Metamaterial‐Based Two Dimensional Plasmonic Subwavelength Structures Offer the Broadest Waveband Light Harvesting

Abstract

Metamaterials, which are composed of metallic and dielectric subwavelength structures arranged in periodic array, are artifi cial materials with the permittivity or permeability less than that of vacuum or with negative values unattainable in nature. [1][2][3] Due to their unique electromagnetic properties, metamaterials have been widely used in many applications, such as sensors, superlenses, miniature antennas, and invisible cloaks. [4][5][6][7] Recently, metamaterial-based perfect absorbers have been attracted considerable attentions and various types of terahertz metamaterial absorbers have been reported. For example, Landy et al. presented a polarization-insensitive metamaterial absorber composed of metallic split ring resonators and cutting wires with singe-band absorption. [ 8 ] X.-J. He et al. proposed a dual-band metamaterial absorber made of two stacked metallic cross resonators and a lower metallic ground plane, separated by an isolation material spacer. [ 9 ] Cheng-Wen Cheng presented wide-angle polarization independent infrared dual band absorbers based on metallic multisized disk arrays. [ 10 ] Yanxia Cui proposed a sawtooth anisotropic metamaterial slab absorber for Transverse Magnetic (TM) polarized light with absorptivity higher than 95% covering a waveband ranging from 3 to 5.5 μ m. [ 11 ] However, current metamaterial absorbers suffer from many disadvantages such as narrow operating waveband, sensitivity to the polarization state of the incident light, narrow accepted angles and a fi xed azimuthal angle, which greatly limit their potential applications to spectroscopic detection and phase imaging. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Hence, a light absorbing device that is broadband, wide-angle and insensitive to the incident light polarization state is urgently needed for its applications in areas mentioned above. In this letter, we propose a two-dimensional (2D) pyramidal shape metamaterial-based absorber. In comparison with previous designs, this pyramid metamaterial absorber has a very high absorptivity performance that is polarization-insensitive, wide-angle and omni-directional at full infrared waveband.The proposed two-dimensional pyramid absorber is composed of alternating metallic and dielectric thin fi lms as shown in the insets of Figure 1 a. The metal thin fi lm is made of gold with thickness t m = 10 nm; dielectric thin fi lm is made of germanium with thickness t d = 190 nm. The total number of metal/dielectric pairs ( N) is 15. These multiple thin fi lm layers are carved into a pyramid structure for each unite cell. The periods of the unit cell in both x and y directions are 1600 nm. A gold fi lm with a thickness ( t = 100 nm) is added under the pyramid metamaterial absorber to block any incident light transmission. The optimized pyramid absorber structure was obtained through fi nite-difference time-domain (FDTD) simulations (Lumerical Inc.). [ 24 ] The material properties of gold and germanium were chosen from the software database-Gold Palik and Ger...

A reflective-backing-free metamaterial absorber with broadband response

“…Moreover, due to the effects of multiple metal/dielectric thin films and the truncated cone shapes, the proposed metamaterial structure can greatly suppress the reflection of light by effectively providing a graded transition of refractive index, and thus acts as an ultra-broadband multilayer antireflection coating as well. 19 Thus, the present simulation results demonstrate that the broadband absorber structure have excellent transmissivity in low-frequency.…”

“…Therefore, the absorption of multilayered structure is formed not only by the electric resonance but also by the magnetic resonance. 19 Figure 6 (b) shows the y-component electric field at the metal/ dielectric interface, it can be seen that the magnetic field and electric field were concentrated in dielectric layers obviously, the strong absorption mostly root in dielectric loss of dielectric layers. It should be mentioned that the induced magnetic field is located at the center while the induced electric field is formed at the sides.…”

Advances in Full Control of Electromagnetic Waves with Metasurfaces

“…Previously, in order to obtain a broad band response, multiple modes resonant at difference wavelengths are combined either transversely or longitudinally to form a super unit cell. [60][61][62][63][64] Similarly, by composing two coupled rectangular dielectric resonator within one unit cell ( Figure 1 g), silicon metasurface has been demonstrated to enable defl ecting or focusing multiply wavelengths achromatically. [ 65,66 ] It further broadens the capabilities of metasurfaces and suggests an unparalleled approach to circumvent the stubborn limitation of existing optical elements.…”

Broadband Absorption Engineering of Hyperbolic Metafilm Patterns

“…dielectric in one direction and metallic in other directions), which is promising for a variety of applications, including three-dimensional indefinite cavities 26 , spontaneous emission enhancement 22,53 , active nanoplasmonic devices 27,28 , etc. Recently, an interesting concept was proposed to realize an on-chip ultra-broadband and tunable super absorber in near-IR, mid-IR to microwave domain [29][30][31] using patterned HMM waveguide taper arrays constructed by multilayered metal/dielectric thin films. The physical mechanism of this intriguing ultrabroadband absorption was attributed to slow light modes confined in HMM waveguide tapers, leading to the enhanced light-matter interaction and therefore, strong/perfect absorption of the light.…”

“…For most periodic grating structures, their optical properties are usually sensitive to the periodicity of patterns. In previously reported theoretical design [29][30][31] , the period of the array was generally selected based on the bottom width of the HMM waveguide taper. It has not been revealed that how the period selection will affect the absorption properties of the patterned HMM films.…”