光纤参变放大器光纤长度的优化设计

随着高输出功率掺铒光纤放大器和高非线性光纤的出现和使用，光纤参变放大器(OPAs)中出现了越来越多的增益饱和现象，这是光放大器中应该尽量避免的。对此，提出了依据光纤参变放大器的光纤非线性系数、抽运光功率、信号输入功率等参量对光纤长度进行优化设计的解决思路。明确提出最佳光纤长度的概念，即在其他参量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，而且最佳光纤长度有利于提高光纤参变放大的增益带宽和波长转换带宽。通过数值积分求解描述光纤参变放大过程的非线性耦合方程，并运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，该解析式可很好地用来计算和优化光纤参变放大的光纤长度。

Optimized Design of the Fiber Length for Fiber Optical Parametric Amplifier

With the increasing availability of high outpu t power erbium-doped fiber amplifier and the development of highly nonlinear fibe rs, more gain saturation phenomena are observed in fiber optical parametric ampl ifiers (OPAs), which are expected to be avoided. A practicable method is propose d to avoid the gain saturation phenomenon, that is optimizing fiber length accor ding to other parameters of fiber OPA, such as nonlinear coefficient, input pump power and input signal power. The concept of optimum fiber length is introduced , namely the minimum fiber length needed for the maximum signal gain or signal o utput power with other parameters fixed. The optimum fiber length is of great be nefit to boost the gain bandwidth and the conversion bandwidth. By solving the n onlinear coupled equations that govern the fiber parametric amplifying process w ith numerical integration as well as adopting controlled variable method, the op timum 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 o ptimum fiber length is presented. Compared with existing experimental result, th is analytical expression could be soundly used to optimize fiber length for fibe r OPAs.