Market Adoption and Use Case Expansion
Coherent pluggables have seen remarkable market adoption, with 400G ZR/ZR+ coherent optics becoming the most widely adopted coherent technology in history. While some in the industry predicted early on that 400ZR pluggables would only be a small portion of the coherent market, Acacia has been laser focused on bringing these solutions to its customers to deliver the architectural change needed to transform networks to meet ever-growing bandwidth demands. As a result, Acacia is a market leader in shipments of 400G+ coherent pluggables.

During 2024, Acacia expanded this market-leading portfolio with the introduction of 800ZR and 800G ZR+ pluggables with Interoperable PCS in QSFP-DD and OSFP form factors. These solutions have already been proven in field trials, with Colt being the first provider to successfully trial enhanced performance 800G ZR+ coherent pluggable optics. These 800G router-based optics provide the capability to double Colt’s packet core capacity per link while reducing power per bit by 33.3%.

Acacia also introduced a 400G Ultra Long Haul QSFP-DD module for expanding 400G applications from DCI/metro to long haul applications. The 400G UHL has been proven in field trials, with Arelion announcing that it completed a live network field trial on its route from Chicago to Denver that demonstrated successful IP transmission at a spectrum of 112.5 gigahertz over 2,253 kilometers, with healthy margins, providing longer transmission distances and greater cost savings than currently deployed transponders. Acacia’s 400G ULH pluggables enable Arelion to reduce CAPEX by 35 percent and OPEX costs by 84 percent when expanding its network, providing wider reach with high capacities that support customers’ AI/ML and cloud applications.

The Terabit Era is Going Strong
According to Cignal AI, in 2025, 1.2T+ performance optimized solutions will contribute significantly to bandwidth growth as those solutions continue to be introduced. Acacia’s 1.2T Coherent Interconnect Module 8 (CIM 8), powered by the Jannu DSP, has proven its outstanding performance with multiple record-breaking field trials across Metro, Long Haul and Subsea with Microsoft, Verizon, Windstream, and others. Acacia is also engaged with multiple webscale customers and expects CIM 8 to continue its ramp in 2025.

Looking Ahead…..Artificial Intelligence, 1600ZR/ZR+ and More!
AI certainly was a hot topic during OFC and ECOC in 2024 and Acacia believes it will continue to be in 2025. While a year ago, the industry was focused on single-site AI clusters, we will begin to hear more about methods for distributing AI training over different locations in 2025. And while there is still a lot of work to happen in this area, the optics industry is well positioned to be at the forefront of this evolution since higher speed optical interconnections will be necessary to mitigate bandwidth constraints within an AI networks. Read this recent blog for more information on future proofing your network for AI.

Router-based Coherent Optics
The proliferation of router-based coherent optics is paving the way to a converged IP+Optical network architecture. The benefits in 2024 were clear. Infrastructure provider Colt Technology Services reported a stunning 97% energy savings, and Arelion saved 64% in CapEx and 76% in OpEx. In 2025, we can expect to see more providers leveraging this architecture to achieve increased capacity, reduced energy consumption, and lowered network costs, complexity, and footprint.

1600ZR and 1600ZR+ Standards Agreement
The OIF launched efforts last year on 1.6T coherent optical interconnect solutions and is making progress towards interoperable 1600ZR and 1600ZR+ implementation agreements.  In 2025, the industry will be looking at ways to advance this migration using advanced technologies for high baud rate modulation and smaller CMOS nodes.

Looking to the Future
Acacia is looking forward to another year of industry-wide innovation. Helping to solve some of our customers’ most challenging problems has been part of our DNA since Acacia was founded in 2009 and as you can see from this historic timeline, we have continued to set new benchmarks for performance and efficiency. These innovations are not only addressing the current demands of high capacity networks, but are also paving the way for future growth and scalability. Key to this success has been listening to our customers and designing the products and features that they need to be successful. We look forward to continuing that tradition.

Network operators need to efficiently scale their networks to keep up with growing user bandwidth demands.  To meet this need, it is going to be increasingly important to develop next-generation solutions based on scalable technologies that are aligned with industry trends.

Trends Driving Coherent Optical Development

Coherent Moving to Shorter Reaches
As the industry moves to higher data rates, coherent is being adopted in shorter reach interfaces, which is increasing the share of coherent ports that are deployed in pluggable form factors. For example, the 400ZR specification targeted 80-120km reaches, and subsequently the OIF is now working on a project to define an 800LR that targets 10km and below. As this trend continues, it is likely that we’ll also see coherent move into the data center in future generations. These shorter reach interfaces tend to be higher volume than traditional transport applications, and as we look at this transition, it becomes more important to have interoperability and pluggable form factors that can plug directly into router interfaces.

Standardization is Key
The industry has been steadily moving to more standardization. 400G was a significant step forward and today we have a variety of standardized interfaces including 400ZR/ZR+ and Open ROADM – all of which are growing. These standardized interfaces are displacing both proprietary solutions in more traditional transport applications as well as direct detect solutions in shorter reach interfaces. Over time, most optical industry analysts agree that these standardized pluggable interfaces are expected to contribute a larger and larger portion of all the coherent ports in the industry.  Multi-haul solutions that address multiple applications will still be needed, but it will be important to align these multi-haul investments with standards.

Approaching the Shannon Limit
From a development perspective, incremental improvements in spectral efficiency are being made as we approach the Shannon Limit, but we need to find ways to grow network bandwidth more efficiently over time. In the past, we were able to scale the amount of data being transmitted over a single set of optics, while also increasing capacity on the fiber. Today, we are scaling as we increase baud rate, but the amount of data on the fiber is growing more incrementally. This is changing the way we develop products for the future and increasing baud rate cost-effectively is critical moving forward.

These three trends point to high-volume standardized solutions having a greater influence on next generation industry investment.

Coherent Technology Classifications

The below figure illustrates how coherent technology has evolved in response to growing bandwidth demands. Different baud rate classes are grouped based on technological capabilities, industry standardization (such as OIF, IEEE, Open ROADM, OpenZR+ MSA, CableLabs, ITU, IEEE) and common industry investments. Throughout this evolution, it has been critical that each successive class support similar reaches to the previous class.

Baud rate has doubled for each coherent technology class.

