Wavelength Division Multiplexing (WDM)

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Motivation
With ever increasing number of users there is constant demand for ultra high speed data rates with improved bandwidth capacity. i.e. high bandwidth capacity of transmission link.
More fibers
Fast electronics
WDM
Wavelength Division Multiplexing(WDM)
Simultaneous transmission of several independent signals using wave transmission.
Each colour of light (wavelength) carries separate data channel
Increase in overall capacity of transmission
WDM Operation
Multiplexer aggregates sources for transmission over single fibre.
Optical amplifiers amplify all wavelengths.
Demultiplexer separates channels at the destination The
photo detector corresponding t o each wavelength detects the desired transmitted signal.
Mostly 1550nm range transmission window is used.
WDM History
64-128 channels in 1550 nm window. Channel spacing
0.4-0.8nm
16-32 channels in 1550 nm.
channel spacing 0.8-1.6nm
2-8 channel in 1550 nm.
Channel spacing ~3.2nm
2 channel WWDM(Wideband WDM) 1310nm and 1550 nm
WDM Evolution
Faster(high speed per channel)
Channel are narrower and very close to each other i.e. increased no. of channels.
Longer individual links before regeneration.
WDM Evolution (contd.)
WDM(contd..)
Optical Fiber Performance
Optimum performance is hampered by
Attenuation
loss or reduction in signal power during transmission.
Dispersion
broadening of pulses as they travel over the fiber.
Remedy: a)dispersive shifted fiber(DSF) 4 wave mixing
b) Non zero dispersive shifted fiber(NSDSF)