How Corning Makes Super-Pure Glass for Fiber-Optic Cable

To make glass that's pure enough for fiber-optic cable, you cannot just melt sand. Instead you send gas traveling through flames to create glass soot particles that are deposited on a rod in a controlled pattern. Corning

One hot July morning in Corning, New York, I opened the door of my car and gazed across the parking lot at the huge steel and glass building. I had driven alone across the entire width of the state of Massachusetts and most of New York over two days. In this building, I hoped, someone would be able to explain to me the magic of how fiber-optic cables are made.

Excerpted from "Fiber: The Coming Tech Revolution—and Why America Might Miss It," by Susan Crawford. Yale University Press

For me, the name Corning had meant hefty, chipped white cookware, seemingly hand-painted with a primitive looping swirl on the rims of the lids. But in the building I was looking at now, Corning had been researching high-tech glass for decades, often without a clear commercial application in view—the kind of pure science that many companies can’t afford these days. The superthin, scratch-resistant glass on the iPhone was developed by Corning scientists. And the company is not just about smartphone glass: The nine-story glass building in front of me was the home of Corning’s long-term research in fiber optics. Corning is a small place—once a village, then a hamlet, now a town, population about 11,000—that grew up around the glass-making industry in the 19th century. Walking around the town’s historic downtown district the afternoon before, I’d found restaurants, shops, and art galleries; it’s a welcoming few blocks that seems to be thriving.

But first, coffee.

Claudio Mazzali, a bright-eyed, energetic Brazilian physicist who has been with the company since 1999 and now leads technology efforts for two of its divisions, met me in the lobby of the research building and showed me to a large room lined by screens and gadgets.

I spent many hours with Dr. Mazzali that day, and I was delighted by his wry sense of humor and somewhat goofy smile; he had first worked in Corning’s Brazilian regional office as an optical communications specialist and had transferred to upstate New York about 15 years earlier. I could see that he loved his job. He’s helping to run the enormous centralized research lab—the Bell Labs of our era—for a company that keeps reinventing itself as a manufacturer and annually invests about 10 percent of its revenue, no matter what, in research and development.

Susan Crawford is the John A. Reilly Clinical Professor of Law at Harvard Law School, a columnist for WIRED, and author of the 2013 book Captive Audience . Crawford served as Special Assistant to the President for Science, Technology, and Innovation Policy (2009) and co-led the FCC transition team between the Bush and Obama administrations.

Mazzali brought me a cup of steaming coffee; as I drank, he said emphatically: “When you think about glass, some people say, ‘Oh, I get sand, and I melt that, and then I make glass.’ Of course it’s much more sophisticated than that for optical fiber. It’s totally different.”

Fiber-optic cable is made in an almost incomprehensibly precise way. It has to be so pure, so clear, that it can transmit light over many dozens of miles without any boosting or encouragement, and without losing any of the information that has been encoded onto that light. To get that clarity, its manufacturers control every micron and every second of the manufacturing process.

Fiber-optic cable carries voice, video, and data in the form of light signals. Corning

The history of fiber optics goes back to the 1960s, with the invention of the laser. Lasers apply energy to billions of atoms, exciting their electrons and making them emit photons that then turn around and make already-excited atoms give off even more photons.

When some of the photons are allowed to escape, the result is an amplified, concentrated beam of light—"light amplification by stimulated emission of radiation," or LASER. That light has a frequency; it is wobbling at a rate of millions of millions of times a second, and each of those wobbles can be modulated to carry data. That data then travels at the speed of light.

The trouble was how to transmit that focused data reliably from point A to point B. Light can be carried by water—just imagine a nighttime fountain lit by purple light from below—but light can’t carry information through water very far. You need the light waves to maintain their strength and definition in order for the information they carry, encoded in the height or frequency of these waves, to be understood. Back in the late 19th century, a Viennese medical team identified only as “Dr. Roth and Prof. Reuss” experimented with guiding light through bent glass rods to illuminate body parts during surgery. With the arrival of the laser, scientists saw the possibility of guiding information across many miles with very little loss of accuracy.

