Wednesday, April 15, 2020

Optical amplifiers have several significant

Optical amplifiers have several significant advantages over electrical repeaters. First, an optical amplifier can amplify a very wide band at once which can include hundreds of individual channels, eliminating the need to demultiplex DWDM signals at each amplifier. Second, optical amplifiers operate independently of the data rate and modulation format, enabling multiple data rates and modulation formats to co-exist and enabling upgrading of the data rate of a system without having to replace all of the repeaters.

Third, optical amplifiers are much simpler than a repeater with the same capabilities and are therefore significantly more reliable. Optical amplifiers have largely replaced repeaters in new installations, although electronic repeaters are still widely used as transponders for wavelength conversion.
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Wavelength-division multiplexing
Main article: Wavelength-division multiplexing
Wavelength-division multiplexing (WDM) is the technique of transmitting multiple channels of information through a single optical fiber by sending multiple light beams of different wavelengths through the fiber, each modulated with a separate information channel. This allows the available capacity of optical fibers to be multiplied.

This requires a wavelength division multiplexer in the transmitting equipment and a demultiplexer (essentially a spectrometer) in the receiving equipment. Arrayed waveguide gratings are commonly used for multiplexing and demultiplexing in WDM. Using WDM technology now commercially available, the bandwidth of a fiber can be divided into as many as 160 channels[21] to support a combined bit rate in the range of 1.6 Tbit/s.

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