Photonic devices utilizing subwavelength light confinement have been of interest due to many interesting optical properties introduced by the peculiar field distributions in the structures of subwavelength feature sizes. As a result of recent advances in nanofabrication, these photonic devices can now be experimentally demonstrated. We present our theoretical and experimental studies of several subwavelength structures showing the optical responses different from other structures.;First, we investigated the optical properties of deep subwavelength metallic structures with finding their magnetic and electric resonances. These magnetic and electric resonances can lead to electromagnetic properties not existing in nature. We designed a new split-ring resonator (SRR) geometry which has negative permeability and negative permittivity in order to construct low loss negative index materials. The new design helped to make the operating wavelength shifted down to visible region from the infrared region where most of other SRR geometries operate. Next, because of the field enhancements arising from the electric resonances, metallic nanoparticles had been previously studied for sensing using the amplitude response of the electronic resonances. However, the phase response could also carry important information. We investigated both the amplitude and phase responses of anisotropic and uniformly oriented gold nanoparticles and the relation between them.;Additionally, we studied the guidance of light utilizing the surface modes. Surface modes supported at metal surface propagates with a larger effective index, a larger confinement factor, and a smaller mode size than modes in an air-cladded waveguide. We proposed metal-capped microdisk cavities supporting surface modes in the transverse dimension. Having a larger effective index reduces the radiation loss and can increase the cavity Q factor. Having a larger cavity Q factor, a larger confinement factor, and a smaller mode size can lower the threshold for lasing. However, these benefits are accompanied by the additional propagation loss of surface modes introduced by the metal absorption. To reduce this metal absorption, we designed alternative structures which incorporate metal-sandwiched and photonic crystal structures in the transverse dimension. By improving the performances of subwavelength cavities, they can serve as the substantial building blocks for integrated optics.
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