© N. Ganesan, Ph.D. , All rights reserved.

Chapter

Electronic and Optical Transmission

Chapter Objectives

• Describe the basic transmission features of electronic and optical transmission– Variation in the voltage of digital

signals etc.

• Briefly discuss the electronic-to-optical and optical-to-electronic interfaces

Chapter Modules

• Basics of electronic transmission• Basics of optical transmission• Fiber optic connections

© N. Ganesan, Ph.D. , All rights reserved.

Module

Basics of Electronic Transmission

Simple Digital Encoding of Data

1 0 0 0 0 0 1

Pulse

TIME

Sig

nal

Str

en

gth

Pulse Duration

A -------------> ASCII -----------> 1000001

Transmission of AVoltage

Summary of Digital Electronic Transmission

ABCode and generate

Electronic signalsReceive andDecode electronicSignals

Both points operate under the same rulesand guidelines for effective communication.

Square waves are coded based on voltages to represent either a one and a zero.

An Early Introduction to the Concept of Protocol

• Communication protocol is a set of rules and guidelines for transmission

• A simple protocol that applies to the previous example is as follows:– 0 = 0.05 Volts– 1 = 0.1 Volts– Pulse duration is 1 nanosecond

• In practice, the protocols are much more sophisticated

An Example of a Widely Used Protocol

• TCP/IP– Transmission Control

Protocol/Internet Protocol– De facto protocol of the Internet– TCP/IP is a stack of protocols

• Some examples of protocols in the TCP/IP stack– UDP, SMTP, POP3 etc.

End of Module

© N. Ganesan, Ph.D. , All rights reserved.

Module

Basics of Optical Transmission

Optical Transmission

Optical Transmission

Light Pulse

Pulses of different wave lengths (frequencies) are used for representing 0s and 1s.

Origin Destination

Wave Length

• Wave length is inversely proportional to frequency– Wave length = 1/Frequency

• Higher the frequency, the shorter the wave length

Fiber-Optic Transmission Characteristics

• Signal encoding (0 and 1) can be based on light rays of different wave lengths

• Possible light sources are, for example:– Laser – Light Emitting Diode (LED)

• Conversion from light to electricity– Photo Electric Cell

Characteristics of Optical Transmission in a Fiber

• In general, the laws of physics say that light travels along a straight line

• In optical fibers, however, light travels along the path of the fiber

Example of Path of Propagation of Light Waves in Fiber Cables

Vase Ornament

Light Source

Tips glow

FiberLight travels along thepath of the fiber

Optical Transmission In Fiber

Light bounces and travels along the fiber

Optical Transmission Alternatives

• Multimode Step Index– Lower speed optical transmission

• Multimode Graded Index– Intermediate speeds of transmission

• Single Mode– Higher speed in transmission

Optical Transmission Alternatives Cont.

MultimodeStep

MultimodeGraded

Single Mode

Light PropagationSource: Corning Tutorial

Fiber Properties• Glass (silicon) is used in most

cases as the material for producing fiber strands

• Low cost plastic fibers are also available at present

• However, the connections involving plastic fibers are limited by distance compared to silicon fibers

Rule of Thumb

• Purer the fiber, the smaller the loss in signal strength and hence, further the light travels

Multi-Mode FiberSource: Corning Tutorial

Single Mode FiberSource: Corning Tutorial

Example of Fiber Cables

Fiber Connections

• For full duplex transmission there are two connectors in the case of fiber connections– Transmitting connection is denoted as

TX– Receiving connection is denoted as

RX

End of Module

© N. Ganesan, Ph.D. , All rights reserved.

Module

Fiber Optic Connections

Optical-to-electronic Conversion

Photo-Electric

CellLight Electricity

Optical Signals Electronic Signals

Electronic-to-optical Conversion

Light EmittingDiode (LED)/

LaserLight Electricity

How Fiber Works:Source: Corning Tutorial

Electro-Optical Fiber Interface

Source: Black Box

Example in Extending the Communication Link Between

Two Computers

Computer/Comm.System

A

Computer/Comm.System

B

Fiber Interface

Elect. Elect.Optic.

Typical Use Of Optical Technology

• Extending the distance between two communication points – Line drivers

• Telecommunications– Long distance telephone trunks

• Large-scale network backbones– FDDI

• Internetworking– Connection between switches

Fiber Connection for Extending a T1 Line Connection

1.5 Miles at 256 Kbps and 3 miles at 64 Kbps.

Multimode Fiber cable

Source: Black Box

Fiber Connection for Extending LAN Connection

Up to 31 miles. Speeds from 56-2048 Kbps.Source: Black Box

Fiber Line Driver

Fiber cableport.

Source: Black Box

Fiber Connection Between Switches

FiberConnection

References

• Corning Library• Corning Tutorial

– This can be downloaded and played

• Locally hosted fiber-optic reference on the reference page of this web (Week 6)

• Other useful references can be obtained from the web as well

Key Words

• Pulse duration• Square wave• Protocol• TCP/IP• Wave length• Laser and LED• Photo Electric Cell• Multi-mode and single mode fiber

Key Words (Continued)

• Fiber transmission advantages• ST and SC connections• RX and TX• Media interface• Fiber usage

– Telecommunications, campus backbone, FDDI and Internetworking

End of Module

End of Chapter

End of ModuleEnd of ModuleEND OF CHAPTER END OF CHAPTER