Extended S² diagnosis of mode degradation in fiber components through group delay stretching

The separate diagnosis of mode degradation in few-mode fiber components (FMFCs) is a challenging task due to the reciprocal mode cross talk. In this work, we propose the group delay stretching, combined with the extended spatially and spectrally (S²) resolved imaging technique, to decouple and analyze the mode coupling within the body of the FMFC with short-length pigtails. Through stretching the mode delay by a delay fiber, the degraded modes related to different origins are effectively separated, and the extended S² technique quantifies the individual modal weight for each component. Experiments on different types of FMFCs have verified the validity of our method. This method paves the way for optimizing and manipulating the fiber components in the dimensionality of modes.