Class 1
There was a long period during the early days of coherent technology development with multiple investment nodes. At 30-34 Gbaud, there were 100G and 200G products and the industry made a significant investment at this stage. In this generation, there was widespread standardization of components such as modulators and receivers. However, standardized optical interfaces sacrificed significant performance compared to proprietary implementations, so they were not widely adopted.

Class 2
This is where the industry is today, and it is during this stage that standardized optical interfaces are being widely deployed for the first time. The first Class 2 products were proprietary interfaces supporting multi-haul applications in embedded module form factors. Later, 400G faceplate pluggables, driven by standardization efforts that drove heavy investments into products centered around 16QAM, 60+Gbaud per 75GHz channel transmission were introduced with strong industry adoption. When we migrated to Class 2, we doubled the baud rate and enabled an increase in the data rate.

Class 3
These products once again represent a doubling of baud rate compared to the class before it, with products migrating to 120-136 Gbaud. This approach of doubling baud rate is utilized in standards because it allows for this doubling of data rate using the same modulation format as the previous class. 4 bits/symbol was chosen for 400G standards because it supports a wide range of applications. When scaling from 400G to 800G, doubling the baud rate is the logical path forward.

Class 4
These products will continue the trend we saw in the earlier classes where the model is to increase baud rate but take additional steps to cover all applications. Like earlier trends, we expect the baud rate to also double from Class 3 to Class 4 products, while utilizing the same modulation order.

“These classifications basically mirror industry investment cycles, which is absolutely the right way to align coherent technology development around,” said Alan Weckel, Founder and Technology Analyst at 650 Group. “At the end of the day, operators need solutions to be cost effective and the best way to do that is to leverage the investment across all the various applications and benefit from higher volume production and scale. Increasingly coherent ports are moving to pluggable form factors and as we approach the Shannon Limit, further improvement in cost will come from going to higher baud rates, but in cost effective way.”

Acacia’s Class 3 Solution
Acacia’s recently announced Coherent Interconnect Module 8 (CIM 8)  is a Class 3 solution that can address transmission of multiple 400GbE client interfaces over virtually any network application, delivering 1.2T per carrier capacity for high-capacity DCI interfaces and 800G per carrier capacity over most optical links using 4 bits/symbol (~16QAM) modulation. This product supports 150GHz channels with double the capacity per carrier and longer reach than that of the previous class, providing a simple, scalable path that is compatible with the previous network architecture generation.

Acacia’s CIM 8 is the industry’s first 1.2 faceplate pluggable coherent module, powered by Acacia’s Jannu 5nm CMOS digital signal processor (DSP) ASIC. This solution delivers industry-leading performance with single carrier 1.2T operation and combines the Jannu DSP with 3D Siliconization packaging technology which includes the silicon photonics integrated circuit (SiPh PIC), high-speed modulator driver and transimpedance amplifier (TIA) in a single opto-electronic package. With 3D Siliconization, the high-speed RF interfaces are tightly coupled together, resulting in improved signal integrity for high baud rate signals. The high-density packaging as well as an advanced high-speed modulator design that enables the 140Gbaud performance as explained in this white paper.

The Future of Coherent Development

As the coherent technology classifications chart highlights above, the industry has undergone several large investment phases.  This has been good for the industry because it allowed vendors to have a significant ROI, worked well with network operator upgrade cycles, and avoided many small iterative steps in between. However, moving forward it is going to be important to align with these industry investments. As a result, we need to think about how to develop solutions that scale to high volume in a power-efficient and cost-effective way. Silicon photonic based coherent interfaces have proven to be successful in meeting these challenges generation after generation and we believe this technology can continue to help effectively meet bandwidth demands of the future.

Acacia was a pioneer of silicon photonics in 2012 when it was the first coherent module vendor to envision silicon as the platform for the integration of multiple discreet photonic functions while increasing the density and reducing cost of optical interconnect products. According to Gazettabyte, Acacia’s choice to back silicon photonics for coherent optics was an “industry trailblazing decision.”

Leveraging advancements in silicon photonics processing, Acacia was able to deliver generations of high-volume silicon photonics-based products that continually enabled higher transmission data rates, lower power, and higher performance than the generation before it. Early on, some skeptics dismissed silicon photonics as incapable of achieving the performance required for coherent optical transmissions over long-haul distances. As evidenced by today’s deployments of Acacia’s 1.2T multi-haul AC1200 coherent optical module in well over a hundred customer networks which include subsea, long-haul, regional, metro and DCI applications, it is clear that silicon photonics can achieve industry leading performance.

Today, Acacia’s solutions leveraging silicon photonics are available in a wide range of coherent optical interfaces, from edge and access to subsea applications, to enable high-speed transmission and excellent performance.

Acacia’s silicon photonics leadership timeline for coherent transmission.

The Power of Silicon Photonics

Using silicon as an optical medium and leveraging CMOS fabrication processing technology, silicon photonics allows tighter monolithic integration of many optical functions within a single device. While traditional optics systems used many discrete pieces, silicon photonics allows all those pieces to fit onto a single silicon chip.  This tight integration is what has allowed component vendors to continually drive reductions in the cost and size of optical solutions. For network equipment manufacturer customers, using the silicon photonics chip means they can design more ports per linecard, increasing the capacity of their system.

Below are a few reasons that silicon photonics has been so successful and has emerged as a key technology for existing and future optics solutions.

• Leverages CMOS Processes– Silicon photonics leverages the higher yields and lower cost associated with CMOS. Leveraging mature silicon process technologies means that much larger wafers can be made in silicon than traditional optics materials. Today’s silicon photonics solutions run on lines that accommodate up to 12-inch wafers or larger. These larger wafers result in an order of magnitude more dies per wafer, which lowers cost.
• Enables Package Level Integration – As the industry continues to move toward higher data rates and lower power, the interface between the DSP and high-speed optics is quickly becoming a bottleneck. Every time a high-speed signal needs to transition across an additional electrical interface (solder bumps, wire-bonds, vias, PCB traces) there is loss and distortion. Compensating for this additional loss adds power dissipation, and distortion limits performance. Using silicon photonics enables package-level integration that can better optimize these high-speed interfaces and accelerate the realization of higher data rates at lower power.  In addition, silicon photonics is temperature tolerant and thus is not affected by the heat-generating DSP.
• Ensures High Reliability –
  • Overall, silicon photonics increases reliability with the high level of integration reducing the number of component interconnects, which are a common source of failure
  • Traditional optics degrade in high-moisture environments, requiring optics to be packaged in costly hermetic gold boxes, which are historically one of the most common sources of failure for optics. Silicon, on the other hand, does not require hermiticity so by using silicon photonics the costly gold boxes are eliminated which improves reliability
  • In addition to having higher yields than traditional optics materials, silicon photonics can also be tested at the wafer level. Good die can be identified early in the process, and there is no labor wasted on material that will ultimately fail thereby reducing cost.
• Simplifies Deployment and Management – Pluggable modules with industry standard interfaces allow vendors to simplify their networks.

