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Metamaterial perfect absorbers (MPAs) with dynamic thermal tuning features are able to control the absorption performance of the resonances, providing diverse applications spanning from optical switches and filters to modulators. In this paper, we propose an MPA with diverse functionalities enabled by vanadium dioxide (VO2) embedded in a metal-dielectric plasmonic structure. For the initial design purpose, a silicon (Si) nanograting on a silver (Ag) mirror is proposed to have multiple resonant responses in the near infrared (NIR) region. Then, the insertion of a thin VO2 layer at the right position enables the design to act as an on/off switch and resonance tuner. In the insulator phase of VO2, in which the permittivity data of VO2 is similar to that of Si, a double strong resonant behavior is achieved within the NIR region. By increasing the temperature, the state of VO2 transforms from insulator to metallic so that the absorption bands turn into three distinct resonant peaks with close spectral positions. Upon this transformation, a new resonance emerges and the existing resonance features experience blue/red shifts in the spectral domain. The superposition of these peaks makes the overall absorption bandwidth broad. Although Si has a small thermo-optic coefficient, owing to strong light confinement in the ultrasmall gaps, a substantial tuning can be achieved within the Si nanogratings. Therefore, the proposed hybrid design can provide multi-resonance tunable features to cover a broad range and can be a promising strategy for the design of linearly thermal-tunable and broadband MPAs. Owing to the proposed double tuning feature, the resonance wavelengths exhibits great sensitivity to temperature, covering a broad wavelength range. Overall, the proposed design strategy demonstrates diverse functionalities enabled by the integration of a thin VO2 layer with plasmonic absorbers. [ABSTRACT FROM AUTHOR]

A new design of a triple band perfect metamaterial absorber based on Pythagorean fractal geometry is proposed and analyzed for terahertz sensing applications. The proposed design showed an enhanced sensing performance and achieved three intensive peaks at 33.93, 36.27, and 38.39 THz, corresponding to the absorptivity of 98.5%, 99.3%, and 99.6%, respectively. Due to the symmetrical nature of the recommended design, the structure exhibited the characteristics of independency on the incident wave angles. Furthermore, a parametric study was performed to show the effects of the change in substrate type, resonator material, and substrate thickness on the absorption spectrum. At a fixed analyte thickness (0.5 μm), the resonance frequency of the design was found to be sensitive to the refractive index of the surrounding medium. The proposed design presented three ultra-sensitive responses of 1730, 1590, and 2050 GHz/RIU with the figure of merit (FoM) of 3.20, 1.54, and 4.28, respectively, when the refractive index was changed from 1.0 to 1.4. Additionally, the metamaterial sensor showed a sensitivity of 1230, 2270, and 1580 GHz/μm at the three resonance frequencies, respectively, when it was utilized for the detection of thickness variation at a fixed analyte refractive index (RI) of 1.4. As long as the RI of the biomedical samples is between 1.3 and 1.4, the proposed sensor can be used for biomedical applications.

As solar energy is a low-cost and clean energy source, there has been a great deal of interest in how to harvest it. To absorb solar energy efficiently, we designed a broadband metamaterial absorber based on the principle of Fabry–Pérot (FP) cavities and surface plasmon resonance (SPR). We propose a broadband perfect absorber consisting of a four-layer structure of silica–tungsten–silica–titanium (SiO2–W–SiO2–Ti) for the incident light wavelength range of 300–2500 nm. The structure achieves perfect absorption of incident light in the wavelength range of 351.8–2465.0 nm (absorption > 90%), with an average absorption of 96.3%. The advantage of our proposed structure is that it combines the characteristics of both high and broadband absorption, and has high overall absorption efficiency for solar radiation. It is also independent of polarization and insensitive to incident angle. We investigated how absorption was affected by different structures, materials, geometric parameters, and refractive indices for different dielectric materials, and we explored the reasons for high absorption. This structure is refractory and ultrathin, and it offers a good tradeoff between bandwidth and absorption. It therefore has premium application prospects and value.

In this work, a new metamaterial design is proposed to yield an ultra-thin and dual band metamaterials perfect absorber (MPA) to be operated in the frequency range from 15 to 35 THz. The proposed structure is consisted of a copper resonator deposited on a very thin Zinc Selenide ZnSe (0.6 μm) substrate, where the backside of the structure is covered with a metal plate to block the transmission of electromagnetic waves. Computer Simulation Technology (CST) was used to design and investigate the proposed structure. The absorption response of the proposed structure was found to be high enough with absorptivity of 98.44 and 99.28 at 22.46 THz and 28.95 THz, respectively. Results showed that the absorber is insensitive to the incident angle of 0°–60° in both transverse electric (TE) and transverse magnetic (TM) modes, respectively. The MPA was seen to be highly independent on the angles of polarization of the incident waves. The working mechanism of the proposed design was revealed by multiple reflection interference theory and a good agreement was confirmed between the calculated and simulated results. The proposed design can be used for possible applications of stealth technology and imaging.

The graphene based metal-insulator-metal (MIM) metamaterial is numerically investigated to realize an active and adjustable multi-band perfect absorber, which is composed of an asymmetric double T-shaped cavity on the top layer. As the symmetry of T-shaped cavities is broken, the previous dual-band absorption will be converted to tri-band absorber. The corresponding electric field distribution at each resonant position is invesitgated to figure out the physical mechanism. More interestingly, these resonant peaks will split into multiband with further destruction of the central symmetry. In addition, non-contact dynamic control of perfect absorption is explored by tuning the Fermi energy, the polarization angle and the incident angle. Finally, the sensitivity of our proposed design is elaborately examined with different concentrations of CS2 dropped into the cavities. The results demonstrate that the refraction index per unit can reach up to a high value of 1673.33 nm/RIU. Therefore, this work delivers a new strategy to design tunable multi-band absorbers and has potential applications in highly tunable optical switchers, sensors and filters.

