Advancing Integrated Photonic Circuits: Design, Fabrication, and Characterization of Key Photonic Components

Abstract

The aim of this work is to advance the field of Photonic Integrated Circuits (PICs) by designing, fabricating, and characterizing various photonic devices. These devices or functions include an on-chip laser, a fiber-to-chip coupler, an optical resonator, and optical coupling between III-V and Ta2O5 waveguides to enhance photonic integration further. One of the main contributions of this research is the development of an on-chip laser source that employs a Multi-Mode Interference Reflector (MMIR) based on InAs Quantum Dot (QD) lasers. MMIRs have been shown to have advantages over other on-chip mirrors, such as Distributed Bragg Reflectors (DBR), Distributed-Feedback lasers (DFB), and loop mirrors because it is compact and versatile. The results indicate that MMIR lasers outperform traditional Fabry-Perot ridge waveguide (FP-RWG) lasers with two cleaved-facets, demonstrating lower threshold currents, reduced temperature dependency, and higher optical slope efficiency. This makes MMIRs promising candidates for on-chip laser reflectors in integrated photonics. The study also focuses on a low-loss III-V waveguide with a thin high-index AlOx layer to enhance waveguide confinement. It addresses substrate waveguide loss and leads to improved coupling efficiency of GaAs-based Surface Grating Couplers (SGC). Simulation results reveal a significant enhancement in coupling efficiency for a grating with oxidized underlayer compared to unoxidized grating design. The compatibility of high aluminium-containing layers with laser diode epi-layer structures is demonstrated, suggesting the potential of this approach for active-passive integrated platforms. The design and optimization of low-loss Ta2O5 waveguides, which are important for high-quality integrated photonic devices are described. These are expected to be useful to provide non-linear properties although that is not tested within this work, a ring resonator based on Ta2O5 waveguides is designed. The task of connecting and integrating III-V and Ta2O5 waveguides, presenting a hybrid platform with potential applications in compact, energy-efficient, and high-performance photonic circuits, is explored Overall, this research contributes to the evolution of PICs, offering innovative solutions for advanced photonic circuit development.