Latest / Zero Shot Podcast DEMO / The Evolution of Fiber Optics: From Glass Rods to Global Communication

Transcript

The Evolution of Fiber Optics: From Glass Rods to Global Communication · Zero Shot Podcast DEMO

• 0:00
  speakers: In this conversation, the development of fiber optics revolutionized telecommunications, enabling high-capacity data transmission. That opening sets the stakes we'll follow.
• 0:14
  Interviewee: In 1887, a young physics teacher attached a thin glass rod to the end of an arrow, loaded it into his homemade crossbow.
• 0:21
  He torched the rod's end into a molten glass bead roughly the size of a pin's head was barely hanging on.
• 0:28
  And then he fired the arrow.
• 0:29
  speakers: The story begins with a physics teacher experimenting with glass fibers.
• 0:34
  Interviewer: Bright sunlight streaming into the room glinted off a tiny glass fiber.
• 0:39
  At its thinnest, it was less than a tenth of the diameter of a human hair.
• 0:43
  Interviewee: Now, legally, we cannot shoot a crossbow indoors.
• 0:46
  Luckily, I am pretty quick.
• 0:49
  Interviewer: That's cool.
• 0:50
  Look at that.
• 0:51
  Look how thin we got.
• 0:52
  Interviewee: The physics teacher was using these fibers to measure very small forces.
• 0:55
  But in the decades that followed, other researchers found a different use for them.
• 0:59
  Interviewer: Sending light signals.
• 1:00
  speakers: Sending light signals is just the beginning of this journey.
• 1:04
  The best way to increase capacity is to increase the bandwidth.
• 1:08
  But they'd already reached the limit for copper.
• 1:11
  The telecoms industry didn't have another alternative.
• 1:13
  But then they saw the light.
• 1:15
  Visible light has frequencies in the hundreds of terahertz.
• 1:19
  As one researcher for Bell Labs put
• 1:25
  Despite the potential of glass fibers, early attempts faced significant challenges, including high signal loss.
• 1:33
  Interviewee: At the time, phone calls were mostly transmitted over copper wires.
• 1:36
  Now, imagine I'm trying to phone my buddy Gregor.
• 1:39
  Now, when I pick up, a constant current immediately flows through the wire to supply power to the phone.
• 1:44
  When I speak, my voice vibrates a tiny diaphragm in the mouthpiece that modulates the current.
• 1:49
  The louder I am, the bigger the current swing.
• 1:51
  My voice's pitch changes how fast the current oscillates.
• 1:54
  At Gregor's end, that current reaches a speaker that turns it back into sound.
• 1:58
  Now, this works for one call on one line.
• 2:01
  But phone companies aren't gonna install wires between every single house.
• 2:05
  One cable needs to carry multiple calls.
• 2:07
  So, phone companies figure out a neat little trick.
• 2:10
  Even though humans can hear frequencies up to 20 kilohertz, you really only need to hear the ones between 300 and 3 ,400 hertz to understand
• 2:18
  what someone's saying.
• 2:19
  So, phone companies drop frequencies above 4 kilohertz.
• 2:22
  Or anything outside the voice band.
• 2:24
  But if everyone used that 0 to 4 kilohertz band on the same line, well, then all the conversations would be on top of each other.
• 2:31
  And you wouldn't be able to hear the person that you're talking to.
• 2:33
  Luckily, we can shift those electrical signals.
• 2:36
  So, my conversation can use 0 to 4 kilohertz.
• 2:39
  Well, another person's can use 4 to 8.
• 2:40
  And so on, all the way down the same copper wire.
• 2:43
  At the other end, a filter separates out the different frequency bands, similar to how a radio can tune in to one station.
• 2:50
  Then, the signal is shifted back down to the 0 to 4 kilohertz range before it hits the speaker.
• 2:54
  So, it sounds like a normal voice.
• 2:56
  But as phone companies started using higher and higher frequencies, they started running into problems.
• 3:01
  That oscillating current carrying the signal generates additional fields.
• 3:05
  A magnetic field, shown here in red, and little loops of current called eddy currents, which are shown here in blue.
• 3:15
  Interviewer: Between 1960 and 1973, the number of daily calls doubled in the U .S., from 285 million to 576
• 3:23
  million.
• 3:23
  In that same time period, NASA sent people to the moon for a total cost of $26 billion.
• 3:29
  While AT &T had to spend nearly triple that amount just to install new telephone infrastructure.
• 3:34
  They just couldn't keep up with the demand.
• 3:36
  speakers: The rapid increase in phone calls highlighted the need for better technology.
