Interchangeable Electric/Magnetic Responses And Optical Activity In Metamaterials

The interest to construct metamaterial has being promoted by its attractive optical properties, such as negative refractive index, ultrahigh spatial resolution, invisibility cloaking, and optical magnetics. These fantastic properties facilitate potential applications in extraordinary optical transmission, microscopy, and antennas, etc. In traditional research of metamaterials, scientists used to treat the electric response and magnetic response as two separate things. To realize negative refractive index in the earliest metamaterial research, short metal wires and split-rings were used to provide electric response and magnetic response separately. There is no design of metamaterial which can include the electric response and magnetic response simultaneously in one single structure. In this thesis, we suggest a kind of metamaterial design to realize the interchangeable electric/magnetic response in the same frequency with only one structure. Chiral structures of different chirality are used to construct optically non-active metamaterial. The electric/magnetic response can be switched only by changing the polarization of incident light. Further, negative permittivity and negative permeability can be realized and switched in the same frequency band. We also use the chiral structure to build chiral optically active metamaterial. The chirality not only changes the polarization of incident light effectively but also offers a new way to realize negative refractive index.The main parts of this thesis are included as follows:1. We report that in an assembly of double-layered metallic U-shaped resonators with two resonant frequencies ωH and ωL, the effective induced electric and magnetic dipoles, which originate from the specific distribution of induced surface electric current, are collinear at the same frequency. Consequently, for left circularly polarized incident light, negative refractive index occurs at ωH, whereas for right circularly polarized incident light it occurs at ωH.2. We demonstrate that in an assembly of stacked metallic U-shaped resonators, pure magnetic and electric responses are respectively realized, and the magnetic and electric responses can be switched at the same frequency by changing the polarization of incident light for 90°. This unique feature originates from the topological symmetry of the structure.3. We focus on simultaneous realization of pure magnetic and electric responses by changing topological structures of the building block in an array of metallic structure. The building block changes from double-layered orthogonally rotated symmetric H-shaped metallic pattern to un-symmetric U-shaped metallic pattern. By rotating the polarization of incident light for 90°, the magnetic and electric responses can be switched at the same frequency. Meanwhile, on and ωL approach each other, and overlap eventually. This means that the negative refractive index can be achieved.4. We report the designing of a chiral metamaterial by assembling metallic helix array. The effective induced electric and magnetic dipoles originate from the specific distribution of induced surface electric current upon the illumination of incident light, are collinear at the resonant frequency. Consequently, for left circularly polarized incident light, negative refractive index can be realized.5. We report the designing of an optically-nonactive metamaterial by assembling metallic helices with different chirality. With linearly polarized incident light, pure electric or magnetic response can be selectively realized which accordingly leads to negative permittivity or negative permeability. Further, we show that pure electric or magnetic response can be interchanged at the same frequency band by merely changing the polarization of incident light for 90°.