Broken Symmetry Dielectric Resonators for High Quality Factor Fano Metasurfaces

Abstract

We present a new approach to dielectric metasurface design that relies on a single resonator per unit cell and produces robust, high quality-factor Fano resonances. Our approach utilizes symmetry breaking of highly symmetric resonator geometries, such as cubes, to induce couplings between the otherwise orthogonal resonator modes. In particular, we design perturbations that couple "bright" dipole modes to "dark" dipole modes whose radiative decay is suppressed by local field effects in the array. Our approach is widely scalable from the near-infrared to radio frequencies. We first unravel the Fano resonance behavior through numerical simulations of a germanium resonator-based metasurface that achieves a quality-factor of ~1300 at ~10.8 µm. Then, we present two experimental demonstrations operating in the near-infrared (~1 µm): a silicon-based implementation that achieves a quality-factor of ~350; and a gallium arsenide-based structure that achieves a quality-factor of ~600 -the highest near-infrared quality-factor experimentally demonstrated to date with this kind of metasurfaces. Importantly, large electromagnetic field enhancements appear within the resonators at the Fano resonant frequencies. We envision that combining high quality-factor, high field enhancement resonances with nonlinear and active/gain materials such as gallium arsenide will lead to new classes of active optical devices.Metasurfaces are currently the subject of intensive research worldwide since they can be tailored to produce a wide range of optical behaviors. However, metasurfaces generally exhibit broad spectral resonances, and it is difficult to obtain narrow (i.e. high quality-factor, Q) spectral features. Attaining such high-Q features from metasurfaces would greatly expand their application space, particularly in the areas of sensing, spectral filtering, and optical modulation. Early metasurfaces were fabricated from metals and exhibited particularly broad resonances at infrared and optical frequencies as a result of Ohmic losses. Dielectric resonator-based metasurfaces were introduced to overcome these losses and have enabled, among others, wave-front manipulation and cloaking devices, perfect reflectors, and ultrathin lenses [1-10] but, although absorptive losses were reduced, the metasurface resonances remained broad due to strong coupling with the external field (i.e. large radiation losses).Recently, new strategies based on "electromagnetically induced transparency" or "Fano resonances" have been developed that show great promise for achieving high-Q resonances [11][12][13][14][15]. In this approach, the resonator system is designed to support both "bright" and "dark" resonances. The incident optical field readily couples to the bright resonance, but cannot couple directly to the dark resonance. Through proper design, a weak coupling between the two resonances can be introduced, allowing energy from the incident wave to be indirectly coupled to the dark resonance. The metasurface transmission and reflection spectra resulting from ...

Symmetry Breaking in Photonic Crystals: On-Demand Dispersion from Flatband to Dirac Cones

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High Q-Factor Resonance in a Symmetric Array of All-Dielectric Bars

“…The lattice periods in the x and y direction are fixed as Px = 800 nm and Py = 900 nm, respectively. or Fano resonances with Q value over thousands have been numerically presented in all-dielectric metasurfaces consisting of asymmetric rods and rings [5,6,[35][36][37], and experimentally reachable of ~600 in the near-IR wavelength range [6,35]. And strong field enhancement either inside the dielectric resonators or in SRR gaps accompany with high Q, which is useful for nonlinear interaction [7,38] or sensing applications [6,36,37].…”

“…And it can be easily fabricated by plasma-enhanced chemical vapor deposition (PECVD), electron-beam lithography, residual resist etching and lift-off process [6,35]. Unlike most previously reported rod-type all-dielectric metasurfaces, where normal incident light polarized along the rods is used to excite a broad ER [5,6,36,37,39], in this paper, the electric field of the incident wave is polarized perpendicular to the rods (i.e., in x-axis).…”

Revealing photonic symmetry-protected modes by the finite-difference-time-domain method

“…Thus, two obvious solutions exist to break the symmetry: an intrinsic one by modifying the geometry of the structure itself [6][7][8][9][10] or an extrinsic one induced by modifying the illumination conditions (oblique incidence for instance) [3,11,12]. Two-dimensional (2D) [8] or three-dimensional (3D) [9,[13][14][15][16] structures were proposed in this context to present symmetry protected modes at normal incidence. The spatial discretization exercised in the FDTD combined with the Yee scheme [17], for which two different components of the electromagnetic field are located at two different spatial positions, leads to naturally break the geometrical symmetry of the structure.…”