Optically-Controlled Waveguide Architectures for Advanced Tunable and Reconfigurable THz Circuits

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This project will investigate and develop a simple and powerful approach for efficiently generating advanced tunable and reconfigurable terahertz (THz) components based on novel waveguide architectures. These advancements will provide the building blocks needed to implement reconfigurable and high-performance sensing and communication systems that will provide much larger bandwidths than current microwave and millimeter-wave systems. This is an important technological area with a wide range of applications that will generate significant benefit to the society. High-performance variable THz modulators and attenuators based on rectangular waveguide configuration can be applied to radio astronomy, scientific instrumentation, and metrology. Tunable THz filters using programmable electromagnetic bandgap structures will enable spectroscopic sensing and imaging for enhancing defense and security screening (e.g., substance identification and detection), chemical and biological sensing, and disease or cancer diagnostics. More advanced reconfigurable THz circuits generated using photo-induced substrate-integrated waveguides will find applications in adaptive ultra-high-speed wireless communications. By using the proposed techniques, virtual circuit patterns that can be dynamically reconfigured will be implemented without complex circuit fabrication and device integration processes, leading to tunable and reconfigurable THz circuits that could not be realized using conventional approaches. The project also provides significant educational opportunities for students. The graduate students in this program will be exposed to the full scope of semiconductor physics, electromagnetic wave propagation, microwave engineering, advanced THz system design and testing process, from single device to the circuit/component/system level. Undergraduate students will be involved through summer and honors thesis research. The PIs will advise and mentor students from underrepresented groups. The objective of this project is to explore three optically-controlled waveguide architectures including 1) optically-controlled rectangular waveguide modulator, 2) photo-induced electromagnetic bandgap structure, and 3) photo-induced substrate-integrated waveguide. The interaction between the propagating THz mode in the waveguide or transmission line sections and the photo-induced patterns (formed by spatially-modulated optical generation of electron-hole pairs) on the semiconductor substrate allows dynamically tunable and reconfigurable functions with high performance to be realized efficiently. The tunability and reconfigurability is realized by illuminating virtual circuit patterns on mesa- or pillar-array structures using a digital micromirror device chip without the use of pre-patterned circuits and devices. The mesa- or pillar-array structures employed will significantly improve the performance including higher conductivity, higher spatial resolution, and higher control speed, making it possible to dynamically generate reconfigurable THz components. The three proposed architectures represent increasing levels of tunability and reconfigurability. In particular, the photo-induced substrate-integrated waveguide architecture could potentially provide nearly unlimited possibilities for realizing real-time programmable passive THz components with multiple functionalities. The project will involve semiconductor physics, transmission line theories, THz science and technology, high frequency testing and characterization to implement and demonstrate the proposed novel approach and three waveguide architectures. If successful, the project will greatly advance the knowledge to demonstrate tunable/reconfigurable waveguide-based passive components and potentially produce a paradigm shift on how tunable and reconfigurable THz circuits will be realized in future THz systems.