A disadvantage of EDFAs is that some electrons at the higher energy level generate uncorrelated optical noise by falling into the lower-energy band spontaneously. Because DWDM links usually contain a chain of OLAs, this optical noise is amplified in the following EDFAs, and the resulting noise accumulation lowers the receiver's signal-to-noise ratio compared with that of systems without OLAs. What's more, this optical noise is asymmetric, because it affects logic "high" levels more than "low" levels.

Depending on the distance between optical mux and demux, several EDFAs can be cascaded with a typical span of about 100 km. That technique allows optical transmission links of several hundred kilometers without the need for an electronic signal regeneration. At the receiver side, an optical demultiplexer converts the incoming wavelength-multiplexed signal into the corresponding individual wavelengths launched at the transmitter side. This demultiplexing function includes very narrow optical filters, for which smaller wavelength separations require greater design effort.

Apart from these basic system elements, a DWDM system may include other functions such as an optical booster after the optical mux, dispersion compensation, or an optical preamplifier in front of the optical demux, with the aim of improving system performance and extending the link length.

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