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Topological Inspirations in Photonic Devices

Abstract

Material topology is an exotic degree of freedom in the condensed matter physics. It was initially proposed to explain the electron transportation in ferroelectric materials in 1954, and eventually made its way to the 2016 Nobel Prize in Physics. In recent decades, researchers are dedicated to transplanting the concepts in the condensed matter to the optics and photonics realm. Nowadays, the field of topological photonics is thriving, which allows us to mimic the behaviors of the electrons using photons and discover phenomena exclusive to the Bosonic systems.

In this dissertation, I present my work to show how we can get inspirations from the electronic system, then design the photonic device with new functionalities. Chapter 1 is dedicated to the cornerstone of material topology: geometric phase. The geometric phase determines the topological invariant in a crystal, but we can also use this concept to engineer the phase front in the diffractive optics devices. I show the first-ever metasurface for ultra-violet wavelengths using the geometric phase. In Chapter 2, I discuss the one-dimensional topological insulator and how to realize it in an optical waveguide array. Besides, I reveal the relation between the one-dimensional model and the topological edge states in the two-dimensional nanoribbons. It deepens our understanding of topological behaviors and the Bloch theorem. Finally, in Chapter 3, I investigate the bound-state-in-continuum, which is a topological singularity in the photonic crystals. Then I show the photonic integrated circuits that utilize this concept and result in a versatile optical filter. All the devices proposed are made of silicon, which is a promising material choice in terms of fabrication and scalability.

In general, I introduce the essential concepts in topological photonics and explain the physical pictures to my best knowledge, in the hope of inspiring readers to explore this field and design novel photonic devices.

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