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CableLabs Clears Coherent Optics for Takeoff

Jeff Baumgartner

Taking a step toward pumping more capacity into installed fiber and extending the life of HFC networks, CableLabs has put the finishing touches on the first two specifications focused on Point-to-Point Coherent Optics.

The specs, released June 29, aim to bring coherent optics techniques traditionally used in long-haul networks to cable's access networks. They provide the technical guidance for vendors (makers of optical transceivers, in this instance) to amp up development of interoperable products. (See Full Duplex, Coherent Optics Specs Advance and New CableLabs Optical Tech Promises Big Bandwidth Boost.)

But the grander vision is to squeeze more juice out of installed fiber in a cost-effective way as cable operators start to pursue a distributed access architecture (DAA) that will see MSOs deploy fiber deeper into the network and place key electronics toward the edge of the network. One key idea also is to use Ethernet links as deeply into the network as possible, where new remote PHY or remote MACPHY devices can convert those high-capacity signals to RF for final delivery over the coax portion of the HFC network. (See Cable DAA Debuts Worldwide .)

Though DAA is viewed as the primary use-case for coherent optics in cable networks, another is to take wavelengths and that new, unlocked capacity to enterprise customers, said Curtis Knittle, VP of wired technologies at CableLabs.

The ability to ratchet up capacity delivered to the aggregation node and then split out to the remote devices also feed into cable's chase of Full Duplex DOCSIS, an annex to DOCSIS 3.1 that's designed to deliver symmetrical multi-gigabit speeds. (See Full Duplex Is a Go; Cable Aims for 10 Gig.)

As the numbers go, CableLabs said the new specs aim for 100 Gbit/s or more on each wavelength, compared to the 10 Gbit/s for each wavelength that cable operators can deliver today without coherent optics. And while a 40-channel fiber network could have a capacity of 400 Gbit/s, the use of coherent optics can push that to 4 Tbit/s, Matt Schmitt, CableLabs's principal architect, explained in this blog post.

CableLabs's work with coherent optics is also anticipated to factor in for cable operators that are also eyeing remote optical line terminals (OLTs) for fiber-to-the-premises situations and the densification of the network to provide high-capacity backhaul for future 5G networks.

The initial duo of P2P Coherent Optics specs includes a reference design of the architecture and a 1.0 version of the physical layer that defines the requirements for coherent optics transceivers to interoperate with each other on the fiber network at 100 Gbit/s for each wavelength. The specs arrive more than a year after CableLabs announced the project.

The new specs focus on optical transceivers that would be deployed in an operator's headend or hub on one and the aggregation node on the other. That scenario will likely create opportunities for suppliers such as Viavi Solutions Inc. , Applied Optoelectronics Inc. (AOI) and Sumitomo Electric Industries Ltd. , that have been working on helping MSOs upgrade optics modules at the node, according to Jeff Heynen, consulting director at SNL Kagan.

Those suppliers won't be able to cash in right away. Knittle said the hope is that some "limited trials" could get underway by early 2019, with initial deployments conceivable by late 2019 or into 2020.

Heynen believes it might take a bit longer for this new technology become economically feasible, noting that volumes for coherent optics will likely rise and costs come down as the technology is increasingly emphasized for long-haul and data center interconnect networks.

In the meantime, CableLabs plans to kick off initial interoperability events later this year, Knittle said.

Analysts believe that the use of Coherent Optics on the access network will help to extend the life of HFC and position MSOs to contend with next-gen FTTP technologies.

“It’s pretty amazing. Cable technologists just keep finding fresh ways to draw more capacity out of their existing HFC networks,” said Alan Breznick, Light Reading’s cable/video practice leader. “Coherent Optics pushes back cable’s once seemingly inevitable shift to all-fiber networks even further. So now the big question may be whether that shift is really still so inevitable.”

With respect to competition, cable operators such as Comcast Corp. (Nasdaq: CMCSA, CMCSK) could be eyeing this emerging approach as a way to deliver symmetrical 10 Gbit/s services amid the threat of Verizon Communications Inc. (NYSE: VZ)'s use of NG-PON2. (See Verizon Preps NG-PON2 Rollout for Q1 and Verizon, Calix Roll Out Commercial NG-PON 2.)

"They [cable operators] want to have all options available to them, both from a cost standpoint and a bandwidth standpoint. They're just trying to weigh their options," Heynen said.

Looking beyond the 1.0 version of the specs, CableLabs and its partners are now working on future iterations that will expand the capacity of each wavelength to 200 Gbit/s or more, according to Schmitt. Also under development is an Operational Support Systems Interface spec to bring consistent management of the coherent optics transceivers.

— Jeff Baumgartner, Senior Editor, Light Reading

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