Study Of The Energy Level Properties And Configuration Optimization Of Coupled Quantum Well

This thesis investigates the energy level properties of coupled quantum well and its configuration optimization. Quantum well materials have stronger electro-optic effect than bulk materials, so Quantum well materials can produce a large absorption coefficient change and refractive index change in the case of lower applied field, and used in all sorts of waveguide devices, for example, traveling-wave modulators and electro-optic switches. Unfortunately, these waveguide devices based on the widely used square-potential quantum well exist large absorption loss and low extinction-ratio. In order to make quantum well materials utilized widely in integrated optical devices, it is imperative to search for a novel quantum well with a large refractive index change in the case of low applied field and low absorption loss.The main research results include:Firstly, the formation of the symmetric and antisymmetric energy levels of electron, heavy-hole and light-hole by perturbation theory is analyzed and found that the six energy levels arise from the splitting ground states in single quantum well. The symmetric- and antisymmetric -energy levels can be treated as a two energy level system and split into the high- and low-energy levels with larger level splitting in the present of applied electric field. The eigenstates corresponding to the high- and low-energy levels include antisymmetric state as well as symmetric state.Secondly, the lowest and next lower energy levels of electron and hole in asymmetric coupled quantum well is analyzed and found that the six energy levels arise from the coupled ground states of the conduction and valence bands of the two different single quantum wells. The advantages and disadvantages of symmetric- and asymmetric-coupled quantum wells are discussed when they are applied to traveling-wave modulators and electro-optic switches, and then a novel coupled quantum well—quasi-symmetric coupled quantum well is projected.Thirdly, based on the properties of quasi-symmetric coupled quantum well potential, the selected principle of quantum well materials is put forward, and InP-based InGaAs/InAlAs material parameters are modified. By Bastard' s two-band model, the influence of band mixing effect between the conduction band and valence band on electron and light hole effective masses is considered and the tunneling resonance method is utilized for solving out the eigenenergies and eigenstates of quantum well.Fourthly, based on the six rules for optimizing quasi-symmetric coupled quantum well potential configuration, all parameters for InP-based InGaAs/InAlAs quasi-symmetric coupled quantum well are calculated, then the electro-optic properties of the optimized coupled quantum well are presented. The simulating results manifest that the polarization dependence of quantum well materials is solved perfectly, and in the case of low applied electric field (F<15Kv/cm) and lowabsorption loss (a ? = 0.0108;for TM mode, Ah = 0.0107) isobtained in the optimized coupled quantum well.Fifthly, the waveguide configuration for validating the performance of the optimized InP-based InGaAs/InAlAs quasi-symmetric coupled quantum well is designed.Finally, the domain of waveguide devices is completed, and the fabrication process of waveguide is researched.