Higher baud rate designs

The next battle for the industry is achieving higher baud rates in a cost-effective way. As the gap to Shannon’s Limit narrows, it is becoming more difficult to increase channel capacity by increasing the modulation order while keeping the same transmission distance. This leaves higher baud rates as a preferred method to increase capacity and decrease cost per bit. Silicon photonics and advances in packaging technology enabled by silicon photonics are key for enabling higher baud rate designs.

Component Stacking

In component stacking, electrical impairments are reduced due to very short electrical connections between key RF components, creating a robust signal path for extremely high frequency/baud rate operation. In this stacked design, the gold-box packaging is eliminated, the DSP, and PIC are tightly co-packaged on the same substrate, and the high-speed modulator driver and TIA components are stacked on the PIC.  Stacked design has a higher (better) frequency response than the traditional gold-box design. Advanced stacking designs can further reduce interconnect impairments, resulting in even higher frequency response.

Illustration of example electrical interconnect frequency response comparing traditional gold-box and stacking integration shows that stacking provides a path to >100Gbaud.

New, Innovative Architectures and Future Innovations

Because of its ability to drive performance and volume manufacturability, silicon photonics has the potential to unlock new architectures needed to keep up with rising demand.  An example is pluggable coherent transceivers that can be plugged directly into switches and routers offering the same density for both coherent DWDM and client optics in the same chassis.  It can also drive future generations of optics design that push the envelope on performance, cost, complexity, and size.

The industry is now turning to silicon to produce a wide variety of devices, using mainstream silicon manufacturing process technologies that have matured over many years.  As optical transceivers need to support higher data-rate, driven by the demand for higher speed networks that can handle the rising bandwidth demand, we believe silicon photonics will once again allow the capacity to grow without significantly increasing the size and cost of the devices needed for the future. For this reason and the benefits discussed above, Acacia plans to use silicon photonics in all coherent applications going forward to help customers stay ahead of the curve.

400G Pluggables Enter Deployment Phase
We are now seeing our service provider and hyperscaler customers preparing for an aggressive ramp to 400G services in the second half of 2021. They see significant opportunities to use coherent optics in switches and routers to simplify architectures and achieve reductions in CapEx and OpEx. In the last 6 months, there have been trial and testing announcements from Windstream Wholesale , Telia Carrier, and Colt highlighting the use of 400G pluggables in a carrier network environment. More recently, ADVA announced interoperability of Acacia’s high-performance coherent platform in a QSFP-DD form factor with ADVA’s new DCI OLS, providing DCI networks a clear path to a compact and cost-efficient optical layer assembled with best-in-class innovation. The success of these ongoing trials and tests have demonstrated the architectural benefits that 400G pluggables can provide to cloud data center interconnect (DCI) and service provider network operators.

Going Further Faster with High-Performance Embedded Solutions
Demand for high-performance embedded solutions continues to climb as network operators look for solutions that improve efficiency and maximize capacity utilization while reducing network cost.

To meet these requirements, next generation embedded coherent solutions should be able to maximize spectral efficiency and include features such as 150GHz-wide channels that double the channel bandwidth of current 75GHz. A 150GHz channel plan is important for accommodating higher aggregate baud rates (128Gbaud and beyond) that can expand 400G capacity over a much greater distance compared to 64Gbaud.

With their ability to operate beyond 100Gbaud, next-generation embedded solutions can allow network operators to evolve their networks to meet growing bandwidth demands, without sacrificing reach or stranding network bandwidth when migrating from current-generation solutions. SiPh opto-electronic integration and packaging are important tools for delivering this increased performance and functionality in the future.

Today, solutions such as Acacia’s Pico-based, AC1200 1.2 Terabit coherent optical module are meeting the needs of many markets including cloud, metro, long-haul, and submarine network applications by providing high performance and flexibility features required to address these demanding requirements.  In fact, the AC1200 module is deployed in more than one hundred networks around the globe and adopted by three of the four largest hyperscalers.

Coherent in Access Networks
The wired and wireless network infrastructure supporting today’s aggregated residential customer traffic and enterprise business services is driving bandwidth capacity higher than legacy infrastructure can support based on traditional optical transmission technology. While direct-detect solutions in service provider edge and access links encounter capacity and reach limitations, coherent technology can bridge the gap to higher bandwidth and longer distances on any deployed fiber type. Coherent also provides an operationally simple solution and comes in a range of form factors, such as QSFP-DD and CFP2, to address different network applications for cable, 5G wireless X-haul and enterprise services such as single-transmission P2P links, DWDM links, and single-fiber BiDi links. Read more in this white paper.

Come See us During OFC
This year we are excited to be participating in 6 panels that cover some of the key trends mentioned.

Here’s the full line up of Acacia speakers at this year’s show. On behalf of all our speakers below, we hope to see you there virtually.

• Status of Optoelectronics Multi-chip Modules in Acacia, Long Chen
  Sunday, June 6, 2021 1:00 PM – 3:30 PM PDT
• Market Watch Panel III: Terabit WDM Channels: Beyond 100GBaud Operation, Tom Williams
  Tuesday, June 8 14:30 – 16:00 PDT
• Challenges of Coherent Transponders Approaching the Shannon Limit, Christian Rasmussen
  Tuesday, June 8, 2021 14:00 PM – 16:00 PM PDT
• Next Generation Optical Interfaces, an IEEE and Industry Update, Tom Williams
  Wednesday, June 9 13:30 – 14:30 PDT
• 400ZR Deployment and What’s Next – an OIF Update, Tom Williams
  Friday, June 11 11:30 – 13:00 PDT
• Silicon Photonic Based Stacked Die Assembly for 4×200-Gbit/s Short-Reach Transmission, Ying Zhao
  Friday, June 11 6:00 AM PDT

Acacia will have a virtual booth (#1041) during the show, which you can access at this link.  We look forward to virtually meeting with our customers, partners, and suppliers.  We are also excited that this is Acacia’s first year participating as part of Cisco. You can find their virtual booth (#1441) at this link.

