Wavelength Division Multiplexing (WDM)
Wavelength Division Multiplexing (WDM) is a series of optical carrier signals of different wavelengths carrying various information, which are combined at the transmitting end through a multiplexer and coupled to the same fiber for transmission, while At the receiving end, the optical signals of various wavelengths are separated by a demultiplexer. This technique of simultaneously transmitting two or more optical signals of different wavelengths in the same fiber is called wavelength division multiplexing, or WDM. WDM technology can double the transmission capacity of a single light, and can easily expand the capacity in the existing optical network. Depending on the direction of the transmitted signal, WDM can be used for multiplexing or demultiplexing.
Performance parameters
Multiplexing/demultiplexing devices (MUX/DEMUX) are key devices in WDM, and they affect the performance of the entire system. What are the main performance parameters of the multiplexing/demultiplexing device?
1. Working band
The working band of the multiplexer/demultiplexer, such as 1550 wavelength, distinguishes three bands: S band (short wavelength band 1460~1528nm), C band (regular band 1530~1565nm), L band (long wavelength band 1565~1625nm) .
2. Number of channels and channel spacing
The number of channels refers to the number of channels that can be synthesized or separated by the wavelength division multiplexer/demultiplexer. This number can vary from 4 to 160. The design is enhanced by adding more channels. Common channel numbers are 4, 8, 16, 32, 40, 48, etc. Channel spacing refers to the difference between the nominal carrier frequencies of two adjacent channels and can be used to prevent inter-channel interference. According to the recommendation of ITU-T G.692, there are 100GHz (0.8nm), 50GHz (0.4nm) and 25GHz with the spacing less than 200GHz (1.6nm), and the channel spacing of 100GHz and 50GHz is currently preferred.
3. Insertion loss
Insertion loss is the attenuation caused by the insertion of a wavelength division multiplexer (WDM) in an optical transmission system. The attenuation of the optical signal by the wavelength division multiplexer directly affects the transmission distance of the system. In general, the lower the insertion loss, the less the signal is attenuated.
4. Isolation
The isolation degree refers to the isolation degree between the signals of each channel, and a high isolation degree value can effectively prevent the crosstalk between the signals from causing the distortion of the transmission signal.
5. Polarization Dependent Loss PDL
The polarization dependent loss PDL is the distance between the maximum and minimum Loss caused by different polarization states at a fixed temperature, wavelength and the same Band, that is, the maximum deviation of insertion loss under all input polarization states.
