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ECE 4C > WIRED COMMUNICATIONS (midterm) > Flashcards

WIRED COMMUNICATIONS (midterm) Flashcards

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1
Q

_________ use light to transmit information from one place to another.

A

Optical Communication System

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2
Q

Light is a type of ____ like radio waves

A

electromagnetic radiation

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3
Q

The optical spectrum is made up of _____,_____, and ______

A

Infrared, Visible, and Ultraviolet

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4
Q

The frequency and wavelength of violet visible light

A

668-798 THz and 380-450nm

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5
Q

The frequency and wavelength of blue visible light

A

606-668 THz and 450-495nm

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6
Q

The frequency and wavelength of green visible light

A

526-606THz and 495- 570 nm

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7
Q

What is the speed of light in free space?

A

300,000,000 m/s

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8
Q

What is the role of a modulator in an optical communication system?

A

To vary the intensity of the light beam

A modulator in an optical communication system varies the intensity of the light beam based on the modulating baseband signal. This process, known as amplitude or intensity modulation, allows the transmission of information through changes in light brightness.

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9
Q

What is the primary function of optical communication systems?

A

To transmit information using light

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10
Q

Which type of light is increasingly used as a carrier for information in communication systems?

A

Infrared light

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11
Q

_____ and _______ are key in optical communication as they serve as light sources. They can modulate signals at high speeds (up to 10 GHz).

A

LED and Lasers

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12
Q

_______ produces coherent, monochromatic light, creating narrow beams that enhance data transmission over long distances, increasing bandwidth and reliability.

A

LASER

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13
Q

The frequency and wavelength of yellow visible light

A

508 - 526 THz and 570-590 nm

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14
Q

The frequency and wavelength of orange visible light

A

484 -508 THz and 590-620 nm

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15
Q

The frequency and wavelength of red visible light

A

400 -484 THz and 620 - 750 nm

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16
Q

What is the other unit of measurement for light?

A

angstrom

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17
Q

1 angstrom is equal to ___ m

A

10 ^-10

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18
Q

The speed of light is approximately ___ mi/s in free space

A

186 000 mi/s

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19
Q

It refers to the ways light can be processed

A

Physical Optics

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20
Q

The simplest way of manipulating light is to _____ it

A

reflect

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21
Q

what is the concept of reflection?

A

When light rays strike a
the reflective surface, the light
waves are thrown back or
reflected.

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22
Q

Law of reflection

A

angle of incidence is equal to the angle of reflection

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23
Q

The light ray from the light source is called the _____

A

incident ray

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24
Q

The direction of the light can also be changed by ____

A

refraction

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25
Q

_______ occurs because light travels at different speeds in different materials.

A

refraction

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26
Q

The amount of refraction of the light of a material is usually expressed in terms of

A

index of refraction

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27
Q

Optical communication systems use ____ as the carrier of the information to be transmitted.

A

light

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28
Q

An optical communication system consists of

A
  1. light source
  2. photodetector
  3. amplifier
  4. demodulator
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29
Q

In light wave communication system the ___ is used as a light source

A

transmitter

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30
Q

what are common light sources

A

LED AND LASER

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31
Q

In light wave communication, what is used to vary the intensity of the light beam in accordance with the modulating baseband signal

A

modulator

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32
Q

Amplitude modulation is also referred to as

A

intensity modulation

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33
Q

_____ is used where the information or intelligence signal controls the brightness of the light

A

amplitude modulation

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34
Q

A modulator for analog signals can be a _____ in series with the light source and its DC power supply

A

power transistor

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35
Q

Who are the Corning scientists who developed low attenuation silica glass fibers?

A

Kapron, Keck and Maurer

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36
Q

The modulated light wave is picked up by the _____

A

photodetector

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37
Q

What type of component is usually used as a photodetector?

A

photodiode or transistor

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38
Q

Why are fiber-optic cables preferred for long-distance communication?

A

They have less signal attenuation over distance.

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39
Q

How can attenuation in fiber-optic cables be minimized?

A

Using high-quality materials to reduce absorption and scattering

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40
Q

Optical communication is essential for modern systems due to its ability to ______

A

carry vast amounts of data efficiently and reliably.

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41
Q

What advantage does using infrared light provide in optical communication?

A

Increased data rates from higher frequencies

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42
Q

Increased data rates from higher frequencies

A

It provides higher bandwidth and lower signal loss.

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43
Q

Why is laser used in lightwave communication?

A

Because it can penetrate through atmospheric obstacles

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44
Q

At the receiving end of the optical communication system, a _____ is used to detect the light pulses.

A

photocell or light detector

45
Q

The _____ converts light pulses into an electrical signal

A

photocell

46
Q

the electrical signals are then _____ and _____ back into digital form

A

amplified and reshaped

47
Q

Once the signal is back into digital form, it is fed to ____, where the original information is recovered

A

decoder

48
Q

______ are microscopic strands of very pure glass with about the same diameter as human hair.

A

fiber optics or optical fiber

49
Q

Light propagates through the fiber upon the _____

A

laws of optics

50
Q

The portion of a fiber-optic cable that carries the light is made from ________

A

glass, silica, plastic

51
Q

______ are less expensive and more flexible than glass fiber optic

A

plastic fiber optic cables

52
Q

the glass or plastic optical fiber is contained within an outer _____

A

cladding

53
Q

The fiber, which is called the ______, is usually surrounded by a protective cladding.

