Petal: Engineering Petabit-Class Transoceanic Subsea Cables with Multi-Core Fiber
This article from Meta Engineering details the Petal project, a groundbreaking transoceanic subsea cable connecting France and the United States with petabit capacity. It highlights the architectural innovations, primarily the adoption of 2-core fiber technology and specialized repeater designs, to achieve unprecedented data throughput while managing power and physical infrastructure constraints. The discussion focuses on the engineering challenges and partnerships required to advance global connectivity infrastructure.
Read original on Meta EngineeringThe Petal project represents a significant leap in global network infrastructure, aiming to deliver the world's first petabit-class transoceanic subsea cable. This initiative is crucial for meeting the ever-growing demand for intercontinental data traffic, which predominantly relies on subsea cables. The article underscores the continuous innovation required to push the boundaries of data capacity, particularly in overcoming the physical limitations of fiber optics and power consumption.
Key Innovations Driving Petabit Capacity
Historically, increases in subsea cable capacity have come from advances like erbium-doped fiber amplifiers (EDFA) and coherent optical transmission. When these approached the Shannon Limit, the industry pivoted to Spatial Division Multiplexing (SDM) by increasing the number of fiber pairs. Petal takes this further by deploying 2-core fiber technology at scale, effectively doubling the capacity per fiber strand compared to traditional single-core fibers.
Multi-Core Fiber Technology
2-core fiber allows two separate optical signals to propagate within a single fiber strand, doubling capacity without a proportional increase in the cable's physical size or power requirements. This is analogous to adding more lanes to a highway without widening the entire road significantly.
Engineering Challenges of 2-Core Fiber
- Low Attenuation: Ensuring minimal signal loss over 7,000 km while maintaining the standard 125 μm fiber width.
- Minimal Crosstalk: Preventing interference between the two optical signals within a single fiber core. This is achieved through precise control of refractive indexes and counter-propagating signals.
- Repeater Design: Traditional repeaters are designed for single-core fibers. Petal requires specialized repeaters to amplify 96 fiber cores (2 cores per fiber x 48 effective fiber pairs) in a single body. This is solved using a Fan-In/Fan-Out (FIFO) interface within the repeater to convert 2-core to single-core for amplification and back, ensuring efficiency and reliability while staying within existing power constraints.
The design of the repeaters is particularly critical for maintaining signal integrity over such vast distances. The FIFO interface, combined with SDM pump-sharing architecture, allows for efficient amplification without exceeding the power feeding equipment limits, which are typically rated up to 18 kV. This avoids the need for costly requalification of the entire subsea ecosystem, demonstrating a pragmatic approach to innovation.
This project highlights the collaborative nature of large-scale infrastructure development, involving partners like NEC for system engineering and manufacturing, Sumitomo Electric Industries for fiber development, and Orange for landing infrastructure and terrestrial interconnection. Such partnerships are essential for integrating cutting-edge technology into a robust and reliable global network.