Numerical Modeling Of A Single-Mode Fiber Laser Doped With CdSe/ZnS (Core-Shell)Nanocrystal Quantum Dots

In recent years, researches on semiconductor nanocrystal quantum dots (QDs) attract much attention due to their unique optical and electrical properties. As an application of QDs in lasers, more and more researches show that QDs have optical gain and excited radiation being possible.In this dissertation, a QD doped fiber laser (QDFL) is presented, where CdSe/ZnS (core/shell) QD is used as active medium instead of conventional bulk materials. We focus on four hands in this dissertation as follows.(1) Following discussion on spectrum characteristics of CdSe/ZnS QDs, a configuration of CdSe/ZnS QDFL is presented in chapter4. We establish a two-level system for CdSe/ZnS QDFL, numerically solving its population rate equations and power propagation equations according to the observed absorption and photoluminescence spectra of the QDs.(2) We develop several preparation methods of quantum dot doped fiber (QDF). According to the measured PL spectra of QDF, we find that the red shift of PL-peak wavelength depends on the core material, fiber length, and doping concentration. Moreover, correlated with the FWHM of the first absorption peak of the QD, the maximum red shift will approach to a saturated value as the fiber length increases.(3) Using a genetic algorithm and taking the output laser power as an objective function, the optimal parameters (pump wavelength, doping concentration, fiber length, reflectivity of output mirror) of QDFL are determined. Compared with the conventional Nd3+doped fiber laser, QDFL shows a higher pump efficiency, a lower saturated doping concentration, and a shorter saturated fiber length. Upon pumping power of2W, the simulated output laser power of QDFL reaches to1.5W.(4) Thermal stability of CdSe/ZnS QDs and CdSe/ZnS QDFL are numerically simulated. There is evidence to show that such thermal stability of the QDs is better than that of bulk materials and conventional Er-Yb doped fiber lasers.The results presented in this dissertation provide an analysis base for the development of QDFL in the future. Further, the single-wavelength QDFL simulated in this dissertation can be developed into a novel multi-wavelength laser due to sized dependent effect of QDs.