3 Advanced aspects of optical modulations in achieving high bit rates and immunity to signal degradation
3.4 Avoidance of nonlinear effects caused by advanced modulations

XPM is a non-desired phenomenon in telecommunication systems using WDM, since it can damage transmission. XPM leads to inter-channel crosstalk (wavelength conversion) in DWDM systems.

One of the solutions to the XPM effect is to separate wavelength bands used for each modulation format running in a fibre and set appropriate safety bands:

Spectral split of 10G and 40G by safety band can help reducing the cross phase modulation from the 10G system.

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Safety band (100 GHz) splitting two systems (RZ-DQPSK and P-DPSK 40G channels).