| Summary: | 碩士 === 國立臺灣大學 === 光電工程學研究所 === 92 === In an optical communication system, a semiconductor laser is usually applied to serve as a modulated light source. Especially in a wavelength division multiplexing scheme, it is required that wavelengths in different channels do not interfere each other under modulation. Therefore the stability of a laser on frequency domain is important. In order to judge the potential of a laser diode applied in the high speed operation, the linewidth enhancement factor ?will be investigated intensively in this study.
The ?factor implies the frequency chirping with changing the driving excitation on a device. Particularly in a QD laser, it offers a smaller ?value than the conventional QW lasers, and a smallest ?value of 0.1 is demonstrated up to now in the literature.
In the determination of the ?factor, firstly we adopt the Hakki-Paoli method to measure the spontaneous emission of a diode then calculate the gain spectra. With the gain spectra, the KK relation is used to observe the refractive index perturbation accordingly. From these information, the ?factor can be determined by the definition in which the relation between the gain spectra and the refractive index is involved.
Moreover, the rate equation model and the master equation model will be applied to explain the phenomenon obtained in the experiment. Prediction of vanishing �� factor at lasing wavelength will be checked by MEM model with no thermal coupling among QDs. Influence of excited states on a factor will be investigated with different energy separation between ground states and excited states respectively. Other major factors influencing the ?factors will be also discussed. Results in this study will be helpful in designing QD lasers with appropriate energy diagram and operation conditions for high-speed operation.
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