There is only so much bandwidth you can shove down a glass fiber and networking vendors are closer than ever to hitting the speed limit, said Dell’Oro analyst Jimmy Yu.

This boundary, called the Shannon Limit, refers to the maximum rate data that can be transmitted without introducing errors. And it's a big problem for optical vendors, contends Yu.

"The old way of growing the bandwidth of fiber is going to be increasingly difficult," he said in an interview with SDxCentral. "We need to look at different solutions."

Yu explained that for years, the way that the telecom market kept up with demand while keeping costs in check was by steadily increasing their network data rates. And for the past decade, vendors have been able to maintain an annual 20% reduction in cost by driving the spectral efficiency of the optics ever higher.

But there's a trade-off: While the cost-per-bit declines as the data rate goes up, so does the distance that signal can travel.

Overcoming this is the first challenge facing vendors, while the second is how to increase capacity, said Yu.

Why 800G matters

The latest generation of 800G optical equipment will help address the first problem.

Yu explains that for metro spans, 800 Gb/s line cards will significantly reduce the cost-per-bit by eliminating the need for multiple slower line cards. Meanwhile, 800G has another advantage for long-haul traffic: When tuned to 400 Gb/s data rates, the signal can travel thousands of kilometers without the need for costly repeaters.

"It's not really about running 800 gig, it's about being able to do 400 gig longer," said Yu.

Recent trials by leading optical vendors have already shown the capabilities of their 800G optics.

Last week, Infinera claimed it had successfully trialed an 800 Gb/s single-wave transmission on a production network over a distance of 950 kilometers. According to Rob Shore, SVP of Marketing at Infinera, while the vendor is still evaluating the capabilities of its ICE6 optics at 600 Gb/s, initial tests have already exceeded 1,600 kilometers.

Meanwhile, Ciena earlier this month announced an 800-kilometer pilot deployment of its own 800 Gb/s-capable WaveLogic 5 Extreme (WL5e) optics in collaboration with Comcast. However, Ciena claims that its WL5e-based optics are capable of far greater distances at 600 Gb/s. To test this, the vendor had Comcast loop back the traffic, effectively doubling the distance.

More spectrum

To address the second challenge, Yu said the telecom industry needs to expand the usable spectrum. He explained that traditionally, optical equipment is designed to operate in a 4-THz swath of spectrum located in the C-band, which is typically divided into 80, 50-gigahertz channels.

Widening the available spectrum isn't a new idea, Yu said. Equipment manufacturers have long since shifted to a 4.8-THz swath called the extended C-band.

"This is one of the key pieces to allow operators to keep using their current fiber plant and squeeze out more capacity," he said.

Moving to 6 THz, what China-based vendor Huawei calls "super C-band," could allow network operators to increase the bandwidth per wavelength by as much as 25%.

"Using super C-band or expanding the amount of spectrum is one of the easier avenues to try and leverage higher capacity for fiber," he said.

Untapped potential

Yu notes that there has also been some talk within the industry of using L-band spectrum in conjunction with C-band to further expand the capacity of the fiber.

"Historically, the industry hasn't used L-band," he said, adding that it likely won't be ideal for existing fiber deployments as L-band would require new transponders and amplifiers.

Yu said that while there may be some other technology on the horizon that will keep the 20% decline in price-per-bit, there will be a point where it's no longer sustainable.

"People will have to accept the fact that it won't be a 20% decline and it may turn to 15% and then eventually 10% at some point in the future, but hopefully that future is more than 10 years away," said Yu.