Optical nanocavities in two-dimensional photonic crystal planar waveguides.

摘要

One of the most fundamental properties of a physical system is its energy-momentum dispersion. The electronic dispersion present in semiconductor crystals results in energy gaps which play an extremely important role in the physics of many of the electronic and optical devices we use today. A similar dispersion for electromagnetic waves can be found in periodic dielectric structures. Owing to their strong dispersion, these “photonic crystals” can be used to manipulate light at sub-wavelength scales. The majority of this thesis is concerned with the design and implementation of optical resonant cavities formed by introducing small local imperfections into a periodically perforated slab waveguide. Light becomes localized to these “defect” regions, forming optical cavities with modal volumes approaching the theoretical limit of a cubic half-wavelength.; The resonant cavities studied in this thesis are fabricated using electron-beam lithography, anisotropic dry etching, and selective wet etching. These methods are used to create a two-dimensional array of cylindrical air holes in a free-standing waveguide structure. A multi-quantum-well Indium Gallium Arsenide Phosphide (InGaAsP) active region is epitaxially grown within the waveguide in order to provide light emission in the 1.5 μm band. Optical pumping of the active region is then used to probe the resonant structure of the photonic crystal cavities.; Numerical finite-difference time-domain simulations and qualitative predictions based on symmetry arguments are used to label the different resonant modes present in the cavity photoluminescence spectra. It is found that both donor and acceptor type modes are localized within the defect cavities. Pulsed lasing action is observed in cavity modes with modal volumes as small as 2(λ/2 n)3. Lithographic adjustments in the scale and symmetry of the cavity geometry are also used to tune the resonant mode wavelength, split mode degeneracies, and adjust the emission pattern and polarization of the defect modes.