Abstract
In this work, a novel all-dielectric metasurface made of arrayed circular slots etched in a silicon layer is proposed and theoretically investigated. The structure is designed to support both Mie-type multipolar resonances and symmetry-protected bound states in the continuum (BIC). Specifically, the metasurface consists of interrupted circular slots, following the paradigm of complementary split-ring resonators. This configuration allows both silicon-on-glass and free-standing metasurfaces and the arc length of the split-rings provides an extra tuning parameter. The nature of both BIC and non-BIC resonances supported by the metasurface is investigated by employing the Cartesian multipole decomposition technique. Thanks to the non-radiating nature of the quasi-BIC resonance, extremely high Q-factor responses are calculated, both by fitting the simulated transmittance spectra to an extended Fano model and by an eigenfrequency analysis. Furthermore, the effect of optical losses in silicon on quenching the achievable Q-factor values is discussed. The metasurface features a simple bulk geometry and sub-wavelength dimensions. This novel device, its high Q-factors, and strong energy confinement open new avenues of research on light-matter interactions in view of new applications in non-linear devices, biological sensors, and optical communications.
Highlights
The study of periodic subwavelength structures has attracted much attention in recent years. Such structures can be broadly classified in three categories, namely metamaterials (MM) [1], photonic crystals (PhC), and high contrast metastructures (HCM) [2]
While the MM properties are the result of local resonances of its subwavelength elements, PhC and HCM are based on Bragg resonances of the structure as a whole
We propose a novel type of MS based on building blocks of slot geometrical shapes, complementary split-ring resonator (CSRR) ultrathin slots, which can be etched in a silicon layer by standard techniques, such as electron-beam lithography or reactive ion etching
Summary
The study of periodic subwavelength structures has attracted much attention in recent years. All-dielectric MS composed by high refractive index materials have attracted equal or more interest than their metallic counterparts, as they do not suffer from ohmic losses and allow for the excitation of Mie-type magnetic and electric resonant multipole modes Based on this concept, numerous metasurfaces have been extensively used in a broad range of applications: to achieve arbitrary reflection/refraction [9,10,11], wavefront control and lensing [12,13], control of light emission [14], photoluminescence [15], polarization control [16], generation of vortex beams [17], sensing [18,19], microwave waveguide design [20], ultra-high quality factor resonant response [21], highly-selective filtering [22,23], or enhancement of nonlinear processes [24,25]. This novel approach opens new avenues of research in resonant periodic structures and more precisely in dielectric MS for narrowband filtering, sensing, or the enhancement of non-linear processes
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