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March 3 at 1:30 pm, AE108 Paul Allen

March 3 at 1:30 pm, AE108 Paul Allen
Dr. Tobias Kippenberg Ultra-high-Q Optical Microcavities Optical micro-cavities confine light within dielectric volumes and are important in a variety of fields such as cavity Quantum Electrodynamics (cQED), photonics, bio-chemical sensing and nonlinear optics. The optical trajectories occur near the interface of the dielectric cavity volume making them highly sensitive to the interface quality. With a nearly atomic scale surface roughness, surface-tension-induced microcavities such as liquid microdroplets or silica microspheres are superior to all other dielectric microresonators (e.g. photonic crystal defect cavities, micro-posts or microdisks resonators) when their photon lifetime or the equivalent quality factor (Q) is compared. In this seminar I will present recent advances in demonstrating an ultra-high-Q microcavity on a silicon chip. The “whispering gallery” modes (WGM) of these microcavities can be accessed using tapered optical fibers, which allow highly efficient coupling both to and from the WGM. The resulting high field intensity within these structures allows accessing the regime where nonlinear optical processes can be observed. In particular, stimulated Raman scattering, optical parametric oscillation and radiation pressure driven mechanical oscillations are discussed. I will conclude the presentation with an outlook on rare-earth and silicon nanocrystal doping of toroid microcavities.

Dr. Tobias Kippenberg

Ultra-high-Q Optical Microcavities

Optical micro-cavities confine light within dielectric volumes and are important in a variety of fields such as cavity Quantum Electrodynamics (cQED), photonics, bio-chemical sensing and nonlinear optics. The optical trajectories occur near the interface of the dielectric cavity volume making them highly sensitive to the interface quality. With a nearly atomic scale surface roughness, surface-tension-induced microcavities such as liquid microdroplets or silica microspheres are superior to all other dielectric microresonators (e.g. photonic crystal defect cavities, micro-posts or microdisks resonators) when their photon lifetime or the equivalent quality factor (Q) is compared. In this seminar I will present recent advances in demonstrating an ultra-high-Q microcavity on a silicon chip. The “whispering gallery” modes (WGM) of these microcavities can be accessed using tapered optical fibers, which allow highly efficient coupling both to and from the WGM. The resulting high field intensity within these structures allows accessing the regime where nonlinear optical processes can be observed. In particular, stimulated Raman scattering, optical parametric oscillation and radiation pressure driven mechanical oscillations are discussed. I will conclude the presentation with an outlook on rare-earth and silicon nanocrystal doping of toroid microcavities.

March 3 at 3:00 pm, 155 Mueller

March 3 at 3:00 pm, 155 Mueller
Dr. Ana Claudia Arias Conjugated Polymer Phase Separation and Three-Dimensional Thin-Film Structures for Flexible Electronics The performance of polymer based electronic devices has shown great improvements over the past years. Polymer light emitting diodes (LEDs) show high luminescence efficiency and thin film transistors (TFTs) show field effect mobilities of 0.1 cm2/Vs. Polymeric materials are easily processed from solution providing the potential of a vacuum free fabrication process. The work presented here focuses on the fabrication and characterization of electronic devices based on phase-separated blends of conjugated polymers. A systematic study on device structure is presented, including the use of polymeric electrodes and the influence of the microstructure of thin films on device performance. Conventional fluorescence, fluorescence scanning near-field optical microscopy and atomic force microscopy have been combined to relate film morphology with photovoltaic and photoluminescence efficiencies as a function of surface treatment, concentration, and processing conditions. The optimized self-organization process, in conjunction with phase compositions, has resulted in the demonstration of the highest photovoltaic efficiencies reported for the polyfluorene materials. Polymer blends were also used to improve the environmental stability of two polythiophene derivatives often used on the fabrication of thin film transistors. Vertical segregation of blend components was induced through specially developed solution-coating processes to produce a self-encapsulated structure. Bottom gate TFT were fabricated with blends of semiconducting and insulating polymers at different concentrations and mobilities as high as 0.05 cm2/Vs were found. TFT devices fabricated in air show stable sub-threshold voltages up to 21 days in air. This self-encapsulating process is compatible with inkjet printing techniques, flexible substrates and significantly improves the integration of TFT backplanes with display media.

Dr. Ana Claudia Arias

Conjugated Polymer Phase Separation and Three-Dimensional Thin-Film Structures for Flexible Electronics

The performance of polymer based electronic devices has shown great improvements over the past years. Polymer light emitting diodes (LEDs) show high luminescence efficiency and thin film transistors (TFTs) show field effect mobilities of 0.1 cm2/Vs. Polymeric materials are easily processed from solution providing the potential of a vacuum free fabrication process. The work presented here focuses on the fabrication and characterization of electronic devices based on phase-separated blends of conjugated polymers. A systematic study on device structure is presented, including the use of polymeric electrodes and the influence of the microstructure of thin films on device performance. Conventional fluorescence, fluorescence scanning near-field optical microscopy and atomic force microscopy have been combined to relate film morphology with photovoltaic and photoluminescence efficiencies as a function of surface treatment, concentration, and processing conditions. The optimized self-organization process, in conjunction with phase compositions, has resulted in the demonstration of the highest photovoltaic efficiencies reported for the polyfluorene materials. Polymer blends were also used to improve the environmental stability of two polythiophene derivatives often used on the fabrication of thin film transistors. Vertical segregation of blend components was induced through specially developed solution-coating processes to produce a self-encapsulated structure. Bottom gate TFT were fabricated with blends of semiconducting and insulating polymers at different concentrations and mobilities as high as 0.05 cm2/Vs were found. TFT devices fabricated in air show stable sub-threshold voltages up to 21 days in air. This self-encapsulating process is compatible with inkjet printing techniques, flexible substrates and significantly improves the integration of TFT backplanes with display media.