单模—多模光纤合束器的传输特性研究
发布时间：2018-09-08 13:01
【摘要】：单模-多模光纤合束器,用于将多路单模或准单模光纤激光输出合束到一路多模光纤中,是全光纤非相干合成技术中的关键器件。目前,对于单模-多模光纤合束器的研究虽然取得了一定进展,但是其中对于光场在合束器中的具体传输过程以及合束器设计规律等方面的研究仍非常有限。因此,本文针对套管法制作的单模-多模光纤合束器,以3×1单模-多模光纤合束器为例,从传输特性入手展开数值研究,分析光场在其中的传输过程,研究输入、输出光纤参数及拉锥参数对合束器性能的影响,给出单模-多模光纤合束器的设计规律。主要工作如下:首先,介绍了单根拉锥光纤的理论分析方法——几何光学法和光束传输法。论文分别给出了两种方法的理论思路和算法实现,并结合单模-多模光纤合束器的特点和结构,分析对比了两种方法的差异及适用范围,指出研究单模-多模光纤合束器的传输特性需要使用光束传输法。其次,针对采用石英套管(折射率与包层折射率相等)拉制合束器的情况,建立了无限包层数值模型,研究了光场在合束器中的演化过程和规律,讨论了合束器结构及参数对传输效率的影响。结果表明,输出光纤的数值孔径对于传输效率的影响较小;输出光纤的纤芯和拉锥长度应该足够大以保证传输效率。此外,需要匹配拉锥比和输出光纤纤芯直径,使输出光纤纤芯尽可能小,以获得较好的光束质量输出。最后,针对采用低折射率掺氟套管(折射率小于包层折射率)拉制合束器的情况,建立了有限包层数值模型,研究了有限包层及其他主要参数对合束器性能的影响。结果表明:第一,由于低折射率外部介质的存在,使得有限包层在约束和分离光场中起到了重要作用,并提高了合束器的拉锥比和传输效率;第二,光场在输入光纤包层中仍保持单模传输,使得在输出光纤纤芯数值孔径远小于熔融拉锥光纤束包层数值孔径的情况下,合束器依然保持了高传输效率,因此可以通过减小输出光纤纤芯数值孔径的方式来提高输出光亮度;第三,由于熔融拉锥光纤束中的损耗,合束器传输效率的提升存在一个极限值,该值随拉锥比增大而减小;第四,拉锥长度应足够长以满足绝热拉锥条件,数值模拟结果显示绝热拉锥长度随拉锥比增大而增大。此外,增大输入光纤纤芯数值孔径和纤芯包层比有利于提高合束器传输效率。以上结论对单模-多模光纤合束器的设计有着重要的指导意义。
[Abstract]:Single-mode and multi-mode fiber beam synthesizer is a key component in all optical fiber incoherent synthesis technology, which is used to output multiple single mode or quasi single mode fiber laser beam to a single mode fiber. At present, although some progress has been made in the study of single-mode and multi-mode optical fiber beam combiners, the research on the specific transmission process of light field in the beam combiner and the design rules of beam combiner are still very limited. Therefore, in this paper, for the single mode multimode fiber bundle combiner fabricated by casing method, taking 3 脳 1 single mode multimode fiber bundle combiner as an example, a numerical study is carried out from the transmission characteristics, the transmission process of the light field in it is analyzed and the input is studied. The influence of the output fiber parameters and the tapered parameters on the performance of the buncher is discussed. The design rule of the single-mode and multi-mode fiber bundle combiner is given. The main work is as follows: firstly, the theoretical analysis methods of single tapered fiber, geometric optics method and beam propagation method, are introduced. In this paper, the theoretical thinking and algorithm realization of the two methods are given, and the differences and application range of the two methods are analyzed and compared by combining the characteristics and structure of the single-mode and multi-mode fiber beam combiner. It is pointed out that the beam propagation method is needed to study the propagation characteristics of single-mode multimode optical fiber combiner. Secondly, an infinite cladding numerical model is established to study the evolution process and law of the light field in the beam combiner, aiming at the case that the quartz casing (the refractive index is equal to the cladding index) is used to fabricate the beam holder, and the infinite cladding numerical model is established. The influence of the structure and parameters of the beam combiner on the transmission efficiency is discussed. The results show that the numerical aperture of the output fiber has little effect on the transmission efficiency, and the core and tapered length of the output fiber should be large enough to ensure the transmission efficiency. In addition, it is necessary to match the tapered ratio and the diameter of the output fiber core to make the output fiber core as small as possible in order to obtain better beam quality output. Finally, a finite cladding numerical model is established to study the influence of the limited cladding and other main parameters on the performance of the beam binder by using a low refractive index fluoride-doped casing (refractive index less than the cladding index). The results show that: first, due to the existence of the external medium with low refractive index, the limited cladding plays an important role in restraining and separating the light field, and improves the tapered ratio and transmission efficiency of the beam combiner. The optical field still maintains a single mode transmission in the input fiber cladding, which makes the beam combiner maintain a high transmission efficiency when the output fiber core numerical aperture is much smaller than the melt tapered fiber cladding numerical aperture. Therefore, the output brightness can be improved by reducing the numerical aperture of the output fiber core. Thirdly, due to the loss in the fused tapered fiber bundle, there exists a limit value for the increase of the transmission efficiency of the beam combiner, which decreases with the increase of the tapered ratio. Fourthly, the tapered length should be long enough to satisfy the adiabatic cone condition. The numerical simulation results show that the adiabatic cone length increases with the increase of the tapered ratio. In addition, increasing the input fiber core numerical aperture and the core-cladding ratio can improve the transmission efficiency of the beam combiner. The above conclusions are of great significance to the design of single-mode-multi-mode fiber beam combiner.