• 3:42
  Interviewee: For a while, telephone companies were able to work around the high loss by boosting signals every few kilometers.
• 3:47
  But past 65 megahertz, well, the high frequencies died off in less than two kilometers.
• 3:53
  So, they were too impractical to use.
• 3:55
  And this trade -off between signal power and data rate was actually discovered back in 1948.
• 4:00
  Interviewer: The Shannon -Hartley theorem described the maximum capacity of a communication channel based on the signal power, noise, and bandwidth, or the difference between the
• 4:08
  highest and lowest frequencies.
• 4:09
  speakers: Understanding the Shannon-Hartley theorem is crucial for grasping fiber optics.
• 4:15
  Interviewee: So the question was, why was the loss so high?
• 4:18
  Well, you might think it's because light is exiting through the sides of this fiber.
• 4:22
  But glass is really good at trapping light, even through bends.
• 4:26
  Here's how.
• 4:27
  I've got a bucket of propylene glycol here, and a green laser.
• 4:31
  speakers: Charles Kao's research led to a significant reduction in signal loss in fiber optics.
• 4:38
  Interviewee: Charles Cow.
• 4:39
  In 1960, he started working for an English telecoms lab that was looking for a way to communicate with higher frequencies.
• 4:45
  But not with fiber optics.
• 4:47
  speakers: Cow's persistence in the face of skepticism is inspiring.
• 4:51
  Dorado, always beckoning us onward.
• 4:55
  But if you're going to use light, there are two problems.
• 4:58
  First, there wasn't a strong enough light source to send a signal.
• 5:01
  A light bulb couldn't produce enough power.
• 5:03
  There just weren't any options.
• 5:05
  And along in 1960, Ted Beaman invented the laser.
• 5:09
  A science fiction weapon that melts steel.
• 5:11
  A death ray that could be more deadly than a nuclear bomb.
• 5:15
  It's a beam of light.
• 5:17
  This is called a laser.
• 5:19
  Interviewee: There's a running joke that the laser was a solution looking for a problem.
• 5:23
  But that's not really true.
• 5:25
  That rejuvenated the interest in possible optical communications.
• 5:31
  speakers: Glass is not as clear as it looks. How does this next moment reframe what we just heard?
• 5:37
  Interviewee: Glass is not as clear as it looks.
• 5:40
  Only a small amount of light actually makes it through.
• 5:43
  In fact, only a year after the laser's invention, a Bell Labs scientist started looking into fiber optics.
• 5:49
  His boss told him to check its loss, or how much a light signal weakens as it travels through the glass.
• 5:55
  Now, signal loss is measured with decibels, similar to how you measure audio volume.
• 5:59
  Both are on a logarithmic scale.
• 6:01
  But while volume uses sound pressure, loss uses signal power.
• 6:05
  His boss said it would only be worthwhile if the loss was less than 20 decibels a kilometer, so it was comparable to copper.
• 6:13
  Interviewer: understand just how bad that was, imagine a leaky truck carrying sand over one kilometer.
• 6:18
  If the truck starts with 100 kilograms, and it ends up with one, well, that represents a loss of 20 decibels per kilometer.
• 6:25
  That's only 1 % of the signal left.
• 6:27
  It's what was happening with copper.
• 6:29
  Bad, but still manageable.
• 6:31
  A loss of 1 ,000 decibels a kilometer is like starting with the mass of the observable universe, and ending up with less than the mass of a
• 6:39
  single atom.
• 6:40
  To be practical, these fibers would need to improve by a factor of 10 to the 98.
• 6:45
  It sounded impossible.
• 6:47
  It would have to be one of the most absurd engineering improvements in history.
• 6:50
  So Bell Labs gave up.
• 6:52
  And fiber optics might have died
• 6:54
  speakers: Understanding signal loss is key to improving fiber optics.
• 6:58
  Cow's boss said that it was a wild goose chase, and the rest of the lab agreed.
• 7:03
  But Cow kept coming back to it, asking, why is glass so lossy?
• 7:07
  And can we remove those factors, or are they intrinsic to the material?
• 7:12
  If it was the latter, then fiber would be dead in the water.
• 7:15
  But if not, then maybe
• 7:16
  The journey to low-loss fibers is filled with scientific inquiry.
• 7:20
  Interviewer: the laser bounces one, two, three times.
• 7:24
  And there are two things working together here that actually trap the light.
• 7:27
  speakers: See, light travels slower in some materials than others. To understand just how bad that was, imagine a leaky truck carrying sand over one kilometer. Cow's boss said that it was a wild goose chase. The laser bounces one, two, three times.
