# Toward SDM-Based Submarine Optical Networks: A Review of Their Evolution and Upcoming Trends
## 3 Recently Announced Submarine Cable Systems
### Attainable Capacity of Submarine Cable Systems  
As already pointed out, all technologies (including SDM) target an increase in the transmission bandwidth. If we use both C + L bands for transmission (instead of only using the C-band), the attainable transported capacity is higher by approximately a factor of 2. In other words, we can achieve higher system capacity either by doubling the number of FPs (with SDM) or by using the C + L bands and not changing the number of FPs. However, C + L transmission (e.g., PLCN cable system in Figure 13) is less efficient compared with the doubling of FPs because C + L bands must be separated and recombined (mux/de-mux) in the repeater for each span. Figure 12: Traditional vs. SDM cable granularity. \begin{table}
\begin{tabular}{c c c c c} \hline Topology & **Submarine Cable** & **Cable Length** & **Landing** & **Number of** \\  & **System** & **(Km)** & **Points** & **Operators** \\ \hline
**SeaMeWe-3** & 39,000 & 39 & **52** \\
**FLAG Europe-Asia (FEA)** & 28,000 & 17 & **Global Cloud** \\
**AsiaAfrica Europe-1 (AAE-1)** & 25,000 & 20 & **18** \\
**SeaMeWe-4** & 20,000 & 16 & **16** \\
**SeaMeWe-5** & 20,000 & 18 & **18** \\
**Africa Coast to Europe (ACE)** & 17,000 & 22 & **20** \\ \hline
**SDM Repeater** & **Peace** & 15,000 & 14 & **International Network** \\  & & & **Co.** Ltd. \\  & **EuropeIndia Gateway (EIG)** & 15,000 & 12 & **16** \\  & **Southern Cross NEXT** & 13,700 & 7 & **Southern Cross Cable** \\  & **Polar Express** & 12,650 & 10 & **Russian Government** \\  & **BRUSA** & 11,000 & 4 & **Telxius** \\  & **Africa-1** & 10,000 & 10 & **Etisalat UAE** \\  & **South Atlantic Express (SAEx)** & 10,000 & 5 & **SAEx International** \\ Trunk\&Branch & & 6792 & 5 & **3** \\  & **TE North/TGN-Eurasia/\(\dots\)** & 3634 & 4 & **6** \\  & **Malbec** & 2600 & 3 & **Facebook, GlobeNet** \\ \hline
* SDM Technology & **2 Africa** & 45,000 & 29 & **8** \\
* SDM Technology & **Hawaiki Nui** & 22,000 & 13 & **Hawaiki Submarine** \\  & **Cable** & & **Cable** \\
* SDM Technology & **ECHO** & 17,184 & 6 & **2** \\
* SDM Technology & **Bifrost** & 15,000 & 5 & **3** \\
* SDM Technology & **Equiano** & 12,000 & 7 & **Google** \\
* SDM Technology & **Apricot** & 12,000 & 4 & **7** \\
* SDM Technology & **Medusa** & 8760 & 16 & **AFRIX Telecom** \\
* SDM Technology & **Grace Hopper** & 7191 & 3 & **Google** \\
* SDM Technology & **Amitie** & 6792 & 3 & **5** \\
* SDM Technology & **Caribbean Express (CX)** & 3472 & 11 & **OceanNetworks (ONI)** \\
* SDM Technology & **Confluence-1** & 2571 & 5 & **Confluence Networks** \\ \hline  & **EAC-C2C** & 36,500 & 16 & **Telstra** \\ Mesh & **Trans-Pacific Express (TPE)** & 17,000 & 6 & **7** \\  & **MedNautilus Submarine System** & 7000 & 7 & **Telecom Italia Sparkle** \\ \hline  & **Apollo** & 13,000 & 2 & **Vodafone** \\  & **CAP-1** & 12,000 & 2 & **Amazon Web Services,** \\  & & & & **Facebook** \\  & & & & **Seaborn Networks,** \\  & & & & **Telecom Italia Sparkle** \\
**Point-to-Point** & **MAREA** & 6605 & 2 & **Facebook, Microsoft,** \\  & **INDIGO-Central** & 4850 & 2 & **5** \\  & **JGA-N** & 2600 & 2 & **RTI** \\  & **BlueMed** & 1000 & 2 & **Telecom Italia Sparkle** \\
* SDM Technology & **Dunant** & 6400 & 2 & **Google** \\ \hline  & **Japan-U.S. Cable Network (JUS)** & 22,682 & 6 & **24** \\  & **Pacific Crossing-1 (PC-1)** & 22,900 & 4 & **NTT** \\ Ring & **TPC-5** & 22,560 & 6 & **13** \\  & **Atlantic Crossing-1 (AC-1)** & 14,301 & 4 & **Lumen** \\ \hline \end{tabular}  
* The cable system incorporates the SDM technology; ** The cable system incorporates at least one SDM-based device (e.g., SDM repeater).  
\end{table} 
Table 5: A taxonomy of existing submarine cable systems based on their topology [1, 2, 3, 4, 5]. Figure 13 presents the evolution of the submarine systems' capacity through time. Blue and red dots represent non-SDM and SDM cable systems, respectively. Orange dots represent multiband (C + L) cable systems.