Plasmonic Optical Metasurfaces for Passive and Active Wavefront Shaping

Metasurfaces, ultrathin surfaces engineered at the nanoscale with artificial nanostructures, have fundamentally revolutionized optical wavefront manipulation by providing superior and precise control over light properties, such as polarization, amplitude, and phase. This innovation has facilitated the development of miniaturized and highly performant photonic systems, driving significant advancements in energy, sensing, imaging, and computing through novel light-matter interactions, thereby showing promise in supplanting traditional bulky optics used for wavefront control. The advanced and refined micro- and nano-fabrication techniques render metasurfaces exceptionally well-suited for integration with a wide range of nanotechnology platforms, unlocking substantial potential for the creation of state-of-the-art optical devices. Building on the foundation of these passive metasurfaces characterized by well-defined optical responses set during fabrication, the integration of active control mechanisms promises to further revolutionize these structures, transforming them into versatile components for reconfigurable and adaptive optical networks and systems, and substantially enhancing their functionality and application potential. Furthermore, the pursuit of extremely fast responses among these dynamic control mechanisms enables real-time and flexible control of light, potentially improving the performance and adaptability of optical systems in applications such as high-speed communications, adaptive optics, and rapid sensing technologies.

In this thesis, I first review recent advancements in metasurface-based wavefront shaping, focusing on both passive and active methodologies and their applications in optical waveplates, beam steering, metalenses, as well as dynamic chirality and polarization control, providing an overview of the cutting-edge developmentsin this swiftly advancing field. Following this, I present the key theoretical concepts and analytical methods employed in this thesis, including the fundamental principles of polarization states and their mathematical representations, three common phase control techniques, the numerical simulation method, the detailed sample fabrication process, as well as the characterization setup. Then I present an account of passive wavefront shaping using gap-surface plasmon metasurfaces, detailing our research works on optical waveplates, beam steering, and metalenses. Lastly, transitioning from passive to active metasurfaces, I highlight our pioneering dynamic platform developed through the integration of metasurfaces with piezoelectric thin-film PZT microelectromechanical systems. Two research projects based on this platform are introduced in detail: dynamic linear polarizers and applications, as well as non-Hermitian metasurfaces for tunable topological phase transitions. In summary, this thesis centers on wavefront shaping through both passive and active approaches to develop ultra-thin and compact optical metasurface devices, laying a solid foundation for a diverse array of industrial applications.