WDM (optical Division Multiplexing) is the technology to combine two or more optical carrier signals of different wavelengths (carrying various information) at the transmitting end through a Multiplexer coupled to the same optical fiber for transmission. At the receiving end the optical signals of various wavelengths are separated by Demultiplexer, and then restored to the original signal by the optical receiver for further processing. The main purpose of WDM is to increase the bandwidth capacity of optical fibers. Therefore, WDM systems are widely used by telecom operators to expand capacity through WDM without laying more optical fibers. https://www.glsunmall.com/fiber-optic-articles/what-are-wdm-cwdm-ccwdm-dwdm-fwdm-lwdm-multiplexer.html