Metamaterials, which are called as left-handed materials, exhibit electromagnetic properties that do not exist in nature, such as negative refractive index and reverse Doppler effect, at the frequency range for which they are designed. These unique properties of metamaterials have made them indispensable in a wide variety of applications such as sensor applications, signal absorption, antenna, and energy harvesting. In this study, the design and analysis of a metamaterial (MTM) perfect absorber at 5 GHz frequency band were performed to investigate the usability of the proposed structure in energy harvesting applications. A negative refractive index of -0.15 was obtained at 5GHz. The variation of absorption, transmission, and reflection of the proposed MTM structure exhibited that a maximum absorbance was monitored at 5 GHz as 0.9949. According to the harvesting application study, the proposed structure has a maximum absorption of 88.3% at 4.98 GHz which is close to resonant frequency in 8000 O resistor value. The results of the study revealed that the proposed MTM structure has potentials to be used in energy harvesting applications. [ABSTRACT FROM AUTHOR]

Utilizing the solar radiations mainly concentrated in the optical region requires the perfect absorption of light by photovoltaic cells. In this paper, we have demonstrated a broadband perfect metamaterial absorber (PMA) based on tungsten (W) metal in the Visible to Near-Infrared region. The proposed metamaterial absorber has 98% average absorbance for 375-1100 nm wavelength region. A very large absorption bandwidth over 90% is obtained, and the maximum absorption is around the unity. Perfect absorption (>99%) was found between the 422 to 962 nm range of the proposed absorber. The polarization-insensitive-based proposed absorber tolerates a large incident for both transverse magnetic (TM) and transverse electric (TE) modes. Moreover, we have investigated the optimization of the geometric parameters of the unit cell to gain the best absorption results. The improved conversion efficiency under the solar radiation (AAM1.5) has been investigated and also calculated the short circuit density. The proposed broadband PMA shows a promising expectance in various applications such as solar energy harvesting, solar cell, thermal imaging, photodetectors, and durable optoelectronics devices. [ABSTRACT FROM AUTHOR]

We report the design and simple spray coating fabrication process of a perfect absorber based on carbon nanotubes (CNTs) and carbon black particles with omnidirectional high absorption efficiency beyond 99.9% over the broad wavelength range from 400 nm to 20 μm. The carbon black particles are introduced into the CNT solution to form multi-scale all-carbon-based nanomaterials, effectively modifying the morphology of the sprayed layer to improve the light absorption. The promising absorption characteristics of the CNT–carbon black layer are attributed to not only the intrinsic optical properties of the carbon nanomaterials but also the unique surface nanostructures that efficiently trap light. In addition to serving as absorbers in the coating layer, the CNTs, more importantly, act as connectors between carbon black particles for absorber preparation at a large scale, which is the key to modifying the surface morphology. The all-carbon-based coating layer is also shown to be effective for solar thermal harvesting and self-cleaning function. The developed mixing method for CNTs and carbon black particles in solutions opens a new path for the realization of multi-functional sprayed layers based on CNTs and advances the technology of CNT coatings for scale-up to industry applications. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, we designed a dual band metamaterial perfect absorber (MPA) for Ku band applications. The overall ultrathin layer of proposed absorber consists of square patch with 450 diagonal slot structure within a copper square patch which loaded on both sides of dielectric thickness 1.6 mm FR-4 substrate. The results show that designed MPA gives two absorption bands at 12.45 and 14.18 GHz and absorption rates are 99.73% and 99.87% respectively. The proposed dual-band absorber has a polarization sensitive characteristic, the absorption performance is almost changing with different polarization angles. Furthermore, resonance centres of two absorption bands can be adjusted by changing related parameters. The novelties of proposed structure are simple, easy fabricate, low cost, durable, suitable for real-time applications and long-term stability considering the fabrication technique and non-destructive measurement method. The dualband absorber can be used in practical applications such as bolometer, EM wave spatial filter and satellite communications. [ABSTRACT FROM AUTHOR]

An optically tunable perfect light absorber as a refractive index (RI) metamaterial (MM) nanobiosensor (NBS) is designed for sensing chemicals, monitoring the concentration of water-soluble glucose, and detecting viruses. This plasmon induced tunable metasurface works based on multiband super-absorption in the infrared frequency regime. It consists of a metal mirror that facilitates the MM to work as an absorber where the metal pattern at the top layer creates an enhanced evanescent wave that facilitates the metasurface to work as a RI optical sensor. The modelling and numerical analysis are carried out using Finite Difference Time Domain (FDTD) method-based software, CST microwave studio where a genetic algorithm (GA) is used to optimize the geometric parameters. We demonstrate multiband super-absorption spectra having maximum absorption of more than 99%. Furthermore, we show how the multiband super-absorber nanostructure can be used as a RI NBS, where the resonance frequency shifts with the RI of the surrounding medium. The achieved opto-chemical sensitivity is approximately 65 nm/RIU RIU, the bio-optical sensitivity to detect viruses is approximately 76 nm/RIU; and the optical sensitivity of the water-soluble glucose concentration is about 300 nm/RIU; all sensitivities are comparable in comparison with the reported values in the literature. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a tunable graphene-based metamaterial absorber (MA) at dual terahertz band to achieve perfect absorption. The electric field intensity distributions of demonstrated structure is illustrated to explain the origin of two absorption peaks. Simulation result shows the proposed MA owning polarization-insensitive property and wide incident angle tolerance. An inversion algorithm is used to extract the equivalent impedance and explore the physical mechanism of multiple-peak absorption. The equivalent impedance is explored through algorithm when the Fermi energy level alters, consequently the variation of resonant frequency of corresponding absorption peak is determined. Simultaneously, the resonant frequencies of absorption peaks can be adjusted by changing the geometric parameters of the graphene. Furthermore, we adapt the proposed structure into reversely designed pattern, achieving similar characteristic of dual-band absorption peaks and tunability. Thus, our work provides new insight and useful design guidance to various tunable multiple band terahertz metamaterial perfect-absorbers. [ABSTRACT FROM AUTHOR]

