Fu Zhe, Zhang Junjie, Zhang Ziheng, Fu Songnian, Qin Yuwen, Shen Lei, Cheng Mengfan, Yang Qi, Tang Ming, Liu Deming, Deng Lei
Opt Lett. 2021 Jun 15;46(12):2856-2859. doi: 10.1364/OL.423950.
In this Letter, we propose a simple and high-precision differential modal group delay (DMGD) characterization method for few-mode fibers (FMF) by using the frequency-modulated continuous wave. Since the detected signals are located at the low-frequency range, our DMGD characterization method waives the use of expensive equipment, such as vector network or optical spectrum analyzers. Due to the high linearity of the used Mach-Zehnder modulator, our DMGD measurement is free from the complex auxiliary interferometer, leading to an improvement of characterization precision. Meanwhile, we propose a novel spectrum recovery algorithm to overcome the shortcoming that the traditional fast Fourier transform (FFT) method is incapable to deal with spectrum features arising in a periodic signal. Therefore, the characterization precision is no longer limited by the FFT length. When a commercial 23299.8 m two-mode fiber is used in the experiment, the DMGD measurement of mode relative to mode has a high precision of ±0.007/ over the C-band. Our proposed method shows the potential for characterizing the wavelength-dependent DMGD of FMF with more than two LP modes.
在本信函中，我们提出了一种通过使用调频连续波来对少模光纤（FMF）进行简单且高精度的差分模式群时延（DMGD）表征的方法。由于检测到的信号位于低频范围，我们的DMGD表征方法无需使用诸如矢量网络分析仪或光谱分析仪等昂贵设备。由于所使用的马赫 - 曾德尔调制器具有高线性度，我们的DMGD测量无需复杂的辅助干涉仪，从而提高了表征精度。同时，我们提出了一种新颖的频谱恢复算法，以克服传统快速傅里叶变换（FFT）方法无法处理周期性信号中出现的频谱特征这一缺点。因此，表征精度不再受FFT长度的限制。当在实验中使用一根商用的23299.8米双模光纤时，在C波段上，相对于模式的模式的DMGD测量具有±0.007 /的高精度。我们提出的方法显示了表征具有两个以上LP模式的FMF的波长相关DMGD的潜力。
