基于相位-强度调制转换的光纤色散精确测量方法

Accurate measurement of chromatic dispersion of optical fibers based on phase-intensity modulation conversion

在分析光纤色散导致的相位-强度调制转换的基础上,提出了一种利用电光相位调制的光纤色散扫频测量方法。方法的原理为光纤色散使相位调制信号获得附加相移并产生周期性衰落,从衰落曲线的特征性凹陷频率确定出光纤色散。实际运用中,由于凹陷频率附近的信号弱,因此噪声大且不稳定。为了解决这一问题,通过衰落曲线的多项式拟合,进一步提高凹陷频率和光纤色散的测量精度。实验中,对长光纤或者短光纤分别测试以验证本文方法对于不同色散的适应性。实验结果表明,本文方法的相对误差小于0.22%。使用矢量网络分析仪(VNA)和相位调制器进行测试,可工作于不同光波长,适用于测量不同种类的光纤的色散;并且可以利用简单的实验系统,实现光纤色散的大小和符号的测量。

For an accurate characterization of fiber dispersion,we propose a swept-frequency measurement of chromatic dispersion based on the phase-intensity modulation conversion in a dispersive optical fiber. In principle, the fiber dispersion introduces additional phase shifts and causes the periodical fading of the phase-modulated signal, which allows to determine the dispersion from the fading frequency. In practice, the fading signals are very noisy and unstable due to close to the unavoidable noise floor,which makes it very difficult to precisely determine the notch frequencies. For an improved accuracy of characteristic notch frequency,the polynomial fitting of the fading curve is adopted in our method. In the experiment, our method is verified by long and short fibers with different amounts of dispersion. Experimental results show that our measurement holds a relative error of less than 0.22%. Moreover,our method is applica- ble for the chromatic dispersion measurement at different operating wavelengths and dispersive fibers on- ly by using a vector network analyzer and an optical phase modulator,and it gives both the value and the sign of the chromatic dispersion with very simple configuration.