Hello Gaurav Rajya
You have raised a good question about continuous laser power.Usually we consider 0dBm power of laser source due the fact that low power levels of input signals are less vulnerable to non linear effects in optical fiber.No doubt with the increase of input power,system performance increase to some extent but it decrease after the power cross elastic limits of toleration and kerrs efects,FWM, SPM and XPM comes into play.There is great importance of systems operates at lower power level because these systems operates for long time and less prone to heating effects introduced by laser at higher power level.Basically these are some important reasons,Rest you can see other benefits over internet regarding this concept.
Regards
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