UC San Diego

Nanophotonic with tunability had attracted great interest in recent years due to its novel performance, extremely small footprint and low deployment difficulty, make it a promising plate in information technology, super resolution bio-imaging, photon emitting and optical sensing. Nonlinear optics, are the basic of many modern optical components in optical telecommunication systems, optical sensing, and material research. It also have broad application in optical frequency generation and conversion in continuous wave and ultrafast lasing system which facilitate the fundamental scientific research on the particle dynamics, photolithography system for nano device fabrication and optical machining. Topological photonics, as one of the most rapidly growing fields in nanophotonic, has been proved to have great potential to revolutionize many applications in nanophotonic platform stem from the fundamental symmetry of the universe. In this dissertation, we explore the basic interactions between photons on different structured photonic devices at different interaction strength and demonstrate how to manipulate light at nanoscale and realize photon emission at the same time.In the first section, we demonstrated ultrafast Kerr nonlinearity in metallic thin film. The optical nonlinear susceptibility is enhanced by orders of magnitude stem from the high carrier concentration in metallic system and resonant dipole momentum. We theoretically calculate the resonance wavelength using first principle calculations and experimentally realize sub-nm ultrathin silver on MgO substrate which possess third order Kerr nonlinearity at the ultra-violet wavelength, and the giant second order and third order optical nonlinearity in TiN coupled quantum well. In the second section, we focused on the novel phenomenon enabled by the embedded eigenstates. Our design features a two-dimensional bound state in the continuum (BIC) metasurface arrays with a sequential of extremely sharp resonances, and each of them is tuned to discrete frequency in different optical communication band. Compared with other spectroscopy setup, high-resolution one-shot spectroscopy measurement and switchable bandwidth can happen in this setup, which greatly benefits from the topological property of BIC and modulation depth of PCM. In the third section, we discussed the photonic analogue of spin Hall effect in the photonic crystal waveguide. We propose and design a reconfigurable on-chip topological photonic device using optical phase-changing material. The topological photonic structure utilizes the extra valley degree of freedom from inversion symmetry breaking in honeycomb lattice and realizes the transition from topologically trivial to topologically non-trivial. In addition to that, light can propagate at sharp corners and pseudo-spin photon coupling are simulated at the topological boundary. Compare with previous works related to utilizing the valley degree of freedom, they mainly focused on plasmonic system in microwave regime, non-tunable valley photonics at optical regime and all-optical topological edge frequency modulation. However, in our work, topological phase transition from topological trivial to topological non-trivial can happen by electrically changing the material phase of phase changing material (PCM) in the half of the unit cell, without altering the photonic crystal geometrical setup. The configuration and topological property of the interface state can be rearranged with the different electrical connection of heater beneath. In the last section, we systematically studied the multi-photon photoluminescence (MPPL) in ultrathin gold films with percolation effect induced localized surface plasma resonances (LSPRs). Because of the quantum sized effect, the rise of quantized energy levels provides momentum-match-free mechanisms for intersubband to d-band transition. Theoretical analysis including the first principal calculation in bulk and quantum gold film is conducted. The overall conversion efficiency is over 3 orders higher than bulk gold.