Communicating by Light Dr Martin Ams MQ Photonics Research Centre Centre for Ultrahigh bandwidth Devices for Optical Systems (CUDOS) Department of Physics.

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 is the process of exchanging information, messages or ideas

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?

• 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

Absorption of Energy

Emission of Energy

how a LASER worksLight Amplification by Stimulated Emission of Radiation (LASER)

1 2

3 4

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

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

GlassCORE

GlassCLADDING

BUFFER COATING

how optical fibre works

• Light rays are governed by two laws:– Law of reflection θincidence = θreflection

– Law of refraction (Snell’s Law) n1sinθ1 = n2sinθ2

n = refractive index, θ = light ray angle

High refractive index glassCORE

Low refractive index glassCLADDING

BUFFER COATING

Total internal reflection:– n1 > n2

– θ1 > θc = sin-1(n2/n1)

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

Analogue Voice Signal

light encoding

0

256

00110010 01011101 .........

Typical telephonecall ~ 64 kb/s

50

92

optical communication

Optical Fibre

Encoder

Decoder

Transmitter

Receiver

bridge the world

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

assign a colour to each signal

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

• 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

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

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• 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