Title:  A Hybrid Platform for Wideband Reconfigurable Nonlinear Metamaterials

Committee:

Dr. Ali Adibi, ECE, Chair, Advisor

Dr. Benjamin Klein, ECE

Dr. Stephen Ralph, ECE

Dr. Hayk Harutyunyan, Emory Physics

Dr. Phillip First, Physics

Abstract: Optical frequency conversion processes, such as second- and third-harmonic generations, are commonly realized in nonlinear optics, offering application opportunities in photonics, chemistry, material science, and biosensing. Limited by intrinsically weak nonlinear responses of bulk materials, complex phase-matching techniques are typically required to realize significant nonlinear frequency conversions. Frequency preserving nonlinear processes, such as the optical Kerr effect, have potential for computing applications, due to efficient optical-intensity-dependent operations. Metamaterials and metasurfaces of artificially engineered and properly ordered building block arrays have been introduced to manipulate linear and nonlinear light-matter interactions at the subwavelength scale. I leverage high-refractive-index phase-change materials (PCMs) germanium antimony telluride (GST) and antimony sulfide (Sb2S3) that inherently exhibit strongly active tunable large optical nonlinearities to enhance the tunability of nonlinear metamaterials and metasurfaces in this thesis. I also demonstrate enhanced optical nonlinearities in passive high-index silicon (Si)-based metasurfaces that have various mode engineering opportunities and are easy to fabricate with mature techniques. The objective of research in this thesis is to demonstrate a hybrid platform for wideband reconfigurable nonlinear photonic metamaterials. The platform is composed of hybridized reconfigurable PCMs GST and Sb2S3 as well as static Si nano-building blocks. In the PCM-based research part, I demonstrate wideband-tunable third-harmonic generation (THG) devices with subwavelength features using multiple crystallinity states of GST. I also demonstrate efficient fixed-band second-harmonic generation and THG switches with metamaterials based on and tuned by GST, respectively. Additionally, I numerically demonstrate all-Sb2S3 linear and THG metasurfaces for tunable focusing. These structures are of interest for on-chip nonlinear optical imaging, microscopy, and communication applications. The Si-based research part is focused on the use of high-quality-factor bound states in the continuum resonance phenomena and a deep learning technique to accelerate designing efficient nonlinear all-Si metasurfaces, which have potentials for addressing the existing challenges in nonlinear optical computing.