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

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 symmetry-broken 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 (theta), 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 x 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 a(1)=118 nm, a(2)=400 nm and b(1)=160 nm, b(2)=406 nm, and that the CD response intensity can be tuned by varying theta and 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 square-column and elliptical-column all-media. The CD response of the structure can be tuned by varying the dimensional size, theta, 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 x 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.