I would like to mention that multibeam FSO network has provided a significant improvement in the link distance, received optical power, geometrical loss, and scalability. The network performance has been analyzed, and the study concludes that a maximum channel spacing beyond 0.4 nm is applicable for this network. The power receiver sensitivity difference of the receiver for different wavelengths at a BER of 10−9 was noted to be a small value, which is approximately less than 1 dB. Meanwhile, in terms of scalability, four users can access data each at 1.25 Gb/ss, which is considered suffi- cient compared to conventional multibeam technique accessing data to only one EU. The hybrid WDM/multibeam FSO network can be a good candidate to solve the last mile problem and the rapid increase in capacity demand without requiring
new FSO transceivers. At the moment, the evaluation is going on for a real-time system operating in heavy rain as compared to simulation presented here. In the future, increasing the capacity of the hybridWDM/multibeam FSO network can be studied and implemented to reach up to 32 channels.
Refer to this paper http://download.springer.com/static/pdf/356/art%253A10.1007%252Fs11107-014-0482-y.pdf
Hope this will help