Optical Communications

1
Optical Communications
2
Learning Objectives
3
Learning Objectives

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

4
Optical Communications

• light is used as a carrier of data
• infrared,
• fibre optic,
• laser

5
Infra Red

• used in remote controls
• early laptops used IR to communicate with
  printers
• mobile phones use IR to communicate with each
  other
• to share files
• now mainly superseded by Bluetooth
• requires line of sight
• only works at short distances (lt10m)
• bandwidth 100kbps

6
Fibre Optic

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

7
Optical Communications
8
Optical Communications
9
Optical Communications
10
Advantages of Fibre Optic cable

• signal doesnt degrade over distance
• gt100km (60 mile) lengths possible
• needs fewer repeaters for amplification
• 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

11
Advantages of Fibre Optic cable

• 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
• less maintenance/downtime than copper wire
• more secure than wired/wireless
• difficult to tap in to since doesnt leak light
• carries digital signals
• no need for signal conversion

12
Disdvantages of Fibre Optic cable

• 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)
• physical disruption if cable needs to be housed
  underground
• damage to cable means entire cable needs
  re-laying
• initial set up cost
• electronic signals require conversion by a source
  and a receiver at both ends of transmission
• optical regenerators/laser amplifiers needed
• impurities in the glass and the wavelength used
  cause the signal to degrade over large distances

13
Lasers

• used to connect LANs between two buildings
• where line of sight is available
• 2 laser devices used in line of sight
• send and receive light pulses representing binary
  data
• no physical connection between devices
• less invasive, no need to use cables
• good for buildings that cant be cabled
• no likelihood of damage to cables
• bandwidth gt1Gbps
• distance up to 4km
• can have interference due to atmospheric
  conditions
• rain, snow, fog, cloud