WDM is the abbreviation for Wavelength Division Multiplexing, it is a popular technology used in currently fiber optic communication systems. By WDM, we can split a number of optical lights in an optic fiber into a number of discrete wavelengths. Each wavelength can be considered to an independent channel running at a special data rate of 5Gbit/s, 10Gbit/s, 40Gbit/s or even 100Gbit/s. If the light in the fiber is split into 16 channels, and each channel running at 40Gbit/s, the total data transmission rate will be 640Gbit/s. In effect, this means maximized use of a single fiber optic to transmit and receive a large number of signals, minimizing costs for telecom companies. WDM technology is also the working principle of optical amplifiers, multiplexers and de- multiplexers. Next I will give a separate introduction about WDM/CWDM/DWDM technologies.

DWDM and Conventional WDM
DWDM stands for Dense Wavelength Division Multiplexing. It means the divided wavelength channels are very narrow and close to each other. It is widely used for the 1550nm band so as to leverage the capabilities of EDFA (Erbium Doped Fiber Amplifiers), which are effective for wavelengths between approximately 1525–1565 nm (C band), or 1570–1610 nm (L band). Conventional WDM Conventional WDM uses the 3rd transmission window with a wavelength of 1550nm, accommodating up to 8 channels. DWDM is the same but with a higher density channel. The ultra dense WDM is capable of working at a spacing of only 12.5 GHz, allowing more channels.

CWDM
CWDM refer to Coarse wavelength division multiplexing, in CWDM technology, it shared the fact that the choice of channel spacing and frequency stability which is the EDFA could not use. There is an increasing in channel space, it can not be used in EDFA. One common meaning for CWDM meant two (or possibly more) signals multiplexed onto a single fiber, where one signal was in the 1550 nm band, and the other in the 1310 nm band. Currently there is an increasing in the channel space. This means the need of less sophisticated and less costly transceivers devices. Operating in the same window of 1550 nm and making use of OH-free silica fibers, maximum efficiencies are achieved in channels 31, 49, 51, 53, 55, 57, 59 and 61 using the wavelengths from 1270 nm through 1610 nm with a channel spacing of 20 nm. CWDM devices are commonly used in less precision optics and lower cost, un-cooled lasers with lower maintenance requirements.?Compared with DWDM and Conventional WDM, CWDM is much more cost effective and less power consumption of laser devices.

Currently kinds of related CWDM MUX/DEMUX or DWDM MUX/DEMUX or optical amplifiers are available in the market. Networking solutions provider are the right ones to ask for guidance for use of CWDM, DWDM or WDM technology. Choosing the right one means the correct, integrated devices for error-free high speed data transmission over fiber optic networks. Cost-effective CWDM solutions with optimized performance and built in expansion capabilities are available from a host of online network solution companies. Choosing the most experienced one to get the reliable CWDM solution is critical.