Wavelength-tunable perfect absorber based on guided-mode resonances

Design of multilayer planar film structures for near-perfect absorption in the visible to near-infrared

In this work, a near-perfect broadband absorber, consisting of Fe, MgF₂, Fe, TiO₂ and MgF₂ planar film, is proposed and investigated through simulations and experiments. The Fe material is first applied in the multilayer film structure, and it is proved to be more favorable for achieving broadband absorption. MgF₂ and TiO₂ are chosen as anti-reflection coatings to decrease unwanted reflections. The proposed absorber is optimized by employing a hybrid numerical method combining the transfer matrix method (TMM) and the genetic algorithm (GA). Under normal incidence conditions, the average absorption of the absorber is 97.6% in the range of 400 to 1400 nm. The finite difference time domain (FDTD) method and phase analysis reveal that the anti-reflection property and the Fabry-Perot resonance result in broadband absorption performance. Furthermore, when an additional Fe-MgF₂ layer is inserted on the bottom Fe layer, an average absorption of 97.9% in the range of 400 to 2000 nm can be achieved. Our approach could be of vital significance for numerous applications involving solar energy.

Broadband and Wide-Angle Performance of a Perfect Absorber Using a MIM Structure with 2D MXene

Due to the extraordinary optoelectronic properties and surface-rich functional groups, MXene has shown great promise in many applications, such as electromagnetic shielding, catalysis, sensors, ultrafast photons, etc. In this work, we propose a wide-angle absorber based on a metal-insulator-metal (MIM) metamaterial consisting of MXene. By optimizing the design, the absorption efficiency can be further improved throughout the entire wavelength range. More importantly, the absorber exhibits high-efficiency broadband and wide-angle (20–80°) absorption in the near-infrared range (NIR: 1.1–1.7 μm) by numerical calculation. It is foreseeable that the excellent absorption characteristics and easy-to-manufacture structure of the designed absorber will bring some inspiration to the absorption device in the NIR and its practical application.

Design of Narrow-Band Absorber Based on Symmetric Silicon Grating and Research on Its Sensing Performance

In this paper, using the surface plasmon and Fabry–Pérot (FP) cavity, the design of a symmetric silicon grating absorber is proposed. The time-domain finite difference method is used for simulation calculations. The basic unit structure is a dielectric grating composed of silicon dioxide, metal and silicon. Through the adjustment of geometric parameters, we have achieved the best of the symmetric silicon grating absorber. A narrowband absorption peak with an absorption rate greater than 99% is generated in the 3000–5000 nm optical band, and the wavelength of the absorption peak is λ = 3750 nm. The physical absorption mechanism is that silicon light generates surface plasmon waves under the interaction with incident light, and the electromagnetic field coupling of surface plasmon waves and light causes surface plasmon resonance, thereby exciting strong light response modulation. We also explore the influence of geometric parameters and polarization angle on the performance of silicon grating absorbers. Finally, we systematically study the refractive index sensitivity of these structures. These structures can be widely used in optical filtering, spectral sensing, gas detection and other fields.

Graphene-Based Cylindrical Pillar Gratings for Polarization-Insensitive Optical Absorbers

In this study, we present a two-dimensional dielectric grating which allows achieving high absorption in a monolayer graphene at visible and near-infrared frequencies. Dielectric gratings create guided-mode resonances that are exploited to effectively couple light with the graphene layer. The proposed structure was numerically analyzed through a rigorous coupled-wave analysis method. Effects of geometrical parameters and response to the oblique incidence of the plane wave were studied. Numerical results reveal that light absorption in the proposed structure is almost insensitive to the angle of the impinging source over a considerable wide angular range of 20°. This may lead to the development of easy to fabricate and experimentally viable graphene-based absorbers in the future.

Geometric frustration in ordered lattices of plasmonic nanoelements

Inspired by geometrically frustrated magnetic systems, we present the optical response of three cases of hexagonal lattices of plasmonic nanoelements. All of them were designed using a metal-insulator-metal configuration to enhance absorption of light, with elements in close proximity to exploit near-field coupling, and with triangular symmetry to induce frustration of the dipolar polarization in the gaps between neighboring structures. Both simulations and experimental results demonstrate that these systems behave as perfect absorbers in the visible and/or the near infrared. Besides, the numerical study of the time evolution shows that they exhibit a relatively extended time response over which the system fluctuates between localized and collective modes. It is of particular interest the echoed excitation of surface lattice resonance modes, which are still present at long times because of the geometric frustration inherent to the triangular lattice. It is worth noting that the excitation of collective modes is also enhanced in other types of arrays where dipolar excitations of the nanoelements are hampered by the symmetry of the array. However, we would like to emphasize that the enhancement in triangular arrays can be significantly larger because of the inherent geometric incompatibility of dipolar excitations and three-fold symmetry axes.

Polarization-sensitive tunable absorber in visible and near-infrared regimes

A broadband tunable absorber is designed and fabricated. The tunable absorber is comprised of a dielectric-metal-dielectric multilayer and plasmonic grating. A large size of tunable absorber device is fabricated by nano-imprinting method. The experimental results show that over 90% absorption can be achieved within visible and near-infrared regimes. Moreover, the high absorption can be controlled by changing the polarization of incident light. This polarization-sensitive tunable absorber can have practical applications such as high-efficiency polarization detectors and transmissive polarizer.

Ultrabroadband absorber based on single-sized embedded metal-dielectric-metal structures and application of radiative cooling

The realization of ultrabroadband absorption is a fundamental part of a thermal emitter, especially in the application of radiative cooling. This study involved proposing and systematically analyzing a novel structure termed as an embedded metal-dielectric-metal (EMDM) structure. The results in the case of an individual resonator indicated that the EMDM resonator displayed a broader full width at half maximum (FWHM) that was 1.9 times that of the metal-dielectric-metal (MDM) resonator due to mode matching at the terminated end and enhanced scattering intensity. With respect to the case of periodic resonators, single-sized periodic EMDM resonators are employed to achieve a broader FWHM that is 3.8 times that of the MDM resonators. In addition, a strong coupling effect is confirmed between localized MDM and hybrid modes. An application of lossy-dielectric based periodic three-dimensional EMDM resonators indicated that an average absorptivity of 0.85 in the entire atmospheric window (8-13 μm). The results revealed the potential of EMDM structures for radiative cooling devices and other ultrabroadband absorbers.

Control of light absorbance using plasmonic grating based perfect absorber at visible and near-infrared wavelengths

Conventional metamaterial absorbers have multilayer designs, where the dielectric interlayer is sandwiched between a top patterned metallic structure and bottom metallic film. Here, we demonstrate that a highly polarization-sensitive perfect absorber canbe realized by replacing the bottom metallic film with a plasmonic grating. Designs for broadband and narrowband of wavelength are proposed and numerically investigated. The designed absorbers perform high light absorption, which is above 90% over the wavelength range of 0.4-1.4 µm for the broadband absorber and 98% for the absorption peak in case of the narrowband design, with a specific polarization of incident light. We find that the absorption is tunable by changing the polarization. Such absorbers offer new approach for active control of light absorbance with strong impacts for solar energy harvesting, light emitting and sensing.