光纤中线性偏振模式的选择是影响模分复用系统传输质量的关键因素。为此首先设计了基于模分与波分混合复用的直接检测光纤传输系统；其次, 基于光纤中线性偏振模式理论, 利用Optisystem15.0软件仿真研究LP01、LP11、LP02、LP12、LP215个模式在该光纤传输系统中的传输特性；然后, 将LP01、LP11、LP02、LP12四模式复用, 仿真得到了折射率渐变多模光纤纤芯半径在19~25 μm范围内变化时, 各通道Q因子均在7以上的纤芯半径最优化值为21~22 μm, 且此最优值不随传输距离而变化；最后, 在八通道混合复用系统中采用直接检测方式实现了误码率在10-9以下的2.0 km短距离传输。

The choice of linear polarization mode in optical fiber is a key factor affecting transmission quality of mode division multiplexing system. Firstly, a direct detection optical fiber transmission system based on hybrid multiplexing of mode division and wavelength division is designed. Secondly, based on the theory of linear polarization mode in fiber, the transmission characteristics of LP01, LP11, LP02, LP12 and LP21 five modes in the optical fiber transmission system are simulated by Optisystem15.0 software. Then, four modes of LP01, LP11, LP02 and LP12 are multiplexed, and the simulation results show that when the core radius of graded-index multimode fiber changes in the range of 19~25 μm, the optimal core radius for each channel with Q factor above seven is 21~22 μm, and the optimal value does not change with the transmission distance. Finally, in the eight-channel hybrid multiplexing system, the direct detection method is used to realize the short distance transmission with bit error rate below 10-9 at 2.0 km.