An Unrepeatered Submarine Transmission System is an undersea optical communication link that transmits signals over long distances without intermediate optical amplifiers or repeaters. It relies on high-power transmitters, low-loss optical fiber, and sensitive receivers to maintain signal integrity across the span. These systems are typically used for shorter submarine routes, island connections, or backup links where deploying powered repeaters is impractical, offering simpler infrastructure and reduced deployment and maintenance complexity.

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Integration of Distributed Acoustic Sensing and Unrepreatered Transmission for Undersea Cable Monitoring by ESF

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We present techniques to extend the sensing range in unrepeatered submarine cable systems by utilizing Enhanced-Scattering Fibre (ESF), large-area ultra-low-loss (ULL) fibre, and a digital Distributed Acoustic Sensing (DAS) interrogator. A DAS sensing range of up to 200.6 km has been achieved using 156km SCUBA125 fibre, followed by three segments of ESF. Additionally, we demonstrate long-range sensing capabilities and high-capacity data transmission over a 270.6 km unrepeatered submarine system, where DAS and 400G DWDM data transmission coexist. The impact of Distributed Raman Amplification (DRA) on sensing performance, and crosstalk between DAS and 400G DWDM channels in coexistence of DAS and unrepeatered transmission system are studied. Finally, we briefly discuss the potential application scenarios for monitoring undersea cables using ESFs.

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