Statistical Analysis of Modal Dispersion in Field-Installed Coupled-Core Fiber Link

This study presents a statistical analysis of modal dispersion of a 69-km-long field-deployed coupled-core four-core fiber link. The link is characterized over a band of approximately 5 THz at 1550 nm, in terms of complex modal dispersion vector, eigenvalues of its modal dispersion matrix, and intensity impulse response. Experimental statistical results are in very good agreement with the theoretical models based on the assumption of strong mode mixing. We also show that a careful analysis of the modal dispersion vector enables the accurate assessment of the skew between channels, distinguishing the contribution of the input patch cords from that of the output ones. Notably, we show that the Stokes-space representation of modal dispersion allows to compensate for the delays introduced at the fiber input and output by the optical vector network analyzer used for measurements. In addition, we provide evidence and theoretical justification of spectral persistence of the principal states in fibers with strong mode mixing. That is, although the modal content and the group delays of the principal modes change from frequency to frequency, the sorting of the principal modes with respect to their group delays is largely frequency independent.