大功率半导体激光器单管合束及光纤耦合的研究
摘要
近年来大功率半导体激光器在激光材料加工、光纤激光器泵浦，激光再制造以及国防安全等领域广泛地应用，因此采用半导体激光合束技术研制高亮度、高功率输出半导体激光光源的研究成为了热点。以往采用的半导体激光叠阵由于光束质量差，bar条存在“smile”效应等原因，使其很难获得较细芯径的光纤输出，因此亮度较低。单管半导体激光器具有光束质量好，可靠性高，寿命长等优点，利用多只单管半导体激光器合束制成的光纤耦合模块可以获得较细芯径的光纤输出，很大程度上提高了光纤输出的亮度，因此具有重要的研究意义。本论文根据各种应用对光纤耦合模块的功率要求设计并研制出多种光纤芯径、多种功率输出的808nm单管合束半导体激光器光纤耦合模块，并针对光纤耦合模块的调试和散热情况进行了讨论。本文主要研究内容和成果如下：
1.提出了一种新型单管合束内部排列结构，并获得发明专利一项。通过使用多个反射棱镜对其相对应的单管半导体激光器发出的光进行空间合束，通过反射棱镜及单管半导体激光器的适当排列，可以使合束后的光斑成近圆形分布，这样聚焦后的光斑呈圆形，与光纤端面形状相匹配，解决了光纤耦合过程中存在的填充比例小以及耦合效率低等问题。 2.设计并研制出多种光纤芯径、多种功率级别的光纤耦合模块。首先通过微透镜对每个单管半导体激光器进行快慢轴准直，通过空间合束使准直后的光束在快轴叠加，再利用偏振合束技术对空间合束后的光束进行偏振合束，最后利用自行设计的扩束聚焦系统将合束后的光束进行扩束，聚焦进入光纤，极大地提高光纤耦合模块的亮度。其中芯径为105μm、NA0.2的光纤耦合模块输出功率15.22W，亮度超过1.4MW/cm2-str；芯径为300μm、NA0.2的光纤耦合模块输出功率162W，国内尚未见报道。 3.采用光线追迹法对单管合束的装调误差进行了定量分析。利用光学设计软件的非序列模式模拟了单管合束装调过程中FAC、SAC的位置误差Δx、Δy、Δz、角度误差βx、βy、βz、光束扩束系统中的ΔL以及聚焦光束与光纤的失配对光路传播及耦合效率造成的影响并定量地给出了模拟结果，对今后单管合束的光路调试有一定的指导作用。 4.设计了百瓦级全固态风冷、小型工程化半导体激光光源。结合强制风冷散热原理，通过对散热片的尺寸，热管位置，风扇转速的优化，设计并研制出百瓦级光纤耦合模块风冷散热器，通过对光纤耦合模块界面热阻的优化使得整个模块的热阻小于0.15℃/W，将风冷散热器用于160W单管合束光纤耦合模块的散热，通过对光纤耦合模块进行了频率红移测试，表明散热器的性能可靠，从而实现了百瓦级全固态风冷、小型化、工程化半导体激光光源，此结构申请发明专利一项。 Because of the widely application of high power diode laser in materialprocessing, fiber laser pumping, laser remanufacturing and country security, theresearch of high brightness, high power laser source based on diode laser combinationbecame the research focus. Because of the poor beam quality and “smile” effect ofdiode laser stacks, it is difficult to increace the output power from small core fiber,which results in a low brightness. The fiber coupled module based on multiple singleemitter diode lasers can realize the high brightness with good beam quality, highreliability and long lifetime. Therefore the researching of single emitter diode laserscombination is a very significant subject. According to the demand of output power inmany applications, many kinds of modules with different fiber core and output powerwere designed and manufactured, the adjustment of fiber coupling and air-cooled heatwere discussed in this paper. The main contents and results of this paper are asfollows: 1. A new structure of single emitter diode lasers combination was created, whichobtained the patent of invention. Many diode lasers light were space combined by theuse of multiple reflection prisms. Through adjusting the position of reflection prismsand diode lasers, the beam spot after combination was a nearly circular distribution, sothe focusing spot was circular, which matched the shape of fiber end. This structuresolved the problems of low filling ratio and low coupling efficiency in fiber coupling. 2. Many kinds of modules with different fiber core and output power weredesigned and manufactured. First, the fast axis and slow axis of each diode laser werecollimated by micro-lens. The collimated beam of diode lasers was combined in fastaxis direction. Then the combined beam was polarization combined by PBS prism.Finally we utilized a suit of optical system designed by ourselves to expand and focusthe beam into a optical fiber. Which greatly increase the brightness of module of fibercoupled LDs. One of the modules could output15.22watts from a105μm multimode optical fiber. The numerical aperture of fiber was0.2. The brightness of moduleexceeded1.4MW/cm2-str. Another module could achieve162watts output powerfrom a300microns fiber core with a numerical aperture of0.22. Such high powermodules with single emitters combination were not reported before in homeland. 3. The alignment error in single emitter diode lasers combination was analysisedby using the ray tracing method. Using the sequence model of optical design softwareto simulate the error of optical adjustment，the impact of beam propagation andcoupling efficiency was discussed. Which included the position error Δx, Δy, Δz,angle error βx, βy, βz of FAC and SAC, the position error ΔL in beam expandingsystem and the mismatch of a focused laser beam and optical fiber, which would havedirective function in the optical adjustment of single emitter diode lasers combination. 4. A hundred-watt all-solid-state air-cooled, small engineering diode laser sourcewas designed. Combined with the principle of forced air cooling, through theoptimization of the size of radiator fan, the position of heat pipe and fan speed, ahundred-watt fiber coupling module air-cooled radiator was design and manufactured.Through the optimization of interface thermal resistance of optical fiber coupledmodule, the thermal resistance of whole module was less than0.15℃/W, which wasused in the air-cooled of160W fiber coupled module. Through the frequency red-shifttesting of fiber coupled module, which showed the reliable of radiator. So thehundred-watt all-solid-state air-cooled, miniaturization, engineering diode laser sourcewas achieved. A patent of invention based on this structure was applied.
引文
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