Thank you Damian Mareck and Ravil for your explanation . In fact it is a work I have to present, so I don’t know if you have documents about the operation of Ber Test Set, the parameter ”Sequence length for BER per iteration,” and why it is better to using the ”Ber Test Set instead” of the ”eye diagram analyzer” or the ”BER analyzer”, the reason why the Bessel Optical Filter at 15 GHz was used instead of (2 * 2.6GHz= 5.2 GHz, theorem of Shanon), the role of connecting the OFDM modulation and OFDM demodulation block by a link , the advantage of using OFDM blocks directly in the optisystem instead of implementing it in matlab and do the cosimulation with optisystem … I need these elements to better master my work and by the way, better justify the results. Thank you for your help