Realization of an acoustic third-order topological insulator

The recent discovery of higher-order topological insulators (TIs) has opened new possibilities in the search for novel topological materials and metamaterials. Second-order TIs have been implemented in two-dimensional (2D) systems exhibiting topological 'corner states', as well as three-dimensional (3D) systems having one-dimensional (1D) topological 'hinge states'. Third-order TIs, which have topological states three dimensions lower than the bulk (which must thus be 3D or higher), have not yet been reported. Here, we describe the realization of a third-order TI in an anisotropic diamond-lattice acoustic metamaterial. The bulk acoustic bandstructure has nontrivial topology characterized by quantized Wannier centers. By direct acoustic measurement, we observe corner states at two corners of a rhombohedron-like structure, as predicted by the quantized Wannier centers. This work extends topological corner states from 2D to 3D, and may find applications in novel acoustic devices

Novel topological phases in gyromagnetic photonic crystals

Topological phases have revolutionized both condensed matter and classical wave physics, and photonic systems have proven to be versatile platforms for exploring exotic topological phenomena. This thesis investigates novel topological phases in gyromagnetic photonic crystals, including an unpaired Dirac point, antichiral edge states, three-dimensional Chern insulators, amorphous topological insulators, and topological Anderson insulators. In Chapter 1, a brief history and classification of various topological phases in condensed matter and photonic systems are reviewed, and the topological invariants used in the subsequent chapters are introduced. Chapter 2 explores the photonic realization of Haldane models and the observation of an unpaired photonic Dirac point. Chapter 3 investigates the photonic realization of modified Haldane model and the observation of antichiral edge states. In Chapter 4, three-dimensional Chern insulators are studied, and linked and unlinked Fermi loop surface states are discovered. Chapter 5 examines disorder-induced topological phases in gyromagnetic photonic crystals, resulting in the experimental construction of an amorphous topological insulator and a topological Anderson insulator. Finally, Chapter 6 provides concluding remarks and proposes future research directions. Overall, this thesis contributes to the growing body of knowledge on topological phases in photonic systems and provides a platform for the development of new technologies based on these exotic phenomena.Doctor of Philosoph

Two-Photon Polymerization Enabled Multi-Layer Liquid Crystal Phase Modulator

The performance of liquid crystal (LC) spatial light modulators depends critically on the amount of cumulative phase change. However, for regular phase modulators, a large phase change comes with a slow time response penalty. A multi-layer liquid crystal (LC) spatial light modulator offers a large phase change while keeping fast response time due to the decoupling between phase change and time response through engineered sub-micron scaffold. Here, we demonstrate specially designed 2- and 3-layer LC cells which can achieve 4 times and 7 times faster response time than that of conventional single-layer LC phase modulator of equivalent thickness, respectively. A versatile two-photon laser lithography is employed for LC cell scaffolding to accurately verify theoretical predictions with experimental measurements