Hybrid Silicon-Vanadium Dioxide Photonic Devices for Optical Modulation
Miller, Kevin Joseph
The integration of optical components with silicon complementary metal–oxide–semiconductor (CMOS) technology may lead to the increase in information carrying capacity and reduction in power consumption necessary to continue the scaling the performance of microelectronic devices historically predicted by Moore’s law. Silicon photonic structures that can guide light are well suited for such integration. However, the indirect band gap and relatively weak electro-optic responses of silicon provide challenges for chip-based lasing and modulation, two key functions necessary for an integrated photonic platform. For this reason, incorporation of materials possessing superior optical properties to silicon is actively being explored on silicon photonic platforms. The focus of this dissertation is to advance the scientific understanding and performance metrics of silicon-based optical modulators through hybridization with the actively tunable optical phase change material, vanadium dioxide (VO2). First, integration of VO2 onto a silicon ring resonator photonic platform and the subsequent electro-optic modulation of this hybrid structure are demonstrated. A tradeoff between extinction ratio and device response times is found when different VO2 patch lengths are utilized. Second, a platform in which VO2 is embedded within a silicon waveguide is realized. This embedded geometry increases interaction between the guided mode and VO2 in comparison to a geometry in which VO2 is placed on top of the silicon waveguide. Theoretical and experimental characterization through finite-difference time-domain analysis and temperature-dependent transmission measurements, respectively, demonstrates the tradeoff between extinction ratio and insertion loss as a function of VO2 patch length. Finally, the potential implementation of the hybrid silicon/VO2 embedded waveguide as an all-optical modulator with in-plane excitation is considered and its expected performance is compared to state-of-the-art all-optical modulators.