The Optical Internetworking Forum (OIF) kicked off the 400G MSA pluggable generation with development of the 400ZR implementation agreement enabling point-to-point amplified links up to 120km operating at 60+Gbaud data rates. Around the same timeframe, the OpenROADM MSA defined 400G interfaces for ROADM networks and extended reaches; the OpenZR+ MSA leveraged these higher performance interfaces to enable interoperable enhanced performance links for 400G pluggable modules (Figure 1).

The introduction of high-transmit optical power (>0dBm) ZR+ modules such as Acacia’s Bright 400ZR+ module further expanded the 400G MSA pluggable space to include brownfield ROADM network architectures (with existing transponder channels ~0dBm). Driven by increasing bandwidth demands from applications such as AI, network operators are now looking towards a new generation of MSA pluggable products that further expand applicable networking scenarios that operators can leverage to scale and meet these demands.

How Industry Standards Benefit MSA Pluggable Module Adoption
The latest array of MSA pluggable products introduces a new set of capabilities that network operators can utilize to increase capacity and extend reach. These products provide the ability to deploy 800G with ZR, ZR+, and high-transmit optical power capabilities, as well as extending the capabilities of existing 400G router interfaces to support ultra-long-haul (ULH) reach capabilities. This new generation of modules continues to leverage industry standardization while also borrowing capabilities from performance-optimized coherent solutions. These capabilities include high-baud rate transmission allowing for a doubling of baud rates from the previous Class 2 (~60+Gbaud range) generation to Class 3 (~120+Gbaud range) baud rates, the use of probabilistic constellation shaping (PCS) for enhanced transmission performance, and L-band support for spectrum range expansion.

Figure 1.  Interoperability approaches at 400G vs. 800G.

Industry standardization of coherent solutions plays a key role in enabling economies of scale. Users of 400G coherent MSA pluggable modules such as 400ZR/ZR+ have benefited from the efforts of OIF, OpenZR+ MSA, and OpenROADM MSA to provide industry agreements on module specifications resulting in a diverse supply base. We have seen similar efforts to garner industry standardization as users transition to 800G MSA pluggables. There are three main elements that differentiate 800G relative to 400G and are adapted from previously developed performance-optimized solutions.

1. Interop PCS for Enhanced Performance
   A key difference between 400G and 800G interoperability approaches for an enhanced performance “ZR+” is that instead of using enhanced performance forward error correction, oFEC, to provide improved 400G performance, 800G uses industry standard interoperable probabilistic constellation shaping (PCS) for enhancing performance. PCS is a transmission shaping technique that provides additional link performance beyond traditional transmission modes such as 16QAM. Industry standardization of an interoperable PCS transmission shaping function, once relegated to proprietary performance-optimized transponder platforms including those for submarine applications, is a tremendous leap forward in the progress of MSA pluggable module capabilities. Multi-vendor 800G module supply chain diversity from a DSP ASIC perspective is possible when the 800G ZR+ performance enhancement mode utilizes the industry standard interoperable PCS mode.
2. High Baud Rate Design
   PCS is not the only technology that has been adapted from performance-optimized solutions for MSA pluggables. 800G as well as a 400G ULH pluggable solutions require a high-baud rate design operating in the Class 3 ~120+ Gbaud data rate range. Acacia’s performance-optimized CIM 8 module capable of 140Gbaud speeds has already proven that its deployed technology far exceeds the requirement for the new generation of MSA pluggables. Operation at these high baud rates benefits heavily from the advanced integration and RF signal optimization techniques that Acacia introduced in our 400G MSA pluggable product family.

Figure 2.  Tightly integrated components enable 120+Gbaud data-rate capabilities.

3. C & L Band Support
A third element of the latest 800G MSA pluggable generation that is borrowed from performance-optimized designs is the capability to transmit in the L-band wavelength range, in addition to the traditional C-band DWDM range. By adding L-band supporting infrastructure to a network, the network capacity is approximately doubled. Network operators now have an option beyond utilizing a transponder platform if they wish to use L-band expansion to increase network capacity.

