Date of Award
Doctor of Philosophy (PhD)
Electrical & Systems Engineering
Recent emergence of photonic topological insulators paves a route to disorder-immune light confinement and propagation for potential applications in information processing, communication, and computing. In parallel, non-Hermitian photonics based on parity-time symmetry expands the design principles in optics to the entire complex domain of materials permittivity, providing a versatile toolbox to enable novel photonic functionality. Despite being fundamentally different, photonic topological structures integrated with optical non-Hermiticity exhibit unusual features that leverage robust light control with extraordinary degrees of freedom. This dissertation explores the synergy of topological photonics and non-Hermitian physics from the demonstrations of phenomena to the prototype of devices. We start with a complex-indexed variant of the classical Su-Schrieffer-Heeger model respecting the charge-conjugation symmetry, where non-Hermitian modulation of gain and loss enforces robust single-mode lasing with the topological zero mode selectively enhanced in a hybrid microlaser array. Beyond the selection of the topological mode, we show the creation of a topological state in the bulk of a topologically uniform photonic lattice via strategic patterning of optical non-Hermiticity, even in the absence of a topological interface. Such novel non-Hermitian control enables arbitrary topological light steering in reconfigurable non-Hermitian junctions, where chiral topological states can propagate at an interface of the gain and loss domains dynamically configured by pumping patterns. Our strategy has solved the long-standing problem of redefining the topological domain wall without altering the topological order of the structure, which would be otherwise static. The ultra-flexible and robust nature of the non-Hermitian topological light control opens the avenue to highly integrated multifunctional photonic circuitry for high-density data processing. Additionally, we exploit the highly asymmetric light transport feature associated with the unique topology in the vicinity of the non-Hermitian degeneracy, namely an exceptional point, facilitating sensitive thermal imaging and power-efficient interferometric optical modulation on-chip.
Zhao, Han, "Non-Hermitian Topological Photonics: From Concepts To Applications" (2019). Publicly Accessible Penn Dissertations. 3609.