针对单模光纤的容量极限问题，利用少模光纤实现了4×100 Gbit/s的双偏振正交相移键控交叉复用的长距离准单模双向传输，达到了1700 km的传输距离。对系统中多径干扰(MPI)和二次瑞利散射(DRS)分别进行了研究。利用301个抽头的恒模算法有效补偿了长距离传输过程中的MPI损伤，使系统的传输性能提高了约1 dB。使用波形整形器有效抑制了DRS导致的信号质量劣化。结果表明，这些处理方法可将系统的传输距离从1400 km延长到1700 km。

Aiming at the capacity limit of single-mode fiber, a 4×100 Gbit/s dual polarization quadrature phase-shift keying (DP-QPSK) interleaved long-distance quasi-single-mode bi-directional transmission is achieved when we use a few-mode fiber, and the transmission distance is over 1700 km. We also study the effects of multi-path interference (MPI) and double-Rayleigh scattering (DRS) on the system. The loss caused by MPI can be effectively compensated by the constant modulus algorithm (CMA) with 301 taps, and the performance of the system increases about 1 dB. Meanwhile, a waveform shaper is used to suppress signal degradation resulting from DRS. The results show that the transmission distance can be extended from 1400 km to 1700 km by these methods.