How Optical Fiber Connected the World — Transcript

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1. 0:03Starting in the 1970s, the world moved  from communicating through copper to
2. 0:07glass - and that demanded  a series of breakthroughs.
3. 0:11The optical fiber network connecting our world  is a technical marvel. Light bouncing from one
4. 0:16end of the world to the other, encased  in some of the purest glass in the world,
5. 0:20modulated to carry billions or  even trillions of bits per second.
6. 0:25In this video, we talk about how  optical fiber helped connect the world.
7. 0:29## Beginnings
8. 0:30In 1933, a boy named Charles Kao was born in the  city of Shanghai inside the French Concession.
9. 0:37Fleeing the chaos of the Chinese Civil  War, his family moved to British Hong
10. 0:41Kong. Charles then traveled to the  United Kingdom to do his studies,
11. 0:46eventually receiving his PhD in electrical  engineering at the University of London.
12. 0:52Then in 1960, Charles joined Standard  Telecommunications Laboratories - the
13. 0:56research arm of Standard Telephones  and Cables - in the United Kingdom.
14. 1:01At the time, the world and their telecom  carriers sent electrical signals through
15. 1:06copper wires. But the world - even just through  phone calls - thirsted for more bandwidth.
16. 1:12Telecoms thus turned to millimeter  wave transmitters. Millimeter wave
17. 1:17transmission uses extremely high frequency  waves - some 35-70 gigahertz - to send data
18. 1:23at high rates. It is today used in 5G  networks, with somewhat iffy results.
19. 1:29The telecoms were installing chains of relay  towers beaming microwave and millimeter wave
20. 1:34signals from one point to the next. But  people soon realized that the atmosphere
21. 1:40absorbed too much of the waves to  make a good point to point signal.
22. 1:44You needed a waveguide - a medium  that can facilitate the travel of
23. 1:48those waves. Like how a paved  road makes it easier to drive.
24. 1:53## Light's Potential
25. 1:53At around this time, news arrived  of the invention of the laser.
26. 1:57One of the first uses people envisioned for  the laser was in communications. Theoretically,
27. 2:03they can replace all those  point-to-point relay towers.
28. 2:07Light held so much potential for data  transmission, if not simply on the basis
29. 2:11of its frequency - 3,000 terahertz  compared to microwaves' 3 gigahertz.
30. 2:17Yet Charles' cohorts quickly tried the technology,
31. 2:20only to dismiss it. Glass fibers and the  term "fiber optics" have been around since
32. 2:25the 1920s. They were even used in  1954 to convey images with light.
33. 2:31But when scientists tried firing laser  light through fiber optics to send data,
34. 2:36it didn't work. Unless the fiber was perfectly  straight, there was too much light lost.
35. 2:42The fancy term for that is called "attenuation",  and it is measured in "decibels per kilometer".
36. 2:48Imagine a glass window. You  can easily see through it,
37. 2:51right? Most glass windows have an  attenuation of 200 decibels per
38. 2:56kilometer. Make a glass window a few meters  thick, and you could barely see through it!
39. 3:02## Charles' Discovery
40. 3:02Charles decided to stick with it and after many  simulations and experiments, a breakthrough.
41. 3:08He concluded that attenuation was largely caused  by external impurities in the glass - particles
42. 3:15of copper or iron - rather than the  glass's inherent material properties.
43. 3:20He published his findings in a 1966 paper  - "Dielectric-Fibre Surface Waveguides for
44. 3:26Optical Frequencies". In it, he said that if  you get the iron and copper impurities to less
45. 3:32than 1 parts per billion, then the attenuation  would not be 200 decibels per kilometer but 20.
46. 3:39In other words, if the glass is pure enough then  you can see through a window many miles thick.
47. 3:46Few people noticed Charles' paper  at the time of its posting. Most
48. 3:50people were focused on satellites as the future of
49. 3:52communications. But Charles persisted  in bringing his idea around the world.
50. 3:58It did not take long for him to be  proven right. A team at the glass
51. 4:02manufacturer Corning led by Bob Maurer took on the
52. 4:06challenge. Corning has made optic fiber  before, but never with glass this pure.
53. 4:12Through experimentation, they stumbled across  a method. You place a mixture of precursor
54. 4:18gases inside a tube, and then spin it around  quickly while running a heat source over it.
