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As there are three different WDM types, whereof one is called "WDM", the notation "xWDM" is normally used when discussing the technology as such. The optical filtering devices used have conventionally been etalons (stable solid-state single-frequency Fabry–Pérot interferometers in the form of thin-film-coated optical glass). With the right type of fiber, it is possible to have a device that does both simultaneously and can function as an optical add-drop multiplexer. The data rate in practical systems is a fraction of the carrier frequency.Ī WDM system uses a multiplexer at the transmitter to join the several signals together and a demultiplexer at the receiver to split them apart.
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In glass fiber, it is substantially slower, usually about 0.7 times c. In a vacuum, this is the speed of light, usually denoted by the lowercase letter, c. Specifically, frequency (in Hertz, which is cycles per second) multiplied by wavelength (the physical length of one cycle) equals the velocity of the carrier wave.
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This is purely conventional because wavelength and frequency communicate the same information. The term WDM is commonly applied 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. This technique enables bidirectional communications over a single strand of fiber, also called wavelength-division duplexing, as well as multiplication of capacity. In fiber-optic communications, wavelength-division multiplexing ( WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e., colors) of laser light.