Modeling and Characterization of Strained Quantum - Lasers and Modulators.
Strained quantum-well lasers and modulators are studied in this dissertation. Both dc and high-speed performances of these two devices are studied. Theoretical models are developed, and we show very good agreement between the theoretical and experimental results. Strain and quantum size effects on the optical -matrix elements for both TE and TM polarizations of strained quantum wells are studied theoretically, including the spin-orbit coupling. A set of universal curves for the polarization-dependent optical-matrix elements as a function of strain is shown. These curves are very helpful for a quick estimate of the optical-matrix elements for strained quantum-well structures. A complete model with the spin-orbit coupling for strained quantum-well lasers is then presented. Explicit formulas for the momentum-matrix elements are given. The improvement in the threshold current density of tensile strained quantum-well lasers, as compared with that of the unstrained quantum well, is shown to result from the enhanced momentum matrix. The theoretical results show a smaller linewidth enhancement factor for compressively and tensile strained quantum wells than that of the unstrained structure, as has been experimentally observed. Amplified spontaneous emission spectroscopy is used to extract the gain and refractive index spectra systematically. The measured optical gain and refractive index are then compared with our theoretical model for strained quantum-well lasers. We show that a comprehensive theoretical model for calculating the electronic band structure, the optical constants, and the linewidth enhancement factor agrees very well with the experiment. Nonlinear gain coefficients are modeled based on the two-level density matrix formalism. Both spectral -hole burning and carrier beating vibration are included for strained quantum-well structures. Formulas for both self- and cross-polarization nonlinear coefficients are presented. A theoretical model for strained quantum-well modulators including the spin-orbit coupling is then presented. The exciton equation is solved in the momentum space. The symmetrical properties of the exciton Hamiltonian are investigated carefully and shown to reduce the computation time. An interpolation scheme is proposed to properly take into account the continuous exciton states. The strained effects on the performances of modulators are shown and compared with the experimental data.
- Pub Date:
- Engineering: Electronics and Electrical; Physics: Optics