• The operating frequency range is 4.75 THz to 9.25 THz, which is in the terahertz band. • The proposed perfect absorber gives four perfect absorption peaks in the frequency range of 4.75 THz to 9.25 THz (0.998 (5.331 THz), 0.994 (6.606 THz), 0.989 (7.917 THz), 0.998 (9.127 THz)). • Proposed a new fabrication process for Al-Cu-Fe quasicrystals absorber. • The absorption peak of the perfect absorber can be individually adjusted to three bands, four bands, and five bands. • The absorber with a simple structure, multi-narrowband, tunability, symmetric excitation of the electric field, polarization-independence and high sensitivity. This paper introduces a four-band tunable perfect absorber built on Al-Cu-Fe quasicrystal. The operating frequency range is 4.75 THz to 9.25 THz, which is in the terahertz band. The absorber exhibits multiple narrow bands, polarization incoherence, high sensitivity, and tunability. The structure comprises a gold layer, a silica dielectric layer, and a top layer of Al-Cu-Fe quasicrystal from bottom to top. The Al-Cu-Fe quasicrystal structure at the top consists of a circular ring left after being cut by a 45° rotation of the cruciform and a cruciform design containing a central circular cavity. Simulation results reveal four absorption peaks attributed to cavity resonance and surface plasmon resonance, with absorption efficiencies of 0.998, 0.994, 0.989, and 0.998, respectively. Furthermore, changing the radius of the inner ring in the top layer structure allows for varying the number of absorption peaks. We also propose a new fabrication process for Al-Cu-Fe quasicrystals absorbers. The calculated results demonstrate that the designed absorber, characterized by a simple structure and high sensitivity of 2620 GHz/RIU, holds significant potential for applications in optical switches, optical modulators, biomedicine, and sensing. [ABSTRACT FROM AUTHOR]

• A novel concept of singularity engineering of the perfect absorber (PA) is proposed. • The Polology is used to obtain the absorption spectra of PAs efficiently. • A straightforward design method for MDM PAs is proposed and experimentally validated. The metal-dielectric-metal (MDM) perfect absorber (PA) is an important kind of resonant metasurface with promising applications in selective thermal emitting, solar energy harvesting, biosensing and so on. Establishing a direct link between resonant features and structural parameters is essential for guiding design processes and exploring novel applications. In this paper, we conduct a comprehensive investigation of the MDM PA, utilizing scattering singularity (pole/zero) engineering. We propose a straightforward design methodology to achieve a MDM PA operating at a specific wavelength, and demonstrate a design example with a maximum absorption of 99.93 % at 1200 nm and a full width of half maximum of about 155 nm, which is subsequently experimentally validated. The results indicate high absorption across a wide range of angles. This study sheds new light on fast design and analysis of MDM PAs. [ABSTRACT FROM AUTHOR]

In this work, silicon dioxide based four-fold swastika shaped metamaterial nano structure absorber for solar radiation absorption in the near infrared (NIR) regime is proposed. The dimension of the unit cell is 648.50 × 648.50 nm2 which is designed on dielectric silicon dioxide and metallic conductor aluminum. The proposed structure is investigated by the finite-deference time domain (FDTD) method based software CST microwave studio. The metamaterial absorber (MMA) unit cell is simulated within the frequency range (200–398) THz that yielded dual resonance peaks at 260 THz and 378.0 THz with 95.50 % and 97.32 % of absorbance of solar energy, respectively. Additionally, the proposed nano design structure of unit cell was boosted up to attain the dual absorption band by engineering the design parameters. The electromagnetic response of the MMA was theoretically inspected and the excellent properties of the proposed designed absorber have promising applications in plasma-enhanced photovoltaic, optical absorption switching and infrared modulator optical communication. [Display omitted] • Silicon dioxide based four-fold swastika shaped metamaterial nano structure absorber developed for solar radiation absorption in the near infrared (NIR) regime. • The proposed nano design structure of unit cell was boosted up to attain the dual absorption band such as 260 THz and 378.0 THz with 95.50 % and 97.32 % absorbance respectively. • The dimension of the unit cell is 648.50 × 648.50 nm2 which is designed on dielectric silicon dioxide and metallic conductor aluminum. • The designed absorber has promising applications in plasma-enhanced photovoltaic, optical absorption switching and infrared modulator optical communication. [ABSTRACT FROM AUTHOR]

In recent years, sub-wavelength metamaterials-based light perfect absorbers have been the subject of many studies. The most frequently utilized absorber configuration is based on nanostructured plasmonic metals. However, two main drawbacks were raised for this design architecture. One is the fabrication complexity and large scale incompatibility of these nano units. The other one is the inherent limitation of these common metals which mostly operate in the visible frequency range. Recently, strong interference effects in lithography-free planar multilayer designs have been proposed as a solution for tackling these drawbacks. In this paper, we reveal the extraordinary potential of bismuth (Bi) metal in achieving light perfect absorption in a planar design through a broad wavelength regime. For this aim, we adopted a modeling approach based on the transfer matrix method (TMM) to find the ideal conditions for light perfect absorption. According to the findings of our modeling and numerical simulations, it was demonstrated that the use of Bi in the metal-insulator-metal-insulator (MIMI) configuration can simultaneously provide two distinct functionalities; a narrow near unity reflection response and an ultra-broadband near perfect absorption. The reflection behavior can be employed to realize additive color filters in the visible range, while the ultra-broadband absorption response of the design can fully harvest solar irradiation in the visible and near infrared (NIR) ranges. The findings of this paper demonstrate the extraordinary potential of Bi metal for the design of deep sub-wavelength optical devices.

Abstract Various kinds of structure designs have been proposed to achieve the multiple-band metamaterial absorbers. However, the discrete distance of adjacent frequencies of multiple absorbers is considerably large, which will inevitably overlook a large amount of information hidden in the off-resonance absorption areas. Herein, a narrow discrete distance of dual-band terahertz absorber based on two pairs of an Au strip/dielectric layer backed by Au film is designed. Two nearly 100% absorptivities of resonance peaks having the discrete distance of only 0.30 THz are realized. The relative discrete distance of the device is 13.33%, and this value can be adjusted via the length change of an Au strip. Furthermore, we present two narrow discrete distances of a triple-band absorber through stacking one more pair of an Au strip and dielectric layer. Results prove that two discrete distances of only 0.14 THz and 0.17 THz in adjacent absorption modes of the first two and the last two are achieved, respectively; the relative discrete distances of them are respectively 6.57% and 7.22%, which are far from previous reports. Narrow discrete distances (or low values of relative discrete distance) of the multiple-band absorbers have a large number of applications in the investigation of some hidden information in very near frequencies.

We present a metamaterial-based perfect absorber (PA) that strongly supports four resonances covering a wide spectral range from 1.8 µm to 10 µm of the electromagnetic spectrum. The designed perfect absorber has metal–dielectric–metal layers where a MgF2 spacer is sandwiched between an optically thick gold film and patterned gold nanoantennas. The spectral tuning of PA is achieved by calibrating the geometrical parameters numerically and experimentally. The manufactured quad-band plasmonic PA absorbs light close to the unity. Moreover, the biosensing capacity of the PA is tested using a 14 kDa S100A9 antibody, which is a clinically relevant biomarker for brain metastatic cancer cells. We utilize a UV-based photochemical immobilization technique for patterning of the antibody monolayer on a gold surface. Our results reveal that the presented PA is eligible for ultrasensitive detection of such small biomarkers in a point-of-care device to potentially personalize radiotherapy for patients with brain metastases.

