Shaping High‐<i>Q</i> Planar Fano Resonant Metamaterials toward Futuristic Technologies

Lim, Wen Xiang; Manjappa, Manukumara; Pitchappa, Prakash; Singh, Ranjan

doi:10.1002/adom.201800502

Cited by 78 publications

(35 citation statements)

References 131 publications

(200 reference statements)

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“…A slight perturbation induces leakage of an ideal bound state, and thus leads to a quasi‐BIC that has observable spectral features with finite linewidth. For clarity, we define the two eigenmodes as quasi‐BIC I, which leaks as a Fano resonance and quasi‐BIC II that weakly radiates as electromagnetically induced transparency (EIT) for y ‐ and x ‐ polarizations, respectively.…”

mentioning

confidence: 99%

Symmetry‐Protected Dual Bound States in the Continuum in Metamaterials

Cong

Singh

2019

Advanced Optical Materials

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218

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to access extreme confinement of photons into micro-or nanoscale region [3,10,11] above the light line within the radiation continuum. In general, EM wave is usually interpreted in terms of frequency spectrum, and it propagates as a spectral continuum above the light line in different media. Different orders of resonances may be found in the propagating continuum at specific frequencies described by i n n n 0  ω ω γ = + , where the real part indicates resonance frequencies and the imaginary part indicates the leakage rates of the n-order mode. [12] For a strongly confined mode, the leakage rate is significantly reduced, and goes to zero if photons are perfectly trapped in a so-called bound state in an ideal scenario. [13] However, such a bound state in the continuum (BIC) is not observable from the spectrum due to the nonradiative feature with vanishing spectral linewidth. As an embedded eigenvalue of the photonic system, [14] it becomes visible in the spectrum with a finite leakage rate as a quasi-BIC by introducing external perturbations. Such a BIC-inspired mechanism for light confinement allows a general strategy to access extremely high quality factor (Q, Q = ω 0 /2γ) resonance in optical cavities.Dielectric photonic crystals (PhCs) are an excellent platform to explore the BICs which largely avoid the intrinsic Ohmic loss for extremely high Q generation by exciting displacement current. [15,16] Nevertheless, the geometric size of unit cells in PhCs is usually at the scale of resonance wavelength, and resonant energy is thus loosely confined in the resonator cavity with a relatively large mode volume (V). In this condition, Purcell factor proportional to Q/V is largely reduced in the traditional PhCs despite a large Q, which hinders the efficient spontaneous emission rates in the context of cavity quantum electrodynamics. [17] An efficient approach to densely confine photons is by using metamaterials whose building blocks are in the subwavelength scale, and the resonant mode volume could be further reduced to a deep subwavelength scale by carefully designing the resonator geometry and mode properties. Here, we demonstrate dual symmetry-protected BICs in a subwavelength metamaterial that are independently induced by orthogonal polarizations of incident light. The features of the subwavelength BICs are experimentally observed in the terahertz spectrum by slightly breaking the C 2 symmetry with large Q factors. We also show the inverse square dependence of Q factor on the structural asymmetry parameter which describes a Bound state in the continuum (BIC) is a mathematical concept with an infinite radiative quality factor (Q) that exists only in an ideal infinite array of resonators. In photonics, it is essential to achieve high Q resonances for enhanced light-mater interactions that could enable low-threshold lasers, ultrasensitive sensors, and optical tweezers. Hence, it is important to explore BICs in different photonic systems including subwavelength metamaterials where symmetry-protected dual BICs exist. Th...