If you are attending the show virtually and want to connect, we’d welcome the opportunity to meet with you. Click here to set up a meeting with Acacia spokespeople.

Here are a few notable accomplishments from the past year.

The Rise of 400G Pluggables
Bandwidth demands have continued to grow, putting pressure on cloud providers to increase the data center interconnects (DCI) that link their facilities around the globe. This has helped to drive the emergence of new architectures that could support coherent transport in the same form factors as client optics, to satisfy those demands in a cost-effective and operationally efficient way. 400G pluggables were designed to be plugged directly into switches and routers, offering the same density for both coherent DWDM and client optics in the same chassis.

Utilizing our 3D siliconization technology, Acacia introduced a family of 400G pluggable solutions featuring an expansive list of interoperability modes (400ZR, OpenZR+, Open ROADM MSA and CableLabs Coherent Optics Physical Layer Specification). These solutions were designed to enable DCI and service provider network operators to address increasing bandwidth demand through a simplified network architecture, helping to reduce both capital and operational expenditures.

Modules based on multi-sourced 400ZR DSPs are now being validated for readiness in DCI applications and network operators are evaluating OpenZR+ solutions with enhanced functionality.  For example, Acacia and Inphi recently demonstrated interoperability of 400ZR over 120km. In addition, Acacia and NTT Electronics announced successful interoperability testing of 400ZR and OpenZR+. At Acacia, we believe we will see system vendors and network operators announcing trials in the near future.

Coherent Moves to Edge and Access
The benefits of coherent have already been demonstrated in the metro, long-haul and submarine markets, and with the coming of 5G and edge computing, the time is right for coherent optics to take the next step and migrate to edge and access networks. We believe this market can benefit from the scalability, operational simplicity and improved total cost of ownership that coherent has to offer.

To address the wide variety of requirements in the edge and access market, Acacia recently announced a portfolio of products, including a coherent bi-directional pluggable optical module for cable and 5G wireless X-haul applications, a 100G coherent point-to-point edge and access solution for 5G Wireless X-haul and Enterprise Services, and a 100G coherent DWDM module for cable/fiber deep and 5G wireless X-haul applications.

Multi-Haul Coherent Solutions Take Off
With bandwidth demands continuing to rise, network operators have been looking for solutions that improve efficiency and maximize capacity utilizing while reducing network cost.  Multi-haul solutions have emerged to meet the needs of many markets including cloud, metro, long-haul and submarine network applications by providing the high performance and flexibility features required to address meet these demanding applications.

Acacia’s AC1200 product family offers customers a multi-haul solution designed to cost-effectively improve network utilization in a wide range of network architectures. Supporting transmission speeds of up to 1.2 Tbps, the AC1200 utilizes Acacia’s 3D shaping technology designed to optimize fiber capacity and reach by filling gaps in margin and spectrum. In addition to its higher capacity and density, Acacia’s AC1200 product family, when embedded inside a number of our network equipment manufacturer partners’ products, provides features designed to enable network operators to improve efficiency while reducing network costs.

Here are a few examples.

Long-haul Terrestrial Applications
ADVA announced that the FSP3000 TeraFlex broke multiple industry records in live network trial. ADVA also announced that FUNET trialed ADVA FSP 3000 TeraFlex to dramatically expand network capacity and Serverius, one of the Netherlands’ largest data center service suppliers, is leveraging its FSP 3000 TeraFlex terminal to massively increase the capacity of its deployed infrastructure.

Submarine Applications
Cisco is making waves in the subsea market having demonstrated the benefits of the NCS 1004 over a subsea cable in production achieving record results. 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.

Oh What a Year – But the Show Must Go On
As NGON & DCI World and ECOC go virtual this year, I am looking forward to presenting in the following two panels. I hope to see many of you online and from all of us at Acacia…stay safe and healthy and have a great rest of the year.

• NGON & DCI World on Dec 1 at 9:00 am ET: “Next Generation Optics for Increased Capacity”
• ECOC Market Focus on Dec 7 at 17:00 CET: “A Path to Next Generation Coherent”

Contact us if you would like to schedule a meeting with myself or one of my colleagues.

Acacia has many reasons to be excited about this year’s European Conference on Optical Communications (ECOC) and one of the top ones is demonstrating our new AC1200-SC² (SC ‘squared’) coherent module, the first single-chip coherent module to deliver 1.2 Terabit (1.2T) on a single-channel. Not only did we announce the details around the AC1200-SC² today, but we also had four customers participate in our press release by providing supporting quotes. Thank you to ADVA, Cisco, ECI Telecom, and ZTE for your continued support of our product innovations. Everything we develop is to make you and our other customers successful, and we’re proud to once again have the opportunity to help you solve your greatest optical networking challenges.

Powered by Acacia’s 1.2T Pico DSP chip, the AC1200-SC² was designed to enable network operators to support today’s 100GbE clients, as well as emerging 400GbE clients, across key network segments such as DCI edge, metro, long-haul and submarine in an efficient, scalable, and cost-effective manner. The module’s high-performance and flexibility make the AC1200-SC² module ideally suited for multi-haul applications ranging from high- capacity 1.2T DCI edge to the most challenging terrestrial and submarine networks that require 400G channels and QPSK modulation.

Optimize your Network

The AC1200-SC² leverages Acacia’s 3D shaping technology designed to optimize fiber capacity and reach by filling gaps in margin and spectrum. Fine-tune adjustment of the modulation order and baud rate

provides network operators with the ability to adapt the transmission characteristics to meet the requirements of both greenfield and brownfield deployments. Capable of adapting to any channel spacing up to 150 GHz, the AC1200-SC² provides network operators with a straightforward channel plan roadmap.

