空间激光通信用掺镱光纤放大器的研究
文献类型：学位论文
| 作者 | 孔勇 |
| 学位类别 | 博士 |
| 答辩日期 | 2004 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 陆雨田 |
| 关键词 | 空间激光通信 声光锁模器 掺镱光纤放大器 增益 |
| 其他题名 | Research on Yb3+-Doped Fiber Amplifier of Space Laser Communication |
| 中文摘要 | 随着国家信息基础设施NII（Nat 1 onal Information Infrastructure）和全球信息基础设施GII（Global Information Infrastructure）的提出［1，2］，对通信的要求越来越高，而目前卫星通信所采用的微波通信技术将受到体积、重量、功耗等方面的严格限制不能无限制地提高传输速率与容量。在卫星通信日益拥挤的今天，采用光频波段通信具有极大的潜力，是实现高速大容量通信的最佳方案，这己经取得了通信领域许多专家的共识。激光通信与微波通信相比，具有不少独特的优点：（1）与微波相比，光波频率高3～5个数量级，频率资源丰富得多，可以获得高得多的数据传输速率，能满足大容量传输的要求，并为实现空间多功能任务提供了时间保障。（2）激光波束比微波波束的发散角小3～5个数量级，这将大大增加接收端的电磁波能量密度，有利于终端重量的减轻、体积的减小，系统功耗的降低。（3）保密和抗干扰性能极好，这对军事应用十分有利。目前，比较好的光发射系统是中小功率半导体激光器（或固体激光器）加上高功率光纤放大器构成主振功放系统，接收系统则采用光纤放大器进行前置放大以便提高接收系统的灵敏度和提高整个系统的传输距离与码率。空间激光通信对掺杂光纤放大器系统输出激光提出了高增益、低噪声、高光束质量输出、较低的非线性效应和一定的偏振态输出等要求，而我们的理论和实验研究将围绕这几个要求进行展开研究。本论文从理论和实验方面对掺臆双包层多模光纤放大器开展了大量的研究工作，并取得一些重要的成果。论文第一章主要由三部分组成，第一节论述了空间通信的概述、发展、优点和展望，第二节论述了用于空间激光通信中信号光的产生和放大系统的状况，第三节论述了掺镱光纤放大器的工作原理、发展、制备、应用、光纤与泵浦光的祸合方式、系统中常用的器件、特性参量和相关参量测量以及光纤放大器对光纤通信系统的影响。第二章理论上分析了光纤放大器中导模的空间分布，在“弱导波近似”条件下，对阶跃型折射率光纤求解波动方程，推导出各阶LP模横向功率密度归一化分布。将YDFA作为一个简单的二能级系统，利用重叠因子的方法，列出了粒子数速率方程，泵浦光、信号光及自发辐射在光纤中的传播方程；并利用场分布的方法列出了对应的方程组。第三章主要进行了理论方面的创新研究，第一节为引言部分，在第二节中我们首次提出了利用重叠因子和场分布相混合的方法，通过求解相关的方程组，求得多模信号光中基模的重叠因子，然后利用模式间功率分布的关系，分析了掺镱多模光纤放大器的一些重要特性，我们采用的是双包层多模掺镱光纤放大器，而重叠因子求解的方法只适用于双包层单模掺杂光纤的分析，对于多模的分析是利用场传输的方法，计算量相当的大，不利于参数的直观分析，本作者提出的这种重叠因子和场分布相混合的方法有效的解决了双包层多模掺镱光纤放大器特性的分析。第三节中在一定的近似下，我们推导了掺镱光纤放大器锁模信号光放大所对应的信号光和泵浦光的传输方程，从而分析了锁模信号光经过掺镱光纤放大器输出的一些重要特性。我们实验中所采用的信号光为锁模信号光，相关文献中没有见到锁模光经掺镱光纤输出特性的理论分析，所以开展这方面的数值模拟研究对该实验系统的研究起着重要的指导意义。第四节中为了提高光纤的输出功率我们提出了将光纤缠绕到一跑道型物体上，并利用数值分析的方法，模拟了它的特性，结果表明这种方法使得输出功率得到大大的提高，并为工艺的加工和实验操作带来了很大的方便。第五节我们首次分析了多模弯曲损耗对基模和高阶模的影响，提出了利用弯曲光纤的方法将高阶模滤掉，从而获得更好的输出光束质量，并讨论了数值孔径对弯曲半径的影响，这为既获得高的输出功率又可获得衍射极限的光束提供了重要的参考价值。第六节我们利用前人对掺饵光纤输出偏振增益研究的理论模型，通过数值模拟的方法分析了不同因素对掺臆光纤放大器输出偏振态增益的影响，并首次分析了信号功率和泵浦功率对掺镱光纤输出偏振态的研究，这对于相干通信来说，是相当重要的。第七节利用我们的实验参数、薛定鄂方程、快速傅立叶的方法对掺镱光纤放大器的非线性效应进行了分析，结果表明，当信号功率增大或脉宽减小时，输出波型基本没有发生变化，但光波会出现兰移现象，这和实验上的结果是一致的。第八节根据Kramers-Kronig关系，利用前人分析掺铒光纤非线性折射率的模型对掺镱光纤中信号光和泵浦光导致的纤芯折射率的改变进行了详细的数值模拟研究，这使我们更清楚的理解了光纤放大器增益、偏振、非线性效应等特性的影响机制。第四章主要进行了实验方面的研究：第一节为引言部分，第二节首先设计了锁模激光系统和掺镱光纤放大器系统的一些重要参数，根据参数通过相应的机械设计和加工组建了整个系统，报道了用激光二极管（LD）端面泵浦Nd：YVO4激光器的实验结果。第三节利用5米的掺镱光纤得到了20dB左右的增益输出，测量了增益随泵浦和信号源电流变化的数值，并对其它一些重要的参数进行了测量分析，这和理论方面的模拟结果基本是一致的。第四节首先从实验上分析了各因素对掺镱光纤放大器自振谱线的影响，并结合数值模拟提出了有效减小自激功率和移动自激谱线波长位置的方法，为有效降低噪声系数和提高增益系数起到了重要的指导作用。第五节提出利用弯曲光纤的方式来提高光束的输出质量，并用CCD拍摄相应的光束输出图象，为既得到高的输出光功率又可获得高的输出光束质量带来了重要的参考价值。第六节结合理论分析的结果，提出利用聚焦透镜、棱镜和握拉斯顿偏光棱镜可对光纤输出的斯托克斯分量进行测量，并利用测量结果即可分析光纤输出的偏振态和偏振增益。第五章首先对本论文的创新点做了总结，然后结合国外的研究现状和本课题的研究进展对该课题提出了各种可能开展的方案，为有效提高各指标提供了重要的参考价值。 |
| 英文摘要 | With introduction of NII(National Information Infrastructure) and GII(Global information Infrastructure),the higher requirement for the communication, and strict limitation in the micro-wave communication's capacity, weight and power consumption of satellite communication, the transmit speed and capacity can not be improved unlimitedly. In this satellite communication congestion day, there is a big potentiality in optical frequency band communication, which is the optimum scheme for high speed and big capacity communication, and get the common cognition to many experts. Contrast to micro wave communication, Laser communication has many merits :l)it has 3-5 order higher optical frequency than the microwave, can get high digital transmit speed for more usable resource, which meet to the high capacity transmit, and offer time safeguard to realize much more space function assignment.2)laser beam has 3-5 order lower divergence than