**7. Conclusion**

This chapter summarizes the simulation results and their interpretations of the comparison of two configurations of EYDWA (post-and preamplifier) in the WDM/FSO system. The mentioned amplifiers were evaluated based on values of BER and the quality -factor. WDM over FSO communication system is very suitable and effective in providing high data rate transmission with low bit error rate (BER). Therefore, WDM – FSO system has achieved very good results, it has many problems, such as heavy attenuation coefficient.

For the heavy rain condition the maximum link range about 8 km at BER = 10<sup>9</sup> . Also, It can be noticed from simulation that the best results achieved EYDWA postamplifier configuration, this later was able to reach transmission distance of WDM/ FSO up to 26 Km however the worst results in terms of FSO range are obtained with EYDWA preamplifier and the distance of transmission is limited at 16 Km.

Furthermore the gain flatness and the noise figure of EDFA have been studied. The gain non-uniformity for each channel using the optimization of erbium doped and length fiber doped in order to equalize the amplitude gain in the WDM-FSO system have been simulated. The simulation results prove that the proposed method by optimization of erbium doped and length of fiber doped offers and improved the best performance in terms of the gain flatness GF = 0.7 for fiber length L = 7.5 m and erbium concentration C = 5,5.10+24/m<sup>3</sup> .
