基于光纤放大器的超连续谱光源研究

发布时间：2018-06-03 03:35

本文选题：超连续谱 + 光纤放大器　；参考：《国防科学技术大学》2015年博士论文

【摘要】：超连续谱光源的宽光谱、高亮度的优异特性使得其在光谱学、生物医学、高光谱成像以及光电对抗等领域有着重要的应用前景。在光纤放大器中直接产生超连续谱是实现高功率超连续谱光源的有效途径,该方法将激光增益放大过程与非线性效应结合在一起,使得系统简单紧凑,但同时也使得其中的物理过程十分复杂。本文对基于光纤放大器的超连续谱光源开展了理论与实验研究,进行了超连续谱光源的非相干合束技术研究,提出了超连续谱光源的光束质量评价方法。主要内容包括:结合动态速率方程组与广义非线性薛定谔方程,建立了光纤放大器中超连续谱产生的理论模型,实现了对脉冲序列在增益光纤中的功率放大、非线性光谱及时域演化等动态过程的数值模拟,可以表征光纤放大器中超连续谱产生的物理过程。以掺镱光纤放大器为例,理论与实验研究了光纤长度与信号脉冲宽度对放大器中超连续谱产生的影响,获得了拓展光谱范围、提高输出功率的条件。结果表明增益光纤越长,拉曼效应阈值越低,孤子自频移作用距离越长,超连续谱的光谱越宽,同时输出功率越低;在增益光纤之后熔接一段被动光纤有助于光谱的拓展与平坦化。但是过长的光纤将会使过多功率转移到2μm以上,引入较大损耗,降低输出功率,因此需要优化增益光纤与被动光纤长度,以保证超连续谱光谱宽度与输出功率。信号光为超短脉冲(飞秒至皮秒量级)时,在光谱展宽的初始阶段主要受到自相位调制的作用,因此最终光谱展宽很小;而当脉冲宽度大于10 ps时,信号光谱将在受激拉曼散射效应的作用下拓展至反常色散区,从而使光谱极大展宽,最终形成超连续谱,且脉宽越宽,光谱展宽越宽。基于保偏光纤放大器实现了百瓦级线偏振超连续谱光源。研究了保偏光纤熔接对轴方式对超连续谱偏振特性的影响,在大模面积保偏光纤放大器中实现了最高功率124.8 W的超连续谱光源输出,这是文献报道的保偏光纤放大器输出超连续谱光源的最高功率,光谱覆盖1060 nm-1800 nm,全光谱偏振消光比为84.85%。设计与制作了光纤宽谱功率合束器,通过理论研究获得了宽谱范围内具有高传输效率的合束器制作原则:入射光纤束的包层均拉锥至被输出光纤纤芯包围,同时拉锥过渡区足够长(通常大于1 cm)。使用制作的光纤宽谱功率合束器开展了超连续谱非相干合束的原理性实验,证实了超连续谱光源非相干合束的可行性;其次实现了功率300 W光谱范围1060 nm-1600 nm的超连续谱光源非相干合束输出。设计制作了输出光纤纤芯100μm的宽谱合束器,最终实验获得了1064 nm处M2因子~9的输出功率200 W的超连续谱非相干合束光源,光谱范围覆盖1060nm-1900 nm,超连续谱功率传输效率达96.6%。引入功率谱重心的概念,提出了三种超连续谱光源光束质量的评价因子。对窄带激光的空间传输模型进行拓展,推导了超连续谱光源的空间传输模型,验证了提出的超连续谱光束质量评价方法的合理性。对实验中获得的不同功率与光谱分布的超连续谱光源的光束质量进行了评价与比较,结果表明提出的三种评价因子均可以综合体现传输模式以及功率谱分布对光束质量的影响,适合对超连续谱光源的整体光束质量进行评价与比较,对高光束质量超连续谱光源的获得及其实际应用具有指导意义。
[Abstract]:The wide spectrum and high luminance of the supercontinuous spectral light have an important application prospect in the fields of spectroscopy, biomedicine, hyperspectral imaging and optoelectronic countermeasures. It is an effective way to produce supercontinuous spectra directly in optical fiber amplifier. The combination of linear effect makes the system simple and compact, but also makes the physical process very complicated. In this paper, the theoretical and Experimental Research on the supercontinuous spectral light source based on optical fiber amplifier is carried out in theory and experiment. The non coherent beam technology of the supercontinuous spectral light source is studied and the method of evaluating the beam quality of the supercontinuous spectral light source is proposed. The main contents include: combining the dynamic rate equation group and the generalized nonlinear Schrodinger equation, the theoretical model of the supercontinuum generation in the optical fiber amplifier is established, and the numerical simulation of the power amplification, nonlinear spectrum and the time domain evolution of the pulse sequence in the gain fiber can be realized, and the supercontinuum in the optical fiber amplifier can be characterized. Taking the ytterbium doped fiber amplifier as an example, the effect of the length of the fiber and the pulse width on the supercontinuum generation in the amplifier is studied theoretically and experimentally. The conditions of expanding the spectrum range and increasing the output power are obtained. The results show that the longer the gain fiber is, the lower the threshold value of the Raman effect, the self frequency shift distance of the soliton. The longer the spectrum of the supercontinuum is wider and the output power is lower, the fusion of a passive optical fiber after the gain fiber will help to expand and flatten the spectrum. However, the excessive fiber will transfer