Active Photonic Integrated Circuits Enabled by Reconfigurable Materials

Abstract

The increasing demand for high-speed, energy-efficient, and multifunctional photonic systems motivates the development of integrated platforms capable of dynamically controlling light at the chip scale. Photonic integrated circuits (PICs) provide a versatile framework for manipulating optical signals through tunable elements, enabling applications ranging from optical memory and signal processing to sensing and free-space light projection. Featuring compact footprints, low power consumption, and Complementary Metal-Oxide-Semiconductor (CMOS) compatibility, these platforms support scalable and reconfigurable operation across a variety of photonic functionalities. This work focuses on exploiting nanoscale light-matter interactions using phase-change materials (PCMs) and thermo-optical (TO) materials. PCMs offer reversible and nonvolatile control over light through refractive index changes upon material phase transformations. Their ability to scale down to nanometer dimensions enables seamless integration with silicon waveguides. Complementarily, materials with high TO coefficients enable fast, reversible, and continuous refractive index modulation without phase transitions. Together, these mechanisms provide a foundation for integrating material-level tunability into on-chip photonic devices, enabling multifunctional and reconfigurable optical circuits. The thesis first explores passive photonic devices that utilize PCMs for nanoscale optical control, laying the groundwork for subsequent active and reconfigurable architectures. Chapter 3 presents tunable devices based on Sb2Se3 for post-fabrication trimming and Bragg grating response control. Chapter 4 builds on this approach by integrating microheaters with Sb2Se3-loaded microring resonators (MRRs) for content-addressable memory (CAM) applications, enabling configurable, multilevel on-chip control. Motivated by the desire to expand functionality beyond Sb2Se3, Chapter 5 develops a comprehensive characterization library for emerging optical and phase-change materials, expanding the library of materials with tailored optical properties. The focus then shifts to application-oriented photonic systems. Chapter 6 explores photonic analog-to-digital conversion (ADC), leveraging high TO coefficient materials for all-optical and hybrid electrical-to-optical quantization. Finally, Chapter 7 presents a fully active silicon photonic platform that converts the output of an on-chip point source into a free-space collimated beam. By studying on-chip thermo-optic phase shifters and grating couplers, efficient coupling to free-space beams is demonstrated for LiDAR applications. By integrating reconfigurable materials with photonic architectures, this work bridges material-level tunability and system-level functionality, establishing a pathway toward scalable, multifunctional, and reconfigurable photonic circuits, and demonstrating the potential of PCMs and on-chip control for next-generation integrated photonics.