To date, multiple system vendors have converged around Class 3-based solutions (Figure 1), recently announcing their next generation offerings. This industry convergence creates the benefit of economies of scale and broad industry investments into the technology used in this baud rate class, the same class being used for 800G MSA pluggable solutions.

Figure 1.  Acacia and other coherent vendors have announced Class 3 Terabit Era solutions.

Advancements Resulting in 65% Power-per-Bit Savings Over Current Competing Solutions
Doubling the baud rate from Class 2 to Class 3 in silicon was a significant engineering achievement, combining design advancements in high-speed Radio Frequency (RF) and Analog to Digital Converter (ADC) and Digital to Analog Converter (DAC) components plus well-designed co-packaging integration of silicon and silicon photonic (SiPh) components. These achievements led to Acacia’s successful 140Gbaud in-house capability that is being leveraged in the commercially available CIM 8 solution.

With high-volume shipments of multiple coherent Class 2 module products utilizing Acacia’s 3D Siliconization, this proven co-packaging integration solution provided the foundation for extending this capability to Class 3 140Gbaud implementation utilized in the CIM 8 (Figure 2). 3D Siliconization maximizes signal integrity by co-packaging all high-speed components including the coherent Digital Signal Processor (DSP) application-specific integrated circuit (ASIC), transmitter and receiver silicon photonics, and 3D stacked RF components into a single device that is manufactured in a standard electronics packaging house. Silicon technology has demonstrated cost and power advantages over alternative technologies, making it the material system of choice for these higher baud rates. These advancements enabling a doubling of the baud rate have led to a 65% power-per-bit savings of CIM 8 over current competing solutions that utilize alternative optical material systems. In addition, the size and power savings of this latest generation enabled the ability to house this 1.2T 140Gbaud solution in a pluggable form-factor.

Figure 2.  An example of 3D Siliconization used in the CIM 8 module, resulting in a volume electronics manufacturable high-speed single device larger than a quarter.

2^nd Generation 3D Shaping Advances Coherent Performance
The CIM 8 is powered by Jannu, Acacia’s 8^th generation coherent DSP ASIC. The design greatly expands on the success of the Pico DSP ASIC predecessor used in the widely deployed performance-optimized Class 2 AC1200 module (Figure 1). The AC1200 was the first module to introduce 3D Shaping, which provided finely tunable Adaptive Baud Rate up to 70Gbaud as well as finely tunable modulation up to 6 bits/symbol. The AC1200 had achieved record breaking spectral efficiency at the time of its introduction, as evidenced by a subsea trial over the MAREA submarine cable connecting Virginia Beach, Virginia to the city of Bilbao in Spain. Finely tunable baud rate helps maximize spectral efficiency in any given passband channel, converting excess margin into additional capacity/reach, and avoids wasted bandwidth due to network fragmentation.

Figure 3.  A popular feature is the fine-tunability of baud rate introduced by Acacia with the Class 2 AC1200; CIM 8 incorporates the same Adaptive Baud feature (as part of 2^nd Generation 3D Shaping) for Class 3 baud rate tunability.

The 5nm Jannu DSP ASIC in CIM 8 intelligently optimizes optical transmission using 2^nd Generation 3D Shaping with an increased Adaptive Baud Rate tunable range up to 140Gbaud, as well as finely tunable modulation up to 6 bits/symbol using enhanced Probabilistic Constellation Shaping (PCS). With 2^nd Generation 3D Shaping, the CIM 8 module can achieve a 20% improvement in spectral efficiency.

Terabit Era Solutions Provide Full Network Coverage
Class 3 technology not only ushers in the terabit era, but also enables full multi-haul network coverage as the high baud rate capabilities transport nx400GbE client traffic across a service provider’s entire network. Full network coverage is not only enabled by adjustment of the modulation, but also implies the capability to optimize for various network conditions which include overcoming transmission impairments.

Figure 4. CIM 8 1.2T, 1T, 800G, and 400G transmission constellations operating at Class 3 baud rates providing wide network coverage addressing multiple applications.

CIM 8 offers significant power-per-bit reductions as well as cost efficiencies for various optical network transport applications.

DCI/Metro Reaches
For transporting 3x400GbE or 12x100GbE client traffic with metro reaches in a single carrier, the CIM 8 is tuned to ~6 bits/symbol (equivalent to 64QAM, example constellation on left). Data center interconnect (DCI) applications would take advantage of this high-capacity 1.2T transport capability to tie data center locations together. This amounts to 38.4T per C-band fiber capacity.

Long-Haul Reaches

For transporting 2x400GbE with long-haul reaches, the CIM 8 is tuned to ~4 bits/symbol (equivalent to 16QAM, example constellation on the right). Wide 800G network coverage is achieved with the Class 3 140Gbaud capabilities enabling service providers to provide end-to-end 2x400GbE, 8x100GbE, or native 800GbE transport across their networks, covering essentially all terrestrial applications.

Ultra-Long-Haul/Subsea Reaches

And for ultra-long-haul/subsea reaches, the CIM 8 is tuned to ~2 bits/symbol (equivalent to QPSK, example constellation on the left). As with the previous scenarios, spectral efficiency with a wavelength channel is optimized by fine-tuning of the baud rate. These high spectrally efficient modes can carry mixed 100GbE and 400GbE traffic over the longest subsea routes in the world with lowest cost per bit. It’s worth noting that almost a decade ago, Acacia demonstrated SiPh capabilities for subsea coherent deployments. CIM 8 incorporates second generation non-linear equalization (NLEQ) capabilities to mitigate the non-linear effects of optical transmission especially for these ultra-long-haul/subsea links providing additional OSNR.

