Geophysical sensing using Jones matrices extracted from submarine optical cable transceivers carrying live traffic

We present a general and rigorous theoretical framework for analyzing polarization evolution in optical fibers in the presence of random polarization coupling. This framework enables the extraction of all available information about external perturbations from the Jones matrix retrieved by a coherent receiver during normal operation without compromising the privacy of the data. We apply the theory to telemetry data collected from commercial coherent transponders deployed on both ends of two links that connect Catania, Italy, to Tel Aviv and Haifa, Israel, belonging to Sparkle’s MedNautilus undersea fiber-optic system. The dataset comprises Jones matrices describing the input–output polarization transformations of the fiber. By comparing the Jones matrices of counter-propagating signals transmitted through two fibers sharing the same cable, we demonstrate that the sensing information encoded in the polarization changes is unaffected by random polarization coupling. This is achieved by comparing spectrograms of the perturbation-induced variations of the rotation vectors derived from Jones matrices. Finally, we validate the capability of the method to detect seismic events by analyzing data from four receivers carrying live traffic during the Mw 5.8 earthquake that struck the Dodecanese Islands on June 2, 2025, at 23:17:27.8 UTC.