Study on polarization mode dispersion suppression in optical transmission network based on optical circulators

ZHU Yongqin; TIAN Erlin

doi:10.7510/jgjs.issn.1001-3806.2018.05.021

In order to reduce influence of polarization mode dispersion(PMD) on the quality of transmission signal, an optical circulator was applied in the front-end of the optical amplifier of the optical transmission network. The effect of PMD in optical transmission network was simulated. After PMD suppression, transmission eye diagram opened more obviously. Transmission performance of the system was improved to a certain extent.The PMD in the optical transmission network was suppressed to a certain extent, and the quality of signal was effectively improved. The results show that the bit error rate of PMD decreases about one time with and without the optical circulator. The optical circulator has a significant inhibitory effect on PMD in the optical transport network. The polarization delay at different transmission speeds is compensated equivalently with this scheme so that the PMD is compensated finally.

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引言

光传送网(optical transmission networks, OTN)以密集波分复用(dense wavelength division multiplexing, DWDM)系统作为光传输层平台^[1-7]。现阶段，该系统主要通过G.652光纤进行信息传输，在传输期间受到布里渊散射、四波混频等各类非线性效应的影响程度较低。但是采用光纤进行距离较长的传输时, 信号受到群速度色散以及偏振模色散(polarization mode dispersion, PMD)效应的影响程度将明显增加。上述各项效应会在DWDM系统的传输阶段中发生持续积累，使光信号的性能发生显著下降。因此，为了有效控制光信号性能的恶化程度，只有将传送网的链路距离控制在合理范围内。

掺铒光放大器(erbium doped waveguide amplifiers, EDFA)是一种能够有效降低光纤信号在传输阶段衰减程度的部件。对于色度色散问题，可通过啁啾光纤布喇格光栅(chirped fiber Bragg grating, CFBG)对特定传输距离中发生的色散进行有效补偿，从而有效避免色度色散的问题^[8-10]。对于偏振模色散问题，则可以通过电域补偿、光域补偿以及光电混合补偿方式得到有效解决^[11-14]。对于偏振模色散光补偿过程，可以通过光可调延迟线对光信号传输期间的两个偏振态传输速率差异导致的时延进行补偿，通过增加速度较快偏振方向的光路距离来消除偏振模色散现象；光电混合补偿需使光信号首先从偏振分束器中经过，形成互相垂直的两个偏振方向, 再利用两个光电检测模块把上述两个不同的偏振方向信号都转变成电域信号, 再通过对射频时延线长度进行合理调节来消除偏振模的色散问题^[15-17]。

通过以上分析可知，当前对于偏振模色散的抑制方法基本都是采取主动补偿的处理方式，需要设置复杂的光传输结构，在系统结构方面也存在较大的差异，因此需要对目前的光传送网进行系统改造，极大增加了经济成本^[18-19]。为了更好地解决上述问题，本文中提出了以光环形器作为基础的色散抑制偏振模方案。该方案的设计思路是将光环形器置于光放大器的前端部位，使光信号偏振方向发生等效变化，从而对这两个具有不同传输速度的偏振态光信号延迟进行等效补偿，最终实现补偿偏振模色散的效果。

3. 结论

设计了一种基于光环形器与相结合的偏振模色散抑制方案，通过加入控制光信号的偏振方向，使得在速度较快的偏振方向的光信号进入速度较慢的偏振方向中传递，而在速度较慢的偏振方向的光信号进入速度较快的偏振方向中传递，实现了对偏振模色散的补偿，从而减小系统展宽大小，降低了偏振模色散对于光传送网传输的误比特率的影响。通过仿真可以看出，经过偏振模色散抑制后，系统的传输性能有一定的提高，有效抑制了光传送网通信中的偏振模色散。

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Study on polarization mode dispersion suppression in optical transmission network based on optical circulators

Abstract

References

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通讯作者: 陈斌, bchen63@163.com

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