Towards Ultrafast Communications: Nonlinear Coupling Dynamics and Light-Semiconductor Interaction
This thesis deals with some specific problems concerning the processing of ultrashort optical pulses and their interaction with semiconductors. It includes the investigation of the ultrashort optical pulse propagation and coupling dynamics in the nonlinear coupled waveguide, and the coherent and incoherent processes of the light-semiconductor interactions, therewith the arising nonlinearities. The subpicosecond optical pulse propagation in the coupled nonlinear waveguide is investigated in chapter 2. The new feature found is that the waveguide’s optical switching characteristics do not depend on the pulse profile, like a soliton, but on the product of the dispersion length and the coupling coefficient. By investigating the pulse propagation in the cascaded nonlinear coupled waveguide, a method for the subpicosecond rectangular optical pulse generation is proposed. In a nonlinear coupled waveguide with one self-focusing and one self-defocusing channel, the limiting feature is demonstrated for both continuous wave and ultrashort pulses. After the general theory of the semiconductor electrical and optical properties is described and discussed in chapter 3, we focus on the polarization dependence of optical transitions. It is shown that the polarization dependence of the semiconductor optical amplifier is much better reproduced if a weak valence band non-degeneracy is introduced in a heterostructure SOA than when it is simply attributed to the confinement factor difference. In chapter 4, the correlation between the electron spin polarization and circular polarization of the emitted light is studied. We notice that, in uniaxially strained bulk semiconductors, it is possible to achieve high spin polarization of the electrons in certain parts of the energy spectrum by circularly polarized light. In chapter 5, the induced transient birefringence in semiconductors due to an ultrashort pulse is studied. In chapter 6, the polarization dependence of the coherent light-semiconductor interaction on an ultrashort time scale is studied within a model that emphasizes the coherence of the photo-excited electron-hole pair correlation. Based on this model, the polarization dependence of quantum beats in four wave mixing signal of semiconductors is studied.