Chapter II Fiber Optics Unit 1

WORD STUDY

Exercise 1. Check the transcription in the dictionary and read the words listed below.

Nouns

atmosphere, facsimile, fountain, frequency, phenomenon, semaphore, spectrum, turbulence.

Verbs

confine, illustrate, install, languish, mount.

Adjectives

analogous, dielectric, inaccessible, transparent.

Exercise 2. Make adverbs from the following adjectives according to the model and translate them.

Adjective + -ly = adverb

a) careful – carefully

experimental, essential, practical, total, virtual;

b) simple – simply

gentle, probable, suitable, terrible;

c) easy – easily

lazy, noisy;

d) complete – completely

efficient, brilliant, effective, ultimate.

Adjective + -ally = adverb

e) heroic – heroically

atomic, automatic, tragic, analytic, symbolic.

UNDERSTANDING A PRINTED TEXT

List of Terms:

bandwidth – диапазон

bundle of optical fibres – оптоволоконный кабель

core – сечение

critical specification – технические условия

inaccessible – неудобный, недоступный

decode – декодировать, расшифровывать

glass-clad fibre – волокно со стеклянным покрытием

in the intervening years – в период (между)

fused silica – плавленое стекло

lossy – с большими потерями

melting point – точка плавления

one wave-guide mode – передатчик определенных длин волн,

одномодовый тип колебаний

optical-frequency amplifier – усилитель оптических частот

phenomenon of total internal reflection – эффект полного внутреннего отражения

refractive index – показатель преломления

theoretical specification – теоретические условия (спецификации)

transparent – прозрачный

wave-guide – волновод

world’s long-distance traffic – международное сообщение

Comprehensive reading The History of Fiber Optics

Optical communication systems date back two centuries to the "optical telegraph" that French engineer Claude Chappe invented in the 1790s. His system was a series of semaphores mounted on towers, where human operators relayed messages from one tower to the next. It reduced the need in hand-carried messages, but by the mid-19th century it was replaced by the electric telegraph.

Alexander Graham Bell patented an optical telephone system, which he called the Photophone, in 1880, but his earlier invention, the telephone, proved far more practical. He dreamed of sending signals through the air, but the atmosphere didn't transmit light as reliably as wires carried electricity. In the decades that followed, light was used for a few special applications, such as signalling between ships, but otherwise optical communications, like the experimental photophone Bell donated to the Smithsonian Institution, languished on the shelf.

In the intervening years, a new technology slowly took root that would ultimately solve the problem of optical transmission, although it was a long time before it was adapted for communications. It depended on the phenomenon of total internal reflection, which can confine light in a material surrounded by other materials with lower refractive index, such as glass in air. In the 1840s, Swiss physicist Daniel Collodon and French physicist Jacques Babinet showed that light could be guided along jets of water for fountain displays.

Optical fibers went a step further. They were essentially transparent rods of glass or plastic stretched so they were long and flexible. During the 1920s, John Logie Baird in England and Clarence W. Hansell in the United States patented the idea of using arrays of hollow pipes or transparent rods to transmit images for television or facsimile systems. However, the first person known to have demonstrated image transmission through a bundle of optical fibers was Heinrich Lamm, then a medical student in Munich. His goal was to look inside inaccessible parts of the body. During his experiments, he reported transmitting the image of a light bulb.

By 1960, glass-clad fibers fine for medical imaging were made, but they didn’t match communication purposes.

Meanwhile, telecommunications engineers were seeking more transmission bandwidth. Radio and microwave frequencies were in heavy use, so they looked to higher frequencies to carry loads they expected to continue increasing with the growth of television and telephone traffic.

The next step towards optical communications was the invention of laser. The July 22, 1960 issue of Electronics magazine introduced its report on Theodore Maiman's demonstration of the first laser by saying "Usable communications channels in the electromagnetic spectrum may be extended by development of an experimental optical-frequency amplifier." But rain, haze, clouds, and atmospheric turbulence limited the reliability of long-distance atmospheric laser links. Optical wave-guides were proving to be a problem.

Optical fibers had attracted some attention because they were analogous in theory to plastic dielectric wave-guides used in certain microwave applications. In 1961, Elias Snitzer demonstrated the similarity by drawing fibers with cores so small that they carried light in only one wave-guide mode. However virtually everyone considered fibers too lossy for communications.

1964, a critical (and theoretical) specification was identified by Dr. C.K. Kao for long-range communication devices, the 10 or 20 decibels of light loss per kilometer standard. Kao also illustrated the need for a purer form of glass to help reduce light loss.

In 1970, one team of researchers began experimenting with fused silica, a material capable of extreme purity with a high melting point and a low refractive index. Corning Glass researchers Robert Maurer, Donald Keck and Peter Schultz invented fiber optic wire or "Optical Waveguide Fibers" capable of carrying 65,000 times more information than copper wire, through which information carried by a pattern of light waves could be decoded at a destination even a thousand miles away. The team had solved the problems presented by Dr. Kao.

The first optical telephone communication system was installed about 1.5 miles under downtown Chicago in 1977, and each optical fiber carried the equivalent of 672 voice channels. Today more than 80 percent of the world's long-distance traffic is carried over optical fiber cables. About 25 million kilometers of the cable Maurer, Keck and Schultz designed has been installed worldwide.