The Spatial Optical Solitons Properties In Electromagnetically Induced Transparency Media Of Semiconductor Quantum Dots

Spatial optical solitons, which are localized optical beams, form in optical mediawhen the refractive nonlinearity effect compensates for the beam diffraction effect.However, in passive media (for example, optical fibers), the generation of theconventional spatial optical solitons required high-powered lasers but the nonlineareffect is extremely weak. As a result, spatial optical solitons is hardly generated underthe condition of a weak excitation. Fortunately, electromagnetically inducedtransparency (EIT) was found to lead to great enhancement in nonlinear effects evenunder weak driving optical pulsed field. EIT, which is a quantum interference effectsamong the transitions of atomic levels induced by laser in the interaction process oflaser and atomic system, can render an otherwise opaque medium transparent to thelight field. It is also possible to realize EIT phenomenon in semiconductor quantumdots. This is because the quantum dot possesses some properties which are similar tothose of atomic system, such as discrete energy levels and controllable coherentquantum evolution. At the same time, such a system also has the inherent advantagessuch as large electric dipole moments of the transitions, as well as easily operatingand integrating. Consequently, it is of interest to extend the quantum coherent andinterference effects from atomic system to semiconductor nanostructures, not only forcomprehending of the nature of quantum coherence and interference effects insemiconductor nanostructures, also for the possible realization of optical devicesbased on such coherent and interference properties. The thesis is divided into fourchapters, which is organized as follows:In the first chapter, we introduce the elementary knowledge, concept and theoryof EIT. In particular, based on the EIT effects, we spotlight the work of the theenhanced Kerr nonlinearity. Subsequently, we introduce some background of researchof EIT and spatial optical solitons. Finally, we present the methods of our study andgive a briefly summary of our work.As a matter of fact, the exciton-biexciton coherence plays a major role in thesingle quantum dot. In chapter two, we analytically study the linear absorption andnonlinear propagation properties of the probe and signal field in a semiconductorquantum dot. It is found that, in the linear case, the system takes placeelectromagnetically induced transparency phenomenon. Furthermore, we obtain that the system occurs one-, two transparency window, or optical gain property, which iscontrolled by adjusting the coupling control field. For the nonlinear case, the weakprobe field, which is induced by a signal field, splits into two parts. When they excitethe self-Kerr and cross-Kerr nonlinear effects balancing the refractive effect of thebeam, the system exhibits bright-bright, bright-dark, dark-bright, dark-dark solitonpairs.In contrast to single quantum dot, the quantum dot molecule (QDM) consists ofdouble semiconductor quantum dots, which can be coupled by some ways such as tunnelingcoupling. Consequently, the impact of the interdot tunneling coupling (ITC) strengthmust be considered in the properties of linear absorption and spatial optical soliton ofthe QDM. In chapter three, We study analytically the properties of the opticalabsorption and the spatial weak-light solitons in a QDM system with the ITC. It isshown that, for the linear case, there exists tunneling induced transparency (TIT) inthe context of a weak ITC, while the TIT can be replaced by Autler-Townes splitting（ATS）with the presence of a strong ITC in such a system. For the nonlinear case, itis probable to accomplish the spatial optical solitons even under weak light intensityalong with the appearance of transformation behavior between the bright and darksolitons by properly turning both the ITC strength and the detuning of the probe field.It is meanwhile likely to achieve the transformation condition of the bright and darksolitons. Additionally, it is also found that the amplitude of the solitons first descendsand then rises with the increasing of ITC strength.Finally, we make a brief summary of our work and look forward to a furtherinvestigation on the related phenomena of EIT in the field of nonlinear optics in thesemiconductor quantum dot.