In traditional optical fiber networks, information is transmitted through optical fiber by a single lightbeam. In a wavelength division multiplexing (WDM) network, the vast optical bandwidth of a fiber is carved up into wavelength channels, each of which carries a data stream individually. The multiple channels of information (each having a different carrier wavelength) are transmitted simultaneously over a single fiber. The reason why this can be done is that optical beams with different wavelengths propagate without interfering with one another. When the number of wavelength channels is above 20 in a WDM system, it is generally referred to as Dense WDM or DWDM.
What Is DWDM
DWDM, short for dense wavelength division multiplexing, is an optical technology used to increase bandwidth over existing fiber optic backbones. DWDM works by combining and transmitting multiple signals simultaneously at different wavelengths on the same fiber. It increases the capacity of embedded fiber by assigning incoming optical signals to specific frequencies (wavelengths) with a designated frequency band and then multiplexing the resulting signals out onto one fiber. In effect, one fiber is transformed into multiple virtual fibers. So, if you were to multiplex eight OC-48 signals into one fiber, you would increase the carrying capacity of that fiber from 2.5 Gb/s to 20 Gb/s. DWDM has the ability to transport up to 80 wavelengths in what is known as the Conventional band or C band spectrum, with all 80 channels in the 1550nm region. A key advantage of DWDM is that it’s protocol- and bit-rate-independent. DWDM-based networks can transmit data in IP, ATM, SONET/SDH, and Ethernet.
Advantages of DWDM
DWDM is designed for long-haul transmission where wavelengths are packed tightly together, providing a high-capacity solution in telecom networks. In DWDM system, far more channels are possible within the same fiber and dispersion compensation can be applied. Besides, it stays completely within the C-band where attenuation and dispersion are far lower than other bands. Moreover, DWDM takes advantage of the operating window of the Erbium Doped Fiber Amplifier (EDFA) to amplify the optical channels and extend the operating range of the system to over 1500 kilometers. The use of DWDM technology has proven to be the optimal way of combining cost efficient transport with advanced functionality, which can cope with the bandwidth explosion from the access network.
DWDM is a core technology in an optical transport network. The essential components of DWDM (DWDM Equipment) are shown in the following picture. The first one is transmitter (transmit transponder) which changes electrical bits to optical pulses. It is frequency specific and uses a narrow-band laser to generate the optical pulse. The second one is the multiplexer or demultiplexer which combines and separates discrete wavelengths respectively. The link is optical fiber that exhibits low loss and transmission performance in the relevant wavelength spectra, as well as the flat-gain optical amplifiers to boost the signal on longer spans. On the end is the receiver (receive transponder) which changes optical pulses back to electrical bits and uses wideband laser to provide the optical pulse.
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