混合增益型随机分布反馈光纤激光器特性研究

发布时间：2018-05-18 13:27

本文选题：光纤激光器 + 随机激光　；参考：《电子科技大学》2015年硕士论文

【摘要】：2010年,S.K.Turitsyn等学者提出了随机分布反馈光纤激光器(RDF-FL)的概念,即基于单模光纤(SMF)中随机分布的瑞利散射(RS)和拉曼放大增益的光纤激光器。得益于其稳定连续的输出、很高的光子简并度和较低的空间相干性,RDF-FL在激光光源,光通信和光传感等应用领域具有独特优势,其中涉及的激光物理,无序系统理论及非线性光学等问题也具有重要的学术价值。目前,基于SMF的RDF-FL增益由拉曼(Raman)放大提供,其激射阈值较高、需要光纤长度较长,且输出光谱依赖于SMF的增益谱,如随着泵浦功率的增加,激光光谱会出现双峰结构,峰值也会移动。基于有源光纤的RDF-FL阈值很低,但在短距离的有源光纤中瑞利散射效应较弱,通常无法得到随机激光激射现象。鉴于上述原因,本文通过两种不同增益类型光纤的组合及一定反馈增强手段,实现了高效、低阈值的随机激光输出。主要工作和发现如下:首先,基于非线性薛定谔方程并融入拉曼增益、光纤损耗及瑞利散射的频谱相关性,获得拉曼放大系统的稳态传输方程;通过Giles速率方程获得增益与泵浦的关系,由此建立EDF增益系统的仿真模型;利用边界条件,结合两类增益系统的稳态传输模型,实现了混合光纤结构的理论仿真。结果能够反映RDF-FL的功率分布、阈值及频谱演变特性,且与实验结果吻合。其次,我们实验分析了EDF的随机激光激射情况。在中心波长1480 nm泵浦单独激励下,100 m EDF的自发放大辐射谱(ASE)上出现了少量随机模式激射。当加入SMF后,不管是非对称还是对称结构,单独泵浦下的EDF产生的光谱都在1569 nm波长附近出现了大量无序混乱的随机激射模式,且ASE背景噪声明显被压窄。然后,我们分析了非对称结构下的RDF-FL输出特性。EDF在腔内时,可为SMF中产生的背向散射光提供增益,前向传输的功率输入-输出曲线没有明显的阈值现象,且几乎不随EDF的泵浦功率变化;后向传输的激光存在明显的阈值,且随着EDF泵浦功率的增加,曲线整体向高功率平移。当EDF不在腔内及从外部提供种子光时,前后两端同样得到了宽带的输出光谱,而且EDF泵浦的功率可以调控前后向传输的激光的出光效率。最后,我们分析了对称结构下的RDF-FL输出特性。混合增益条件下,随机激射的阈值极大的降低,光谱输出经历了从混乱-稳定-混乱-稳定的交替变化过程,稳定输出时,光谱为单波长、无模式的随机激光输出,其线宽约1 nm、信噪比大于25 dB,且中心波长稳定,几乎不随泵浦功率变化。
[Abstract]:In 2010, S. K. Turitsyn and others put forward the concept of random distributed feedback fiber laser (RDF-FL), which is based on random distributed Rayleigh scattering RSs and Raman gain fiber lasers. Thanks to its stable and continuous output, high photon degeneracy and low spatial coherence RDF-FL have unique advantages in applications such as laser light sources, optical communications and optical sensing, which involve laser physics. The theory of disorder system and nonlinear optics are also of great academic value. At present, the RDF-FL gain based on SMF is provided by Raman Raman amplification, which requires a long optical fiber length, and the output spectrum depends on the gain spectrum of SMF. For example, with the increase of pump power, the laser spectrum will have a double peak structure. The peak also moves. The threshold of RDF-FL based on active fiber is very low, but the Rayleigh scattering effect is weak in the short distance active fiber. In view of the above reasons, the high efficient, low threshold random laser output is realized by the combination of two kinds of optical fiber with different gain types and a certain feedback enhancement method. The main works and findings are as follows: firstly, based on the nonlinear Schrodinger equation and the spectral correlation of Raman gain, fiber loss and Rayleigh scattering, the steady state propagation equation of Raman amplification system is obtained. The relationship between gain and pump is obtained by Giles rate equation, and the simulation model of EDF gain system is established, and the theoretical simulation of hybrid optical fiber structure is realized by using boundary conditions and the steady-state transmission model of two kinds of gain systems. The results can reflect the power distribution, threshold and spectrum evolution characteristics of RDF-FL, and are in good agreement with the experimental results. Secondly, we analyze the random laser emission of EDF experimentally. A small number of random mode excitations have been observed on the spontaneous amplified emission spectra of 100m EDF pumped at a central wavelength of 1480 nm. With the addition of SMF, no matter asymmetric or symmetric structure, the spectra produced by EDF pumped by single pump have a large number of disordered random emission modes near the wavelength of 1569 nm, and the background noise of ASE is obviously compressed. Then, we analyze the output characteristics of RDF-FL in asymmetric structure. When the RDF-FL is in the cavity, it can provide the gain for the backscattered light generated in SMF. The power input-output curve of forward transmission has no obvious threshold phenomenon. The back propagation laser has obvious threshold, and the curve shifts to high power with the increase of EDF pump power. When the EDF does not provide seed light in the cavity and from the outside, the broadband output spectrum is obtained at both the front and the back, and the output efficiency of the backward and backward laser can be regulated by the power pumped by the EDF. Finally, we analyze the output characteristics of RDF-FL in symmetric structure. Under the condition of mixed gain, the threshold of random laser emission is greatly reduced, and the spectral output goes from chaos to stability and from chaos to stability. When the output is stabilized, the spectrum is a single wavelength, modeless random laser output. The line width is about 1 nm, the SNR is more than 25 dB, and the center wavelength is stable, almost no change with pump power.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN248

【共引文献】