Near-field signature of electromagnetic coupling in metamaterial arrays: a terahertz microscopy study

Wallauer, Jan; Bitzer, Andreas; Waselikowski, Stefan; Walther, Markus

doi:10.1364/oe.19.017283

Cited by 49 publications

(32 citation statements)

References 35 publications

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“…The operation of most metamaterial devices depends on the designs employed to control the fundamental resonances of SRRs, since the major tuning of material permittivity and permeability is enabled by these resonances . Apart from the single-SRR approach, several research groups have explored lateral coupling between nearest neighbor SRRs and its effects on the resonances [30][31][32][33][34][35][36][37][38][39][40][41][42]. It turns out that one of the prominent schemes to passively tune the metamaterial resonances is achieved by changing either the intercell distance or the relative orientation of SRRs with respect to each other.…”

Section: Introductionmentioning

confidence: 99%

Coupling Schemes in Terahertz Planar Metamaterials

Chowdhury

Singh

Taylor

et al. 2012

International Journal of Optics

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We present a review of the different coupling schemes in a planar array of terahertz metamaterials. The gap-to-gap near-field capacitive coupling between split-ring resonators in a unit cell leads to either blue shift or red shift of the fundamental inductive-capacitive (LC) resonance, depending on the position of the split gap. The inductive coupling is enhanced by decreasing the inter resonator distance resulting in strong blue shifts of theLCresonance. We observe theLCresonance tuning only when the split-ring resonators are in close proximity of each other; otherwise, they appear to be uncoupled. Conversely, the higher-order resonances are sensitive to the smallest change in the inter particle distance or split-ring resonator orientation and undergo tremendous resonance line reshaping giving rise to a sharp subradiant resonance mode which produces hot spots useful for sensing applications. Most of the coupling schemes in a metamaterial are based on a near-field effect, though there also exists a mechanism to couple the resonators through the excitation of lowest-order lattice mode which facilitates the long-range radiative or diffractive coupling in the split-ring resonator plane leading to resonance line narrowing of the fundamental as well as the higher order resonance modes.

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Section: Introductionmentioning

confidence: 99%

Coupling Schemes in Terahertz Planar Metamaterials

Chowdhury

Singh

Taylor

et al. 2012

International Journal of Optics

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“…Thus far, there are reports of different strategies in metamaterial research to achieve electromagnetic coupling. 6 near-field coupled metamaterials can involve electric coupling, 7,12,16 magnetic, 8,10,14,17,[19][20][21][22][23][24][25][26] as well as both electric and magnetic coupling. 9,[11][12][13] Resonance mode splitting in magnetically coupled system based on bright and dark resonators is demonstrated earlier in the context of weakly inductive and strongly conductively coupled cases.…”

mentioning

confidence: 99%

Probing the transition from an uncoupled to a strong near-field coupled regime between bright and dark mode resonators in metasurfaces

Singh

Al-Naib

Chowdhury

et al. 2014

Applied Physics Letters

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The coupling of multiple plasmonic resonators that sustain bright or dark modes provide intriguing spectral signatures. However, probing the onset of coupling effects while engaging the resonators with an increasing proximity has not yet been studied experimentally in detail. Nevertheless, this is of utmost importance to bridge the phenomenological understanding with the peculiarities of realworld-samples. Here, we take advantage of the ability to control spatial dimensions of THz metasurfaces deep in the sub-wavelength domain to study different regimes that occur while coupling split-ring-resonators that sustain a bright and a dark mode with increasing strength. We identify the length scales at which the resonators are uncoupled and then enter the regimes of weak, moderate, and strong coupling. It is shown that a strong coupling takes place only at distances smaller than one hundredth of the resonance wavelength. Understanding the features that emerge from such hybridization is important to take advantage of fundamental effects in metamaterials such as classical analogs of electromagnetically induced transparency, lasing spaser, near-field manipulation, and sensing with dark mode resonances. V C 2014 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4893726]Metasurfaces are thin films of artificially structured materials with unusual but highly beneficial electromagnetic properties. 1,2 These properties are provided at user-defined frequencies while relying on periodically or amorphously arranged unit cells with critical dimensions smaller than the operational wavelength. 2 While relying on unit cells, usually dubbed as meta-atoms that do provide an electromagnetic response that deviates from an ordinary electric dipole, properties inaccessible with naturally occurring materials fall within reach. 3-6 A canonical meta-atom in this stream of research is the split-ring-resonator (SRR) but many others can be considered as well. The key to tailor all anticipated properties upon demand is the ability to control the design and the geometrical detail of these meta-atoms with high precision.However, spectral properties with an even larger sophistication fall within reach while considering unit cells that consist of multiple coupled meta-atoms. These advanced unit cells are called metamolecules in analogy to metaatoms. A basic categorization of metamolecules can be made while considering designs for which the coupling is enforced by electromagnetic fields. [7][8][9][10][11][12][13][14][15] Recently, there have been several works where near-field coupling among metaatoms was investigated that sustain a bright and a dark mode. [8][9][10]14,15 The term bright and dark mode refers here to the ability to excite a particular resonance with the given polarization of the illumination if the individual metaatoms that form the metamolecule are uncoupled. These laterally coupled resonators lead to fascinating effects such as classical analogs of electromagnetically induced transparency and slow light. 9 However, the critical length-s...

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“…By controlling the size8, pitch9101112, or shape13 of the meta-atom on a single substrate, researchers have demonstrated metamaterials with exotic properties that do not exist in nature, such as negative refractive index14, polarization conversion of an incident wave1516, and electric field enhancement17. In particular, the frequency selectivity of meta-atoms is one of the most important characteristics in designing metamaterials for terahertz applications; significant progress has been made in engineering resonance tendencies by manipulating the gap size or position of the entire structure1819, coupling effects between adjacent meta-atoms1220212223 such as Fano resonance242526, lattice modes of the metamaterial array2728, and dielectric effects of metamaterial substrates2930.…”

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confidence: 99%

“…However, Rockstuhl et al18 were the first to conclude that the gap size variation of SRR structures could results in the resonance frequency change for perpendicular polarization in comparison to the half wave frequency of the side length of the SRRs. Since then, the unified interpretation of the anisotropic resonance mechanism for SRRs for different orders of standing waves (or plasmonic eigenmodes) has been suggested and widely utilized13273738.…”

mentioning

confidence: 99%

Anisotropy Modeling of Terahertz Metamaterials: Polarization Dependent Resonance Manipulation by Meta-Atom Cluster

Jung

Choi

et al. 2014

Sci Rep

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Recently metamaterials have inspired worldwide researches due to their exotic properties in transmitting, reflecting, absorbing or refracting specific electromagnetic waves. Most metamaterials are known to have anisotropic properties, but existing anisotropy models are applicable only to a single meta-atom and its properties. Here we propose an anisotropy model for asymmetrical meta-atom clusters and their polarization dependency. The proposed anisotropic meta-atom clusters show a unique resonance property in which their frequencies can be altered for parallel polarization, but fixed to a single resonance frequency for perpendicular polarization. The proposed anisotropic metamaterials are expected to pave the way for novel optical systems.

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Near-field signature of electromagnetic coupling in metamaterial arrays: a terahertz microscopy study

Cited by 49 publications

References 35 publications

Coupling Schemes in Terahertz Planar Metamaterials

Coupling Schemes in Terahertz Planar Metamaterials

Probing the transition from an uncoupled to a strong near-field coupled regime between bright and dark mode resonators in metasurfaces

Anisotropy Modeling of Terahertz Metamaterials: Polarization Dependent Resonance Manipulation by Meta-Atom Cluster

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