Spectrum Absorption And Scattering Cross-Sections Of Ⅱ-ⅥCdS, CdSe And CdTe Quantum Dots In Usual Fiber Materials

The current communication technologies are toward high-bandwidth and high-security directions. Fibers have advantages in weight, price and security compared with traditional materials. In recent years, nanocrystal quantum dots (QDs) have attracted much attention due to their unique optical and electrical performance. The fluorescent characteristic of QDs can be tunable by changing their sizes. Thus, QDs are widely used in biomedical, fluorescent probe, optical gain devices and quantum dot doped LED.The optical amplifier (OA) is an important component in fiber communication system. QDs are not only the transport media but also the gain media in quantum dot-doped fiber amplifier (QDFA). The light extinction is caused by absorption and scattering of fiber materials and QDs when the pumping laser transported in the fiber. Excited by the pumping laser, the ground states or valence-band electrons of the QDs are jumped into conduction bands by absorbing energy of the pumping laser, and then produce stimulated emissions described by a term called "cross-sections". Therefore, it is particularly important to determine the absorption and scattering cross-sections of QDs.This dissertation discusses in details of the computational method of absorption and the scattering cross-sections about II-VI QDs.First, according to the Mie scattering theory, we determine the key factor that the sizes of II-VI QDs (CdSe, CdS and CdTe) determine the absorption and scattering cross-sections in usual fiber materials. Then, we determine optical absorption and scattering cross-sections of CdSe, CdS and CdTe QDs in usual fiber materials (Polymethyl methacrylate (PMMA) and SiO2) as a function of wavelength. We summarize a compact expression of the absorption and scattering cross-sections. However, there is no cross-section peaks shown in results obtained in such a way because the Mie scattering theory is a classical theory not involving quantum effect. Thereafter, we determine the absorption-peak wavelengths that depend on the QD diameters by using the effective mass approximation (EMA). Finally, a comparison of absorption cross-sections at the peak wavelengths is made between our computational results and experimental measurements. It is shown that absorption cross-sections calculated by the Mie scattering theory is much closed to the measurements.The method introduced in this dissertation to calculate optical absorption and scattering cross-sections can be generalized use in other QDs. As primary data, these cross-sections can be utilized in numerical modeling and theoretical analysis for gained devices as well as other types QD optoelectronic devices, e.g. optical amplifiers, lasers, and solar cells.