1. What is WDM?
Wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical signals onto a single optical fiber by using different wavelengths of laser.
2. Work principle
WDM networks use multiple colors of wavelength over the same common path (fiber). Optical transmitters tuned to specific wavelengths send it into a passive combiner called a Mux (short for multiplexer). All the wavelengths travel down a common fiber pair and are separated using a passive splitter or demultiplexer (also called a demux). It enables bidirectional communications over one single fiber as well as multiplication of capacity, like increasing the number of lanes on a highway to make the flow of traffic more efficient.
3&4. Classification
There are two types of WDM: Coarse WDM (CWDM)and Dense WDM (DWDM). They are two technologies developed based on WDM, but with different wavelength patterns and applications.
—Difference in wavelength:
CWDM systems typically transmit 8 wavelengths with a channel spacing of 20 nm from 1470 nm to 1610 nm. (It also defined 1471nm-1610nm for for distinguishing with the common wavelengths).
DWDM wavelengths are typically from 1525 nm to 1565 nm (C-band) and 1570 nm to 1610 nm (L-band), which can carry 40, 80, 96 or up to 160 wavelengths with a narrower spacing 0.8/0.4 nm (100 GHz/50 GHz grid).
—Difference in application:
CWDM is commonly deployed point-to-point in enterprise and telecom access networks while DWDM is for networks that require higher speeds, greater channel capacity or applications requiring transmitting data for much longer distance such as interconnect data centers. Therefore CWDM is a cost-effective option when transmission distance is under 80km or 10Gb.
