Doing it all with fiber?

20 In relatively few years research has taken fibers from being a passive light transmission medium into roles that were traditionally the domain of compound semiconduc­tors: amplifiers and lasers. All we need for an all-fiber communication system are fiber switches, fiber modula­tors and fiber isolators. Prototype switches based on fiber nonlinearity are still in an early stage of research. Re­cent reports of optoelectronic effects in silica glass give some optimism for fiber modulators. One might expect fibers doped appropriately with magnetic ions to provide practical isolators if the problems associated with fiber birefringence can be overcome.

21 Fiber optic technology and the communications revolu­tion made possible by this technology have their origins in the base of fundamental knowledge developed over many decades: Glass science itself has evolved over centuries. Light-wave propagation in fibers begins with Maxwell. Communication by light dates back to Alexander Graham Bell. Concepts of bound states and modes have their origins in quantum mechanics and Einstein's work on stimu­lated emission. In most of these cases the motivation of the research work was fundamental knowledge.

22 As the field of fiber optics has matured, the technol­ogy has supplied new challenges to physical theory and experiments: The theoretical prediction of new low-scat­tering glass compositions has pointed the way to glasses with ultimate losses lower than that of silica. The ran­dom structure of the glass network makes the usual spectroscopic probes, which have provided so much in­sight into the behavior of crystalline material, difficult to interpret in glasses. Indeed, even the concept of a structural defect in glass is poorly defined, and current understanding of defect properties of silica is based largely on empirical studies. Deeper understanding of the structures of network glasses such as silica and the electronic structure of defects is emerging from research on molecular modeling and quantum chemistry. Studies of nonlinear propagation of light in fibers are leading to new concepts for devices and systems as well as to an understanding of the limits of fiber optic systems. The field of rare earth spectroscopy has been rejuvenated by the demand for novel fiber devices. The pull of technology on all these areas of physics is great, and deeper fundemtntal understanding is likely to reap rewards in improved technology.

We are still far from the ultimate limits of fiber communication, and new concepts will be required to make full use of the fiber bandwidth. Optical fiber communication is driving the entire photonics revo­lution, a vision that was surely beyond the imagination of the founders of this science.

 

 

IV. Reading for General Understanding

A Check the comprehension of the text by

1. answering the following questions:

1. What anniversary does the Physical Review celebrate?

2. What materials of interest were discussed a century ago?

3. What characteristic is common to all dielectrics?

4. Where does the “optic window” lie between?

5. Was it possible in 1978 to imagine how rapidly silica fiber technology would evolve?

6. What are the advantages of silica fibers?

7. What are the disadvantages of glass?

8. In what way are these disadvantages eliminated?

9. What are the applications of optical fibers?

10. What is the bottleneck for long-distance communication?

 

- By choosing the right answer, which you think is correct.

1. When did the erbium doped fiber amplifier appear?

a) 1837                  b) 1937                   c) 1987

 

2.What is the effect o f the invention

a) it has stopped the advance in communication network design

b) it has shown disadvantages of optical fiber research and development

c) it has changed completely the telecommunication network design.

3. What are the advantages of the optical amplifier?) it hastages of optical fiber research and development

c) 1987

 

a) the simplicity of design

b) low cost

c) one channel operation

 

4. What are the limits of optical fiber amplifiers?

a) the rate of data transmission

b) pulse narrowing

c) low significant dispersion at 1.55 µm

 

5. What is the solution to the problem of limitations?

a) adding amplified spontaneous noise to the system

b) equalizing the dispersion at each optical amplifier

c) continuing to improve erbium – doped fiber design and performance

 

B Answer the following questions to the text “Nonlinearity” and “Fiber Lasers”

 

1. What is the effect of nonlineatiry of the silica fiber on long – distance transmission?

2. What does nonlinearity result in?

3.  Does one take into account nonlinearities in designing a system?

4.  What is the solution to the problem of nonlinearity?

5. What is the soliton?

6.  When were the limits for amplification overcome? Who were the designers?

7.  What does the term “optical fiber component” imply?

8.  What makes possible a new family of passive fiber deviced?

9.  Can the same semiconductor laser pump the fiber laser?

10.  What field of fiber optics is undergoing the rapid growth?

11.  What are fiber lasers based on?

 

C Pick out from the text all the word combinations with the following words (terms) and give their Russian equivalents

 

- device                       - communication

- wavelength                - channel

- range                         - network

- band                           - signal

- dispersion                  - fiber

 

 

 

V. Reading for Detail and Language Study

 

A  Find in the whole text the English equivalents for the following phrases:

- волоконная оптика

- коэффициент преломления

- волновод

- канал связи

- оптические устройства

- потери

- развиваться

- загрязнители

- разработка лазера на полупроводниках

- диапазон длины волны

- ограничения по расстоянию и скорости передачи битов

- волоконно-оптический лазер

- оптический импульс

- воздействие

- накачка

- передача

- точность

 

В Explain the meanings of the following words and expressions

a) transmission spectra of certain substances in the infra-red; канал связи

Преломления

 English equivalents for the following phrases"s (terms) and give their Russian equivalents. silica-based waveguides; relative transparency to electromagnetic radiation; milestone; residual losses are attributed to defects, abundant, the tiny strands of glass; revolution; stress-accelerated corrosion; long-term stability; to name a few, an expensive solution; erbium-doped fiber amplifier, during fiber fabrication, a wavelength multiplexer, stimulated emission of the excited erbium ions, tunable semiconductor laser sources, erbium-doped fiber design, because of the availability, upgrading, over the entire wavelength range of interest, commercially available, long-distance transmission, pulse broadening, to overcome, time domain, frequency domain, guiding frequency filter; pulse shape; solution propagation; optical fiber amplifier, bit rate; breakthrough; induced index changes; phase gratings.

 

b) Give some sentences with the words given above.

C Translate part of the text, which is of greatest interest to you, in written form