Enter “optical fiber.” In 1964, researcher Charles Kao (now Sir Kao), while a PhD student in Harlow, England, posited that glass—a later generation of the glass tubes that had been used to illuminate surgery—could be used to guide many “colors,” or frequencies, of laser beams. But Kao pointed out that for this guidance to occur without significant loss, the glass had to be much purer than anything then available; his work was purely theoretical.

Kao's work got Corning interested in the idea of optical fiber. In 1965, Corning was in the glass business but not the telecommunications business. Telecommunications companies were using copper lines to transmit the electrical pulses that carried voice calls and data between cities and into homes. To make it worthwhile for those companies—a potentially huge new group of customers—to replace their copper lines with glass fiber, Corning would have to show that the fiber was much better at conveying data. But at the time, there was no glass strand that could transmit light more than about 15 centimeters before the signal fell off. Corning needed to figure out how to create glass that could transmit a signal not for centimeters but for many miles.

The head of Corning Glass Works research at the time, William Armistead, was skeptical. Nevertheless, he approved funding for Robert Maurer, a physicist, as well as colleagues Pete Schultz, a senior chemist, and Donald Keck, an engineer and physicist, to work on the problem. And they did, without a customer in sight. Maurer and his team knew that the glass would have to have a clear core surrounded by a skin—called cladding, and also made of glass—so that the cladding could reflect laser light back into the core and keep it traveling along its path. For four years, he and his team at Corning kept experimenting with different chemical compositions of the core to create the greatest possible clarity. Failure followed failure.

One Friday evening in August 1970, Donald Keck was alone in the Corning R&D lab, testing one last piece of fiber before the weekend. In their book The Silent War , Ira Magaziner and Mark Patinkin tell the story of Keck bending over his microscope and lining up the laser, watching as the narrow beam of light got closer and closer to the core. Suddenly, Keck was hit right in the eye by a bright beam of light. The fiber had transmitted light without losing more than a tiny amount of the beam’s strength. “Eureka,” Keck wrote in the lab notebook that day. It would be 10 more years before Corning found a customer for its optical fiber.

The remarkable thing about the hair-thin strands of optical fiber that Corning and other companies sell today is that any single strand of glass can carry many different beams of light at the same time, each beam wobbling at its own frequency and using its own method of encoding information. This is the enormous advantage of fiber: Its overall bandwidth potential (how many different signals it can transmit and how fast you can encode or modulate them) is much higher than any other transmission medium. Unless the transmission medium itself somehow gets in the way, as a deep pothole or a truck might block the road when a car wants to go by, a single fiber-optic cable could carry the entire weight of data on the internet.

As the saying goes, one strand of optical fiber is about the diameter of a human hair. Corning

It’s an amazing idea. Now, copper wires—sometimes called “twisted pair” because they are made of pairs of strands of copper twisted around one another—also carry data and telephone signals to homes and farms in much of rural America. But because of the characteristics of copper as a transmission medium, signals that travel over copper don’t have the extraordinary frequency range that light signals do, are subject to interference from other signals, and in general degrade very quickly over more than a short distance. That’s why if you have a copper-wire DSL (digital subscriber line) subscription, you have to be very close to the phone company’s “central office” to get a download signal into your house. A DSL house is connected to a copper wire, not a fiber-optic cable. Not only can light travel over fiber for hundreds of miles with little attenuation (impossible with copper), but signals zipping around via fiber don’t get interfered with by other electrical transmissions nearby (which happens all the time with copper). Fiber is also, once it’s installed, far cheaper to maintain than a copper line.

As Mazzali explained, the traditional ways of making glass—blowing and pressing melted silica, for example—create a bubble-filled, flawed product that can’t do what Maurer’s team required. “Because you need purity and transparency,” he said, “you cannot start from sand or anything like that and melt it and make glass.”

