# Toward SDM-Based Submarine Optical Networks: A Review of Their Evolution and Upcoming Trends
## 3 Recently Announced Submarine Cable Systems
### A Detailed Overview of SDM-Based Technology Cable Systems
It will give over 320 Tb/s of capacity divided in three segments by using 12 and 16 FPs. ASN will provide the system, which is expected to go commercial in the first quarter of 2022. Confluence-1 will connect Miami and New York. It will travel for 2571 km and will use 24 FPs (ultra-high fiber count) achieving a 50% improvement in fiber count compared to the previous 16 FPs cable systems. Confluence-1 highlights another possible use of the submarine networks, which is to provide a more direct and/or a backup alternative to terrestrial ones. Note however that this possible use can be applied only along long coastlines (like the Miami-New York coastline) or in closed seas (like the Aegean Sea in Greece or the Mediterranean Sea). Confluence-1 hopes to be ready for service in 2023. The Echo submarine system will connect Eureka (USA), Guam, Indonesia, Singapore, and other countries. Echo will be the first subsea direct connection from the US to Singapore. It will travel 16,200 km from Singapore to Eureka and will use 12 FPs. Providing 12 Tb/s/FP, Echo aims at a total system capacity of 144 Tb/s. Google and Facebook are the joint builders. Indonesian Telco, Google Singapore PTE Ltd., and Facebook Edge USA deal with the dry plant in Indonesia, Singapore, and the US (& Guam), respectively. NEC will supply the system, which is expected to be ready in 2023. The Firmina cable system is a new investment of Google. It will travel for more than 3500 km and will have four landing points in Las Toninas (Argentina), Praia Grande (Brazil), Punta del Este (Uruguay), and the East Coast of the United States. It will consist of 12 FPs, and it will be the world's longest undersea cable, capable of maintaining operations with single-end feed power by using 18-kV power technology. The cable system is expected to be ready for service by the end of 2023. Topaz cable system is the first-ever submarine optic-cable to connect Canada and Asia invested by Google. It will travel from Vancouver to the small town of Port Alberni on the west coast of Vancouver Island in British Columbia, and across the Pacific Ocean to the prefectures of Mie and Ibaraki in Japan. It will use state-of-the-art Wavelength Selective Switches (WSSs) to provide flexible routing and resilience. It will consist of 16 FPs giving a total capacity of 240 Tb/s and is expected to be ready for service in 2023. The India-Asia-Xpress (IAX) and India-Europe-Xpress (IEX) cable system will connect Mumbai and Chennai to Singapore and to Europe, respectively. IAX will also connect several Far East countries to the US West Coast, whereas IEX will connect to the East Coast of the US. The IAX and IEX cable systems will adopt open cable system technology (which means that it can be connected to any type of technology or brand) and the innovative wavelength-switched ROADM/branching units, providing rapid upgrade deployment and flexibility to add/drop wavelengths across multiple stations. Both the IAX and IEX cable systems are built by Reliance Jio Infocomm and are expected to be ready for service in mid-2023 and early 2024, respectively. The Sea-Me-We 6 (SMW6) cable system will be the latest project of the Southeast Asia-Middle East-West Europe (SEA-ME-WE) series and it will connect Singapore and Marseille via Egypt. It will travel 19,200 km, and it will consist of up to 10 fiber pairs, with 12.6 Tb/s/FP and a total system capacity of 126 Tb/s. It will adopt the latest SDM technology. The SMW6 consortium comprises Bharti Airtel, Bangladesh Submarine Cable Company Limited (BSCCL), China Telecom, China Mobile, China Unicom, Djibouti Telecom, Orange, Singtel, Sri Lanka Telecom, Telecom Italia, and TSA. It is expected to be ready for commercial usein early 2025. 2 Africa (initially announced in May 2020) aims to connect 46 cable landing stations in 33 countries in Africa, Asia, and Europe, and will travel for 45,000 km (Figure 11).