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Photonics1

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Information about Photonics1
Travel-Nature

Published on March 14, 2008

Author: Laurie

Source: authorstream.com

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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 :  Outline 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?:  What is Photonics? The use of photons, the fundamental particles of light to transmit, store and process information. Why do we need Photonics?:  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:  Evolution of optical communication x More channels x More speed = Greater bandwidth Evolution of optical communication:  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 statue (1893 - 1942) Claude’s machine Claude’s portrait Evolution of optical communication Melted down during WW2 to make ammunition Evolution of optical communication:  Some of Claude’s stations survive to this day ... A map of Europe’s first telecommunications network Lines established 1793 - 1852 These are analogous to today’s fibre optic “repeater stations” Evolution of optical communication 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 Evolution of optical communication:  Alexander Graham Bell (1847 - 1922) ... … interrupted by a phone call during a meeting... Evolution of optical communication 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 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). Sketches from Bell’s own notebook Evolution of optical communication 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 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 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 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 Evolution of optical communication:  Building-to-Building (“B2B”) Laser communications 1.3 metres Laser transceivers in customer premises are placed near windows in line of site from a hub One possible solution to span the “last mile” with an optical frequency connection Fairly large! Evolution of optical communication 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 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 Evolution of optical communication

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