Toward SDM-Based Submarine Optical Networks: A Review of Their Evolution and Upcoming Trends
Abstract
:1. Introduction
2. Submarine Optical Networks Basics and Demonstrations Technologies on Submarine Cable Systems
2.1. The Past Evolution of Submarine Transmission Systems
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- 1884: The first submarine cable supporting phone data (from San Francisco to Oakland).
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- 1954: The first submarine (high-voltage direct current) cable connected the island of Gotland to mainland Sweden.
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- 1956: The first deployment of repeaters (in the 1940s) boosted the TAT-1, which was the first telephone cable crossing Atlantic.
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- 1964: The first transpacific submarine coaxial telephone cable linking Japan, Hawaii, and the US mainland.
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- 1986: The first submerged international fiber-optic cable that connected Belgium to the United Kingdom.
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- 1988: The first submerged transoceanic fiber-optic cable, (named TAT-8), that connected the USA to the United Kingdom and France.
2.2. Important Milestones at Submarine Systems Evolution
2.3. Submarine Systems’ Performance Metrics
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- In submarine networks the service performance can be determined by information describing the health status of basic network components (BUs, intermediate repeaters). This information is obtained by coherent transponders which are placed at the ends of a submarine cable. Their terrestrial counterparts are by far more easy to monitor. Terrestrial networks can process more data with regard to each unit’s contribution to the whole system’s performance.
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- Total output power (TOP) constraint is another key difference between terrestrial and submarine systems as it changes the way that total SNR is calculated. The TOP constraint in submarine amplifiers results in signal depletion whereas amplifier noise is accumulated because the total channel power (S+N) remains fixed with distance.
2.4. SDM Transmission Technologies in Long Haul Transoceanic Systems
2.4.1. Features of SDM-Based Submarine Cable Systems
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- A relatively high count of FPs (in the same cable) in order to increase the transported capacity.
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- The deployment of lower effective area fibers in order to optimize cost through the use of a smaller number of regenerators.
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- The implementation of the novel “pump farming” repeaters’ technology. Pump farming means that a set of pump lasers isused to amplify a set of FPs. Reliability, redundancy, and better power management are the main advantages. In particular, reliability can be a cost-reduction factor as submarine cables’ failures and repairs (bringing downtime in provided services) are very costly.
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- SDM aims to achieve higher capacities by using the same amount of used power through a more efficient power management. The key concept is to reduce the optical power provided to each FP as a way to decrease the nonlinearities as implementing high count of FPs in the same cable.
2.4.2. Multiple Spatial Channels in SDM: MCF (Multi-Core Fibers)-MMF (Multi-Mode Fibers)-Bundles of Single-Mode Fibers (Bu-SMFs)
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- Multiplying the number of conventional fibers (thus implementing a parallelism that consists of single-core/single-mode fibers), considering the existence of at least one element that performs spatial integration, e.g., an amplifier with sharing pumps, a switching node, or terminal equipment.
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- Multiplying the number of cores in MCF fibers.
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- Multiplying the number of modes in MMF fibers.
2.5. Basic Segments (“Plants”) of a Submarine System
2.6. Cable-Installing Ships
3. Recently Announced Submarine Cable Systems
3.1. A Detailed Overview of SDM-Based Technology Cable Systems
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- pushing the limits of theoretical design capacity;
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- minimizing nonlinear effects to reduce needed equipment, cost, and complexity;
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- designing an efficient optical and electrical network based on repeater pump farming, low Aeff submarine fibers, and higher fiber counts; and
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- working in the optimum spectral efficiency of submarine line terminal equipment (SLTE): 2–3 b/s/Hz and lower chromatic dispersion compensation.
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- a high fiber count submarine repeater which broke through the fiber count limitation of existing products and can support up to 16 fiber pairs which can double the capacity;
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- an industry-leading 39.5 nm ultrawide bandwidth, which covers C-band and extended C-band, to maximize the capacity of one fiber pair; and
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- a significantly reduced cost/bit.
3.2. Attainable Capacity of Submarine Cable Systems
3.3. Experimental Demonstrations That Show a Glimpse to Possible Future Evolution
4. Submarine Amplifiers
4.1. Overview and History Evolution of Submarine Amplifiers
4.2. Differences between Terrestrials and Submarine Amplifiers
4.3. Multiband Amplification Technology
4.4. Pump Farming (SDM) Technology
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- 4 Pumps/2 Fiber Pairs, 4 Pumps/4 Fiber Pairs;
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- 8 Pumps/4 Fiber Pairs, 8 Pumps/8 Fiber Pairs; and
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- 16 Pumps/8 Fiber Pairs, 16 Pumps/16 Fiber Pairs.
