What is WDM channel isolation?

WDM is divided into DWDM (Dense Wavelength Division Multiplexing). Single-core optical fiber can transmit n channels at the same time, and the channel spacing is 0.8nm and 0.4nm, and each channel can carry an SDH system. At present, the largest commercial system in China is 160 wave * 10G, and the system of 80 wave *40G has also been commercialized. CWDM (Sparse Wavelength Division Multiplexing), N channels can be transmitted simultaneously in a single-core optical fiber, and the channel interval is 20nm. In general, the system can carry more than 20 channels, mainly used to carry GE services in MAN. )

The simple point of WDM channel isolation theory is to investigate the interference degree of one channel signal to another channel in demultiplexer.

For example, the demultiplexer D40 of Huawei Optix 1600G equipment is a 40-channel demultiplexer with 1 in ports and 40 out ports. The light from the main optical path contains 40 signals, which are input from the in port and then output from the out 1~out40 according to different wavelengths. Theoretically, the light of the first path is strictly output from out 1, the light of the second path is strictly output from out2, and so on. This is not entirely the case. The first wave will also have a very small amount of light output from out2, which will interfere with the signal of the second channel. Channel isolation is to examine how big this interference is.

For example, the first optical power input from the in port is -5dBm, and the output from the out 1 is-10dBm, so -5dBm-(- 10dBm)=5dB, and this 5dB is the insertion loss of the first channel. The output of out2 is -40dBm, so -5dBm-(-40dBm)=35dB, which is the channel isolation between the second channel and the first channel.

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