Dear Aziz
Unfortunately now I do not have optisystem to check your system. I am sure there is a small error somewhere. you can attach the photo of optisystem design so I can comment on it. I have four papers about UWB signal generation from monocycle to fifth-order derivative Gaussain pulses operated with OOK and BPM modulation formats and all implemented in Optisystem.
It is incorrect to transmit Gaussian pulses for UWB communication. The UWB signal must be Gaussian monocycle or higher order derivative of Gaussian pulse for example Doublet or Triplet so that the power spectrum density will be comply with FCC mask..
This link is my latest paper published in British journal regarding the optical generation of Gaussian monocycle and doublet pulses with OOK and BPM modulation.