The single-chip, single-channel AC1200-SC² supports 3 x 400G transmission using 64QAM modulation for DCI edge applications, as well as 1 x 400G transmission using QPSK modulation for long-haul and submarine applications. This application flexibility facilitates network savings by enabling common hardware to address multiple deployment scenarios, including 100GbE/400GbE, as well as reducing the need for costly regeneration nodes for long-haul and ultra-long-haul links.

The software intelligent AC1200-SC² coherent module supports 1.2T in a footprint that is 40% less than the size of 5” x 7” modules supporting transmission speeds of 400G today.

Come See us at ECOC

If you are attending the show, we’d love to see you and show you a demonstration of our new AC1200-SC². To set up a meeting, contact us.

As we head to OFC next month, we thought it would be a great opportunity to look back at some of the developments since last year’s show. It was a year of much activity in the optical coherent space.

There was an increased interest in pluggable coherent CFP2 in the marketplace, as evidenced by the numerous module and system product announcements at OFC 2018. In May of 2018, we announced our collaboration with Lumentum (formerly Oclaro) to enable a second source CFP2 based on our Meru DSP. We are proud to have been the first supplier to introduce CFP2 to the market back in late 2016, and we welcome the growing interest in this form-factor because of the density and power consumption benefits for 100G and 200G coherent pluggable links in the metro and access space.

600G Era is here

The past year was also when the industry saw the introduction of 600G era technology with numerous announcements of DSPs and systems capable of up to 600Gbps per wavelength transmission. For example, ECI unveiled a 1.2T (dual 600G channel) optical blade and Tencent trialed ADVA FSP 3000 TeraFlex 600G DCI technology over its open line system OPC-4.

Acacia’s AC1200 1.2Tbps coherent module, powered by Acacia’s Pico DSP ASIC, has been well received, with its high performance, high-baud rate 70+Gbaud capabilities, as well as its flexible 3D Shaping capabilities as explained in this video.

We have participated in a couple of trials including ADVA’s 300G submarine demo using the FSP 3000 TeraFlexplatform, and the first demonstration of 400G per wavelength transmission over the 6,600 km trans-Atlantic Marea submarine cable. The AC1200’s rich set of features was designed to provide benefits to submarine, long-haul, metro, and edge DCI applications for network optimization and cost-per-bit savings.

2018 was a busy year for Acacia’s thought leaders, who had the privilege to speak at numerous venues last year. Key topics included silicon photonics, optics, and DSP ASICs. You can learn more about the topics and presentations by reading the blog post on each event including OFC, NGON, CIOE, ECOC, Light Reading’s 5G Transport Event, and GFP2018 Group IV Photonics Conference.

Throughout the year, Acacia continued our support for industry efforts to standardize coherent interconnects within OIF, IEEE, Open ROADM, CableLabs and ITU. These efforts are expanding existing coherent standards to address higher data rates, as well as adoption of coherent in shorter reach access and DCI edge applications. In next generation Remote PHY and 5G applications, network operators are looking at coherent as an access aggregation technology. These access applications are also driving new environmental requirements for coherent interfaces.

2019 and beyond

According to the Cisco VNI report, annual global IP traffic is forecasted to increase threefold over the next five years, reaching 4.8 ZB per year by 2022. Growth is expected to be driven by connected technologies such as autonomous vehicles and the adoption of the Internet of Things (IoT). The optics industry faces the continued challenge to support this network expansion with technology innovation that drives more efficient network architectures.

Multi-haul Solutions

With the introduction of systems supporting higher baud rates, flexible modulation and advanced performance, network operators are leveraging common hardware for applications ranging from metro through submarine. Whether the benefits of these solutions are utilized for higher capacity, such as in DCI edge applications, or greater reach these solutions offer improvements in operational flexibility and efficiency. Our AC1200 customers are demonstrating the benefits of this new deployment model to network operators.

IP over DWDM

For many years, it has been desirable to place transport optics directly in switches and routers, eliminating the need for bookended transport solutions. Deployment of this architecture has been limited, though, by a couple drawbacks. First, transport optics have typically been larger form factors than client optics, which results in stranded switch capacity. The increased adoption of pluggable coherent optics, such as our CFP2 and the 400ZR modules are designed to address this concern. Second, closed line systems have meant that alien wavelengths have sacrificed performance compared to bookended solutions. Through many industry efforts, open line systems are closing the gap and in some cases can offer benefits by allowing for faster adoption of new technology.

Standardization

As mentioned earlier, the trend toward standardization of coherent interconnects for certain emerging applications has already started. This momentum behind these efforts continues to grow as it becomes clear that standardization of these technologies can be achieved. New applications and higher data rates are likely to continue this trend in 2019 and beyond.

We’re excited to have a front row seat as the optical networking industry looks forward to the next set of challenges to be overcome in 2019 and beyond. We look forward to seeing you all next month at OFC!

A Brief History

Coherent optical technology was first introduced in long haul applications to overcome fiber impairments that required complex compensation techniques when using direct detection receivers. Leveraging advanced CMOS processing nodes and reduction in design complexity, coherent solutions have moved from long haul to metro and even shorter reach optical interfaces.

With the introduction of Acacia’s CFP-DCO module in 2014, coherent became an even more compelling solution for metro and data center interconnect (DCI) applications due to its pluggable pay-as-you-grow benefits, and integrated DSP design. Today, coherent is moving from metro core to access aggregation networks (Figure 1). Looking forward, the industry is working to standardize coherent solutions for even shorter reach interfaces.

Figure 1. Coherent solutions transitioning to shorter reaches.

This model of new technology adoption in long haul interfaces, followed by a migration to shorter reach applications, has been demonstrated in the industry before: the copper-to-fiber optics transition followed a very similar path starting in the 1980’s. Technologies, such as dense wavelength division multiplexing (DWDM) and forward error correction (FEC), also followed this same pattern. It is anticipated that this trend of shorter reach applications benefiting from initial long-haul technology investment as it applies to coherent will be no different.

