Negative Index Materials With Gain Media for Fast Optical Modulation

We discuss the origin of negative index behavior that is observed in certain artificial structures known as metamaterials that are periodic structures supporting backward optical waves with generally antiparallel phase and group velocities. Slab-like metamaterials, metal-dielectric, and purely dielectric ones support surface-plasmon polaritons that may be coupled into by an incident field. When this is the case, these surface waves can be pumped by the source, lead to pumping of the evanescent waves, and, as a result, enable subwavelength resolution. The main limiting factors for subwavelength resolution are losses and surface imperfections. Metal-dielectric metamaterials and systems are of special interest to nanophotonics, the focus of this paper, since they obviously provide high dielectric contrast, much larger than all-dielectric/semiconductor systems. This makes them promising for applications in dense integrated optical systems, since the mode volume is small. We consider various ways of combining metallic materials for negative dielectric constant and a gain medium to compensate for optical losses. Ultimately, one would like to make Si-compatible subwavelength optical components using metamaterials.