局域表面等离激元共振是金属纳米粒子表面的自由电子在光子作用下发生集体震荡而产生的一种共振现象。 提出了一种方体及环/盘阵列结构, 该结构主要由左侧单圆环和右侧方体及偏心圆环盘组成。 利用时域有限差分算法(FDTD solutions)对该结构进行了光学性质的探究。 仿真结果表明, 当线性偏振光入射到金属表面时, 在结构中激发局域表面等离子体共振现象, 表现出明显的共振效应, 在600～1 700 nm范围形成了不同位置的共振谷。 通过对结构电场电荷仿真图的对比分析, 发现共振谷是由圆环内所激发的偶极共振模式与方体及环/盘激发的四偶极共振模式相互耦合杂化产生的混合等离子共振而形成的。 当调整金属结构的各项参数时, 金属纳米颗粒之间的局域表面等离激元共振会因电场耦合效应发生改变, 因此法诺共振的产生对于金属结构的各项参数有着极大的依赖性(如左圆环直径L、 右圆环直径R, 结构高度H, 左圆环到方体的距离D等), 通过对结构各项参数的改变, 可以实现对结构共振谷波长位置和共振强度的有效调控, 达到对结构光学性质可控的目的。 由于该结构具有独特的非对称性, 进一步探究了入射光源偏振方向(即电矢量与x轴的夹角)对结构的共振谷波长位置以及共振强度的影响。 结果表明, 随着光源偏振角度的增加, 共振谷J2处的波长位置出现明显的红移现象。 但当偏振角度为90°时, 共振谷J3处不能产生法诺共振现象。 由此, 可以通过改变光源的偏振方向来实现对该结构的光谱的共振强度及共振波长位置的调控。 更为重要的是, 该结构对周围的环境折射率有着较高的敏感度, 最高可达755 nm·RIU-1, 传感的品质因数(figure of merit, FOM)为18.4, 该结构在环境折射率等生物传感器及微纳光子器件方面有着潜在的应用前景。

Local surface plasmon resonance is a kind of resonance phenomenon caused by collective oscillation of free electrons on the surface of metal nanoparticles under the action of photons. A kind of square and ring/disk array structure is proposed in this paper, which is composed of the left single ring, the right square and the eccentric ring disk. The optical properties of the structure are investigated by the finite difference time domain (FDTD) method. Fano resonances appear in the transmission spectra due to the electric field couplings between the arrays when linearly polarized light is incident to the metal surface. Obvious resonant valley characteristics are formed at different positions in the wavelength range of 600～1 700 nm. Comparison and analysis of electric field and charge simulation diagram, it is found Fano resonance is formed by the coherent interference between the dipole resonance of the ring and the four dipole resonance modes excited by the square and the ring/disk. The local surface plasmon resonance between metal nanoparticles changed by the coupling effect of the electric field. Therefore, the Fano resonance is dependent on the parameters of the structure (such as the diameter of the left ring L, the diameter of the right ring R, the height of the structure H, the distance from the left ring to the square D, etc. ). By changing the parameters of the structure, the wavelength position and the resonant intensity of the resonant valley can be effectively controlled and the optical properties also can be controlled. Because of the unique asymmetry of the structure, the influence of the polarization direction of the incident light source (the angle between the electric vector and the x axis) on the position of the resonant valley wavelength and the resonant intensity of the structure is further investigated. The structure shows that with the increase of the polarization angle of the light source, the wavelength position at the resonant valley J2 appears obvious red shift phenomenon. However, when the polarization angle is 90°, the Fano resonance can not occur at the resonance valley J3. Therefore, the resonant intensity and the resonant wavelength position of the structure can be controlled by changing the polarization direction of the light source. More importantly, the structure has a high sensitivity to the environmental refractive index, up to 755 nm·RIU-1, and the figure of merit (FOM) can reach 18.4. The results show that the structure has potential application prospects in the applications of environmental refractive index sensors and micro-nanophotonic devices.