When it comes to metasurfaces, bound state in the continuum (BIC) and surface lattice resonances (SLRs) are two convenient approaches for achieving high-quality factors (Q-factors).
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A research team headed by Dr. Guangyuan Li from the Shenzhen Institute of Advanced Technology (SIAT) of the Chinese Academy of Sciences has disclosed that the hybridization of SLRs can lead to dual-band BICs in silicon metasurfaces. The quantified Q-factors could achieve as high as 1240.
They also demonstrated that the resonance wavelengths and Q-factors of the dual-band quasi-BICs could be tuned by altering the lattice period or the nanoparticle size.
This study was reported in the journal Nanophotonics on November 1st, 2022.
Up until now, most of the symmetry-protected BICs in periodic nanostructures depended on the structural symmetry that split the unit-cell nanoparticles. Reported methods consist of bipartite nanoparticles and asymmetrically-shaped nanoparticles of various sizes.
To obtain high Q-factors for quasi-BICs, the structural asymmetry parameter must be fairly compact, thereby making nanofabrication rather challenging.
A size difference below 10% is particularly difficult, especially when the nanoparticle diameter is just a few hundred nanometers. However, the positions of nanoparticles could be precisely regulated in the top-down nanofabrication.
This motivated us to propose periodic bipartite nanoparticles with the central one slightly shifted from the center of the unit cell. To our surprise, the electric dipole SLRs (ED-SLRs) supported by two individual silicon lattices are totally canceled with each other in the bipartite arrays.
Dr. Guangyuan Li, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences
Li added, “Instead, we observed dual-band BICs due to the hybridizations of two in-plane electric quadrupole SLRs (EQ-SLRs) and of two out-of-plane magnetic dipole SLRs (MD-SLRs) that are supported by the two individual silicon lattices.”
Moreover, the scientists also discussed the tunability and the possible applications. They discovered that the tunability of SLRs is inherited by the dual-band BICs by varying the silicon nanodisks' diameter and the lattice period.
We hope this concept will help to suppress the inherent losses and to achieve high Q-factors for plasmonic metasurfaces.
Dr. Guangyuan Li, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences
Journal Reference:
Du, X., et al. (2022) Dual-band bound states in the continuum based on hybridization of surface lattice resonances. Nanophotonics. doi.org/10.1515/nanoph-2022-0427.
Source: https://english.cas.cn/