Exploring temporal states in optically pumped semiconductor lasers
| Autor: | Tsou,Chia-Han, 鄒家翰 |
|---|---|
| Rok vydání: | 2017 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 105 This thesis presents several optical experiments to investigate the phenomenon of self mode locking (SML) in optically pumped semiconductor lasers (OPSLs). First of all, we systematically explore the criterion for achieving the SML operation in an optically pumped semiconductor laser with a linear cavity. Experimental results reveal that the occurrence of SML can be assisted by the existence of the first high-order transverse mode, the continuous SML cannot be observed in the absence of high-order transverse modes. Numerical analysis is performed to confirm that the critical pump power for obtaining the SML operation agree very well with the pump threshold for exciting the TEM1,0 mode. Moreover, we quantitatively investigate the influence of multiple high-order transverse modes on the temporal state in an OPSL with a nearly hemispherical cavity. A physical aperture is inserted into the cavity to manipulate the excitation of high-order transverse modes. While more high-order transverse modes are excited, it is experimentally found that the pulse train is modulated by more beating frequencies of transverse modes. The temporal state becomes the random dynamics when too many high-order transverse modes are excited. Nonlinear refractive index is strongly associated with SML operation. Therefore, we propose another method to measure the nonlinear lensing in the OPSL gain chip. We precisely measure the values of transverse frequency spacing and longitudinal frequency spacing, and find that a focus lens must be considered for the numerical fitting based on ABCD law. According to comparison with experimental results and theoretical calculations, the focal length is found to be independent with pump power, pump mode size, cavity length, and radius of curvature of the output coupler. In addition to typical mode-locked pulses, we originally observe an intriguing phenomenon of SML in an OPSL related to the formation of bright-dark pulse pairs. We experimentally demonstrated that under the influence of the tiny reflection feedback, the phase locking between lasing longitudinal modes can be assisted to form bright-dark pulse pairs in the scale of round-trip time. A theoretical model based on the multiple reflections in a phase-locked multi-longitudinal-mode laser is developed to confirm the formation of bright-dark pulse pairs. Finally, we present a simple and cost-efficient OPSL design supporting stable high power operation. This design is based on the combination of a concave output coupled with an output reflectivity of 88% and a set of coupled resonators. With a coupled mirror reflectivity of 50% and an incident pump power of 24 W, we can achieve 6.3 W of average output power and the slope efficiency was 41%. Moreover, we have observed dark pulse emission with strong external reflection. The great agreement between experimental results and the numerical fitting validates that the strong external reflection is necessary for the generation of self-mode-locked dark pulse emission in an OPSL. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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