Research On Dual-Wavelength Semiconductor Laser Based On The Coupled-Cavity Structure

In the thesis we propose a novel quarter-wave coupled-cavity dual-wavelength semiconductor laser structure and the mode-competition problem in such laser is analyzed using Langevin noise-driven rate equations. The dual-wavelength laser consists of two coupled active cavities with monolithically integrated mode-selection filters. It has the advantages of compactness, simple fabrication and can achieve simultaneous emission of two optical modes as a doublet with the same threshold while the frequency difference of the two lasing wavelengths can be tuned by the injection currents in the two cavities. It is shown that the dual-wavelength semiconductor laser has great potential for tunable millimeter wave generation in radio-over-fiber systems. The analytical expressions for the spectral positions of the doublet and the threshold gain are derived for the first time using the Transfer Matrix Method (TMM). To simulate the competition process between two emitting optical modes, a numerical model is established with enhanced physical insight (involving spatial hole burning effect) using a saturation coefficient and a suppression coefficient instead of the more commonly used nonlinear gain coefficient. The saturation and suppression coefficients are calculated for various pumping level ratios between the two active cavities and the influence of the Langevin noise sources is studied on the dual-mode stability. We show that the threshold gain difference of the two competing modes can be fine-tuned dynamically based on an electrical feedback signal using a monolithically integrated filter to achieve stable simultaneous dual-mode emission. The fabrication of such coupled-cavity laser is studied and a complete fabrication process flow is proposed. Techniques such as protection of the deep-etched trench and the formation of ridge-waveguide with low ICP power are also studied. The experimental test to our fabricated sample is also performed, which confirms the practical feasibility of the dual-wavelength semiconductor laser based on the coupled-cavity structure.