Structures to enhance light-plasmonic interactions

Remarkable data processing and transport capabilities provided by the devlopment of chip scale electronics and photonic technology have affected almost every facet of our lives. The ever-increasing demand for faster data transfer and processing has driven electronic technology to smaller, faster and more efficient devices. Plasmonics exploits the unique properties of miniature metallic structures to control light at the nano-scale, integrating with micro-photonic devices. Among many circuitry elements, plasmonic-enhanced photodetectors are particularly promising, since the size of the active semiconductor absorber is constrained laterally by the diffraction limit, and in the longitudinal dimension by the finite absorption depth of the semiconductor. In this thesis, we study three important plasmonic elements including plasmonic gratings and specifically the plasmonic focusing property of curved gratings, dielectric microspheres as the potential elements for replacing metallic nano-antennas and plasmonic enhanced graphene photodetectors for amplifying photocurrent generation by graphene. The ability of curved gratings to couple incident light into surface plasmons and to focus the surface plasmons is investigated. It is demonstrated by simulation and experiment that the focal spot of the curved gratings depends on the sector angle and can reach as low as 300 nm (~{cedil}{9D}{9C}{86}0/2.3) at a wavelength of {cedil}{9D}{9C}{86}0 = 700 nm for sector anglesgreater than 100{phono}{mllhring}. The application of curved gratings in launching surface plasmons onto micro-stripline wave guides is investigated and it is shown that curved gratings with small sector angles ~20 {phono}{mllhring} have 5% increased coupling efficiency in comparison to linear gratings. For larger sector angles the coupling efficiency of the curved grating decreases in comparison to linear gratings. In comparison to circular gratings that need to be illuminated with circularly polarized light and also do not give access to the focal spot because of the closed loop geometry, curved gratings can focus surface plasmons with linearly polarized light and also give access to the focal region for further process.In addition, the numerical aperture of curved gratings is defined for the first time based on the curvature of the gratings. The ability of dielectric microspheres with a rather high refractive index to couple out propagating surface plasmons and radiate directionally is also investigated by simulation and experiment. It is shown that TiO{acute}{82}{82} microspheres can scatter and radiate propagating surface plasmons. It is also shown by simulation that such radiation canbe directional suggesting the dielectric microsphere as an antenna. Finally, the photocurrent amplification of graphene photodetectors using electromagnetic near-field enhancement of surface plasmons is investigated. We use the novel idea of tunnelling light photons into surface plasmons at the graphene-metalcontact to enhance the photocurrent generation in a graphene gap-photo detector consisting of two gold strips separated with a gap and covered with a graphene sheet. Maximum photocurrent amplification of 8 was achieved at 730 nm wavelength of incident light. The enhancement by tunnelling light photons through the evanescent field of the incident light is valuable for photodetection and sensing. Such a photodetector can be used as a plasmonic detector for plasmonic waveguides in a plasmonic circuit.