Size reduction is a key issue in the development of contemporary integrated photonics. This thesis is mainly devoted to study some integrated photonic components in sub-wavelength or nanometric scales, both theoretically and experimentally. The possible approaches to reduce the sizes or to increase the functionalities of photonic components are discussed, including waveguides and devices based on silicon nanowires, photonic crystals, surface plasmons, and some near-field plasmonic components. First, some numerical methods, including the finite-difference time-domain method and the full-vectorial finite-difference mode solver, are introduced. The finite-difference time-domain method can be used to investigate the interaction of light fields with virtually arbitrary structures. The full-vectorial finite-difference mode solver is mainly used for calculating the eigenmodes of a waveguide structure. The fabrication and characterization technologies for nano-photonic components are reviewed. The fabrications are mainly based on semiconductor cleanroom facilities, which include thin film deposition, electron beam lithography, and etching. The characterization setups with the end-fire coupling and the vertical grating coupling are also described. Silicon nanowire waveguides and related devices are studied. Arrayed waveguide gratings with 11nm and 1.6nm channel spacing are fabricated and characterized. The dimension of these arrayed waveguide gratings is around 100 μm, which is 1--2 order of magnitude smaller than conventional silica based arrayed waveguide gratings. A compact polarization beam splitter employing positive/negative refraction based on a photonic crystal of silicon pillars is designed and demonstrated. Extinction ratio of ~15dB is achieved experimentally in a wide wavelength range. Surface plasmon waveguides and devices are analyzed theoretically. With surface plasmons the light field can be confined in a sub-wavelength dimension. Some related photonic devices, e.g., directional couplers and ring resonators, are studied. We also show that some ideas and principles of microwave devices, e.g., a branch-line coupler, can be borrowed for building corresponding surface plasmon based devices. Near-field plasmonic components, including near-field scanning optical microscope probes and left handed material slab lenses, are also analyzed. Some novel designs are introduced to enhance the corresponding systems. / QC 20100908