WDM systems are divided into three different wavelength patterns: Normal (WDM), Coarse (CWDM) and Dense (DWDM).
- Normal WDM (sometimes called BWDM) uses the two normal wavelengths 1310 and 1550 on one fiber.
- Coarse WDM provides up to 16 channels across multiple transmission windows of silica fibers.
- Dense wavelength division multiplexing (DWDM) uses the C-Band (1530 nm-1565 nm) transmission window but with denser channel spacing. Channel plans vary, but a typical DWDM system would use 40 channels at 100 GHz spacing or 80 channels with 50 GHz spacing. Some technologies are capable of 12.5 GHz spacing (sometimes called ultra dense WDM). New amplification options (Raman amplification) enable the extension of the usable wavelengths to the L-band (1565 nm-1625 nm), more or less doubling these numbers.
WDM, DWDM and CWDM are based on the same concept of using multiple wavelengths of light on a single fiber, but differ in the spacing of the wavelengths, number of channels, and the ability to amplify the multiplexed signals in the optical space. EDFA provide an efficient wideband amplification for the C-band, Raman amplification adds a mechanism for amplification in the L-band. For CWDM, wideband optical amplification is not available, limiting the optical spans to several tens of kilometres.
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