55. 4:24The gases react together to create silicon  dioxide gas. And then that silicon dioxide
56. 4:29gas crystallizes onto the tube's inside  as a solid, pure fused silica glass.
57. 4:36This procedure is now known as Inside Vapor  Deposition and it is still used today.
58. 4:43After enough time, we got a solid  glass rod called a "preform".
59. 4:48Then we take the preform to a drawing  tower, which can be many meters tall.
60. 4:52It heats the preform - just the tip - and  then pulls down a fine strand of pure glass.
61. 4:59In 1970, Corning announced the creation of a  pure fused silica fiber with attenuation of
62. 5:05just 20 decibels per kilometer. Further  attenuation improvements were made by
63. 5:09other teams. With that, optical  fiber began connecting the world.
64. 5:15## The Fiber
65. 5:15Modern optical fiber is a flexible  strand of plastic or glass capable
66. 5:19of transmitting light from one end to the other.
67. 5:22We want to send some data - like  a digital picture of a Corgi in a
68. 5:25bathroom - over a fiber line. The digital  picture exists in the form of 1s and 0s.
69. 5:31We then take a laser's light  and modify, or modulate it,
70. 5:35in a variety of ways in order to encode those  1s and 0s. Then that light goes into the fiber.
71. 5:42The fiber is made up of two components - a  central core that is about ten to a few tens
72. 5:46of micrometers wide; and a 125-micrometer  thick cladding that surrounds it.
73. 5:53The fiber's core has a higher refractive index
74. 5:56than the cladding that surrounds  it. So once inside the fiber,
75. 6:00that light internally reflects back and forth  at the boundary between core and cladding.
76. 6:06That modified light will basically internally  reflect throughout the optical fiber - ideally
77. 6:11its whole length - and then exit without any power  loss. Even if the optical fiber bends and curves.
78. 6:18These light pulses not only travel at a very  high speed - 70% of the speed of light - but
79. 6:24they also do not suffer heat losses, nor  latency delays due to electrical resistance.
80. 6:29## Fiber Networks
81. 6:31That first ultra pure glass that Corning made back
82. 6:33in 1970 could carry 65,000 times  more information than copper wire.
83. 6:40In April 1977, General Telephone and  Electronics installed in Long Beach
84. 6:45the first commercial telephone  line powered with fiber optics.
85. 6:49That single 1-inch wide optical fiber carried as
86. 6:53much data as a 2,100-strand copper  cable, four times its diameter.
87. 6:59But first generation optical lines had  attenuation, causing the light signals
88. 7:04to deteriorate over distances. So  they needed "repeater" stations to
89. 7:09"regenerate" the light signal. This  involved receiving the light signal,
90. 7:13converting it to electric signals, and then  re-converting that into light again - or OEO.
91. 7:21Then in the second half of the 1980s,  a team at Southampton University in
92. 7:25the United Kingdom was studying  fiber sensing - how variations in
93. 7:29the temperatures surrounding a fiber  affects how light travels through it.
94. 7:34From there, they had these  experiments where they mixed
95. 7:37rare earths like neodymium and erbium into  fiber cores, which caused them to emit light.
96. 7:44Add some mirrors to the fibers  like with traditional lasers and
97. 7:47fire some light through these cores  - and you get some very long lasers.
98. 7:52Which was cool because it's lasers and all,
99. 7:54but nothing particularly useful. It took some  time before they saw the real killer use case.
100. 8:01Take off the mirrors, and the team realized  that they had boosted a light signal within
101. 8:05a fiber by 30 decibels. Unwittingly, they  invented the erbium doped fiber amplifier.
102. 8:13In 1986, Bell Labs adopted the amplifier,  allowing them to amplify the light and send
103. 8:19signals through long stretches of fiber without  needing to have so many repeater stations.
104. 8:25The Southampton team won the 2008 Millennium  prize for their invention. It was a significant
105. 8:31breakthrough in optical fiber adoption  that not only greatly improved fiber's
106. 8:35economic prospects, but also  exploded its capacity limits.
107. 8:41## Wavelength Division Multiplexing
108. 8:41These amplifiers not only boosted a  single wavelength, but multiple ones.
