Engineering Dispersion and Polarization of Light Using Moiré-Inspired Photonic Crystals

Abstract

Modern optical systems are increasingly expected to do more within less: to process, route, filter, and encode larger amounts of information within smaller footprints, with lower energy cost, less crosstalk, and greater functional density. Across applications ranging from communications and sensing to integrated and free-space photonics, the central challenge is no longer simply to realize an optical response, but to engineer sufficiently rich and controllable optical complexity within a compact platform. In practice, this means creating more usable channels, sharper and more selective resonances, and more programmable modal responses within the same physical and spectral budget. Over the past two decades, photonic crystals (PhCs) have emerged as one of the most powerful nanophotonic platforms for achieving such control at subwavelength scales. Because they support optical band structures composed of multiple eigen-resonant states, they naturally offer a rich set of controllable channels in frequency and momentum space, enabling precise engineering of optical dispersion, radiation, and polarization for compact implementations of filtering, modulation, signal conversion, and wavefront control. To further expand the design space and functional complexity of PhCs, moiré-inspired PhCs offer a new route by introducing an emergent superperiod beyond the underlying lattice periodicity. Enabled by geometric degrees of freedom absent in conventional single-period lattices, bilayer and superlattice moiré PhCs use relative twist, lattice mismatch, dual periodicities, and interlayer coupling to reshape optical eigenstates and fold more bands into the same spectral and momentum window, thereby enabling higher resonance density and richer control over optical dispersion and polarization. In this dissertation, I develop moiré-inspired PhCs as a framework for engineering both the dispersion and the polarization of light. I begin by realizing moiré photonic structures in twisted bilayer PhCs, establishing the theoretical basis for engineering optical band structures and experimentally uncovering moiré scattering, band reconfiguration, and intrinsic optical chirality phenomena. I then move beyond twisted bilayers to develop new moiré-inspired approaches, including programmable photonic superlattices and geometric operations inspired by moiré systems, showing that the essential mechanisms of moiré photonics can be generalized into broader design principles for multifunctional photonic crystals. Across these studies, moiré-inspired PhCs are shown to access richer bands, denser resonant states, and more structured polarization responses than are available in conventional single-period lattices. More broadly, this dissertation shows that moiré physics offers not only a route to twisted photonic structures, but also a transferable design principle for future reconfigurable, programmable, and topological photonic crystals.