• 7:46
  Interviewee: See, light travels slower in some materials than others.
• 7:49
  And it travels as a wave, shown here as a line of crests, with the beam always pointing perpendicular to that line.
• 7:55
  When the wave meets a boundary at an angle, one end of the crest crosses into the new material first, and it changes speed before the rest.
• 8:03
  If light travels slower in that new material, then that end drags behind, and the beam bends, or refracts, away from the boundary.
• 8:11
  How much it bends depends on the angle it hits the boundary, and on how much each material slows light down, which is described by their index of refraction.
• 8:18
  This relationship is defined by Snell's law.
• 8:23
  Interviewer: Now, if light is moving from a material with a higher index of refraction into one with a lower index, like propylene glycol to air,
• 8:31
  well then one part of the wave crest speeds up, and the beam bends toward the boundary.
• 8:35
  But as you increase the angle of the light, the refracted beam gets closer and closer to the boundary, until it's running right along it.
• 8:43
  That's the critical angle.
• 8:44
  A little bit more, and all the light reflects back into the glycol.
• 8:49
  That's total internal reflection, and you get the exact critical angle by setting the angle of refraction to 90 degrees, and then rearranging Snell's law.
• 8:56
  speakers: The impact of refractive indices on light behavior is crucial.
• 9:00
  The key of it is, the bigger the difference in index of refraction, the more powerful this effect is.
• 9:08
  If I have a really subtle difference between these two, then the amount of bending that takes place will be smaller.
• 9:15
  Let's explore how different materials affect light transmission.
• 9:19
  Interviewer: You can do the same demo with water, but propylene glycol works a bit better because it has a higher refractive index, 1 .43 compared with 1 .33.
• 9:28
  See, once the liquid is low enough for the angle of the stream to be much sharper, the light breaks through the water stream, but it stays trapped in the propylene glycol.
• 9:36
  And if you use something with an even higher refractive index, like the glass types Cal was investigating, well then the critical angle decreases even more, which
• 9:44
  traps the light signals through even sharper turns.
• 9:46
  speakers: Okay, but the light has to move from a high refractive index to a low one. Now, if light is moving from a material with a higher index of refraction into one with a lower index. The key of it is, the bigger the difference in index of refraction. You can do the same demo with water, but propylene glycol works a bit better.
• 10:07
  Interviewee: Okay, but the light has to move from a high refractive index to a low one.
• 10:11
  An air that works, right up until something touches the glass.
• 10:15
  If you disturb that boundary, well, light can leak out the side.
• 10:19
  So about a decade before Cal, researchers realized that a fiber needed to have two types of glass.
• 10:24
  The middle, the core, has the higher refractive index.
• 10:28
  And around it goes a second glass, the cladding, with the lower refractive index.
• 10:32
  Together, they keep the light trapped.
• 10:34
  speakers: The durability of fibers is essential for their practical use.
• 10:38
  Now the fiber could be touched, coated in plastic, buried in a cable, bent around things, and the light would still travel down the core and come out the other
• 10:46
  end.
• 10:52
  So Cal knew that if the high loss wasn't from light leaking out the sides. Now the fiber could be touched, coated in plastic, buried in a cable.
• 11:02
  Interviewee: He spoke with material scientists and glass experts, but no one seemed to know what was really causing it.
• 11:07
  He kept looking, and eventually he landed on two potential sources, scattering and absorption.
• 11:12
  speakers: The relationship between temperature and light scattering is intriguing.
• 11:17
  Interviewer: If you shine light through a perfect crystal that's transparent, there's gonna be a little bit of reflection, but almost all of the electromagnetic energy will keep going down
• 11:25
  in the same direction that it started.
• 11:26
  But glass isn't a crystalline solid.
• 11:29
  The basic building block is silica, or silicon dioxide, one silicon atom connected to four oxygen atoms in a tetrahedron, or
• 11:37
  pyramid shape.
• 11:38
  In the glass, the pyramids are connected at the corners, so every oxygen is shared with another silicon.
• 11:43
  That's why it's called silicon dioxide.
• 11:45
  For every two oxygens, there's one silicon atom.
• 11:48
  This is an amorphous solid.
• 11:50
  Unlike a crystal, its atoms have no long -range order.
• 11:53
  Instead, its disordered liquid -like structure locks in as it cools, with the exact arrangement depending on the glass type and cooling speed.
• 12:01
  For example, if you quench the glass really fast, the structure locks at a higher temperature.
• 12:07
  The final solid has lots of dense regions, which re -radiate more light than the sparse ones.
