The Design Of Fano-Resonant Metamaterials And Its Electromagnetic Properties

Understanding the interactions between light and matter and manipulating light or electromagnetic waves have always been the people’s pursuit, and also been the essential issues in science and technology. With the development and advance of the nanotechnology in recent years, some periodic nanostructures with artificial shapes can be fabricated. Metamaterials are artificial composite materials constructed by periodically arranging special geometric elements. The electromagnetic properties of metamaterials depend highly on the element’s geometry, arrangment, and so on. Through designing special geometric elements, extraordinary optical properties not found in naturally occurring materials or compounds can be achieved by mematerials which opens a new channel to manipulate and control the light and electromagnetic waves.Nobel metals are usually chosen for the metamaterials. When light interacts with metallic nanostructures, it can couple to the coherent oscillation of free-electrons near metallic surfaces, forming a special resonant mode-surface plasmons. Fano resonance in metallic nanostructures usually arises from destructive or constructive interference between a super-radiant (bright) and a sub-radiant (dark) plasmon mode. Compared with localized or propagation surface plasmon resonances, Fano resonance possesses narrower spectral linewidth and leads to more intense localized EM enhancement and higher refractive index sensing, providing a promising platform for applications, such as biological or chemical sensors, surface enhanced Raman spectroscopy (SERS) and light trapping components. Metamaterials supporting Fano resonance have been one of the hottest topics in the field of nanophotonics. How to achieve Fano resonances with relatively simple configurations for easy preparation and with good performance for practical applications has always been a challenging problem so far. In this thesis, based on the electromagnetic wave theory and some numerical simulations including FEM and DDA, several Fano-resonant metamaterials are designed and investigated, which achieve Fano resonance or other related effects with superior optical properties.The mechanisms therein are also clarified. The main progress and innovation of this works are listed as follows:(1) Two Fano-resonant metamaterials and their near-field enhancments and refractive-index sensing. We designed an asymmetric nanoring and a heptamer-hole array, and demonstrated the Fano resonances in optical frequencies, and investigated their near-field localized enhancments and refractive-index sensing, respectively. The origin of the Fano resonance in two structures was also revealed by using plasmon hybridization theory. They possess potential applications in SERS and biological or chemical sensing.(2) The PIT-resonant metamaterial and its slow light effect. Plasmon induced transparency (PIT) is a special form of Fano resonance. In this work, we designed a "T" shaped PIT-resonant metamaterial, and investigated the influence of the structural parameters on both the transmittance and the group velocity of PIT resonance, and demonstrated that the gain could eliminate the trade-off between the group velocity and the transmittance. The PIT-resonant metamaterial possesses potential applications in integrated slow light devices and optical data storage.(3) Polarization-tunable PIT-resonant metamaterial. Now the PIT resonances in most of work are tuned passively by changing structural parameters. In this work, we proposed a novel disk/rod hybridized PIT-resonant metasurface. By rotating the polarization orentation of excitation light, an on-to-off modulation of PIT resonance was achieved, and an analytical expression was developed based on the dipole-dipole interaction model for intuitively clarifying the related mechanisms.(4) Narrow-band perfect absorber based on the PIA-resonant metamaterial. Plasmon induced absorption (PIA) originates from constructive interference between a bright and a dark resonant mode. In this work, we designed a vertically stacked two-layered metamaterial, which achieved a PIA resonance with the absorptivity of up to 98% and the linewidth less than 8nm, and produced an enhancement of-130 times in is-field and of-50 times in H-field. The underlying physics were revealed by the two-coupled-oscillator model.(5) Near-field engineering of Fano resonance in a plasmonic assembly for maximizing surface enhanced coherent anti-Stokes Raman scattering (SECARS).In this work, we presented a SECARS substrate consisting of three asymmetric gold disks, and discussed two strategies for maximizing the enhancement factor (EF) of SECARS signal:By changing the incident angle, the near-field "hot spots" of Fano resonance corresponding to three different frequencies involved in SECARS process (pumping, Stokes and anti-Stokes beams) can be brought to the same spatial locations, giving rise to a high SECARS EF up to 1010; By changing the geometrical parameters of trimer, double Fano resonances were realized, which produces a higher SECARS EF of 1012-13.