光纤激光器中包层功率剥离器的热效应

The thermal effect of cladding power stripper for high power fiber lasers

为了将光纤激光器输出光纤包层中未完全被增益光纤吸收的残余泵浦光及非线性因素产生的高阶激光高效率剥离,提高剥离功率和得到较为均匀的热分布,采用优化的高折胶法制作包层功率剥离器,通过实验和有限元仿真模拟对包层功率剥离器的热效应进行了研究.实验表明包层功率剥离器剥离功率为132 W时,稳定工作温度最高为50.0℃,在此剥离条件下仿真模拟的结果与实验基本吻合,证明了仿真模型及参数的正确性,并证明了该种结构包层功率剥离器的实用可靠性.

Lasers have been widely used in many fields such as machinery, medicine, and military. With the development of fiber lasers, high power lasers become more and more desirable. Although lasers with power level of kilowatt or even million watt have been fabricated, there could be many problems associated with the increased power. The most important problem needed to be solved is how to strip unnecessary pump light before laser emit out from the devices. With the progresses in the past years, people have developed some methods to overcome this problem. However, these methods also have some disadvantages, such as too small stripping area to achieve high power light emission, and unsuitability of the technology for mass production. Glue method is the earliest proposed way for stripping the unnecessary light. Its biggest advantage is the simple process. But it also has a big disadvantage that glue cannot endure underhigh temperature in the range of 60°C to 70°C. To solve this problem, people have made attempts for years by either forced cooling or rasing the bearing temperature of glue, however, there is still no good solution. In fiber lasers, the superfluous pump light is dense, which has contributions from the pump light that is not fully absorbed by gain fiber and from high order laser due to misalignment elements. To efficiently strip the inner cladding light, and to get higher stripping power and more uniform heat distribution, we have used an optimized high index glue to fabricate the cladding power stripper. The basic idea is to improve the heat distribution in cladding power stripper by handle the structure of double clad fiber. The specific method is to rotate the cutting area at outsourcing, so the pump light can emit out uniformly, and the glue will have a low working temperature. Experiments and FE simulation are conducted to study the thermal effect of cladding power stripper. The results show that the highest stable operating temperature is 50.0°C when the cladding power is 132 W, and the temperature of cladding power stripper increases linearly with the increase of the stripping power. There is no overheating point in the stripper in the test indicating that the proposed method is applicable for kilowatt level fiber lasers. The experimental results are consistent with FE simulations, which verifies the correctness of simulation model and parameters. As the working temperature is much lower than 60°C, the results demonstrate that such stripper structure is reliable and its properties can be well described by simulations. Such a cladding power stripper only changes the structure of the double clad fiber to optimization the heat distribution, and the result shows this method are useful. The cooling effect of heat source was not perfect, which is the reason why the stripper temperature is 50.0°C when stripping power are only 132 W. So there is an opportunity to change the structure of heat source or use water-cooling or air-cooling to auxiliary heat dissipation for heat source. If both the structures of double clad fiber and heat source are optomized, this cladding power stripper can be used for million watts level lasers without problem. In addition, the simple structure of glue method cladding power stripper, enables its mass production, therefore, this stripper has a great application potential.