the excess power to more than 2 m, which will lead to large loss and reduce the output power. Therefore, the length of the gain fiber and the passive fiber will be optimized, so the length of the gain fiber and the passive fiber will be optimized. The spectrum width and output power are guaranteed. When the signal is ultrashort pulse (femtosecond to picosecond), the initial phase of the spectrum broadening is mainly modulated by self phase modulation, so the final spectrum broadening is very small, and when the pulse width is more than 10 PS, the signal spectrum will be expanded to abnormal under the effect of stimulated Raman scattering. The dispersion region, which makes the spectrum broadened greatly, eventually forms the supercontinuum spectrum, and the wider the pulse width, the wider the spectrum broadening. Based on the polarization maintaining fiber amplifier, the 100 watts line polarization supercontinuous spectral light source is realized. The effect of the axis mode on the polarization characteristics of the supercontinuum is studied. The high power 124.8 W supercontinuous spectral light source output is the highest power of the output supercontinuous spectral light source of the biased fiber amplifier reported in the literature. The spectrum covers 1060 nm-1800 nm and the optical spectrum polarization extinction ratio is designed and made the optical fiber wide spectrum power beam splitter. The high transmission efficiency in the wide spectrum range is obtained through the theoretical study. The principle of beam closing is that the cladding cones of the incident fiber bundle are encircled to the output fiber core, and the transition region of the taper is long enough (usually more than 1 cm). The non coherent beam output of a supercontinuous spectral light source with a power 300 W spectrum range of 1060 nm-1600 nm is presented. A wide spectrum beam splitter is designed and produced for the output fiber core of 100 u m. The final experiment obtains a supercontinuous spectral non coherent beam source with the output power of 200 W of M2 factor ~9 at 1064 nm, and the spectral range covers 1060nm-1900 nm, and the supercontinuous spectrum power transmission. The transmission efficiency reaches the concept of 96.6%. introducing the center of gravity of the power spectrum. Three kinds of evaluation factors of the beam quality of the supercontinuous spectral light source are put forward. The space transmission model of the narrow band laser is expanded and the space transmission model of the supercontinuous spectral light source is deduced. The rationality of the proposed super continuous spectral beam quality evaluation method is verified. The beam quality of the supercontinuous spectral light source with the same power and the spectral distribution is evaluated and compared. The results show that the three evaluation factors can comprehensively reflect the effect of the transmission mode and the power spectrum distribution on the beam quality. It is suitable for the evaluation and comparison of the overall beam quality of the supercontinuous spectral light source, and the high beam quality superconnection. The continuous spectrum source and its practical application are instructive.
【学位授予单位】：国防科学技术大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TN722

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