Abstract: Free space optics (FSO) uses air as a transmission medium and is significantly affected by the various weather conditions such as haze, rain, fog, snow, wind, etc. In this paper, the behaviour of 16 2.5Gb/s FSO system under the effect of the most critical weather conditions using RZ format has been investigated. The operating channel frequencies range from 193.4THz to 189.7THz with the frequency spacing of 100GHz.The performance of the 10th channel has been considered being the worst case scenario to analyse the system. The FSO system is evaluated by varying attenuation from 4.2850dB/km to 116dB/km under different weather conditions. It has been found that as attenuation increases the performance drastically degrades owing to scattering, absorption, free space path loss, geometric losses and other losses suffered by the FSO system. The faithful transmission distance achieved is 9000m in clear weathers and has reduced to 2000m and 100m in case of heavy rain and dense snow respectively. Further, it is shown that channel 2 operating at 193.16THz, gives best results for the FSO system at 40Gb/s where the highest value of Q factor is 29.16dB and OSNR is 80.060dB and 4.9dB value of OSNR for heavy rain has been achieved thus, dense snow, fog and heavy rain are the worst weather conditions which intensely degrade the performance of FSO system.

Keywords: BER, RZ, MZM, Q-Factor, FSO,PD