【作者】 雷大军；

【导师】 文双春；

【作者基本信息】 湖南大学 ， 计算机应用技术， 2006， 硕士

【摘要】 光纤放大器由于具有高效率、结构紧凑、机械和热稳定性好,以及与单模光纤耦合良好等优点在许多领域有着广泛的应用。大容量、超长距离全光通信系统和超快激光的需求极大的刺激了宽频带光纤放大器的研究。宽频带激光是高功率光纤放大器的发展趋势;随着输入脉冲的带宽不断增大;放大过程中由于丰富的非线性效应使脉冲频谱极大的展宽。在这种趋势下,增益介质的带宽和非均匀加宽效应在放大过程中的作用越来越明显,因此分析增益带宽以及非均匀加宽效应对宽带脉冲放大的影响就显得很重要了。本文主要研究了光纤放大器中宽频带激光脉冲的放大,取得的主要成果如下:第一,建立了一种描述宽频带激光脉冲放大特性的理论模型。已有的Ginzburg-Landau方程仅能描述皮秒脉冲的放大,当脉冲的带宽较大时或与放大器的增益带宽相接近时,Ginzburg-Landau方程就不适用了。我们建立的宽频带激光脉冲放大模型在推导过程中没有作增益带宽近似,因此,可用于计算宽频带脉冲的放大。此外,基于宽频带脉冲放大的物理模型开发了能模拟光脉冲线性和非线性传输过程的程序。第二,利用建立的宽带激光脉冲放大的理论模型,采用分步傅里叶方法研究了增益带宽、脉冲的初始啁啾、失谐以及增益系数等因素对脉冲频谱的影响。理论结果表明,放大器有限的增益带宽是脉冲质量的主要限制,它使得宽带脉冲频谱产生畸变,由此影响了压缩效率。初始啁啾使脉冲的频谱趋向于对称,并减缓了频谱的展宽。当脉冲的载频和增益介质的中心频率不重合时,增益带宽越窄,脉冲频谱畸变越严重。随着放大器增益系数的增加,在一定情况下产生超连续谱。第三,研究了宽带啁啾脉冲在非均匀加宽介质中的放大特性。在啁啾较大时,啁啾脉冲在时域和频域满足线性关系。利用啁啾脉冲的这种线性关系,将总的啁啾脉冲看成是由一系列时间上依次排列的准单色子脉冲所组成,利用已有的准单色脉冲放大模型来计算非均匀加宽系统中的脉冲放大。结果表明,非均匀加宽系统中输出脉冲的前后沿对称;随着脉冲带宽的增加,增益变窄效应和脉冲畸变越来越显著,且脉冲波形过渡到增益介质的线型形状。更多还原

【Abstract】 Fiber amplifiers are widely used for pulse amplification owing to their intrinsically robust, good coupling efficiency, high reliability and compactness. The desirability of high-capacity, long-distance, all-optical communication systems and ultrafast lasers have motivated extensively studies of the ultrabroad bandwidth pulse amplification. The ultrabroadband laser is the trend of high power lasers. As the pulse grows shorter, the spectrum becomes broader, and is greatly broaden by the versatile nonlinear effects in fiber amplifier. Under such situation, the effect of gain bandwidth and inhomogeneous broadening for the amplification of ultrabroad bandwidth pulse in fiber amplifier becomes important. Therefore, the exploration and investigation on the amplification of ultrabroad bandwidth pulse in fiber amplifier is of great importance and essential. The main research results are listed below:Firstly, an extended version of the nonlinear Schr?dinger equation which describes the amplification of ultrabroadband pulse is derived. The existing Ginzburg-Landau model is valid only when the amplifier gain bandwidth is significantly larger than the signal’s spectral bandwidth. Since the equation that we work out does not assume that the pulse’s spectral width remains small in comparison with the gain bandwidth, it can be used to describe the ultrabroad bandwidth pulse amplification. In addition, we have independently developed the computer program which simulates the process of broadband pulse amplification based on the amplification equation of ultrabroadband pulse.Secondly, on the basis of the amplification equation of ultrabroadband pulse, the amplification of chirped-free or chirped pulse with ultrabroad bandwidth in the fiber amplifier is considered by the means of split-step Fourier method. Also, the effect of the gain bandwidth of the amplifier is analyzed. The effects of the relation between the bandwidth of the pulse and the gain bandwidth of amplifier in amplification are studied numerically. The results show that when the gain bandwidth of fiber amplifier is comparable to the bandwidth of pulse, it plays an important role in determining the final spectrum shape. And when the gain is large enough, the supercontinuum comes into being.Thirdly, according to the characteristics of linearly chirped pulse, the input chirped pulses are considered to consist of many quasi monochromatic pulses with更多还原