Observation of polarization modulation at the output of a submarine link, extracted from a standard coherent telecom receiver, can be used to monitor geophysical events such as sea waves and earthquakes occurring along the cable. We analyze the effect of birefringence perturbations on the polarization at the output of a long-haul submarine transmission system, and provide analytical expressions instrumental to understanding the dependence of the observed polarization modulation on the amplitude and spatial extension of the observed events. By symmetry considerations, we show that in standard single mode fibers with random polarization coupling, if polarization fluctuations are caused by strain or pressure, the relative birefringence fluctuations are equal to the relative fluctuations of the polarization averaged phase. We finally show that pressure induced strain is a plausible explanation of the origin of polarization modulations observed in a long submarine link. The presented analysis paves the way for the transformation of transoceanic fiber optic links during operation into powerful sensing tools for otherwise inaccessible geophysical events occurring in the deep ocean.

中文翻译：

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使用海底光缆进行偏振传感

从标准相干电信接收器提取的海底链路输出端极化调制的观测可用于监测地球物理事件，例如沿电缆发生的海浪和地震。我们分析了双折射扰动对远程海底传输系统输出端极化的影响，并提供了有助于理解观测到的偏振调制对观测事件幅度和空间扩展的依赖性的分析表达式。通过对称性考虑，我们表明在随机偏振耦合的标准单模光纤中，如果偏振波动是由应变或压力引起的，则相对双折射波动等于偏振平均相位的相对波动。我们最终表明，压力引起的应变是对在长海底链路中观察到的极化调制起源的合理解释。所提出的分析为将运行期间的跨洋光纤链路转变为强大的传感工具铺平了道路，以应对深海中发生的其他无法访问的地球物理事件。