effect of adjucent channel on OSNR

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For example, the demultiplexer D40 board of Huawei OptiX OSN 8800 is a 40-channel demultiplexer with one in port and 40 out ports. The light from the main optical path contains 40 channel signals. The signals are input through the in port and then output from OUT to out40 according to the wavelength. Theoretically, the light of the first channel is strictly output from the OUT1 port, and the light of the second channel is strictly output from OUT2. And so on.

The actual situation is incomplete. A small part of optical signals of the first wavelength are output from the OUT2 port(at the same time，a small part of optical signals of the second wavelength is also output from the OUT1 port), which interferes with the signals of the second channel, thereby reducing the OSNR value of the second channel.

Channel isolation is used to determine the degree of interference. In Huawei WDM equipment, Adjacent channel isolation is usually greater than 25 dB. Non-adjacent channel isolation is usually greater than 30 dB

If more channels are added to the same multiplexer, as long as the isolation of adjacent channels is large enough, the wavelength spacing is reasonable, and the optical power difference (flatness) between adjacent wavelengths is small, then the mutual influence capability of these channels is small, and which can meet normal communication requirements.

Insightful. Thank you.

Are those figures (25dB and 30 dB) empirical? or there is some theory behind?

Also is there any theory applicable to power balancing, or its a matter of making all signals equal (regardless of the power magnitude)?

Insightful. Thank you.

Are those figures (25dB and 30 dB) empirical? or there is some theory behind?

Also is there any theory applicable to power balancing, or its a matter of making all signals equal (regardless of the power magnitude)?

This is the data obtained in the experiment. During optical power commissioning, ensure that the flatness between adjacent wavelengths is within ±2 dB. The flatness of the input optical power of each wavelength is within ±3 dB of the nominal single-wavelength input optical power.

Formula:

Optical power flatness = Max. (|Normalized actual single-wavelength optical power of each channel —  Average optical power|)

For more information：https://forum.huawei.com/enterprise/en/the-optical-power-flatness-of-the-wdm-system/thread/786327-875

Thanks！