WIRED COMMUNICATIONS (midterm) Flashcards by Unknown Unknown

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

Optical Communication System

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Light is a type of ____ like radio waves

electromagnetic radiation

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

Infrared, Visible, and Ultraviolet

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The frequency and wavelength of violet visible light

668-798 THz and 380-450nm

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The frequency and wavelength of blue visible light

606-668 THz and 450-495nm

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The frequency and wavelength of green visible light

526-606THz and 495- 570 nm

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What is the speed of light in free space?

300,000,000 m/s

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

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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What is the primary function of optical communication systems?

To transmit information using light

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

Infrared light

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

LED and Lasers

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

LASER

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The frequency and wavelength of yellow visible light

508 - 526 THz and 570-590 nm

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The frequency and wavelength of orange visible light

484 -508 THz and 590-620 nm

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The frequency and wavelength of red visible light

400 -484 THz and 620 - 750 nm

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What is the other unit of measurement for light?

angstrom

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1 angstrom is equal to ___ m

10 ^-10

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

186 000 mi/s

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It refers to the ways light can be processed

Physical Optics

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The simplest way of manipulating light is to _____ it

reflect

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what is the concept of reflection?

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

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Law of reflection

angle of incidence is equal to the angle of reflection

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The light ray from the light source is called the _____

incident ray

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The direction of the light can also be changed by ____

refraction

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

refraction

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

index of refraction

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

light

An optical communication system consists of

1. light source 2. photodetector 3. amplifier 4. demodulator

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

transmitter

what are common light sources

LED AND LASER

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

modulator

Amplitude modulation is also referred to as

intensity modulation

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

amplitude modulation

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

power transistor

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

Kapron, Keck and Maurer

The modulated light wave is picked up by the _____

photodetector

What type of component is usually used as a photodetector?

photodiode or transistor

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

They have less signal attenuation over distance.

How can attenuation in fiber-optic cables be minimized?

Using high-quality materials to reduce absorption and scattering

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

carry vast amounts of data efficiently and reliably.

What advantage does using infrared light provide in optical communication?

Increased data rates from higher frequencies

It provides higher bandwidth and lower signal loss.

Why is laser used in lightwave communication?

Because it can penetrate through atmospheric obstacles

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

photocell or light detector

The _____ converts light pulses into an electrical signal

photocell

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

amplified and reshaped

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

decoder

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

fiber optics or optical fiber

Light propagates through the fiber upon the _____

laws of optics

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

glass, silica, plastic

______ are less expensive and more flexible than glass fiber optic

plastic fiber optic cables

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

cladding

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

core

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

strength

_____ is a glass core with a plastic cladding

Plastic-clad silica (PCS) cable

Benefits of fiber optic cables

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

What are the disadvantages of fiber optics?

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

The French used ____ to transmit messages in the 1790s

semaphores

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

1840s

in 1880, Alexander Graham Bell created _______

Photophone

When did Alexander Graham Bell invent the photophone?

1880

what is the photophone by Alexander Graham Bell constructed from?

mirrors and selenium detectors

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

mirrors and selenium detectors

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

photophone

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

J.L Baird and C.W. Hansell

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

1920-1950

who successfully transmitted images through a single glass fiber?

H. Lamm

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

Van Heel, Hopkins and Kapany

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

flexible fiberscope

the term "Fiber Optics" was coined by _____ in 1956

Kapany

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

6.2 Mbps and 45Mbps

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

Charles H. Townes and Arthur L. Schawlow

who built the first optical maser?

Theodore H. Maiman

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

1960

when were glass-clad fibers available for medical instruments?

1960

who proposed a new communication medium using cladded fiber cables?

Charles Kao and Bockham

Charles Kao and Bockham's fiber can transmit ______

1GHz (1 billion bits per second)

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

1000 dM/km limited optical transmission

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

Kapron, Keck and Maurer

Kapron, Keck and Maurer developed a ______________ in 1970

low-attenuation silica glass fiber

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

850nm

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

repeaters

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

0.16dB/km

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

NEC Corporation

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

AT&T

The first fiber-optic telephony cable connected ___ to ______

North America to France

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

40 miles

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

565 Mbps

the first fiber-optic transatlantic telephony cable used ____ light

1300nm

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

0.4 dB/km

ANSI meaning

American National Standards Institute

SONET meaning

Synchronous Optical Network

who published SONET?

ANSI

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

Index of refraction Mode

This quantity varies across the cross-section of the cable

Index of refraction

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

Mode

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

step-index graded index

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

Step index

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

graded index cable

what are the two classifications of mode?

single mode multimode

Three types of fiber optic cable

multimode step index single mode step index multimode graded index

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

Multimode step index

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

short to medium distances

what is the main advantage of multimode step index?

large size

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

50 to 1000um

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

multimode step index

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

spreading