文章提出了一种新的应用于高速光纤通信系统接收端的数字背向传输（DBP）算法的步长变换选择方法。通过采用斜线方法对光纤非线性系数的指数形式曲线进行近似，找出使斜线的斜率与原曲线各点斜率差值最小情况下的步长，再用于变步长DBP算法中对光纤传输中的非线性损伤进行补偿。在3 200 km单信道25 Gbaud光纤传输系统中对所提步长选择方案进行了仿真。结果表明，在相同系统中，与其他步长选择方法相比，在最佳入纤功率时所提步长选择方案的Q值提升了0.5 dB；当入纤功率越大、非线性效应越强时，所提方法对于光纤传输非线性损伤的补偿能力更好，而算法复杂度没有改变。

This paper proposes a new step size distribution method in variable step size Digital Back Propagation (DBP) algorithm. Several oblique lines are used to estimate the effective nonlinear coefficient which exponentially increases with the distance. Then a step size distribution is determined to ensure the difference of the slope between the oblique lines and the exponential curve is minimum. The optimal step size distribution is used in split-step Fourier method to compensate the nonlinear impairments. Simulation is implemented in a 3 200 km Daul-Polarization Quadrature Phase Shift Keying (DPQPSK) system with single channel rate of 25 Gbaud using the proposed step size distribution method. Simulation results show that the Q-value based on the step size distribution method is increased about 0.5 dB when compared with uniform step size distribution method. The proposed algorithm has larger tolerance on the nonlinear effects with low complexity.