| Compared with other kinds of lasers, the diode lasers are featured with highelectrical-optical conversion efficiency, small size, long life time, high reliability, largewavelength range and low cost. However, due to their intrinsic structural characteristicsof waveguide, the poor and extreme asymmetrical beam quality in the two-dimensionaldirections make semiconductor lasers very limited in their direct applications.Nevertheless, after beam shaping, the advantages of fiber-coupled diode lasers lie ingood beam quality, flexible transmission, high brightness, strong immunity frominterference, convenience of use, and circular symmetrical and uniform output facula,all of which allows them to take a significant role in the field of optical fibercommunications, materials processing, laser pumping as well as medical cosmetology.Therefore, it has become a research highlight to achieve the high power output of fiber-coupled diode lasers through study on the novel beam shaping techniques and designthe high efficient fiber-coupled systems.An efficient way of achieving high power output, small volume and lowmaintaining cost for fiber coupling is to use multiple LD bars with conduction-cooledpackaging structures. Recently, the majority of beam shaping schemes are suitable fora single bar, and there are only a few research works related to the light source ofmultiple LD bars source. On the basis of the above problems, a study concerned withbeam shaping and fiber coupling technology for multi-LD bars was conducted.(1) The design of D-shaped aspherical collimation cylindrical lens in fast-axis andmicro cylindrical lens arrays in slow-axis was theoretically analyzed. Throughthe combination of theoretical calculation and Zemax software simulation, thestructural parameters of aspherical collimation cylindrical lens were optimized.Thevariationofcollimationerrorsresultingfrom assemblyerrorsofcollimatinglens in fast axis was also simulated, which provided a reference when adjustingcollimating lens in practice. (2) Space beam combination was carried out in three conduction-cooled bar diodelasers by designing a medal step heat sink. ANSYS was used to analyze thevariation of step sizes influencing on the temperature of diode lasers, whichprovided a basis for optimization of structural parameters of step heat sink.Simulating and experimental results show a good heat dissipation of thedesigned step heat sink structures. Meanwhile, according to the highpolarization degree of diode lasers, an idea of composing half wavelength plate-polarizing beam splitter with compact structures for polarization beamcombining was proposed, aiming at improving the beam quality of diode lasers.(3) On the premise of full investigation of beam transformation technologies, anovel “double-cutting” beam transformation technique was proposed. In thisproposal, prism group arrays were adopted to achieve cutting, rearrangementand compression of area light source of multiple LD bars with high efficiency.According to the geometrical optical principles, the structural parameters ofprism group were theoretically derived. Analog simulation and experimentaloperations were conductedforthenovel project, andtheresults indicatethat thisstructure is highly efficient in beam conversion and suitable for the multiple-bars beam conversion.(4) Ahectowatt fiber-coupled module made from three ordinary marketed cm-barswasdesignedbyusingtheabovetechnologiesofbeamcollimation,combination,conversion and fiber coupling. The maximum continuous output power of thefiber-coupled module is129.8W, and the output beam quality is44mm mrad.The optical-optical coupling efficiency of the whole system is72.76%, and theelectrical-optical conversion efficiency is40.5%. The novel beam conversiondevice shows a high efficiency of93.37%, which has reached the domesticleading level in terms of multiple-bars beam conversion. |
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