低抖动锁模光纤激光器及其泵浦产生超连续谱的展宽机理研究

发布时间：2018-03-01 01:00

本文关键词： 锁模光纤激光器超连续谱光怪波超连续谱相干度硫化物波导　出处：《华中科技大学》2015年博士论文　论文类型：学位论文

【摘要】：低噪声被动锁模光纤激光器作为一种特殊的脉冲激光器,因其能实现超低的强度噪声和时间抖动而被广泛应用在光学采样、频率计量等领域,同时还是产生超稳定光纤超连续谱(Supercontinuum, SC)的理想泵浦光源。本论文以激光器作为突破口,设计并实现了一种高重复频率低抖动锁模光纤激光器,通过优化腔结构从而降低激光器的噪声。并利用该激光器作为泵浦光源,在已有的理论基础上进一步研究皮秒脉冲泵浦超连续谱的展宽机理并优化其噪声特性与相干性。本论文的主要研究成果如下： (1)通过对泵浦相对强度噪声(RIN)到激光器RIN的转换率进行建模发现,在低偏移频率区域,RIN的转换率大小是以激光器斜率效率大小的平方为尺度的。定量证明了高重复频率低抖动锁模光纤激光器的腔内泵浦反射在有效减小锁模阈值并增大斜率效率的同时也会恶化激光器的噪声特性,为光纤锁模激光器的设计提供了新的优化思路。 (2)利用光纤延迟脉冲干涉技术,在实验上证明了相邻脉冲的平均干涉谱条纹可见度可作为SC产生过程中的相位波动(即光谱相位相干度)的判据。并利用低噪声锁模激光器作为泵浦光源,在皮秒量级脉冲宽度下,深入研究了SC产生过程中调制不稳定区域对全带宽光谱相位相干度的影响机理。 (3)利用低噪声锁模激光器作为泵浦光源,从实验上深入研究了光怪波(Rogue Waves)产生的原因：受噪声驱动的调制不稳定性。当泵浦激光器中的随机量子噪声恰巧发生在调制不稳定性增益谱的最大值处或附近时,会大大增强SC的调制不稳定性强度,增大SC的光谱宽度,从而产生光怪波。并从理论上解释了利用连续光和泵浦光共同作用下使得光纤SC的调制不稳定性增强的原因：谐振种子调制不稳定性的级联四波混频和布拉格散射。研究发现在给定色散值和非线性系数后,存在一个关键功率值cr,当泵浦功率小于该值时,则不会发生种子光增强调制不稳定性效应的现象。 (4)通过理论与仿真研究并设计了基于硫化物As2Se3波导产生SC,并分析了所产生SC的相干度。硫化物As2Se3具有极高的非线性折射率n2,因而能够有效的降低泵浦脉冲的功率并缩短波导长度,从而降低脉冲的传输损耗。通过对平面波导进行色散管理,得到理想的色散曲线。结果表明优化后的波导仅需峰值功率为24W初始泵浦激光,通过长度约10mm的波导,就能产生相干性较好的SC。
[Abstract]:As a special pulse laser, low noise passive mode-locked fiber laser is widely used in optical sampling, frequency measurement and other fields because of its ability to achieve ultra-low intensity noise and time jitter. At the same time, it is also an ideal pump source for producing supercontinuum (SCS) of ultra-stable fiber. In this paper, a high repetition rate and low jitter mode-locked fiber laser is designed and implemented with the laser as the breakthrough point. By optimizing the cavity structure to reduce the noise of the laser, and using the laser as the pump light source, Based on the existing theories, the broadening mechanism of picosecond pulse pumping supercontinuum spectrum is further studied and its noise characteristics and coherence are optimized. The main results of this thesis are as follows:. 1) by modeling the conversion rate from pump relative intensity noise to laser RIN, we find that, The conversion rate of RIN in low offset frequency region is measured by square of slope efficiency of laser. It is proved quantitatively that intracavity pump reflection of high repetition rate and low jitter mode-locking fiber laser can effectively reduce mode-locking threshold. And increasing the slope efficiency will also worsen the noise characteristics of the laser. It provides a new optimization idea for the design of fiber mode-locked laser. Using optical fiber delay pulse interferometry, It is proved experimentally that the visibility of the average interference fringes of adjacent pulses can be used as a criterion for the phase fluctuation (i.e. spectral phase coherence) in the process of SC generation, and the low noise mode-locked laser is used as the pump light source. At picosecond pulse width, the effect of modulation instability on the full bandwidth spectral phase coherence during SC generation is studied. Using low noise mode-locked laser as pump source, In this paper, the causes of Rogue Waves-induced modulation instability driven by noise are studied experimentally. When the random quantum noise in the pump laser happens to occur at or near the maximum value of the modulation instability gain spectrum, It will greatly enhance the modulation instability of SC and increase the spectral width of SC. The reason why the modulation instability of optical fiber SC is enhanced by the interaction of continuous light and pump light is explained theoretically: the cascaded four-wave mixing and Bragg dispersion with resonant seed modulation instability. The study found that, given the dispersion and nonlinear coefficients, There is a critical power value cr. when the pump power is less than this value, the effect of seed light-enhanced modulation instability will not occur. (4) by theoretical and simulation study, the SC-generated As2Se3 waveguide based on sulfide is designed and the coherence degree of SC generated is analyzed. Sulfide As2Se3 has extremely high nonlinear refractive index n _ 2, so it can effectively reduce the power of pump pulse. And shorten the length of the waveguide, In order to reduce the transmission loss of the pulse, the ideal dispersion curve is obtained by the dispersion management of the planar waveguide. The results show that the optimized waveguide only needs a 24W initial pumped laser and passes through the waveguide with a length of about 10mm. SCS with good coherence can be produced.
【学位授予单位】：华中科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TN248

【相似文献】