Bound States in the Continuum in Anisotropic Plasmonic Metasurfaces

Abstract

The concept of optical bound states in the continuum (BICs) currently drives the field of dielectric resonant nanophotonics, providing an important physical mechanism for engineering highquality (high-Q) optical resonances in high-index dielectric nanoparticles and structured dielectric metasurfaces. For structured metallic metasurfaces, realization of BICs remains a challenge associated with strong dissipative losses of plasmonic materials. Here, we suggest and realize experimentally anisotropic plasmonic metasurfaces supporting high-Q resonances governed by quasi-BIC collective resonant modes. Our metasurfaces are composed of arrays of vertically oriented doublepillar meta-molecules covered by a thin layer of gold. We engineer quasi-BIC modes and observe experimentally sharp resonances in mid-IR reflectance spectra. Our work suggests a direct route to boost the resonant field enhancement in plasmonic metasurfaces via combining a small effective mode volume of plasmonic systems with engineered high-Q resonances provided by the BIC physics, with multiple applications to enhance light-matter interaction for nanooptics and quantum photonics.

High‐Q Transparency Band in All‐Dielectric Metasurfaces Induced by a Quasi Bound State in the Continuum

“…On the other hand, recall the classical analogue of quantum electromagnetically‐induced transparency (EIT) has been widely explored in metasurfaces, where the three level system needed is typically replaced by mode coupling of two resonances of various kinds. [ 34–45 ] Nonetheless, even though, as mentioned above for BICs in general, metasurface quasi‐BICs with high Q‐factors have been widely investigated, [ 5,13,18,46–48 ] the use of BICs to achieve ultra‐narrow EIT has not been explored thus far.…”

Frontiers of light manipulation in natural, metallic, and dielectric nanostructures

“…This condition is achieved, as first recognized for special Fano resonances [373] and erlier in plasmonic effective mode volume picture [374], at the critical coupling. Feasible near field enhancement up to 10 4 in quasi-BIC regime under critical coupling is claimed even in hybrid dielectric-plasmonic nanostructures, and found correspondent to perfect absorption condition [369] (Fig. 19c).…”

Plexcitonic Quasi‐Bound States in the Continuum

“…Therefore, the resonance peak at around 725 nm in Figure 3a can be determined to be a quasi‐BICs that originates from the interference between the Rayleigh anomaly line (1, 1) sub and the plasmonic resonances of Ag nanopyramid arrays. While plasmonic quasi‐BICs has been achieved due to symmetry in the middle‐IR wavelength range, [ 55 ] our study presents a general approach to realize visible plasmonic quasi‐BIC by two coupled resonances, that is, the interference between plasmonic resonances and Rayleigh anomalies. Given the predicted frequency degeneracy in Equation (10) for the two hybrid modes but with considerably different energy loss rates, the combined spectral profile is thus featured by a narrow and sharp peak from the quasi‐BICs and a spectral background largely from the bare plasmonic resonance.…”