A subwavelength metamaterial perfect absorber (MPA) in optical communication band was proposed and tested using the finite-difference time-domain method. The absorber is periodic and comprises a top layer of diamond silicon surrounded by L-shaped silicon and a gold layer on the substrate. It can achieve dual-band perfect absorption, and one of the peaks is in the optical communication band. By changing the gap (g) between two adjacent pieces of L-shaped silicon, and the thickness (h) of the silicon layer, the resonance wavelength of absorption peak can be tuned. When the incident electromagnetic wave entered the absorber, the metamaterial absorber could almost completely consume the incident electromagnetic waves, thereby achieving more than 99% perfect absorption. The absorption peak reaches 99.986% at 1310 nm and 99.421% at 1550 nm. Moreover, the MPA exposed to different ambient refraction indexes can be applied as plasma sensors, and can achieve multi-channel absorption with high figure of merit (FOM*) value and refractive index (RI) sensitivity. The FOM* values at 1310 nm and 1550 nm are 6615 and 168, respectively, and both resonance peaks have highly RI sensitivity. The results confirm that the MPA is a dual-band, polarization-independent, wide-angle absorber and insensitive to incident angle. Thence it can be applied in the fields of optical communication, used as a light-wave filter and plasma sensor, and so on.

Highly efficient color filtering and broadband perfect absorption are achieved by asymmetric Fabry–Pérot nanocavities incorporating a platinum (Pt) film, which are fabricated on rigid and flexible substrates via a lithography-free deposition process. The absorption band induced by the strong resonance in the asymmetric nanocavity plays a key role in suppressing the corresponding spectral reflection with a high efficiency of over 87% in the nonresonant bands, hence yielding vivid colors. A near-perfect absorption reaching up to 99% is concurrently achieved at the resonance wavelength. The proposed nanocavity configuration features a broad absorption band mediated by an ultra-thin Pt layer and provides a substantially extended color gamut compared to other nanocavities resorting to other noble metals such as silver and gold. Flexible color filters, in conjunction with vivid color printing, are practically demonstrated to provide an outstanding operation largely independent of the angle of incidence and bending/strain in the substrate. A broadband perfect absorber integrated with an antireflection coating is also manufactured to deliver an absorption exceeding 90% in the entire visible band (from λ = 400 to 800 nm). The proposed nanocavity is expected to expedite the development of prominent applications spanning displays, color printing, stealth, and thermal photovoltaics. [ABSTRACT FROM AUTHOR]

This study proposes using double-layer wire-grid structures to create narrow-band, perfect plasmonic absorbers, which depend on polarization, for the short-wavelength visible and near-ultraviolet regions of the electromagnetic spectrum. A rigorous coupled-wave analysis reveals that the maximum absorption attained using Ag and Al is ~ 90% at 450 and 375 nm. Experiments using Ag yielded results similar to those predicted by simulations. These results demonstrate that narrow-band perfect plasmonic absorbers, which depend on the polarization, can be realized at 450 and 375 nm using Ag or Al. [ABSTRACT FROM AUTHOR]

We report a theoretical study of a perfect absorber based on the metal-insulator-metal (MIM) structure, which achieves perfect absorption of single and double peaks in the visible range. The top Ag and middle SiO2 are arranged in a periodic nanopillar array. Adjusting the structural parameters of the nanopillars to indirectly control the absorption spectrum, theoretically the maximum single-peak absorption can reach more than 99.0% and the maximum double-peak absorption can reach more than 90.0%. We investigate its absorption mechanism through simulations and calculations, and explain the results well with the SPP scattering mode and F-P cavity theory. We find that through the double-peak absorption process, the mode split phenomenon appears as the thickness of SiO2 increases. Therefore, the selective appearance of absorption peaks can be achieved, which provides the possibility of application in absorbers. [ABSTRACT FROM AUTHOR]

Nowadays, graphene is one of the most used materials in the manufacturing of optical instruments, such as sensors, photovoltaic cells, and especially absorbers. The unrivaled ability of graphene in the formation of high-quality surface plasmons creates extraordinary features for absorber devices. Here, by exploiting the nanoplasmonic structure consisting of one-dimensional nanophotonic crystal made of graphene-silver half-ellipse grating next to the dielectric layer, the aim of this research is to achieve broadband absorption and perfect absorber in addition to increasing single-layer and multi-layer graphene absorption by creating surface plasmons and study the absorption spectrum in the near-infrared region. For this purpose, the studied nanostructure is optimized under different incident angles, geometric parameters of the structure, and also the dielectric refractive index. The proposed structure increases the absorption of graphene up to 85% along with wondrous absorption bandwidth over the entire near-infrared region from 770 to 3000 nm. In addition to achieving broadband plasmonic perfect absorber, an ultra-broadband, nearly perfect absorber, with the absorption of more than 80% in the whole near-infrared spectral zone has been introduced whose wide range of 1497 nm has an absorption above 90%. This range is far beyond the bandwidth of less than 1200 nm of conventional absorbers. In addition to high strength and low angular sensitivity, this absorber has the wonderful ability to effective absorb the solar radiation and can display abundant applications in solar cells, thermal emitters, and infrared detectors. [ABSTRACT FROM AUTHOR]

In this paper, a refractive index plasmonic nano-sensor based on a tunable perfect absorber has been proposed in the near-infrared region. The proposed sensor consists of a truncated cone resonator with more than 99% absorption and ultra-narrow bandwidth. Liquid crystal has been used in the designed nano-structure to tune the structure by variation of the incident angle and applying the external bias field to obtain the near perfect and ultra-narrow absorption peak. The proposed nano-sensor has a high sensitivity of 1363.63 nm/RIU and a high figure of merit of 1136.36 RIU−1 at the telecommunication wavelength of 1550 nm. Furthermore, after obtaining appropriate conditions for the liquid crystal layer, we have suggested a new resonator to boost the interaction of surface plasmons and the test medium. Therefore, the sensitivity and figure of merit are increased to the values of 1509 nm/RIU and 1257.5 RIU−1, respectively. This excellent performance of the sensor has huge potential for precision applications such as biomedical science and biosensor. Hence, the capability of the proposed nano-sensor in the field of histopathology for cancerous tissue diagnosis and detection of toxic and flammable gases to prevent endangering human health has been studied. In this case, the high sensitivity of 1368.06 nm/RIU and high figure of merit of 1179.36 RIU−1 have been obtained. [ABSTRACT FROM AUTHOR]

