Nanogap enhancement of the refractometric sensitivity at quasi-bound states in the continuum in all-dielectric metasurfaces
Nanogap enhancement of the refractometric sensitivity at quasi-bound states in the continuum in all-dielectric metasurfaces
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DOI：
10.1515/nanoph-2022-0565
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发表时间：
2023-01
期刊：
影响因子：
7.5
通讯作者：
Keisuke Watanabe;M. Iwanaga
中科院分区：
文献类型：
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作者：
Keisuke Watanabe;M. Iwanaga
全介质亚表面凭借其光谱位移作为高灵敏度的折射率传感器具有巨大的潜力，因为它具有广泛的设计灵活性和比等离子体平台更小的吸收损失。然而，在这种光子传感器中同时实现高质量(Q)因素和光与外部介质的大相互作用仍然是其更好性能的关键挑战之一。本研究基于连续体中的准束缚态(BIC)，提出了具有纳米GaP的硅块亚表面来克服这一挑战。结果表明，准表面存在磁偶极(MD)和电四极(EQ)两种准BIC模式，在∼30 nm能隙区域，其电场有较大幅度的增强。因此，将纳米GaP引入到准表面中，在保持高Q因子的同时，在MD模式下将环境折射率灵敏度提高了2.7倍，并获得了239的品质因数(FOM)。此外，在FOM和光谱信噪比之间的权衡下，需要适当地选择不对称量，这为基于准BIC的高灵敏生物传感器的设计提供了指导。
Abstract All-dielectric metasurfaces have great potential as highly sensitive refractometric sensors relying on their spectral shifts because of an extensive range of design flexibilities and their smaller absorption losses than plasmonic platforms. However, simultaneously realizing both high quality (Q) factors and the large interplay of light with external medium in such photonic sensors remains one of the key challenges for their better performance. This study proposes silicon block metasurfaces with nanogaps to overcome this challenge based on quasi-bound states in the continuum (BICs). We show that the metasurface has two quasi-BIC modes—magnetic dipole (MD) and electric quadrupole (EQ)—and their electric fields experience large enhancement at the ∼30 nm nanogap regions. Consequently, introducing nanogaps into the metasurfaces increases the environmental refractive index sensitivity by up to 2.7 times in the MD mode while keeping the high Q factors and achieves the figure-of-merit (FOM) of 239. In addition, we show that the appropriate selection of the amount of asymmetry is needed under the trade-off between the FOM and spectral signal-to-noise ratio, which provides design guidelines for highly sensitive biosensors based on quasi-BICs.