【作者】 曹辉；

【导师】 孙军强；

【作者基本信息】 华中科技大学 ， 光学工程， 2006， 博士

【摘要】 光纤参量放大器(FOPA)是未来密集波分复用全光网络的关键器件,它具有许多优点,例如:高增益,高饱和输出功率,低噪声,工作在任意波长,宽带宽,内在的增益反应时间短等。本文围绕光纤参量放大器的饱和增益、增益平坦化、带宽、最佳光纤长度、脉冲信号传输和波长转换应用等方面进行了深入的理论和实验研究,具体内容如下:　(1)研究了光纤参量放大器的基本理论。由基本传播方程出发,推导出描述光纤参量放大器中光波演变情况的耦合非线性薛定谔方程。通过分析光纤参量放大器增益带宽与光纤参数、光纤长度、泵浦功率、系统结构的关系,给出了提高增益带宽的具体方法。实验研究了FOPA的增益谱,实验结果与理论分析结果相吻合。　(2)研究了光纤参量放大器的饱和增益特性。用数值分析的方法得到两个简洁、实用的解析式用于描述光纤参量放大器的饱和信号增益和饱和信号输出功率。得到的结论是:饱和信号增益与泵浦功率和信号功率有关而饱和信号输出功率仅与泵浦功率有关,但两者都与光纤非线性系数和光纤长度无关,这与小信号增益截然不同但更好地满足能量守恒定律。　(3)首次提出最佳光纤长度概念。最佳光纤长度定义为其他参数一定的情况下使信号增益或信号输出功率达到最大所需的最小光纤长度。通过数值积分求解描述光纤参量放大过程的非线性耦合方程,并应用控制变量法深入研究了最佳光纤长度与光纤非线性系数、抽运光功率、信号输入功率的关系。最后用最小二乘法进行数据拟合确定系数,得到简洁、实用的最佳光纤长度解析表达式。与已有实验结果比较表明,该解析式可很好的用来计算和优化光纤参量放大器的光纤长度。　(4)提出一种新颖的基于超结构光纤布拉格光栅的梳状增益均衡器。采用基于LP(layer-peeling)算法的IS(inverse scattering)技术设计光纤光栅,将整体加窗切趾法改进为各信道独立加窗切趾,成功地设计出所需的超结构光纤布拉格光栅。用传输矩阵法分析反射谱、时延曲线和群时延抖动,结果表明,所设计的SFBG满足各项设计指标要求。光纤参量放大器增益均衡后,在ITU-T规定的16个信道内,增益抖动小于±0.4dB,信道隔离度为35dB。　(5)皮秒脉冲在光纤参量放大器中放大时,就群速度色散和三阶色散的作用进行了研究。发现任何由于色散引起的信号光或闲频光脉冲形状的改变都将被耦合到闲频光或信号光引起闲频光或信号光脉冲相应的形状变化,这对以后的实验研究很有帮助。　(6)研究综合考虑到泵浦损耗、走离效应、色散效应和非线性效应,强脉冲信号在光纤参量放大器中的放大情况通过分步傅立叶方法求解耦合方程而进行了数值模拟研究,计算结果表明,一个信号脉冲可以分裂为两个子脉冲。脉冲分裂这一现象用光纤参量放大器的饱和增益特性给出了很好的物理解释,同时也指明了其在脉冲压缩、信号抽样、时分复用等方面的潜在用途。　(7)进行了基于光纤参量放大器的宽带可调波长转换的实验研究。将信号波长固定在光纤零色散波长附近,将强信号光作为泵浦源,当连续可调激光器的波长往长波方向调节时,新生成的闲频光波长就可连续地往短波方向调节。更多还原

【Abstract】 Fiber optical parametric amplifiers(FOPAs) will become essential devices in future dense wavelength-division multiplexed (DWDM) all-optical networks because of their several advantages: high gain, high saturated output power, low noise, flexible use of signal wavelengths, a broad gain bandwidth,ultrafast intrinsic gain response . In this dissertation, we focus on the saturated gain, gain flat, gain bandwidth, optimum fiber length, pulse signal propagation and application of FOPA. Several theoretical and experimental studies have been carried out as followings:(1) Principal theory for FOPAs is investigated. The coupled nonlinear Schr?dinger (NLS) equations that govern wave propagation in a FOPA are derived from basic propagation equation. The methods to improve the gain and gain bandwith of FOPAs are presented based on analyzing the variation of the parametric gain with the fiber parameters, fiber length, FOPA configuration and pump power. Gain spectrums are studied experimentally. Experiment results coincide well with theoritical results.(2) Saturated gain property of FOPAs is studied. Two pithy and powerful analytical expressions for saturated signal gain and signal output power of FOPAs are educed with numerical analysis.It comes to a conclusion that saturated signal gain of fiber optical parametric amplifiers is related to pump and signal power while saturated signal output power only rely on pump power, but both have nothing to do with nonlinear coefficient and fiber length, which is quite different from small-signal gain but accords well with law of conservation of energy.(3) For the first time, the concept of optimum fiber length is introduced, namely the minimum fiber length needed for the maximum signal gain or signal output power with other parameters fixed. By solving the coupled NLS equations that govern the fiber parameter process with numerical integration as well as adopting control variable method, the optimum fiber length as a function of nonlinear coefficient, input pump power and input signal power is profoundly studied. Finally, coefficients are figured out with least square method, and a pithy and useful analytical expression for the optimum fiber length is presented as well. Compared with existing experimental result, this analytical expression can be soundly used to optimize fiber length for FOPAs. (4) A novel superstructure fiber Bragg grating (SFBG) -based comb gain equalizer for FOPA is proposed. Based on layer-peeling inverse scattering technique, adopting independent channel-by-channel apodizing-windowing method rather than integral apodizing-windowing procedure, the desired SFBG is figured out successfully. Reflection spectrum, group time delay and group time delay ripple are analyzed by the method of transformation matrix. The results show that this SFBG satisfied all requirements of designing target. Using the designed SFBG, the gain variation of the FOPA is flattened to be within±0.4dB for 16 ITU-T channels and the channel isolation is as high as 35dB.(5) On amplifying of picosecond pulses in FOPAs, group-velocity dispersion (GVD) and third-order dispersion (TOD) effects are numerically investigated. It comes to a conclusion that any dispersion-induced modifying of the signal (idler) pulse shape will be coupled to the idler (signal) and result in corresponding modifying of the idler (signal) pulse shape. It is extremely helpful for further experimental study.(6) Taken into account pump depletion, walk-off effect, dispersion and nonlinear effect, amplification of strong pulse signal in FOPAs are numerically studied by solving the coupled NLS equations with split-step Fourier method. Calculation results show that a very interesting phenomenon occurred, that is one signal pulse splitting into two sub-pulses. At the same time, the unique strong pulse signal amplification characteristics are finely explained by saturated gain properties of FOPA, and the potential applications of pulse splitting phenomenon in pulse compression, signal sampling and time-division multiplex system are pointed out as well.(7) A simple technique for widely tunable wavelength conversion between picosecond pulses based on Four-wave mixing in highly nonlinear fiber is demonstrated experimentally. When the signal wavelength is fixed near zero-dispersion wavelength of the highly nonlinear fiber to act as the pulsed pump, the newly generated idler wavelength can be tuned continuously towards the short-wavelength side while the wavelength of a continuous tunable laser is tuned towards the long-wavelength side.更多还原