• 12:12
  Light scatters, which weakens the signal.
• 12:14
  This is called Rayleigh scattering, and you can't get rid of it completely.
• 12:18
  But if you cool the glass slowly, those pyramids have more time to settle and pack together evenly.
• 12:23
  speakers: The structure locks in at a lower temperature. If you shine light through a perfect crystal that's transparent.
• 12:30
  Interviewee: Was it 10 decibels a kilometer?
• 12:32
  100?
• 12:33
  1000?
• 12:33
  He needed something concrete.
• 12:35
  speakers: Maurer's contributions to fiber optics cannot be overlooked.
• 12:39
  Interviewer: Finally, he stumbled on a paper by Robert Maurer, a scientist from Corning Glass, who measured the Rayleigh scattering across several glass types and cooling rates.
• 12:47
  speakers: 's calculations were pivotal in advancing fiber optics.
• 12:51
  Interviewee: Kau used his calculations to estimate that if the glass's structure was locked at 1000 degrees Celsius, well, its scattering loss would be
• 12:59
  around one decibel a kilometer.
• 13:01
  speakers: The unexpected findings in Kau's research were surprising.
• 13:05
  Interviewer: He was surprised.
• 13:06
  He expected scattering loss to increase with higher temperatures.
• 13:09
  That's what causes more density fluctuations.
• 13:12
  But 1000 degrees Celsius was pretty hot compared to other glass types.
• 13:16
  So then scattering couldn't be behind those crazy high losses.
• 13:20
  Absorption had to be the problem.
• 13:22
  But Kau didn't know what exactly was absorbing so much light.
• 13:25
  Was it the glass itself or something else?
• 13:32
  Kao spoke with more experts who estimated that without those metal ions, the loss would drop to around 20 decibels a kilometer, copper will the copper, just by
• 13:40
  removing impurities.
• 13:41
  speakers: The theoretical aspects of fiber optics are fascinating.
• 13:45
  Interviewee: It was all theoretical at this point, but it was enough for Kao.
• 13:49
  In 1966, his team published a paper on their theories, concluding with, the crucial material problem appears to be one which is difficult, but not
• 13:57
  impossible.
• 13:58
  But nobody really paid attention to his paper because it really seemed impossible.
• 14:04
  A 10 to the 98 times improvement was unprecedented.
• 14:07
  And Kao didn't actually measure the loss in glass.
• 14:10
  He didn't have anything concrete.
• 14:13
  So he needed proof.
• 14:14
  speakers: Kao's vision for fiber optics was revolutionary.
• 14:18
  Interviewer: Kao was trying to invent a new way to communicate, but even today, actually staying connected can be hard.
• 14:24
  In fact, we just traveled to Spain for the eclipse a few weeks ago, but with so many other projects going on, we still need to check in and set updates to the rest of the team.
• 14:32
  Not to mention my mom.
• 14:34
  We drove seven hours to Burgos, but the Wi -Fi when we got there was a little touch and go.
• 14:39
  We needed to have everything set before we arrived on site.
• 14:42
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• 14:44
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• 14:49
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• 14:52
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• 14:54
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• 14:59
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• 15:05
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• 15:09
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• 15:12
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• 15:14
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• 15:18
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• 15:21
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• 15:28
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• 15:30
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• 15:36
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• 15:40
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• 15:47
  Now, let's go back to Cow.
• 15:48
  speakers: The challenges of proving theoretical concepts are significant.
• 15:53
  Interviewer: Cow needed to prove that his theoretical low -loss glass was really possible.
• 15:58
  So he decided to measure the purest glass anyone had ever made, few silica.
• 16:02
  Now, the reason glass manufacturers had added all those extra ingredients was to bring sand's melting point down to around 1400 degrees Celsius.
• 16:10
  But few silica was pure silicon dioxide, melted at over 2000 degrees Celsius.
• 16:15
  So it was a lot harder to make.
• 16:17
  And that meant that Cow couldn't get his hands on much of it.
• 16:21
  Measuring loss normally takes hundreds of meters of cable, if not kilometers.
• 16:25
  But he only had pieces less than 30 centimeters long.
• 16:28
  To measure the loss in something that small, he and his colleagues invented a new, very precise instrument.
• 16:34
  Cow spent the next three years working on it.
• 16:36
  But when he finally measured a sample, he found that few silica had zero loss.
• 16:43
  That couldn't be right.
• 16:44
  In a panic, Cow ran his experiment again.
• 16:47
  It turned out that the loss was so low that it was within their margin of error, a mere plus or minus four decibels a kilometer.
