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Maxim > Design Support > Technical Documents > Application Notes > Optoelectronics > APP 3258
Keywords: DWDM, fiber transmission systems, bandwidth, demultiplexers, optical multiplexer, EFDA,
APD, data transmission technology
APPLICATION NOTE 3258
HFTA-08.0: Receivers and Transmitters in DWDM
Systems
Jun 22, 2004
Abstract: The rapidly growing internet traffic demands a near-continuous expansion of data-transmission
capacity. To avoid traffic jams on the data highways, network providers need a technique that provides
fast, flexible, and cost-effective bandwidth expansions. One such technique is the data-transmission
technology called Dense Wavelength Division Multiplexing (DWDM), which augments network data
through the existing fiber infrastructure.
DWDM Technology
In conventional long-haul fiber-transmission systems, data is transmitted at a certain bit rate, using (for
low signal dispersion) a single wavelength from the second optical window (1300nm range), or (for low
signal attenuation) a single wavelength from the third optical window (1500/1600nm range). To achieve
higher transmission capacity, you can raise the bit rate based on Time-Division Multiplexing (TDM), or
install additional fiber cables in parallel with the existing ones, or both.
The second approach requires expensive and time-consuming construction work, therefore increasing
the bit rate would seem to be the more cost-effective way to achieve higher bandwidth within an existing
fiber network. The absence of technologies like a mature and cost-effective process for high-speed IC
development, and the limitations of physical fiber media (like fiberpolarization mode dispersion) do not
allow the realization of practical commercial transmission systems beyond 40Gbps. Upgrading a single
fiber link from 2.5Gbps (for example) to 10Gbps quadruples the bandwidth capacity, but a transmission
technology called Dense Wavelength Division Multiplexing (DWDM) can multiply the capacity by multiples
as high as 160.
DWDM takes advantage of a physical phenomenon that allows multiple wavelengths of light to travel
simultaneously through a single-fiber cable. It allows multiple high-bit-rate signals to ride through the
fiber media together, each on a different color of light.
Another significant advantage of WDM transmission (compared with TDM long-haul trunks) is "bit-rate
transparency" as conferred by the purely optical functions that are mandatory in such systems - like
optical multiplexers and demultipexers, optical line amplifiers (OLAs), and in future, optical 3R
regenerators for ultra-long-link distances. In principle, therefore, the link includes no bit-rate-limiting
elements that would require a change of optical line components to achieve a higher bit rate.
Overview of DWDM System Components
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