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mentioning

confidence: 99%

Symmetry‐Protected Dual Bound States in the Continuum in Metamaterials

Cong

Singh

2019

Advanced Optical Materials

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218

117

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“…The difference between the line shapes indicates that the S-Fano and AS-Fano possess opposite signs of Fano parameters, which is different from the previous reports of double-Fano resonances with merely positive or negative Fano parameters. [45,46] In Figure 2b, we exhibit the case that f s and f as are brought in close proximity with f s = 0.49 THz and f as = 0.48 THz, where one can see an EIT-like transparency peak between the two dips. This unique feature is due to the supposition effect of the double-Fano resonances with opposite symmetries.…”

Section: Design Principle and Analytical Modelmentioning

confidence: 95%

Symmetry‐Assisted Spectral Line Shapes Manipulation in Dielectric Double‐Fano Metasurfaces

Wang¹,

Tang

Feng³

et al. 2020

Advanced Optical Materials

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Spectral line shapes feature many essential resonant phenomena when diagnosing light–matter interactions. Particularly, tailoring spectral line shapes in photonics unveils a robust scheme to control electromagnetic waves and design functional optical devices. Here, the symmetry‐assisted manipulation of spectral line shapes in dielectric double‐Fano metasurfaces is theoretically proposed and experimentally demonstrated. Composed by a free‐standing silicon membrane with subwavelength aperture arrays, the metasurfaces simultaneously support two orthogonal localized modes (symmetric and antisymmetric) with high‐quality (high‐Q) factors and a propagating mode with a low‐Q factor. The symmetric and antisymmetric modes interfere with the propagating mode, resulting in the double‐Fano resonances with opposite signs of Fano parameters. The superposition of such double‐Fano resonances can produce multiple spectral line shapes, including double‐Fano resonances, a single Fano resonance, an electromagnetic‐induced‐transparency‐like (EIT‐like) window, and a complementary EIT‐like window, which have been analytically, numerically, and experimentally verified. Moreover, the EIT‐like window exhibits a steep dispersion, which is beneficial in slow light devices. Due to the anisotropy of the design, this EIT‐like window can transform into a complementary EIT‐like window when the incident polarization is rotated by 90°. Thus, such asymmetry‐assisted double‐Fano metasurfaces provide a new route to reveal photonic phenomena and construct multifunctional metadevices.

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“…Furthermore, the complete modulation of Fano resonance with crystalline GST limits the adoption of mechanical curvature as added control to manipulate Fano resonance. There are several ways to enhance the resonance strength such as-i) by using higher asymmetric Fano resonators which provide enhanced resonance strength, [47,48] ii) reducing the thickness of GST thin film, as shown in Figure S1d in the Supporting Information or, iii) by reducing the crystalline proportion in as-deposited GST film with limited stimulus time or power as shown in Figure 2c,d, respectively.…”

Section: (4 Of 8)mentioning

confidence: 99%

Volatile Ultrafast Switching at Multilevel Nonvolatile States of Phase Change Material for Active Flexible Terahertz Metadevices

Pitchappa

Kumar

Prakash

et al. 2021

Adv Funct Materials

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Phase change materials provide unique reconfigurable properties for photonic applications that mainly arise from their exotic characteristic to reversibly switch between the amorphous and crystalline nonvolatile phases. Optical pulse based reversible switching of nonvolatile phases is exploited in various nanophotonic devices. However, large area reversible switching is extremely challenging and has hindered its translation into a technologically significant terahertz spectral domain. Here, this limitation is circumvented by exploiting the semiconducting nature of germanium antimony telluride (GST) to achieve dynamic terahertz control at picosecond timescales. It is also shown that the ultrafast response can be actively altered by changing the crystallographic phase of GST. The ease of fabrication of phase change materials allows for the realization of a variable ultrafast terahertz modulator on a flexible platform. The rich properties of phase change materials combined with the diverse functionalities of metamaterials and all-optical ultrafast control enables an ideal platform for design of efficient terahertz communication devices, terahertz neuromorphic photonics, and smart sensor systems.

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Shaping High‐Q Planar Fano Resonant Metamaterials toward Futuristic Technologies

Cited by 78 publications

References 131 publications

Symmetry‐Protected Dual Bound States in the Continuum in Metamaterials

Symmetry‐Protected Dual Bound States in the Continuum in Metamaterials

Symmetry‐Assisted Spectral Line Shapes Manipulation in Dielectric Double‐Fano Metasurfaces

Volatile Ultrafast Switching at Multilevel Nonvolatile States of Phase Change Material for Active Flexible Terahertz Metadevices

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