In this paper, a new model of multi-layer metamaterial perfect absorber (MPA) in the terahertz region has been introduced. This model is similar to the classic absorber model, ie the three traditional layers of metal-dielectric-metal. The difference is that the middle layer has changed in height and consists of 3 separate layers with the same material. Therefore, the middle layer of the proposed structure is metamaterial. Numerical results of the simulation show that the absorption rate of the perfect absorber at 6.86 THz is 99.99%. Also, by changing the width of the two middle layer columns w, a dual-band perfect absorber with an average absorption rate of 97.18% is obtained at frequencies of 4.24 THz and 6.86 THz. A significant advantage of this paper over other works is that this absorber is adjustable, in addition to obtaining a nearly perfect dual-band absorber with a narrow-band peak by adjusting the parameters and also a nearly broad-band absorber can also be obtained by changing the parameters without re-manufacturing the structure. We believe that the proposed absorber has potential in filtering, detection and imaging. [ABSTRACT FROM AUTHOR]

Metamaterial absorbers have attracted more and more attention because they can achieve perfect absorption in some specific structures. At present, although most absorbers can achieve perfect absorption in one or more frequencies of the visible or near infrared regions, its cannot achieve ultra-narrow band absorption. Ultra-narrow band absorption means that devices have the opportunity to improve the effectiveness and accuracy of detection in many applications. Here, a novel design of narrowband perfect absorber based on a dielectric-dielectric-metal structure is studied, which comprises of an Al2O3 nanodisk arrays, a SiO2 dielectric layer, an Au film, and a substrate layer. The simulated results reveal that the optimized nanoabsorber can excite resonances with a narrow absorption bandwidth (FWHM) of 0.45 nm and a high-quality (Q) factor up to 1499 in the visible regime. Moreover, when it as a refractive index (RI) sensor, the maximum sensitivity(S) of 108.32 nm/RIU and figure of merit (FOM) reaching 240.7 are obtained. The device exhibits angle and polarization independence, which will eliminate the polarization and angle requirement of the equipment. As a consequence, we believe our narrowband absorber could be used in many potential applications such as the detection of photodetectors, biological, chemical and so on.

Optically anisotropic materials show important advantages in constructing polarization-dependent optical devices. Very recently, a new type of two-dimensional van der Waals (vdW) material, known as α-phase molybdenum trioxide (α-MoO3), has sparked considerable interest owing to its highly anisotropic characteristics. In this work, we theoretically present an anisotropic metamaterial absorber composed of α-MoO3 rings and dielectric layer stacking on a metallic mirror. The designed absorber can exhibit ultra-narrowband perfect absorption for polarizations along [100] and [001] crystalline directions in the visible light region. Plus, the influences of some geometric parameters on the optical absorption spectra are discussed. Meanwhile, the proposed ultra-narrowband anisotropic perfect absorber has an excellent angular tolerance for the case of oblique incidence. Interestingly, the single-band perfect absorption in our proposed metamaterials can be arbitrarily extended to multi-band perfect absorption by adjusting the thickness of dielectric layer. The physical mechanism can be explained by the interference theory in Fabry–Pérot cavity, which is consistent with the numerical simulation. Our research results have some potential applications in designs of anisotropic optical devices with tunable spectrum and selective polarization in the visible light region.

In this paper, we propose a highly selective and efficient gas detection system based on a narrow-band IR metasurface emitter integrated with a resistive heater. In order to develop the sensor for the detection of specific gases, both the microheater and metasurface structures have been optimized in terms of geometry and materials. Devices with different metamaterial structures and geometries for the heater have been tested. Our prototype showed that the modification of the spectral response of metasurface-based structures is easily achieved by adapting the geometrical parameters of the plasmonic micro-/nanostructures in the metasurface. The advantage of this system is the on-chip integration of a thermal source with broad IR radiation with the metasurface structure, obtaining a compact selective radiation source. From the experimental data, narrow emission peaks (FWHM as low as 0.15 μm), corresponding to the CO2, CH4, and CO absorption bands, with a radiant power of a few mW were obtained. It has been shown that, by changing the bias voltage, a shift of a few tens of nm around the central emission wavelength can be obtained, allowing fine optimization for gas detection applications.

A very large dynamic optical reflection modulation from a simple unpatterned layered stack of phase‐change material ultra‐thin films is experimentally demonstrated. Specifically, this work demonstrates that properly designed systems comprising deeply subwavelength GeSbTe (GST) films, a dielectric spacer, and a metallic mirror produce a dynamic modulation of light in the near‐infrared from very strong reflection (up to R≈80%) to perfect absorption (A>99.995%) by simply controlling the crystalline state of the phase‐change material. While the amplitude of modulation experimentally reaches an optical contrast higher than 104, intermediate levels of reflection in between extreme values can also be actively encoded, corresponding to partial crystallization of the GST layer. Several layered system designs are further explored and guidelines are provided to tailor the efficient wavelength range, the angle of operation, and the degree of crystallization leading to perfect absorption. [ABSTRACT FROM AUTHOR]

Metasurfaces allow for the spatiotemporal variation of amplitude, phase, and polarization of optical wavefronts. Implementation of active tunability of metasurfaces promises compact flat optics capable of reconfigurable wavefront shaping. Phase‐change materials (PCMs) are a prominent material class enabling reconfigurable metasurfaces due to their large refractive index change upon structural transition. However, commonly employed laser‐induced switching of PCMs limits the achievable feature sizes and restricts device miniaturization. Thermal scanning‐probe‐induced local switching of the PCM germanium telluride is proposed to realize near‐infrared metasurfaces with feature sizes far below what is achievable with diffraction‐limited optical switching. The design is based on a planar multilayer and does not require fabrication of protruding resonators as commonly applied in the literature. Instead, it is numerically demonstrated that a broad‐band tuning of perfect absorption can be realized by the localized tip‐induced crystallization of the PCM. The spectral response of the metasurface is explained using resonance mode analysis and numerical simulations. To facilitate experimental realization, a theoretical description of the tip‐induced crystallization employing multiphysics simulations is provided to demonstrate the great potential for fabricating compact reconfigurable metasurfaces. The concept can be applied not only for plasmonic sensing and spatial frequency filtering, but also be transferred to all‐dielectric metasurfaces. [ABSTRACT FROM AUTHOR]

