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Karen Downey

Ph.D. 2007:"Combinatorial Preparation and Characterization of Thin-film Amplifier Oxides"

Optical integration is an attractive approach to reducing the cost of optical functions in data networks, while also offering the promise of increasing performance and decreasing size. The integration of materials providing necessary functionality (i.e., on-chip Karen Downeyamplification) presents a challenge, which our research addresses. We have used a combinatorial composition-spread approach to identify and evaluate possible amplifier materials rapidly. Using a combination of off-axis and on-axis reactive sputtering, we are able to explore five-component systems. This high-throughput synthesis technique is complemented by rapid optical characterization of the resulting thin films.

Compositionally dependent properties such as the lifetime and amplitude of Er 3+ fluorescence are investigated using a 980 nm pump beam and collection with a time-resolved detector. Promising materials are identified by a figure of merit produced by multiplying the fluorescence lifetime with its amplitude. The composition-spread technique allows us to determine precisely the maximum Er concentration that can be incorporated before Er-Er interactions quench the transition; we can simultaneously determine the optimum levels of substitutions in the SiO 2 matrix to increase the radiative transition probability and/or decrease Er-Er interactions. We have identified compositions in the Er-Bi-Al-Si-O system that perform significantly better than any composition in the benchmark Er-Ln-Al-Si-O system. We will report on the systematic dependence of fluorescence on composition in a range of inorganic oxide systems, with an eye toward identifying the most promising candidates for further development.