4.5. Core Pumping (EDFA) Combined with SDM Technology
4.6. SDM Technology-Cladding Pumping EDFA (MC-EDFA)
4.7. Pump Recycling (SDM) Technology
4.8. Hybrid Core and Cladding Pump-Sharing EDFA (SDM) Technology
4.9. SDM Technology-Multi-Mode EDFA (MM-EDFA)
4.10. Experimental Demonstrations of Submarine SDM-Based Amplifiers at Transoceanic Distances
5. Internal Architectures of Submarine Cable Systems and BUs
6. Submarine Power Feeding
7. Economic Aspects of Submarine Networks
8. Submarine Networks Security
9. Can We Predict the Future in Submarine Networking?
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Year | Cable System | Key Technology | Capacity/Channels | Length |
---|---|---|---|---|
1956–1978 | TAT-1 | First transatlantic * telephone cable, electronic repeaters, hotline | 36 (initial), 48 final telephone channels | 1942 km |
1978–1994 | TAT-7 | Employs coaxial cable technology | 4000 (initial), 10,500 final telephone channels | 8910 km |
1988–2002 | TAT-8 | First * fiber-optic transatlantic cable | 295.6 Mbit/s traffic or 40,000 phone circuits | 6705 km |
1991 | TAT-9 | First system to switch traffic on demand between five landing points | 560 Mbit/s traffic or 80,000 voice circuits | 9305 km |
1996–2008 | TAT-12/13 | EDFA technology implemented | 2 × 5 Gb/s | 12,307 km |
2001 | TAT-14 | Employs 4 fiber-pair (2 FPs active + 2 FPs backup) WDM technology with direct detection | 3.2 Tb/s | 15,428 km |
2008 | TPE | Employs 10 G DWDM technology | 5.12 Tb/s | 17,968 km |
2013 | PC-1 | Employs 100 G coherent technology | 8.4 Tb/s | 21,000 km |
2018 | PLCN | First submarine cable employs C + L band optical technology | 144 Tb/s | 12,971 km |
2021 | Dunant | First submarine cable employs 12 FPs introduces first-generation SDM technology, pump lasers, pump-sharing technology | 250 Tb/s | 6600 km |
2021 | H2HE | The world’s first 16-fiber-pair repeated submarine cable system. A milestone in technological innovation | 300 Tb/s | 675 km |
2022 | Peace | WSS ROADM BU, 200 G technology, SDM repeater | 90 Tb/s | 15,000 km |
2022 | Equiano | First submarine cable employs optical switching at the fiber-pair level (instead of wavelength-level switching) | 200 Tb/s | 15,000 km |
2023 | Confluence-1 | First submarine cable employs 24 fiber-pair SDM technology and it will be the largest to be recently installed | >500 Tb/s | 2571 km |
2023 | Ellalink | First submarine system to incorporate state-of-the-art ICE6 800 G coherent technology | 100 Tb/s | 6200 km |
2023 | Firmina | To be the world’s longest undersea cable capable of maintaining operations with single-end feed power by using 18-kV power technology | N.A | 2500 km |
2023–2024 | 2Africa | 2Africa aims to be one of the largest submarine cable systems (46 landing stations, 45,000 km) | 180 Tb/s | 45,000 km |
2025 | Arctic. Connect | To be the first transarctic cable system with new innovative cable type and will connect three continents (85% of total world population) | 200 Tb/s | 14,000 km |
2024–2025 | Apricot | To incorporate 400 G technology, all new submersible ROADM, flexible bandwidth management based on SDM-based design. | 190 Tb/s | 12,000 km |
2025 | SEA-ME-WE-6 | Utilizes SDM cable, supporting up to 24 FPs and incorporates enhanced branching units (eBUs) providing flexible electrical power and optical fiber routing with shore-based telemetry control | 126 Tb/s | 19,200 km |
PROS | CONS | |
---|---|---|
