Hi Younis Ahmad Dar

optical communication depends on optical sources.Numerous sources are present in open space which acts as noice .More over to beam an optical signal we need to convert it either like laser or x-ray to transmit  to longer distances which is dangerous  or should have a medium that carries it to longer distances without scattering(optical fiber cable)These  are the challenges in optical communcation

The answer of your question needs more details. You can find these details on the book entitled by " Free-Space Optical Communication Systems in Turbulent Channels"  By Mohammed Abaza

Good Luck.

Prof. S. El-Rabaie

􀀁􀀂􀀃􀀄􀀅􀀅􀀆􀀇􀀈􀀉􀀊􀀈􀀋􀀌􀀄􀀍􀀄􀀈􀀁􀀂􀀃􀀄􀀅

1. Light very easy absorbed by rain , particle and some gases

2. Need high power laser source which is very dangerous

3. interfere with sun and any other light sources

So better use fiber optic

there are different parameters effect on optical communication in space:

1. line of sight

2. beam divergence angle

3. weather (fog, rain, dust ....).

 in optical communication system suffers from fog, for radio wave communication suffers from rain.

these problems leads to use hybrid FSO/RF communication system

Thanks everyone for your answer