micro-wave beam, which will improve electromagnetic energy density at the acceptance end face greatly and can be favorable to lighten weight, reduce capacity and power consumption at the termination.3)high secrecy and high anti-interference ability lead to high advantage for military application. At present, good optical emission system is mid-small power semiconductor (or solid laser) with power fiber amplifier system that make up master oscillator power amplifier system, and reception system use the fiber amplifier to amplify signal for preposition amplification in order to increase reception system sensitivity -, the whole system transmit distance and code rate. The requirement in the space laser communication for output laser is high gain, low noise, high beam quality, low nonlinear effect and certain polarization output light. Profound research on the theory and experiment for Yb +-doped fiber amplifier system was developed, and we have got some important results. The thesis consist of five major chapters. The first chapter consist of three parts, in first part, the space communication's survey, development, merits, advances were presented, in second part the general situation of the signal generation and amplification system were presented ,in third part Yb3+-doped fiber amplifier were presented, including: the performance principle, development, preparation, application, coupling with pump light, the major equipment in system, character parameter and measurement, and influence on the fiber communication system. In second chapter we narrated space district of the fiber transmission mode, on the condition of "weak transfer approximation", the fluctuation equation of the step refraction was solved, all kinds of order LP mode transverse power density normalization district was deduced. YDFA was treated as two simply energy system, through the overlapping factor way, the population speed rate equation, pump, signal and amplification spontaneous emission propagation equation were listed, and through the electromagnetic field, the relative equation was listed. In third chapter, we had some innovation research in theory. The first part is introducing, and in second part, by combining the overlapping factor with electromagnetic field, and solving the equation set, we get the multi-mode overlapping factor, and simply effectively analyzed some important characters of the fiber amplifier, in third part, with a certain approximate for the signal pump propagation equation, we deduced mode-locked signal transmission equation in Yb3+-doped fiber amplifier, analyzed some important characters of the fiber amplifier simply and effectively, in fourth part ,based on the micro-prism coupling of side pump ,we winded the fiber into a coil around a object of racetrack shape to make the micro-prism couple the pump light in many positions, by using population speed rate equation, pump and signal propagation equation, we had a numerical simulation, which can not only offer a simple way to design the micro prism but also operate conveniently, and the signal output gain was improved effectively. In the fifth part, we had a numerical, simulation on the Yb3+-doped fiber amplifier gain changed by the fiber bending loss, analyzed the influence of the fiber bending loss on the fiber's gain by changing different radius and made a relative discussion, which will have important instructing to the experiment research. The signal-transverse-mode operation of a multimode Yb3+-doped fiber amplifier in which the gain fiber is coiled to induce significant bend loss for four