Industry organizations such as the Optical Internetworking Forum (OIF), IEEE, and Cable Labs have initiated coherent standardization activities, recognizing the trend towards using coherent for shorter distances. The OIF is defining a coherent standard for DWDM interfaces in DCI applications with reaches up to 120km; CableLabs is defining coherent standards for cable access networks; and IEEE is considering coherent for unamplified applications beyond 10km. All of this standardization activity reinforces the view of coherent moving to shorter reach, high volume applications. As the applications move from 100G to 400G and beyond, it is likely that coherent will be used in even shorter reach interfaces.

Demand for Bandwidth is Driving New Coherent Markets

Today, coherent technology is already being deployed into markets with a wide array of applications ranging from 10’s of kilometers to 1000’s of kilometers. While network operators in each of these markets need to manage network expansion at the lowest cost, differences in network architectures and demands drive a unique set of priorities for each. Some of these key market applications we’ll explore in this blog include: Long Haul, Metro, DCI, Remote PHY Cable Access, 5G, and applications with unamplified interfaces. We’ll discuss these applications and the factors that drive solutions for their optical interconnecting requirements.

100G Long Haul: Many Fiber Spans with Optical Amplifiers

The long haul market, where coherent was first widely adopted, is still a large segment of the coherent ports shipped each year.

Figure 2. Typical Long Haul network.

This market is highly sensitive to performance because longer reach interfaces eliminate the need for additional costly regeneration. A key optical interconnection performance parameter for coherent DWDM long haul networks is optical signal-to-noise ratio (OSNR).

OSNR & Optical Amplifier Refresher

OSNR describes the relative energy of the signal carrying the information to the energy of the noise from other sources. Optical receivers are specified based on their ability to detect the desired signal in the presence of noise.

So, why is OSNR so critical to long haul DWDM networks? Optical signals are amplified as they are transmitted across the network. At each amplifier, the signal is degraded slightly–the level of the noise is amplified relative to the signal. When the signal level is so close to the noise that it is nearly un-detectable, it needs to be regenerated—the optical signal is converted to the electrical domain where the data can be accurately decoded. The same data is then recoded, retimed, and converted back to the optical domain with a high signal to noise ratio capable of passing through additional amplifiers.

Higher performance coherent optical interfaces allow longer reaches without needing regeneration, which ultimately lowers the cost of deploying and managing these networks.

Currently, 100G QPSK modulation is still widely used in long haul networks because it offers exceptional performance due to achievable OSNR margins and maturity of technology based on 25G electronics. Fiber capacity can be further enhanced by reducing channel spacing from 50GHz to 37.5GHz. Alternatively, capacity can also be increased over the channel by increasing the baud rate. For example, doubling to 200G capacity can be achieved by maintaining QPSK modulation while doubling the baud rate. However, this would require an increase to the channel spacing.  To ensure the required channel spacing remains unaltered (e.g., 50GHz), the modulation order also needs to be increased (e.g., from QPSK to 8QAM) as the baud rate is increased.

Simply put, there is an interdependency among baud rate, modulation order, required OSNR, and channel spacing. Transmission capacity can be increased by: (1) increasing the baud rate without changing modulation order, requiring wider channel spacing; (2) holding baud rate constant while moving to a higher modulation order, resulting in narrower channel spacing at the cost of OSNR margin—higher modulation order requires higher OSNR margin; or (3) increasing baud rate and moving to a higher modulation order, requiring no changes to channel spacing but assumes there is sufficient OSNR margin when moving to the higher modulation order. Thus to upgrade to higher capacity with minimal changes to the line system optics, (3) is an attractive option assuming there is sufficient OSNR margin.

Metro: High Density Solutions for ROADM Networks

Coherent interconnections have also been widely adopted in metro core networks (Figure 3). The dynamics in these networks are somewhat different from long haul. Metro core networks usually consist of many reconfigurable optical add-drop multiplexer (ROADM) nodes where wavelengths are dropped, added, or routed to other destinations. This is done using wavelength selective switches (WSSs)–each WSS is effectively an optical filter that can narrow the total bandwidth of the channel. Passing through multiple ROADM nodes can result in significant narrowing of the available spectrum of the complete optical path. These WSSs can introduce additional impairments, such as polarization dependent loss. Though the reaches in these applications are less than long haul, they still require a high level of performance due to the many link impairments.

Metro networks are not entirely about optical performance, though. Central offices can often be crowded and power limited. High density solutions that are power efficient can be particularly valuable in these applications.

Figure 3. Typical Metro network.

In addition, metro networks handle a wide range of traffic. These networks quickly become complex to manage, with different equipment required depending on the requirements. Common solutions that can be leveraged across multiple platforms, supporting a wide variety of traffic types, and scale capacity in a cost effective manner allow network operators to manage their operational costs more effectively.

Data Center Interconnect: Cost and Power Optimized Coherent

In the last 10 years, the optical networking industry has been transformed by the requirements of large cloud network operators. High capacity interconnections are necessary between these hyperscale data centers to enable cloud functionality (Figure 4).

Figure 4. Typical DCI/Cloud network.

These DCI connections differ from traditional carrier networks in that they are usually point-to-point with no ROADMs in between, and can be within the same city or across oceans. Cost and power are generally the most critical parameters for these applications. Some use cases can be fiber constrained, making spectral efficiency a higher priority. Customers in these markets tend to be early adopters of new technology and have short product life cycles.

Large cloud network operators, along with some of the more traditional carriers, are driving changes in how network functions are partitioned between vendors, allowing them greater freedom to transition between vendors and product generations with minimal changes in the software used to control the network.

Remote PHY/Fiber Deeper: Coherent Technology for Cable Access

Access networks are an emerging opportunity for coherent interconnections. The cable industry is taking the lead in this segment by driving standardization of coherent for access aggregation.

Figure 5. Remote PHY network.

As the hybrid fiber-coax (HFC) networks evolve toward remote PHY architectures, fiber is being deployed deeper in the network (Figure 5), resulting in increased available bandwidth to residential end-user customers, while eliminating bottlenecks in the HFC network. 10G optical interfaces are pushed closer to the end users resulting in aggregation points in the network where 10-20 remote PHY devices come together.

Coherent can be an effective way to transport these aggregated signals back to the hub. In some cases, it may only be necessary to transport a single coherent wavelength back to the hub, but since coherent is inherently a DWDM technology, this approach provides the capability to expand capacity by up to two orders of magnitude in the future.