We design and simulate a tunable dual-band perfect absorber. This absorber is composed of a circular graphene layer with an ellipse cut out in the centre, separated by a dielectric layer in the middle and a gold mirror at the bottom. Results reveal that there exist two perfect absorption peaks in the terahertz band. The position of the absorption peak can be changed by adjusting the Fermi level and geometric parameters of the graphene pattern. Furthermore, the absorber is insensitive to the polarized incident light with a wide incident angle. Functionalities are achieved based on a simple and symmetrical single-layer graphene pattern, which can greatly reduce the manufacturing costs. The proposed absorber can be applied in the field of graphene-based photonic devices, such as detectors, sensors, and filters. [ABSTRACT FROM AUTHOR]

Multiple-band metamaterial absorbers as an important branch of metamaterial-based resonant devices have shown considerable application prospects in real life. However, current designs have many shortcomings in the realization of multiple-band absorption, including complex pattern structure, time-consuming fabrication steps, and strong interaction between sub-elements. Herein, a simple design of multiple-band metamaterial absorber based on single metallic resonator is presented. Basic cell of the multiple-band absorption is formed by a square metallic patch (cut by a concentric air gap) placed on a metallic mirror separated by an insulating medium material. The metamaterial structure can interact strongly with the incident beam to produce the fundamental mode resonance, third-order resonance, and two other resonances resulted from the concentric air gap introduction. The combining effect of the four discrete resonance modes provides the ability to achieve quad-band absorption. The quad-band absorption shows great dependence on the structure dimensions. Based on this, we further design a kind of multiple-band absorption having the adjustable number of absorption peaks by introducing photosensitive silicon material in the initial area of the air gap. The number of resonance peaks can be tuned flexibly from quad-band absorption to dual-band absorption by changing the conductivity (i.e., material property) of photosensitive silicon material. [ABSTRACT FROM AUTHOR]

Broadband perfect absorbers are of great importance for various applications such as stealth technologies, thermal photovoltaic cells, optical communication, photodetection, and photovoltaic devices. However, they are often made by lithographic techniques with high cost and complexity, which hinders their practical applications. The design of broadband and ultrahigh absorber at low cost and ease in fabrication is still a big challenge in the field of optics. Here, an all‐solution‐processed plasmonic perfect absorber is proposed and demonstrated by incorporating Mxene Ti3C2Tx (Tx = F, O or OH) and gold nanoparticles (NPs) in metal–insulator–metal configuration. The absorption of the designed plasmonic absorber can reach up to 99% with polarization‐ and angle‐independence in a broad range of wavelengths from ultraviolet to near‐infrared region. This ultrahigh and broadband absorbance is attributed to the synergy of plasmon resonance, magnetic resonance, and cavity effect between gold NPs layer and Mxene film, which is further corroborated by simulations of the finite element method for both random and patterned orientation of the gold nanoparticles. The excellent optical property together with the easy fabrication method paves the way for preparing photon‐absorbing nanostructures in photocatalysis and solar photovoltaics. [ABSTRACT FROM AUTHOR]

In this paper, we propose a metamaterial perfect absorber (MPA), which is a three-layer structure composed of a periodically placed “ǂ” type graphene array on top of a gold layer separated by a SiO2 dielectric spacer, to achieve dual band perfect absorption. The absorption mechanism is analyzed, and the simulation results show that at the frequencies of 5.16 THz and 10.30 THz, the absorption rates are as high as 99.7% and 99.6%, respectively. In addition, the absorber is insensitive to the polarization of the incident wave and has a good tolerance to the incident angle. Moreover, the position and peak absorption of the absorber can be adjusted flexibly by changing the structure parameters and the Fermi level μc of graphene. In addition, the position of absorption frequency is sensitive to the surrounding medium, so the proposed MPA has potential applications in the field of refractive sensor. This paper provides a new idea for the design of tunable dual-band ideal terahertz absorber. Because of its good performance, the proposed absorber has a wide range of application prospects in terahertz and mid-infrared optical filter, optical sensor, and radiation thermal imaging, stealth and communication fields.

Multiple-band metamaterial absorbers have been widely reported using the co-planar or layered design methods. However, these obtained absorption devices are of complex structure, large unit size, heavy weight, and time-consuming construction steps. Herein, an alternative design strategy is suggested to realize the multiple-band absorption at terahertz frequency. By introducing air gaps into the rectangular metallic patch, the original rectangular resonator can be divided into multiple sub-structures (or separated sections), and the combined effect of the localized resonance response of these sub-structures (or separated sections) gives rise to the multiple-band absorption. More importantly, the size, position and number of air gaps play the important roles in controlling the resonance performance of the absorption peaks and even in regulating the amount of the absorption peaks. Compared with the existing multiple-band absorption design strategies, the proposed approach does not increase the unit size, nor need to stack multiple layers, which provides important guidance for the design of multiple-band terahertz metamaterial absorbers with simple, compact, and easy to fabricate for full details.

In this work, a metal-dielectric-metal (MDM) multi-layer perfect absorber for infrared detection technology is proposed. Its absorption and sensing properties are numerically studied by finite-different time-domain (FDTD) method. Numerical results show that the MDM structure has located surface plasmon resonance (LSPR) peak at 955 nm and the maximum absorption can obtain 99.8%. More interestingly, the absorption characteristics of the structure are independent of polarization and polarization angle, which greatly improves the convenience of the device in practical application. It also can be used as a refractive index sensor. Therefore, we believe this structure has some applications in near-infrared detection technology such as gas or liquid detection at the laboratory, plasmon absorption switches, nanosensors and other fields.

It is quite urgent to obtain multiple-band light absorbers because they are of great important in many technology related fields. However, the realization of them is typically based on a plurality of resonators which are at least equal to the number of absorption peaks. Here an alternative structure design to reduce the number of the resonators for multiple-band light absorption at terahertz regime is demonstrated. The obtained results exhibit that penta-band terahertz light absorber with large absorption intensity and discrete frequency point is realized using five localized resonance responses in only three resonators (composed of two parallel arranged bars and a square patch). Near field patterns of the penta-band terahertz light absorber are given to clarify the absorption mechanism of each frequency point. We further explore and analyze the influence of the geometric parameters of the structure design on the performance of the penta-band light absorption.

