Fig. 6. Optical fibers

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:

bundles, c ore, coating, strands, mode

1. Fiber-optic lines are … of optically pure glass as thin as a human hair that carry digital information over long distances. 2. Optical fibers come in two types: s ingle-… fibers and multi- … fibers. 3. Thin glass center of the fiber where the light travels is called the …. 4. To protect the fiber from damage and moisture the plastic … is necessary. 5. Hundreds or thousands of optical fibers are arranged in … in optical cables.

8. Вставьте пропущенные предлоги:

1. A fiber-optic strand is not much subject... electromagnetic interference. 2. Owing … fiber-optic strand properties, the information sent … a strand of glass can reach most remote places. 3. Optical fibers consist... two parts: a core and a protective coating. 4. A detector receives the light... the other end of the fiber. 5. The first studies of fiber optics were made... the late 1800s, but practical development did not begin... the early 1950s.

9. Составьте предложения, подбирая к левой части соответствующее продолжение:

10. Переведите текст на английский язык:

Структура оптоволоконного кабеля очень проста и похожа на структуру коаксиального электрического кабеля, только вместо центрального медного провода здесь используется тонкое (диаметром порядка 1-10 мкм) стекловолокно, а вместо внутренней изоляции - стеклянная или пластиковая оболочка, не позволяющая свету выходить за пределы стекловолокна. В данном случае мы имеем дело с режимом так называемого полного внутреннего отражения света от границы двух веществ с разными коэффициентами преломления (у стеклянной оболочки коэффициент преломления значительно ниже, чем у центрального волокна). Металлическая оплетка кабеля обычно отсутствует, так как экранирование от внешних электромагнитных помех здесь не требуется, однако иногда ее все-таки применяют для механической защиты от окружающей среды.