Lower capacity per FP, as FP becomes consequently the new granularity | Higher quantity of FP used | |
C-Band | FP switching used to drop a whole FP in a branch | Bigger cable needed to contain all the FPs |
Easier to sell FP | - | |
Easier to swap FP | - | |
- | Less efficient as MUX/DMUX should be used (~1 dB losses) | |
- | Attenuation is slightly higher in L band (beyond 1600 nm) | |
(C + L) Band | Limits the number of FP in the cable | Interband effects between C and L bands |
No need to develop big cable to contain all the FPs | Spectrum sharing needed to sell/swap a portion of a FP | |
- | Higher cost for BU with WSS to manage spectrum sharing | |
- | L band amplifier needed |
Submarine Cable System | RFS | Cable Length (Km) | Capacity (Tb/s) | Technology | Fiber Pairs (FPs) | SDM Nature/Info |
---|---|---|---|---|---|---|
Dunant | 2021 | 6400 | 250 | SDM 1 ASN | 12 | Pump Sharing Repeater/(12 FPs) |
Malbec | 2021 | 2600 | 108 | SDM | 8 | Fiber Count ≥ * 8FPs (8 FPs) |
Hainan to Hong Kong Express (H2HE) | 2021 | 675 | 307 | SDM 1 HMN | 16 | High Fiber Count (16 FPs) |
Peace | 2022 | 15,000 | 90 | SDM 1 ASN | † 16 | SDM Repeater/(16 FPs) |
Equiano | 2022 | 12,000 | 200 | SDM | 12 | Fiber Count ≥ * 8FPs (12 FPs) |
Grace Hopper | 2022 | 7191 | 352 | SDM | 16 | High Fiber Count (16 FPs) |
Amitie | 2022 | 6792 | 320 | SDM | 16 | High Fiber Count (16 FPs) |
2Africa | 2023 | 45,000 | 180 | SDM 1 ASN | 16 | Fiber Count ≥ * 8FPs/(12FPs) |
ECHO | 2023 | 17,184 | 144 | SDM | 12 | Fiber Count ≥ * 8FPs (12 FPs) |
IAX | 2023 | 5791 | 200 | SDM | † 12 | Fiber Count ≥ * 8FPs (12 FPs) |
Confluence-1 | 2023 | 2571 | ≥500 † | SDM | 24 | Ultrahigh Fiber Count (24 FPs) |
Firmina | 2023 | 2500 | N.A | SDM | 12 | Fiber Count ≥ * 8FPs (12 FPs) |
Bifrost | 2024 | 15,000 | 180 | SDM 1 ASN | 12 | Fiber Count ≥ * 8FPs (12 FPs) |
Apricot | 2024 | 12,000 | 190 | SDM | † 16–20 | Fiber Count ≥ (12 FPs), † (16–20 FPs) |
IEX | 2024 | 9775 | 200 | SDM | † 16 | High Fiber Count (16 FPs) |
Medusa | 2024 | 8760 | 480 | SDM | 24 | Ultrahigh Fiber Count (24 FPs) |
Blue Raman | 2024 | 7500 | 400 † | SDM | 16 | High Fiber Count (16 FPs) |
Caribbean Express (CX) | 2024 | 3472 | 280 | SDM | 18 | Very High Fiber Count (18 FPs) |
Hawaiki Nui | 2025 | 22,000 | 240 | SDM | 12 | Fiber Count ≥ * 8FPs (12 FPs) |
Sea-We-Me 6 | 2025 | 19,200 | 126 | SDM | 10 | Fiber Count ≥ * 8FPs (10 FPs) |
Subsea Component | SDM Cable | Traditional Cable |
---|---|---|
Submarine Cable | High Count of FPs (12, 16 FPs and more in future) | Limited number of FPs (6 FPs and maximum 8 FPs) |
Fiber Effective Area (Aeff) | Low effective area, Aeff 110–80 μm2, att. 0.155 dB/km | High effective area, Aeff 150–125 μm2, att. 0.15 dB/km |
Repeater | Low power repeaters: (+14 to 20 dBm) | Very high power repeaters: (>+20 dBm) |
Repeater Type | Repeater pump farming | Each fiber has own laser pumps |
Branching Unit ROADMs | Fiber pair switching in (BUs) | No fiber pair switching in (BUs) |
OSNR | Low OSNR | High OSNR |
Modulation Formats | PCS (probabilistic constellation shaping) | BPSK, QPSK, 8-QAM and 16-QAM |
C + L Band Technology | Currently only C-Band | C + L Band supported up to 144 channels per FP |
PFE | Same PFE, capacity can be increased | Same PFE |
Topology | Submarine Cable System | Cable Length (Km) | Landing Points | Number of Operators |
---|---|---|---|---|
SeaMeWe-3 | 39,000 | 39 | 52 | |
FLAG Europe-Asia (FEA) | 28,000 | 17 | Global Cloud Xchange | |
