Cavities and waveguide-cavity coupling in a three-dimensioanl layer-by-layer photonic crystal
Kohli, Preeti (2005) Cavities and waveguide-cavity coupling in a three-dimensioanl layer-by-layer photonic crystal. Masters thesis, Iowa State University.
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This thesis examines the fundamental characteristics of defect cavities in three-dimensional(3-D) layer-by-layer photonic crystals (PCs). Photonic crystals are engineered materials in which a 3-D periodic variation in the dielectric constant is used to prevent propagation of electromagnetic waves within a range of frequencies, thus creating a photonic band gap. By introducing a cavity defect within the periodic structure of the crystal, narrow transmission bands are formed within the photonic gap. This can be viewed as photonic resonant tunneling, in which photons tunnel through PC cladding layers surrounding the cavity. The transmission modes correspond to the resonant frequencies of the cavity. Using a microwave-scale photonic crystal structure, we studied the effects of changing cladding layer thicknesses on resonant frequencies and the quality factors (Q) of measured transmission peaks. We found that, for a given cavity size, the quality factor increased with increasing cladding thickness, indicative of better photonic confinement within the cavity. Also, the peak transmission level decreased with increasing cladding thickness. Both of these results are consistent with resonant tunneling behavior. We also studied the effect of changing the cavity size, while keeping cladding thicknesses constant. We found that the resonant frequencies changed very little as the cavity sizes changed. Again, this is consistent with the theoretical picture of cavities within PCs. We also studied coupling between waveguides and cavities, in which electromagnetic radiation would travel down a waveguide within a PC, couple to a nearby cavity, which would, in turn, couple to a second waveguide. By studying variations in the placement of the coupling cavity with respect to the two waveguides, we were able to find conditions that would lead to almost 100% transfer from one waveguide to the other, within a narrow band of frequencies. These results suggest that waveguide-cavity coupling may be a useful component for building complex photonic waveguide networks within a photonic crystal.
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