The Next Big Fiber Upgrade

CableLabs recently wrote a blog announcing the release of the specifications for CPON (Coherent Passive Optical Networks), a new fiber technology that can deliver 100 gigabits of bandwidth to home and business nodes. The CPON specification working group that developed the new specification includes seventeen optical electronics vendors, fourteen fiber network operators, CableLabs, and SCTE (Society for Cable Telecommunications Engineers). For those interested, a link to the new specifications can be downloaded here.

The blog notes the evolution of PON from the first BPON technology that delivered 622 Mbps to today’s PON that can deliver 10 gigabits. The blog notes that current PON technology relies on Intensity-Modulation Direct-Detect (IM-DD) technology that will reach its speed limitations at about 25 gigabits.

The CPON specification instead relies on coherent optical technology, which is the basis for today’s backbone fiber networks that are delivering speeds up to 400 Gbps. The specification calls for delivering the higher bandwidth using a single wavelength of light, which is far more efficient and less complicated than a last-mile technology like NG-PON2 that balances multiple wavelengths on the customer path. This specification is the first step towards adapting our long-haul technology to serve multiple locations in a last-mile network.

There are a few aspects of the specification that ISPs are going to like.

  • The goal is to create CPON as an overlay that will coexist with existing PON technology. That will allow a CPON network to reside alongside an existing PON network and not require a flash cut to the new technology.
  • CPON will increase the effective reach of a PON network from 12 miles today to 50 miles. This would allow an ONT placed in a hut in a city to reach customers well into the surrounding rural areas.
  • CPON will allow up to 512 customers to share a neighborhood node. That means more densely packed OLT cards that will need less power and cooling. On the downside, that also means that a lot of customers can be knocked out of service with a card failure.

The blog touts the many benefits of having-100 gigabit broadband speeds in the last-mile. CPON will be able to support applications like high-resolution interactive video, augmented reality, virtual reality, mixed reality, the metaverse, smart cities, and pervasive communications.

One of the things not mentioned by the blog is that last-mile fiber technology is advancing far faster than the technology of the devices used in the last mile. There aren’t a lot of devices in our homes and businesses today that can fully digest a 10-gigabit data pipe, and stretching to faster speeds means developing a new generation of chips for user devices. Releasing specifications like this one puts chipmakers on alert to begin contemplating those faster chips and devices.

There will be skeptics who will say that we don’t need technology at these faster speeds. But in only twenty years, we’ve gone from broadband delivered by dial-up to bandwidth delivered by 10-gigabit technology. None of these skeptics can envision the uses for broadband that can be enabled over the next twenty years by newer technologies like CPON. If there is any lesson we’ve learned from the computer age, it’s that we always find a way to use faster technology within a short time after it’s developed.