Research On Plasmonic Devices

Recently, rapid development of research has taken place in the area of surface plasmon polaritons, i.e., collective electron excitations supported on metallic nano-objects. Although this phenomenon is well known for decades, the research has gained new momentum in advantage of state-of-the-art nanofabrication techniques and powerful electromagnetic simulation methods. Because of the promise of surface plasmon polaritons to manipulate light far beyond the diffraction limit, recent efforts are ongoing to miniaturize conventional light emitting devices, lasers, sensors and photovoltaic cells at unprecedented nano-scale dimensions. In this thesis, we demonstrate our research work on plasmonic devices focused on three aspects, including extraordinary optical transmission, manipulation of field pattern and thin film optical absorbers.First, in the research field of extraordinary transmission, we present that the slit-to-groove distance for a maximal transmission through the nano-slit surrounded with periodic grooves cannot be predicted by the theory of constructive interference between the groove-generated surface plasmon wave and the incident wave. A clear physical explanation is given and it is shown that generally the groove-generated SPW is the main factor determining the local field distribution around the nano-slit opening when the groove is not very shallow. We also show that the extraordinary transmission of light through a vertical nano-slit in a metal film can be enhanced by introducing a nano cavity antenna formed by a nearby metallic nano-strip over the slit opening. We note that the slit should be opened at a position with maximal magnetic field in the horizontal resonant cavity. Furthermore, we increase the number of the nano-strips and show that by using an array of six pairs of nano-cavity antennas, the transmission of light through a single nanoslit milled in the metallic film can be greatly enhanced.Second, in the field of manipulation of field pattern, we predict an optical curtain effect, i.e., formation of a spatially invariant light field as light emerges from a set of periodic metallic nano-objects. The underlying physical mechanism of generation of this unique optical curtain can be explained in both the spatial domain and the wave-vector domain. In particular, in each period we use one metallic nanostrip to equate the amplitudes of lights impinging on the openings of two metallic nanoslits and also shift their phases byπdifference. To reduce the reflection, we etch a groove on the top surface of the strip and form a U-shape structure.Third, we present four proposals in designing thin film optical absorbers with the purpose of overcoming the limitation of bandwidth. The first proposal is realized by exciting plasmonic phase resonances based on a modified T-shape metallic groove surface. We demonstrate that the addition of grooves can cause mode splitting of the plasmonic waveguide cavity modes and all the new resonant modes exhibit large absorptivity greater than 90%. The second proposal is by placing a metallic nanostrip array above a metallic nanogroove surface with a separation of 120 nm. We show that such an absorber has absorptivity greater than 90% at three bands which is addressed on the individual resonant configurations, like the nanostrips, nanogrooves, and the interaction between the nanostrips and the nanogrooves. The third kind of absorber is based on an array of nanostrip antennas of several different sizes and it has the broadband property due to the collective effect of magnetic responses excited by these nano-antennas at distinct wavelengths. By manipulating the differences of the nanostrip widths in experiment, the measured spectra clearly validate our design for the purpose of broadening the absorption band. The last kind of absorber is composed by an array of ladder-shaped anisotropic metamaterial waveguides. The anisotropic metamaterial is composed by alternated layered metal and dielectrics. Numerically, we calculated the dispersion curve of a three layered anisotropic waveguide of fixed width, which shows that such a waveguide excites slow light with group velocity approaches zero at certain wavelength.At the end of this thesis, we summarize all the content and also give the research plan for future.