Shibata Nori, Watanabe Kimitaka, Ohashi Masaharu, Sasaki Yusuke, Aikawa Kazuhiko
Appl Opt. 2021 Dec 20;60(36):11050-11057. doi: 10.1364/AO.442256.
We provide differential mode delay (DMD) diagnostics for linearly polarized (LP) modes traversing a few-mode fiber (FMF). We employ a modal interferometer method with a butt coupling mechanism to measure the DMD between any two modes guided in FMFs with step-index (SI) and depressed-cladding profiles. The measurement principle is based on investigating a transmitted spectrum through temporal decomposition by means of a Fourier transform. At least four different temporal waveforms are needed for an FMF supporting four LP modes to estimate the DMD between two different LP modes. A butt coupling mechanism with an air gap between an FMF and a dispersion-shifted fiber is employed for simultaneous DMD measurement. The present diagnostics requires some knowledge of the bending loss characteristics of the FMFs and the butt coupling properties of the circular symmetry modes or circular asymmetry modes in their electric fields. The DMD diagnostics are realized taking the bending loss and butt coupling characteristics into consideration. We present experimental results for the DMD and DMD slope as a function of the wavelength in a 1450-1625 nm telecommunication band.
我们为穿过少模光纤（FMF）的线偏振（LP）模式提供差分模式延迟（DMD）诊断。我们采用具有对接耦合机制的模态干涉仪方法来测量具有阶跃折射率（SI）和凹陷包层分布的FMF中任意两个导模之间的DMD。测量原理基于通过傅里叶变换进行时间分解来研究传输光谱。对于支持四个LP模式的FMF，需要至少四个不同的时间波形来估计两个不同LP模式之间的DMD。采用在FMF和色散位移光纤之间具有气隙的对接耦合机制进行同步DMD测量。当前的诊断需要了解FMF的弯曲损耗特性以及其电场中圆对称模式或圆不对称模式的对接耦合特性。考虑到弯曲损耗和对接耦合特性，实现了DMD诊断。我们给出了在1450 - 1625 nm电信波段中DMD和DMD斜率随波长变化的实验结果。
