随机光纤激光器的功率提升及光场调控技术研究

发布时间：2019-03-15 13:32

【摘要】：当前高功率光纤激光放大系统中,基于振荡器的常规种子源存在时域不稳定的现象,进而导致激光的高峰值功率并降低非线性效应阈值,限制系统功率的进一步提升。随机光纤激光器作为一种结构简单、时域稳定的新型光纤激光器,有望成为种子源时域不稳的解决方案。本文以随机光纤激光器为研究对象,分析其在功率提升和光场调控上的实现方式与应用潜力。随机光纤激光器利用长距离被动光纤中的拉曼增益和随机分布式反馈,具有结构简单、转换效率高、光谱平滑、时域稳定等显著特点。本文基于激光速率方程,确定合适的边界条件并考虑瑞利散射的影响,构建随机光纤激光器的理论模型。首先,基于构建的理论模型,通过数值模拟计算随机光纤激光器受光纤长度、端面反馈等因素影响的激光阈值特性;同时考虑二阶拉曼斯托克斯光的阈值,计算不同光纤长度下随机光纤激光器前、后向输出的最高功率与光学转换效率。其次,修改边界条件建立半腔结构的随机光纤激光器理论模型,研究半腔结构设计对激光阈值和沿光纤功率分布的影响。计算结果表明,半腔结构的随机光纤激光器可以有效降低出光阈值,并且将前、后向传输的随机激光集合起来实现单端的高功率、高效率输出。最后,着重对短腔的随机光纤激光器进行数值模拟,发现减小光纤长度是继续提升随机激光器最高输出功率的直接方案,并且短腔模型的阈值对寄生反馈尤其敏感。以上的理论分析与数值计算结果表明,构成半腔结构的短腔随机光纤激光器是获得高功率、高效率随机光纤激光输出的理想方案。对实现随机光纤激光功率提升的方案进行了实验研究。首先基于数值计算结果设计短腔随机光纤激光器系统,采用120 m被动光纤与半腔结构,获得近200 W1173 nm的随机光纤激光输出,光学转换效率约89%,功率和效率均为已公开报道的国际最高水平。其次,构建1070 nm波段的随机光纤激光器实验系统,通过对比时域和频域特征分析其噪声滤波特性,验证泵浦噪声被有效滤除的随机激光发射过程并获得时域稳定的激光输出,首次实现随机光纤激光工作波长与掺镱光纤放大器的增益谱相匹配。最后,利用构建的1070 nm随机光纤激光器作为时域稳定的种子源,基于MOPA结构的掺镱光纤放大器进行千瓦级的功率放大,功率放大的过程中未观察到光谱展宽现象,最终实现1030 W半高全宽约1 nm的激光输出,放大过程中斜率效率约为79.7%。该高功率放大过程中的光谱不展宽(spectral-broadening-free)现象为高功率窄线宽激光以及光谱合成等方面的研究提供了重要参考。对随机光纤激光器光谱、模式的调控技术进行了实验探索。基于可调谐滤波器和保偏光纤环形镜,设计实现分别具有可调谐和多波长光谱特性的随机光纤激光器系统,获得的可调谐和多波长光谱均具有数十纳米的宽光谱范围和较高的信噪比。基于少模光纤布拉格光栅和随机分布式反馈,并利用错芯熔接方式激发高阶模,获得空间模式可调的随机分布式反馈光纤激光输出;另外通过全保偏的随机光纤激光器结构设计和光纤弯曲缠绕的偏振模选择技术,国际上首次实现线偏振的随机光纤激光输出。
[Abstract]:In the current high-power optical fiber laser amplification system, the time-domain instability phenomenon exists in the conventional seed source based on the oscillator, so that the peak value power of the laser is reduced and the non-linear effect threshold is reduced, and further improvement of the system power is limited. As a new type of fiber laser with simple structure and stable time-domain, the random-fiber laser is expected to be a solution to the time-domain instability of the seed source. In this paper, a random fiber laser is used as a research object to analyze its implementation and application potential in power and light field control. The random fiber laser uses the Raman gain and the random distributed feedback in the long-distance passive optical fiber, and has the characteristics of simple structure, high conversion efficiency, smooth spectrum, stable time domain and the like. In this paper, based on the laser rate equation, the appropriate boundary conditions are determined and the influence of Rayleigh scattering is taken into account, and the theoretical model of the random fiber laser is constructed. Firstly, based on the constructed theoretical model, the laser threshold characteristic affected by the factors such as the optical fiber length and the end surface feedback of the random optical fiber laser is simulated by numerical simulation; meanwhile, the threshold value of the second-order Raman Stokes light is taken into account, and the random optical fiber laser is calculated before the different optical fiber lengths are calculated, The highest power and the optical conversion efficiency of the backward output. Secondly, the effect of the half-cavity structure design on the laser threshold and the power distribution along the fiber is studied. The results show that the random-fiber laser of the half-cavity structure can effectively reduce the light-emitting threshold and set up the random laser at the front and back to realize the high-power and high-efficiency output of the single-end. In the end, the numerical simulation of the short-cavity random-fiber laser is focused on, and it is found that the reduction of the length of the fiber is a direct solution to the increase of the maximum output power of the random laser, and the threshold of the short-cavity model is particularly sensitive to the parasitic feedback. The above theoretical analysis and numerical calculation results show that the short-cavity random-fiber laser making up the half-cavity structure is an ideal solution for obtaining high-power and high-efficiency random-fiber laser output. The experimental research of the scheme for realizing the laser power of the random optical fiber is carried out. First, based on the numerical results, a short-cavity random-fiber laser system is designed, and a 120m passive optical fiber and a half-cavity structure are adopted to obtain a random optical fiber laser output of nearly 200 W1173 nm, the optical conversion efficiency is about 89%, and the power and the efficiency are the highest levels of the published report. secondly, constructing a random fiber laser experiment system of 1070 nm wave band, analyzing the noise filtering characteristic of the frequency domain and the frequency domain characteristic, verifying that the pump noise is effectively filtered out by a random laser emission process and obtaining a time-domain stable laser output, And the wavelength of the random optical fiber laser is matched with the gain spectrum of the doped fiber amplifier for the first time. and finally, using the constructed 1070 nm random fiber laser as a seed source with stable time domain, the doped fiber amplifier based on the MOPA structure is used for carrying out the power amplification of the kilowatt level, the spectrum broadening phenomenon is not observed in the process of power amplification, and the laser output of the 1030W semi-high full width of about 1 nm is finally realized, The slope efficiency in the amplification process is about 79.7%. The spectrum-free-free phenomenon in the high power amplification process provides an important reference for the research of high-power narrow line-width laser and spectral synthesis. The control technology of the spectrum and mode of the random optical fiber laser has been explored. Based on the tunable filter and the polarization-maintaining fiber ring-shaped mirror, a random optical fiber laser system with tunable and multi-wavelength spectral characteristics is designed, and the obtained tunable and multi-wavelength spectrum both have a wide spectral range of tens of nanometers and a higher signal-to-noise ratio. a random distributed feedback optical fiber laser output with adjustable spatial mode is obtained based on the small-mode fiber Bragg grating and the random distributed feedback, and the high-order mode is excited by the cross-core welding mode; In addition, the optical fiber laser output of the linear polarization is realized for the first time on the basis of the design of the whole polarization-maintaining random fiber laser and the polarization mode selection technique of the fiber bending and winding.
【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】：TN248

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