CableLabs is the standards organization of the cable industry and has recognized the need for this solution in the market. In 2017, they kicked off a project to define coherent standards for cable access aggregation applications. Acacia is participating in this project, along with many other leading optical networking vendors, as well as several large MSOs.

5G Drives Backhaul Growth

Another emerging access application is 5G backhaul (Figure 6). It is clear that backhaul demands in wireless networks are going to need to increase significantly. As more capacity is delivered to end users, the connections back to the core network must scale, as well.

Coherent offers several benefits in these access aggregation applications compared to traditional direct detect solutions. At higher data rates, it becomes very challenging to deploy direct detect solutions over 10’s of km’s without using dispersion compensation. Alternatively, solutions may consider many parallel optical interfaces, but that drives up the cost of the solution.

Figure 6. 5G Backhaul network.

Today’s coherent implementations are generally based on tunable laser technology. While fixed laser implementations are a consideration in these applications, tunable solutions can offer operational benefits by significantly reducing the number of spares that need to be stocked. Tunable solutions also tend to support shorter lead times, accelerating the ability to turn up new services. Lastly, coherent solutions are future proof with the ability to scale capacity by increasing data rate or adding additional wavelengths.

Adoption of coherent technology in access networks could offer an additional benefit that may not be obvious at first. Since the same solutions can address a wide range of network interfaces (e.g., access aggregation, metro, and regional), it may be possible to collapse the supply chain for multiple applications into a single solution. This could offer significant operational efficiencies for network operators.

Unamplified Point-to-Point Interfaces

Unamplified point-to-point interfaces are essentially client optical interfaces for connections between buildings (Figure 7). As data rates have increased, it has been more and more challenging for direct detect solutions to address these kinds of applications. At 100G and 200G, proprietary coherent solutions are already used for links in the 40-80km range.

Figure 7. Point-to-point.

Looking forward to 400G, this application is within the scope of the OIF 400ZR project. In addition, the IEEE study group that is considering solutions beyond 10km for data rates of 50G, 100G, 200G, and 400G is evaluating coherent alternatives for these applications.

Since these interconnections are not amplified, they are not characterized by their tolerance to low OSNR. In these applications, transmitter power and receiver sensitivity are the key parameters that define the usable link budget.

Coherent detection offers the same increase in performance for power limited sensitivity as it does for noise limited applications. Volumes for these applications can be larger than transport applications and coherent implementations will need to be cost effective and extremely power efficient.

Coherent is moving to shorter reach as data rates increase

As we’ve outlined in this blog, there are a number of applications for which coherent is well suited. DCI, metro, and long haul are existing markets that have benefited from coherent for several years now. Emerging applications such as Remote PHY for cable access, 5G backhaul, and unamplified “ZR” interfaces are evolving as standards efforts and deployment strategies are still in the early stages. What is clear is that operators struggling to meet the growing demands of bandwidth are motivated to optimize their optical networks for capacity and reach in order to minimize cost. And space and power restrictions continue to be a challenge as additional hardware is deployed in constrained environments. Standardization will help advance the coherent evolution underway.

Stay tuned for upcoming blog posts in which we will focus on how advanced 3D shaping of coherent modulation can optimize various types of coherent networks.

Silicon photonics can enable reduced development time, higher levels of integration, and fewer manual assembly steps than more traditional optics. The result? A powerful, easier-to-manage product that empowers cloud, content, and service providers to stay ahead of increases in network capacity demand.

Proven technology

Silicon-based photonic integrated circuits (PICs), which integrate all the high-speed optics necessary for both transmit and receive functionality, enable the density required for pluggable coherent modules. These PICs include the optical polarization-controlling functions that may require external components when integrating using Indium Phosphide (InP). By reducing the number of active alignment steps, SiPh-based products improve yield and ramp more efficiently.

While metro applications served as the primary market for SiPh’s initial service provider network implementations, SiPh is used in long-haul — even submarine — applications today. The submarine market has always required high-performance technology, even if it came at higher price points. Combining SiPh with high-performance digital signal processing (DSP) technology enables submarine-network performance equal to or better than the more expensive, discrete component-based approaches (Figure 1).

Figure 1. The coherent SiPh PIC reduces cost and size versus the use of more expensive, discrete components.

That said, InP technology remains important for laser functionality. But separating that laser function from the high-speed optics can produce several benefits. For example, InP generally requires thermo-electric coolers (TECs) to maintain tight temperature stability. SiPh, on the other hand, can operate over a wide temperature range with no impact on performance. The high-speed interface is optimized by putting the optics close to the DSP and moving the laser further from the DSP, where the TEC doesn’t have to work as hard to maintain constant chip temperature.

Silicon photonics provides further benefits

Using SiPh in coherent applications creates products with rich feature sets that offer high density and pluggability.

There are a number of reasons why SiPh has proven well suited for many applications, including coherent optics:

• Yield: Beyond improving manufacturing costs, high yield reduces development time by limiting the number of variables during prototyping. When working with low-yield optics technologies, it is difficult to determine if performance limitations derive from design defects or process variation. At higher levels of integration, this uncertainty is compounded. When developing complex PICs with many integrated functions, it is imperative to know that the individual building blocks are well understood and repeatable. These attributes enable the designers to focus on optimizing the interfaces between each function.
• Polarization Control: Coherent transmission increases the data rate via polarization multiplexing – two orthogonal polarizations are transmitted simultaneously at the same wavelength. This approach requires transmit and receive components that can manipulate the polarization state of an optical signal. When working with InP, polarization control is usually done using external components. Not only do these extra components increase material cost, they also add extra alignment steps that integration of these polarization control functions in the SiPh PIC can eliminate.
• Thermal Operating Range: As mentioned previously, InP components are sensitive to temperature variation and must be mounted on a TEC. Since TECs have a limited control range, they fundamentally limit the operating temperature range of InP components. In addition, TECs consume significant power in cooling mode, where the thermal design is most challenging. By comparison, the optical characteristics of SiPh vary little over temperature. SiPh doesn’t require a TEC and supports a wide operating temperature range.
• Humidity: Traditional optics degrade in high-moisture environments. For this reason, optics are packaged in vacuum-sealed gold boxes. These hermetic gold boxes contribute significantly to the cost of optical interconnects, particularly when they require high-speed interfaces. In addition, hermetic seals are historically one of the most common sources of failure for optics. Silicon is well known to be insensitive to humidity. Millions of silicon electronic components are shipped every year in non-hermetic plastic packages; moving optics to non-hermetic packaging is an important step for the industry.
• Wafer Level Testing: In addition to having higher yields than traditional optics materials, SiPh can also be tested at the wafer level. Good die can be identified early in the process, and there is no labor wasted on material that will ultimately fail. Wafer-level test is commonplace in high-volume electronics applications, but new to the world of optics.
• Wafer Size: Leveraging mature silicon process technologies means that much larger wafers can be made in silicon than traditional optics materials. Three-inch wafers are state of the art for InP fabs. Today’s SiPh runs on lines that accommodate 8-inch wafers or larger. These larger wafers result in an order of magnitude more die per wafer, which lowers cost.
• Package Level Integration: As the industry continues to move toward higher data rates and lower power, the interface between the DSP and optics is quickly becoming a bottleneck. Every time a high-speed signal needs to transition across an additional interface (IC package or pluggable connector) there is loss and distortion. Compensating for this additional loss adds power dissipation, and distortion limits performance. Using SiPh enables package-level integration that can better optimize these high-speed interfaces and accelerate the realization of higher data rates at lower power.