• 16:55
  He spent months fine -tuning his equipment, and in 1969, he finally reported that few silica had a loss of less than five
• 17:02
  decibels a kilometer.
• 17:04
  Now that got everyone's attention.
• 17:06
  One scientist at Bell Labs said, Cow gave everyone a jolt.
• 17:09
  That was the first practical measurement which said, hey, you're not just whistling Dixie.
• 17:14
  Now everyone was interested.
• 17:15
  Telecom labs around the planet rushed to fund fiber optics groups.
• 17:19
  But Cow had only worked with small samples.
• 17:22
  Nobody knew whether kilometers of low -loss fiber were even possible.
• 17:25
  The problem caught the attention of one Robert Maurer, Corning researcher and author of the scattering paper that Cow had referenced.
• 17:32
  To make a practical fiber, he saw three major problems to tackle.
• 17:36
  First, he needed to decide which glass to use.
• 17:39
  He could try purifying raw materials for normal glass, or he could try using fused silica, which Cow had already proven to be very pure.
• 17:46
  Most labs were avoiding fused silica because of how hard it was to work with.
• 17:50
  But luckily, Corning had a secret technique.
• 17:54
  speakers: It simply didn't exist.
• 17:56
  So everyone abandoned fused silica, except for Maur.
• 18:00
  He said, I had no reason to think fused silica was any better, but nobody else was working on it.
• 18:05
  If you do something that's different from what everybody else is doing, you've got two advantages.
• 18:09
  One is you may succeed where they fail, of course, but even if you fail, you will gather information that they don't gather.
• 18:15
  The competition in fiber optics research was intense.
• 18:19
  Interviewee: All the other labs were thinking of using a fused silica core.
• 18:22
  After all, that's where the light travels.
• 18:24
  But Maur decided to use fused silica for the cladding.
• 18:27
  Then he could easily raise the refractive index at the core by adding some impurities, or dopants.
• 18:33
  The only glass that we had with a slightly higher index than fused silica was this titanium -doped glass.
• 18:41
  But that would mean adding titanium right where light needed to travel.
• 18:45
  speakers: The quest for purity in glass production is ongoing.
• 18:49
  Interviewer: Cal worked hard to prove that glass could be pure enough.
• 18:52
  speakers: The innovative approaches to glass production are noteworthy.
• 18:55
  All the other labs were trying to get rid of impurities, and Maur wanted to add some back in.
• 19:01
  But he wasn't completely crazy.
• 19:03
  Like silicon, the titanium in glass can easily share electrons with four oxygen atoms, forming the same pyramid shape.
• 19:10
  So it wouldn't disrupt the overall glass structure too much.
• 19:13
  The challenges of glass composition are complex.
• 19:18
  Interviewer: Now that he had the composition, Maur needed to tackle that second problem.
• 19:21
  How do you make a tiny fiber with that perfect core and cladding cross -section?
• 19:26
  To help, he hired two more scientists, Peter Schultz, a ceramics engineer, and Donald Keck, a physicist.
• 19:31
  speakers: The problem-solving nature of scientific research is crucial.
• 19:35
  Interviewee: Each time you find a problem, you put a development team on it and strike it down and make it happen.
• 19:41
  To understand their technique, I went to the Bay Area Glass Institute for some hands -on demos.
• 19:46
  speakers: The process of creating fiber optics is intricate.
• 19:49
  Interviewer: Here, our instructor Aaron is taking a colored rod of glass and then dipping it in a bowl of clear molten glass.
• 19:56
  In fiber optics, this large cylinder is called a preform.
• 19:59
  speakers: The relationship between color and glass is fascinating.
• 20:03
  Interviewee: We have two colors of glass here.
• 20:05
  We have a colored core and a clear outside.
• 20:07
  speakers: The technical aspects of fiber optics are essential to understand.
• 20:12
  Interviewer: If you want your inner rod to say be a quarter of the diameter of your outer one, you just set that in the preform and then all the length along your pole, the cross -section is going to
• 20:20
  be identical.
• 20:20
  And this is pretty similar to how hard candies with patterns are made.
• 20:28
  speakers: Moving from want inner to another Corning, what changed?
• 20:31
  Interviewee: Back in the 1930s, another Corning scientist had ran silicon tetrachloride gas through an oxygen flame.
• 20:37
  In the heat, water vapor from the flame would break silicon tetrachloride into hydrogen chloride gas and silicon dioxide.
• 20:44
  The latter would then start clicking together in a fine glassy silica powder.
• 20:49
  Then the powder would be pressed into shape and melted to make fused silica.
