Date of Award

Fall 2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical Engineering (ENAS)

First Advisor

Tang, Hong

Abstract

Integrated silicon photonics, as a post-Moore technology, has been intensively studied and proven to be particularly advantageous due to its compatibility to the CMOS processing technology and feasibility of dense integration. The rapid progress of various low-loss photonic platforms has also opened up new possibilities of nonlinear sciences at nanoscale due to high optical confinement and enhanced light-matter interactions assisted by the high-Q microcavities. However, as a centrosymmetric material, silicon lacks intrinsic second-order (χ(2)) nonlinearity, which fundamentally limits its performance in terms of electro-optic modulation, second harmonic generation, parametric down conversion process, etc. Possessing significant χ(2)&χ(3) nonlinearities, broad transparency window from 350 nm to 4.5 μm, and flexibility in ferroelectric domain engineering, lithium niobate is dubbed by many as ”silicon of photonics” and has recently risen to the forefront of chip-scale nonlinear and quantum photonics research since its demonstration as a ultralow-loss photonics platform. This thesis presents my work on the systematic developments of several state-of-the-art χ(2) nonlinear photonic devices as well as chip-based optical frequency comb generation, assisted by the meticulous device design and advanced nanofabrication of ultralow-loss photonic structures. By first achieving a high-Q, periodically poled lithium niobate microring resonator (PPLNMR), we demonstrate the world-record-high second harmonic generation efficiency at 1550 nm via quasi-phase-matching, which finds important application in precision frequency metrology and quantum information processing. As a reversed process, optical parametric oscillation based on PPLNMR is subsequently achieved and proven to have the lowest threshold among all integrated platforms and broadband wavelength tunability over 200 nm. It opens new opportunities for chip-based tunable classical and quantum light sources and provides a potential platform for realizing photonic neural net- works. Furthermore, by investigating the quasi-phase matching condition and pumping the PPLNMR device at telecom wavelength with high power, multi-color microcombs into ultraviolet wavelength regime were first observed due to the cascaded χ(2) nonlinearities and hold great promises for on-chip ultraviolet-visible spectroscopic sensing and atom-photonic interfaces. Lastly, ultrabroadband supercontinuum generation from the dispersion-engineered nanowaveguides using femtosecond pump laser at 1560 nm would be presented.

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