Degenerate critical coupling in all-dielectric metasurface absorbers

Ming, Xianshun; Liu, Xinyu; Sun, Liqun; Padilla, Willie J.

doi:10.1364/oe.25.024658

Cited by 81 publications

(44 citation statements)

References 25 publications

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“…As can be observed, both the resonance frequency (open red triangles in Figure a) and the material loss rate (open purple triangles in Figure b) for the odd eigenmode show a strong dependence on fluence in comparison to the even eigenmode. Indeed, prior studies have shown that the odd eigenmode is about three times more sensitive to changes in height than the even eigenmode . We thus conclude that since the top photodoping is dominant in the study presented here, the optical excitation primarily affects the effective height of the all‐dielectric array, and thus chiefly alters the odd eigenmode.…”

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confidence: 45%

“…Thus, for example, a different type of all‐dielectric metasurface—an absorber—may be fashioned through incorporating a small amount of material loss in the resonators. The specific value of dielectric loss necessary to achieve peak absorption is determined by balancing the radiative dissipation—set by the geometrical parameters—and the material dissipation loss at the resonant frequency . This optimal state is termed degenerate critical coupling and realizes a total quality factor (Q‐factor) of 1/4 .…”

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confidence: 99%

“…We utilized two‐port S‐parameter simulations and temporal coupled mode theory (TCMT) to elucidate the physics underlying the dynamical response. We simulated the absorbance of each eigenmode separately using the two‐port eigenexcitation method on a freestanding silicon cylinder array (see Figure ). The absorption peak occurs near 1 THz with cylindrical dimensions of h = 51.3 µm, r = 60 µm, and p = 217 µm.…”

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confidence: 99%

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Phototunable Dielectric Huygens' Metasurfaces

et al. 2018

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Conventional dielectric metasurfaces achieve their properties through geometrical tuning and consequently are static. Although some unique properties are demonstrated, the usefulness for realistic applications is thus inherently limited. Here, control of the resonant eigenmodes supported by Huygens' metasurface (HMS) absorbers through optical excitation is proposed and demonstrated. An intensity transmission modulation depth of 99.93% is demonstrated at 1.03 THz, with an associated phase change of greater than π/2 rad. Coupled mode theory and S-parameter simulations are used to elucidate the mechanism underlying the dynamics of the metasurface and it is found that the tuning is primarily governed by modification of the magnetic dipole-like odd eigenmode, which both lifts the degeneracy, and eliminates critical coupling. The dynamic HMS demonstrates wide tunability and versatility which is not limited to the spectral range demonstrated, offering a new path for reconfigurable metasurface applications.

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confidence: 99%

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Phototunable Dielectric Huygens' Metasurfaces

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“…Electromagnetic wave absorbers may alternatively be fashioned from all‐dielectric metasurfaces, which consist of arrays of high permittivity geometrical shapes (cubes, spheres, cylinders, etc. ), and realize Mie resonances, permitting them to achieve novel electromagnetic responses .…”

Section: Comparison Of the Scattering Matrix Properties Of The Zero‐rmentioning

confidence: 99%

“…Dielectric resonators may support a large number of different types of resonances, and here we utilize electric and magnetic quasi‐dipole and multipole modes, which have been shown to be equivalent to hybrid waveguide modes in dielectric materials . Notably, the lowest order hybrid waveguide modes (i.e., HE 111 and EH 111 modes) have been shown to be the even‐eigenmode (electric dipole) and odd‐eigenmode (magnetic dipole) of the resonator, when the structure possesses mirror symmetry with respect to a perpendicular plane at the midpoint of its directrix . A key feature of the cylindrical geometry is that the center frequency ω 0 of each eigenmode can be tuned as a function of height (odd eigenmode) and diameter (even eigenmode).…”

Section: Comparison Of the Scattering Matrix Properties Of The Zero‐rmentioning

confidence: 99%

A Zero‐Rank, Maximum Nullity Perfect Electromagnetic Wave Absorber

Suen

Fan

Padilla

2019

Advanced Optical Materials

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structured metal and metal-dielectric composites using metamaterial and metasurface absorbers, or unpatterned low-loss substrates which constitute coherent perfect absorbers (CPAs).Electromagnetic wave absorbers may alternatively be fashioned from all-dielectric metasurfaces, [8][9][10][11] which consist of arrays of high permittivity geometrical shapes (cubes, spheres, cylinders, etc.), and realize Mie resonances, permitting them to achieve novel electromagnetic responses. [12][13][14][15] To-date dielectric metasurfaces have demonstrated exotic phenomena including, bound-states-in-thecontinuum, [16] generalized refraction, [17][18][19][20][21][22][23] holographic surfaces, [24] Huygens' surfaces, [13,25] and dynamic lenses. [26][27][28] Metasurfaces that consist purely of dielectric materials have broad benefits over conventional metal-dielectric structures. At terahertz and shorter wavelengths, the optical loss of metals increases, making it difficult to design efficient metamaterial resonators. In the infrared range, applications such as thermophotovoltaics require very high operating temperatures which would otherwise require the use of poorly conductive refractory metals such as tungsten. [29] Dielectric metasurfaces are thus a versatile platform to realize a host of unconventional physical responses and phenomena and may be utilized to realize future technologies.Here we propose and experimentally demonstrate an alldielectric metasurface absorber which attains zero-rank and maximum nullity in the scattering matrix. We term this new class of absorbers a zero-rank absorber (ZRA) and demonstrate that it is more fundamental than both CPAs [30,31] and metallic metamaterial absorbers. [31][32][33][34] Specifically, we show it is possible to construct a higher symmetry group absorber by combining two lower symmetry groups of opposite eigenmode symmetry. The ZRA operates in a state of degenerate critical coupling, where each mode absorbs half of the total incident energy, independent of phase. We experimentally characterize two all-dielectric metasurfaces to show directly that, through modification of the ZRA geometry, the degeneracy may be lifted resulting in two CPAs of opposite phase dependence.The ZRA presented here consists of a square array of cylindrical resonators with a circular generatrix (diameter d) lying perpendicular to its directrix (line of length h) and fashioned from a high permittivity material with an optimized material loss rate (depicted in Figure 1). Dielectric resonators may support a large number of different types of resonances, and here we utilize electric and magnetic quasi-dipole and multipole modes, Electromagnetic wave absorbers formed from a metamaterial layer are demonstrated and near-perfect absorption is realized across much of the spectrum. Alternatively, an unpatterned low-loss dielectric layer forms an absorber of coherent light and shows near-zero reflectance and high absorption. The latter is termed a coherent perfect absorber (CPA) and may be described as a time-reversed la...

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