• 20:57
  speakers: In 1887, a young physics teacher attached a thin glass rod to the end of an arrow. Now, legally, we cannot shoot a crossbow indoors. What claim should we test as this continues?
• 21:10
  This sugar is an amorphous solid, just like glass.
• 21:14
  So the process is the same, just at a lower temperature.
• 21:18
  But there is one problem with this method.
• 21:20
  Resting glass on a surface like this introduces a ton of stress and impurities.
• 21:24
  But when I try and suspend it in the air, well, it sags.
• 21:28
  But yeah, from all that movement, it did create stress.
• 21:31
  So now it's a curved piece of glass.
• 21:35
  Thankfully, there's another option.
• 21:37
  Now gravity is pulling our glass for us and the surface tension is keeping
• 21:41
  The cooling process of fibers is crucial for their integrity.
• 21:45
  Interviewer: we get a much more straight and consistent fiber.
• 21:49
  That's awesome.
• 21:51
  speakers: Moving from much more to companies world, what changed?
• 21:55
  Corning was one of the few companies in the world using this technique, called flame hydrolysis, to make ultra -pure glass.
• 22:06
  The challenges of producing high-quality fiber optics are numerous.
• 22:10
  Interviewee: It has a refractive index of 1 .46, which is the lowest of any glass.
• 22:15
  But for total internal reflection to work, the core needs to have a higher refractive index than the cladding.
• 22:21
  So if Maur wanted to use a fused silica core, well then finding another glass with a lower refractive index for the cladding, well, that'd be a
• 22:28
  nightmare.
• 22:33
  speakers: Well, instead of starting with a core and adding the cladding, Schultz and Keck decided to start from the cladding and work in.
• 22:39
  They used the flame hydrolysis technique to make titanium -doped silica powder, or soot as they called it.
• 22:46
  Next, they took a pure fused silica tube and tried spreading soot down the inside.
• 22:50
  They could get an even layer, well, then they could melt and collapse the tube into a solid rod, a perfect preform.
• 22:56
  But the soot collected at one end, no matter how they sprayed it.
• 23:01
  So one of the technicians grabbed a vacuum cleaner from the corner of the room.
• 23:06
  They held it up to the backside of this tube and it sucked a stream of titanium -doped silica glass down through the center of the
• 23:14
  tube, coated it just like we'd hoped it would.
• 23:17
  Vacuum did not survive that experiment, but they tinkered with a new setup until they got the gas flow just right.
• 23:23
  The innovations in fiber optics are remarkable.
• 23:26
  Interviewee: All through the summer of 1969, their furnace burned hotter than Hades.
• 23:31
  They drew kilometers of fiber from preform after preform, testing various compositions, but none of it was good enough.
• 23:38
  Titanium was breaking down in the high heat and absorbing too much light.
• 23:42
  They ran finished fibers through a second heat treatment in an oxygen environment before they finally started seeing results.
• 23:52
  speakers: So the question was, why was the loss so high? The Shannon-Hartley theorem described the maximum capacity of a communication channel.
• 24:03
  By 1977, AT &T trialed a fiber system underneath Chicago.
• 24:08
  Two years later, a fiber team from Japan was able to get a loss of just 0 .2 decibels a kilometer.
• 24:14
  The standard up to today.
• 24:16
  Fiber networks continued to grow, with the first transatlantic fiber optic cable installed by 1988.
• 24:22
  And it transmitted those phone calls differently than in copper.
• 24:25
  The audio wave was split up, or sampled into discrete values, and then converted into binary to get a long string of ones and zeros.
• 24:33
  Then a laser flashed on for one and off for zero, 280 million times a second.
• 24:38
  These pulses of light traveled down the fiber, but that wasn't all.
• 24:42
  Multiple conversations could now be weaved together.
• 24:45
  One bit from one conversation, then from another, and so on, slotting in together like a zipper.
• 24:51
  As long as the receiver knew the timing of each conversation and the sampling rate, well, they could reconstruct the original waves.
• 25:07
  The impact of fiber optics on communication is profound.
• 25:12
  Interviewer: This insane capacity opened up a whole new world, and with digital signals, people realized that they weren't limited to phone calls.
• 25:22
  A year later, on July 22nd of 1970, a preform slipped against the furnace wall after Keck only got a few meters of fiber.
• 25:30
  The preform was ruined, but he decided to test the short fiber anyway after its heat treatment.
• 25:36
  When I slid it across and the laser light hit the core of the fiber, all of a sudden, I had another beam coming back in my face.
