Study On The Key Technologies Of Optically-pumped Vertical-external-cavity Bottom-emitting Semiconductor Lasers

OPSL(Optically pumped vertical-external-cavity surface-emitting semiconductor lasers) combines the advantages of solid-state lasers and semiconductor lasers, and so has a very obvious comprehensive advantages on beam quality, laser power, tuning range and wavelength range. Since 1997 M. Kuznetsov achieved near diffraction limited laser beam with 0.5W power, OPSL has great potential due to engineering applications, so the field has gained wide attention all over the world, and the landmark research emerges. Based semiconductor bandgap engineering, currently OPSL output wavelengths cover from visible to far-infrared region, which has a significant advantage to achieve special band which is difficult to achieve by conventional lasers; In addition, OPSL has a simple cavity structure with low cost and small package, which has been widely used in a variety of portable spectrum space equipment.International research of OPSL includes theoretical, material, high power, and applied with external cavity. In theory domain, mostly research is on the gain characteristics, optimizing the design of the quantum well structure and dynamics of frequency doubling and mode-locking; and the thermal management of OPSL, including quantum well active region flux distribution and numerical analysis of laser temperature field. Epitaxial growth OPSL material system has evolved from the visible band with In Ga P substrate, near-infrared with Ga As substrate, to the far infrared with Pb S and Ga Sb substrate. For the high-power lasers, after structural design optimization on OPSL, mainly to improve thermal management performance, the measures include substrate-removed, window heatspreader, multi-chip and in-well pumping, and so on. Applied research about external cavity focuses on frequency extension technology, single frequency and tuning techniques, and mode-locking technology.With theoretical analysis, numerical simulation and experimental methods, relevant characteristics of OPSL bottom emission structure, this paper completed structural analysis of OPSL epitaxial wafers, wafer packaging experiments and experimental laser performance. The results are as follows:① Based heterojunction strain theory, the band edge model and square potential well model, this paper studied the theory and In Ga As / Ga As strained quantum well energy level distribution, and analyzed the effect of In component content and well width on the lasing wavelength, and found In component should be more reasonable in the range of 0.15 to 0.18, when quantum well width is 8nm with the lasing 1000 nm wavelength,; using vector potential variables, the paper established a common form of multilayer film structures include light field intensity distribution, and studied the distribution characteristics of the DBR and micro-cavity, discussed the relationship of DBR reflection bandwidth of Al As/Ga As and Al As/Alx Ga As material system and number of repeated pairs, as well as the difference of application. Results shows the relationship between gain peak of longitudinal confinement factor with the window layer thickness, which can provide a reference for optimizing high power OPSL chip design.②Based on the gain factor of OPSL laser, this paper proposed a principle for structure design with high power OPSL, That is, in order to realizes quantum well gain, periodic gain, and longitudinal confinement factor matching with curve peak related to temperature, wavelength in the working temperature range, it is needed to precisely adjust the window layer thickness, optimize etching stop layer, strictly control the quality of epitaxial growth. This paper also discussed the issues and improved method of structure design about our OPSL chip.③ By separating responding region of the Peltier effect and the Joule effect in TEC, the thermal transfer model of TEC which does not depend on the surface temperature parameter has been established for the first time, and the thermal management system temperature field model of OPSL including TEC has also been established. This paper also studied in detail the thermal management system, the impact of various factors, especially the heat sink parameters of OPSL on the maximum temperature of the quantum well. The study found that the oxygen-free copper material is suitable for bottom-emitting structure OPSL wafer heat sink, and in the several wattage laser power, cooling systems does not need high heat transfer coefficient.④ Experiment has been conducted to study packing technology of bottom emission structure OPSL, including metallization, welding, direct bonding and etching. The paper also discussed the basic principle and various problems in the experiment, as well as their solutions, to achieve a welding and direct wafer bonding technology, and a bright light surface after etching.⑤This paper analyzed theoretically and numerically simulated impact of cavity length, coupling mirror and pump power in the resonator structure on laser performance. Experiments show that spontaneous emission spectrum of OPSL chip changes with temperature and the pump power. This paper completed OPSL laser experiment, and got near diffraction limited fundamental mode Gaussian beam, where M square factor in the x and y directions are 1.01 and 1.02, the maximum output power is 0.5W, and the slope efficiency is 28.4%. With the data of wafer edge emission spectrum changing with temperature, the main reason for the low output power has been analyzed. This study also analyzed the performance of LBO and completed the experiment of OPSL intra-cavity frequency-doubling experiments, with doubling efficiency of about 27%.