WDM (wavelength division multiplexing) technology transmitting multiple signals on a single optical fiber by using different wavelengths to carry each signal has been used since 1980s. In the middle of 1990s, dense wavelength division multiplexing (DWDM) enabled carriers to extend the capacity of the SONET/SDH rings in the network core, without installing new fiber. As the development of data service, MAN has become a hot topic of network construction. However, DWDM system brings telecom operators very high costs in MAN construction. So the other kind of WDM technology, CWDM (coarse wavelength division multiplexing) emerged. CWDM has fewer channels than DWDM. The energy from the lasers in a CWDM system is spread out over a larger range of wavelengths than is the energy from the lasers in a DWDM system. CWDM has many advantages like low cost, low power consumption and small volume. As an economical and practical short-distance WDM transmission system, CWDM becomes more and more recognized by people in many MAN applications just as follows. Fiber Exhaust Relief Fiber exhaust which means lack of network capacity occurs in metropolitan networks. CWDM is a simple and cost-effective way for people to solve fiber exhaust. By using CDWM, new services can be added over an existing single optical fiber. So to increase optical network capacity, people don’t need to replace existing equipment with higher bit rate transmission rate and install new fibers. Otherwise, it will cost too much because installing new fiber is a costly venture in metropolitan areas. Low-cost WDM Deployments CWDM system with reduced channels is beneficial for carriers in the metro-regional areas. It supports 4-channel configuration. Systems with 4 channels can quadruple the available capacity over an existing network segment, while offering a lower firstin deployment cost than an 8-channel system. For carriers, they should pay attention to two important points including cost and scalability when they need to upgrade to 8 channels systems. So CWDM is a good choice. Central Office to Customer Premise Interconnection CWDM is a good fit for metro-access applications such as Fiber to the Building (FTTB). An 8-channel CWDM network can deliver 8 independent wavelength services from the Central Office to multiple business offices located in the same building. Due to the low cost, simplicity and scalability features of the latest products such as CWDM modules, CWDM systems is a good choice for overbuilding with Next Generation SONET, DWDM, and proprietary solutions. CWDM is becoming more and more popular among carriers who need to upgrade their networks to accommodate current of future needs while minimizing the use of valuable fiber strands especially in the metropolitan areas.