109. 8:45This made it practical for the  telecoms to transmit even more
110. 8:49data through the same fiber using  different light wavelengths that
111. 8:52won't interfere with each other -  "Wavelength Division Multiplexing".
112. 8:57So we have multiple lasers modulating data in  those different wavelengths. Then before sending
113. 9:02them into the fiber, we combine them together  using a thingamajig called a multiplexer.
114. 9:08The telecoms have long known  about wavelength multiplexing,
115. 9:12but never before implemented it because the  repeater stations would also have to split
116. 9:17all those wavelengths again before  regenerating them. Not practical.
117. 9:22The optical amplifiers  changed all that and by 2001,
118. 9:26the industry was regularly putting 80  wavelengths on a single fiber line.
119. 9:31If each of those wavelengths has a  bit rate of 10 gigabits per second,
120. 9:36then that whole line suddenly has total  bandwidth capacity of about 800 gigabits.
121. 9:41This was a major breakthrough, allowing  us to do far more with the same fiber.
122. 9:47In 1980, we used optical fiber to transmit images
123. 9:50for the first time - carrying pictures  of the Winter Olympics at Lake Placid.
124. 9:56Fourteen years later, optical fibers  were carrying video images for the
125. 9:59first time - carrying video back  from the Winter Olympics in Norway.
126. 10:04## Submarine Cables
127. 10:04Most of the world's data  infrastructure on land is modular.
128. 10:08This means information might hop from one city to
129. 10:10another. And that modularity makes the  network easier to build and maintain.
130. 10:15But it is a different story for the  cables that must plunge under the water
131. 10:19and span entire oceans - undersea  cables. It costs a lot of money
132. 10:23to lay down and maintain an undersea  cable, sometimes billions of dollars.
133. 10:29The first submarine cables used coax technology,  using a copper core to carry electrical signals.
134. 10:35But as voice bandwidth demands grew,  the technology strained to keep up.
135. 10:40Notably, they were getting fatter - which made  them harder to produce and maintain. For instance,
136. 10:45the 1976 TAT-6 cable which went from the  United States to Europe was 2 inches thick.
137. 10:51And at around $180 million, it also cost  twice as much as the previous cable, TAT-5.
138. 10:58Worse yet, the cost curve valued on a  per-voice-circuit basis was not trending in
139. 11:02a particularly good direction. TAT-6 cost twice  as much as TAT-5, but its $45,000 per-circuit
140. 11:10cost was more than half that of its predecessor -  indicating slowing coaxial technology progression.
141. 11:17Facing a significant challenge  from the satellite providers
142. 11:20and with landline fiber optics  already in the market in 1977,
143. 11:25AT&T took a chance on fiber optics for  their next cross-Atlantic submarine cable.
144. 11:31They spun segments of fiber - 5 miles  each - and spliced them together to
145. 11:3520 mile long segments which was how far  apart the repeater stations would be.
146. 11:41Then, work had to be done to adapt existing  submarine cable housings for the new fiber optic
147. 11:46material. After a series of extensive tests and  sea trials, AT&T laid down TAT-8 in 1988 - with
148. 11:54two optic fibers, carrying 280 megabits per  second or about 40,000 simultaneous phone calls.
149. 12:02There were some initial issues with  sharks attacking the cables near the
150. 12:05Canary Islands - the cables were not properly  insulated and the electric fields attracted them.
151. 12:11But the $335 million cable drastically  cut per-voice-circuit costs - tilting
152. 12:17the weight of the industry away from  the satellites and back to cable again.
153. 12:22## The Boom Then came the Internet boom of the late 1990s.
154. 12:24Data rate needs skyrocketed.  Throughout the decade,
155. 12:27internet traffic in the US doubled every year  into 2001. That’s amazing growth of course,
156. 12:34but nowhere near the oft-cited  statistic of doubling every 3 months.
157. 12:38But like any good urban legend it  did once have a basis in fact. It
158. 12:43was apparently true during an unusually  fast period of growth from 1995 to 1996.
159. 12:51That was a different time and going  off a far smaller base. Nevertheless,
160. 12:56the phrase circulated like a chant - even showing  up in a 1998 US Department of Commerce report.
161. 13:03In response to this perception of massive demand,
162. 13:06the telecoms spent billions of dollars to build  and light up national long haul fiber networks.
