对称破缺二聚体混合结构高Q圆二色性

Circular Dichroism with High Q Factor of Symmetry-Broken Dimeric Hybrid Structure

圆二色性(CD)通常用来表征手性响应强度,在手性检测领域极具应用前景。本文提出了一种金衬底上对称性破缺的全介质二聚体混合结构,可在721.1 nm波段处产生高达0.42的强CD,并且CD谱具有极窄的线宽,仅为0.16 nm。通过琼斯矩阵对该结构进行了理论分析,采用时域有限差分(FDTD)法进行建模与仿真,研究结果表明,通过改变介质二聚体的尺寸大小或椭圆柱介质的旋转角(θ)和两个介质体的相对位置(G)等参数可以对结构的CD响应进行相应的优化。并且通过电场分析发现,圆偏振光激发了二聚体的表面晶格共振(SLR),导致其CD谱具有高品质因子(Q)特性。基于此结构传感的灵敏度为718.3 nm/RIU(灵敏度单位),Q值可高达4489.4。此外,该手性结构的周期单元可以实现数字成像功能,不同偏振光下具有不同的成像信号。高Q值CD的研究结果为高性能的手性传感及光学成像的研究奠定了一定的理论基础。

Objective Circular dichroism(CD)molecular spectroscopy is often employed to determine the glucose content in food and is also an important tool to analyze the secondary structure of proteins and related property information of some viral molecules.However,chromatographic methods commonly adopted for chiral analysis are difficult to meet the rapid development in food,medicine,and biochemistry due to their shortcomings such as cumbersome sample processing,high cost,and much consumed time.Thus,there is an urgent need for more high-performance chiral analytical methods.High-Q and high-speed chiral sensors can solve these problems to a large extent and thus have been extensively applied to the chiral analysis of various fields,with the emergence of various high-Q chiral metamaterial structures.Methods Compared with the traditional chiral structure approaches,we can not only achieve stronger CD and maximize the higher Q factor by avoiding the metal radiation loss but also have a relatively simple structure.By placing a symmetrybroken dielectric dimer structure with a low refractive index on the bottom Au film,the mirror properties of the Au film are utilized to transfer the local field generated by surface lattice resonance(SLR)from the metal surface to the media top,which produces a resonant mode with a narrow linewidth.We simulate the structure using finite difference time domain(FDTD)solutions and theoretically analyze it by the Jones matrix method.The effects of parameters on the CD mode are discussed,such as the dimensional size of the dimer structure,the rotation angle of the ellipsoid column(θ),the relative distance between the square column and the ellipsoid medium(G),and the refractive index of the surrounding environment.Meanwhile,the sensitivity(S)and Q are calculated to quantitatively analyze sensing properties of the refractive index,and a cell with a period of 4×16 is arrayed to validate the structure for specific applications in imaging.Results and Discussions First,we verify the mechanism that the proposed dielectric dimer hybrid structure has a strong CD response and narrow linewidth by analyzing the x-z planar electric field.Then the parameter scanning optimization reveals that the CD of the structure can be optimal at a1=118 nm,a2=400 nm and b1=160 nm,b2=406 nm,and that the CD response intensity can be tuned by varyingθand G.The data results show good performance in sensing,with a sensitivity of(718.3±24.2)nm/RIU,a minimum FWHM of 0.16 nm,and a corresponding maximum Q factor of 4489.4.Additionally,the cell structure exhibits two different digital imaging signals"1010"and"0101"under RCP and LCP lights respectively,which can be manipulated by controlling the polarized light.Thus it is possible to manipulate the imaging signal by controlling the polarized light,which is valuable in areas such as imaging encryption.Conclusions We present a symmetry-broken dielectric dimer hybrid structure on a Au substrate.The structure consists of a gold substrate below and an asymmetric dimer structure above,where the dimer consists of a mixture of squarecolumn and elliptical-column all-media.The CD response of the structure can be tuned by varying the dimensional size,θ,and G of the dimer structure.By electric field analysis,the field intensity generated by the SLR excitation in the presence of circularly polarized light will be fully localized at the top of the dimer,leading to a high Q factor.Meanwhile,the sensing performance of the structure is also verified and calculated to show a sensitivity of(718.3±24.2)nm/RIU and a Q factor of up to 4489.4.Finally,we array a structured unit with a period of 4×16,and the results of the digital signals of the near-field response under RCP and LCP lights are"1010"and"0101".Thus,the results of the imaging signals can be modulated by manipulating circularly polarized light.This has potential applications in high-performance sensing and polarization manipulation devices.