少模光纤通信系统中的自适应频域均衡算法

Adaptive frequency-domain equalization for few-mode fiber transmission systems

少模光纤模式复用存在模式耦合和差分模式时延,必须通过自适应均衡算法补偿。为了降低长距离少模光纤通信系统中自适应均衡算法的复杂度,采用基于变步长-频域块最小均方算法的多输入多输出均衡器对2×2模分复用系统解复用。利用频域块最小均方自适应算法修正均衡器权系数,并通过变步长函数调整步长因子,兼顾算法收敛速度和收敛性能。算法可通过快速傅里叶变换降低计算复杂度。在112Gbit/s的1000km少模光纤高速通信仿真系统中,保证相同收敛速度情况下,提高信号Q2因子3.7d B,并在可编程现场门阵列上验证了100km少模光纤通信系统时的算法性能。结果表明,该算法能够实现模分复用系统的信号解复用,达到快速收敛、低稳态失调的目的。

Modal crosstalk and differential mode delay in mode-division multiplexing in few-mode fiber must be compensated for with adaptive equalization algorithm. For the purpose of decreasing complexity of adaptive equalization algorithm in long-haul few-mode fiber communication system, a multiple-input multiple-output equalizer with variable step-size frequency-domain-block least mean square（VS-FBLMS） algorithm was proposed to uncouple a 2×2 mode-division multiplexing system. Compromising the conflicting requirements of convergence speed and convergence performance, FBLMS adaptive algorithm was employed to update equalizer taps and modify step-size factor with variable step-size function. Furthermore, the algorithm decreased the computational complexity by using fast Fourier transform. In a 112Gbit/s high-speed communication simulation system over 1000km in few-mode fiber, signal Q2 factor increased 3. 7dB with same convergence speed. The performance of the algorithm was tested on field programmable gate array with a 100km few mode fiber communication system. The study demonstrates that the algorithm successfully uncouples the signals of mode-division multiplexing system and realizes fast convergence and low disorder.