In all the above scenarios, the CIM 8 utilizes advanced power-efficient algorithms to compensate for chromatic and polarization dependent dispersion. In addition, the module accounts for coverage of aerial fiber network segments that require fast state-of-polarization (SOP) tracking and recovery due to lightning strikes. The SOP tracking speed of CIM 8 is double the speed of its predecessor. This fast SOP tracking feature can also be utilized for sensing applications.

Network Operators Achieve Record Breaking Field Trials with CIM 8
CIM 8 capabilities have already been put to the test as illustrated by multiple record breaking field trials across a wide range of applications. These include >5600km 400G transmission over a mobile carrier’s backbone network, 2200km 800G transmission over a research and education network, and >540km 1T transmission over a wholesale carrier’s network.

Acacia continues to demonstrate its technology leadership by leveraging mature knowledge in proven silicon-based coherent technology, producing the first shipping coherent solution to lead the industry into the Terabit Era with the 1.2T pluggable CIM 8 module. With the breakthrough capability of 140Gbaud transmission along with the advanced Jannu DSP ASIC using 2^nd Gen 3D Shaping and leveraging 3D Siliconization, network operators can support full network coverage for multi-haul applications, especially to support growing demands for nx400GbE and upcoming 800GbE traffic.

References:
Blog: Terabit Today: Maximize Network Coverage
Blog: How Industry Trends are Driving Coherent Technology Classifications
Blog Series: The Road Ahead for Next-Generation Multi-Haul Designs Part 1, Part 2, Part 3

The world’s leading annual submarine communications gathering – Submarine Networks World –  takes place this week virtually. Despite other communications networks being adopted, subsea networks still transport more than 99 percent of all intercontinental traffic.  The increase in the amount of people working from home in 2020, increases in e-commerce, more online digital platforms, and reliance on big data have all led to an increase in global bandwidth demand and a key factor driving the growth of the submarine cable system. There are currently hundreds of submarine fiber optic cables buried in oceans around the world stretching over approximately 750,000 miles that connect land cables from one continent to another. It’s these same cables that enable Submarine Networks World to be brought to you live into homes and offices this week. This cable map from TeleGeography provides a comprehensive view of each cable’s owner and endpoints.

Source: TeleGeography, Copyright © 2020 PriMetrica, Inc.

Submarine networks are critical pieces to the global flow of network data. While submarine cables were traditionally owned by telecom carriers, it’s been the content providers themselves, such as Google, Facebook, Microsoft and Amazon that have started investing in the build-out of new undersea cables in recent years to ensure they meet the internet bandwidth required for the cloud and streaming media services they provide. Key to meeting this demand is the use of fiber optics technology and advanced coherent transmission systems in both new and older cables.

Maximizing Transmission Capacity is Critical
Because it’s very expensive to build and lay undersea cables, maximizing transmission capacity is extremely important. However, a key challenge with submarine cables is overcoming chromatic dispersion and non-linear impairments which reduce capacity. In this video, Acacia’s Valeria Arlunno explains how using coherent optical communications technology overcomes this challenge.  As Valeria points out, to help maximize capacity and spectral efficiency, additional Digital Signal Processing (DSP) features are required. Continuous adjustment of the coherent modulation format and baud rate have enabled submarine network operators to improve the performance by finely tuning the balance between capacity and impairment penalty. In a submarine link, these fine-tuning capabilities are a key asset is maximizing the cable capacity using coherent optical transmission in either new or legacy fiber. These key capabilities are embodied in Acacia’s 3D shaping technologies in the Acacia Pico DSP.

Using Acacia’s AC1200 coherent module powered by Acacia’s Pico Digital Signal Processor (DSP), Acacia successfully transmitted the first 400G single carrier DWDM signal over the 6600km transatlantic Marea submarine Cable, achieving a spectral efficiency of 6.41 b/s/Hz.  Completed in 2017, this massive 10-million pound cable is located 17,000 feet under sea in some places, and runs between Virginia Beach, Virginia and Bilbao, Spain.

Cisco Makes Waves in Subsea Market
Acacia’s customer Cisco has announced multiple subsea trials and deployments with its NCS 1004 packet optical transport system that leverages Acacia’s AC1200 powered by Acacia’s Pico DSP chip including Cisco demonstrating 26.4Tbps on the MAREA transatlantic subsea cable.

In this blog, they discuss how they were able to demonstrate the benefits of the NCS 1004 over a subsea cable in production. The cable Cisco tested ran over 10,000km with accumulated chromatic dispersion of 210,000 ps/nm. This cable was designed as an open cable and had a ROADM line system already deployed with over 20 percent of the spectrum consumed by 200G channels from a current generation transponder. As part of the trial with the NCS 1004, Cisco tested 200G and 300G over different baud-rates across different parts of the spectrum.

With this test, Cisco’s solution achieved significant milestones. The NCS 1004 drove a single wavelength of 300G over a 10,000km sub-sea link. The spectral efficiency achieved was 43 percent better than any other option available in the industry today. As part of the testing, Cisco validated multiple combinations of bits per symbol and baud-rate for 200G line rate that provided granular control of spectral efficiency and Q-margin. This was demonstrated with the NCS 1004 operating as an alien wavelength over an existing third party SLTE platform running live traffic.

In addition, Cisco and Superloop announced two deployments of up to 400G for 4600km on the INDIGO West cable from Singapore to Australia, and the INDIGO Central cable from Perth to Sydney, featuring a two-fibre pair ‘open cable’ design with new spectrum sharing technology.

Connect with Us
Even though Submarine Network World will be virtual, we expect it to be an informative and interesting show – and we expect coherent technology to be a key topic to address growing bandwidth demand. To learn more about Acacia’s coherent optical solutions for submarine cable applications, contact us to set up a meeting.