Optical Pluggables Evolution: Higher Performance Brings Extended Usability

Emir Halilovic, Principal Analyst

Summary Bullets:

  • The next generation of digital optical pluggable interfaces will have deep implications on traditional optical transport platforms.
  • The attraction of pluggable form factors, and further standardization, will shape the optical transport market going forward.

When networking giant Cisco acquired optical solutions specialist Acacia Communications in 2019, one of the proclaimed goals of this high-profile move was powering the next stage of IP-optical integration. Mating Cisco’s routers with miniaturized coherent pluggable optical interfaces allows clients to simplify their transport networks and, in some scenarios, eliminates the need for some optical transport network elements in the architecture. This approach works best in metro aggregation scenarios, where span lengths match the capacity sweet spot of the currently available crop of pluggables, like 400G-capable 400ZR.

However, coherent optical pluggables, like 400G ZR+, have reached capacity/reach performance that allows them to serve in applications like high-capacity metro links or even long-haul, where high-performance, 800G-capable embedded solutions currently dominate. Among optical systems vendors, Ribbon and Nokia have made first moves in this regard:

  • In June 2021, Ribbon introduced a 400G ZR+-powered module for its Apollo optical platform line. Compared to 800G-capable solutions, Ribbon’s approach is to deploy a higher number of wavelengths in the same fiber with lower capacity per wavelength. In metro, with comparable reach, two 400G pluggables carry the same traffic as one 800G embedded module; likewise, in the long haul, two 400G ZR+ pluggables carry 200G each, compared to 400G for the embedded module.

The 800G module uses somewhat less spectrum in the fiber, but Ribbon claims that in many applications this spectral efficiency penalty is less important than the cost savings that interoperable and standardized 400G pluggables bring. Soon after the launch, Ribbon announced that Rogers Communications has chosen its solution utilizing 400G ZR+ modules for its optical transport network, validating its market readiness.

  • Shortly after Ribbon’s announcements, Nokia started shipping a 400G CFP2-DCO module (named 400G Multihaul), and like Ribbon, it expects the solution to serve a growing number of scenarios that lie between 400ZR’s short-haul metro sweet spot and the most demanding applications requiring 800G, like links combining high-capacity and long-haul demands. Nokia, one of the leading carrier IP network suppliers as well, expects the 400G Multihaul module to serve in both its routers (as a part of its IP-optical integration strategy) and in optical transponders.

Ribbon and Nokia’s moves confirm the value of a modular approach to coherent optics, but the story of modular coherent optics is far from over. The Optical Internetworking Foundation (OIF) – the standardization body behind the 400ZR pluggable – is working on standardizing an 800G coherent pluggable that would match the capacity of next-generation 800G Ethernet interfaces; meanwhile, Cisco’s Acacia Communications announced in September that its next-generation 1.2T-per-wavelength coherent solution will also come in a pluggable format – albeit a non-standard one.

The push toward pluggables in both IP-optical integration and traditional optical systems thus continues. The bigger question is how deep optical solution and systems vendors will go when it comes to standardization and interoperability of their products. Currently, the market climate favors more standardization, but embedded modules and non-standard formats may continue, if leading coherent solution vendors continue to deliver strong performance and spectral efficiency advantages over pluggables.

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