Optical Optical CommunicationsCommunications

Learning Objectives:Learning Objectives:

Learning Objectives:Learning Objectives:

describe describe optical communication methodsoptical communication methods; ;

describe describe advantages and disadvantagesadvantages and disadvantages of of optical communication methods; optical communication methods;

describe describe typical applicationstypical applications of optical of optical communications;communications;

Optical CommunicationsOptical Communications

lightlight is used as a carrier of data: is used as a carrier of data: infrared, infrared, fibre optic, fibre optic, laser laser

Infra RedInfra Red

used in remote controlsused in remote controls early laptops used IR to communicate with early laptops used IR to communicate with

printersprinters mobile mobile ‘‘phones use IR to communicate phones use IR to communicate

with each otherwith each other to share filesto share files

now mainly superseded by Bluetoothnow mainly superseded by Bluetooth requires line of sightrequires line of sight only works at short distances (<10m)only works at short distances (<10m) bandwidth ~100kbpsbandwidth ~100kbps

Fibre OpticFibre Optic

uses infra-red lasers to uses infra-red lasers to convert data into convert data into light pulseslight pulses electrical 0s & 1s converted into light on/light electrical 0s & 1s converted into light on/light

off pulsesoff pulses uses uses optical cableoptical cable ( (fibre optic cablefibre optic cable) to ) to

carry the datacarry the data rather than copper cable for electrical datarather than copper cable for electrical data

Optical CommunicationsOptical Communications

Optical CommunicationsOptical Communications

Optical CommunicationsOptical Communications

AdvantagesAdvantages of Fibre Optic of Fibre Optic cablecable

signal doesnsignal doesn’’t degradet degrade over distance over distance >100km (60 mile) lengths possible>100km (60 mile) lengths possible needs fewer repeaters for amplificationneeds fewer repeaters for amplification

greater data carrying capacitygreater data carrying capacity higher volume of data per second (10-15Tbps) more data can be exchanged simultaneously many strands in one cable

so future growth can be handledso future growth can be handled

AdvantagesAdvantages of Fibre Optic of Fibre Optic cablecable

not susceptible to electrical not susceptible to electrical interferenceinterference better quality of data transmission than

wired/wireless less errors = higher transmission speed

fibre optic cablefibre optic cable not subject to corrosion not subject to corrosion less maintenance/downtime than copper wireless maintenance/downtime than copper wire

more secure than wired/wireless difficult to tap in to since doesn’t leak light

carries digital signals no need for signal conversion

DisdvantagesDisdvantages of Fibre Optic of Fibre Optic cablecable

costcost of cable is more expensive than copper wire of cable is more expensive than copper wire network segment needs to be down if new nodes network segment needs to be down if new nodes

are to are to be spliced in (= disruption in productivity)be spliced in (= disruption in productivity) physical disruption physical disruption if cable needs to be housed if cable needs to be housed

undergroundunderground damage to cable means entire cable needs re-layingdamage to cable means entire cable needs re-laying initial set up costinitial set up cost electronic signals require conversion by a source electronic signals require conversion by a source

and a receiver at both ends of and a receiver at both ends of transmissiontransmission optical regenerators/laser amplifiers neededoptical regenerators/laser amplifiers needed impurities in the glass and the wavelength used impurities in the glass and the wavelength used

cause the signal to cause the signal to degrade over large distancesdegrade over large distances

LasersLasers used to connect LANs between two buildings

where line of sight is available 2 laser devices used in line of sight2 laser devices used in line of sight

send and receive light pulses representing binary data

no physical connection between devicesno physical connection between devices less invasive, no need to use cables less invasive, no need to use cables good for buildings that cangood for buildings that can’’t be cabledt be cabled no likelihood of damage to cablesno likelihood of damage to cables

bandwidth >1Gbps distance up to 4km can have interference due to atmospheric

conditions rain, snow, fog, cloud