Network operators face multiple priorities and challenges, including the need to increase capacity and network efficiency while reducing costs, simplifying operations, improving reliability, and reducing energy consumption. One constant in the networking industry is the continuous effort to optimize total cost of ownership. Fortunately, technology innovations have helped the industry continue to step up to this challenge. For example, the introduction of 400G coherent pluggable optics in metro reach applications enabled the convergence of the optical transport and IP layers. As stated in a recent Cignal AI report, major hyperscalers were the early adopters to capitalize on this new paradigm, applying IP-over-DWDM to their metro data center interconnects. Service providers are also leveraging this type of architecture at 400G, resulting in significant network cost savings. For example, Bell Canada calculated that it would enable savings of 125 million Canadian dollars over the next ten years by reducing CAPEX by approximately 27%.
With the initial adoption of 400G coherent pluggables for IP-over-DWDM networks being driven by router interconnects, these pluggable modules based on coherent technology have been referred to as router-based coherent optics. There are now more than 200 network operators that have embraced this cost-saving paradigm.
400G Coherent Modules and Open Line Systems Led the Way
As previously mentioned, the introduction of 400G interoperable coherent MSA modules that plug directly into router ports helped accelerate network operator adoption of router-based coherent optics, enabling high-capacity optical connections within a metro reach network without traditional transponder hardware. Two different mechanical form-factors for these 400G modules, QSFP-DD and OSFP, were introduced to the market, with the former being the primary form-factor being shipped today for 400G, matching the widely adopted host platform QSFP-DD slots.
The disaggregation of optical line systems has also helped progress the adoption of router-based coherent optics. These open line systems enable the insertion of wavelength transmission from router-based coherent MSA pluggable modules rather than from transponders sold by the same line system vendor. Many of the recently deployed networks utilizing router-based optical modules have been over these open line systems. In fact, approximately 70% of the above mentioned 200 end-users were utilizing an open line system.
In addition, the introduction of 400G coherent modules with high transmit optical power, such as Acacia’s Bright 400ZR+ module, helped accelerate service provider adoption because higher transmit power helps to avoid performance penalties when connecting to typical brownfield ROADM architectures. Modules such as the Bright 400ZR+ also include a transmitter tunable optical filter (TOF) to minimize adjacent channel interference that could impact performance, especially if colorless ROADMs are present in the network.
An ongoing challenge that the industry is making progress with is the ability for seamless management of coherent MSA modules. Industry groups such as the Optical Internetworking Forum (OIF) have made great progress to address this challenge, with the OIF driving the Common Management Interface Specification (CMIS). This effort continues to be an area of industry focus to further lower the adoption barrier of router-based optics.
Continuing the Momentum of Router-based Coherent Optics
To continue the adoption of router-based coherent optics, expanding interoperable MSA pluggable module capabilities were required to address network operator use cases such as long haul and ultra long haul reaches as well as a migration from 400G links to 800G links. Thanks to recent advances in coherent technology, these capabilities have been recently introduced.
400G ultra-long-haul (ULH) modules leveraging Class 3 (~120+ Gbaud data) rate technology enables the reach capability of 400G to extend from metro/regional reaches to ultra long-haul reaches, reducing the barrier for network operators to deploy router-based coherent optics in virtually any network application. Arelion recently announced a successful trial using Acacia’s Delphi-DSP based 400G ULH modules over 2,253km with margin, enabling a 35% reduction in CAPEX and 84% reduction in OPEX.
To take advantage of the latest generational increase in switch/router chip capacity resulting in I/O ports transitioning from 400G to 800G speeds, the same Class 3 generation coherent technology support 800G interoperable coherent MSA modules that plug directly into host platforms. This enables network operators who have already embraced an IP-over-DWDM architecture using router-based coherent optics at 400G to now migrate to 800G. For example, Colt recently announced that it is the first provider to successfully trial enhanced performance 800G ZR+ coherent pluggable optics, in their Cisco 8000 series router ports, in its production network. These 800G router-based coherent optics provide the capability to double Colt’s packet core capacity per link while reducing power per bit by 33.3%.
While the initial adoption of router-based coherent optics for deploying an IP-over-DWDM network were from hyperscalers and service providers, the momentum of adoption has expanded to research and education networks, enterprise networks, and many other network operators looking to optimize total cost of ownership. And the application is not limited to using coherent pluggable optics in routers, but also in network switches for fabric extension requiring an interconnect to a distant site.
Acacia’s Interoperable Modules Enabling the Future
Acacia is enabling the adoption of 400G and 800G IP-over-DWDM architectures with router-based coherent optics. The latest generation of MSA pluggable modules include 800ZR and 800G ZR+ variants as well as 400G ULH for ultra-long-haul reaches. These are all powered by Acacia’s 9th generation Delphi DSP ASIC and 130+Gbaud high-speed silicon photonic PIC technology enabling a low-power industry standard based solution. The 800G ZR+ module also includes the industry’s first standardized interoperable probability constellation shaped (PCS) mode. In addition, Acacia is a leading supplier of 400ZR and OpenZR+ compliant modules including high Tx power Bright modules for 400G based metro/regional IP-over-DWDM network.
Enabled by coherent pluggable modules, the adoption of IP-over-DWDM using router-based coherent optics continues to grow, providing significant reduction in TCO for network operators.
