09-24-2021-1220 - wavelength-division multiplexing (WDM)

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 laserlight.^[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 which is 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 the velocity of the carrier wave. In a vacuum, this is the speed of light, usually denoted by the lower case letter, c. In glass fiber, it is substantially slower, usually about 0.7 times c. The data rate, which ideally might be at the carrier frequency, in practical systems is always a fraction of the carrier frequency. 

Dense WDM[edit]

Dense wavelength division multiplexing (DWDM) refers originally to optical signals multiplexed within the 1550 nm band so as to leverage the capabilities (and cost) of erbium doped fiber amplifiers (EDFAs), which are effective for wavelengths between approximately 1525–1565 nm (C band), or 1570–1610 nm (L band). EDFAs were originally developed to replace SONET/SDH optical-electrical-optical (OEO) regenerators, which they have made practically obsolete. EDFAs can amplify any optical signal in their operating range, regardless of the modulated bit rate. In terms of multi-wavelength signals, so long as the EDFA has enough pump energy available to it, it can amplify as many optical signals as can be multiplexed into its amplification band (though signal densities are limited by choice of modulation format). EDFAs therefore allow a single-channel optical link to be upgraded in bit rate by replacing only equipment at the ends of the link, while retaining the existing EDFA or series of EDFAs through a long haul route. Furthermore, single-wavelength links using EDFAs can similarly be upgraded to WDM links at reasonable cost. The EDFA's cost is thus leveraged across as many channels as can be multiplexed into the 1550 nm band.

https://en.wikipedia.org/wiki/Wavelength-division_multiplexing#Dense_WDM

https://en.wikipedia.org/wiki/space-division_multiplexing

https://en.wikipedia.org/wiki/Space-division_multiple_access

https://en.wikipedia.org/wiki/Multiplex

https://en.wikipedia.org/wiki/Multiplexer

https://en.wikipedia.org/wiki/Multiplex_(television)

https://en.wikipedia.org/wiki/Multiplexing

https://en.wikipedia.org/wiki/Multiplex_(assay)

https://en.wikipedia.org/wiki/string

https://en.wikipedia.org/wiki/operand

https://en.wikipedia.org/wiki/operator

https://en.wikipedia.org/wiki/Flow_cytometry

https://en.wikipedia.org/wiki/Mixer

https://en.wikipedia.org/wiki/Modulation#Analog_modulation_methods

https://en.wikipedia.org/wiki/analog

https://en.wikipedia.org/wiki/parameter

https://en.wikipedia.org/wiki/spectrum

https://en.wikipedia.org/wiki/continuous

https://en.wikipedia.org/wiki/range

https://en.wikipedia.org/wiki/cascade

https://en.wikipedia.org/wiki/Vacuum

https://en.wikipedia.org/wiki/electron_avalanche

https://en.wikipedia.org/wiki/Modulation#Analog_modulation_methods

https://en.wikipedia.org/wiki/Amplitude_modulation

https://en.wikipedia.org/wiki/maths

https://en.wikipedia.org/wiki/map

https://en.wikipedia.org/wiki/interface

https://en.wikipedia.org/wiki/Audio_signal

https://en.wikipedia.org/wiki/Carrier_wave

https://en.wikipedia.org/wiki/overtone_band

https://en.wikipedia.org/wiki/microwave

https://en.wikipedia.org/wiki/Cosmological_principle

https://en.wikipedia.org/wiki/Cosmic_microwave_background

https://en.wikipedia.org/wiki/Cosmic_neutrino_background

https://en.wikipedia.org/wiki/Gravitational_wave_background

https://en.wikipedia.org/wiki/Lambda-CDM_model

https://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis