Abstract
Metamaterials are artificial electromagnetic materials in which the size of building elements is smaller than the wavelength of illuminating light. Based on the collective resonances in internal designed structures, metamaterials enable physical and optical properties that have not been achieved in naturally existing materials. Among diverse metamaterials, it is the split-ring resonator (SRR) structure a pioneering design proposed by Pendry et al. as magnetic meta-atoms to achieve negative magnetic permeability and high-frequency magnetism. The fundamental resonant behaviors of SRRs are conventionally understood by the equivalent LC circuit model and the multiple resonant reflectance peaks under normal incidence can be elucidated by model of standing-wave plasmonic resonances. More importantly, such a resonance condition depends on the local dielectric environment so sensitively that the SRRs can be readily employed as refractive-index (RI) sensors, especially for real-time, label-free and cell-level bimolecular detections by monitoring the shifts of reflectance peaks as analytes binding to molecular receptors immobilized on the SRR surface. Thus, we present a comprehensive understanding of the relative sensitivity and the detection length about the multi-mode plasmonic resonances in the planar SRR structure. By applying thin dielectric layers with different thicknesses on the SRR array, we demonstrate a quantitative interpretation to the distinct sensing behaviors (including sensitivity and detection length) of each resonance mode in the multi-resonance reflectance spectra based on both simulation and experimental results, present a coupler-free, scalable and multi-mode refractive index sensor based on nano-structured split ring resonators. Next, we develop a compact plasmonic bioimages based on SRRs. Owning advantages such as label-free, coupler-free, tunable spectrum range (from MIR to VIS) and longer detection length, the SRR microscopy (SRRM) is a strong competitor compared to the surface plasmon resonance microscopy (SPRM) for observing bio-target. Our experimental results has successfully demonstrated its capability of constructing the refractive index distribution images of human bone marrow-derived mesenchymal stem cells (hMSCs) and meanwhile, obtaining the information of functional groups from the target cells. Therefore, we expect that the SRR microscopy (SRRM) delivers much simple optical configuration and better penetration depth for truly whole-cell imaging applications. In addition, we utilize high dielectric constant ceramic materials such as zirconia, alumina to design negative refractive index media (NRIM) in the microwave region that have attracted significant attention for their potential to revise conventional electromagnetic rules involving refractive indices such as inverse optical rules. From a periodic array of commercially available zirconia (Alumina) cubes, we demonstrate artificial magnetic and electric dipoles due to the combination of displacement currents and Mie resonance. By scaling the size and periodicity of these dielectric resonators, the corresponding magnetic and electric responses are shifted to the desired frequencies. To further overlap the magnetic and electric resonances in the same frequency, we create a negative refractive index medium from single-dielectric resonators. On the other hand, we hybridize commercially available zirconia and alumina structures to harvest their individual artificial magnetic and electric response simultaneously, presenting a negative refractive index medium. Finally, we introduce the coupling of Mie resonances in the dielectric resonator pairs, especially in the asymmetric case that supports an extraordinary electromagnetic response such as metamaterials-induced transparency (MIT) phenomena. Using two hybrid structures of identical-dielectric-constant resonators (IDRs) and distinct-dielectric-constant resonators (DDRs), we demonstrate a larger group index (ng~354), better bandwidth-delay product (BDP~0.9) than metallic-type metamaterials. The keys to enable these properties are to excite either the trapped mode or the suppressed mode resonances, which can be managed by controlling the contrast of dielectric constants between the dielectric resonators in the hybrid metamaterials. Comparing with the conventional metamaterials-based applications constructed by metallic elements, the demonstrated all-dielectric metamaterials possesses low-loss and high-symmetry advantages, thus benefiting practical applications in communication components, perfect lenses, invisible cloaking and other novel electromagnetic devices.