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

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, (hilaladnan@unimap.edu.my) Prof. Dr. Syed Alwee Aljunid (hp: 0135842667)

• 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

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

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.

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

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

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

Short

band

Optical Wavelength Bands

C-band: Conventional Band

L-band: Long Band

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

Applications of Fiber Optics

• Military• Computer• Medical/Optometric• Sensor• Communication

Military Application

Computer Application

Sensors

Gas sensors

Chemical sensors

Mechanical sensors

Fuel sensors

Distance sensors

Pressure sensors

Fluid level sensors

Gyro sensors

Medical Application

• Endoscope

• Eyes surgery

• Blood pressure meter

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).

Li-Fi Technology

Real time usage of Li-Fi

• Li-Fi advantages: High Speed, Green Information

Technology, Lighting points used as Hotspot

Fiber Optic Fundamentals

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

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.

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.

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.

Principles of Fiber Optic Transmission

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

(EM) spectrum

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.

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.

• 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

• 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

• 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)

• 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)

• 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

Fiber Optic Components

• 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)

A FIBER STRUCTURE

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

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

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

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?