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06 Aug 2015

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 of laser light. This technique enables bidirectional communications over one strand of fiber, as well as multiplication of capacity. A WDM system uses a multiplexer at the transmitter to join various signals together, and a demultiplexer at the receiver to split them apart When dealing with optical communication system, there are two main types of WDM systems which are used to transmit the necessary data: CWDM and DWDM.

WDM operating principle

Coarse Wavelength Division Multiplexing (CWDM) is the technology of choice for cost efficiently short-haul transmission in telecoms or enterprise networks. While Dense Wavelength Division Multiplexing (DWDM) is designed for long-haul transmission where wavelengths are packed tightly together, providing a high-capacity solution in telecom networks. Generally speaking, DWDM and CWDM are based on the same concept of using multiple wavelengths of light on a single fiber, but differ in the wavelengths spacing, number of channels and the ability to amplify the multiplexed signals in the optical space.
The major difference between them is that DWDM multiplexing systems are made for longer haul transmission, by keeping the wavelengths tightly packed. They can transmit more data over a significantly larger run of cable with less interference than a comparable CWDM system. CWDM cannot travel long distances because the wavelengths are not amplified, and therefore CWDM is limited in its functionality over longer distances. Therefore, DWDM technology is one of the best choices for transporting extremely large amounts of data traffic over long distance in optical networks.
Compared with DWDM which is a more tightly packed WDM system, CWDM has larger wavelengths spacing with fewer wavelengths be transported on the same fiber. For instance, CWDM typically has 20 nm wavelengths spacing while DWDM typically has approximately 0.8 nm, hence can pack 40 plus channels compared to CWDM in the same frequency range. Thus, more channels and higher capacity can be achieved using DWDM.

CWDM and DWDM wavelengths

CWDM systems, on the other hand, use DFB lasers that are not cooled. These systems typically operate from 0 to 70°C with the laser wavelength drifting about 6 nm over this range. This wavelength drift, coupled with the variation in laser wavelength of up to ±3 nm (due to laser die manufacturing processes), yields a total wavelength variation of about ±12 nm. However, DWDM systems require larger cooled DFB lasers for a semiconductor laser wavelength drifts about 0.08 nm/°C with temperature. The use of uncooled lasers causes lower energy consumption, which has positive financial implications for systems operators. For instance, the cost of the battery is minimized with the decreasing of energy consumption, which reduces operating costs. So DWDM systems are more expensive than CWDM systems for the application of cooled lasers.

From the above analysis, we can draw a conclusion that CWDM is a cost efficient solution in short-haul transmission and DWDM is a high-capacity solution in long-haul transmission. It’s wise to choose them properly according to our special needs. Fiberstore provides various types of CWDM and DWDM products with high performance which enable the cost efficient and fast-speed optical communications.



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