Wavelength-division multiplexing

:The original version of this article was based on FOLDOC, with permission

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

In telecommunications wavelength-division multiplexing (WDM) is a technology which multiplexes several optical carrier signals on a single optical fibre by using different wavelengths (colours) of laser light to carry different signals. This allows for a n-fold increase in capacity, in addition to making it possible to perform bidirectional communications over one strand of fibre.

Related Topics:
Telecommunication - Optical carrier - Optical fibre - Wavelength - Laser - Light - Bidirectional

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Note that this term applies to an optical carrier (which is typically described by its wavelength), whereas frequency-division multiplexing typically applies to a radio carrier (which is more often described by frequency). However, since wavelength and frequency are inversely proportional, and since radio and light are both forms of electromagnetic radiation, the distinction is somewhat arbitrary.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The device that joins the signals together is known as a multiplexer, and the one that splits them apart is a demultiplexer. With the right type of fibre you can have a device that does both at once, and can function as an optical add-drop multiplexer. The optical filtering devices used in the modems are usually etalons, stable solid-state single-frequency Fabry-Perot interferometers.

Related Topics:
Multiplexer - Add-drop multiplexer - Etalon

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The first WDM systems combined two signals and appeared around 1985. Modern systems can handle up to 160 signals and can expand a basic 10 Gbit/s fibre system to a theoretical total capacity of over 1.6 Tbit/s over a single fiber pair.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

WDM systems are popular with telecommunications companies because they allow them to expand the capacity of the network without laying more fibre. By using WDM and optical amplifiers, they can accommodate several generations of technology development in their optical infrastructure without having to overhaul the backbone network. All they have to do is to upgrade the multiplexers and demultiplexers at each end.

Related Topics:
Telecommunications companies - Optical amplifier

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

This is often done by using optical-to-electrical-to-optical translation at the very edge of the transport network, thus permitting interoperation with existing equipment with optical interfaces.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~