Hi Abu Bakar,
I agree with you Sech pulse generator is more convenient for the soliton pulse for an ideal system.
As you know Gaussian distribution represents all natural phenomena with some mean value and standard deviation. So if you have some disturbance in the system even if it is soliton, you can use Gausian shape as a general one. But again Sech profile is more accurate.
Hope this clarifies the issue to you.
thanks
Mohamed abouseif