Optical Material Characterization Using Microdisk Cavities

Citation

Michael, Christopher Paul (2009) Optical Material Characterization Using Microdisk Cavities. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/G2P2-DY72. https://resolver.caltech.edu/CaltechETD:etd-05282009-103510

Abstract

Since Jack Kilby recorded his "Monolithic Idea" for integrated circuits in 1958, microelectronics companies have invested billions of dollars in developing the silicon material system to increase performance and reduce cost. For decades, the industry has made Moore’s Law, concerning cost and transistor density, a self-fulfilling prophecy by integrating technical and material requirements vertically down their supply chains and horizontally across competitors in the market. At recent technology nodes, the unacceptable scaling behavior of copper interconnects has become a major design constraint by increasing latency and power consumption—more than 50% of the power consumed by high speed processors is dissipated by intrachip communications. Optical networks at the chip scale are a potential low-power high-bandwidth replacement for conventional global interconnects, but the lack of efficient on-chip optical sources has remained an outstanding problem despite significant advances in silicon optoelectronics. Many material systems are being researched, but there is no ideal candidate even though the established infrastructure strongly favors a CMOS-compatible solution.

This thesis focuses on assessing the optical properties of materials using microdisk cavities with the intention to advance processing techniques and materials relevant to silicon photonics. Low-loss microdisk resonators are chosen because of their simplicity and long optical path lengths. A localized photonic probe is developed and characterized that employs a tapered optical-fiber waveguide, and it is utilized in practical demonstrations to test tightly arranged devices and to help prototype new fabrication methods. A case study in Al_xGa_1−xAs illustrates how the optical scattering and absorption losses can be obtained from the cavity-waveguide transmission. Finally, single-crystal Er₂O₃ epitaxially grown on silicon is analyzed in detail as a potential CMOS-compatable gain medium due to its high Er³⁺ density and the control offered by the precise epitaxy. The growth and fabrication methods are discussed. Spectral measurements at cryogenic and room temperatures show negligible background losses and resonant Er³⁺ absorption strong enough to produce cavity-polaritons that persist to above 361 K. Cooperative relaxation and upconversion limit the optical performance in the telecommunications bands by transferring the excitations to quenching sites or by further exciting the ions up to visible transitions. Future prospects and alternative applications for Er₂O₃ and other epitaxial rare-earth oxides are also considered.

Thesis Files