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Telecommunications Revolution. The Charge-Coupled Device (CCD)
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Unit 9
Telecommunications Revolution. The Charge-Coupled Device (CCD)
The Nobel Prize in Physics 2009 — Popular Information
The masters of light
The 2009 Nobel Prize in Physics honors three scientists, who have had important roles in shaping modern information technology, with one half to Charles Kuen Kao and with Willard Sterling Boyle and George Elwood Smith sharing the other half. Kao’s discoveries have paved the way for optical fiber technology, which today is used for almost all telephony and data communication. Boyle and Smith have invented a digital image sensor — CCD, or charge-coupled device — which today has become an electronic eye in almost all areas of photography.
When the Nobel Prize in Physics is announced in Stockholm, a large part of the world receives the message almost instantly. At almost the speed of light, the highest of speeds, the message is spread around the world. Text, images, speech and video are shuffled around in optical fibers and through space, and are received instantly in small and convenient devices. It is something that many people have already come to take for granted. The optical fiber has been a prerequisite for this extremely rapid development in the field of communications, a development that Charles Kao predicted over 40 years ago.
Just a few years later, Willard Boyle and George Smith radically altered the conditions for the field of photography, because film is no longer needed in cameras where the images can be captured electronically with an image sensor. The electronic eye, the CCD, became the first truly successful technology for the digital transfer of images. It opened the door to a daily stream of images, which is filling up the optical fiber cables. Only optical fiber is capable of transferring such large quantities of data that electronic image sensor technology yields.
I. The principles of the work of optical fiber.
The arrival of light
It is via sunlight that we see the world. However, it would take a long time before humans acquired the skills to control light and direct it into a waveguide. In this way coded messages could be transmitted to many people simultaneously.
This development required numerous inventions, big and small, which form the foundations for the modern information society. The optical fiber required modern glass technology in order to be developed and manufactured. A reliable source of light was also needed and this was provided by semiconductor technology. Finally, an ingenious network needed to be assembled and extended, consisting of transistors, amplifiers, switches, transmitters and receivers, as well as other units, all working together. The telecommunications revolution was made possible by the work of thousands of scientists and inventors from all around the world.
Playing with light
The 1889 World Exhibition in Paris celebrated the centenary of the French revolution. The Eiffel tower was to become one of the most well-known monuments of this exhibition. However, a remarkable play of lights proved a less memorable spectacle. It was performed with water fountains filled with colorful beams of light. This show was made possible with electricity. A source of inspiration was also provided by earlier attempts, in the middle of the 19th century, to create beams of light guided by water. Those trials had shown that when a beam of water is exposed to sunlight, the light travels through the beam and follows its curving shape. Of course, the effects of light in glass or water had been discovered much earlier than that. Already 4 500 years ago, glass was manufactured in Mesopotamia and Egypt. The Venetian glass masters could not have been ignorant of the beautiful play of light that occurred in their swirling decorations. Cut glass was used in candelabras and crystal chandeliers, and the elusive mystery of the rainbow challenged the imagination of many men and women long before the laws of optics provided the answer in the 17th century. However, it was only about 100 years ago that these ideas surfaced and people tried to make use of captured beams of light.
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Capturing light
A ray of sunlight that falls into water bends when it hits the surface, because the so-called refractive index of water is higher than the refractive index of air. If the direction of the light beam is inverted, travelling from water into air, it is possible that it will not enter the air at all, and instead will be reflected back into the water. This phenomenon forms the basis for optical waveguide technology where light is captured inside a fiber with a higher refractive index than its surrounding environment. A ray of light that is directed into a fiber, bounces against the glass wall and moves forward since the refractive index of glass is higher than the surrounding air.
The medical profession has used short and simple optical fibers since the 1930s. With a bundle of thin glass rods, they could peek inside the stomachs of patients or highlight teeth during operations. However, when the fibers touched each other they leaked light, and they also easily became worn out. Coating the bare fiber in a glass cladding with a lower refractive index led to considerable improvements, which in the 1960s paved the way for industrial manufacturing of instruments for gastroscopy and other medical uses.
For long distance communication, however, these glass fibers were useless. Furthermore, few were really interested in optical light; these were the days of electronics and radio technology. In 1956, the first transatlantic cable was deployed, and it had a capacity for 36 simultaneous phone calls. Soon satellites would begin to cover the growing communication needs — telephony increased dramatically and television broadcasting required ever higher transfer capacities. Compared to radio waves, infrared or visible light carries tens of thousands times more information, so the potential of optical light waves could not be disregarded any longer.
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