Transcript 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 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 works
Light Amplification by Stimulated Emission of Radiation (LASER)
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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
Glass
CLADDING
Glass
CORE
BUFFER COATING
• Light travels through the core by constantly
bouncing from the cladding (mirror-lined walls) via a
principle called total internal reflection (TIR)
how optical fibre works
Low refractive index glass
CLADDING
High refractive index glass
CORE
BUFFER COATING
Total
reflection:
• Light rays are governed
by internal
two laws:
– n=1 >
n2
– Law of reflection  θincidence
θreflection
-1(n /n )
–
θ
>
θ
=
sin
1
c
– Law of refraction (Snell’s Law)  n1sinθ1 =2n21sinθ2
n = refractive index, θ = light ray angle
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
256
Typical telephone
call ~ 64 kb/s
92
50
0
00110010 01011101 .........
optical communication
Optical Fibre
Encoder
Transmitter
Receiver
Decoder
bridge the world
why use light?
• Advantages of optical fibre
–
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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
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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