Dear Polyxena,
The most important parameters for the LED is the bandwidth and center frequency (wavelength). You need to set up the frequency window to be suitable for the LED bandwidth and used data rate. The frequency window is affected by the bit rate and samples per bit parameters that you set in the project main layout.
I hope this information is helpful. If you need to discuss further, please email me at ahmad.atieh@optiwave.com.
Regards,
Ahmad