Hello aadil,
as i could see from the screenshot , you BER Vs power graph is not that so bad. If i could understand by “smooth” , do you mean BER max and then doping suddenly such that it looks like a waterfall? Is it?
If you want smooth transition of the curve without much fluctuations you can use more sweep iterations for power levels. I guess here you have swept power for 5-6 iterations.
Hope it helps.
Best regards