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 | |
** SDM Repeater | Peace | 15,000 | 14 | Peace Cable 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 | Amitie | 6792 | 5 | 3 |
TE North/TGN-Eurasia/… | 3634 | 4 | 6 | |
Malbec | 2600 | 3 | Facebook, GlobeNet | |
* SDM Technology | 2Africa | 45,000 | 29 | 8 |
* SDM Technology | Hawaiki Nui | 22,000 | 13 | Hawaiki Submarine Cable |
* SDM Technology | ECHO | 17,184 | 6 | 2 |
* SDM Technology | Bifrost | 15,000 | 5 | 3 |
* SDM Technology | Equiano | 12,000 | 7 | |
* SDM Technology | Apricot | 12,000 | 4 | 7 |
* SDM Technology | Medusa | 8760 | 16 | AFRIX Telecom |
* SDM Technology | Grace Hopper | 7191 | 3 | |
* SDM Technology | Amitie | 6792 | 3 | 5 |
* SDM Technology | Caribbean Express (CX) | 3472 | 11 | OceanNetworks (ONI) |
* SDM Technology | Confluence-1 | 2571 | 5 | Confluence Networks |
EAC-C2C | 36,500 | 16 | Telstra | |
Mesh | Trans-Pacific Express (TPE) | 17,000 | 6 | 7 |
MedNautilus Submarine System | 7000 | 7 | Telecom Italia Sparkle | |
Apollo | 13,000 | 2 | Vodafone | |
CAP-1 | 12,000 | 2 | Amazon Web Services, Facebook | |
Seabras-1 | 10,800 | 2 | Seaborn Networks, Telecom Italia Sparkle | |
Point-to-Point | MAREA | 6605 | 2 | Facebook, Microsoft, Telxius |
INDIGO-Central | 4850 | 2 | 5 | |
JGA-N | 2600 | 2 | RTI | |
BlueMed | 1000 | 2 | Telecom Italia Sparkle | |
* SDM Technology | Dunant | 6400 | 2 | |
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 |
Reference | C (Tb/s) | L (Km) | ↓ SE (b/s/Hz) | Technology |
---|---|---|---|---|
[26] | 71.65 | 6970 | 7.36 | non-SDM |
[26] | 70.46 | 7600 | 7.23 | non-SDM |
[16] * | 24.6 | 6664 | 6.21 | non-SDM |
[27] | 30.58 | 6630 | 6.10 | non-SDM |
[28] | 105.1 | 14,350 | 3.20 | SDM |
[15] | 8.12 | 9750 | 3.20 | SDM |
[14] | 12 | 17,680 | 2.91 | SDM |
[29] | 9.0 | 15,050 | 2.00 | SDM |
Core Pumping | Cladding Pumping | |
---|---|---|
Mode | Single-Mode | Multi-Mode |
Pump Power (W) | Low (−5) | High (−30) |
Wavelength(λ) (nm) Direction | 1480 Backward | 980 Forward |
Number of Pump LD’s | N-Cores | 1 |
Presence of Cooling subsystem | Yes | No |
Pumping Scheme | Acronym | Core Pumping | Clad Pumping | Comments |
---|---|---|---|---|
Individual Core Pumping | ICP | Yes | No | Reference |
Shared Core Pumping | SCP | Yes | No | With 3 dB coupler |
Variable Shared Core Pumping | VSCP | Yes | No | With tunable coupler |
Common Cladding Pumping | CCP | No | Yes | Need of core attenuation |
Hybrid with Individual Core Pumping | HICP | Yes | Yes | - |
Hybrid with Shared Core Pumping | HSCP | Yes | Yes | With 3 dB coupler |
Hybrid with Variable Shared Core Pumping | HVSCP | Yes | Yes | With tunable coupler |
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Papapavlou, C.; Paximadis, K.; Uzunidis, D.; Tomkos, I. Toward SDM-Based Submarine Optical Networks: A Review of Their Evolution and Upcoming Trends. Telecom 2022, 3, 234-280. https://doi.org/10.3390/telecom3020015
Papapavlou C, Paximadis K, Uzunidis D, Tomkos I. Toward SDM-Based Submarine Optical Networks: A Review of Their Evolution and Upcoming Trends. Telecom. 2022; 3(2):234-280. https://doi.org/10.3390/telecom3020015
Chicago/Turabian StylePapapavlou, Charalampos, Konstantinos Paximadis, Dimitrios Uzunidis, and Ioannis Tomkos. 2022. "Toward SDM-Based Submarine Optical Networks: A Review of Their Evolution and Upcoming Trends" Telecom 3, no. 2: 234-280. https://doi.org/10.3390/telecom3020015