Plasmonics could bridge the gap between photonics and electronics at the nanoscale,
by allowing the realization of surface-plasmon-based circuits and plasmonic chips in the
future. To build up such devices, elementary components are required, such as a passive
plasmonic lens to focus free-space light to nanometre area and an active plasmonic modulator
or switch to control an optical response with an external signal (optical, thermal or
electrical). This thesis partially focuses on designing novel passive and active plasmonic
devices, with a specific emphasis on the understanding of the physical principles lying
behind these nanoscale optical phenomena.
Three passive plasmonic devices, designed by conformal transformation optics, are
numerically studied, including nanocrescents, kissing and overlapping nanowire dimers.
Contrary to conventional metal nanoparticles with just a few resonances, these devices
with structural singularities are able to harvest light over a broadband spectrum and focus
it into well-defined positions, with potential applications in high efficiency solar cells
and nanowire-based photodetectors and nanolasers. Moreover, thermo-optical and electrooptical
modulation of plasmon resonances are realized in metallic nanostructures integrated
with either a temperature-controlled phase transition material (vanadium dioxide,
VO2), or ferroelectric thin films.
Taking advantage of the high sensitivity of particle plasmon resonances to the change of
its surrounding environment, we develop a plasmon resonance nanospectroscopy technique
to study the effects of sizes and defects in the metal-insulator phase transition of VO2 at
the single-particle level, and even single-domain level. Finally, we propose and examine the
use of two-dimensional metallic nanohole arrays as a refractive index sensing platform for
future label-free biosensors with good surface sensitivity and high-throughput detection
ability.
The designed plasmonic devices have great potential implications for constructing nextgeneration
optical computers and chip-scale biosensors. The developed plasmon resonance
nanospectroscopy has the potential to probe the interfacial or domain boundary scattering
in polycrystalline and epitaxial thin films.