What are main differences of WDM vs FDM multiplexing? Let us delve in details.
In this type of multiplexing, every subchannel is having its own frequency band, which is the reason technology is called frequency division multiplexing. Each subchannel has been modulated with different frequencies before being multiplexed to the single channel. It allows usage of single line for up to 24 telephone users instead of making separate line to each residence. Technology allows demultiplexing signal at the receivers end. The signal that is received by the user on the telephone is multiplexed – the data that is not designed for this node is transmitted with frequency over 3400 Hz, so it cannot be heard by the human ear. There are multiple types of FDM existing for different purposes.
WDM Multiplexing
Wave division multiplexing is using same basic principle as the FDM, while having fiber-optic cable as a media. WDM allows transmission of 20 million telephone signals over single fiber at the same time. Since it is using lasers, WDM can be used only with fiber-optic cable.
WDM is dividing light into up to 40 different carrier waves of different color and wavelength. Capacity of each wave is 10 Gbps. When data is needed to be transmitted it should be modulated with the carrier wave and translated by the laser it is issued to a multiplexer. Multiplexer combines waves to a single white light beam using prism principle.
Finally, optical signal is transmitted over optic-fiber by a laser to the receiver end, where demultiplexer receives signal. The process inverts and single waves are sent to their receivers. If the signal strength is going to reduce between mux and demux, it might be amplified in the middle of transmission.
Latest version of WDM is DWDM (Dense Wave Division Multiplexing) that carry from 80 to 160 channels due to usage of more wavelengths. You can see ITU DWDM grid right here. The carrier waves are located closer than in WDM. DWDM is used for connection between large ISP and network service provider. To mention some product examples, we can see DWDM SFP+ transceiver module or DWDM XFP transceiver module. Along with passive DWDM muxes it allows to set up quick DWDM multiplexing scheme at low costs. In a most simple cases, equipment with SFP slots like a SFP mini switches can be used, or even simple media converter with SFP slot will do. Previously and till now widely used are CWDM multiplexing systems, particularly using CWDM grid wavelengths.
Examples of WDM also no need search too far – this WDM media converteruses 1310/1550 nm wavelengths to split RX – Receiving direction with TX – Transmit Direction, while EPON series, use 1490/1310 for a RX/TX separation, leaving 1550 nm to CATV over fiber.
