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Chapter 1

Introduction

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Introduction

For years fiber optics has been merely a system for piping light around corners and into in accessible places so as to allow the hidden to be seen. But now, fiber optics has evolved into a system of significantly greater importance and use. Throughout the world it is now being used to transmit voice, video, and data signals by light waves over flexible hair-thin threads of glass or plastics. Its advantages in such use, as compared to conventional coaxial cable or twisted wire pairs, are fantastic. As a result, light-wave communication systems of fiber optics communication system are one of the important feature for today’s communication.

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John Tyndall, 1870 water and light experiment demonstrated light used

internal reflection to follow a specific path

William Wheeling, 1880 “piping light” patent never took off

Alexander Graham Bell, 1880 optical voice transmission

system called a photophone free light space carried voice

200 meters

Fiber-scope, 1950’s

Light

A History of Fiber Optic Technology

The Nineteenth Century

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The Twentieth Century

Glass coated fibers developed to reduce optical loss Inner fiber - core Glass coating - cladding Development of laser technology was important to fiber optics Large amounts of light in a tiny spot needed 1960, ruby and helium-neon laser developed 1962, semiconductor laser introduced - most popular type of

laser in fiber optics

cladding

core

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The Twentieth Century (continued)

1966, Charles Kao and Charles Hockman proposed optical fiber could be used to transmit laser light if attenuation could be kept under 20dB/km (optical fiber loss at the time was over 1,000dB/km)

1970, Researchers at Corning developed a glass fiber with less than a 20dB/km loss Attenuation depends on the wavelength of light

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Fiber Optics Applications

Military 1970’s, Fiber optic telephone link installed aboard the U.S.S. Little Rock 1976, Air Force developed Airborne Light Fiber Technology (ALOF)

Commercial 1977, AT&T and GTE installed the first fiber optic telephone system Fiber optic telephone networks are common today Research continues to increase the capabilities of fiber optic transmission

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Applications of Fiber Optics

Military Computer Medical/Optometric Sensor Communication

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Military Application

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Military Application

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Computer Application

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Sensors

Gas sensors

Chemical sensors

Mechanical sensors

Fuel sensors

Distance sensors

Pressure sensors

Fluid level sensors

Gyro sensors

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Medical Application

Endoscope Eyes surgery Blood pressure meter

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The Future

Fiber Optics have immense potential bandwidth (over 1 teraHertz, 1012 Hz)

Fiber optics is predicted to bring broadband services to the home interactive video interactive banking and shopping distance learning security and surveillance high-speed data communication digitized video

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Fiber Optic Fundamentals

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Advantages of Fiber Optics

Immunity from Electromagnetic (EM) Radiation and Lightning

Lighter Weight Higher Bandwidth

Better Signal Quality Lower Cost Easily Upgraded Ease of Installation

The main advantages:

Large BW and Low loss

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Immunity from EM radiation and Lightning:

- Fiber is made from dielectric (non-conducting) materials, It is un affected by EM radiation.

- Immunity from EM radiation and lightning most important to the military and in aircraft design.

- The fiber can often be run in same conduits that currently carry power, simplifying installation.

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Lighter Weight:

- Copper cables can often be replaced by fiber optic cables that weight at least ten times less.

- For long distances, fiber optic has a significant weight advantage over copper cable.

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Higher Bandwidth

- Fiber has higher bandwidth than any alternative available.

- CATV industry in the past required amplifiers every thousand feet, when copper cable was used (due to limited bandwidth of the copper cable).

- A modern fiber optic system can carry the signals up 100km without repeater or without amplification.

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Better Signal Quality

- Because fiber is immune to EM interference, has lower loss per unit distance, and wider bandwidth, signal quality is usually substantially better compared to copper.

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Lower Cost

- Fiber certainly costs less for long distance applications.

- The cost of fiber itself is cheaper per unit distance than copper if bandwidth and transmission distance requirements are high.

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Principles of Fiber Optic Transmission

Electronic signals converted to light Light refers to more than the visible portion of the electromagnetic

(EM) spectrum

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The Electromagnetic Spectrum

- Light is organized into what is known as the electromagnetic spectrum.

- The electromagnetic spectrum is composed of visible and near-infrared light like that transmitted by fiber and all other wavelengths used to transmit signals such as AM and FM and television.

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Principles of Fiber Optic Transmission

Wavelength - the distance a single cycle of an EM wave covers For fiber optics applications, two categories of wavelength are used

visible (400 to 700 nanometers) - limited use near-infrared (700 to 2000 nanometers) - used almost always in modern

fiber optic systems

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Fiber optic links contain three basic elements transmitter optical fiber receiver

Transmitter ReceiverUser

Input(s)User

Output(s)

Optical Fiber

Electrical-to-OpticalConversion

Optical-to-ElectricalConversion

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Transmitter (TX) Electrical interface encodes user’s information through AM, FM or

Digital Modulation Encoded information transformed into light by means of a light-emitting

diode (LED) or laser diode (LD)

ElectricalInterface

Data Encoder/Modulator

LightEmitter

UserInput(s)

OpticalOutput

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Receiver (RX) decodes the light signal back into an electrical signal types of light detectors typically used

PIN photodiode Avalanche photodiode made from silicon (Si), indium gallium arsenide (InGaAs) or germanium (Ge)

the data decoder/demodulator converts the signals into the correct format

Light Detector/Amplifier

Data Decoder/Demodulator

ElectricalInterface

OpticalInput

UserOutput(s)

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Transmission comparison metallic: limited information and distance free-space:

large bandwidth long distance not private costly to obtain

useable spectrum

optical fiber: offers best of both

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Fiber Optic Components

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2.3.1 Fiber Optics Cable

Extremly thin strands of ultra-pure glass Three main regions

center: core (9 to 100 microns) middle: cladding (125 or 140 microns) outside: coating or buffer (250, 500 and 900 microns)

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A FIBER STRUCTURE

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Light Emitters

Two types Light-emitting diodes

(LED’s) Surface-emitting (SLED):

difficult to focus, low cost Edge-emitting (ELED):

easier to focus, faster

Laser Diodes (LD’s) narrow beam fastest

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Detectors

Two types Avalanche photodiode

internal gainmore expensiveextensive support electronics required

PIN photodiodevery economicaldoes not require additional support circuitryused more often

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Interconnection Devices

Connectors, splices, couplers, splitters, switches, wavelength division multiplexers (WDM’s)

Examples Interfaces between local area networks and devices Patch panels Network-to-terminal connections

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Manufacture of Optical Fiber

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Introductions

1970, Corning developed new process called inside vapor deposition (IVD) to first achieve attenuation less than 20dB/km

Later, Corning developed outside vapor deposition (OVD) which increased the purity of fiber

Optical fiber was developed that exhibits losses as low as 0.2dB/km (at 1550nm). This seemed to be adequate for any application.

As the Internet expanded, more capacity was needed. Electronics can handle about 40Gbps, but not much more. Researchers developed Dense Wavelength-Division Multiplexing (DWDM) - 80 or more simultaneous data streams can now be combined on a single fiber, each being transmitted at a slightly different color of light

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Manufacture of Optical Fiber - MCVD

Modified Chemical Vapor Deposition (MCVD) another term for IVD method vaporized raw materials are deposited into a pre-made silica tube

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Manufacture of Optical Fiber - OVD

Outside Vapor Deposition (OVD) vaporized raw materials are deposited on a rotating rod the rod is removed and the resulting preform is consolidated by heating