Hi Md. Asraful Sekh,
i agree to the points of Damian Marek sir that simulation of Multiple OWC channels can be done by splitting a modulated signal into several branches (power splitter) and attaching each branch to an OWC.
I want to share some links:
http://www.hindawi.com/journals/ijo/2015/945483/
https://www.researchgate.net/publication/273917945_Hybrid_WDMmultibeam_free-space_optics_for_multigigabit_access_network
http://www2.engr.arizona.edu/~vasiclab/files/papers/ANV_06_WDD.pdf
Thanks,