- Lumen Technologies is buying free space optical technology from Attochron
- A Lumen director said Attochron’s ultra short pulsed laser solves some tough problems for free space optical
- Lumen is interested in free space optical for a number of use cases
There is a lot of skepticism about the feasibility of free space optical (FSO) technology in the broadband industry. Nevertheless, Lumen Technologies worked with Attochron to test FSO for numerous possible use cases and is now buying the technology from the vendor.
Lumen and Attochron put the technology to the test in the Blue Ridge Mountains of Virginia, an area selected because it is foggy and rainy. Those types of weather conditions usually defeat the best attempts to use FSO.
Tom Barnett, director of Strategic Innovation with Lumen Technologies, told Fierce Network in an email that Lumen is looking at FSO for a variety of use cases, including enterprise connectivity in areas where it’s difficult to dig up streets for fiber.
“FSO links are a natural for interconnecting local area network segments that are housed in buildings separated by public streets or other right-of-way property,” said Barnett. He added FSO could provide a much lower-cost alternative to fiber in dense urban corridors.
FSO could also help Lumen in last-mile access situations. “FSO technology can provide gigabit per second connections to Lumen Quantum Fiber or to other existing networks,” he said.
And he noted FSO could be a good solution for fiber backup and backhaul. The technology can be deployed in redundant links to back up fiber in place of a second fiber link. And it can also be used to carry cellular traffic from antenna towers back to facilities.
Pushback on FSO feasibility
In August, Fierce Network published a story about a vendor, X-Lumin, that was touting its FSO technology.
But there was some pushback to X-Lumin’s claims by some industry folks on LinkedIn, including telecom industry analyst Dan Grossman.
Fierce reached out to Grossman for an interview, and he said there have been quite a few FSO vendors over the years, but while some have had success in defense and satellite use cases, none have been successful in providing their technology to terrestrial telecom operators.
“In aerospace applications for satellite cross-links, free-space optical was fine because a lot of the physical issues don’t exist in space,” said Grossman. “A lot of the problems are atmospheric and weather related.” For instance, he explained that light has problems passing through heavy snow, rain, fog and pollution.
He also said, “It’s a hard problem to keep the receiver and transmitter exactly aligned.”
Asked if FSO would make a good option for relatively short spans where fiber needs to cross railroad tracks or rivers, Grossman said, “I absolutely agree with that; you could use for diversity.”
But Grossman added, “I don’t know if you could build a business case around railroads and rivers.”
For longer spans of FSO, Grossman said he remains skeptical and would need to see extensive testing and lots of field results including extreme situations before he would say, “yeah, they’ve solved it.”
FSO technology trialed by Lumen
Attochron is supplying Lumen with ultra-short pulsed laser (USPL) free space optical technology.
Tom Chaffee, CEO of Attochron, said he first became involved with FSO a couple of decades ago, working with the University of New Mexico and the trade group EPRI to help power plants protect their infrastructure from lightning. They worked with a type of ultra-short pulse laser called a femtosecond laser.
Chaffee said FSO uses either coherent or direct detection. With coherent, the signal has to remain almost perfect from the transmitter to the receiver. “That’s why it works so well in fiber or in space,” said Chaffee. “There are no successful coherent free space optical detection systems that are being run by any carrier in the world that I know of at the market distances carriers require.”
In contrast, direct detection technology turns the laser on and off in pulses. Attochron’s USPL technology is a form of direct detection.
Lumen’s Barnett said the company tested Attochron’s technology in the Blue Ridge Mountains due to the extreme nature of the environment. “This area has the densest fog and rain in the U.S.” he said. “The goal was to test the system in this environment over a long distance. Using a reflective system, we used two test sites 3.7 miles apart to produce a 7.4-mile FSO circuit.”
Lumen also successfully tested the technology in New York City.
He said normal atmospheric perturbations can cause interference for coherent FSO technologies. But the tests did not show any interference using Attochron’s USPL beam.
Barnett said, “Our goal is to create a solution that can be used for reliable backhaul and redundant fiber circuit (telecom use) as well as a cost-effective access solution (consumer) that can be mounted virtually anywhere.
Chaffee added, “We have proven this technology and are now making product for Lumen and a Fortune 200 retailer and another major carrier in the U.S.”
He said enterprises and retailers are a big market for FSO because many of them will never have fiber optic cable connected directly to their premises.
“It’s a big hole in telecom; they will never be able to afford the fiber trench dedicated to them at scale,” he concluded. “We can bridge that divide with a carrier grade signal.”
