The New Unrepeatered Landscape

And how to Get the Most Out of Your Infrastructure

By Luca Possidente, Delphine Rouvillain and Maurizio Pizzi
July 28, 2021

Unrepeated optical networks are a key and vital infrastructure in today's global communication landscape, supporting local and international economic growth by providing regional connectivity across both terrestrial and subsea links. In addition, they also serve as interconnection with larger international subsea and terrestrial networks.

Unrepeatered  links usually spans for hundreds of kilometres and in contrast with repeatered systems, they rely only on optical amplifiers at the terminal stations. No active components are inserted in the middle of the link. Consequently, no electrical power feeding is required.

To enable this, different combinations of High powered EDFAs amplifiers, back-ward and forward Raman based amplifiers are used to cover those long distances. On longer links, ROPAs (Remote Optically Pumped Amplifier) are inserted along the cable to provide supplementary amplification with the purpose of increasing reach and performances. Usually, a ROPA is inserted between 80Km to 130km from the terminal. Being a passive device, the required energy is provided remotely by ROPA pumps, installed at the terminal.

Unrepeatered systems are mostly used in subsea links to connect land masses across bodies of water that are smaller than traditional trans-oceanic networks.  In these applications, their unpowered nature, makes unrepeated cables an attractive and cost-effective solution. They keep CAPEX and OPEX low, they are simple to manage form an operational prospective, and they permit fast and flexible capacity upgrades.

For all the reasons mentioned above, it has also been possible for the industry to use a consolidated disaggregated approach, where subsea cable design and procurement is conducted independently from the transmission terminal equipment and associated amplifiers.

These attributes make unrepeated submarine links the optimal choice for regional inter-country and intra-country systems, inter-island connections, costal festoons and for connecting offshore platforms.

Often, they are also used to close transoceanic rings, providing a protection path between two repeatered submarine cables.

To continue reading the rest of this article, please read it in Issue 119 of the SubTel Forum Magazine on page 51 or on our archive site here.