Figure 3.  New generation of coherent MSA pluggable modules to take advantage of L-Band transmission window, adding to existing C-Band support.

Pluggable Interoperable Interfaces are Driving Adoption of 800G Modules
Acacia’s latest family of coherent solutions are powered by its 9th generation DSP ASIC called Delphi. These modules include support for OIF 800ZR, interoperable 800G ZR+ using the OpenROADM interop PCS mode, and 400G ULH for ultra-long-haul reaches. These modules utilize Acacia’s 3D Siliconization providing a highly integrated design enabling high-baud rate modulation. With support for QSFP-DD and OSFP form factors, as well as >+1dBm transmit optical power and L-band support, Acacia’s Delphi generation of products leverage the deployment successes of our performance-optimized CIM 8 module to provide MSA pluggable products that offer increased capacity and longer reaches.

Figure 4.  Acacia’s latest generation of MSA pluggable 800G and 400G ULH modules.

Similar to the successful path we saw 400G pluggables experience, these modules are delivering the performance and interoperability that is critical for driving economies of scale and widespread adoption. With data center bandwidth continuing to grow rapidly, fueled by emerging new applications such as AI, these high-performance pluggable modules are on track to become an important tool for network operators to cost-efficiently scale their networks to meet this surging demand.

See Us at ECOC 2024!
Acacia is excited to be participating in the OIF interoperability demo at ECOC 2024 showcasing both its 400G and 800G pluggables; demos will take place in the OIF booth #B83. Acacia will also be demonstrating the Interoperable 800G ZR+ module in our meeting room at ECOC. Click here to set up a meeting.

We hope to see you in Frankfurt!

Introduction
In Part 2 of this blog series, I discussed how the approach of common development based on silicon photonics (SiPh) benefits both performance-optimized multi-haul and MSA pluggable coherent products. In this blog, I expand on why the adoption of standardized baud rates to support Nx400GbE client traffic has been advantageous for MSA pluggable adoption as well as for maximizing multi-haul 400G network coverage in a service provider network. I also discuss how the growth in coherent pluggable shipments impacts the development of performance-optimized multi-haul coherent solutions.

Intuitive Coherent Classifications
With 400GbE becoming today’s unit of traffic currency, it is important to understand what coherent operating conditions are required to efficiently transport 400GbE client traffic. Prior generation leading-edge modulation technology for commercialization was at ~60-68Gbaud (Class 2), which utilized ~4 bits/symbol (~16QAM) modulation to support 1x400GbE client traffic over a 400G wavelength. We saw OIF 400ZR, OpenZR+ MSA, and Open ROADM adopt this transmission scheme for high-volume MSA pluggable applications. Performance-optimized multi-haul coherent solutions also leveraged Class 2 baud rates with dynamic transmission shaping that was centered at ~4 bits/symbol. In addition, multi-haul solutions supported higher capacity with 6 bits/symbol (~64QAM) for shorter reach DCI/Edge applications as well as maximum reach using 2 bits/symbol (~QPSK) for subsea applications. Multi-haul coherent DSPs can dial up or down the desired bits/symbol transmission within this dynamic range.

Moving to the next generation of coherent solutions, a similar approach is being followed to support Nx400GbE traffic per wavelength. In this case, leading edge ~120-136Gbaud Class 3 modulation technology can double the transport capacity compared to Class 2. With Class 3 technology, and using ~4 bits/symbol range, near complete coverage of a service provider’s network with 2x400GbE traffic (800G per wavelength line rate transmission) is possible, as discussed in a previous blog. By dialing the modulation bits/symbol down to ~2 bits/symbol, 1x400GbE subsea applications are possible, while dialing up to ~6 bits/symbol, 3x400GbE client traffic can be transported over a 1.2T wavelength for shorter reach DCI/Edge applications.

Figure 1 shows the number of supported 400GbE clients that can be transported over a single coherent wavelength as a function of baud rate class and ~2, ~4, and ~6 bits/symbol values.

