OPTICAL FIBER TRANSMISSION MEDIA (C13 Tomasi)

CHAPTER 13

OPTICAL FIBER TRANSMISSION MEDIA

1)Uses light as a carrier of information.

Optical communications system

2)Electronic communications system is directly proportional to bandwidth.

Information-carrying capacity

3)Bandwidth of an analog communications system as a percentage of its carrier frequency.

bandwidth utilization ratio

4)Device constructed from mirrors and selenium detectors that transmitted sound waves over a beam of light.

Photophone

5)Experimented with an apparatus called photophone.

Alexander Graham Bell

6)Used extensively in medical field.

Flexible fiberscope

7)Invented in 1960.

Laser (light amplification by stimulated emission of radiation)

8)Advantages of Optical Fiber cables.

1. wider bandwidth and greater information capacity

2.immunity to crosstalk

3. immunity to statistic interference

4. environmental immunity

5. safety and convenience

6. lower transmission loss

7. security

8. durability and reliability

9. economics

9)Disadvantages of Optical Fiber cables.

1. interfacing cost

2. strength

3. remote electrical power

4. optical fiber cables are

more susceptible to losses introduced by bending the cable

5. specialized tools, equipment, and training

10)Reduces the possibility of the occurrence of a detrimental phenomenon.

Stress corrosion

12)Protective coating.

Buffer jacket

14)Increases the tensile strength of the over all cable assembly.

Strength member

15)Process of decaying from one energy level to another energy level.

Spontaneous decay or spontaneous emission

16)Science of measuring only light waves that are visible to human eye.

Photometry

17)Measures the rate at which electromagnetic waves transfer light energy.

Optical power

18)Spectral separation of white light.

Prismatic refraction

19)Simply the ratio of velocity of propagation of a light ray in free space to the velocity of propagation of a light ray in a given material.

Refractive index

20)Angle at which the propagating ray strikes the interface with respect to the normal.

Angle of incidence

21)Angle formed between the propagating ray and the normal after the ray has entered the second medium.

Angle of refraction

22)Closely related to acceptance angle and is the figure of merit commonly used to measure the magnitude of the acceptance angle.

Numerical aperture

23)Simply means path.

Mode

24)More than one path.

Multimode

26)Probably the most important characteristic of the cable.

Power loss

27)Three factors that contribute to the absorption losses in optical fibers:

1. ultra violet absorption

2. infrared absorption

3. ion resonance absorption

28)Caused mainly by small bends and kinks in the fiber.

Radiation losses

29)Caused by excessive pressure and tension and generally occur when fibers are bent during handling or installation.

Contants-radius bends

30)Caused by the difference in the propagation times of light rays that take different path down a fiber.

Modal dispersion

32)A p-n junction made from two different mixtures of the same types of atom.

Mojunction structure

33)Generally constructed of silicon-doped gallium-arsenide.

Epitaxially grown

34)Homojunction LED’s output approximately 500 μ at a wavelength of 900 nm.

Planar diffused

35) Advantages of heterojunction devices over homojunction devices;

1. increase in current density generates a more brilliant light spot.

2. smaller emitting area makes it easier to couple its emitted light into a fiber.

3. small effective area has a smaller capacitance, which allows the planar heterojunction LED to be used at a higher speed.

36)Depletion-layer photo diode and is probably the most common device used as a light detector in fiber optic communications system.

PIN diode

37)Characteristic of a light detector.

1. responsivity

2. dark currents

3. transit time

4. spectral response

5. light sensitivity