Abstract Background An increasing interest has been recently grown in the development of nearly perfect absorber materials for solar energy collectors and more in general for all the thermophotovoltaic applications. Methods Wide angle and broadband perfect absorbers with compact multilayer structures made of a sequence of ITO and TiN layers are here studied to develop new devices for solar thermal energy harvesting. Genetic Algorithms are introduced for searching the optimal thicknesses of the layers so to design a perfect broadband absorber in the visible range, for a wide range of angles of incidence from 0° to 50°, and for both polarizations. Results Genetic Algorithms allow to design several optimized structures with 6, 8, and 10 layers reaching a very high average absorbance of 97%, 99% and 99.5% respectively together with a low hemispherical total emissivity (

A three-dimensional dual-band perfect absorber in the THz range (3-10 THz) is theoretically investigated. The absorber is composed of periodically placed cross-and disk-shaped graphene arrays on the top of a gold layer separated by a thick SiO2 dielectric spacer. The simulated results show two absorption peaks with near-unity absorbance (99.923% and 99.601%) at wavelengths 43.747 μm and 69.94 μm, respectively. Also, the absorber is insensitive to the polarization of the incident light and has a good tolerance to the incident angle whether it is TE or TM waves. Moreover, the peak wavelengths of the absorber can be flexibly modulated by varying the Fermi level μC of graphene while no need to refabricate the structure. This paper provides a new perspective for the design of graphene-based tunable multiband perfect THz absorbers, but not limited to THz absorbers, and may also be used in other THz graphene-based photonic devices.

Graphene is a powerful 2-D matter with the capability of extraordinary transparency, and tunable conductivity is employed in emerging optoelectronics devices. In this article, the design of an electrically tunable graphene-based perfect terahertz absorber is proposed and evaluated numerically. The introduced structure is composed of two graphene layers with a sharp absorption peak in the terahertz band. These graphene layers are combline and stripline separated by the insulator substrate. The position of the absorption peak is tunable on the absorption band by means of manipulation in geometric parameters of the combline graphene layer. Furthermore, the intensity and frequency of the absorption peak can be flexibly modulated by varying Fermi potential of the combline graphene layer, which can be controlled through external DC voltages without the need of changing the geometry of the structure. It is shown that the absorption band can be tuned in the bandwidth from 5 to 15 in terahertz. The findings of this paper can promote a new perspective in designing perfect ribbon absorbers based on graphene properties that can be utilized for future photodetectors, solar cells, and thermal sensors with an absorption intensity above 2 × 105(nm2) with narrow absorption bandwidth of 0.112 THz.

With the rapid development of terahertz technology, tunable high-efficiency broadband functional devices have become a research trend. In this research, a dynamically tunable dual broadband terahertz absorber based on the metamaterial structure of vanadium dioxide (VO2) is proposed and analyzed. The metamaterial is composed of patterned VO2 on the top layer, gold on the bottom layer and silicon dioxide (SiO2) as the middle dielectric layer. Simulation results show that two bandwidths of 90% absorption reach as wide as 2.32 THz from 1.87 to 4.19 THz and 2.03 THz from 8.70 to 10.73 THz under normal incidence. By changing the conductivity of VO2, the absorptance dynamically tuned from 2% to 94%. Moreover, it is verified that absorptance is insensitive to the polarization angle. The physical origin of this absorber is revealed through interference theory and matching impedance theory. We further investigate the physical mechanism of dual broadband absorption through electric field analysis. This design has potential applications in imaging, modulation and stealth technology. [ABSTRACT FROM AUTHOR]

An approach to realize a multiple-band perfect light absorber is demonstrated using a simple metamaterial design featuring a composite metallic structure consisting of a closed ring and a rectangular patch atop a metallic substrate separated by an insulator. Three narrow-band and discrete resonance peaks with nearly 100% absorption rates are obtained. The first absorption peak is due to the dipole resonance of the closed ring, while the last two absorption peaks are caused by the coupling effect of the closed ring and rectangular patch. The field distribution of the three absorption peaks is given to provide additional evidence. Unlike traditional multiple-band light absorbers that eliminate (or avoid) the interaction between the metallic array structures, our design is based on the mode coupling of the composite structure. This method can obviously reduce the number of metallic resonators, simplify the structure design and reduce fabrication costs. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a highly efficient light trapping design that is made of a metal-oxide-semiconductor-semiconductor (nanograting/nanopatch) (MOSSg/p) four-layer design to absorb light in a broad wavelength regime in dimensions smaller than the hole diffusion length of the active layer. For this aim, we first adopt a modeling approach based on the transfer matrix method (TMM) to find out the absorption bandwidth (BW) limits of a simple hematite (α-Fe2O3)-based metal-oxide-semiconductor (MOS) cavity design. Our modeling findings show that this design architecture can provide near-perfect absorption in shorter wavelengths. To extend the absorption toward longer wavelengths, a nanostructured semiconductor is placed on top of this MOS design. This nanostructure supports the Mie resonance and adds a new resonance in longer wavelengths without disrupting the lower wavelength absorption capability of MOS cavity. By this way, a polarization-insensitive absorption above 0.8 can be acquired up to λ=565 nm. Moreover, to have a better qualitative comparison, the water-splitting photocurrent of this design has been estimated. Our calculations show that a photocurrent as high as 10.6 mA cm−2 can be achieved with this design that is quite close to the theoretical limit of 12.5 mA cm−2 for hematite-based water-splitting photoanode. This paper proposes a design approach in which the superposition of cavity modes and Mie resonances can lead to a broadband, polarization-insensitive, and omnidirectional near-perfect light absorption in dimensions smaller than the carrier's diffusion length. This can be considered as a winning strategy to design highly efficient and ultrathin optoelectronic designs in a variety of applications including photoelectrochemical water splitting and photovoltaics. [ABSTRACT FROM AUTHOR]

In this work, we theoretically propose an anisotropic metasurface absorber, unit cell of which consists of a continuous monolayer black phosphorus (BP) sheet, sandwiched between a circular silver ring and a dielectric layer stacking on a silver substrate. Numerical results reveal that perfect enhancement absorption can be achieved in both armchair and zigzag directions, in which the resonant absorption peaks occur at different wavelengths due to the anisotropic property of BP. The calculated results by finite-difference time domain (FDTD) simulations have a good agreement with the coupled-mode theory. The physical mechanism of the perfect absorption is attributable to the critical coupling effect. Furthermore, the anisotropic perfect absorber not only exhibits tunable characteristics by varying the electron doping concentration, but also shows a wide-angle tolerance. In addition, our proposed absorber can achieve an arbitrary number of absorption bands by setting a suitable thickness of the dielectric layer. These results may have great potential applications in spectral imaging and photodetectors in the mid-infrared region. [ABSTRACT FROM AUTHOR]

