Pattern Generation and Control in Semiconductor Quantum Well Microcavities

Abstract

Many physical phenomena have been observed in semiconductor quantum well microcavities, such as polariton Bose-Einstein condensation, pattern formation, optical spin Hall effect (OSHE), solitons and more. An optically pumped cavity system has the advantage of strong nonlinear couplings between polaritons, and easy detection with photons emitted from the cavity. This thesis presents the theoretical studies of far-field pattern formations, transfer matrix calculations, optical control of the OSHE, and generation of orbital angular momentum (OAM) in optically pumped single- and double-cavities, and comparison with experimental outcomes. This work is a collaboration between theoretical groups at the University of Arizona (USA), Chinese University of Hong Kong (Hong Kong), University of Parderborn (Germany), and an experimental group at CNRS (France). Far-field transverse patterns originates from the nonlinear coupling of polaritons. Patterns, such as 2-spot and hexagon, are observed in optically pumped semiconductor quantum well microcavities when the pumping intensity is above the modulation instability threshold. The first part of this work studies the generation of far-field patterns in an optically pumped semiconductor double quantum well microcavities using a microscopic model of exciton and cavity photon fields, and introduce a simple control mechanism utilizing the light-house effect to control the orientation of 2-spot patterns. Transfer matrix calculations are performed to provide the connection between the microscopic model and the experimental cavity. This work aims to provide simple and robust control mechanisms for future optical communication devices. The second part of this work shows the formation and control of the OSHE in an optically pumped double-cavity. The OSHE is a linear optical effect of exciton polaritons in semiconductor microcavities. It originates from the polaritonic spin-orbit coupling, and can lead to observable spin/polarization textures in the near and far field under appropriate excitation conditions. An alternative description is based on a pseudo-spin model. The formation of the OSHE texture can be described by an effective magnetic field generated by the splitting of the transverse-magnetic and transverse-electric (TE-TM) polariton modes. Here we show theoretically that the orientation of the pseudo-spin texture can be controlled all-optically, which matches the experimental observation. We establish the relation between the incident light intensity and the degree of rotation of the far-field pattern using both the simplified pseudo-spin model and the double-cavity spinor-polariton equations. This scheme provides a simple and robust control mechanism for future spinoptronic devices utilizing OSHE. Potential applications of the orbital angular momentum (OAM) of light range from the next generation of optical communication systems to optical imaging and optical manipulation of particles. In the third part of this work we propose a micron-sized semiconductor source, based on a polaritonic quantum fluid in a single-cavity, that emits light with predefined OAM pairs. We show how modulational instabilities can be controlled and harnessed for the spontaneous formation of OAM pairs not present in the pump source. Once created, the OAM states exhibit exotic flow patterns in the quantum fluid, characterized by generation-annihilation pairs.