Instead, you use gas traveling through flames to create particles of soot—glass soot particles—that are deposited on a rod in a controlled pattern. And then he showed me a line of small blue flames that were slowly, mechanically being moved sideways up and down a white rod. This was the beginning of the creation of a strand of fiber: printing soot in carefully orchestrated layers on a solid rod. The composition of every layer of each hair-thin strand of glass—and each strand consists of thousands of layers—is controlled by tweaking the composition of gases traveling through the flames.

Once you have laid each one of those thousands of layers meticulously on top of the previous one, and you have heated the whole thing at a precisely controlled rate to a precise temperature, when it cools you will have glass with very specific properties. “That’s how you control the light,” Mazzali said. “That’s how you can trap the light inside, by playing with different attributes of the fiber.” He was smiling, excited. I asked for the recipe—the identity of the gases being blown through the flames to create the soot particles—but he wasn’t telling. “A little bit of germanium, a little bit of this, a little bit of that.”

Mazzali was showing me a demonstration version of the printing-on-a-rod process that Maurer and Keck had created at Corning; the real process, he says, takes several hours. He led me to a tubby, short white tube and had me touch it. This was what all the printing of soot I had seen ends up creating. A white chalky substance came off on my fingers. “Sorry about that,” said Mazzali. “Those are actually particles of glass. It’s not just silica. We are doping each one of those layers with different materials and different amounts of materials, to change how they reflect light.”

That white tube, called a blank, already has most of the attributes of the end product; all the ways that glass will treat light are already built in. “When you make that,” Mazzali said, “you know exactly that that fiber will have that dispersion, that attenuation, that geometry, all that.” When companies transform the blank by pulling or “drawing” it into a single skinny glass strand thousands of kilometers long (think of pulling a very long single strand from a thick skein of wool), all they’re doing is making the chunky blank thinner.

Mazzali was warming to his task. “Now,” he said, “you have to transform this coarse white thing into glass.” The fat tube certainly did not look like glass to me. “So now we go to the next step, consolidation.”

Consolidation involves placing the chalky thick blank into a giant furnace. The heat gets all the water out of the blank, and then the material starts to consolidate, or “sinter.” This sintering step transforms it into a transparent and smaller thing that is labeled a “preform.”

Mazzali handed me a sample transformed preform, sleek and transparent, about the same size as a very large salami from a local supermarket. The ceramic rod on which the soot had been printed was gone.

“If you look very carefully in the middle, can you see a different sort of color?” Mazzali asked me. I looked, and saw a very narrow, thin band of something-ness in nothing-ness. “That’s the core,” Mazzali said. “That’s where the light will be.”

Maurer’s team had decided that the way to make glass transmit light most effectively was, somewhat paradoxically, to make the core less pure than the cladding so that the latter would act as a mirror, trapping light inside the core. So chemicals were mixed into the core—through the tweaking of the soot layering—that did that. “You put a light in that core,” said Mazzali, “it keeps reflecting back and forth.”

The light signals are transmitted through the core of the fiber. The cladding layer keeps the light from escaping. Corning

It all seemed magical, and it was about to get even better. That sleek preform goes into a draw tower—imagine a grain silo on stilts up near the ceiling of a giant warehouse—to be melted. Then from the gob of stuff that initially protrudes from the bottom of the tower following the melting process, a single strand is pulled or drawn straight down toward the ground. That is the hair-thin strand that is a single fiber-optic cable.

The melting and drawing process, like the other steps, is tightly controlled. First, the tip of the preform is heated, causing a gob of hot glass to descend. Once the gob drops, it’s taken away, and the thin thread behind it is threaded through a device that minutely controls the speed of the draw (the speed at which the strand is drawn toward the ground) and the diameter of the resulting fiber. Every micron is documented.

