Micro lasers
Confinement and manipulation of light in microcavities is important for a wide range of research areas and applications, e.g., cavity quantum electrodynamics or novel light sources. Efficient confinement of light in optical microcavities requires recirculation of that light. The price of this efficiency is usually isotropic emission, making extraction and collection of light highly inefficient. We have utilized cavity shape variation and phase space engineering to achieve simultaneously strong light confinement and directional output.

LEFT: A scanning electron micrograph of a GaAs microdisk whose shape is described by the limacon of Pascal. Although the intracavity ray dynamics is predominantly chaotic, it produces universal directionality of all lasing modes. RIGHT: Angular distribution of emission intensity for two lasing modes.		Directional emission of light is obtained from a mushroom shaped microcavity where the differential trick is to let the light escape the cavity but subsequently re-enter in order to focus it to specific directions.

Nano lasers
We recently developed a subwavelength semiconductor disk laser which can be fabricated using standard photolithographic techniques and wet chemical etching, making it suitable for mass production. Previous fabrication of nanolasers used electron-beam lithography and dry etching, a much more expensive approach. Subwavelength laser sources are potentially useful for nanophotonic circuits, on-chip optical interconnects, and pinpoint-accuracy biochemical sensing.

LEFT: Tilt-view scanning electron microscope image of a GaAs disk on top of an AlGaAs pedestal. The disk diameter is 627 nm and the disk thickness is 265 nm. InAs quantum wells embedded in the GaAs disk provides optical gain for lasing under optical pumping. The laser emission wavelength (in vacuum) is 870 nm. RIGHT: Spatial field profile of the lasing mode. The number of wavelengths (in GaAs) that fit the disk circumference is 4.

Nanoplasmonics
We investigate transport and localization of optical excitations in metal-dielectric nanocomposites. Utilizing near-field scanning optical microscopy, we have probed the near-field intensity correlations and fluctuations in semicontinuous silver films. As the surface coverage of silver increases, the semicontinuous metal film undergoes a transition from a dielectric waveguide below the percolation threshold to a metallic waveguide above the percolation threshold. At the percolation threshold, substantial structural inhomogeneities result in strong localization of surface plasmons. Well above the percolation threshold, the incident light excites propagating surface plasmon polaritons. Both propagation and localization regimes have important applications. In the former, electromagnetic energy and information can be transferred over long distances, whereas the localization of electromagnetic fields in nano scales can enhance various linear and nonlinear optical processes.

Spatial distribution of electromagnetic field intensity across a percolating metal film measured by a near-field scanning optical microscope. The hot spots show strong localization of surface plasmons.