【学位授予单位】：国防科学技术大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN253
本文编号：2230599
[Abstract]:Single-mode and multi-mode fiber beam synthesizer is a key component in all optical fiber incoherent synthesis technology, which is used to output multiple single mode or quasi single mode fiber laser beam to a single mode fiber. At present, although some progress has been made in the study of single-mode and multi-mode optical fiber beam combiners, the research on the specific transmission process of light field in the beam combiner and the design rules of beam combiner are still very limited. Therefore, in this paper, for the single mode multimode fiber bundle combiner fabricated by casing method, taking 3 脳 1 single mode multimode fiber bundle combiner as an example, a numerical study is carried out from the transmission characteristics, the transmission process of the light field in it is analyzed and the input is studied. The influence of the output fiber parameters and the tapered parameters on the performance of the buncher is discussed. The design rule of the single-mode and multi-mode fiber bundle combiner is given. The main work is as follows: firstly, the theoretical analysis methods of single tapered fiber, geometric optics method and beam propagation method, are introduced. In this paper, the theoretical thinking and algorithm realization of the two methods are given, and the differences and application range of the two methods are analyzed and compared by combining the characteristics and structure of the single-mode and multi-mode fiber beam combiner. It is pointed out that the beam propagation method is needed to study the propagation characteristics of single-mode multimode optical fiber combiner. Secondly, an infinite cladding numerical model is established to study the evolution process and law of the light field in the beam combiner, aiming at the case that the quartz casing (the refractive index is equal to the cladding index) is used to fabricate the beam holder, and the infinite cladding numerical model is established. The influence of the structure and parameters of the beam combiner on the transmission efficiency is discussed. The results show that the numerical aperture of the output fiber has little effect on the transmission efficiency, and the core and tapered length of the output fiber should be large enough to ensure the transmission efficiency. In addition, it is necessary to match the tapered ratio and the diameter of the output fiber core to make the output fiber core as small as possible in order to obtain better beam quality output. Finally, a finite cladding numerical model is established to study the influence of the limited cladding and other main parameters on the performance of the beam binder by using a low refractive index fluoride-doped casing (refractive index less than the cladding index). The results show that: first, due to the existence of the external medium with low refractive index, the limited cladding plays an important role in restraining and separating the light field, and improves the tapered ratio and transmission efficiency of the beam combiner. The optical field still maintains a single mode transmission in the input fiber cladding, which makes the beam combiner maintain a high transmission efficiency when the output fiber core numerical aperture is much smaller than the melt tapered fiber cladding numerical aperture. Therefore, the output brightness can be improved by reducing the numerical aperture of the output fiber core. Thirdly, due to the loss in the fused tapered fiber bundle, there exists a limit value for the increase of the transmission efficiency of the beam combiner, which decreases with the increase of the tapered ratio. Fourthly, the tapered length should be long enough to satisfy the adiabatic cone condition. The numerical simulation results show that the adiabatic cone length increases with the increase of the tapered ratio. In addition, increasing the input fiber core numerical aperture and the core-cladding ratio can improve the transmission efficiency of the beam combiner. The above conclusions are of great significance to the design of single-mode-multi-mode fiber beam combiner.
【学位授予单位】：国防科学技术大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN253
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