Optical Communications

Learning Objectives:

describe optical communication methods; describe optical communication methods; describe advantages and disadvantages of optical communication methods; describe advantages and disadvantages of optical communication methods; describe typical applications of optical communications; describe typical applications of optical communications;

Optical Communications light is used as a carrier of data: light is used as a carrier of data: infrared, infrared, fibre optic, fibre optic, laser laser

Infra Red used in remote controls used in remote controls early laptops used IR to communicate with printers early laptops used IR to communicate with printers mobile ‘ phones use IR to communicate with each other mobile ‘ phones use IR to communicate with each other to share files to share files now mainly superseded by Bluetooth now mainly superseded by Bluetooth requires line of sight requires line of sight only works at short distances (<10m) only works at short distances (<10m) bandwidth ~100kbps bandwidth ~100kbps

Fibre Optic uses infra-red lasers to convert data into light pulses uses infra-red lasers to convert data into light pulses electrical 0s & 1s converted into light on/light off pulses electrical 0s & 1s converted into light on/light off pulses uses optical cable (fibre optic cable) to carry the data uses optical cable (fibre optic cable) to carry the data rather than copper cable for electrical data rather than copper cable for electrical data

Optical Communications

Advantages of Fibre Optic cable signal doesn ’ t degrade over distance signal doesn ’ t degrade over distance >100km (60 mile) lengths possible >100km (60 mile) lengths possible needs fewer repeaters for amplification needs fewer repeaters for amplification greater data carrying capacity greater 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 handled so future growth can be handled

Advantages of Fibre Optic cable not susceptible to electrical interference not susceptible to electrical interference better quality of data transmission than wired/wireless less errors = higher transmission speed fibre optic cable not subject to corrosion fibre optic cable not subject to corrosion less maintenance/downtime than copper wire less 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

Disdvantages of Fibre Optic cable cost of cable is more expensive than copper wire cost of cable is more expensive than copper wire network segment needs to be down if new nodes are to be spliced in (= disruption in productivity) network segment needs to be down if new nodes are to be spliced in (= disruption in productivity) physical disruption if cable needs to be housed underground physical disruption if cable needs to be housed underground damage to cable means entire cable needs re-laying damage to cable means entire cable needs re-laying initial set up cost initial set up cost electronic signals require conversion by a source and a receiver at both ends of transmission electronic signals require conversion by a source and a receiver at both ends of transmission optical regenerators/laser amplifiers needed optical regenerators/laser amplifiers needed impurities in the glass and the wavelength used cause the signal to degrade over large distances impurities in the glass and the wavelength used cause the signal to degrade over large distances

Lasers used to connect LANs between two buildings where line of sight is available 2 laser devices used in line of sight 2 laser devices used in line of sight send and receive light pulses representing binary data no physical connection between devices no physical connection between devices less invasive, no need to use cables less invasive, no need to use cables good for buildings that can ’ t be cabled good for buildings that can ’ t be cabled no likelihood of damage to cables no likelihood of damage to cables bandwidth >1Gbps distance up to 4km can have interference due to atmospheric conditions rain, snow, fog, cloud