| Summary: | 碩士 === 國立中山大學 === 物理學系研究所 === 91 === This work investigated the characteristics of transverse modes and polarization of a VCSEL and attempted to control its transverse mode with optical feedback. The fundamental studies indicated that this solitary VCSEL''s output consisted of two mutually orthogonal linear polarizations with different threshold currents and different transverse mode distributions. Furthermore, the temperature dependence of the transverse modes of the VCSEL revealed a better stability than that of edge-emitted lasers. In the mode controlling experiments, an iris was employed to select a specific transverse mode for feedback, resulting in an enhancement in the power of the feedback mode. A significant improvement was accomplished in the feedback of the fundamental mode of the major polarization component: the laser oscillated in a single mode with a side mode suppression ratio greater than 19.8 dB and with a depression of the relative intensity noise more than 20 dB/Hz. Nevertheless, a week feedback in the minor polarization component would stimulate more competition among transverse modes and degraded the performance of the VCSEL. Finally, no effect was observed in the orthogonal-polarization optical feedback experiment due to the excessively small of feedback ratio.
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