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EKT 465 EKT 465
School of Computer and Communication School of Computer and Communication Engineering, Engineering,
University Malaysia Perlis (UniMAP)University Malaysia Perlis (UniMAP)
Optical Communication system
CHAPTER CHAPTER 11
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Coursework Contribution1. COURSE IMPLEMENTATIONSI)Lecture
3 hours per week for 14 weeks (Total = 42 hours)
Tutorial +assignment 20%
Test 1&2 20 %
Final Exam 60%
Total 100%
Lecturer: Dr. Hilal A. Fadhil, ([email protected]) Prof. Dr. Syed Alwee Aljunid (hp: 0135842667)
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• Course materialCourse text book:
• “Gerd Keiser, Optical Fiber Communications, 3rd Edition, Mc Graw Hill, 2000
Reference Books:– Joseph C. Palais, Fiber Optic Communications, 5th
Edition, Prentice Hall, 2005 – Jeff Hecht, Undestanding Fiber Optics, 5th Edition,
Prentice Hall, 2006
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Course Outcome
Chapter 1-Introduction:
Chapter 2: Light Propagation & Transmission Characteristics of Optical Fiber
Chapter 3: Optical Components/ Passive Devices
Chapter 4: Optical Sources
Chapter 5: Light Detectors, Noise and Detection
Chapter 6: SYSTEM DESIGN
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What are the features of a optical communication system?What are the features of a optical communication system?Why “optical ” instead of “copper wire ”?Why “optical ” instead of “copper wire ”?
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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A History of Fiber Optic Technology
The Nineteenth Century
• 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
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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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Short
band
Optical Wavelength Bands
C-band: Conventional Band
L-band: Long Band
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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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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 using (Li-Fi
Technology).
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Li-Fi Technology
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Real time usage of Li-Fi
• Li-Fi advantages: High Speed, Green Information
Technology, Lighting points used as Hotspot
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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.
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.
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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Optical power Measurement units:
In designing an optical fiber link, it is of interest to establish, measure the signal level at the transmitter, at the receiver,, at the cable connection, and in the cable.
Power: Watt (W), Decibel (dB), and dB Milliwatt (dBm).
dB: The difference (or ratio) between two signal levels. Used to describe the effect of system devices on signal strength. For example, a cable has 6 dB signal loss or an amplifier has 15 dB of gain.
dBPower
Powerlog10Gain
In
Out
dBm: A signal strength or power level. 0 dBm is defined as 1 mW (milliWatt) of power into a terminating load such as an antenna or power meter.
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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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• 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
Principles of Fiber Optic Transmission
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• Fiber optic links contain three basic elements– transmitter– optical fiber– receiver
Transmitter ReceiverUser
Output(s)
Optical Fiber
Electrical-to-OpticalConversion
Optical-to-ElectricalConversion
UserInput(s)
Elements of an Optical Fiber communication
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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
OpticalOutput
UserInput(s)
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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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• Fiber Optics Cable
• Extremely 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 gain
• more expensive
• extensive support electronics required
– PIN photodiode
• very economical
• does not require additional support circuitry
• used 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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Exercises (page no.25/ Text book)
Q1: Convert the following absolute power levels to dBm values: 1pW, 1nW, 1mW.
Q2: What are the advantages of using Optical fiber over other wireless communication system ? Give an example to show the application of fiber optics in the real life.
Q3: A 50-km long optical fiber has a total attenuation of 24 dB. If 500 micro watt of optical power get lanuched into the fiber, what is the output power level in dBm and in Mico watt?
Q4: There are many methods which have been used to fabricate and manufacture an optical fiber, list out at least three methods and explain one of them.
Q5: Convert the following dBm values to power level in mW: -13 dBm, -6 dBm.
Q6: Discuss and sketch the block diagram of an optical fiber communication elements?