【摘要】：皮秒光纖激光器因?yàn)槠浞�(wěn)定性高、容易啟動、脈沖窄、價格低廉等優(yōu)點(diǎn)而被廣泛研究。產(chǎn)生的皮秒脈沖由于高峰值功率、高重復(fù)率、傳輸距離遠(yuǎn)、精度高、能量大等特點(diǎn)而成為新興的研究熱門。結(jié)合可飽和吸收鏡(SESAM鏡)的特性和光纖結(jié)構(gòu)材質(zhì)的優(yōu)越性,使得基于SESAM鏡的皮秒光纖激光器更是成為了各領(lǐng)域研究重點(diǎn)。因此對其進(jìn)行的理論數(shù)值研究,不僅能降低實(shí)驗(yàn)的繁瑣步驟,更能直觀的反應(yīng)出各參數(shù)對脈沖的影響。所以這種理論分析是非常有必要的。通常SESAM鏡的結(jié)構(gòu)主要包含有可飽和吸收體和半導(dǎo)體反射鏡兩個部分。對不同的光強(qiáng)吸收能力不一樣,在未達(dá)到可飽和吸收光強(qiáng)前,吸收損耗能力隨光強(qiáng)的變大而逐漸變?nèi)酢Ｋ圆粌H能充當(dāng)腔鏡,并且能實(shí)現(xiàn)脈沖鎖模,具有很好的鎖模效果,從而降低了結(jié)構(gòu)的復(fù)雜程度。本論文主要研究的是一種基于SESAM鏡的線性腔結(jié)構(gòu)皮秒光纖激光器。主要從摻鐿光纖、SESAM鏡、布拉格光柵(FBG)等角度,利用不同的公式方程,對脈沖波形及功率的影響,以及增益介質(zhì)的選擇進(jìn)行了數(shù)值分析。主要研究內(nèi)容如下:1、分析了所研究的光纖激光器結(jié)構(gòu)和原理,詳細(xì)推導(dǎo)了數(shù)值分析所用到的公式,分析了光纖的傳輸特性,主要從光纖的色散和非線性兩個方面討論了其對脈沖寬度及形狀的影響。2、詳細(xì)分析了增益光纖的結(jié)構(gòu),以及選取Yb3+為增益介質(zhì)的原因,并且利用MATLAB及速率方程,在兩個腔鏡的反射率、泵浦功率、摻雜濃度、光纖長度等方面對腔內(nèi)脈沖功率分布及腔外脈沖功率變化做了一個系統(tǒng)的分析。3、闡述了SESAM鏡的結(jié)構(gòu)優(yōu)點(diǎn)及發(fā)展情況,依據(jù)SESAM鏡的鎖模特性,按照fox-li迭代的方法,利用線性薛定諤方程以及傳輸方程對SESAM鏡的調(diào)制深度對脈沖的影響進(jìn)行了數(shù)值分析。找出了當(dāng)調(diào)制深度△R大于3.8%才能保證理想脈沖效果。4、闡述了FBG的特性及制作方法和對應(yīng)的具體公式,在此基礎(chǔ)上改變FBG的長度及耦合系數(shù),來討論其對脈寬的變化和形成畸變的原因。并對脈沖傳輸特性進(jìn)行了分析,得到當(dāng)4.9nm≤LFBG≤7.9nm和8.1nm≤LFBG≤11.1nm,能夠得到很好的脈沖輸出。
[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，

本文編號：2123236