaces, and transform prototypes to practical functional devices, Advanced Optical Materials decided to launch a special issue on this topic. The leading scientists in this field have been invited to write authoritative reviews on specified topics or share their original discoveries that break the challenges faced by the community. We hope that this could serve as a good celebration of the 20th anniversary of metamaterials and give a flavor for the current and exciting future research directions. This special issue covers a broad range of the cutting-edge research in the fields, such as dielectric metasurfaces, flat lens, light emission, polarization conversion, perfect absorption, plasmonic lithography, spin-orbit interaction, magneto-optical effects, second-harmonic generation, dispersion engineering, and dynamic manipulation. Although there are some differences in the microwave and optical engineering, there is a strong trend to combine all these technologies together, as a result of the merging of civil and military requirements. It should be noted that the field of metamaterials and metasurfaces is not limited to optics and electromagnetics. During the last few years, the spirit of metamaterials has been extended to other disciplines such as acoustics, mechanics and thermal engineering. Owing to the scope of Advanced Optical Materials, we do not consider them in this special issue. This collection comprises 12 high-quality reviews and 8 research articles written by leading experts in this field. As a result of the limited pages and preparing time, some late submissions must be treated as regular articles and not included in this special issue. We apologize for not being able to provide a more comprehensive coverage. Finally, it is a great honor for me to edit this special issue. All the colleagues who contributed their articles are appreciated. Of course, I would give special thanks to Dr. Jipei Yuan for making this special issue possible. Xiangang Luo Chengdu, 2019 Xiangang Luo is currently the director of State Key Laboratory of Optical Technologies on Nano-fabrication and Micro-engineering (SKLOTNM), and the president of the Institute of Optics and Electronics (IOE), Chinese Academy of Sciences (CAS). He received Ph.D. from Chinese Academy of Sciences in 2001. He was a Research Scientist in The Institute of Physical and Chemical Research (RIKEN) of Japan. His research interests include micro/nano-optics, plasmonics, metamaterials, catenary optics and subwavelength electromagnetics. He has published more than 300 scientific papers and 100 patents in optics and related fields. He was elected as Fellow of the Optical Society of America (OSA), International Society for Optical Engineering (SPIE), the International Academy of Photonics and Laser Engineering (IAPLE), and Chinese Optical Society.

Ultra-broadband perfect absorber utilizing refractory materials in metal-insulator composite multilayer stacks.

We present an ultra-broadband perfect absorber composed of metal-insulator composite multilayer (MICM) stacks by placing the insulator-metal-insulator (IMI) grating on the metal-insulator-metal (MIM) film stacks. The absorber shows over 90% absorption spanning between 570 nm and 3539 nm, with an average absorption of 97% under normal incidence. The ultra-broadband perfect absorption characteristics are achieved by the synergy of guided mode resonances (GMRs), localized surface plasmons (LSPs), propagating surface plasmons (PSPs), and cavity modes. The polarization insensitivity is demonstrated by analyzing the absorption performance over arbitrary polarization angles. The ultra-broadband absorption remains more than 80% over a wide incident angle up to 50°, for both transverse electric (TE) and transverse magnetic (TM) modes. The ultra-broadband perfect absorber has tremendous potential for various applications, such as solar thermal energy harvesting, thermoelectrics, and imaging.

Ultra-broadband infrared metasurface absorber: comment.

In a recently published report, an ultra-broadband gradient-metasurface-based absorber (GMBA) with a single layer of metasurface is proposed by Guo et al [Opt. Express24(18), 20586 (2016)] to realize the ultra-broadband perfect absorption. Moreover, the bandwidth of absorption can be broadened by increasing a layer metasurface on the basis of single-layered GMBA. This comment demonstrates that the cross-polarization reflection is neglected by the authors, when they calculate the total absorption in the proposed GMBAs. It is found that there are only two absorption peaks at 8.09 μm and 9.84 μm with real absorption rates of 58.4% and 57.1% in a single-layered GMBA.

Theoretical requirements and inverse design for broadband perfect absorption of low-frequency waterborne sound by ultrathin metasurface

Effective absorption of low-frequency waterborne sound with subwavelength absorbers has always been a challenging work. In this paper, we derive two theoretical requirements for broadband perfect absorption of low-frequency waterborne sound by ultrathin acoustic metasurface under a finite-thickness steel plate followed by semi-infinite air. Based on the theoretical requirements, an acoustic metasurface, a rubber layer embedded periodically with cavities, is inversely designed to achieve perfect absorption at 500 Hz. The metasurface is as thin as 1% of the working wavelength and maintains a substantially high absorptance over a relatively broad bandwidth. The perfect absorption peak is attributed to the overall resonance mode of the metasurface/steel plate system. Besides, high absorption can still be achieved even if the loss factor of the given rubber material cannot meet the ideal requirement. Finally, a strategy to utilize the inherent frequency-dependent characteristics of dynamic parameters of rubber material is suggested to achieve an ultra-broadband perfect absorption. When the frequency-dependent characteristics of the given rubber matrix cannot meet the theoretical requirements, a broadband super-absorption can still be realized by properly designing the frequency position of perfect absorption of the cavity-based metasurface.

Tunable broadband, wide-angle, and polarization-dependent perfect infrared absorber based on planar structure containing phase-change material.

A multilayer absorber composed of SiO2, Fe, Ge2Sb2Te5 (GST), and Al is designed, and the absorptive properties are theoretically investigated based on the Fresnel coefficients method in the wavelength range of 300-2500nm by changing the thickness and crystallization rate of GST, the incident angle, and the polarization. The results show that the thin Fe layer plays a key role in obtaining an ultra-broadband perfect absorption. The absorption properties are polarization-dependent, and the perfect absorption can be nearly realized for a p-polarized wave at the incident angle smaller than 75° with the bandwidth larger than 316nm at 90% of max absorption value. The absorptive peak of this absorber can be tuned with the crystallization rate of GST by temperature, and the peak wavelength moves from 1433nm in the amorphous phase to 2051nm in the crystalline phase. This structure can provide a feasible route to design the tunable broadband, wide-angle, and polarization-dependent perfect absorber without lithographic patterns in the infrared band.

Titanium resonators based ultra-broadband perfect light absorber

We propose a new approach for achieving ultra-broadband perfect absorber by using titanium (Ti) resonators. Near-unity absorption with a high average absorptivity of 91.4% is achieved through the whole spectral range from 0.4 μm to 2 μm for the double-period lattice of Ti resonators array on the top of a silica layer coated on the opaque Ti substrate. In contrast to the common metal-insulator-metal (MIM) absorbers only with tens of nanometers absorption bandwidth, the Ti based ultra-broadband perfect absorber (T-UPA) can show a perfect absorption window (i.e., the absorptivity exceeding 90%) with the spectral bandwidth over 1007 nm from visible to near-infrared region (i.e., from 0.485 μm to 1.492 μm). The cooperative effects of the propagating surface plasmons and the corresponding localized plasmonic resonances of Ti resonators contribute to the broadband absorption response. Moreover, the ultra-broadband perfect absorption is polarization-independent and angle-insensitive, which hold the proposed T-UPA with strong practicality and high tolerance in the complex electromagnetic environment (i.e. sun radiation). Furthermore, the absorption window for this T-UPA can be greatly broadened via using a thin anti-reflection coating film, which shows a perfect absorption with the bandwidth of 1555 nm in the visible and near-infrared range. The numerically demonstrated thin-film absorber configuration facilitates the scalability to optoelectronics applications such as thermal photovoltaics and hot-electron devices.