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Communicating by Light. Dr Martin Ams MQ Photonics Research Centre Centre for Ultrahigh bandwidth Devices for Optical Systems (CUDOS) Department of Physics & Astronomy - Faculty of Science MACQUARIE UNIVERSITY North Ryde, NSW 2109 AUSTRALIA Phone: +61 2 9850 8975 Fax: +61 2 9850 8115

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Communicating by light
Communicating by Light

Dr Martin Ams

MQ Photonics Research Centre

Centre for Ultrahigh bandwidth Devices for Optical Systems (CUDOS)

Department of Physics & Astronomy - Faculty of Science

MACQUARIE UNIVERSITY

North Ryde, NSW 2109

AUSTRALIA

Phone: +61 2 9850 8975

Fax: +61 2 9850 8115

Url: http://web.science.mq.edu.au/~mams


Communication
communication

  • Communication is the process of exchanging information, messages or ideas


Telegraphy
telegraphy

  • 18th Century – discovery and understanding of electricity led to telecommunications

  • Telegraphy in copper wires

    • Morse code, telephone

  • 1887 - Electromagnetic (EM) Wave Theory

    • Radio, TV, wireless, satellite, microwave systems


Can we use light
can we use light?

  • Early 20th Century - suggested that light should be able to transmit data because it is also an EM wave

  • No light source and no medium to transport it

    • 1960s: LASER

    • 1970s: Optical Fibre


How a laser works
how a LASER works

Absorption of Energy

Emission of Energy


How a laser works1
how a LASER works

Light Amplification by Stimulated Emission of Radiation (LASER)

1

2

3

4


How a laser works2
how a LASER works

  • LASER light is

    • Monochromatic: one specific colour

    • Coherent: photons move in step with each other

    • Very directional


How optical fibre works
how optical fibre works

  • Light travels through the core by constantly bouncing from the cladding (mirror-lined walls) via a principle called total internal reflection (TIR)

Glass

CLADDING

Glass

CORE

BUFFER COATING


How optical fibre works1
how optical fibre works

  • Light rays are governed by two laws:

    • Law of reflection θincidence = θreflection

    • Law of refraction (Snell’s Law)  n1sinθ1 = n2sinθ2

Low refractive index glass

CLADDING

  • Total internal reflection:

    • n1>n2

    • θ1 > θc = sin-1(n2/n1)

High refractive index glass

CORE

n = refractive index, θ = light ray angle

BUFFER COATING


Summary
summary

  • Let’s summarise:

    • Light source: LASER

    • Medium: optical fibre

    • Light is an EM wave

  • How do we use light to transmit information?


Let s call germany
let’s call Germany

Analogue Voice Signal


Light encoding
light encoding

256

Typical telephone

call ~ 64 kb/s

92

50

0

00110010

01011101 .........


Optical communication
optical communication

Optical Fibre

Encoder

Transmitter

Decoder

Receiver



Why use light
why use light?

  • Advantages of optical fibre

    • Speed

    • Bandwidth ~ 350 Tb/s

    • Price

    • Physical size and weight

    • Immune to EM interference

    • Low signal loss

    • Non-flammable

    • Flexible



Unused bandwidth
unused bandwidth

  • The problem is not that the fibre is too slow, rather the information travels at the speed of light

  • However, the fibre needs to be connected to electronic detectors, routers and transmitters etc. that transfer information between different users/senders

  • Current detectors, routers and transmitters are not able to modulate light at these incredible speeds

  • Possible solution  Fibre To The Home (FTTH)


43 billion national broadband network
$43 billion national broadband network

  • One of the “top three engineering challenges” in Australia

  • Optical fibres and light will carry data across Australia to homes and businesses

  • Data rates of at least 12 Mb/s to 98% of premises in Australia, and 100 Mb/s for regional towns or cities

  • New optical infrastructure is needed to meet these requirements  Photonic Chips (photonic integrated circuits)


Photonic chip doing my bit
photonic chip & doing my bit

  • I create analogies of optical fibre devices in glass using a high power laser system


Summary1
summary

  • Light can be used to send data signals all over the world using lasers and optical fibres

  • Voice, TV, video, internet, email & gaming can all fit on one fibre as different colours

  • Groups around the world are working on next generation photonic chips for use in all optical networks  faster communication and optical processing systems


Picture sources
picture sources

  • http://www.vislab.uq.edu.au/photonics

  • http://www.okcupid.com/forum

  • http://www.portsdown-tunnels.org.uk

  • http://www.thechemistrynerd.com/benfranklin

  • http://www.irishdentist.ie

  • http://science.howstuffworks.com

  • http://hackaday.com

  • http://media.photobucket.com

  • http://www.next-up.org/Newsoftheworld

  • http://www.solutions-site.org/artman/publish

  • http://www.alibaba.com/showroom

  • http://www.rp-photonics.com


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