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复合二次失真 (CSO:Composite Second Order Distortion)是光纤 CATV中最主要的非线性之一 .理论分析表明 :在外调制 CATV中 ,将调制器偏置在最佳偏置点可以消除 CSO,但外调制器最佳偏置点却随时间及环境温度等漂移 ,因而会导致 CSO的严重恶化 .本文提出了一种易于实现的调制器偏置点控制方案 ,并进行了详细的理论分析与实验研究 ,结果显示该方案能够将 5 0～ 5 5 0 MHz宽频带内电视信号 CSO指标抑制在 -65 d B以下 .
Composite Second Order Distortion (CSO) is one of the most important nonlinearities in fiber CATV.Theoretical analysis shows that offsetting the modulator at the best offset point can eliminate the CSO in the externally modulated CATV, The optimal bias point of the modulator drifts with time and ambient temperature, which will lead to serious deterioration of CSO.This paper presents an easy-to-implement modulator bias point control scheme and detailed theoretical analysis and experimental study The results show that this scheme can suppress the CSO index of TV signals in the range of 50-580 MHz below -65 d B.