Tags:
WDM is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths of laser light. It can be divided into different wavelength patterns, conventional/coarse (CWDM) and dense (DWDM). The main difference between CWDM and DWDM is the channel spacing. Compared to DWDM which is a more tightly packed WDM system, CWDM has larger channel spacing, having fewer wavelengths be transported on the same fiber. For instance, CWDM typically has channels at wavelengths spaced 20 nanometers (nm) apart, compared with 0.4 nm spacing for DWDM. DWDM typically has the capability to transport up to 80 channels (wavelengths) in what is known as the Conventional band or C-band spectrum. With the advancement of DWDM technology, even 160 channels (wavelengths) can be transported within the same fiber, which allows as many as signals be transported simultaneously.
The different channel spacing makes CWDM and DWDM ideal for different networks. CWDM can only transmit a maximum of 18 channels with large spacing between channels, making optical amplifiers not able to be used in CWDM system. So CWDM is typically deployed at short-haul networks. However, DWDM can combine multiple optical signals, which makes them be amplified as a group and transported in high speed and large volume. So DWDM technology is one of the best choices for transporting extremely large amounts of data traffic over metro or long distances in optical networks.
The channel spacing also has a great influence on their cost. 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 the larger cooled DFB Lasers for a semiconductor laser wavelength drifts about 0.08 nm/°C with temperature. The use of uncooled lasers causes lower power consume, which has positive financial implications for systems operators. For instance, the cost of battery is minimized with the decreasing of power consume, which reducing operating costs. So DWDM systems is expensive than CWDM for its application of cooled lasers.