Solar radiation is mainly concentrated in visible light region (50%), to achieve the perfect absorption of this spectral band is significant for many energy-related fields include solar cells, hot-electron devices, and perfect cloaking. In this paper, we theoretically designed and numerically demonstrated a broadband perfect absorber that works in visible light (400–800 nm). The perfect absorber consists of silica-titanium nitride-silica-titanium nitride four-layer structure, which has an ultra-thin thickness of 325 nm. This broadband absorber can continuously achieve light absorption from 400 to 800 nm, with an average absorption rate as 99.52% under normal incidence. This absorber obtained 99.98% maximum absorption rate at wavelength 620 nm and 97.18% minimum absorption rate at 400 nm. The multiple integration of propagating surface plasmon resonance, localized surface plasmon resonance, and Fabry-Perot resonance generates the perfect absorption function for this device. The high refractory, polarization independence, large incident angle insensitivity, and simple manufacturing method make this absorber more suitable for solar energy collection and thermal photovoltaics application. [ABSTRACT FROM AUTHOR]

Broadband light absorbers are highly desirable in various applications including solar-energy harvesting, thermo-photovoltaics, and photon detection. The Fabry–Perot (F–P) cavity comprising metal–insulator–metal (MIM) layers has attracted enormous interest as a lithography-free structure for realizing planar super absorbers. However, typical F–P cavity exhibits a narrow absorption band, and efforts have thus been made to increase the absorption bandwidth. This study demonstrates that near-perfect absorption over a broad spectral range can be obtained from the MIM structure by using thermally evaporated Ag and Au thin films whose dielectric and optical properties are much different from bulk-state properties because of their nanoscale features. A 55 nm thick SiO2 spacer sandwiched between a 10 nm Ag top layer and a 100 nm Al back reflector exhibits absorption >95% in the visible range of 400–700 nm. The broad absorption band shifts to a near-infrared range of 650–1000 nm by replacing the top layer with a 10 nm thick Au film and increasing the SiO2 spacer thickness to 115 nm. The experimental results are supported by finite-difference time-domain simulation. The large absorption bandwidth is attributed to the lossy nature of the nanostructured top metallic layer combined with the resonant absorption of the MIM cavity. [ABSTRACT FROM AUTHOR]

A thin screen exhibiting dynamically switchable transmission/absorption functionalities is highly desired in practice. However, a trilayer transmissive metasurface with active elements controlled in a uniform manner cannot exhibit independently controlled transmission and absorption properties due to intriguing interplays between the scattering and absorbing properties in systems exhibiting inversion symmetries. This motivates to employ the coupled‐mode theory to establish a generic phase diagram for such transmissive metasurfaces with active elements loaded in different layers tuned independently and to guide researchers design tunable metadevices with completely decoupled transmission/absorption responses. Based on such a phase diagram, a microwave metasurface is designed/fabricated with PIN diodes incorporated, and it is experimentally demonstrated that its functionality can switch from perfect transparency to perfect absorption, controlled by external voltages applied across the diodes. In addition to finding immediate applications in practice (e.g., smart radomes), the results of this study also provide a new type of tunable meta‐atom for building metasurfaces with flexible wave‐front control abilities. [ABSTRACT FROM AUTHOR]

A metamaterial perfect absorber based on layered, doped and undoped semiconductors is experimentally and theoretically investigated. Design rules are given to control the multispectral, narrow, strong absorption features (>98% absorption) in the mid‐IR spectrum. The proposed sub‐wavelength grating structures support localized surface plasmons and photonic resonances associated to the quarter wavelength optical thickness of the undoped spacer layer. The resonances hybridize depending on the geometric setup of the metamaterial and the material properties of the heavily doped semiconductor. The angular response of the resonances is studied to determine the acceptance angle. While the absorption is best at near‐normal incidence, the spectral position of the absorption bands is weakly dependent on the angular incidence up to angles of 45°. Complementary to the polarization‐dependent grating design of the metamaterial, an alternative based on a crossed grating nanopattern is also investigated for polarization insensitivity. Furthermore, it is demonstrated that the metamaterial perfect absorber provides a tailored thermal emission spectrum. Based on the heavily doped InAsSb/GaSb metamaterial platform, integrable and miniaturized perfect absorbers and thermal sources can be built. [ABSTRACT FROM AUTHOR]

Featured Application: We applied "Lumerical FDTD Solution" in the simulation process, which develops high-performance photonic simulation software, enabling designers to predict light's behaviour within complex structures and systems. And this software is constantly being update to improve functionality, especially for the simulation of new materials such as graphene, Si3N4 and so on. In this paper, a triple-band hybridization coherent perfect absorber based on graphene metamaterial is proposed, which consists of graphene concentric nanorings with different sizes and a metallic mirror separated by SiO2 layer. Based on the finite-difference time-domain (FDTD) solution, triple-band coherent perfect absorption is achieved at frequencies from 0.6 THz to 1.8 THz, which results from the surface plasmon resonance hybridization. The wavelength of the absorption peak can be rapidly changed by varying the Fermi level of graphene. Most importantly, the wavelength of the absorption peak can be independently tuned by varying the Fermi level of the single graphene nanoring. Moreover, the triple hybridization perfect absorber is angle-insensitive because of the perfect symmetry structure of the graphene nanorings. Therefore, our results may widely inspire optoelectronic and micro-nano applications, such as cloaking, tunable sensor, etc. [ABSTRACT FROM AUTHOR]

In this research, a perfect absorber based on an Au-ZnO-Al structure was studied numerically. The wavelength-selective and angle-independent characteristics of the device were demonstrated by simulation. The roles of the top metallic layer and the middle dielectric layer in producing a wavelength-selective perfect absorber with a high quality factor were investigated. The direction for further improving the quality factor is also pointed out in this paper. The research will be helpful for understanding the origination of perfect absorption in these types of metal-insulator-metal structures and producing a color filter with a high quality factor. [ABSTRACT FROM AUTHOR]