Cabled ocean observatories (COOs) have enabled real-time in situ ocean observations for decades, thereby facilitating oceanic understanding and exploration. This review discusses typical COOs worldwide in terms of system configurations and state-of-the-art technology, including network structures, power supply modes, and communication capabilities, and provides a comprehensive analysis of their technical routes. The main characteristics of line, ring, star, and grid networks and their applicability in COOs are elucidated, and the advantages and disadvantages of various power supply modes, as well as the opportunities brought by the development of communication technologies, are described. The insights gained from these discussions can inform the implementation of grid structures, optimization of cable routings, expansion of COO scales, application of dual-conductor submarine cables, and upgrading of communication capacity. On this basis, the challenges and future research directions related to COOs are presented.

Conventional repeatered optical communication systems face inherent limitations in terms of reliability, flexibility in optical fiber configuration, and power supply modes, particularly when applied to large-scale cabled ocean observatories, which have highly variable load demands. To address these challenges, a novel hybrid optimization algorithm (GA + PSO + SA) has been developed to enable simultaneous optimization of multiple critical parameters, including the pump light wavelength, the length of the erbium-doped fiber, and the placement of the remote optical amplifier. This approach represents a significant advancement over conventional single-algorithm methods because it effectively overcomes local optima and achieves global performance optimization. Comprehensive simulations and experimental validation demonstrate that the optimized unrepeatered system achieves transmission distances of 691.8 km using G.654E fibers and over 400 km with standard G.652D fibers, while maintaining excellent signal quality and exceptional stability. This work provides a systematic framework for the design and optimization of ultra-long-haul unrepeatered systems, highlighting their practical applicability in cabled ocean observatories.

This study experimentally demonstrates the unrepeatered transmission of a 10-channel 100G PDM-QPSK signal over 435.8 km of G.652 fiber by employing an in-line pumped ROPA-Raman hybrid amplification system. A coordinated power management strategy is adopted to mitigate the nonlinear impairments induced by in-line pumping, which jointly optimizes the signal launch power and all pump powers. The curvature constraint on the longitudinal power profile is further tightened to cope with the small effective area and strong nonlinearity of G.652 fiber. In addition, an asymmetric penalty weighting is applied to the backward pump during power optimization to suppress signal-pump nonlinear interactions. Experimental results show that the optimized system achieves an average Q-factor of 6.80 dB and an OSNR of 12.94 dB over the 435.8 km link. Both metrics exhibit channel-to-channel variations of less than 0.3 dB across all 10 channels. Stable operation over 24 hours with minimal Q-factor fluctuation verifies the robustness of the scheme against nonlinear penalties, making it a viable solution for ultra-long unrepeatered transmission in fiber-resource-constrained scenarios.