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

These examples illustrate how the interconnects that make up the data center network infrastructure play an important role in a hyperscaler’s network evolution. Recently introduced 400G switches and pluggable optical modules are new tools that enable hyperscalers to transform how data center networks are being architected, with an anticipated impact of comparable magnitude to when 10G and later 100G solutions were introduced. These 400G solutions are designed to enable network operators to address increasing bandwidth demand through a simplified network architecture, targeting the reduction of both capex and opex.

Figure 1: Data center network operators can scale up DCI bandwidth with 400G 400ZR and OpenZR+ solutions.

High-capacity switch and router platforms with 400 gigabit Ethernet ports are transforming hyperscale data center networks by enabling higher switching capacity (using 12.8/25.6Tbps ASICs). Recently introduced 400ZR and OpenZR+ QSFP-DD or OSFP form-factor coherent optical modules are designed to plug into these ports. A network operator with a sizeable percentage of 400G optical Ethernet connections between switches/routers less than 120km links in their edge network can utilize 400ZR modules, while OpenZR+ modules can be used for regional links greater than 120km. Network operators can plug these modules into ports alongside shorter reach client optics modules.

New deployment opportunities can leverage the capability of having both transport (400ZR/OpenZR+) and client optics plugged in the same switch/router to support an IP-over-DWDM (IPoDWDM) network architecture where switching is performed at the IP layer rather than the optical transport layer. An IPoDWDM network reduces cost per bit as well as operational overhead since a separate transport platform layer is not required, and network management can be consolidated. Eliminating the separate transport layer can also result in solution density improvements and reduced power consumption of approximately 25%.

Figure 2: Two architectures to support 400G IP/Ethernet traffic over an optical infrastructure are (1) traditional separation of the IP/Ethernet layer from the DWDM optical transport layer (top) or (2) IP-over-DWDM using 400ZR or OpenZR+ modules which plug directly into the switch/routers (bottom).

Transport optics in pluggable client form factors plugged directly into routers/switches is not an entirely new concept. What makes 400ZR/OpenZR+ different than earlier 100G solutions (besides the 4x capacity increase) is longer reach capability via coherent transmission, and wavelength tunability which provides operational benefits of deployment ease and spares reduction.

Legacy architectures that use a separate DWDM optical transport platform with a modular design (via line-cards or sleds) can be designed with an upgrade path to support these new 400G interfaces. Ethernet-centric ports can then be economically optimized using pluggable 400ZR or OpenZR+ modules.

Figure 3: Acacia 400G pluggable coherent optical modules supporting 400ZR and OpenZR+ (QSFP-DD on left, OSFP on right).

Some hyperscalers may find it necessary to maintain a separate IP layer from the optical transport layer, especially to support legacy infrastructure. Others may want to reduce the amount of equipment they have to manage using IPoDWDM if they do not require supporting legacy infrastructure, especially given scalability concerns.

To enable the wide adoption of 400ZR, these modules should be designed for volume production. However, packaging optics into the QSFP-DD/OSFP form factors is challenging. Complying with these compact mechanical designs while meeting specifications for performance, power consumption and cost focuses on three important areas: the DSP, optical/electrical component consolidation, and high-density packaging.

Acacia’s 3D Siliconization follows the example of the electronics world, applying integration and co-packaging techniques such as 3D stacking. Advantages of 3D Siliconization include the reduction of electrical inter-connects while preserving robust signal integrity, as well as using silicon photonics to leverage electronics semiconductor fabrication process suitable for volume production and high yields.

After much anticipation, the curtain has been drawn open. Entering onto the stage…400G pluggable coherent transceiver modules! The recent introduction of 400G solutions, such as Acacia’s 400ZR and OpenZR+ pluggable coherent optical modules, were designed to bring about another transformative implementation of optical networking solutions for data center interconnects.

Stay tuned for our next 400G blog, when we will go into more details on the applications driving OpenZR+ requirement.

To address the need for higher DCI bandwidth requirements to meet this growing demand, the optical networking industry began working on a solution known as the 400ZR implementation agreement, with a goal to combine optical line-side fiber capacity with the benefits of client-side solutions.

Spearheaded by the Optical Internetworking Forum (OIF), 400ZR aims to deliver accessible 400 gigabit-per-second (Gbps) Ethernet links for edge DCI applications. The 400ZR implementation agreement addresses edge-DCI applications with link distances targeting 80 km to 120 km and can be implemented in pluggable 400Gbps optical transceiver module form-factors used for client optics.

The primary 400ZR use case is to apply the technology to DCI edge networks.

The 400ZR standard leverages the reach and capacity benefits of coherent optical technology, while challenging the industry to implement the technology in compact pluggable module form-factors such as QSFP-DD and OSFP.

We recently published a market backgrounder that reviews the industry drivers behind the development of 400ZR, the key benefits of the technology, and a product-development roadmap for bringing 400ZR transceivers to market. It also provides a few predictions on how the technology could potentially change the industry. Check it out to learn more and let us know what your predictions are.

Read the White Paper