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Resonant scattering from three-dimensional optical microcavities formed in two-dimensional waveguide-based photonic crystals Cheung, Iva Wai-Yun


Reflectivity properties of indium phosphide-(InP-)based two dimensional (2D) photonic crystals and photonic crystal microcavities were studied via optical experimentation and numerical simulations. Planar InP waveguides textured with a hexagonal array of air holes were studied with a specular white-light reflectivity apparatus. Their reflectivity as a function of wavenumber. as measured at different incident angles with an FTIR spectrometer, was compared to the results of computer simulations of the structure, based on a Green's function model. The simulation fits were used to determine salient fabrication parameters of the waveguide structures, including the filling fraction of the texturing, as well as the configuration of the layered structure of the waveguide and its substrate. The reflectivity properties of InP-based photonic crystal defect structures, which, in principle, serve as high-finesse (high Q-value) resonant microcavities. were also probed using both localized (2-μm spot size) 100-fs pulses from an optical parametric oscillator (tunable from 1.44 μm to 1.58 μm) and a broadband white light source. These reflectivity spectra revealed no evidence of modes in the microcavities. Numerical simulations were performed to study the extent to which the Q values and the field distributions of the defect states are affected by known fabrication imperfections; such as random variations in radii of the air holes in the microcavity arrays, as well as the slanting of hole sidewalks. The simulations were also used to mimic the microreflectivity experiment in order to determine the effect of the relative position of an incident Gaussian beam on the reflectivity properties of ideal photonic crystal defect cavities. The implications and insights arising from this work point to numerous recommendations for future work. These include a sample design comprising both a uniform photonic crystal region as well as a region of several photonic crystal defect microcavities; allowing for better characterization of fabrication parameters; modifications to the microreflectivity apparatus and experimental design that would likely yield better resolution of experimentally measured spectral features from resonant modes; and the controlled exploitation of symmetry-breaking to reduce modal volume for potential applications in cavity quantum electrodynamics.

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