Wavelength-division multiplexing

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Multiplexing
Analog modulation
AM FM PM QAM SM SSB
Circuit mode (constant bandwidth)
TDM FDM / WDM SDMA Polarization Spatial OAM
Statistical multiplexing (variable bandwidth)
Packet switching Dynamic TDMA FHSS DSSS OFDMA SC-FDM MC-SS
Related topics
Channel access methods Medium access control
v t e

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.^[1] This technique enables bidirectional communications over a single strand of fiber (also called wavelength-division duplexing) as well as multiplication of capacity.^[1]

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, more often described by frequency.^[2] This is purely conventional because wavelength and frequency communicate the same information. Specifically, frequency (in Hertz, which is cycles per second) multiplied by wavelength (the physical length of one cycle) equals velocity of the carrier wave. In a vacuum, this is the speed of light (usually denoted by the lowercase letter, c). In glass fiber, velocity is substantially slower - usually about 0.7 times c. The data rate in practical systems is a fraction of the carrier frequency.