Leveraging silicon photonics

Understanding SiPh’s benefits, how do we best use them to drive innovation? Today’s optics architecture is optimized for client interfaces in which the laser is directly modulated. This model is easily extrapolated to external modulation when the modulator technology has the same thermal and packaging limitations as the laser. Thermally sensitive components that need a TEC to maintain a constant temperature are unlikely to be integrated with a DSP chip that also dissipates power.

On the other hand, when working with SiPh, designers can optimize the high-speed interface and separate the thermally sensitive laser. For example, the laser can be placed on another part of the line card and connected to the high-speed optics through an optical fiber. This architecture enables greater thermal flexibility, a high-speed signal path with superior signal integrity, and elimination of costly hermetic packages with high-speed interfaces (see Figure 2).

Figure 2. High-speed electro-optical package integration.

SiPh and coherent are two technologies shifting the landscape of optical communications in parallel. By moving to architectures that can optimize the benefits of each, it can be possible to have the same kind of impact on access networks as we have already seen in applications from the metro core through to submarine. Using a toolbox that includes SiPh and coherent DSP technology, designers can leverage complicated modulation formats, high baud rate, and highly integrated parallel optics to optimize designs for a wide range of applications.

Ball Grid Array Packaging Technology

The transition to low-cost packaging and standard interfacing is an important next step to further the benefits of SiPh technology. As the industry moves toward 600-Gbps capacity per wavelength using higher baud rate and higher order modulation formats, traditional packaging technology can limit performance of the interface between the DSP and optics. Ball grid array (BGA) packages address this challenge by eliminating additional connectors and optical package leads, improving bandwidth and signal integrity.

Here and now

SiPh is no longer a technology of the future. Coherent modules based on highly integrated SiPh PIC technology have been deployed in applications ranging from data center interconnects to submarines. In the next phase of maturity, the industry is learning to understand how to best leverage the benefits of SiPh to achieve the pace of innovation necessary for optical networking to meet the worldwide data traffic demands that such applications as cloud computing, 5G, and the Internet of Things will drive.

Tom Williams is Senior Director of marketing at Acacia Communications. Before joining Acacia, Williams spent 14 years at Finisar Corp. (initially with Optium, which Finisar acquired in 2008), where he was director of product line management for coherent and direct detect transport products above 100 Gbps. He has also held positions at Lucent Technologies and Northrop Grumman Corp. He has an MS in electrical engineering from Johns Hopkins University and BS degrees in electrical engineering and physics from Widener University.

In addition to its higher capacity and density, we are adding new features designed to enable network operators to improve efficiency while reducing network costs. Some of these new features being added include:

• Tunable Baud Rate – enables continuous baud rate adjustment for optimal utilization of the available spectrum
• Patented Fractional QAM Modulation – provides users with the ability to select very fine resolution of QAM constellations for optimal capacity
• Enhanced Turbo Product Code SD-FEC – offers ultra-high net coding gain (NCG) and enables maximum reach, while maintaining low power dissipation.

Let’s take a closer look at these new features to help you understand the benefits.

Optimize Utilization with Tunable Baud Rate

In general, optimal transmission performance is achieved by operating at the highest baud rate that fits within a given channel passband. Channel passbands can vary between networks and even between links in the same network. In most implementations, the baud rate of the coherent interconnect is either fixed or can be selected between a small number of settings. Acacia’s AC1200 coherent module is planned to allow flexible control of the baud rate over a wide range, giving network operators the ability to reduce regeneration stages and increase network margin.

Figure 1: Lower order modulation can more than double reach, reducing the need for expensive regeneration.

Optimize Capacity with Patented Fractional QAM Modulation

Acacia’s AC1200 is planned to support modulation formats where each symbol represents from 2 to 6 bits.  Using just these integer steps allows network operators to select between several baud rates for a given channel capacity.  Acacia’s Fractional QAM Modulation takes this one-step further, though, supporting many small increments between the integer steps.  With this feature, the link margin can be optimized with much greater resolution than traditional interconnect technology.

Figure 2: Fractional QAM modulation can maximize channel capacity and link margin.

Maximize Reach with Low Power Leveraging Enhanced Turbo Product Code SD-FEC

Soft-decision Forward Error Correction (SD-FEC) has been widely used for coherent applications for several years now.  Acacia has developed several SD-FEC implementations, based on Turbo Product Code (TPC) algorithms, achieving an exceptional combination of high performance and low power.  With the AC1200 coherent module, Acacia is introducing a new Enhanced TPC code that is even more efficient.  This high performance SD-FEC technology can reduce capex for network operators by further extending the reach of high capacity optical interconnects.

Acacia’s versatile AC1200 is planned to support multiple network applications, including DCI, metro, long-haul and submarine.   With samples planned to be available in the first half of 2018, the AC1200 is well positioned to help network operators and content providers meet their growing bandwidth demands.

For more information on the AC1200, contact us at marketing@acacia-inc.com.