lowest-order mode(LP01、LP02、LP21 and LP11 mode) was studied numerically. The result indicated by compressing the high order mode can obtain the diffraction-limited beam quality in a fixed bending radius, and obtain the high output power at the same time in MM fiber amplifier. Which is helpful to study the higher pulse energies, peak powers and CW fiber sources to higher average powers while maintaining excellent beam quality, in sixth part, Polarization-dependent gain (PDG) and state of polarization (SOP) of the output signal light in Yb3+-doped fiber amplifiers was studied by stimulation numerically, which showed that PDG of output signal light is not only changed with the input pump power and signal power, input polarization of pump and signal light, but also changed with the doping concentration, the cross-section anisotropy, the fiber length, the phase difference of the fiber and so on. Moreover, we studied SOP of the output signal light, and found that the polarization of output signal light is not only relative to the phase difference of the fiber, polarization of pump and signal light as the non-doped fiber, but also relative to PDG of output signal light, the cross-section anisotropy, the doping concentration and so on, which is different to the non-doped fiber. In seventh part, we numerically simulate the ultrashort pulse's propagation in fiber using the extended model of fiber amplifier, and analyzed the pulse's change with the input pump power, fiber length, the doping concentration and so on, which has a certain instructive to the experiment research .in the last part, we had a numerical simulation on the Yb3+-doped fiber amplifier's nonlinear Refractive Index's and phase's change with the input beam power, input pump power, signal wavelength and made a relative discussion. The fourth chapter we had relative experiment, the first part is introducing, and in second part, we designed the mode-locked system and some parameter of the Yb3+-doped fiber amplifier system, through these parameters, we used the machine design and establish the whole system, and reported the experimental result of the LD end pump Nd: YVO4 laser, in third part we used five meter fiber, through our designed coupling and mode-locked system, 20 dB gain was get, gain change with the pump power and signal power were measured, and some important parameters were analyzed, which agree to the simulation result, in fourth part, we first analyzed all kinds of factors that influence on the Yb3+-doped fiber amplifier self oscillating , and we summarized some ways to reduce the self oscillating and shift its position , which is to decrease the noise coefficient and improve the gain effectively, in fifth part, we used bended fiber to increase the output beam quality , through CCD, we take photos of the output graph, which has important inductive not only to get high out power, but also high output beam quality, in last part, combing with the theory result, focus lens, prism, and Wolston polarization were used and Stokes vector of the output beam was measured, the output polarization and gain were analyzed. In fifth chapter, we first generalize our thesis's originality innovation, and combing with the advances of fiber, we presented some scheme to our system and it is important to guide our experimental system. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15477]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 孔勇. 空间激光通信用掺镱光纤放大器的研究[D]. 中国科学院上海光学精密机械研究所. 2004. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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