基于SESAM镜的皮秒光纤激光器腔内脉冲传输特性数值研究

发布时间：2018-07-15 07:10

【摘要】：皮秒光纤激光器因为其稳定性高、容易启动、脉冲窄、价格低廉等优点而被广泛研究。产生的皮秒脉冲由于高峰值功率、高重复率、传输距离远、精度高、能量大等特点而成为新兴的研究热门。结合可饱和吸收镜(SESAM镜)的特性和光纤结构材质的优越性,使得基于SESAM镜的皮秒光纤激光器更是成为了各领域研究重点。因此对其进行的理论数值研究,不仅能降低实验的繁琐步骤,更能直观的反应出各参数对脉冲的影响。所以这种理论分析是非常有必要的。通常SESAM镜的结构主要包含有可饱和吸收体和半导体反射镜两个部分。对不同的光强吸收能力不一样,在未达到可饱和吸收光强前,吸收损耗能力随光强的变大而逐渐变弱。所以不仅能充当腔镜,并且能实现脉冲锁模,具有很好的锁模效果,从而降低了结构的复杂程度。本论文主要研究的是一种基于SESAM镜的线性腔结构皮秒光纤激光器。主要从掺镱光纤、SESAM镜、布拉格光栅(FBG)等角度,利用不同的公式方程,对脉冲波形及功率的影响,以及增益介质的选择进行了数值分析。主要研究内容如下:1、分析了所研究的光纤激光器结构和原理,详细推导了数值分析所用到的公式,分析了光纤的传输特性,主要从光纤的色散和非线性两个方面讨论了其对脉冲宽度及形状的影响。2、详细分析了增益光纤的结构,以及选取Yb3+为增益介质的原因,并且利用MATLAB及速率方程,在两个腔镜的反射率、泵浦功率、掺杂浓度、光纤长度等方面对腔内脉冲功率分布及腔外脉冲功率变化做了一个系统的分析。3、阐述了SESAM镜的结构优点及发展情况,依据SESAM镜的锁模特性,按照fox-li迭代的方法,利用线性薛定谔方程以及传输方程对SESAM镜的调制深度对脉冲的影响进行了数值分析。找出了当调制深度△R大于3.8%才能保证理想脉冲效果。4、阐述了FBG的特性及制作方法和对应的具体公式,在此基础上改变FBG的长度及耦合系数,来讨论其对脉宽的变化和形成畸变的原因。并对脉冲传输特性进行了分析,得到当4.9nm≤LFBG≤7.9nm和8.1nm≤LFBG≤11.1nm,能够得到很好的脉冲输出。
[Abstract]:Picosecond fiber laser is widely studied because of its high stability, easy to start, narrow pulse and low price. The picosecond pulse has become a new research hotspot because of its high peak power, high repetition rate, long transmission distance, high precision and high energy. Combined with the characteristics of saturable absorber mirror (SESAM) and the superiority of fiber structure material, the picosecond fiber laser based on SESAM mirror has become the focus of research in all fields. Therefore, the theoretical numerical study can not only reduce the tedious steps of the experiment, but also directly reflect the influence of the parameters on the pulse. So this kind of theoretical analysis is very necessary. The structure of SESAM mirror consists of saturable absorber and semiconductor mirror. For different light intensity, the absorption loss becomes weaker with the increase of light intensity before the saturation absorption intensity is reached. Therefore, it can not only act as mirror, but also realize pulse mode-locking, which has a good effect of mode-locking, thus reducing the complexity of the structure. In this thesis, a linear cavity picosecond fiber laser based on SESAM mirror is studied. The influence of pulse waveform and power and the choice of gain medium are numerically analyzed by using different formula equations from the angles of ytterbium-doped fiber mirror and fiber Bragg grating (FBG). The main research contents are as follows: 1. The structure and principle of the fiber laser studied are analyzed, the formulas used in numerical analysis are derived in detail, and the transmission characteristics of the fiber are analyzed. The influence of fiber on pulse width and shape is discussed from two aspects of dispersion and nonlinearity. The structure of gain fiber and the reason of choosing Yb3 as gain medium are analyzed in detail, and the MATLAB and rate equation are used. A systematic analysis of the distribution of pulse power in cavity and the variation of pulse power outside cavity is made in the aspects of reflectivity, pump power, doping concentration and fiber length of the two mirrors. The structural advantages and development of the SESAM mirror are described. According to the mode-locking characteristics of the SESAM mirror and according to the fox-li iterative method, the effects of the modulation depth of the SESAM mirror on the pulse are numerically analyzed by using the linear Schrodinger equation and the transmission equation. The ideal pulse effect .4 can be guaranteed only when the modulation depth R is more than 3.8%. The characteristics, fabrication methods and corresponding formulas of FBG are described. On the basis of this, the length and coupling coefficient of FBG are changed. To discuss the variation of pulse width and the cause of distortion. The characteristics of pulse transmission are analyzed. It is shown that when 4.9nm 鈮，

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