• 25:43
  The core was brightly lit and it took a while to realize that the light was going all the way to the other end of the fiber and
• 25:51
  reflecting off the far end and coming back into my eye.
• 25:55
  The loss was 17 decibels a kilometer.
• 25:57
  speakers: The journey of fiber optics continues to evolve.
• 26:01
  Interviewee: He added a careful must -remeasure in his notebook.
• 26:03
  The team quickly remade the preform, but it took almost a month to get 210 meters of finished fiber.
• 26:13
  speakers: Moving from only word to easier than, what changed?
• 26:17
  It was easier than ever to send text, images, videos, all building up to the internet.
• 26:23
  And since then, demand has only increased.
• 26:30
  Interviewer: It was finally done by late afternoon of Friday, August 21st.
• 26:34
  It was a gorgeous summer day and almost everyone left early, but Keck didn't want to wait.
• 26:39
  Fiber was so fragile, small temperature changes might break it over the weekend.
• 26:42
  speakers: The advancements in fiber optics are exciting.
• 26:45
  It would break if you looked at it gross ways.
• 26:48
  So alone in the lab, he anxiously measured the loss.
• 26:52
  16 .9 decibels per kilometer.
• 26:55
  The technical details of fiber optics are crucial.
• 26:58
  Interviewer: I said QED.
• 27:00
  Quadach.
• 27:01
  Erot demonstratum.
• 27:02
  speakers: The importance of clarity in fiber optics cannot be overstated.
• 27:07
  Interviewee: no Eureka.
• 27:08
  speakers: The journey of fiber optics is filled with discoveries.
• 27:12
  Interviewer: Maurer published their results that fall.
• 27:15
  As Schultz described it, no one believed it.
• 27:18
  Telephone companies all demanded to see the fibers firsthand.
• 27:21
  So Maurer hand -carried a spool of fiber to all the big telephone laboratories.
• 27:26
  He would literally guard to make sure that they didn't snip pieces off and keep them.
• 27:31
  speakers: The evolution of fiber optics is a testament to innovation.
• 27:35
  For two years, they refined their methods.
• 27:52
  The advancements in fiber optics are remarkable.
• 27:55
  Interviewer: When they drew their first germanium fiber, the end lit up with the light from the furnace.
• 27:59
  Even when it reached the bottom and wound up around a large drum, the fiber stayed bright.
• 28:03
  And we kept winding and winding and winding, thinking the light was going to go out.
• 28:09
  And it never went out.
• 28:11
  The loss was only four decibels per kilometer with excellent strength.
• 28:15
  Keck considers that the very first truly practical low -loss fiber.
• 28:23
  This reel right here?
• 28:25
  speakers: The future of telecommunications is bright with fiber optics.
• 28:30
  Yeah.
• 28:37
  Interviewee: That's crazy.
• 28:38
  Like, how much is in this warehouse?
• 28:39
  Oh, there's millions of kilometers here that we're pushing through here every month.
• 28:43
  To see how modern fibers are made, we visited Prismian's North Carolina factory.
• 28:48
  It all starts with the preform.
• 28:50
  Each pass of this microwave source ignites a mixture of gases into a plasma which deposits a thin layer of glass on the inside of the tube.
• 28:58
  And you see when it turns purple, that's when we're making a plasma with that gas.
• 29:02
  So how thick are these deposition like?
• 29:05
  Like how many times are you doing this?
• 29:06
  How thick are you doing this?
• 29:07
  Thousands of passes.
• 29:12
  Interviewer: Next, the finished fiber is tested for loss in strength.
• 29:15
  Fiber is stronger than a steel wire of the same thickness.
• 29:18
  I guess if I try to do it like...
• 29:20
  You just try to do it like that.
• 29:21
  It's really hard.
• 29:22
  Interviewee: Oh my God.
• 29:27
  speakers: Moving from slides down to Several thousand, what changed?
• 29:30
  Interviewer: Several thousand times it's doing this.
• 29:33
  Every time
• 29:33
  Interviewee: what we do is we heat it up.
• 29:35
  We have a furnace that goes back and forth.
• 29:37
  And just by a surface tension, it collapses upon itself.
• 29:40
  Interesting.
• 29:41
  I would have thought maybe you'd like pull it or - So I asked this exact question.
• 29:44
  I said, are you pulling a vacuum in there?
• 29:46
  What's making that thing shrink?
• 29:48
  It's really just a glass phenomena where the molecules are trying to pull together.
• 29:52
  You heat it up, you lower the viscosity of the glass, it just - Now they need to add more silicone on the outside to get the preform to the right proportions.
• 30:00
  The core is very small, just 7 .2 % of the total diameter.
