Event

 

Professor Kevin M. Daniels
Professor Avik Dutt
Professor Amitabh Varshney (Dean’s Representative)

 

Date/Time: Friday, March 28, 2025 at 1:00 PM

Title:  Reprogrammable Integrated Photonics: from Monolithic Phase Change Material Platforms to All-photonic Analog-to-Digital Converter

Abstract:
Photonic Integrated Circuits (PICs) are revolutionizing optical communication and computing by enabling compact, high-speed, and energy-efficient photonic functionalities. By integrating multiple optical components on a single chip, they reduce footprint, lower power consumption, and enhance data transmission rates. PICs are crucial for optical interconnects, high-speed signal processing, LiDAR, biomedical sensing, and quantum information processing. As demand for faster, more efficient photonic technologies grows, PICs address the limitations of traditional electronics, driving advancements in scalable and high-performance optical systems. However, achieving post-fabrication tunability and efficient all-optical signal processing remains a major challenge. Traditional PICs often suffer from static configurations and complex electronic-photonic integration for key functionalities such as reconfigurable switching and all-optical signal processing. This dissertation addresses these challenges through two key approaches: developing tunable phase change materials (PCMs)-based photonic platforms that enable dynamic control over optical properties for reconfigurable photonic circuits and realizing an all-photonic analog-to-digital converter (ADC) for high-speed all-optical signal conversion.

The first part of this dissertation demonstrates the first instance of amorphous Ge₂Sb₂Se₄Te (am-GSST) waveguides integrated on a silicon dioxide (SiO₂) insulator substrate. This platform allows for low-loss PICs in the telecommunication wavelengths with post-fabrication tuning through localized phase transitions. Moreover, this section investigates the different loss mechanisms, linear and nonlinear properties, and the thermo-optic coefficient of am-GSST to understand better the material properties and its potential for tunable photonic applications. Lastly, this section demonstrates post-fabrication tuning of devices using laser irradiation, thus achieving controlled refractive index modulation and enabling optical trimming.

The second part of this dissertation explores am-GSST waveguides integrated on an Indium Tin Oxide (ITO) substrate with a refractive index tuned to 1 (i.e., same as air) through epsilon-near-zero effects. The ITO underlayer plus an air cladding enables mode symmetrization, which is otherwise challenging to achieve in PICs and particularly useful for polarization-insensitive PICs and reconfigurable photonic crystal applications. This section details the material deposition, optical characterization, and device simulations, highlighting how GSST-on-ITO can enable dynamic photonic switching with improved control over optical properties. Furthermore, this section investigates post-fabrication tuning using an electron beam to achieve higher-resolution modifications, offering a finer level of control for device optimization.

Finally, this dissertation presents novel all-photonic analog-to-digital converters (ADCs) on a Silicon-on-Insulator (SOI) platform. The proposed design leverages existing Complementary Metal-Oxide Semiconductor (CMOS) technology to achieve high-speed optical signal conversion, crucial for next-generation optical computing and communication systems. Compared to conventional electronic ADCs, this design performs the conversion entirely in the optical domain, reducing power consumption, increasing speed, and eliminating the complexity associated with electronic-to-optical conversions. The study explores resonator designs, material choices, and fabrication strategies, demonstrating a functional ADC prototype with enhanced precision and efficiency.

This work advances reconfigurable integrated photonics and paves the way for scalable optical computing solutions by integrating tunable material platforms and optical signal processing approaches. Its contributions provide a foundation for future photonic devices that combine high-speed processing, energy efficiency, and dynamic reconfigurability, making them well-suited for next-generation communication and computational systems.