Transcript Victorian Physics Teachers Conference 2002 Physics Oration

Victorian Physics Teachers Conference 2002
Physics Oration
Photonics:
Light waves for communication
New waves in education
Dr Andrew Stevenson
Manager, Educational Development
Photonics Institute Pty Ltd
GPO Box 464
Canberra ACT 2601
Outline
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What is photonics?
Evolution of optical communications
Important physical principles
Photonics technology and frontiers
The Photonics industry now and in 2010
Outlook for careers in photonics
Tertiary study options
Photonics Institute - how can we help?
What is Photonics?
The use of photons, the fundamental particles of light
to transmit, store and process information.
Why do we need Photonics?
• The principal driver for the photonics industry is
growing demand for faster, more efficient
communications.
• World Internet traffic is tripling each year (more
users each day, spending more time on-line,
downloading more Mbytes / hour)
• Photonics technologies enable the provision of
extremely high bandwidth to meet this growing
demand.
Evolution of optical communication
x More speed
x More channels
= Greater bandwidth
Evolution of optical communication
Modulating light to transmit information
1. Smoke signals / fires / lanterns / heliographs / mirrors
• Slow “digital” encoding, simple intensity modulation
• Very trivial messages (“All clear”, “Send help”)
• More of a broadcast than a dedicated channel
2. Claude Chappe invents first “optical telegraph”
• Slow “digital” encoding, using shapes
• Sophisticated codes to improve information content
• Reasonably fast and reliable
• Trained humans needed to encode / decode
• Europe’s first telecommunications network
Evolution of optical communication
Claude Chappe d’Auteroche
(1763 - 1805)
Claude’s portrait
Claude’s machine
Claude’s statue (1893 - 1942)
Melted down during WW2
to make ammunition
Evolution of optical communication
Some of Claude’s stations
survive to this day ...
These are analogous to today’s
fibre optic “repeater stations”
A map of Europe’s first
telecommunications network
Lines established 1793 - 1852
Evolution of optical communication
Modulating light to transmit information
To speed up communications, it is necessary to take humans
“out of the loop”.
A fully automatic optical link is required.
Bell’s Photophone ( ~ 1880)
• Machine codes & decodes in real time, no delays
• Intensity modulation of light
• Analogue encoding of signal in modulated light
• Audio (vocal) bandwidth for fairly rapid information
transmission (as good as any conversation!)
• Single (dedicated) communication channel
Evolution of optical communication
Alexander Graham Bell
(1847 - 1922) ...
… interrupted by a phone call
during a meeting...
Evolution of optical communication
Bell’s Photophone (3 June 1880, 4 years after the telephone)
Sunlight is focussed onto a
small lightweight mirror on a
special cantilevered mount
Speaker’s voice is mechanically
concentrated to vibrate the
mirror at acoustic frequencies
Sketches from Bell’s
own notebook
The mirror modulates (steers)
the light in time with the voice
The fluctuating sunlight is
directed by the mirror to a
selenium receiver that produces
changes in the current driving a
speaker coil, reproducing the
original voice (hopefully).
Evolution of optical communication
Modulating light to transmit information
3. Early optical fibre links - Multimode fibre, LED sources
(1960’s, 1970’s)
• Intensity modulation of an LED (analogue or digital)
• Bandwidth usually limited by multimode fibre
dispersion: longer distance <-> smaller bandwidth
• Over short links, bandwidth limited by LED
modulation rate (usually less than 300 Mbit/s)
• Useful over fairly short links / Local Area Networks
Evolution of optical communication
Modulating light to transmit information
4. Modern single-mode fibre links, Laser sources
(1980’s onwards)
• Fibre supports one optical “mode” - small dispersion
• Can modulate laser diodes up to a several GHz
• Far higher bandwidths are possible using an in-line
intensity modulator after the laser diode
• The only solution for long-haul high bit rate optical
communication links
• Dense Wavelength Division Multiplexing (DWDM)
lets us encode signals on many wavelength channels
at once - uses more of the available optical bandwidth
Evolution of optical communication
The long distance optical ‘medium’
1. Open Air: Beacon fires / semaphore flags on hilltops
• Day or Night operation only, depending on
method used
• Vulnerable to weather, sleepy observers
• Not secure - easy to eavesdrop
• Coding and decoding can be complex OR
Messages take a long time to send
(Tradeoff between bandwidth and complexity)
Evolution of optical communication
The long distance optical ‘medium’
2. Open Air: Lasers on rooftops, building-to-building
• 24 hours a day operation
• Large bandwidth (~ 1GHz)
• Collimated beam (but not totally secure)
• Potential danger (eyes),
• Vulnerable to weather / obstructions ???
• Useful range ~ 1km, due to beam distortion
• Potentially useful for the “last mile”
Evolution of optical communication
Building-to-Building (“B2B”) Laser communications
One possible solution to span the “last mile”
with an optical frequency connection
Laser transceivers
in customer
premises are placed
near windows in line
of site from a hub
1.3 metres
Fairly large!
Evolution of optical communication
The long distance optical ‘medium’
3. Lightpipes - a nice idea perhaps, but then again...
• Large bandwidth
• Sensitive to changes of temperature, alignment etc
• Many reflection losses if solid glass lenses are used
• Complex, not practical, not economic
Evolution of optical communication
The long distance optical ‘medium’
4. Optical Fibres
• Huge bandwidth (esp. when using many wavelengths)
• Flexible, temperature insensitive, low loss, few
alignment issues
• Cheap and able to be mass produced
• Standard long distance communication medium