• 30:04
  And you have a several thousand seed plume of plasma right there.
• 30:08
  There's grains of silica that's flowing into that plume and effectively melting it and spraying it onto that rod.
• 30:15
  Wow.
• 30:16
  That plasma torch is approximately three times as hot at the surface of the pump.
• 30:21
  Plasma always blows my mind.
• 30:23
  This is absurd.
• 30:24
  Once the preform's done, it goes to the top of the draw tower, seven stories up, to start making fiber.
• 30:34
  Interviewer: Yeah, not easy.
• 30:35
  Definitely not easy.
• 30:36
  Ow!
• 30:37
  But it's weak to sharp turns.
• 30:39
  Tied in a knot.
• 30:40
  Tied in a knot?
• 30:41
  Well, watch
• 30:41
  Interviewee: And see how much you can get before
• 30:44
  Interviewer: But after testing, fiber is bundled and wrapped into thicker cables so that it's harder for them to knot and break.
• 30:50
  These cables will join the more than 8 billion kilometers of fiber already installed that carry information around the world, powering the internet and
• 30:57
  letting you watch this video.
• 30:59
  But some experts argue that even with fiber, the internet would not be possible without another key invention.
• 31:05
  The amplifier.
• 31:06
  That's what boosts signals across long stretches and it revolutionized fiber capacity on land and sea.
• 31:13
  So if you'd like to see a video about submarine cables and fiber amplifiers, well, let us know in the comments.
• 31:19
  Interviewee: As for Cao, his dream went further than he ever thought.
• 31:22
  When he received the Nobel Prize in 2009 for his work, he said, the information revolution that started in the 1990s could not have
• 31:30
  happened without optical fibers.
• 31:31
  It is beyond the dreams of the first serious concept of optical communication in 1966
• 31:40
  Interviewer: Really looks like some sort of steampunk thing, you know?
• 31:43
  All these coils and this hot glass going down.
• 31:50
  speakers: gigahertz was only a hope.
• 31:53
  For me, one of the things I kept on coming back to in this story is that Cao was not a material scientist.
• 31:59
  He was an electrical engineer and it was only because he was an outsider that he was able to ask the questions that nobody was asking.
• 32:06
  He was able to push the status quo.
• 32:08
  But he was not the only one.
• 32:10
  Maurer's team were also working with a very unintuitive idea that by making something seemingly worse, they actually were making it better.
• 32:17
  As Cao said, who knows what other forward thinkers will dream of in the future.
• 32:21
  Granted, he was talking about bandwidth, but I think it applies anywhere where people are able to question why things are the way they are, whether
• 32:29
  that's really the limit.
• 32:35
  Interviewee: The bottom of the preform is tapered to a point and heated to over 2 ,000 degrees Celsius.
• 32:40
  Interviewer: The end of the taper slowly drops down to the floor below.
• 32:43
  Interviewee: We call it a gob, but it looks like a teardrop.
• 32:46
  Interviewer: The fiber is a little thick, so it'll be thinned down to the final 125 microns before it passes to the next level.
• 32:53
  Interviewee: It's like a little flash button.
• 32:57
  I don't...
• 33:02
  I didn't expect it to be so violent.
• 33:07
  Interviewer: If the drawing, like the pull down to that final diameter happens in such a short amount of it.
• 33:14
  In a few meters, let's call it.
• 33:16
  A few meters.
• 33:17
  Then, why do you need six more floors?
• 33:20
  You gotta cool the glass before you can apply the coating.
• 33:23
  And if you cool the glass too quickly, it'll have residual stress and then have optical loss, attenuation.
• 33:29
  Interviewee: That's a pretty good one.
• 33:31
  Once the fibers are cool enough, they're dipped in two protective plastic coatings.
• 33:35
  At the bottom of the draw tower, the fiber is wound onto massive spools, each capable of carrying hundreds of kilometers at over 50 meters a second.
• 33:48
  speakers: There's a running joke that the laser was a solution looking for a problem. If you're going to use light, there are two problems.
• 33:57
  Interviewee: One last thing.
• 33:58
  These videos are only possible because of the incredible work done by our team behind the scenes.
• 34:02
  We have world -class editors, animators, researchers, and writers that make these videos possible.
• 34:08
  We'd love to shine more of a light on their work, so we organized a Q &A with the writer of today's video, Sully.
• 34:13
  She discusses the fascinating things she learned while researching this topic and things that didn't make the cut, but that are really interesting.
• 34:19
  So if you want to learn more about that, you can sign up for our newsletter in the description and you can find her Q &A right there.