WET-PLANT: Innovation and Speculation

TONY FRISCH, subsea telecoms

The evolution of subsea cable systems has been remarkable, starting with the UK-Belgium 5 cable in 1986, which utilized 1310 nm single-wavelength transmission and achieved a capacity of 0.75 Gbit/s. Modern systems now employ coherent transmission at 1550 nm, Wavelength Division Multiplexing (WDM), and 16-24 fiber pairs, reaching capacities exceeding 500 Tbit/s across thousands of kilometers—a 600,000-fold improvement.

Key innovations include the shift from fixed-rate regenerators to erbium-doped fiber amplifiers (EDFA) that amplify multiple wavelengths, enhanced pump-sharing for resilience, and higher fiber counts (up to 48 pairs in planned systems). Advances in fiber technology, such as Dispersion-Shifted and Dispersion-Managed Fiber, have minimized non-linear effects, while digital signal processing has enabled efficient dispersion compensation. Multi-core and 200-micron fibers have further addressed the challenge of fitting more fibers into cables, offering better packing density and reduced costs.

Amplifiers remain critical to subsea systems, evolving to handle multi-core fibers and incorporating advanced components like gain-flattening filters and isolators. Emerging technologies, such as photonic integrated circuits and free-space optics, promise compact, efficient solutions for amplifiers. However, challenges like higher power requirements and cost constraints persist.

Future Innovations and Challenges: