CWDM stands for Coarse Wavelength Division Multiplexing which utilizes multiplexer to combine multiple optical signals at different wavelengths on one optic fiber, and then uses de-multiplexer to separate those hybrid optical signals at their own wavelengths at the receiver. CWDM transmits optical signals using 18 channels with the wavelengths between 1270 nm and 1610 nm with a channel spacing of 20 nm.
CWDM is an effective way to meet the rapidly increasing demand of bandwidth in transmission network and it can provide a cost-effective solution for high capacity in metropolitan area network and local area network. For example, when transmitting the signals at the same speed on the same optical fiber, the bandwidth provided by a typical 8-chanel system is eight times larger than that of a traditional SONET/SDH system. Compared with DWDM technology, CWDM is specially designed for short-distance network application with a high performance-price ratio, gradually becoming the focus of telecommunication industry.
CWDM system regenerates the optical signals at each node without using optical amplifier. Optical signal regeneration refers to the process that converting the optical signal to electric signal, and then converting the electric signal back to optical signal by using OEO (optical-electric-optical) transponder. Since all channels are regenerated at each node in CWDM system, and the optical link power budget has nothing to do with the number of channel among nodes, the design of network is simplified.
Due to the technical limitation, CWDM is usually used in metropolitan area network and access network. It has two main functions. One function is to use each wavelength channel to transmit different optical carrier signals at different rates. And the other function is to split optical carrier signals into multiple low-speed signals for saving cost.
CWDM system has a variety of network topology, such as point-to-point, ring, etc. Among them, the ring topology is equipped with self-protection and self-repair function, including link breaking protection and node fault separation. The ring link and point-to-point link of CWDM are very suitable for interconnection between scattered nodes in LAN (local area network) and SAN (storage area network). With low cost, low power consumption, small size and many other advantages, CWDM system has been widely used in LAN and SAN.
With low implementation cost, relatively simple installation and maintenance, Ethernet has been widely used in metropolitan area network and access network. IEEE 802.3 Ethernet standards realized a rapid development of bandwidth from 10 Mbit/s to 100 Mbit/s to 10 Gbit/s. Applying CWDM technology to Gigabit Ethernet can greatly increase network capacity. Compared with TDM (Time Division Multiplexing), CWDM system is characterized by better flexibility and scalability. For metropolitan services, the flexibility, especially the speed and the ability to expand as the business grows, is very important. Using CWDM technology can open the business for the user within a day or a few hours. And with the increasing of business, capacity expansion can be realized by inserting a new OTU board. Therefore, CWDM obtains more and more applications in telecommunication, broadcasting, enterprise network, campus network and other fields.
CWDM technology is also used in PON, a kind of point-to-multiple optical communication way. Combined with PON, each individual wavelength channel of CWDM system can serve as virtual optical link of PON, realizing the bandwidth data transmission between central node and multiple scattered nodes. CWDM and PON system can assign different wavelengths for video signal, data and voice signal to realize single fiber bidirectional transmission.
The very wide channel spacing of CWDM technology allows for the use of cheaper CWDM network components, such as uncooled lasers or lower-quality multiplexers and de-multiplexers. And CWDM technology is a very attractive option in metropolitan networks that require additional bandwidth without overbuilding the infrastructure.