The glass cools rapidly, within seconds, but according to precise timing. Meanwhile, inside the draw tower, a coating made of several layers of different plastics is applied to protect the glass and cured using ultraviolet light.

The secret sauce of all of this is the precise controlling of the timing and temperature of the draw; that’s what gets the pristine transparency and low signal loss that communicators want. “If you do something very abrupt with glass, the material is not homogeneous anymore,” Mazzali said, because the chemicals will clump up and you’ll lose the architecture that has been carefully engineered into the glass. Any variations in density—however minor—will cause the light to scatter. And scatter means loss.

Mazzali led me into the wide white hall outside the prototype demo room to take the elevator to a higher floor of the R&D lab. As we went up, he told me what was about to happen. “We’re going to need safety glasses.” We came out of the elevator, put on the glasses, and looked up at a big steel box with one side missing. “What comes after the blank?” Mazzali quizzed me.

I tried hard to remember what he had told me minutes before: “You’ve got the big thick thing and then you take out all the moisture and all the impurities and slenderize it,” I gamely responded. Mazzali pointed out a clear post-processing glass tube, with the core visible. “After you have that piece of glass, what’s the next step?” He was enjoying being the teacher. “You draw, the globule comes first and then the very skinny stuff comes next,” I said, gabbling a bit.

He pointed up again: “Can you see there, the gob going down?” A big blob, glowing white, was hanging off the end of an enormous clear glass tube. That one tube, he said, would produce a few thousand kilometers of glass strand. He smiled; he wasn’t going to be any more specific. “This is the top of the draw,” he said. “We’re going to go down a few floors.”

We ran down the stairs, with me clattering after Mazzali. He opened the door on the floor just below where we had been and pointed ahead of us: “Can you see the fiber?” he asked. “No,” I said. “Look carefully,” he said. And there it was, an impossibly thin strand, descending from a big hole in the ceiling to the floor. “Now you’re going to see the last stage, which is putting it on a spool,” he said.

We clattered down more stairs into the basement. There a calm, tall man named Matt was watching gauges as the strand of fiber wound onto a spool. He was looking for imperfections. “Remember that the fiber is 125 microns in diameter, plus or minus less than a micron,” Mazzali said. “We have to control the diameter of this glass, every single meter over more than a thousand of kilometers, by all of this equipment that we have on the draw, the tension, the temperature, the speed, and all that,” so that whenever a splice has to be made—a connection between one strand of fiber-optic cable and another—the fiber will transmit perfectly.

“At this point it’s cold already,” Mazzali said. “The coating is there, you can touch the fiber, it goes on the spool. After this, you put it in a box and you can ship it to the customer. There is nothing else to be done other than putting it in a cable.” The strands of fiber would be bundled inside a cable—a cable with 576 strands will have 24 colored “buffer” tubes, each with 24 individual fiber strands inside.

The coating, the layers of plastic cured around the fiber, doesn’t stop the fiber from bending. By serving as a kind of very thin cushion, the coating keeps the individual fibers inside any given cable from interfering with one another. (Corning fiber, these days, is made to bend easily, even around tight corners inside buildings or when wrapped around rods, without losing signal strength.) Months later, many hundreds of miles south of Corning, I would see that coating being carefully removed in order for one strand of bare glass to be precisely spliced to another strand of fiber.

Only fiber will facilitate the exponential growth of innovation and productivity in transportation, energy, health care, manufacturing, education, job training, disability access, augmented/virtual reality, government services, and public safety that will keep our living standards rising as they have in the past. Better lives, a sense that future generations will live better than we do—this sense of hope is not just an economic good but an essential requirement for happiness, tolerance of others, and resilience in the face of difficulty. The countries that have made progress on this issue—South Korea, Japan, Hong Kong, Singapore, China, Sweden—are driving toward this future. We need fiber in the same way, and for many of the same reasons, we need liberal democracy: to ensure that all Americans have opportunities to shape their own lives. It is basic infrastructure for a good life.

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