Realization of nanoscale photonic circuits would require passive and active optical components with subwavelength dimensions. Scaling issues associated with conventional photonic and optoelectronic devices are inherently restricted by the diffraction limit of the light. This prevents the size reduction of photonic devices to the nanoscale and the integration of nanophotonics and nanoelectronics on the same platform. An alternative approach to confine and guide optical fields on the nanoscale relies on surface plasmon polaritons (SPP's). SPPs are coherent oscillations of free electrons at the interface between a conductor and a dielectric, leading to electromagnetic fields confined to the interface with subwavelength lateral dimensions. Different plasmonic nanostructures that potentially allow for lateral confinement and overall size dimensions within the nanoscale have recently been demonstrated. However, the close proximity between the confined modes to the metal layers results in high absorption losses and limits the propagation length to only few microns. In order to overcome this difficulty, a gain material can be used in order to compensate the losses in plasmonic waveguides.

In this talk, we will present results on light confinement and propagation characteristics in plasmonic waveguides that encompass semiconductors as the active gain media. Three different gain-assisted plasmonic waveguides are proposed. We will discuss the influence of fundamental waveguide parameters on the gain required to achieve lossless propagation in each of these structures. Our results reveal strong plasmon mode confinement with corresponding simulated gain values compatible with existing semiconductor technology. The amount of required gain for lossless propagation is primarily determined by the coupling between the guided mode and the active medium of the waveguides. A second factor in importance influencing the required gain is the extension of the metal area in close proximity with the guided mode. We demonstrate that spot sizes with dimensions well below the diffraction limit of light can be obtained by controlling the geometrical parameters of the plasmonic waveguides. The proposed waveguides can be potentially used to fabricate highly integrated optical circuits for sensing, imaging and communication applications.