Lecture 9 10

Lecture 9 10 - EE 555 - Broadband Network Architectures...

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EE 555 - Broadband Network Architectures Section 2.2 Optical Network Technologies Prof. John Silvester Optical Signals and Multiplexing • WAN’s are primarily run over optical fiber facilities • With current optical technology the potential data rate over a fiber is ~Tbps (10 12 bps) A key network issue is multiplexing – how to multiplex in A key network issue is multiplexing how to multiplex in the optical domain? – TDM: time division multiplexing: usually for lower speeds (up to 10Gbps) – WDM: wavelength division multiplexing (aka frequency division multiplexing) to put together multiple 10G (or above) streams – Since some components are electronic which is very expensive or not even possible at very high bit rates usc-den-ee555-spring09 2.2 Optical Technologies 2
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TDM vs WDM Signalling at n electrical/ optical conversion mux times source rate electrical/ optical conversion de- mux (a) Time Division: TDM Ot i ld i t e/o opt mux Optical device to mux/demux e/o o/e o/e (b) Wavelength Division: WDM e/o o/e usc-den-ee555-spring09 2.2 Optical Technologies 3 Optical Transmission Challenges • Power Loss – Increase power input (lasers vs leds) – Reduce loss (better fibers) – Optical amplification (reduce need for regens) • Controlling Differential Delays – Single mode fiber vs Multi-mode fiber • Controlling Chromatic Dispersion – Dispersion compensating fiber – Signalling processing to correct for dispersion usc-den-ee555-spring09 2.2 Optical Technologies 4
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1 st Generation Fiber System LED regens (oeo) core (50-85 μ m) cladding • Multi-mode fiber, different path with different time delays, leads to symbol interference and limits signalling rates Regens necessary every few km due to multipath • LED for input: Cheap and adequate power for short haul; wide spectrum – not a big issue since signalling rates were limited usc-den-ee555-spring09 2.2 Optical Technologies 5 2 nd Generation Fiber System laser fewer regens (oeo) MLM 10km core (8-10 μ m) MLM – 10km SLM – 40 km •S i n gle-mode fiber. Finer fiber designed to allow a single mode of cladding light transmission. More expensive but not terribly so. Allows for much longer distance making higher powered signal input worthwhile (lasers). MLM – multi-longitudional mode; SLM – single-longitudional mode.
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Lecture 9 10 - EE 555 - Broadband Network Architectures...

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