Highly Sensitive Refractive Index Sensors with Plasmonic Nanoantennas−Utilization of Optimal Spectral Detuning of Fano Resonances,ACS Sensors

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Highly Sensitive Refractive Index Sensors with Plasmonic Nanoantennas−Utilization of Optimal Spectral Detuning of Fano Resonances
ACS Sensors ( IF 8.2 ) Pub Date : 2018-04-30 00:00:00 , DOI: 10.1021/acssensors.8b00003
Martin Mesch ₁ , Thomas Weiss ₁ , Martin Schäferling ₁ , Mario Hentschel ₁ , Ravi S. Hegde _{2,

3} , Harald Giessen ₁

Affiliation

We analyze and optimize the performance of coupled plasmonic nanoantennas for refractive index sensing. The investigated structure supports a sub- and super-radiant mode that originates from the weak coupling of a dipolar and quadrupolar mode, resulting in a Fano-type spectral line shape. In our study, we vary the near-field coupling of the two modes and particularly examine the influence of the spectral detuning between them on the sensing performance. Surprisingly, the case of matched resonance frequencies does not provide the best sensor. Instead, we find that the right amount of coupling strength and spectral detuning allows for achieving the ideal combination of narrow line width and sufficient excitation strength of the subradiant mode, and therefore results in optimized sensor performance. Our findings are confirmed by experimental results and first-order perturbation theory. The latter is based on the resonant state expansion and provides direct access to resonance frequency shifts and line width changes as well as the excitation strength of the modes. Based on these parameters, we define a figure of merit that can be easily calculated for different sensing geometries and agrees well with the numerical and experimental results.

中文翻译：

等离激元纳米天线的高灵敏度折射率传感器-利用法诺共振的最佳频谱失谐

我们分析和优化耦合的等离激元纳米天线的折射率传感性能。研究的结构支持亚辐射和超辐射模式，该模式源自偶极和四极模式的弱耦合，从而形成了Fano型光谱线形状。在我们的研究中，我们改变了两种模式的近场耦合，并特别研究了它们之间的光谱失谐对传感性能的影响。令人惊讶的是，谐振频率匹配的情况不能提供最佳的传感器。相反，我们发现适当的耦合强度和频谱失谐可以实现窄线宽和亚辐射模式的足够激发强度的理想组合，因此可以优化传感器性能。我们的发现被实验结果和一阶扰动理论所证实。后者基于谐振状态扩展，可直接访问谐振频率偏移和线宽变化以及模式的激发强度。基于这些参数，我们定义了品质因数，可以很容易地针对不同的感测几何形状进行计算，并且与数值和实验结果非常吻合。

更新日期：2018-04-30

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