CableLabs is making progress in its pursuit of new 100 Gbit/s coherent PON (CPON) technology following the publishing of an initial set of specs that define an architecture and a wide range of use cases for broadband operators. But the commercial readiness of single wavelength CPON products is likely a few years out on the horizon.

CableLabs published the Version I01 specs (PDF) last week. It signals a step forward in the organization's interest in applying coherent technology – typically used in long-haul fiber networks – to the access network. The general idea is to help cable operators reclaim valuable optical spectrum and break through potential bottlenecks as data demands on the network continue to expand.

Figure 1: (Source: Panther Media GmbH/Alamy Stock Photo)

CableLabs believes that CPON is positioned to push past some of the capacity and network reach limits of current PON technologies developed by International Telecommunication Union (ITU) and the Institute of Electrical and Electronics Engineers (IEEE). With respect to reach, CableLabs holds that current PON technologies have trouble reaching distances of 25 kilometers, limiting deployments to urban centers and suburban areas. By comparison, CableLabs claims 100G CPON and its relatively high optical power budget can solve those issues, enabling cost-effective fiber-to-the-home capabilities in unserved areas using a fully passive optical link up to 80 kilometers.

As CableLabs put it in this blog post: CPON "will prove a scalable and extensible technology for fiber networks for the next 30 years."

"I think the biggest takeaway is this work is progressing," Curtis Knittle, VP of wired technologies at CableLabs, said. "It's not just a cable technology, though right now it's just cable operators that are involved. We'd welcome other types of operators."

Operators, suppliers chip in for CPON

The new specs offer a glimpse at some of the cable operators, chip makers, ONT (optical network terminal) and OLT (optical line terminal) and optical transceiver suppliers that have some level interest in CableLabs' CPON work. Examples of the 30-plus contributing companies and organizations include Antronix, Broadcom, Cable One/Sparklight, Calix, Charter Communications, Comcast, CommScope, Cox Communications, GCI, Infinera, Liberty Global, Mediacom Communications, Midco, Rogers Communications, SCTE and Vecima Networks, among others.

The architecture specs released last week focus on high-level operator requirements. Knittle said it's expected that a full suite of CPON specs will follow, including ones that define the PHY and MAC layers and possibly another focused on backoffice systems. CableLabs might explore the MAC element in conjunction with the ITU and/or the IEEE.

As for next steps, CableLabs will focus on the PHY layer first and then tackle the MAC layer sometime in 2024.

As for future product implementations, the focus is on integrating CPON into interoperable OLT and ONU components. Knittle said there's a "big push" on pluggable devices.

"It's not clear yet whether this type of tech, with the addition of burst transmission/burst reception would be a pluggable-type device, but I suspect it will be," he said.

While it's possible that some components in today's coherent transceivers could be reused for CPON, it's also likely that some new silicon would need to be developed. Plus, the burst transmission and reception and the media access element are significantly different than what's used today in point-to-point coherent silicon, Knittle pointed out. CPON uses a point-to-multipoint architecture.

CPON timelines

It's still too early to say if CableLabs would do any formal device qualification testing on future CPON devices, but it's possible that the organization might take on the role of conducting interoperability "plugfests," Knittle said.

But don't expect CPON products to hit the street anytime soon. "We're more or less targeting a four-to-five-year timeframe for having deployable devices," Knittle said. That timeline also has "huge dependency" on how quickly operators ramp up the speeds of their broadband service tiers, he added.

Meanwhile, competition for CPON is likely to center on the next-gen PON work that comes out of the IEEE and ITU. But Knittle argues that CPON does have some advantages for cable operators, including extended reach and high split ratios, as they push ahead with distributed access architectures.

Range of use cases

The new architecture specs also outline several potential use cases for CPON. Using CPON to aggregate traffic at the network edge is among the initial, primary use cases envisioned for the technology. Using CPON as an infrastructure component, rather than a residential services tool, is likely where the CPON market will get seeded first, Knittle said.

Figure 2: Click here for a larger version of this image.
(Source: © CableLabs 2023; used with permission)

Here's a sampling of other use cases referenced in the specs:

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— Jeff Baumgartner, Senior Editor, Light Reading