Fig. 6. Optical fibers

Text 1. Fiber Optics

UNIT 7

1. Выучите следующие слова и выражения:

be subject (to) ['sʌbʤɪktˌtuː] - быть подверженным (чему-л)

reflection [rɪ'flekʃ(ə)n] -отражение

boundary ['baund(ə)rɪ] - граница

eliminate [ɪ'lɪmɪneɪt ], [ə-] - устранять, исключать

cladding ['klædɪŋ] - оболочка

layer ['leɪə] - слой

bundle ['bʌndl] - пучок

multi-mode fiber - многомодовый волоконно-оптический кабель

single-mode fiber - одномодовоеоптоволокно

core [kɔː] - стержень, сердечник

coating - оболочка

covering - покрытие; внешняя оболочка

2. Прочитайте и устно переведите текст:

Fiber optics (or “optical fibre”) refers to the medium and the technology associated with the transmission of information as light impulses along a strand of glass or plastic. A fiber-optic strand carries much more information than a conventional copper wire and is far less subject to electromagnetic interference (EMI). Optical fibers of very pure glass are able to carry light over long distances ranging from a few inches or centimeters to more than 100 miles (160 km) with little dimming, owing to it they can be used to illuminate and observe hard-to-reach places.

Fiber optics is based on the optical phenomenon known as total internal reflection. With the simplest form of optical fiber, light entering one end of the fiber strikes the boundary of the fiber and is reflected inward. The light travels through the fiber in a succession of zigzag reflections until it exits from the other end of the fiber. Other forms of optical fibers are designed in such a way that the zigzagging of the light is greatly reduced or virtually eliminated.

The fiber optic strand is constructed in several layers. Most optical fibers made today consist of at least two parts: a core through which the light is transmitted and a protective coating – called cladding (either glass or plastic) - that surrounds the core and helps prevent light from leaking from the core. The cladding bends or reflects inward the light rays that strike its inside surface. The core, coating and covering are collectively referred to as a “strand”. Fiber strand sizes are always referred to in terms of the diameter of the core. Some individual fibers are thinner than human hair and measure less than 0.00015 inch (0.004 mm) in diameter. A detector, such as a photosensitive device or the human eye, receives the light at the other end of the fiber.

Fiber strands are typically bundled within a cable. Optical fiber bundles are either coherent or incoherent. In a coherent bundle, the fibers are arranged so that images, as well as illumination, can be transmitted. In incoherent bundles, the fibers are not arranged in any particular way and can transmit only illumination.

There are two basic types of optical fibers: single-mode fibers and multi-mode fibers. Single mode fibers are designed for the transmission of a single ray as a carrier and are used for high-speed signal transmission over long distances. They have much smaller cores than multi-mode fibers, and they accept light only along the axis of the fibers. Tiny lasers send light directly into the fiber. Multi-mode fibers are designed to carry multiple light rays. They have much larger core diameter compared to those of single-mode fibers, and they accept light from a variety of angles. Multi-mode fibers use more types of light sources and cheaper connectors than single-mode fibers. They are mostly used for communication over shorter distances.

The first studies of fiber optics were made in the late 1800s, but practical development did not begin until the early 1950s. The development of fiber optics was spurred by the introduction of lasers in the early 1960s and by the production of the first optical fibers of very pure glass in 1970. The commercial use of fiber optics, especially in communications systems, developed rapidly in the 1980s.

Today the uses of optical fibers are numerous. Almost all telephone long-distance (cross country) lines are now fiber optic. Fiber-optic cables are also the common medium whenever people talk about the cable TV system or the Internet.

In medicine, optical fibers enable physicians to look and work inside the body through tiny incisions without having to perform surgery. They are used for endoscopes - instruments for viewing the interior of hollow organs in the body. They can also be used for insertion into blood vessels to give a quick, accurate analysis of blood chemistry.

In scientific research and in manufacturing, fiber optic devices carry light to and from hazardous areas, vacuum chambers, and confined spaces within machines. Some instruments use optical-fiber coils as a sensing device; so optical fibers are used to measure temperature, pressure, acceleration, and voltage in industries.

3. Ознакомьтесь с дополнительными словами и выражениями:

dimming - уменьшение силы света

virtually ['vɜːʧuəlɪ ], ['vɜːtjuəlɪ] - фактически, практически

leak - просачиваться

spur [spɜː] - стимулировать

incision [ɪn'sɪʒ(ə)n] - разрез

surgery ['sɜːʤ(ə)rɪ] - хирургия

confined space - закрытое пространство

acceleration [əkˌselə'reɪʃ(ə)n] - ускорение

4. Ответьте на вопросы, используя информацию текста:

1. What does the term fiber optics refer to? 2. Why is it possible to use optical fibers to illuminate and observe hard-to-reach places? 3. How does the light travel through the fiber? 4. Where is a protective coating situated? 5. What is the difference between coherent and incoherent bundles? 6. How many types of optical fibers exist and what is the difference between them? 7. How are optical fibers used?

5. Найдите в тексте слова и выражения, эквивалентные данным ниже:

Обычный провод; труднодоступные места; полное внутреннее отражение; устранять; отражать внутрь; светочувствительный; кровеносный сосуд; химический состав крови; измерительное устройство (датчик).

6. Переведите на русский язык следующие слова и словосочетания:

Light impulse; pure glass; zigzag reflections; telephone long-distance (cross country) lines; physician; vacuum chamber.

7. Вставьте пропущенные слова:

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