Augmented Low Index Guiding and Hybrid Plasmonic Waveguides: Properties and Applications for On-chip Polarization Management

In recent years, photonic integrated circuits (PICs) have attracted much interest. To achieve a compact size, most recent devices are based on the high index contrast waveguides; however, this high index contrast also introduces large polarization sensitivity. Consequently, there is a need for compact and broadband polarization manipulation elements to handle the polarization state of the optical signal on the chip. In this dissertation, a new guiding structure, dubbed augmented low index guiding (ALIG) waveguide, is introduced to design, fabricate, and characterize polarization manipulation devices. The purely dielectric nature of the structure allows the optical waves to propagate with low losses. In the ALIG structure, the transverse magnetic (TM) mode is mostly confined in the low-index silicon nitride region, while the transverse electric (TE) mode is confined in the high index silicon layer. Because the two orthogonal modes are confined in two separate layers, their properties can be controlled independently. A compact polarization beam splitter and a polarization rotator based on the ALIG waveguide have been proposed, fabricated, and characterized. The good performance of these devices demonstrates the usefulness of the ALIG platform. Another waveguide, which confines the two orthogonal TE and TM modes in separate layers, is the hybrid plasmonic waveguide (HPWG). While the HPWG, as a plasmonic waveguide, has a higher loss than the dielectric waveguide, here an integrated ultra-low loss TE-pass polarizer based on a directional coupler is designed, fabricated, and characterized. The device is compact and offers excellent polarization extinction ratio. I have also compared the integration density and losses associated with several typical waveguides. Results show that for the same propagation losses, the HPWG can achieve higher packing density than other plasmonic waveguides.Ph.D