163. 13:12Leading companies during the boom include Level 3,
164. 13:15which at its peak was installing  about 19 miles of fiber each day.
165. 13:20Or Qwest, which began as a telecommunications  subsidiary of Southern Pacific Railroad. They
166. 13:26took advantage by using railroad "rights  of way" to cheaply lay down fiber.
167. 13:31Or Global Crossing, a telecom company  founded by a bunch of bankers. They
168. 13:36were founded in 1997 and just two  years later, were worth $47 billion.
169. 13:42Another two years later, they were worth just $2
170. 13:44billion - eventually filing for  bankruptcy. That was a wild ride.
171. 13:50And of course Enron and Worldcom,  which are known for being some of the
172. 13:54largest accounting frauds in corporate history.
173. 13:57At the peak in 1999, the telecoms spent  $120 billion in 2000 dollars, worth about
174. 14:03$213 billion today in capital expenditure. Much of
175. 14:08this was funded by billions of dollars of  debt, which eventually became a problem.
176. 14:13After the Dotcom bubble burst, a  long-lasting glut hung over the
177. 14:17industry. Four years later in 2005, it  was estimated that 85% of the fibers
178. 14:23were totally dark or inactive. And  just 5% of capacity was being used.
179. 14:28This "dark fiber" was a great opportunity  for the rising tech companies like Google.
180. 14:33One of their big initiatives in the  early 2000s was to buy "dark fiber"
181. 14:37to connect their own server farms  and save on long-haul data transport.
182. 14:43For a better overview of the fiber boom and glut,
183. 14:45I highly recommend Doug O'Laughlin's piece  on the fiber glut in Fabricated Knowledge.
184. 14:52## Spatial Division Multiplexing
185. 14:52Today, most installed fiber can handle up 50  terabits per second over 10,000 kilometers.
186. 14:58That's great. But thanks to the  rise of social networks, the Cloud,
187. 15:02and streaming, current capacity is  straining again. And unfortunately,
188. 15:06current fibers are nearing their  theoretical capacity limits.
189. 15:10So we either need to build  a lot more fiber again or
190. 15:13do something entirely new. And one of  the more exciting recent developments
191. 15:18in the latter is Space-Division or  Spatial-Division Multiplexing or SDM.
192. 15:25Like Wavelength Division Multiplexing,  which we talked about earlier, this is
193. 15:29where we send multiple signals over the same  fiber path. The difference is that with SDM,
194. 15:35we send the signals over multiple spatial  paths in the fiber, rather than wavelengths.
195. 15:42Light has different ways of moving through space.
196. 15:44They can move the same way,  but in different frequencies.
197. 15:48Most fibers right now installed are  called single-mode fibers - meaning
198. 15:52that the light can only travel through  such a fiber in one way or mode.
199. 15:57So we can create special fibers called multi-mode  fibers that increases the number of modes - maybe
200. 16:04even 100 or more. This is done through making  changes in the fiber core's refractive index.
201. 16:10Or we can make single fibers with  multiple cores sharing the same cladding,
202. 16:15which was previously avoided because it tended  to encourage what we call interfering crosstalk.
203. 16:21And since light can have the same  mode but different frequencies,
204. 16:24we can layer on traditional wavelength  division multiplexing for even more capacity.
205. 16:31There remain challenges. Multi-mode fibers  right now suffer from distortion and power
206. 16:37loss issues at longer distances, so right  now they are best suited for shorter spans.
207. 16:43And the cores need to be thicker,  to accommodate the light's differing
208. 16:47spatial paths. But the gains are big, with the  potential to 10x again the bandwidth capacity.
209. 16:53## Conclusion
210. 16:54In 2009, Dr. Charles Kao (高錕) received  half of the Nobel Prize in Physics for
211. 16:58making the discoveries leading to  our modern optical fiber networks.
212. 17:03He passed away in 2018 at the age  of 84 after a long struggle with
213. 17:07Alzheimer's Disease. A life well lived, indeed.
214. 17:11Nowadays, fast internet data access is a  critical contributor to the betterment of
215. 17:16human life. It is worth some time to  look back and consider the remarkable
216. 17:21infrastructure undergirding this  massive transfer of data across
217. 17:25continents and under oceans. And we  are still pushing its limits today.
218. 17:30It is a stunning technology. Leaves  me a little ... light-headed!