A

core

54
Q

The cladding does not only protect the fiber, but it also gives ______

A

strength

55
Q

_____ is a glass core with a plastic cladding

A

Plastic-clad silica (PCS) cable

56
Q

Benefits of fiber optic cables

A

Wider Bandwidth
Low lost
Lightweight
small size
Security
interference immunity
greater safety

57
Q

What are the disadvantages of fiber optics?

A

Interfacing cost
strength
remote electrical power
more susceptible to loses introduces by bending the cable
specialized tools, equipment and training

58
Q

The French used ____ to transmit messages in the 1790s

A

semaphores

59
Q

When was refraction first demonstrated through a light in a stream?

A

1840s

60
Q

in 1880, Alexander Graham Bell created _______

A

Photophone

61
Q

When did Alexander Graham Bell invent the photophone?

A

1880

62
Q

what is the photophone by Alexander Graham Bell constructed from?

A

mirrors and selenium detectors

63
Q

The ____ and _____ of photophone transmit sound waves over a beam of light

A

mirrors and selenium detectors

64
Q

Bell’s _____ was the first attempt of using a beam of light for carrying information

A

photophone

65
Q

They are the scientist from the USA who were granted patents for scanning and transmitting television images from uncoated fiber cables

A

J.L Baird and C.W. Hansell

65
Q

During ____ to _____, thin, flexible rods of glass or plastics were used to guide light

A

1920-1950

66
Q

who successfully transmitted images through a single glass fiber?

A

H. Lamm

67
Q

In 1951, _____, _____ and ______ experimented with light transmission through bundles of fibers

A

Van Heel, Hopkins and Kapany

68
Q

Van Heel, Hopkins and Kapany’s studies led to the development of ________, which is used extensively in the medical field

A

flexible fiberscope

69
Q

the term “Fiber Optics” was coined by _____ in 1956

A

Kapany

70
Q

Telephone signals used infrared light with a wavelength of 850nm to send data at ___ Mbs and ____ 45Mbps

A

6.2 Mbps and 45Mbps

71
Q

______ and _____ wrote a paper describing how it was possible to use stimulated emission fro amplifying light waves (laser) as well as microwaves (maser)

A

Charles H. Townes and Arthur L. Schawlow

72
Q

who built the first optical maser?

A

Theodore H. Maiman

73
Q

The Laser (LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION) was invented in ____

A

1960

74
Q

when were glass-clad fibers available for medical instruments?

A

1960

75
Q

who proposed a new communication medium using cladded fiber cables?

A

Charles Kao and Bockham

76
Q

Charles Kao and Bockham’s fiber can transmit ______

A

1GHz (1 billion bits per second)

77
Q

what is the disadvantage of Charles Kao and Bockham’s fiber?

A

1000 dM/km
limited optical transmission

78
Q

who developed an optical fiber with losses less than 2dB/km

A

Kapron, Keck and Maurer

79
Q

Kapron, Keck and Maurer developed a ______________ in 1970

A

low-attenuation silica glass fiber

80
Q

Telephone signals use infrared light with a wavelength of ____ to send data at 6.2 Mbps and 45 Mbps

A

850nm

81
Q

These are used to convert light to electricity and then back to light.

A

repeaters

82
Q

In the 1980s the losses in optical fibers were reduced to as low as____

A

0.16dB/km

83
Q

Who set a new long-haul transmission record by transmitting 10 Gigabytes per sec over 80.1 km of optical fiber.

A

NEC Corporation

84
Q

what company laid the first fiber-optic transatlantic telephony cable?

A

AT&T

85
Q

The first fiber-optic telephony cable connected ___ to ______

A

North America to France

86
Q

repeaters are used at every ____ in the first fiber-optic transatlantic telephony cable

A

40 miles

87
Q

what is the bandwidth of the first fiber-optic transatlantic telephony cable

A

565 Mbps

88
Q

the first fiber-optic transatlantic telephony cable used ____ light

A

1300nm

89
Q

what is the attenuation of the first
fiber-optic transatlantic telephony cable

A

0.4 dB/km

90
Q

ANSI meaning

A

American National Standards Institute

91
Q

SONET meaning

A

Synchronous Optical Network

92
Q

who published SONET?

A

ANSI

93
Q

What are the two ways of classifying Fiber-Optic Cables?

A

Index of refraction
Mode

94
Q

This quantity varies across the cross-section of the cable

A

Index of refraction

95
Q

It refers to the various paths the light rays can take in passing through the fiber

A

Mode

96
Q

what are the two ways to define the index of refraction variation across a cable?

A

step-index
graded index

97
Q

It refers to the fact that there is a sharply defined step in the index of refraction where the fiber core and cladding interface

A

Step index

98
Q

The index of refraction of the core is not constant. It varies smoothly and continuously over the diameter of the core

A

graded index cable

99
Q

what are the two classifications of mode?

A

single mode
multimode

100
Q

Three types of fiber optic cable

A

multimode step index
single mode step index
multimode graded index

101
Q

this cable is probably the most common and widely used type of cable because it is the easiest to make and least expensive

A

Multimode step index

102
Q

Multimode step index is widely used for _____ at relatively low pulse frequencies

A

short to medium distances

103
Q

what is the main advantage of multimode step index?

A

large size

104
Q

what is the typical core diameter of the multimode step index?

A

50 to 1000um

105
Q

This cable is easier to couple light because they have a relatively large source to fiber aperture

A

multimode step index

106
Q

light rays in multimode step index cable is _____ which makes the signal more distorted

A

spreading

107
Q
A

ECE 4C (5 decks)

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