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