Figure 1. Matrix showing the number of supported 400GbE clients that can be transported over a single coherent wavelength as a function of bits/symbol and baud rate class. Broad Nx400GbE network coverage becomes possible as we move to Class 3 baud rate implementations.

Figure 1 also illustrates how doubling the baud rate maintains the same network coverage (vis-à -vis reach) while doubling the capacity. With performance innovations, the coverage at this doubled capacity may even be greater than the previous class.

Implications of Shipment Trends
The good news is that the technology investments that went into supporting Class 2 coherent pluggable MSA solutions (green-shaded cell in Figure 1) are coming to fruition with high-volume shipments already occurring. In fact, Acacia recently announced over 50k port shipments of 400G coherent pluggable solutions. This is contributing to a notable transition: the number of pluggable coherent modules shipments is forecasted to exceed that of performance-optimized (embedded) coherent module shipments (Figure 2).

What are the implications of the growing adoption of MSA pluggable solutions? The overarching implication for coherent design evolution is that standardization/industry consensus (e.g., baud rates), design elements (e.g., high-speed electrical components), as well as materials and processes (e.g., silicon, SiPh, CMOS processes, co-packaging) that support high-volume MSA pluggable solutions all have a favorable impact on performance-optimized multi-haul solutions. In Part 2, I went into detail about how a common silicon platform enables a cycle of coherent development. The Figure 2 data below indicates that given this growth in MSA pluggable ports, we should see a greater beneficial impact to performance-optimized multi-haul designs because higher volume pluggable solutions can lead to better cost efficiencies, assuming both the multi-haul and MSA pluggable designs leverage a common technology platform.

Figure 2. LightCounting data showing the number of globally shipped MSA pluggable coherent ports exceeding the number of proprietary form-factor ports.

The Road Ahead for Multi-Haul Solutions—CIM 8
As the industry moves towards supporting higher transmission line rates, a natural path to higher steps in baud rate are becoming clearer. Doubling the Class 2 baud rates aligns with the Class 3 120Gbaud+ rates that are being standardized for transport of 800G client traffic. By leveraging common silicon processes and technology, performance-optimized solutions can benefit from the economies of scale.

The recently announced Acacia Coherent Interconnect Module 8 (CIM 8) powered by Acacia’s Jannu DSP are in line with this approach. The CIM 8 is a performance-optimized multi-haul solution that delivers industry-leading performance with single carrier 1.2T operation using 3D Siliconization packaging technology that includes the silicon photonics integrated circuit (SiPh PIC), high-speed modulator driver and transimpedance amplifier (TIA) in a single opto-electronic package. The miniaturization of the module components has resulted in a 140Gbaud multi-haul module design capable of faceplate pluggability.

Figure 3. Acacia’s Coherent Interconnect Module 8 is designed to incorporate many aspects of technology leveraged from higher-volume products (e.g., SiPh, processes, components, packaging).

The CIM 8 can provide efficient transport of 400GbE client traffic across the entire network, including 90 percent coverage using 800G (2x400GbE client traffic), corresponding to the Class 3 row in Figure 1.

All Roads Lead to Multi-Haul

Figure 4. By utilizing common silicon technology, Acacia can leverage the advantages of volume and high-performance designs creating a generational development cycle, with advancements over time, that can result in cost efficiencies as well as time-to-market advantages.

Coherent solutions have evolved from long-distance applications at relatively moderate volumes and are now at a point in the road where shorter distance high-volume applications are driving a demand exceeding their long-distance counterparts. By leveraging standardized baud rates aligned with the corresponding bits/symbol modulation optimized for Nx400GbE, we can increase the overlap of silicon-based design and investments between high-volume MSA pluggable and performance-optimized multi-haul coherent solutions. This enhances the coherent cycle of development, resulting in multi-haul solutions benefiting from volume manufacturable designs while leveraging common technology, which are important for maintaining cost-efficiencies for network operators as bandwidth demand continues to grow.

Learn More About the Considerations Driving Next Generation Multi-Haul Solutions:

Part 2 of 3
Part 1 of 3