The Difference between CWDM and DWDM

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In my former post I told the next blog item would be in English.
Now, what is the difference between CWDM and DWDM.
CWDM stands for Coarse Wavelength Division Multiplexing (CWDM). This is a special version WDM technique to decrease the overall cost of a fiber transmission system. The major feature of CWDM is that its wavelength spacing is normally very sparse, typically 20nm. With such a large wavelength spacing, there would be no rigid requirement of temperature stabilization on each wavelength transmission laser, which in turn can reduce the cost of the system. Because in CWDM there is no temperature stabilization control, an optical signal tends to transmit a short distance. Thus, CWDM is generally utilized in a system that spans a small range such as a metro area network (MAN), or a local area network (LAN)

DWDM stands for Dense Wavelength Division Multiplexing. As a counterpart of CWDM, DWDM has a much narrower wavelength spacing, which is typically 0.8nm according to the ITU standard. Rather than in a short-distance fiber transmission system, DWDM is often implemented in a ultra-long-haul optical transmission systems, which spans thousands of kilometers. Because of narrow wavelength spacing, DWDM requires a rigid temperature control on each transmission laser, thereby raising the whole transmission system cost. However, viewing ultra-long-haul fibers, where laying fibers can be major investment of  the whole transmission system, the high cost of optical lasers can largely overwhelmed by the high cost of fiber deployment. Thus, transmitting a maximum number of wavelengths in each fiber can achieve the best total cost saving for the whole system. In addition, in a long-haul transmission system, DWDM is often integrated with all optical amplifier techniques such as EDFA and Raman Amplifiers, which amplifies signals in the optical domain without going through any OEO conversion processes as in the traditional systems.

In general CWDM cannot accomodate more than 16 channels depending on the distance and type fibertype.
DWDM in contrast can accommodate more than 160 channels and can span distances up to thousands of kilometers.