NANOPHOTONIC DEVICES BASED ON LOW-DIMENSIONAL QUANTUM EMITTERS

Abstract

Development of advanced nanophotonic devices is currently in rapid growth and revolutionizing the whole fields of integrated optics and photonics. Devices such as nanoscale LEDs & lasers, waveguide couplers and modulators are essential components in applications ranging from light sources to optical circuits and quantum information processing. The optical characteristics of these nanostructures could be engineered to realize strong confinement of optical modes within their low dimensions, which leads to strong light-matter interactions at desirable wavelength range when coupling to high-efficient, low-dimensional quantum emitters such as colloidal nanoplatelets, perovskite nanocrystals and transition metal dichalcogenide monolayers with unique optical properties. These light-matter coupled systems could realize various kinds of nanophotonic devices with high efficiency and nonlinearity in development of more complex optical circuits and quantum networks.

In this thesis, I present my work first on experimental demonstration of spontaneous emission intensity and rate enhancement of both colloidal cadmium selenide/cadmium sulfide core/shell nanoplatelet and cesium halide bromide perovskite nanocrystals in Purcell regime by using silicon nitride photonic crystal nanobeam cavities. The one-dimensional high-quality cavity confines the emission in a small mode volume with high radiative decay mode density, leading to a clear increase in their photoluminescence efficiencies. We next present realization of a continuous-wave nanolaser based on this coupled system operating at room temperature. The high coupling efficiency results in a record-low pump threshold at 1 μW. This result shows that colloidal nanocrystals are suitable for compact and efficient opto-electronic devices based on solution-processable materials.

Besides light generation, furthermore for transmission and processing, we have also realized chiral light-matter interactions in a glide-plane photonic crystal waveguide using spin-valley states in transition metal dichalcogenides tungsten diselenide monolayers. The combination between the unique spin-valley coupling effect of this monolayer material and the chirality of the waveguide leads to a control over the propagation direction based on the helicity of input signal. This system enables on-chip directional control of light and could provide new ways for controlling spin and valley degrees of freedom in a scalable photonic platform.